Quasi-isotropic phase modulator architecture based on thin-film lithium niobate

In this study, a quasi-isotropic phase modulator operating in the C-band is fabricated and verified to address polarization-dependent mode constraints and the imbalance of electro-optic modulation efficiency in a thin-film lithium-niobate photonic platform. By integrating an adiabatic port with the functions of mode shaping and polarization rotation in the chip port, the TE0 mode can be modulated, and the TM0 mode can be converted to the TE1 mode, and then modulated and restored to TM0 for output. The results show that the conversion efficiency from TM0 to TE1 in the C-band is greater than 88%, and the difference in the modulation efficiency between the two orthogonal input polarizations is within 10%. By maintaining the same input and output polarizations, the proposed device achieves a more balanced modulation response under different polarization states, providing a reference for the optical link between polarization-multiplexing and multimode-compatible systems.