Polarization-insensitive and high-efficiency edge coupler for thin-film lithium niobate

In this Letter, we propose and demonstrate a fiber -to -chip edge coupler (EC) on an x -cut thin film lithium niobate (TFLN) for polarization -insensitive (PI) coupling. The EC consists of three width -tapered full -etched waveguides with silica cladding and matches well with a single -mode fiber (SMF). The measured results show that the minimum coupling losses for TE0 /TM0 modes remain to be 0.9 dB/1.1 dB per facet, and the polarization dependent loss (PDL) is <0.5 dB over the wavelength range from 1260 to 1340 nm. Moreover, the EC features large misalignment tolerance of +/- 2 <mu>m in the Z direction and +/- 1.5 mu m in the X direction for both polarizations for a 1 dB penalty. To the best of our knowledge, this is the first realized O -band edge coupler on TFLN with SMF. The proposed device shows promising potential for integration into TFLN polarization diversity devices. (c) 2024 Optica Publishing Group