Spectral Engineering of Optical Microresonators in Anisotropic Lithium Niobate Crystal

Abstract

On‐chip optical microresonators are essential building blocks in integrated optics. The ability to arbitrarily engineer their resonant frequencies is crucial for exploring novel physics in synthetic frequency dimensions and practical applications like nonlinear optical parametric processes and dispersion‐engineered frequency comb generation. Photonic crystal ring (PhCR) resonators are a versatile tool for such arbitrary frequency engineering, by controllably creating mode splitting at selected resonances. To date, these PhCRs have mostly been demonstrated in isotropic photonic materials, while such engineering could be significantly more complicated in anisotropic platforms that often offer more fruitful optical properties. Here, we realize the spectral engineering of chip‐scale optical microresonators in the anisotropic lithium niobate (LN) crystal by a gradient design that precisely compensates for variations in both refractive index and perturbation strength. We experimentally demonstrate controllable frequency splitting at single and multiple selected resonances in LN PhCR resonators with different sizes, while maintaining high Q‐factors up to 1 × 106. Moreover, we experimentally construct a sharp boundary in the synthetic frequency dimension based on an actively modulated x‐cut LN gradient‐PhCR, opening up new paths toward the arbitrary control of electro‐optic comb spectral shapes and exploration of novel physics in the frequency degree of freedom.This article is protected by copyright. All rights reserved

Electro-Optical Comb Envelope Engineering Based on Mode Crossing

“…Until now, there has not been a clear solution or theoretical simulation results for engineering the envelope of an EO comb. K. Zhang et al achieved mode splitting at the design wavelength of a racetrack resonator by designing a photonic crystal cavity [ 32 ], enabling a frequency mirror at a specific wavelength. This approach provides insight into designing the envelope of an EO comb by controlling the resonance frequency of a mode at a specific wavelength.…”