Pulse-driven photonic transitions and nonreciprocity in space-time modulated metasurfaces

TL;DR

This paper introduces a novel approach to induce photonic transitions and nonreciprocity in metasurfaces using ultrafast pulse modulation, avoiding the need for continuous energy input and enabling practical, reconfigurable optical control.

Contribution

The study demonstrates that single ultrafast pulse modulation can mimic periodic modulation-driven photonic transitions, simplifying implementation and expanding possibilities for dynamic photonic systems.

Findings

Controlled frequency transitions achieved via dispersion-engineered metasurfaces

Theoretically demonstrated strong nonreciprocity for free-space waves

Potential for ultrafast, energy-efficient optical technologies

Abstract

Time-varying photonic systems open new possibilities for controlling light, enabling photonic time crystals, time reflection and refraction, frequency conversion, synthetic gauge fields, optical nonreciprocity, among others. These effects emerge from the dynamic modulation of optical properties, which can mediate photonic transitions between eigenstates of different frequencies and/or wavevectors. To achieve such transitions, conventional approaches rely on periodic modulation schemes that demand ultrafast modulation rates and continuous energy input, posing significant practical challenges at optical frequencies. Here, we demonstrate that periodic-modulation-driven photonic transitions within the radiation continuum can be effectively mimicked using a single-period ultrafast pulse modulation, eliminating the need for sustained continuous modulation. By leveraging dispersion engineering in metasurfaces to tailor the density of states in the radiation continuum, we achieve controlled frequency transitions and theoretically demonstrate strong nonreciprocity for free-space waves as a key application. Our findings may guide future experimental research on time-varying photonics using materials such as transparent conductive oxides and semiconductors, expanding the possibilities for ultrafast and reconfigurable optical technologies. More broadly, our work may establish a practical and energy-efficient framework for dynamic photonic systems, with potential applications ranging from spatio-temporal wavefront manipulation to photonic computing and ultrafast signal processing.