Continuously Tunable Thin-film Lithium Niobate Optical Delay Line with 293-ps Tuning Range

We present a compact optical delay line (ODL) with wide-range continuous tunability on thin-film lithium niobate (TFLN) platform. The proposed device integrates an unbalanced Mach-Zehnder interferometer (MZI) architecture with dual tunable couplers, where each coupler comprises two 2×2 multimode interferometers (MMIs) and a MZI phase-tuning section. Experimental results demonstrate continuous delay tuning from 0 to 293 ps through synchronized control of coupling coefficients, corresponding to a 4-cm path difference between interferometer arms. The measured delay range exhibits excellent agreement with theoretical predictions derived from ODL waveguide parameters. This result addresses critical challenges in integrated photonic systems that require precise temporal control, particularly for applications in optical communications and quantum information processing, where a wide tuning range is paramount.