Tunable OpticalDelay Line Based on Thin-Film LithiumNiobate at 2 μm Waveband

Abstract Integrated photonics is rapidly expanding toward the mid-infrared region to meet the growing demand for broader spectral resources and enhanced nonlinear optical efficiency, enabling emerging applications in biomedicine, nonlinear optics, and LiDAR. In these systems, fast and tunable optical delay/phase control is essential for signal processing. In this paper, a tunable optical delay line (TODL) at 2 μm waveband was demonstrated based on a 600 nm-thick thin-film lithium niobate (TFLN) platform for the first time, featuring low propagation loss as well as high switching speed. By analyzing the waveguide loss mechanisms and incorporating high-speed electro-optic switches, we have achieved an ultralow loss of 0.27 dB/cm in TFLN waveguides and an ultrafast switching speed of 27 ns for optical switch operating in the 2 μm waveband. Based on that, we have demonstrated a 9-bit TODL at the 2-μm waveband, providing a delay tuning range from 0 to 511 ps with a step size of 1 ps within a compact footprint of 34.43 mm2. Our proposed TODL holds significant delay/phase tuning for future applications beyond the telecommunication wavelength range.