On-Chip Optical Isolator Based on Periodically Poled Lithium Niobate

Chip-scale optical communication and integrated photonic systems require stable unidirectional light propagation, making the monolithic integration of optical isolators essential. We show a passive, non-magnetic optical isolator based on a periodically poled lithium niobate (PPLN) waveguide that utilizes the difference-frequency generation (DFG) effect to achieve nonreciprocal light transmission. By integrating interleavers, a narrow waveguide, and an asymmetric directional coupler (ADC) on the same thin-film lithium niobate (TFLN) chip, the device achieves nonreciprocal transmission through efficient forward DFG and engineered filtering, enabling strong suppression of backward-propagating signals. Benefiting from these mechanisms, the isolator achieves a simulated isolation ratio exceeding 40 dB at several wavelengths. The proposed structure combines nonlinear frequency conversion and wavelength-selective routing on the same TFLN platform without magnetic materials or continuous electrical modulation.