Simultaneous Control of the Spatial and Temporal Spectra of Light With Space-Time Varying Metasurfaces

Abstract

This paper presents space-time varying (STV) metasurfaces for simultaneously controlling the spatial and temporal spectra of electromagnetic waves. These metasurfaces transform incident electromagnetic waves into specified reflected and transmitted waves, with arbitrary temporal and spatial frequencies.They are synthesized in terms of time-domain generalized sheet transition conditions (GSTCs). Moreover, they are characterized using an analytical method and the unstaggered finite-difference time-domain (FDTD) technique adapted to space-time metasurfaces. STV metasurfaces performing pulse shaping, time reversal and differentiation are demonstrated as examples.

A Dynamically Modulated All‐Dielectric Metasurface Doublet for Directional Harmonic Generation and Manipulation in Transmission

“…Dynamic modulation of a metasurface provides the required momentum for the transition of fundamental frequency to higher‐order frequency harmonics defined as f n = f 0 + nf m with the integer denoting the order of generated frequency harmonics . As such, unlike static and quasi‐static metasurfaces which can only change the spatial features of scattered light, dynamically modulated metasurfaces provide control over the spectral content of the scattered light as well.…”

“…A high‐speed continuous tuning mechanism for all‐dielectric metasurfaces not only allows for real‐time control over the optical response but also enables realization of time‐modulated metasurfaces by applying time‐varying external stimuli. Despite their linearity, time‐modulated metasurfaces exhibit frequency‐mixing property and lead to generation of higher‐order frequency harmonics which are consisted of fundamental frequency up‐ and down‐modulated by the frequency of biasing . Unlike frequency conversion in nonlinear metasurfaces which requires high optical intensities and operates for one excitation at a time, frequency conversion in time‐modulated metasurfaces can be achieved for simultaneous excitations with arbitrary intensities.…”

Non-reciprocity using quadrature-phase time-varying slab resonators

“…It is shown in many articles that a spatio-temporal modulated permittivity can provide non-reciprocity at the incident frequency [16,17,10,5,13,4,14,3,2,1], meaning that the incident wave can pass the structure from one side without losing any power in the central frequency, but it will be blocked when it is incident from the other side. Nevertheless, this method of modulation is hard to be implemented because of partial reflections of the modulating wave at boundaries, so a pure traveling wave modulation cannot be obtained.…”

“…Non-reciprocity in silicon photonics using time-varying methods was first proposed theoretically in [5] and was implemented in a silicon chip [6]. Other applications such as frequency combs [7,8,9] and time-varying metasurfaces [10,11,12,13,14] are also introduced by using time-varying refractive indices.…”

Topological Space‐Time Photonic Transitions in Angular‐Momentum‐Biased Metasurfaces

“…These metasurfaces exhibit frequency mixing property and can enable a myriad of novel physical effects [ 49–51 ] such as nonreciprocity, [ 52–62 ] extreme energy accumulation, [ 63 ] wide band impedance matching, [ 64,65 ] camouflaging, [ 66,67 ] generation of dynamic beams, [ 68–70 ] signal amplification, [ 71 ] and pulse shaping. [ 72–74 ] They can also extend the degree of light manipulation through space‐time photonic transitions and local modulation‐induced phase shift. [ 58,75 ] It has been previously established that the temporal frequency conversion of an optical mode in a spatiotemporally modulated periodic system is accompanied with a correlated change in its spatial frequency which exhibits opposite signs for upward and downward temporal frequency conversion.…”