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Abstract
Time-varying metamaterials are currently at the forefront of research, offering immense possibilities for intriguing wave manipulation. In this Feature Issue, we provide a collection of the most recent results on time-varying artificial photonic metastructures, together with the review paper on the general properties of time-varying dispersive materials and an opinion paper on the topic from A. Boltasseva, V.M. Shalaev and M. Segev.
© 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
The exploration of time-varying metamaterials, characterized by rapid changes of the electromagnetic properties in time, is currently one of the highly promising areas of research with significant impact on applications over the full range of frequencies, from microwaves to optics. These materials represent a transformative paradigm in wave manipulation and information processing, transcending the traditional barriers of reciprocity, energy conservation and time-reversal symmetry.
In this Feature Issue, we compile a selection of relevant and timely contributions from the physics, engineering, and material science communities. These contributions encompass novel models and concepts, innovative dynamic modulation architectures, techniques for fabricating time-varying metastructures, experimental verification of anomalous wave phenomena, and potential applications. The primary goal of the Feature Issue is to showcase recent breakthroughs and future perspectives in the field of time-varying artificial structures, i.e., metamaterials and metasurfaces, as platforms for novel light-matter interaction processes. Time-varying artificial media and surfaces represent a promising material platform to be engineered for operating over a broad frequency range and exploited for designing new advanced devices with capabilities surpassing those constrained by traditional passive limitations.
This feature issue is intended to bring together some of the recent contributions to this vibrant field, including one opinion, two reviews, and seven original research contributions:
- 1. [Invited Opinion contribution] A. Boltasseva, V.M. Shalaev and M. Segev offer historical highlights and recent developments in the field of photonic time-crystals. The paper discusses challenges, disruptive opportunities, and potential impact on both the fundamental science of light and on photonics technologies [1].
- 2. [Invited Review contribution] T.T. Koutserimpas and F. Monticone present a comprehensive review of the general properties of time-varying dispersive materials. They discuss various dispersion models, the role of the causality principle, and the generalization of the Kramers-Kronig relations. The focus is on processes enabling strong and fast temporal modulations at optical frequencies to realize photonic-time-crystal phenomena [2].
- 3. [Invited Review contribution] M.H. Mostafa et al. present an overview of temporal interfaces in isotropic, anisotropic and bianisotropic materials and metamaterials. They highlight extraordinary temporal scattering phenomena at a temporal interface between an anisotropic and bianisotropic media, as well as propose some physical realizations of these temporal interfaces. [3].
- 4. [Invited Research contribution] J. B. Pendry proposes an analytical solution for a time-dependent system involving a moving step-up or step-down in refractive index. This synthetic motion alters the energy level of the radiation passing through it, leading to an effective heating or cooling of photons [4].
- 5. [Invited Research contribution] V. Pacheco-Pena and N. Engheta explore temporal cascading of time-interfaces in spatially cascading guided-wave structures. Their analysis examines the propagation along a dielectric guiding system, comprised by a core and cladding, whose relative permittivity changes over time. Specifically, the cladding of dielectric waveguide is rapidly changed at different moments of time between two cladding permittivity values, while the core remains unchanged in time [5]
- 6. [Spontaneous Research contribution] J. Johnson and C. Scarborough introduce an iterative algorithm for computing soliton solutions in general periodic electrical networks with nonlinear capacitors. This technique enables efficient design and optimization of a wide variety of nonlinear guiding structures [6].
- 7. [Spontaneous Research contribution] P. Garg et al. propose a technique to treat spatiotemporal photonic metamaterials at the effective level, avoiding considering all the mesoscopic details of the artificial structure. They describe a technique to temporally homogenize the metasurface using the eigenmodes of the bulk time-varying materials. Then, the spatial homogenization is performed by inverting the Fresnel coefficients of the slab made from a stationary material [7].
- 8. [Spontaneous Research contribution] J.C. Serra et al. investigate mode coupling induced by the time-varying systems and its implications, including resonant interaction and parametric instabilities. Their work sheds light on the novel phenomena arising from the interaction between positive and negative frequency oscillators [8].
- 9. [Spontaneous Research contribution] Y. Hadad and D. Sounas present spatiotemporally modulated metagratings to achieve strong nonreciprocal responses. Their focus is on wire metagratings loaded with time-modulated capacitances, showcasing effective nonreciprocal anomalous reflection [9].
- 10. [Spontaneous Research contribution] F.V. Kovalev and I.V. Shadrivov design a metasurface loaded with variable capacitors capable of amplifying incident electromagnetic waves through parametric amplification. Their work demonstrates that it is possible to achieve over 10 dB of gain with a single metasurface [10].
While not exhaustive, this Feature Issue offers a timely collection of research in time-varying photonic metamaterials. It underscores the breadth of fundamental physics in the field while also presenting practical structures and devices for achieving extraordinary scattering phenomena. We hope you find this collection enlightening and inspiring.
We are grateful to all the authors, reviewers, and Optica staff members for their contributions and efforts to make this issue possible.
References
1. A. Boltasseva, V.M. Shalaev, and M. Segev, “Photonic time crystals: from fundamental insights to novel applications: opinion,” Opt. Mater. Express 14(3), 592–597 (2024). [CrossRef]
2. T. T. Koutserimpas and F. Monticone, “Time-varying media dispersion and the principle of causality [Invited],” Opt. Mater. Express 14(5), 1222–1236 (2024). [CrossRef]
3. M.H. Mostafa, M.S. Mirmoosa, M.S. Sidorenko, et al., “Temporal interfaces in complex electromagnetic materials: an overview [Invited],” Opt. Mater. Express 14(5), 1103–1127 (2024). [CrossRef]
4. J. B. Pendry, “Air conditioning for photons [Invited],” Opt. Mater. Express 14(2), 407–413 (2024). [CrossRef]
5. V. Pacheco-Pena and N. Engheta, “Spatiotemporal cascading of dielectric waveguides [Invited],” Opt. Mater. Express 14(4), 1062–1073 (2024). [CrossRef]
6. J. Johnson and C. Scarborough, “Iterative technique for computing soliton solutions to periodic nonlinear electrical networks,” Opt. Mater. Express 14(3), 649–663 (2024). [CrossRef]
7. P. Garg, A.G. Lamprianis, S. Rahman, et al., “Two-step homogenization of spatiotemporal metasurfaces using an eigenmode-based approach,” Opt. Mater. Express 14(2), 549–563 (2024). [CrossRef]
8. J. C. Serra, E. Galiffi, P. H. Huidobro, et al., “Particle-hole instabilities in photonics time-varying systems,” Opt. Mater. Express 14(6), 1459–1471 (2024). [CrossRef]
9. Y. Hadad and D. Sounas, “Space-time modulated loaded-wire metagratings for magnetless nonreciprocity and near-complete frequency conversion,” Opt. Mater. Express 14(5), 1295–1308 (2024). [CrossRef]
10. F.V. Kovalev and I.V. Shadrivov, “Parametric metasurfaces for electromagnetic wave amplification,” Opt. Mater. Express 14(2), 494–504 (2024). [CrossRef]