Ultrafast Tunable Lithium Tantalate Photonic Waveguide Delay Lines

On-chip tunable optical delay lines are key building blocks for various applications such as microwave photonics, beamforming networks, and reconfigurable signal processing, where fast switching speed, high delay resolution, and high scalability are simultaneously required. In this work, we propose and demonstrate an ultrafast tunable lithium tantalate photonic waveguide delay line, leveraging the low propagation loss, weak birefringence, and reduced DC drift for electro-optic operation. The chip is developed with the cascade of high-speed electro-optic Mach–Zehnder switches with binary-weighted spiral delay lines. In particular, a post-fabrication phase trimming scheme based on direct laser writing (DLW) is implemented using Sb2Se3-integrated waveguide sections, providing a linear and deterministic phase correction, so that all the Mach–Zehnder switches work bias-free in their OFF state. The present on-chip system achieves a continuous delay tuning range from 0 to 1023 ps with 1 ps resolution. Finally, the system-level measurement shows excellent agreement with the theoretical prediction, validating a scalable and robust bias-free operation for the true-time delay chip.