Electro-optic tunable racetrack resonator based on periodically poled lithium niobate on insulator

High-performance integrated photonic devices based on micro-ring resonators have been proposed successively owing to their multifunctional properties. However, their practical applications are often limited by the lack of fast modulation capability at a predefined resonant wavelength. In this work, we propose an all-pass lithium niobate on insulator (LNOI) racetrack resonator with an integrated periodically poled lithium niobate (PPLN) structure. The internal PPLN structure works as an electro-optically (EO) tunable Bragg reflector, enabling controllable coupling between the two circulating modes of the resonator at a fixed resonant wavelength. Consequently, the output reflectivity and transmittivity of the device can be dynamically modulated over almost the full range (0-1), and their corresponding full width at half maximum (FWHM) can be tuned up to 1.1 nm. The proposed scheme operates free of free spectral range (FSR) limitations. Moreover, the device enables a functional transfer from a single-wavelength filter to a tunable dual-wavelength filter. The proposed device has potential applications in laser engineering, EO modulators and switches, filters, and sensors for optical computing, communications, and networks.