High Quality Lithium Niobate Euler Racetrack Resonators

Abstract Racetrack resonators is widely utilized in integrated photonics which is adaptable for applying electric, heat, or polarization to the resonator for modulation and wavelength conversion. High‐performance optical devices are proposed based on racetrack resonators on thin‐film lithium niobate (TFLN) owing to its multi‐functional character. Nevertheless, mode‐crossing due to the anisotropic properties of lithium niobate degraded the performance of the devices. Here, the systematic investigation of Euler bend structure in TFLN is reported. TFLN Euler racetrack resonators are demonstrated on X‐cut and Z‐cut TFLN with suppressed mode‐crossing, different footprint, and high‐quality factors both in simulation and experiment. The racetrack Euler cavities prepared with a single etching step achieve intrinsic quality factors up to 5.53 million. The standard deviation of free spectral range (FSR) σ FSR of Euler cavity is 33 times lower than the circular cavity for small footprint cavities (1328 × 60 µm 2 ) and 5 times lower for large footprint cavities (4355 × 200 µm 2 ) in X‐cut TFLN cavity. The method paves the way for achieving single‐mode racetrack cavities with reduces mode crossing, which can be applied in integrated optical devices such as electro‐optic (EO) comb generation or EO modulator.