Integrated high-Q cascaded Fabry-Perot resonators based on lithium niobate Sagnac loop reflectors

We demonstrated an integrated high-Q cascaded Fabry-Perot (FP) resonator on lithium niobate on insulator (LNOI) implemented by multi-Sagnac loop reflectors, which was fabricated by femtosecond laser photolithography-assisted chemo-mechanical polishing (CMP). Compared with the resonator that comprised only two Sagnac loop reflectors (SLRs), there is a significant Q factor enhancement in the cascaded resonator formed by multi-SLRs. The loaded Q factor of the cascaded resonator was measured to be 1.16 × 10⁶, a five-fold improvement compared to the state of the art on the same material platform.