Photonics of time-varying media

Abstract

Time-varying media have recently emerged as a new paradigm for wave manipulation, due to the synergy between the discovery of highly nonlinear materials, such as epsilon-near-zero materials, and the quest for wave applications, such as magnet-free nonreciprocity, multimode light shaping, and ultrafast switching. In this review, we provide a comprehensive discussion of the recent progress achieved with photonic metamaterials whose properties stem from their modulation in time. We review the basic concepts underpinning temporal switching and its relation with spatial scattering and deploy the resulting insight to review photonic time-crystals and their emergent research avenues, such as topological and non-Hermitian physics. We then extend our discussion to account for spatiotemporal modulation and its applications to nonreciprocity, synthetic motion, giant anisotropy, amplification, and many other effects. Finally, we conclude with a review of the most attractive experimental avenues recently demonstrated and provide a few perspectives on emerging trends for future implementations of time-modulation in photonics.

Saturable time-varying mirror based on an ENZ material

“…In order to model scattering in our time-modulated structure, while accounting for its strongly dispersive character, we implemented the approximate but efficient method introduced in Ref. [1], which relies on the separation of timescales respectively associated with (a) the wave period T = 2π/ω ≈ 4 fs, which enters the dispersive response of the system and (b) the temporal dynamics induced by the envelope of the pump beam (which is identical to that of the probe), whose timescale ∆ 1 ≈ 220 fs is associated with the duration of the pump pulse for low intensities, but reduces and approaches the response time τ rise ≈ 30 fs of the material at higher intensities in the saturation regime. We briefly report the key equations here for completeness and refer the reader to Ref.…”

“…We briefly report the key equations here for completeness and refer the reader to Ref. [1] for the complete derivation.…”

“…In order to implement the method, we define a double-frequency reflection coefficient [1] valid in the adiabatic limit:…”

“…Time-varying systems are a platform for a wealth of exotic physics [1], including nonreciprocity [2][3][4], amplification [5,6] and topology [7][8][9][10], as well as quantum-relativistic effects [11,12], promising novel applications including photonic refrigeration [13] and temporal aiming [14].…”

Parametric Mie resonances and Kerker effects in time-modulated scatterers

“…Most of the previous works on Mie-type scatterers concentrated on time-invariant particles whose permittivity does not change in time. The time variation of material properties unlocks a new dimension of control in electromagnetic systems [15,16]. Recently, a wide range of novel optical effects was suggested based on timevarying materials, such as photonic time crystals [17][18][19][20][21][22], temporal discontinuities [23][24][25], effective magnetic field for photons [26], optically induced negative refraction [27], synthetic dimensions [28], etc.…”