High-Q Lithium Niobate Microring Resonator with Electro-Optically Reconfigurable Coupling Strength

TL;DR

This paper presents a lithium niobate microring resonator with an integrated Mach-Zehnder interferometer that enables electro-optic tuning of coupling strength, maintaining high Q factor and single-mode operation for advanced photonic applications.

Contribution

The work introduces a reconfigurable coupling mechanism in a high-Q lithium niobate resonator using an integrated interferometer, enabling continuous tuning across coupling regimes.

Findings

Achieved a Q factor of approximately 10^6.

Demonstrated continuous and reversible tuning of coupling strength.

Maintained single-mode operation with high spectral purity.

Abstract

The development of sophisticated integrated photonic circuits demands microresonators that combine exceptional optical confinement with dynamic operational flexibility. Here, we demonstrate a racetrack resonator on the thin-film lithium niobate platform that achieves an electro-optically tunable coupling strength while maintaining a stable, high intrinsic Q factor on the order of 10^6. By incorporating a Mach-Zehnder interferometer into the coupling region, the device facilitates a continuous and reversible transition across the entire coupling spectrum from under-coupling and critical coupling to deep over-coupling. To ensure high spectral purity, we employ Euler bends to facilitate an adiabatic transition between the straight and curved waveguide sections. This design effectively suppresses the excitation of higher-order modes, resulting in a clean transmission spectrum characterized by exclusive fundamental mode operation. At the critical coupling point, the resonator exhibits a high extinction ratio exceeding 30 dB. The integration of stable ultra-high Q, single-mode purity, and full-range coupling reconfigurability positions this device as a vital component for adaptive microwave photonics, high-efficiency nonlinear optics, and programmable quantum photonic networks.