Ultrafast Frequency-Shift Dynamics at Temporal Boundary Induced by Structural-Dispersion Switching of Waveguides

Abstract

We experimentally demonstrate the observation of a frequency-shift dynamics at a temporal boundary in the terahertz (THz) region relying on a scheme that controls the structural dispersion of a metalsemiconductor waveguide. Ultrafast structural-dispersion switching is achieved within a subpicosecond timescale by illuminating a waveguide surface with an optical pump pulse during the propagation of a THz pulse in the waveguide. Owing to the relatively high conversion efficiency, up to 23%, under the condition that the frequency shift is sufficiently larger than the bandwidth of the incident pulse, the rapid variation of the THz frequency around the temporal boundary is directly observed in the time domain.

An Archimedes' screw for light

“…In addition, appropriate tailoring of the temporal dependence of reactive elements can enable arbitrary energy accumulation 9 , whereas the introduction of time-modulated, non-Hermitian elements can lead to nonreciprocal mode-steering and gain 10 , as well as event cloaking and perfect absorption 11 , and surface-wave coupling on spatially flat interfaces 12 . In non-periodic systems, abrupt switching holds the key to new directions such as time-reversal 13 , time-refraction 14 and anisotropy-induced wave routing 15 , as well as frequency conversion 16 – 18 , bandwidth enhancement 19 and Anderson localization 20 .…”

Efficient Phase Conjugation in a Space-Time Leaky Waveguide

“…44 An extensive review for wave engineering with temporal interferences is provided in ref 45. One chief limitation of time slabs is the requirement of altering the electromagnetic properties across the entire space, which may require a large amount of energy and may be technologically challenging, especially since the most interesting wave phenomena arise for fast switching rising times and large switching contrast. In many practical scenarios, switching over a finite region of space 36,44,46,47 or lower dimensions 31,48−52 switched waveguides in pursuit of frequency conversion, for example, ref 36, have investigated switching the waveguide boundaries, but the efficiency of BW scattering, associated with phase conjugation, from space-time interfaces is quite low in this scenario.…”

“…The theoretical investigation of these temporal discontinuities dates back to more than half a century ago − and has been recently revived in the metamaterials community, with the discovery that time switching can offer a new dimension for wave engineering. − In unbounded media, an abrupt switching event of the material properties in time corresponds to the dual of a spatial interface between two media, since at such a time interface momentum is conserved, but frequency can change. Wave scattering at a single temporal discontinuity has been extensively studied in various forms, also involving anisotropy, , material dispersion, − and broken spatial symmetries. − …”

“…One chief limitation of time slabs is the requirement of altering the electromagnetic properties across the entire space, which may require a large amount of energy and may be technologically challenging, especially since the most interesting wave phenomena arise for fast switching rising times and large switching contrast. In many practical scenarios, switching over a finite region of space ,,, or lower dimensions ,− may be more feasible, as recently explored, but in most of these scenarios, energy and momentum are expected to spread over continuous spectra without resonances. For instance, time-switched graphene sheets reported in refs – can engage only the portion of the wave travelling in the region at the time of switching, implying limited efficiency in wave trapping.…”

“…For instance, time-switched graphene sheets reported in refs – can engage only the portion of the wave travelling in the region at the time of switching, implying limited efficiency in wave trapping. Recent efforts dedicated to switched waveguides in pursuit of frequency conversion, for example, ref , have investigated switching the waveguide boundaries, but the efficiency of BW scattering, associated with phase conjugation, from space-time interfaces is quite low in this scenario.…”