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arXiv · 2604.02076

A time grating approach to ultrahigh-Q guided mode resonance

Youxiu Yu·Xiaofeng Xu·Yang Long·Gui-Geng Liu·Dongliang Gao·Xiao Lin·Hao Hu
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Abstract

Guided mode resonance (GMR), the resonant coupling of free-space light into leaky waveguide modes, is traditionally achieved with periodic patterned structures. However, this approach makes its key properties such as quality factor (Q-factor) fabrication-dependent and non-tunable. Here, we introduce a time grating platform, i.e., a homogeneous waveguide whose refractive index is modulated periodically in time, that allows tunable GMRs through temporal modulation engineering rather than spatial structural redesign. We show that the Q-factors of these GMRs diverge as the modulation depth vanishes. Furthermore, unconstrained by energy conservation, the resonances exhibit near-unity reflection for fundamental harmonics and values exceeding 40 for first-order harmonics. Our findings not only apply to yield a giant Goos-H\"anchen shift over 103 times wavelength without sacrificing the reflection magnitude, but also open new avenues for related phenomena such as bound states in the continuum, unidirectional GMRs and beyond.

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Youxiu Yu, Xiaofeng Xu, Yang Long, Gui-Geng Liu, Dongliang Gao, Xiao Lin, Hao Hu. 2026-04-02. A time grating approach to ultrahigh-Q guided mode resonance. https://arxiv.org/abs/2604.02076

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