Our paper on “Short-pulsed metamaterials,”[1] in collaboration with Carlo Rizza (University of l’Aquila), has been published in Physical Review Letters.

1. Rizza, C., Castaldi, G., & Galdi, V. (2022). Short-pulsed metamaterials. Physical Review Letters 128(25), 257402.

We study a class of temporal metamaterials characterized by time-varying dielectric permittivity waveforms of duration much smaller than the characteristic wave-dynamical timescale. In the analogy between spatial and temporal metamaterials, such a short-pulsed regime can be viewed as the temporal counterpart of metasurfaces. We introduce a general and compact analytical formalism for modeling the interaction of a short-pulsed metamaterial with an electromagnetic wave packet. Specifically, we elucidate the role of local and nonlocal effects, as well as the time-reversal symmetry breaking, and we show how they can be harnessed to perform elementary analog computing, such as first and second derivatives. Our theory validated against full-wave numerical simulations suggests a novel route for manipulating electromagnetic waves without relying on long, periodic temporal modulations. Just as metasurfaces have played a pivotal role in the technological viability and practical applicability of conventional (spatial) metamaterials, short-pulsed metamaterials may catalyze the development of temporal and space-time metamaterials.

@article{IJ156_PRL_128_257402_2022,
title = {Short-pulsed metamaterials},
author = {Rizza, Carlo and Castaldi, Giuseppe and Galdi, Vincenzo},
journal = {Physical Review Letters},
volume = {128},
issue = {25},
pages = {257402},
numpages = {6},
year = {2022},
month = jun,
publisher = {American Physical Society},
doi = {10.1103/PhysRevLett.128.257402},
note = {https://journals.aps.org/prl/supplemental/10.1103/PhysRevLett.128.257402}
}


Our paper on “Short-pulsed metamaterials,” in collaboration with Carlo Rizza (University of l’Aquila), has been accepted for publication in Physical Review Letters.

An arXiv preprint is available.

Our review paper on “Digital Coding Metasurfaces: From Theory to Applications,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in the IEEE Antennas and Propagation Magazine.

Our paper on “Nonlocal effects in temporal metamaterials” [1], in collaboration with Carlo Rizza (University of l’Aquila), has been published in Nanophotonics.

1. Rizza, C., Castaldi, G., & Galdi, V. (2022). Nonlocal effects in temporal metamaterials. Nanophotonics 11(7), 1285–1295.

Nonlocality is a fundamental concept in photonics. For instance, nonlocal wave-matter interactions in spatially modulated metamaterials enable novel effects, such as giant electromagnetic chirality, artificial magnetism, and negative refraction. Here, we investigate the effects induced by spatial nonlocality in temporal metamaterials, i.e., media with a dielectric permittivity rapidly modulated in time. Via a rigorous multiscale approach, we introduce a general and compact formalism for the nonlocal effective medium theory of temporally periodic metamaterials. In particular, we study two scenarios: (i) a periodic temporal modulation, and (ii) a temporal boundary where the permittivity is abruptly changed in time and subject to periodic modulation. We show that these configurations can give rise to peculiar nonlocal effects, and we highlight the similarities and differences with respect to the spatial-metamaterial counterparts. Interestingly, by tailoring the effective boundary wave-matter interactions, we also identify an intriguing configuration for which a temporal metamaterial can perform the first-order derivative of an incident wavepacket. Our theoretical results, backed by full-wave numerical simulations, introduce key physical ingredients that may pave the way for novel applications. By fully exploiting the time-reversal symmetry breaking, nonlocal temporal metamaterials promise a great potential for efficient, tunable optical computing devices.

@article{IJ155_Nanophotonics_2022,
author = {Rizza, Carlo and Castaldi, Giuseppe and Galdi, Vincenzo},
doi = {doi:10.1515/nanoph-2021-0605},
title = {Nonlocal effects in temporal metamaterials},
journal = {Nanophotonics},
number = {7},
volume = {11},
pages = {1285--1295},
manth = {Apr},
year = {2022}
}


Our paper on “Nonlocal effects in temporal metamaterials,” in collaboration with Carlo Rizza (University of l’Aquila), has been accepted for publication in Nanophotonics.

An arXiv preprint is available.

19 Nov 2021

Prof. Vincenzo Galdi has been elected an Optica Fellow for “outstanding and sustained contributions to modeling wave interaction with artificially engineered materials, including nonlocal, non-Hermitian, multiphysics, and time-varying scenarios”.

Our paper on “Synthesizing quasi-bound states in the continuum in epsilon-near-zero layered materials” [1] has been published in Applied Physics Letters as an Editors’ Pick.

1. Castaldi, G., Moccia, M., & Galdi, V. (2021). Synthesizing quasi-bound states in the continuum in epsilon-near-zero layered materials. Applied Physics Letters 119(17), 171110.

Bound states in the continuum (BIC) are highly confined, nonradiative modes that can exist in open structures, despite their potential compatibility and coupling with the radiation spectrum, and may give rise to resonances with arbitrary large lifetimes. Here, we study this phenomenon in layered materials featuring epsilon-near-zero constituents. Specifically, we outline a systematic procedure to synthesize quasi-BIC resonances at a given frequency, incidence angle, and polarization and investigate the role of certain critical parameters in establishing the quality factor of the resonances. Moreover, we also provide an insightful phenomenological interpretation in terms of the recently introduced concept of "photonic doping" and study the effects of the unavoidable material loss and dispersion. Our results indicate the possibility of synthesizing sharp resonances, for both transversely magnetic and electric polarizations, which are of potential interest for a variety of nanophotonics scenarios, including light trapping, optical sensing, and thermal radiation.

@article{IJ154_APL_119_171110_2021,
author = {Castaldi, Giuseppe and Moccia, Massimo and Galdi, Vincenzo},
title = {Synthesizing quasi-bound states in the continuum in epsilon-near-zero layered materials},
journal = {Applied Physics Letters},
volume = {119},
number = {17},
pages = {171110},
year = {2021},
doi = {https://doi.org/10.1063/5.0070248},
month = oct
}


Our paper on “Synthesizing quasi-bound states in the continuum in epsilon-near-zero layered materials” has been accepted for publication in Applied Physics Letters.

An arXiv preprint is available.

Our paper on “Simultaneous conversion of polarization and frequency via time-division-multiplexing metasurfaces” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published Advanced Optical Materials.

1. Yang, J., Ke, J. C., Cao, W. K., Chen, M. Z., Cheng, Q., Galdi, V., & Cui, T. J. (2021). Simultaneous conversion of polarization and frequency via time-division-multiplexing metasurfaces. Advanced Optical Materials 9(22), 2101043.

Metasurfaces are artificially engineered two-dimensional materials composed of sub-wavelength meta-atoms, which have shown unprecedented capabilities in manipulating the amplitude, phase, frequency, and polarization states of electromagnetic waves. Specifically, polarization control can be attained via suitable anisotropic, linear, and time-invariant designs, while frequency conversion is realized via nonlinear or time-varying platforms. Simultaneous manipulations of polarization and frequency would be of considerable practical interest in many application scenarios, but remain unattainable with current approaches. Here, a time-division-multiplexing metasurface is proposed to realize the simultaneous conversion of polarization and frequency. The platform relies on time-modulated polarization switches and, by varying the duty cycle and time delays of the polarization channels, can arbitrarily rotate the polarization at the central frequency of operation, and synthesize various polarization states at selected harmonic frequencies. Theoretical predictions are validated via measurements on a prototype operating at microwave frequencies, providing the first experimental evidence of simultaneous polarization and frequency conversions via time-division-multiplexing metasurfaces. The outcomes open a new pathway in manipulating the electromagnetic waves via time-varying metasurfaces, and may be of interest for a broad variety of applications in scenarios ranging from polarization imaging to quantum optics.

@article{IJ153_AdOM_2101043_2021,
author = {Yang, Jin and Ke, Jun Chen and Cao, Wen Kang and Chen, Ming Zheng and Cheng, Qiang and Galdi, Vincenzo and Cui, Tie Jun},
title = {Simultaneous conversion of polarization and frequency via time-division-multiplexing metasurfaces},
volume = {9},
issue = {22},
pages = {2101043},
month = nov,
year = {2021}
}


We have presented an invited talk [1] and a contributed talk [2] at the 15th International Congress on Engineered Material Platforms for Novel Wave Phenomena (Metamaterials), New York (NY), USA, Sep. 20-25, 2021 (online).

1. Galdi, V. (2021). Non-Hermitian line waves. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). New York, NY, USA, Sep. 20-25, 2021 (online).
@inproceedings{Galdi_Metamaterials_2021,
author = {Galdi, V.},
title = {Non-{H}ermitian line waves},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {New York, NY, USA, Sep. 20-25, 2021 (online)},
month = sep,
year = {2021}
}

2. Rizza, C., Castaldi, G., & Galdi, V. (2021). Optical magnetism in temporal metamaterials. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). New York, NY, USA, Sep. 20-25, 2021 (online).
@inproceedings{Rizza_Metamaterials_2021,
author = {Rizza, C. and Castaldi, G. and Galdi, V.},
title = {Optical magnetism in temporal metamaterials},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {New York, NY, USA, Sep. 20-25, 2021 (online)},
month = sep,
year = {2021}
}


14 Sep 2021

We have presented a keynote talk [1] at the VI International Conference on Metamaterials and Nanophotonics (MetaNano 2021), Tblisi, Georgia, Sep. 23-17, 2021 (online).

1. Galdi, V. (2021). Recent advances in space-time coding digital metasurfaces. In VI International Conference on Metamaterials and Nanophotonics (MetaNano 2021). Tblisi, Georgia, Sep. 13-17, 2021 (online).
@inproceedings{Galdi_MetaNano_2021,
author = {Galdi, V.},
title = {Recent advances in space-time coding digital metasurfaces},
booktitle = {VI International Conference on Metamaterials and Nanophotonics (MetaNano 2021)},
organization = {Tblisi, Georgia, Sep. 13-17, 2021 (online)},
month = sep,
year = {2021}
}


1 Sep 2021

We have presented three invited talks [1, 2, 3] at the XXXIV URSI General Assembly (URSI-GASS), Rome, Italy, Aug. 28-Sep. 4, 2021.

1. Zhang, L., Chen, X. Q., Shao, R. W., Dai, J. Y., Cheng, Q., Moccia, M., … Cui, T. J. (2021). Some recent advances in space-time-coding metasurfaces. In XXXIV General Assembly and Scientific Symposium (GASS) of the URSI. Rome, Italy, Aug. 28-Sep. 4, 2021.
@inproceedings{Zhang_URSI-GASS_2021,
author = {Zhang, L. and Chen, X. Q. and Shao, R. W. and Dai, J. Y. and Cheng, Q. and Moccia, M. and Castaldi, G. and Galdi, V. and Cui, T. J.},
title = {Some recent advances in space-time-coding metasurfaces},
booktitle = {XXXIV General Assembly and Scientific Symposium (GASS) of the URSI},
organization = {Rome, Italy, Aug. 28-Sep. 4, 2021},
month = aug,
year = {2021}
}

2. Galdi, V. (2021). Some perspectives on non-Hermitian metamaterials and metasurfaces. In XXXIV General Assembly and Scientific Symposium (GASS) of the URSI. Rome, Italy, Aug. 28-Sep. 4, 2021.
@inproceedings{Galdi_URSI-GASS_2021,
author = {Galdi, V.},
title = {Some perspectives on non-Hermitian metamaterials and metasurfaces},
booktitle = {XXXIV General Assembly and Scientific Symposium (GASS) of the URSI},
organization = {Rome, Italy, Aug. 28-Sep. 4, 2021},
month = aug,
year = {2021}
}

3. Moccia, M., Castaldi, G., & Galdi, V. (2021). Modeling and harnessing wave propagation in nonlocal and non-Hermitian media via extended transformation optics. In XXXIV General Assembly and Scientific Symposium (GASS) of the URSI. Rome, Italy, Aug. 28-Sep. 4, 2021.
@inproceedings{Moccia_URSI-GASS_2021,
author = {Moccia, M. and Castaldi, G. and Galdi, V.},
title = {Modeling and harnessing wave propagation in nonlocal and non-Hermitian media via extended transformation optics},
booktitle = {XXXIV General Assembly and Scientific Symposium (GASS) of the URSI},
organization = {Rome, Italy, Aug. 28-Sep. 4, 2021},
month = aug,
year = {2021}
}


Our paper on “Exploiting space-time duality in the synthesis of impedance transformers via temporal metamaterials” [1], in collaboration with Víctor Pacheco-Peña (Newcastle University) and Nader Engheta (University of Pennsylvania), has been published in Nanophotonics.

1. Castaldi, G., Pacheco-Peña, V., Moccia, M., Engheta, N., & Galdi, V. (2021). Exploiting space-time duality in the synthesis of impedance transformers via temporal metamaterials. Nanophotonics 10(14), 3687–3699.

Multisection quarter-wave impedance transformers are widely applied in microwave engineering and optics to attain impedance-matching networks and antireflection coatings. These structures are mostly designed in the spatial domain (time harmonic) by using geometries of different materials. Here, we exploit such concepts in the time domain by using time-varying metamaterials. We derive a formal analogy between the spectral responses of these structures and their temporal analogs, i.e., time-varying stepped refractive-index profiles. We show that such space-time duality grants access to the vast arsenal of synthesis approaches available in microwave engineering and optics. This allows, for instance, the synthesis of temporal impedance transformers for broadband impedance matching with maximally flat or equi-ripple responses, which extend and generalize the recently proposed quarter-wave design as an antireflection temporal coating. Our results, validated via full-wave numerical simulations, provide new insights and deeper understanding of the wave dynamics in time-varying media, and may find important applications in space-time metastructures for broadband frequency conversion and analog signal processing.

@article{IJ152_Nanophotonics_2021,
title = {Exploiting space-time duality in the synthesis of impedance transformers via temporal metamaterials},
author = {Castaldi, Giuseppe and {Pacheco-Pe{\~n}a}, Victor and Moccia, Massimo and Engheta, Nader and Galdi, Vincenzo},
year = {2021},
month = oct,
journal = {Nanophotonics},
volume = {10},
number = {14},
pages = {3687--3699},
doi = {10.1515/nanoph-2021-0231}
}


Our paper on “Simultaneous conversion of polarization and frequency via time-division-multiplexing metasurfaces,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in Advanced Optical Materials.

Our paper on “Exploiting space-time duality in the synthesis of impedance transformers via temporal metamaterials,” in collaboration with Víctor Pacheco-Peña (Newcastle University) and Nader Engheta (University of Pennsylvania), has been accepted for publication in Nanophotonics.

Our paper on “Exceptional points in flat optics: A non-Hermitian line-wave scenario” [1], in collaboration with Francesco Monticone (Cornell University), has been published in Physical Review Applied.

1. Moccia, M., Castaldi, G., Monticone, F., & Galdi, V. (2021). Exceptional points in flat optics: A non-Hermitian line-wave scenario. Physical Review Applied 15(6), 064067.

Line waves are recently discovered wave entities that are localized along two directions and therefore can be viewed as the one-dimensional counterpart of surface waves. These waves can be supported at discontinuities of the surface reactance and/or resistance of low-dimensional materials such as metasurfaces or graphene. Here, a broader class of non-Hermitian surface-impedance junctions is studied that can support coupled line waves and that allows the investigation of different one-dimensional waveguiding mechanisms in a unified framework. It is theoretically demonstrated that, under parity–time-symmetry conditions, exceptional points can occur in a truly flat-optics scenario, hence endowing these waveguiding systems with the attractive features of both line-wave and exceptional-point physics and shedding further light on the phase transitions existing in these systems. It is also shown that the required surface-impedance parameters are compatible with those attainable with typical models of photoexcited graphene metasurfaces at terahertz frequencies. Besides providing additional understanding in the physics of line waves, which is still in its infancy, these results pave the way toward intriguing developments in the largely unexplored field of non-Hermitian flat optics, with possible applications ranging from sensing to lasing and on-chip optical signal processing.

@article{IJ151_PRAppl_15_064067_2021,
title = {Exceptional points in flat optics: A non-{H}ermitian line-wave scenario},
author = {Moccia, Massimo and Castaldi, Giuseppe and Monticone, Francesco and Galdi, Vincenzo},
journal = {Physical Review Applied},
volume = {15},
issue = {6},
pages = {064067},
numpages = {11},
year = {2021},
month = jun,
publisher = {American Physical Society},
doi = {10.1103/PhysRevApplied.15.064067},
}


Our paper on “Exceptional points in the flatland: A non-Hermitian line-wave scenario,” in collaboration with Francesco Monticone (Cornell University), has been accepted for publication in Physical Review Applied.

An arXiv preprint is available.

12 May 2021

Our paper on “Advanced DNA detection via multispectral plasmonic metasurfaces” [1], in collaboration with Emanuela Esposito’s Group (National Research Council), has been published in Frontiers in Bioengineering and Biotechnology.

1. Di Meo, V., Moccia, M., Sanità, G., Crescitelli, A., Lamberti, A., Galdi, V., … Esposito, E. (2021). Advanced DNA detection via multispectral plasmonic metasurfaces. Frontiers in Bioengineering and Biotechnology 9, 666121.

We propose and demonstrate a sensing platform based on plasmonic metasurfaces for the detection of very low concentrations of deoxyribo-nucleic acid (DNA) fragments. The platform relies on surface-enhanced infrared absorption spectroscopy, implemented via a multispectral metasurface. Specifically, different regions (“pixels”) are engineered so as to separately cover the medium-infrared range of the electromagnetic spectrum extending from the functional-groups to the fingerprint region of a single analyte. In conjunction with a suitable bio-functionalization, this enables univocal and label-free recognition of specific molecules. For experimental validation, we fabricate a large-area gold metasurface on a silicon chip, and functionalize it with a recognition layer of peptide nucleic acid (PNA). Our experimental results indicate the possibility to detect complementary DNA fragments in concentrations as low as 50 fM, i.e., well below the value attained by standard methods, with additional advantages in terms of processing time, versatility and ease of implementation/operation.

@article{IJ150_FBIOE_2021,
author = {Di Meo, Valentina and Moccia, Massimo and Sanit\a, Gennaro and Crescitelli, Alessio and Lamberti, Annalisa and Galdi, Vincenzo and Rendina, Ivo and Esposito, Emanuela},
title = {Advanced {DNA} detection via multispectral plasmonic metasurfaces},
journal = {Frontiers in Bioengineering and Biotechnology},
volume = {9},
pages = {666121},
month = may,
year = {2021},
url = {https://www.frontiersin.org/article/10.3389/fbioe.2021.666121},
doi = {10.3389/fbioe.2021.666121},
issn = {2296-4185},
note = { https://www.frontiersin.org/articles/10.3389/fbioe.2021.666121/full#supplementary-material}
}


13 Apr 2021

Our paper on “Advanced DNA detection via multispectral plasmonic metasurfaces,” in collaboration with Emanuela Esposito’s Group (National Research Council), has been accepted for publication in Frontiers in Bioengineering and Biotechnology.

Our paper on “Surface-wave propagation on non-Hermitian metasurfaces with extreme anisotropy” [1], in collaboration with Andrea Alù (ASRC-CUNY), has been published in the IEEE Transactions on Microwave Theory and Techniques.

1. Coppolaro, M., Moccia, M., Castaldi, G., Alù, & Galdi, V. (2021). Surface-wave propagation on non-Hermitian metasurfaces with extreme anisotropy. IEEE Transactions on Microwave Theory and Techniques 69(4), 2060–2071.

Electromagnetic metasurfaces enable the advanced control of surface-wave propagation by spatially tailoring the local surface reactance. Interestingly, tailoring the surface resistance distribution in space provides new, largely unexplored degrees of freedom. In this article, we show that suitable spatial modulations of the surface resistance between positive (i.e., loss) and negative (i.e., gain) values can induce peculiar dispersion effects, far beyond mere compensation. Taking inspiration from the parity-time symmetry concept in quantum physics, we put forward and explore a class of non-Hermitian metasurfaces that may exhibit extreme anisotropy mainly induced by the gain-loss interplay. Through analytical modeling and full-wave numerical simulations, we illustrate the associated phenomenon of surface-wave canalization, explore nonlocal effects and possible departures from the ideal conditions, and address the feasibility of the required constitutive parameters. Our results suggest intriguing possibilities to dynamically reconfigure the surface-wave propagation and are of potential interest for applications to imaging, sensing, and communications.

@article{IJ149_IEEE-TMTT_69_2021,
author = {Coppolaro, Marino and Moccia, Massimo and Castaldi, Giuseppe and Al\u and Galdi, Vincenzo},
journal = {IEEE Transactions on Microwave Theory and Techniques},
title = {Surface-wave propagation on non-{H}ermitian metasurfaces with extreme anisotropy},
year = {2021},
volume = {69},
number = {4},
pages = {2060--2071},
doi = {10.1109/TMTT.2021.3057632},
month = apr
}


Our paper on “Surface-wave propagation on non-Hermitian metasurfaces with extreme anisotropy,” in collaboration with Andrea Alù (ASRC-CUNY), has been accepted for publication in the IEEE Transactions on Microwave Theory and Techniques.

An arXiv preprint is available.

Our invited review paper on “Recent advances and perspectives on space-time coding digital metasurfaces” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published in EPJ Applied Metamaterials.

1. Zhang, L., Dai, J. Y., Moccia, M., Castaldi, G., Cui, T. J., & Galdi, V. (2020). Recent advances and perspectives on space-time coding digital metasurfaces. EPJ Applied Metamaterials 7, 7.

Within the overarching framework of space-time metastructures, digital metasurfaces based on spatio-temporal coding are emerging as powerful and versatile architectures for complex ﬁeld manipulations, also in view of their inherently programmable nature. Here, we provide a compact survey of our recent results and ongoing studies in this research area. Examples of ﬁeld manipulations include harmonic beam steering and/ or shaping and programmable nonreciprocal effects. Possible applications are abundant and range from wireless communications to radars and imaging.

@article{IJ148_EPJAM_7_2020,
author = {Zhang, Lei and Dai, Jun Yan and Moccia, Massimo and Castaldi, Giuseppe and Cui, Tie Jun and Galdi, Vincenzo},
title = {Recent advances and perspectives on space-time coding digital metasurfaces},
doi = {10.1051/epjam/2020007},
journal = {EPJ Applied Metamaterials},
year = {2020},
volume = {7},
pages = {7},
month = dec
}


1 Dec 2020

Dustin Krogstad has joined the Fields & Waves Lab as a Ph.D. student in Information Technologies for Engineering.

His Ph.D. work will be focused on the study of millimeter-wave radar technologies.

3 Nov 2020

Joseph Tien has successfully defended his Ph.D. thesis in Information Technologies for Engineering entitled “Submillimeter Precision Close Range Active Target Tracking Using mm-Wave FMCW Radar for Artificial Reality”, supervised by Profs. Riccardo DeSalvo and Vincenzo Galdi.

Congratulations Dr. Tien!

Our paper on “Joint multi‐frequency beam shaping and steering via space-time-coding digital metasurfaces” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published in Advanced Functional Materials.

1. Castaldi, G., Zhang, L., Moccia, M., Hathaway, A. Y., Tang, W. X., Cui, T. J., & Galdi, V. (2021). Joint multi-frequency beam shaping and steering via space-time-coding digital metasurfaces. Advanced Functional Materials 31(6), 2007620.

Digital programmable metasurfaces provide a very powerful and versatile platform for implementing spatio-temporal modulation schemes that are of great interest within the emerging framework of space-time metastructures. In particular, space-time coding digital metasurfaces have been successfully applied to advanced wavefront manipulations in both the spatial and spectral domains. However, conventional space-time coding schemes do not allow the joint syntheses of the transmission/scattering angular responses at multiple frequencies, which are potentially useful in a variety of applications of practical interest. Here, a strategy is put forward to lift this limitation, thereby enabling joint multi-frequency beam shaping and steering, i.e., the independent and simultaneous syntheses of prescribed scattering patterns at given harmonic frequencies. The proposed approach relies on a more sophisticated space-time coding, with suitably designed, temporally intertwined coding sub-sequences, which effectively disentangles the joint multi-frequency syntheses. The power and versatility of the approach are illustrated via a series of representative application examples, including multi-beam, diffuse-scattering, and orbital-angular-momentum patterns. Theoretical predictions are experimentally validated by means of microwave measurements. The outcomes of this study hold promising potentials for applications to future imaging, information and mobile-communication systems.

@article{IJ147_AFM_2020,
author = {Castaldi, Giuseppe and Zhang, Lei and Moccia, Massimo and Hathaway, Alisa Y. and Tang, Wen Xuan and Cui, Tie Jun and Galdi, Vincenzo},
title = {Joint multi-frequency beam shaping and steering via space-time-coding digital metasurfaces},
volume = {31},
issue = {6},
pages = {2007620},
year = {2021},
month = feb
}


Our paper on “Joint multi‐frequency beam shaping and steering via space-time-coding digital metasurfaces,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in Advanced Functional Materials.

29 Sep 2020

We have presented an invited talk [1] at the 14th International Congress on Engineered Material Platforms for Novel Wave Phenomena (Metamaterials), New York (NY), USA, Sep. 28-Oct. 3, 2020 (online).

1. Zhang, L., Chen, X. Q., Shao, R. W., Dai, J. Y., Cheng, Q., Moccia, M., … Galdi, V. (2020). Recent advances in space-time-coding digital metasurfaces. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). New York (NY), USA, Sep. 28-Oct. 30, 2020 (online).
@inproceedings{Zhang_Metamaterials2020,
author = {Zhang, L. and Chen, X. Q. and Shao, R. W. and Dai, J. Y. and Cheng, Q. and Moccia, M. and Castaldi, G. and Cui, T. J. and Galdi, V.},
title = {Recent advances in space-time-coding digital metasurfaces},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {New York (NY), USA, Sep. 28-Oct. 30, 2020 (online)},
month = sep,
year = {2020}
}


Our paper on “Metasurface enhanced lab-on-fiber biosensors” [1] has been published in Laser & Photonics Reviews.

1. Consales, M., Quero, G., Spaziani, S., Principe, M., Micco, A., Galdi, V., … Cusano, A. (2020). Metasurface-enhanced lab-on-fiber biosensors. Laser & Photonics Reviews 14(12), 2000180.

The integration of metasurfaces on the tip of optical fibers enables advanced wavefront manipulations in Lab-on-Fiber application scenarios, and brings about new degrees of freedom that can be exploited for optimizing the surface sensitivity to local variations of the refractive index. Here, a novel biosensing platform is reported based on the integration of a phase-gradient plasmonic metasurface on the tip of an optical fiber, able to detect biomolecular interactions with very high sensitivity. Specifically, the capability of the proposed platform to detect very low concentrations of streptavidin in running buffer solutions, with a limit of detection of the order of a few ng mL−1, is demonstrated. In addition, its inherent integrability within medical catheters/needles renders it potentially very attractive for application scenarios of real-time diagnosis via liquid biopsy at precise locations inside the human body.

@article{IJ146_LPR_2020,
author = {Consales, Marco and Quero, Giuseppe and Spaziani, Sara and Principe, Maria and Micco, Alberto and Galdi, Vincenzo and Cutolo, Antonello and Cusano, Andrea},
title = {Metasurface-enhanced lab-on-fiber biosensors},
journal = {Laser \& Photonics Reviews},
volume = {14},
issue = {12},
pages = {2000180},
doi = {10.1002/lpor.202000180},
year = {2020},
month = dec
}


Our paper on “Extreme-parameter non-Hermitian dielectric metamaterials,” in collaboration with Vincenzo Caligiuri (University of Calabria) and Nader Engheta (University of Pennsylvania), has been accepted for publication in ACS Photonics.

Our paper on “Anomalous light transport induced by deeply subwavelength quasiperiodicity in multilayered dielectric metamaterials” [1] has been published in Physical Review B.

1. Coppolaro, M., Castaldi, G., & Galdi, V. (2020). Anomalous light transport induced by deeply subwavelength quasiperiodicity in multilayered dielectric metamaterials. Physical Review B 102(7), 075107.

For dielectric multilayered metamaterials, the effective-parameter representation is known to be insensitive to geometrical features occurring at deeply subwavelength scales. However, recent studies on periodic and aperiodically ordered geometries have shown the existence of certain critical parameter regimes where this conventional wisdom is upended, as the optical response of finite-size samples may depart considerably from the predictions of standard effective-medium theory. In these regimes, characterized by a mixed evanescent/propagating light transport, different classes of spatial (dis)order have been shown to induce distinctive effects in the optical response, in terms of anomalous transmission, localization, enhancement, absorption, and lasing. Here we further expand these examples by considering a quasiperiodic scenario based on a modified-Fibonacci geometry. Among the intriguing features of this model there is the presence of a scale parameter that controls the transition from perfectly periodic to quasiperiodic scenarios of different shades. Via an extensive parametric study, this allows us to identify the quasiperiodicity-induced anomalous effects, and to elucidate certain distinctive mechanisms and footprints. Our results hold potentially interesting implications for the optical probing of structural features at a resolution much smaller than the wavelength, and could also be leveraged to design novel types of absorbers and low-threshold lasers.

@article{IJ144_PRB_102_075107_2020,
title = {Anomalous light transport induced by deeply subwavelength quasiperiodicity in multilayered dielectric metamaterials},
author = {Coppolaro, Marino and Castaldi, Giuseppe and Galdi, Vincenzo},
journal = {Physical Review B},
volume = {102},
issue = {7},
pages = {075107},
numpages = {13},
year = {2020},
month = aug,
publisher = {American Physical Society},
doi = {10.1103/PhysRevB.102.075107}
}


Our paper on “Metasurface enhanced lab-on-fiber biosensors” has been accepted for publication in Laser & Photonics Reviews.

Our paper on “Anomalous light transport induced by deeply subwavelength quasiperiodicity in multilayered dielectric metamaterials” has been accepted for publication in Physical Review B.

An arXiv preprint is available.

Our paper on “Line waves in non-Hermitian metasurfaces” [1], in collaboration with Andrea Alù (ASRC-CUNY), has been published in ACS Photonics.

1. Moccia, M., Castaldi, G., Alù, A., & Galdi, V. (2020). Line waves in non-Hermitian metasurfaces. ACS Photonics 7(8), 2064–2072.

Planar junctions between reactive surface impedances with dual character (capacitive/inductive) can sustain line waves localized both in-plane and out-of-plane around the discontinuity, which propagate unattenuated along one-dimensional paths. Due to their attractive properties, these waves are of potential interest in applications ranging from integrated photonics to optical sensing. Here, we introduce and explore a non-Hermitian platform supporting these exotic modes based on parity−time symmetry. Speciﬁcally, we show that line waves can occur in the presence of a uniform surface reactance (either capacitive or inductive) and a symmetric resistance discontinuity from negative to positive values (i.e., gain and loss). We study analytically and numerically the propagation properties of these waves and the underlying physical mechanisms and also illustrate their intriguing properties in terms of conﬁnement, reconﬁgurability, spin-momentum locking and lasing. Finally, we address possible practical implementations based on photoexcited graphene. Our results hold intriguing potentials for applications in ﬂat optics and reconﬁgurable photonics.

@article{IJ143_ACS-PHOT_2020,
title = {Line waves in non-{H}ermitian metasurfaces},
doi = {10.1021/acsphotonics.0c00465},
journal = {ACS Photonics},
author = {Moccia, Massimo and Castaldi, Giuseppe and Al\{u}, Andrea and Galdi, Vincenzo},
month = aug,
year = {2020},
volume = {7},
issue = {8},
pages = {2064--2072},
note = {https://pubs.acs.org/doi/suppl/10.1021/acsphotonics.0c00465/suppl_file/ph0c00465_si_001.pdf}
}


Our paper on “Line waves in non-Hermitian metasurfaces,” in collaboration with Andrea Alù (ASRC-CUNY), has been accepted for publication in ACS Photonics.

Our paper on “Pixeled metasurface for multiwavelength detection of vitamin D3” [1], in collaboration with Emanuela Esposito’s Group (National Research Council), has been published in Nanophotonics.

1. Di Meo, V., Crescitelli, A., Moccia, M., Sandomenico, A., Cusano, A. M., Portaccio, M., … Esposito, E. (2020). Pixeled metasurface for multiwavelength detection of vitamin D. Nanophotonics 9(12), 3921–3930.

The steadily increasing demand for accurate analysis of vitamin D level, via measurement of its best general marker, 25-hydroxyvitamin D (25(OH)D), pushes for the development of novel automated assays capable of working at very low concentrations. Here, we propose a plasmonic biosensor of 25(OH)D3 (calcifediol) based on surface-enhanced infrared absorption spectroscopy, which exploits the resonant coupling between plasmonic nanoantennas and vibrational excitation of small molecules. Specifically, our proposed platform features a large-area (several mm2) metasurface made of gold nanoantennas fabricated on a silicon substrate, comprising different macroregions (“pixels”) of area 500 × 500 µm2. In each pixel, the nanoantenna geometrical parameters are tuned so as to support localized surface plasmon resonances (and hence large field enhancements at the nanoscale) within different regions of the infrared spectrum. As a result, a single chip is capable of performing analysis from the region of functional groups to that of fingerprint. Two different designs are fabricated via electron beam lithography, functionalized with a correlated antibody for the detection of 25(OH)D3, and characterized via Fourier-transform infrared spectroscopy. Our experiments demonstrate the capability to detect a concentration as low as 86 pmol/L, and an amount of immobilized small molecules of 25(OH)D3 monohydrate (molecular weight: 418.65 g/mol) as low as 4.31 amol over an area of 100 × 100 µm2.

@article{IJ142_Nanophotonics_2020,
author = {Di Meo, Valentina and Crescitelli, Alessio and Moccia, Massimo and Sandomenico, Annamaria and Cusano, Angela M. and Portaccio, Marianna and Lepore, Maria and Galdi, Vincenzo and Esposito, Emanuela},
title = {Pixeled metasurface for multiwavelength detection of vitamin D},
journal = {Nanophotonics},
year = {2020},
doi = {10.1515/nanoph-2020-0103},
pages = {3921--3930},
volume = {9},
issue = {12},
month = sep,
}


Our paper on “Manipulating the scattering pattern with non-Hermitian particle arrays” [1], in collaboration with Andrea Alù’s Group (ASRC-CUNY), has been published in Optics Express.

1. Zhang, Y. J., Li, P., Galdi, V., Tong, M. S., & Alù, A. (2020). Manipulating the scattering pattern with non-Hermitian particle arrays. Optics Express 28(13), 19492–19507.

We show that an array of non-Hermitian particles can enable advanced manipulations of the scattering pattern, beyond what is possible with passive structures. Active linear elements are shown to provide zero forward scattering without sacrificing the total scattered power, and by adding more particles, it is possible to control the zero-scattering direction at will. We apply our theory to realistic implementations of scatterer arrays, using loaded dipole antennas in which we tune the load impedance and investigate the stability of these arrays based on a realistic dispersion model for the gain elements. Finally, we discuss the possibility of controlling multiple frequencies to enable broadband control of the scattering pattern.

@article{IJ141_OpEX_28_19492_2020,
author = {Zhang, Yun Jing and Li, Peng and Galdi, Vincenzo and Tong, Mei Song and Al\{u}, Andrea},
journal = {Optics Express},
number = {13},
pages = {19492--19507},
publisher = {OSA},
title = {Manipulating the scattering pattern with non-Hermitian particle arrays},
volume = {28},
month = jun,
year = {2020},
doi = {10.1364/OE.395942}
}


Our paper on “Non-Hermitian doping of epsilon-near-zero media” [1], in collaboration with Nader Engheta (University of Pennsylvania), has been published in the Proceedings of the National Academy of Sciences of the U.S.A.

1. Coppolaro, M., Moccia, M., Castaldi, G., Engheta, N., & Galdi, V. (2020). Non-Hermitian doping of epsilon-near-zero media. Proceedings of the National Academy of Sciences of the U.S.A. 117(25), 13921–13928.

In solid-state physics, doping is a pivotal concept that allows controlling and engineering of the macroscopic electronic and optical properties of materials such as semiconductors by judiciously introducing small concentrations of impurities. Recently, this concept has been translated to two-dimensional photonic scenarios in connection with host media characterized by vanishingly small relative permittivity (epsilon near zero), showing that it is possible to obtain broadly tunable effective magnetic responses by introducing a single, nonmagnetic doping particle at an arbitrary position. So far, this phenomenon has been studied mostly for lossless configurations. In principle, the inevitable presence of material losses can be compensated via optical gain. However, taking inspiration from quantum (e.g., parity-time) symmetries that are eliciting growing attention in the emerging fields of non-Hermitian optics and photonics, this suggests considering more general gain-loss interactions. Here, we theoretically show that the photonic doping concept can be extended to non-Hermitian scenarios characterized by tailored distributions of gain and loss in either the doping particles or the host medium. In these scenarios, the effective permeability can be modeled as a complex-valued quantity (with the imaginary part accounting for the gain or loss), which can be tailored over broad regions of the complex plane. This enables a variety of unconventional optical responses and waveguiding mechanisms, which can be, in principle, reconfigured by varying the optical gain (e.g., via optical pumping). We envision several possible applications of this concept, including reconfigurable nanophotonics platforms and optical sensing, which motivate further studies for their experimental validation.

@article{IJ140_PNAS_2020,
author = {Coppolaro, Marino and Moccia, Massimo and Castaldi, Giuseppe and Engheta, Nader and Galdi, Vincenzo},
title = {Non-{H}ermitian doping of epsilon-near-zero media},
year = {2020},
month = jun,
volume = {117},
issue = {25},
pages = {13921--13928},
publisher = {National Academy of Sciences},
journal = {Proceedings of the National Academy of Sciences of the U.S.A.},
doi = {10.1073/pnas.2001125117},
}


Our paper on “Manipulating the scattering pattern with non-Hermitian particle arrays,” in collaboration with Andrea Alù’s Group (ASRC-CUNY), has been accepted for publication in Optics Express.

Our paper on “Pixeled metasurface for multiwavelength detection of vitamin D3,” in collaboration with Emanuela Esposito’s Group (National Research Council), has been accepted for publication in Nanophotonics.

Our paper on “Independent control of copolarized amplitude and phase responses via anisotropic metasurfaces” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published in Advanced Optical Materials.

1. Wu, R. Y., Bao, L., Wu, L. W., Wang, Z. X., Ma, Q., Wu, J. W., … Cui, T. J. (2020). Independent control of copolarized amplitude and phase responses via anisotropic metasurfaces. Advanced Optical Materials 8(11), 1902126.

Abstract A class of anisotropic, transmissive electromagnetic metasurfaces is presented, which enable independent and simultaneous control of copolarized phase and amplitude responses to two linear, orthogonal polarizations. By varying the geometrical parameters, the transmission response of the proposed structure can yield a full phase coverage, accompanied by broadly adjustable amplitude and negligible cross-polarized components. The full amplitude-phase control together with the novel anisotropic character allows efficient implementation of complicated field manipulations. As representative application examples, which cannot be realized via conventional (phase-only) metasurfaces, it is presented here: (1) the radiation of multiple equal-power vortex beams (along arbitrarily predesigned directions, with designable orbital angular momentum modes under different polarizations), and (2) the realization of polarization-reconfigurable multifocal metalenses. Full-wave numerical simulations and experimental results demonstrate good agreement and confirm the versatility and effectiveness of the proposed approach to design advanced field-manipulation systems.

@article{IJ139_AdOM_1902126_2020,
author = {Wu, Rui Yuan and Bao, Lei and Wu, Liang Wei and Wang, Zheng Xing and Ma, Qian and Wu, Jun Wei and Bai, Guo Dong and Galdi, Vincenzo and Cui, Tie Jun},
title = {Independent control of copolarized amplitude and phase responses via anisotropic metasurfaces},
volume = {8},
issue = {11},
pages = {1902126},
year = {2020},
month = jun,
keywords = {amplitude and phase control, anisotropic metasurfaces, arbitrary bifocal metalenses, equal-power vortex beams, polarization-reconfigurable},
}


Our paper on “Effects of deterministic disorder at deeply subwavelength scales in multilayered dielectric metamaterials” [1] has been published in [Optics Express].

1. Coppolaro, M., Castaldi, G., & Galdi, V. (2020). Effects of deterministic disorder at deeply subwavelength scales in multilayered dielectric metamaterials. Optics Express 28(7), 10199–10209.

It is common understanding that multilayered dielectric metamaterials, in the regime of deeply subwavelength layers, are accurately described by simple effective-medium models based on mixing formulas that do not depend on the spatial arrangement. In the wake of recent studies that have shown counterintuitive examples of periodic and aperiodic (orderly or random) scenarios in which this premise breaks down, we study here the effects of deterministic disorder. With specific reference to a model based on Golay-Rudin-Shapiro sequences, we illustrate certain peculiar boundary effects that can occur in finite-size dielectric multilayers, leading to anomalous light-transport properties that are in stark contrast with the predictions from conventional effective-medium theory. Via parametric and comparative studies, we elucidate the underlying physical mechanisms, also highlighting similarities and differences with respect to previously studied geometries. Our outcomes may inspire potential applications to optical sensing, switching and lasing.

@article{IJ138_OpEx_28_10199_2020,
author = {Coppolaro, Marino and Castaldi, Giuseppe and Galdi, Vincenzo},
journal = {Optics Express},
number = {7},
pages = {10199--10209},
publisher = {OSA},
title = {Effects of deterministic disorder at deeply subwavelength scales in multilayered dielectric metamaterials},
volume = {28},
month = mar,
year = {2020},
url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-28-7-10199},
doi = {10.1364/OE.388452}
}


Our paper on “Effects of deterministic disorder at deeply subwavelength scales in multilayered dielectric metamaterials” has been accepted for publication in Optics Express.

An arXiv preprint is available.

Our paper on “Independent control of co-polarized amplitude and phase responses via anisotropic metasurfaces,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in Advanced Optical Materials.

7 Jan 2020

Alisa Y. Hathaway has temporarily joined the Fields & Waves Lab within the framework of the MIT student externship program.

She will be working on the study of space-time coding digital metasurfaces.

10 Dec 2019

The call for nominations for the 2020 EurAAP Leopold B. Felsen Award for Excellence in Electrodynamics is open.

The Award was originally established jointly by the University of Siena and the University of Sannio, funded through a donation from Michael and Judy Felsen in fulfillment of the last wishes of their father, Professor Leo Felsen (1924-2005). Since 2015, the Award is established by the European Association on Antennas and Propagation (EurAAP).

The main purpose of the Award is to keep alive Prof. Felsen’s memory and scientific legacy, as well as to foster academic excellence in the electromagnetics community, by giving recognition to outstanding fundamental contributions from early stage researchers in electrodynamics.

The Award, by nomination only, will be presented annually, as a career award, to an early stage researcher. Eligible nominees should be under 40 years of age at the submission deadline. Previous awardees (also from the former Sannio and Siena editions) are not eligible.

The Award consists of a prize of 4,000 euro, which will be funded by the Felsen Family through a donation, and will be officially presented at the banquet of the upcoming 14th European Conference on Antennas and Propagation (EuCAP 2020).

Candidates from all areas of Electromagnetics are eligible to apply. Selection will be based on quality and significance of the candidates’ contributions to the field, and on the recommendation of the referees.

The deadline for submission of the nominations is January 31, 2020.

More details can be found here.

1 Dec 2019

Omar M. Perez has joined the Fields & Waves Lab as a Ph.D. student in Information Technologies for Engineering.

His Ph.D. work will be focused on the study of millimeter-wave radar technologies.

Our paper on “Breaking reciprocity with space-time-coding digital metasurfaces,” [1] in collaboration with Tie Jun Cui’s Group (Southeast University), made the back cover of Advanced Materials.

1. Zhang, L., Chen, X. Q., Shao, R. W., Dai, J. Y., Cheng, Q., Castaldi, G., … Cui, T. J. (2019). Breaking reciprocity with space-time-coding digital metasurfaces. Advanced Materials 31(41), 1904069.

Metasurfaces are artificially engineered ultrathin structures that can finely tailor and control electromagnetic wavefronts. There is currently a strong interest in exploring their capability to lift some fundamental limitations dictated by Lorentz reciprocity, which have strong implications in communication, heat management, and energy harvesting. Time-varying approaches have emerged as attractive alternatives to conventional schemes relying on magnetic or nonlinear materials, but experimental evidence is currently limited to devices such as circulators and antennas. Here, the recently proposed concept of space-time-coding digital metasurfaces is leveraged to break reciprocity. Moreover, it is shown that such nonreciprocal effects can be controlled dynamically. This approach relies on inducing suitable spatiotemporal phase gradients in a programmable way via digital modulation of the metasurface-elements’ phase repsonse, which enable anomalous reflections accompanied by frequency conversions. A prototype operating at microwave frequencies is designed and fabricated for proof-of-concept validation. Measured results are in good agreement with theory, hence providing the first experimental evidence of nonreciprocal reflection effects enabled by space-time-modulated digital metasurfaces. The proposed concept and platform set the stage for “on-demand” realization of nonreciprocal effects, in programmable or reconfigurable fashions, which may find several promising applications, including frequency conversion, Doppler frequency illusion, optical isolation, and unidirectional transmission.

@article{IJ137_AM_1904069_2019,
author = {Zhang, Lei and Chen, Xiao Qing and Shao, Rui Wen and Dai, Jun Yan and Cheng, Qiang and Castaldi, Giuseppe and Galdi, Vincenzo and Cui, Tie Jun},
title = {Breaking reciprocity with space-time-coding digital metasurfaces},
volume = {31},
number = {41},
pages = {1904069},
year = {2019},
month = oct,
}


20 Sep 2019

Our paper entitled “Some ideas for non-Hermitian doping of epsilon-near-zero media” [1] received the Best Poster Award at the 13th International Congress on Engineered Material Platforms for Novel Wave Phenomena (Metamaterials), Rome, Italy, Sep. 16-19, 2019.

1. Coppolaro, M., Moccia, M., Castaldi, G., Engheta, N., & Galdi, V. (2019). Some ideas for non-Hermitian doping of epsilon-near-zero media. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Rome, Italy, Sep. 16-19, 2019.
@inproceedings{Coppolaro_Metamaterials2019b,
author = {Coppolaro, M. and Moccia, M. and Castaldi, G. and Engheta, N. and Galdi, V.},
title = {Some ideas for non-Hermitian doping of epsilon-near-zero media},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {Rome, Italy, Sep. 16-19, 2019},
month = sep,
year = {2019}
}


19 Sep 2019

We have presented five papers [1, 2, 3, 4, 5], at the 13th International Congress on Engineered Material Platforms for Novel Wave Phenomena (Metamaterials), Rome, Italy, Sep. 16-19, 2019.

1. Moccia, M., Castaldi, G., Alù, A., & Galdi, V. (2019). Spectral singularities in non-Hermitian cylindrical geometries. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Rome, Italy, Sep. 16-19, 2019.
@inproceedings{Moccia_Metamaterials2019b,
author = {Moccia, Massimo and Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
title = {Spectral singularities in non-Hermitian cylindrical geometries},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {Rome, Italy, Sep. 16-19, 2019},
month = sep,
year = {2019}
}

2. Coppolaro, M., Moccia, M., Castaldi, G., Engheta, N., & Galdi, V. (2019). Some ideas for non-Hermitian doping of epsilon-near-zero media. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Rome, Italy, Sep. 16-19, 2019.
@inproceedings{Coppolaro_Metamaterials2019b,
author = {Coppolaro, M. and Moccia, M. and Castaldi, G. and Engheta, N. and Galdi, V.},
title = {Some ideas for non-Hermitian doping of epsilon-near-zero media},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {Rome, Italy, Sep. 16-19, 2019},
month = sep,
year = {2019}
}

3. Moccia, M., Castaldi, G., & Galdi, V. (2019). Nonlocal and non-Hermitian transformation optics. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Rome, Italy, Sep. 16-19, 2019.
@inproceedings{Moccia_Metamaterials2019,
author = {Moccia, M. and Castaldi, G. and Galdi, V.},
title = {Nonlocal and non-Hermitian transformation optics},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {Rome, Italy, Sep. 16-19, 2019},
month = sep,
year = {2019}
}

4. Zhang, L., Chen, X. Q., Liu, S., Zhang, Q., Zhao, J., Dai, J. Y., … Cui, T. J. (2019). Space-time-coding digital metasurfaces. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Rome, Italy, Sep. 16-19, 2019.
@inproceedings{Zhang_Metamaterials2019,
author = {Zhang, Lei and Chen, Xiao Qing and Liu, Shuo and Zhang, Qian and Zhao, Jie and Dai, Jun Yan and Bai, Guo Dong and Wan, Xiang and Cheng, Qiang and Castaldi, Giuseppe and Galdi, Vincenzo and Cui, Tie Jun},
title = {Space-time-coding digital metasurfaces},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {Rome, Italy, Sep. 16-19, 2019},
month = sep,
year = {2019}
}

5. Coppolaro, M., Castaldi, G., & Galdi, V. (2019). Enhancement of weak nonlocality in aperiodically ordered multilayered dielectric metamaterials. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Rome, Italy, Sep. 16-19, 2019.
@inproceedings{Coppolaro_Metamaterials2019,
author = {Coppolaro, M. and Castaldi, G. and Galdi, V.},
title = {Enhancement of weak nonlocality in aperiodically ordered multilayered dielectric metamaterials},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
organization = {Rome, Italy, Sep. 16-19, 2019},
month = sep,
year = {2019}
}


6 Sep 2019

We have presented a talk [1] at the Nanophotonics and Micro/Nano Optics International Conference (NANOP), Munich, Germany, Sep. 4-7, 2019.

1. Di Meo, V., Crescitelli, A., Sandomenico, A., Moccia, M., Galdi, V., Portaccio, M., … Esposito, E. (2019). Pixeled metasurface for multiwavelength detection of vitamin D3. In Nanophotonics and Micro/Nano Optics International Conference (NANOP). Munich, Germany, Sep. 4-7, 2019.
@inproceedings{DiMeo_NANOP19,
author = {Di Meo, V. and Crescitelli, A. and Sandomenico, A. and Moccia, M. and Galdi, V. and Portaccio, M. and Lepore, M. and Rendina, I. and Ruvo, M. and Esposito, E.},
title = {Pixeled metasurface for multiwavelength  detection of vitamin D3},
booktitle = {Nanophotonics and Micro/Nano Optics International Conference (NANOP)},
organization = {Munich, Germany, Sep. 4-7, 2019},
month = sep,
year = {2019}
}


19 Aug 2019

Prof. Vincenzo Galdi has been appointed Associate Editor of Optics Express.

Our paper on “Breaking reciprocity with space-time-coding digital metasurfaces” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published in Advanced Materials.

1. Zhang, L., Chen, X. Q., Shao, R. W., Dai, J. Y., Cheng, Q., Castaldi, G., … Cui, T. J. (2019). Breaking reciprocity with space-time-coding digital metasurfaces. Advanced Materials 31(41), 1904069.

Metasurfaces are artificially engineered ultrathin structures that can finely tailor and control electromagnetic wavefronts. There is currently a strong interest in exploring their capability to lift some fundamental limitations dictated by Lorentz reciprocity, which have strong implications in communication, heat management, and energy harvesting. Time-varying approaches have emerged as attractive alternatives to conventional schemes relying on magnetic or nonlinear materials, but experimental evidence is currently limited to devices such as circulators and antennas. Here, the recently proposed concept of space-time-coding digital metasurfaces is leveraged to break reciprocity. Moreover, it is shown that such nonreciprocal effects can be controlled dynamically. This approach relies on inducing suitable spatiotemporal phase gradients in a programmable way via digital modulation of the metasurface-elements’ phase repsonse, which enable anomalous reflections accompanied by frequency conversions. A prototype operating at microwave frequencies is designed and fabricated for proof-of-concept validation. Measured results are in good agreement with theory, hence providing the first experimental evidence of nonreciprocal reflection effects enabled by space-time-modulated digital metasurfaces. The proposed concept and platform set the stage for “on-demand” realization of nonreciprocal effects, in programmable or reconfigurable fashions, which may find several promising applications, including frequency conversion, Doppler frequency illusion, optical isolation, and unidirectional transmission.

@article{IJ137_AM_1904069_2019,
author = {Zhang, Lei and Chen, Xiao Qing and Shao, Rui Wen and Dai, Jun Yan and Cheng, Qiang and Castaldi, Giuseppe and Galdi, Vincenzo and Cui, Tie Jun},
title = {Breaking reciprocity with space-time-coding digital metasurfaces},
volume = {31},
number = {41},
pages = {1904069},
year = {2019},
month = oct,
}


Our paper on “Breaking reciprocity with space-time-coding digital metasurfaces,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in Advanced Materials.

Our paper on “Harnessing spectral singularities in non-Hermitian cylindrical structures” [1], in collaboration with Andrea Alù (ASRC-CUNY), has been published in the IEEE Transactions on Antennas and Propagation.

1. Moccia, M., Castaldi, G., Alù, A., & Galdi, V. (2020). Harnessing spectral singularities in non-Hermitian cylindrical structures. IEEE Transactions on Antennas and Propagation 28(3), 1704–1716.

Non-Hermitian systems characterized by suitable spatial distributions of gain and loss can exhibit “spectral singularities” in the form of zero-width resonances associated to real-frequency poles in the scattering operator. Here, we study this intriguing phenomenon in connection with cylindrical geometries, and explore possible applications to controlling and tailoring in unconventional ways the scattering response of sub-wavelength and wavelength-sized objects. Among the possible implications and applications, we illustrate the additional degrees of freedom available in the scattering-absorption-extinction tradeoff, and address the engineering of zero-forward-scattering, transverse scattering, and gain-controlled reconfigurability of the scattering pattern, also paying attention to stability issues. Our results may open up new vistas in active and reconfigurable nanophotonics platforms.

@article{IJ136_IEEE-TAP_2019,
author = {Moccia, Massimo and Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
journal = {IEEE Transactions on Antennas and Propagation},
title = {Harnessing spectral singularities in non-{H}ermitian cylindrical structures},
year = {2020},
volume = {28},
number = {3},
pages = {1704--1716},
doi = {10.1109/TAP.2019.2927861},
month = mar
}


12 Jul 2019

We have presented two talks [1, 2] at the IEEE AP-S Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (IEEE-APS/URSI), Atlanta, GA, USA, July 7-12, 2019.

1. Coppolaro, M., Moccia, M., Castaldi, G., Engheta, N., & Galdi, V. (2019). Non-Hermitian doping of epsilon-near-zero media. In USNC-URSI Radio Science Meeting. Atlanta, GA, USA, July 7-12, 2019.
@inproceedings{Coppolaro_URSI-USNC2019,
author = {Coppolaro, Marino and Moccia, Massimo and Castaldi, Giuseppe and Engheta, Nader and Galdi, Vincenzo},
title = {Non-Hermitian doping of epsilon-near-zero media},
booktitle = {USNC-URSI Radio Science Meeting},
organization = {Atlanta, GA, USA, July 7-12, 2019},
month = jul,
year = {2019}
}

2. Zhang, L., Chen, X. Q., Liu, S., Zhang, Q., Zhao, J., Dai, J. Y., … Cui, T. J. (2019). Digital metasurfaces based on spatio-temporal coding. In USNC-URSI Radio Science Meeting. Atlanta, GA, USA, July 7-12, 2019.
@inproceedings{Zhang_URSI-USNC2019,
author = {Zhang, Lei and Chen, Xiao Qing and Liu, Shuo and Zhang, Qian and Zhao, Jie and Dai, Jun Yan and Bai, Guo Dong and Wan, Xiang and Cheng, Qiang and Castaldi, Giuseppe and Galdi, Vincenzo and Cui, Tie Jun},
title = {Digital metasurfaces based on spatio-temporal coding},
booktitle = {USNC-URSI Radio Science Meeting},
organization = {Atlanta, GA, USA, July 7-12, 2019},
month = jul,
year = {2019}
}


Our paper on “Harnessing spectral singularities in non-Hermitian cylindrical structures,” in collaboration with Andrea Alù (ASRC-CUNY), has been accepted for publication in the IEEE Transactions on Antennas and Propagation.

An arXiv preprint is available.

3 Apr 2019

We have presented a talk [1] at the 13th European Conference on Antennas and Propagation (EuCAP), Krakow, Poland, Mar. 31-Apr. 5, 2019.

1. Moccia, M., Castaldi, G., & Galdi, V. (2019). Nonlocal and non-Hermitian extensions of transformation optics. In Proc. 13th European Conference on Antennas and Propagation (EuCAP). Krakow, Poland, Mar. 31-Apr. 5, 2019.
@inproceedings{Moccia_EuCAP2019,
author = {Moccia, Massimo and Castaldi, Giuseppe and Galdi, Vincenzo},
title = {Nonlocal and non-Hermitian extensions of transformation optics},
booktitle = {Proc. 13th European Conference on Antennas and Propagation (EuCAP)},
organization = {Krakow, Poland, Mar. 31-Apr. 5, 2019},
month = mar,
year = {2019}
}


Our paper on “Evaluation of fiber-optic phase-gradient meta-tips for sensing applications” [1], in collaboration with Andrea Cusano’s Group, has been published in Nanomaterials and Nanotechnology.

1. Principe, M., Consales, M., Castaldi, G., Galdi, V., & Cusano, A. (2019). Evaluation of fiber-optic phase-gradient meta-tips for sensing applications. Nanomaterials and Nanotechnology 9.

Recently, within the emerging framework of “lab-on-fiber” technologies, we successfully demonstrated the integration of phase-gradient plasmonic metasurfaces on the tip of an optical fiber. The resulting optical-fiber “meta-tips” promise to empower the typical fiber-optics application scenarios (e.g. sensing, telecommunications, imaging, etc.) with the advanced light-manipulation capabilities endowed by metasurfaces. Here, we explore more in detail the possibility to exploit this platform in label-free biological or chemical sensing applications. Specifically, we carry out a parametric study of the surface sensitivity and show that phase-gradient metasurfaces generally outperform their gradient-free counterparts, without imposing additional fabrication complexity. Therefore, the phase gradient can be effectively exploited as an additional degree of freedom in the design of high-sensitivity devices.

@article{IJ135_NMNT_9_2019,
author = {Principe, M and Consales, M and Castaldi, G and Galdi, V and Cusano, A},
title = {Evaluation of fiber-optic phase-gradient meta-tips for sensing applications},
journal = {Nanomaterials and Nanotechnology},
volume = {9},
year = {2019},
doi = {10.1177/1847980419832724}
}


Our paper on “Evaluation of fiber-optic phase-gradient meta-tips for sensing applications,” in collaboration with Andrea Cusano’s Group, has been accepted for publication in Nanomaterials and Nanotechnology.

10 Jan 2019

Olivia Chong and Manuel Morales have temporarily joined the Fields & Waves Lab within the framework of the MIT student externship program.

They will be working on the study of metamaterial-based analog computing.

10 Dec 2018

The call for nominations for the 2019 EurAAP Leopold B. Felsen Award for Excellence in Electrodynamics is open.

The Award was originally established jointly by the University of Siena and the University of Sannio, funded through a donation from Michael and Judy Felsen in fulfillment of the last wishes of their father, Professor Leo Felsen (1924-2005). Since 2015, the Award is established by the European Association on Antennas and Propagation (EurAAP).

The main purpose of the Award is to keep alive Prof. Felsen’s memory and scientific legacy, as well as to foster academic excellence in the electromagnetics community, by giving recognition to outstanding fundamental contributions from early stage researchers in electrodynamics.

The Award, by nomination only, will be presented annually, as a career award, to an early stage researcher. Eligible nominees should be under 40 years of age at the submission deadline. Previous awardees (also from the former Sannio and Siena editions) are not eligible.

The Award consists of a prize of 4,000 euro, which will be funded by the Felsen Family through a donation, and will be officially presented at the banquet of the upcoming 13th European Conference on Antennas and Propagation (EuCAP 2019).

Candidates from all areas of Electromagnetics are eligible to apply. Selection will be based on quality and significance of the candidates’ contributions to the field, and on the recommendation of the referees.

The deadline for submission of the nominations is January 31, 2019.

More details can be found here.

Our paper on “Aperiodic-order-induced enhancement of weak nonlocality in multilayered dielectric metamaterials” [1] has been published in [Physical Review B].

1. Coppolaro, M., Castaldi, G., & Galdi, V. (2018). Aperiodic order induced enhancement of weak nonlocality in multilayered dielectric metamaterials. Physical Review B 98(19), 195128.

Recent studies on fully dielectric multilayered metamaterials have shown that the negligibly small nonlocal effects (spatial dispersion) typically observed in the limit of deeply subwavelength layers may be significantly enhanced by peculiar boundary effects occurring in certain critical parameter regimes. These phenomena, observed so far in periodic and randomly disordered geometries, are manifested as strong differences between the exact optical response of finite-size metamaterial samples and the prediction from conventional effective-theory-medium models based on mixing formulae. Here, with specific focus on the Thue-Morse geometry, we make a first step toward extending the studies above to the middle-ground of aperiodically ordered multilayers, lying in between perfect periodicity and disorder. We show that, also for these geometries, there exist critical parameter ranges that favor the buildup of boundary effects leading to strong enhancement of the (otherwise negligibly weak) nonlocality. However, the underlying mechanisms are fundamentally different from those observed in the periodic case, and exhibit typical footprints (e.g., fractal gaps, quasi-localized states) that are distinctive of aperiodic order. The outcomes of our study indicate that aperiodic order plays a key role in the buildup of the aforementioned boundary effects, and may also find potential applications to optical sensors, absorbers and lasers.

@article{IJ134_PRB_98_195128_2018,
title = {Aperiodic order induced enhancement of weak nonlocality in multilayered dielectric metamaterials},
author = {Coppolaro, Marino and Castaldi, Giuseppe and Galdi, Vincenzo},
journal = {Physical Review B},
volume = {98},
issue = {19},
pages = {195128},
numpages = {12},
year = {2018},
month = nov,
publisher = {American Physical Society},
doi = {10.1103/PhysRevB.98.195128}
}


Our paper on “Aperiodic-order-induced enhancement of weak nonlocality in multilayered dielectric metamaterials” has been accepted for publication in Physical Review B.

An arXiv preprint is available.

Our paper on “Space-time-coding digital metasurfaces” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published in Nature Communications.

1. Zhang, L., Chen, X. Q., Liu, S., Zhang, Q., Zhao, J., Dai, J. Y., … Cui, T. J. (2018). Space-time-coding digital metasurfaces. Nature Communications 9(1), 4334.

The recently proposed digital coding metasurfaces make it possible to control electromagnetic (EM) waves in real time, and allow the implementation of many different functionalities in a programmable way. However, current configurations are only space-encoded, and do not exploit the temporal dimension. Here, we propose a general theory of space-time modulated digital coding metasurfaces to obtain simultaneous manipulations of EM waves in both space and frequency domains, i.e., to control the propagation direction and harmonic power distribution simultaneously. As proof-of-principle application examples, we consider harmonic beam steering, beam shaping, and scattering-signature control. For validation, we realize a prototype controlled by a field-programmable gate array, which implements the harmonic beam steering via an optimized space-time coding sequence. Numerical and experimental results, in good agreement, demonstrate good performance of the proposed approach, with potential applications to diverse fields such as wireless communications, cognitive radars, adaptive beamforming, holographic imaging.

@article{IJ133_NatComm_9_4334_2018,
author = {Zhang, Lei and Chen, Xiao Qing and Liu, Shuo and Zhang, Qian and Zhao, Jie and Dai, Jun Yan and Bai, Guo Dong and Wan, Xiang and Cheng, Qiang and Castaldi, Giuseppe and Galdi, Vincenzo and Cui, Tie Jun},
title = {Space-time-coding digital metasurfaces},
journal = {Nature Communications},
year = {2018},
volume = {9},
number = {1},
pages = {4334},
doi = {10.1038/s41467-018-06802-0},
note = {https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-018-06802-0/MediaObjects/41467_2018_6802_MOESM1_ESM.pdf},
month = oct
}


Our paper on “Boundary effects of weak nonlocality in multilayered dielectric metamaterials” [1], in collaboration with Andrea Alù (ASRC-CUNY), has been published in Physical Review Applied.

1. Castaldi, G., Alù, A., & Galdi, V. (2018). Boundary effects of weak nonlocality in multilayered dielectric metamaterials. Physical Review Applied 10(3), 034060.

Nonlocal (spatial-dispersion) effects in multilayered metamaterials composed of periodic stacks of alternating, deeply subwavelength dielectric layers are known to be negligibly weak. Counterintuitively, under certain critical conditions, weak nonlocality may build up strong boundary effects that are not captured by conventional (local) effective-medium models based on simple mixing formulas. Here we show that this phenomenon can be fruitfully studied and understood in terms of error propagation in the iterated maps of the trace and antitrace of the optical transfer matrix of the multilayer. Our approach effectively parameterizes these peculiar effects via remarkably simple and insightful closed-form expressions, which enable direct identification of the critical parameters and regimes. We also show how these boundary effects can be captured by suitable nonlocal corrections.

@article{IJ132_PRAppl_10_034060_2018,
title = {Boundary effects of weak nonlocality in multilayered dielectric metamaterials},
author = {Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
journal = {Physical Review Applied},
volume = {10},
issue = {3},
pages = {034060},
numpages = {13},
year = {2018},
month = sep,
publisher = {American Physical Society},
doi = {10.1103/PhysRevApplied.10.034060},
}


29 Aug 2018

We have presented four papers [1, 2, 3, 4] at the 12th International Congress on Engineered Material Platforms for Novel Wave Phenomena (Metamaterials), Espoo, Finland, Aug. 27-30, 2018.

1. Scaravilli, M., Micco, A., Castaldi, G., Coppola, G., Gioffrè, Iodice, M., … Cusano, A. (2018). Fiber-tip coupling of Bloch surface waves. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Espoo, Finland, Aug. 27-30, 2018.
@inproceedings{Scaravilli_2018-Metamaterials,
author = {Scaravilli, M. and Micco, A. and Castaldi, G. and Coppola, G. and Gioffr\e and Iodice, M. and La Ferrara, V. and Galdi, V. and Cusano, A.},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
title = {Fiber-tip coupling of Bloch surface waves},
year = {2018},
organization = {Espoo, Finland, Aug. 27-30, 2018},
doi = {10.1109/MetaMaterials.2018.8534044},
month = aug
}

2. Castaldi, G., Alù, A., & Galdi, V. (2018). Revisiting the boundary effects of weak nonlocality in multilayered dielectric metamaterials: A trace and anti-trace map approach. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Espoo, Finland, Aug. 27-30, 2018.
@inproceedings{Castaldi_2018-Metamaterials,
author = {Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
title = {Revisiting the boundary effects of weak nonlocality in multilayered dielectric metamaterials: A trace and anti-trace map approach},
year = {2018},
organization = {Espoo, Finland, Aug. 27-30, 2018},
doi = {10.1109/MetaMaterials.2018.8534149},
month = aug
}

3. Moccia, M., Castaldi, G., Alù, A., & Galdi, V. (2018). A study of spectral singularities in non-Hermitian cylindrical core-shell geometries. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Espoo, Finland, Aug. 27-30, 2018.
@inproceedings{Moccia_2018-Metamaterials,
author = {Moccia, Massimo and Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
title = {A study of spectral singularities in non-Hermitian cylindrical core-shell geometries},
year = {2018},
organization = {Espoo, Finland, Aug. 27-30, 2018},
doi = {10.1109/MetaMaterials.2018.8534116},
month = aug
}

4. Koral, C., Papari, G., Andreone, A., Moccia, M., Castaldi, G., Galdi, V., … Cui, T. J. (2018). Diffuse THz scattering via coding metasurfaces. In International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS). Espoo, Finland, Aug. 27-30, 2018.
@inproceedings{Koral_2018-Metamaterials,
author = {Koral, C. and Papari, G. and Andreone, A. and Moccia, M. and Castaldi, G. and Galdi, V. and Liu, S. and R.Y., Wu and Cui, T.J.},
booktitle = {International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
title = {Diffuse THz scattering via coding metasurfaces},
year = {2018},
organization = {Espoo, Finland, Aug. 27-30, 2018},
doi = {10.1109/MetaMaterials.2018.8534087},
month = aug
}


Our paper on “Boundary effects of weak nonlocality in multilayered dielectric metamaterials,” in collaboration with Andrea Alù (ASRC-CUNY), has been accepted for publication in Physical Review Applied.

An arXiv preprint is available.

Our paper on “Suboptimal coding metasurfaces for terahertz diffuse scattering” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published in Scientific Reports.

1. Moccia, M., Koral, C., Papari, G. P., Liu, S., Zhang, L., Wu, R. Y., … Andreone, A. (2018). Suboptimal coding metasurfaces for terahertz diffuse scattering. Scientific Reports 8, 11908.

Coding metasurfaces, composed of only two types of elements arranged according to a binary code, are attracting a steadily increasing interest in many application scenarios. In this study, we apply this concept to attain diffuse scattering at THz frequencies. Building up on previously derived theoretical results, we carry out a suboptimal metasurface design based on a simple, deterministic and computationally inexpensive algorithm that can be applied to arbitrarily large structures. For experimental validation, we fabricate and characterize three prototypes working at 1 THz, which, in accordance with numerical predictions, exhibit significant reductions of the radar cross-section, with reasonably good frequency and angular stability. Besides the radar-signature control, our results may also find potentially interesting applications to diffusive imaging, computational imaging, and (scaled to optical wavelengths) photovoltaics.

@article{IJ131_SREP_8_11908_2018,
author = {Moccia, Massimo and Koral, Can and Papari, Gian Paolo and Liu, Shuo and Zhang, Lei and Wu, Rui Yuan and Castaldi, Giuseppe and Cui, Tie Jun and Galdi, Vincenzo and Andreone, Antonello},
title = {Suboptimal coding metasurfaces for terahertz diffuse scattering},
journal = {Scientific Reports},
year = {2018},
volume = {8},
pages = {11908},
month = aug,
url = {https://www.nature.com/articles/s41598-018-30375-z},
doi = {10.1038/s41598-018-30375-z},
note = {https://static-content.springer.com/esm/art%3A10.1038%2Fs41598-018-30375-z/MediaObjects/41598_2018_30375_MOESM1_ESM.pdf}
}


Our paper on “Suboptimal coding metasurfaces for terahertz diffuse scattering,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in Scientific Reports.

We have presented two talks [1, 2] at the IEEE AP-S Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (IEEE-APS/URSI), Boston, MA, USA, July 8-13, 2018.

1. Moccia, M., Castaldi, G., Alù, A., & Galdi, V. (2018). Spectral singularities in cylindrical non-Hermitian structures. In USNC-URSI Radio Science Meeting. Boston, MA, USA, July 8-13, 2018.
@inproceedings{Moccia_2018-USNC-URSI,
author = {Moccia, Massimo and Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
booktitle = {USNC-URSI Radio Science Meeting},
title = {Spectral singularities in cylindrical non-Hermitian structures},
year = {2018},
organization = {Boston, MA, USA, July 8-13, 2018},
month = jul
}

2. Castaldi, G., Alù, A., & Galdi, V. (2018). Boundary effects of weak nonlocality in multilayered dielectric metamaterials. In USNC-URSI Radio Science Meeting. Boston, MA, USA, July 8-13, 2018.
@inproceedings{Castaldi_2018-USNC-URSI,
author = {Castaldi, Giuseppe and Al\u, Andrea and Galdi, Vincenzo},
booktitle = {USNC-URSI Radio Science Meeting},
title = {Boundary effects of weak nonlocality in multilayered dielectric metamaterials},
year = {2018},
organization = {Boston, MA, USA, July 8-13, 2018},
month = jul
}


Our paper on “Excitation of Bloch surface waves on an optical fiber tip” [1], in collaboration with Andrea Cusano’s Group, CNR-IMM and ENEA has been published in Advanced Optical Materials.

1. Scaravilli, M., Micco, A., Castaldi, G., Coppola, G., Gioffrè, M., Iodice, M., … Cusano, A. (2018). Excitation of Bloch surface waves on an optical fiber tip. Advanced Optical Materials 6(9), 1800477.

The integration of structures supporting Bloch surface waves (BSWs) with optical fibers is highly desirable, since it would enable the development of high-figure-of-merit miniaturized all-fiber optrodes, opening new pathways within the “lab-on-fiber” roadmap. Here, the first experimental demonstration of grating-assisted excitation of BSWs on the tip of single-mode fibers in the near-infrared region is provided. This is attained via fabrication of a 1D diffraction grating on the fiber facet, and subsequent deposition of a 1D photonic crystal. In spite of a resonance broadening due to grating-induced morphological perturbations, the measured Q-factor of 50 is still higher than typical lab-on-tip plasmonic-probe benchmarks. With a view toward biomolecular sensing, a surface sensitivity of 1.22 nm nm−1 of homogeneous overlay deposited over the active region, which is in line with most plasmonic optrodes largely used in connection with optical fibers, is evaluated. The results also highlight the current limitations and the challenges to face for the development of advanced BSW-based fiber-tip platforms for biological sensing applications.

@article{IJ130_AdOM_2018,
author = {Scaravilli, Michele and Micco, Alberto and Castaldi, Giuseppe and Coppola, Giuseppe and Gioffr\e, Mariano and Iodice, Mario and La Ferrara, Vera and Galdi, Vincenzo and Cusano, Andrea},
title = {Excitation of Bloch surface waves on an optical fiber tip},
pages = {1800477},
volume = {6},
issue = {9},
year = {2018},
month = oct,
keywords = {diffraction gratings, lab-on-fiber, optical fiber sensors, photonic crystals, surface waves},
}


A Tutorial Session on Metamaterials was held at the 5th IEEE International Workshop on Metrology for AeroSpace (MetroAeroSpace 2018) in Rome, Italy. Tutorial lectures were given by Profs. Vincenzo Galdi (University of Sannio), Alessio Monti (Niccolò Cusano University), and Mirko Barbuto (Niccolò Cusano University).

Our paper on “Excitation of Bloch surface waves on an optical fiber tip,” in collaboration with Andrea Cusano’s Group, CNR-IMM and ENEA has been accepted for publication in Advanced Optical Materials.

The paper “Roadmap on transformation optics” [1] has been published in the Journal of Optics. Section 3 contains a perspective on nonlocal and non-Hermitian extensions authored by Prof. Vincenzo Galdi.

1. McCall, M., Pendry, J. B., Galdi, V., Lai, Y., Horsley, S. A. R., Li, J., … Cummer, S. A. (2018). Roadmap on transformation optics. Journal of Optics 20(6), 063001.

Transformation optics asks, using Maxwell’s equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein’s principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell’s equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from ‘few’ to ‘infinity’, and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an ‘interrupt-without-interrupt’ facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled ‘General Relativity in Electrical Engineering’. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell’s theory defines a ‘perfect’ transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field’s status and future development.

@article{IJ129_JO_20_063001_2018,
author = {McCall, Martin and Pendry, John B and Galdi, Vincenzo and Lai, Yun and Horsley, S A R and Li, Jensen and Zhu, Jian and Mitchell-Thomas, Rhiannon C and Quevedo-Teruel, Oscar and Tassin, Philippe and Ginis, Vincent and Martini, Enrica and Minatti, Gabriele and Maci, Stefano and Ebrahimpouri, Mahsa and Hao, Yang and Kinsler, Paul and Gratus, Jonathan and Lukens, Joseph M and Weiner, Andrew M and Leonhardt, Ulf and Smolyaninov, Igor I and Smolyaninova, Vera N and Thompson, Robert T and Wegener, Martin and Kadic, Muamer and Cummer, Steven A},
title = {Roadmap on transformation optics},
journal = {Journal of Optics},
volume = {20},
number = {6},
pages = {063001},
doi = {10.1088/2040-8986/aab976},
url = {http://stacks.iop.org/2040-8986/20/i=6/a=063001},
year = {2018}
}


23 Jan 2018

Michele Scaravilli has successfully defended his Ph.D. thesis in Information Technologies for Engineering entitled “Bloch‐Surface‐Wave Assisted Lab‐on‐Fiber Optrodes”, supervised by Profs. Vincenzo Galdi and Andrea Cusano.

Congratulations Dr. Scaravilli!

1 Dec 2017

Marino Coppolaro has joined the Fields & Waves Lab as a Ph.D. student in Information Technologies for Engineering.

His Ph.D. work will be focused on the study of nonlocal effects in metamaterials.

17 Nov 2017

The call for nominations for the 2018 EurAAP Leopold B. Felsen Award for Excellence in Electrodynamics is open.

The Award was originally established jointly by the University of Siena and the University of Sannio, funded through a donation from Michael and Judy Felsen in fulfillment of the last wishes of their father, Professor Leo Felsen (1924-2005). Since 2015, the Award is established by the European Association on Antennas and Propagation (EurAAP).

The main purpose of the Award is to keep alive Prof. Felsen’s memory and scientific legacy, as well as to foster academic excellence in the electromagnetics community, by giving recognition to outstanding fundamental contributions from early stage researchers in electrodynamics.

The Award, by nomination only, will be presented annually, as a career award, to an early stage researcher. Eligible nominees should be under 40 years of age at the submission deadline. Previous awardees (also from the former Sannio and Siena editions) are not eligible.

The Award consists of a prize of 4,000 euro, which will be funded by the Felsen Family through a donation, and will be officially presented at the banquet of the upcoming 12th European Conference on Antennas and Propagation (EuCAP 2018).

Candidates from all areas of Electromagnetics are eligible to apply. Selection will be based on quality and significance of the candidates’ contributions to the field, and on the recommendation of the referees.

The deadline for submission of the nominations is January 31, 2018.

More details can be found here.

The journal Nanomaterials and Nanotechnology will publish a Special Collection on Recent Advances and Trends in Optical Metamaterials and Metasurfaces, coordinated by the Guest Editors Profs. Mirko Barbuto (Niccolò Cusano University), Alessio Monti (Niccolò Cusano University), and Maria Principe (University of Salerno), and Vincenzo Galdi (University of Sannio).

More details and the call for papers can be found here.

The 5th IEEE International Workshop on Metrology for AeroSpace (MetroAeroSpace 2018) will convene in Rome, Italy, from June 20 - 22, 2018.

A special session on Metamaterials for Aerospace is being organized by Vincenzo Galdi (University of Sannio) and Filiberto Bilotti (University of Roma Tre).

More details and the call for papers can be found here.

The XXXV Edition of the EUPROMETA Distributed Doctoral School on Metamaterials will be held in Rome, Italy, from December 18-22, 2017. The school will be focused on Advanced Electromagnetic Materials and Surfaces for Novel Wave Phenomena.

More details can be found here.

14 Sep 2017

We have presented an invited talk [1] at the 19th International Conference on Electromagnetics in Advanced Applications (ICEAA), Verona, Italy, Sep. 11-15, 2017.

1. Moccia, M., Castaldi, G., & Galdi, V. (2017). Some perspectives in aperiodically ordered antenna arrays and metasurfaces. In Proc. 19th International Conference on Electromagnetics in Advanced Applications (ICEAA) (pp. 733–735). Verona, Italy, Sep. 11-15, 2017.
@inproceedings{Moccia_2017-ICEAA,
author = {Moccia, Massimo and Castaldi, Giuseppe and Galdi, Vincenzo},
booktitle = {Proc. 19th International Conference on Electromagnetics in Advanced Applications
(ICEAA)},
title = {Some perspectives in aperiodically ordered antenna arrays and metasurfaces},
year = {2017},
organization = {Verona, Italy, Sep. 11-15, 2017},
doi = {10.1109/ICEAA.2017.8065352},
page = {733-735},
month = sep
}


We have presented two talks [1, 2] at the 7th EOS Topical Meeting on Optical Microsystems (OµS) and the 3rd EOS Topical Meeting on Optics at the Nanoscale (ONS), Capri, Italy, Sep. 10-14, 2017.

1. Scaravilli, M., Micco, A., Castaldi, G., Gioffrè, M., Coppola, G., Galdi, V., & Cusano, A. (2017). A study of Bloch-surface-wave sensing platforms for lab-on-fiber technology. In Proc. 7th EOS Topical Meeting on Optical Microsystems (OMS’17). Capri, Italy, Sep. 10-14, 2017.
@inproceedings{Scaravilli_OMS_2017,
author = {Scaravilli, Michele and Micco, Alberto and Castaldi, Giuseppe and Gioffr\e, Mariano and Coppola, Giuseppe and Galdi, Vincenzo and Cusano, Andrea},
title = {A study of Bloch-surface-wave sensing platforms for lab-on-fiber technology},
booktitle = {Proc. 7th EOS Topical Meeting on Optical Microsystems (OMS'17)},
organization = {Capri, Italy, Sep. 10-14, 2017},
year = {2017},
month = sep
}

2. Moccia, M., Castaldi, G., Galdi, V., Liu, S., Wu, R. Y., Cui, T. J., … Andreone, A. (2017). Coding THz metasurfaces with sub-optimal design for diffuse scattering . In Proc. 3rd EOS Topical Meeting on Optics at the Nanoscale (ONS’17). Capri, Italy, Sep. 10-14, 2017.
@inproceedings{Moccia_ONS_2017,
author = {Moccia, M. and Castaldi, G. and Galdi, V. and Liu, S. and Wu, R. Y. and Cui, T. J. and Koral, C. and Papari, G. P. and Andreone, A.},
title = {Coding THz metasurfaces with sub-optimal design for diffuse scattering },
booktitle = {Proc. 3rd EOS Topical Meeting on Optics at the Nanoscale (ONS'17)},
organization = {Capri, Italy, Sep. 10-14, 2017},
year = {2017},
month = sep
}


30 Aug 2017

We have presented an invited talk [1] at the 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena (Metamaterials), Marseille, France, Aug. 28-31, 2017.

1. Galdi, V. (2017). Metasurfaces for field manipulation and sensing. In Proc. International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS) (pp. 112–114). Marseille, France, Aug. 28-31, 2017.
@inproceedings{Galdi_2017-Metamaterials,
author = {Galdi, Vincenzo},
booktitle = {Proc. International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS)},
title = {Metasurfaces for field manipulation and sensing},
year = {2017},
organization = {Marseille, France, Aug. 28-31, 2017},
doi = {10.1109/MetaMaterials.2017.8107857},
page = {112-114},
month = aug
}


Our paper on “Enhancement and interplay of first- and second-order spatial dispersion in metamaterials with moderate-permittivity inclusions” [1], in collaboration with Carlo Rizza (University of l’Aquila) and Alessandro Ciattoni (CNR-SPIN), has been published in Physical Review B as a Rapid Communication.

1. Rizza, C., Galdi, V., & Ciattoni, A. (2017). Enhancement and interplay of first- and second-order spatial dispersion in metamaterials with moderate-permittivity inclusions. Physical Review B 96(8), 081113.

We investigate a class of multilayered metamaterials characterized by moderate-permittivity inclusions and low average permittivity. Via first-principles calculations, we show that in such a scenario, first- and second-order spatial dispersions may exhibit a dramatic and nonresonant enhancement, and may become comparable with the local response. Their interplay gives access to a wealth of dispersion regimes encompassing additional extraordinary waves and topological phase transitions. In particular, we identify a configuration featuring bound and disconnected isofrequency contours. Since they do not rely on high-permittivity inclusions, our proposed metamaterials may constitute an attractive and technologically viable platform for engineering nonlocal effects in the optical range.

@article{IJ128_PRB_96_081113_2017,
title = {Enhancement and interplay of first- and second-order spatial dispersion in metamaterials with moderate-permittivity inclusions},
author = {Rizza, Carlo and Galdi, Vincenzo and Ciattoni, Alessandro},
journal = {Physical Review B},
volume = {96},
issue = {8},
pages = {081113},
numpages = {5},
year = {2017},
month = aug,
publisher = {American Physical Society},
doi = {10.1103/PhysRevB.96.081113},
}


Our paper on “Enhancement and interplay of first- and second-order spatial dispersion in metamaterials with moderate-permittivity inclusions,” in collaboration with Carlo Rizza (University of l’Aquila) and Alessandro Ciattoni (CNR-SPIN), has been accepted for publication as a Rapid Communication in Physical Review B.

An arXiv preprint is available.

Our paper on “Coding metasurfaces for diffuse scattering: Scaling laws, bounds, and sub-optimal design” [1], in collaboration with Tie Jun Cui’s Group (Southeast University), has been published (early view) in Advanced Optical Materials.

1. Moccia, M., Liu, S., Wu, R. Y., Castaldi, G., Andreone, A., Cui, T. J., & Galdi, V. (2017). Coding metasurfaces for diffuse scattering: Scaling laws, bounds, and suboptimal design. Advanced Optical Materials 5(19), 1700455.

Coding metasurfaces, based on the combination of two basic unit cells with out-of-phase responses, have been the subject of many recent studies aimed at achieving diffuse scattering, with potential applications to diverse fields ranging from radar-signature control to computational imaging. Here, via a theoretical study of the relevant scaling-laws, the physical mechanism underlying the scattering-signature reduction is elucidated, and some absolute and realistic bounds are analytically derived. Moreover, a simple, deterministic suboptimal design strategy is introduced that yields results comparable with those typically obtained by approaches based on brute-force numerical optimization, at a negligible fraction of their computational burden, thereby paving the way to the design of structures with arbitrarily large electrical size. Results are corroborated by rigorous full-wave numerical simulations and microwave experiments, and may be of interest in a variety of application fields, such as the design of low-scattering targets and illumination apertures for computational imaging, not necessarily restricted to electromagnetic scenarios.

@article{IJ127_AdOM_2017,
author = {Moccia, Massimo and Liu, Shuo and Wu, Rui Yuan and Castaldi, Giuseppe and Andreone, Antonello and Cui, Tie Jun and Galdi, Vincenzo},
title = {Coding metasurfaces for diffuse scattering: Scaling laws, bounds, and suboptimal design},
issn = {2195-1071},
year = {2017},
volume = {5},
issue = {19},
month = oct,
pages = {1700455},
}


14 Jul 2017

We have presented two talks [1, 2] at the IEEE AP-S Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (IEEE-APS/URSI), San Diego, California, USA, July 9-14, 2017.

1. Moccia, M., Liu, S., Wu, R. Y., Castaldi, G., Andreone, A., Cui, T. J., & Galdi, V. (2017). Coding metasurfaces for diffuse scattering: Theoretical bounds and sub-optimal design. In Proc. USNC-URSI Radio Science Meeting. San Diego, CA, USA, July 9-14, 2017.
@inproceedings{Moccia_2017-USNC-URSI,
author = {Moccia, Massimo and Liu, Shuo and Wu, Rui Yuan and Castaldi, Giuseppe and Andreone, Antonello and Cui, Tie Jun and Galdi, Vincenzo},
booktitle = {Proc. USNC-URSI Radio Science Meeting},
title = {Coding metasurfaces for diffuse scattering: Theoretical bounds and sub-optimal design},
year = {2017},
organization = {San Diego, CA, USA, July 9-14, 2017},
month = jul
}

2. Principe, M., Consales, M., Micco, A., Crescitelli, A., Castaldi, G., Esposito, E., … Cusano, A. (2017). Fiber-optics meta-tips for light manipulation and sensing. In Proc. USNC-URSI Radio Science Meeting. San Diego, CA, USA, July 9-14, 2017.
@inproceedings{Principe_2017-USNC-URSI,
author = {Principe, M. and Consales, M. and Micco, A. and Crescitelli, A. and Castaldi, G. and Esposito, E. and La Ferrara, V. and Cutolo, A. and Galdi, V. and Cusano, A.},
booktitle = {Proc. USNC-URSI Radio Science Meeting},
title = {Fiber-optics meta-tips for light manipulation and sensing},
year = {2017},
organization = {San Diego, CA, USA, July 9-14, 2017},
month = jul
}


Our paper on “Coding metasurfaces for diffuse scattering: Scaling laws, bounds, and sub-optimal design,” in collaboration with Tie Jun Cui’s Group (Southeast University), has been accepted for publication in Advanced Optical Materials.

Our paper on “Transformation-optics-based design of a metamaterial radome for extending the scanning angle of a phased array antenna” [1], in collaboration with MBDA, has been published (early view) in the IEEE Journal of Multiscale and Multiphysics Computational Techniques.

1. Moccia, M., Castaldi, G., D’Alterio, G., Feo, M., Vitiello, R., & Galdi, V. (2017). Transformation-optics-based design of a metamaterial radome for extending the scanning angle of a phased array antenna. IEEE Journal on Multiscale and Multiphysics Computational Techniques 2, 159–167.

We apply the transformation-optics approach to the design of a metamaterial radome that can extend the scanning angle of a phased-array antenna. For moderate enhancement of the scanning angle, via suitable parameterization and optimization of the coordinate transformation, we obtain a design that admits a technologically viable, robust and potentially broadband implementation in terms of thin-metallic-plate inclusions. Our results, validated via finite-element-based numerical simulations, indicate an alternative route to the design of metamaterial radomes which does not require negative-valued and/or extreme constitutive parameters.

@article{IJ126_IEEE-JMMCT_2017,
author = {Moccia, M. and Castaldi, G. and D'Alterio, G. and Feo, M. and Vitiello, R. and Galdi, V.},
journal = {IEEE Journal on Multiscale and Multiphysics Computational Techniques},
title = {Transformation-optics-based design of a metamaterial radome for extending the scanning angle of a phased array antenna},
year = {2017},
doi = {10.1109/JMMCT.2017.2713826},
volume = {2},
number = {},
pages = {159--167},
month = {}
}


Our paper on “Transformation-optics-based design of a metamaterial radome for extending the scanning angle of a phased array antenna,” in collaboration with MBDA, has been accepted for publication in the IEEE Journal of Multiscale and Multiphysics Computational Techniques.

An arXiv preprint is available.

28 Apr 2017

We have presented a talk [1] at the 25th Optical Fiber Sensors Conference (OFS), Jeju, Korea, Apr. 24-28, 2017.

1. Principe, M., Consales, M., Micco, A., Crescitelli, A., Castaldi, G., Esposito, E., … Cusano, A. (2017). Optical fiber meta-tips: Perspectives in sensing applications. In Y. Chung, W. Jin, B. Lee, J. Canning, K. Nakamura, & L. Yuan (Eds.), Proceedings of SPIE (Vol. 10323, p. 103233F). 25th Optical Fiber Sensors Conference (OFS), Jeju, Korea, Apr. 24-28, 2017.
@inproceedings{Principe_2017-OFS,
author = {Principe, M. and Consales, M. and Micco, A. and Crescitelli, A. and Castaldi, G. and Esposito, E. and La Ferrara, V. and Cutolo, A. and Galdi, V. and Cusano, A.},
editor = {Chung, Youngjoo and Jin, Wei and Lee, Byoungho and Canning, John and Nakamura, Kentaro and Yuan, Libo},
booktitle = {Proceedings of SPIE},
title = {Optical fiber meta-tips: Perspectives in sensing applications},
year = {2017},
volume = {10323},
pages = {103233F},
doi = {10.1117/12.2265002},
month = apr,
organization = {25th Optical Fiber Sensors Conference (OFS), Jeju, Korea, Apr. 24-28, 2017}
}


Our paper on “Exceptional points of degeneracy and PT-symmetry in photonic coupled chains of scatterers” [1] in collaboration with Filippo Capolino’s Group (University of California at Irvine), has been accepted for publication in Physical Review B.

1. Othman, M. A. K., Galdi, V., & Capolino, F. (2017). Exceptional points of degeneracy and PT symmetry in photonic coupled chains of scatterers. Physical Review B 95(10), 104305.

We demonstrate the existence of exceptional points of degeneracy (EPDs) of periodic eigenstates in non-Hermitian coupled chains of dipolar scatterers. Guided modes supported by these structures can exhibit an EPD in their dispersion diagram at which two or more Bloch eigenstates coalesce, in both their eigenvectors and eigenvalues. We show the emergence of a second-order modal EPD associated with the parity-time (PT) symmetry condition, at which each particle pair in the double chain exhibits balanced gain and loss. Furthermore, we also demonstrate a fourth-order EPD occurring at the band edge. Such a degeneracy condition was previously referred to as a degenerate band edge in lossless anisotropic photonic crystals. Here, we rigorously show it under the occurrence of gain and loss balance for a discrete guiding system. We identify a more general regime of gain and loss balance showing that PT symmetry is not necessary to attain EPDs. Moreover, we investigate the degree of detuning of the EPD when the geometrical symmetry or balanced condition is broken. Furthermore, we demonstrate a realistic implementation of the EPD in a coupled chain made of pairs of plasmonic nanospheres and active core-shell nanospheres at optical frequencies. These findings open avenues toward superior light localization and transport with application to high-Q resonators utilized in sensors, filters, low-threshold switching and lasing.

@article{IJ125_PRB_95_104305_2017,
title = {Exceptional points of degeneracy and PT symmetry in photonic coupled chains of scatterers},
author = {Othman, Mohamed A. K. and Galdi, Vincenzo and Capolino, Filippo},
journal = {Physical Review B},
volume = {95},
issue = {10},
pages = {104305},
numpages = {12},
year = {2017},
month = mar,
publisher = {American Physical Society},
doi = {10.1103/PhysRevB.95.104305},
}


Our paper on “Optical fiber meta-tips” [1], in collaboration with Andrea Cusano’s Group (University of Sannio), has been published in Light: Science & Applications.

1. Principe, M., Consales, M., Micco, A., Crescitelli, A., Castaldi, G., Esposito, E., … Cusano, A. (2017). Optical fiber meta-tips. Light: Science & Applications 6, e16226.

We report on the first demonstration of a proof-of-principle optical fiber ‘meta-tip’, which integrates a phase-gradient plasmonic metasurface on the fiber tip. For illustration and validation purposes, we present numerical and experimental results pertaining to various prototypes implementing generalized forms of the Snell’s transmission/reflection laws at near-infrared wavelengths. In particular, we demonstrate several examples of beam steering and coupling with surface waves, in fairly good agreement with theory. Our results constitute a first step toward the integration of unprecedented (metasurface-enabled) light-manipulation capabilities in optical-fiber technology. By further enriching the emergent ‘lab-on-fiber’ framework, this may pave the way for the widespread diffusion of optical metasurfaces in real-world applications to communications, signal processing, imaging and sensing.

@article{IJ124_LSA_6_6226a_2017,
author = {Principe, Maria and Consales, Marco and Micco, Alberto and Crescitelli, Alessio and Castaldi, Giuseppe and Esposito, Emanuela and La Ferrara, Vera and Cutolo, Antonello and Galdi, Vincenzo and Cusano, Andrea},
title = {Optical fiber meta-tips},
journal = {Light: Science {\&} Applications},
volume = {6},
pages = {e16226},
year = {2017},
month = mar,
doi = {10.1038/lsa.2016.226},
note = {http://www.nature.com/lsa/journal/v6/n3/suppinfo/lsa2016226s1.html?url=/lsa/journal/v6/n3/full/lsa2016226a.html}
}


Our paper on “Magnified imaging based on non-Hermitian nonlocal cylindrical metasurfaces” [1], in collaboration with Andrea Alù’s Group (University of Texas at Austin), has been published in Physical Review B.

1. Savoia, S., Valagiannopoulos, C. A., Monticone, F., Castaldi, G., Galdi, V., & Alù, A. (2017). Magnified imaging based on non-Hermitian nonlocal cylindrical metasurfaces. Physical Review B 95(11), 115114.

We show that a cylindrical lensing system composed of two metasurfaces with suitably tailored non-Hermitian (i.e., with distributed gain and loss) and nonlocal (i.e., spatially dispersive) properties can perform magnified imaging with reduced aberrations. More specifically, we analytically derive the idealized surface-impedance values that are required for “perfect” magnification and imaging and elucidate the role and implications of non-Hermiticity and nonlocality in terms of spatial resolution and practical implementation. For a basic demonstration, we explore some proof-of-principle quasilocal and multilayered implementations and independently validate the outcomes via full-wave numerical simulations. We also show that the metasurface frequency-dispersion laws can be chosen so as to ensure unconditional stability with respect to arbitrary temporal excitations. These results, which extend previous studies on planar configurations, may open intriguing venues in the design of metastructures for field imaging and processing.

@article{IJ123_PRB_95_115114_2017,
title = {Magnified imaging based on non-Hermitian nonlocal cylindrical metasurfaces},
author = {Savoia, Silvio and Valagiannopoulos, Constantinos A. and Monticone, Francesco and Castaldi, Giuseppe and Galdi, Vincenzo and Al\u, Andrea},
journal = {Physical Review B},
volume = {95},
issue = {11},
pages = {115114},
numpages = {13},
year = {2017},
month = mar,
publisher = {American Physical Society},
doi = {10.1103/PhysRevB.95.115114}
}
`

Our paper on “Magnified imaging based on non-Hermitian nonlocal cylindrical metasurfaces,” in collaboration with Andrea Alù’s Group (University of Texas at Austin), has been accepted for publication in Physical Review B.

An arXiv preprint is available.

Our paper on “Exceptional points of degeneracy and PT-symmetry in photonic coupled chains of scatterers,” in collaboration with Filippo Capolino’s Group (University of California at Irvine), has been accepted for publication in Physical Review B.

An arXiv preprint is available.

9 Feb 2017

The new website is on!

Details on the design and implementation can be found here.