High extinction-ratio thin-film lithium niobate modulator integrated with TE-pass waveguide polarizer

Thin-film lithium niobate (TFLN) modulators are expected to play a key role in next-generation optical communication systems. In this work, we present the design, fabrication, and characterization of a TFLN Mach-Zehnder modulator (TFLN-MZM) with high extinction ratio (ER). The fabricated modulator has achieved the ER of 41 dB by integrating a waveguide polarizer, an intentional input-output waveguide misalignment, and a Mach-Zehnder interferometer (MZI) structure composed of 1 × 2 multimode interferometers (MMIs). The polarization extinction ratio (PER) of this integrated waveguide polarizer is 38 dB, effectively filtering out all polarizations except the transverse electric (TE) mode. The measured half-wave voltage (V_π) for the fabricated modulator with a modulation arm length of 3.3 mm is 7.9 V, corresponding to a voltage-length product of 2.6 V·cm. The proposed modulator improves the extinction ratio without the need for additional control circuits, and thus it has wide applications in optical communication, quantum key distribution, lidar, fiber-optic distributed acoustic sensing (DAS), etc.