Integrated Waveguide Fourier Transform Spectrometer on Thin-Film Lithium Niobate

Integration of photonic circuits is a key technology for the miniaturization of optical devices, including high-resolution near-infrared spectrometers. Compact spectrometers are beneficial in size, weight and power consumption compared to standard ones and can be designed without any moving parts. One approach is based on the direct detection of the interference pattern formed by counterpropagative modes in a silicon-on-insulator waveguide (SWIFTS) [1]. However, the size of current sensors limits the retrievable bandwidth considerably due to the Nyquist-Shannon criterion. Attempts to solve this undersampling issue were demonstrated by using the thermo-optic nonlinearity in silicon [2] and by combining the SWIFTS technology with commercially available lithium niobate (LiNbO ₃ ) Mach-Zehnder modulators [3]. The availability of thin-film lithium niobate-on-insulator allows the integration of on-chip electro-optic devices [4]. In this work, we demonstrate the sampling of a broadband interferogram with a single closed-loop circuit by employing the electro-optic effect of LiNbO ₃ .