Compact Subwavelength Grating-Assisted TFLN Wavelength Demultiplexer with Ultra-Low Loss

We present an ultra-low-loss, broadband two-channel wavelength demultiplexer designed on a thin-film lithium niobate (TFLN) platform. The proposed design leverages subwavelength grating (SWG)-assisted directional coupling on both sides of the SWG to achieve efficient wavelength splitting at 780 nm and 1550 nm. This approach not only minimizes the device footprint and significantly reduces insertion losses but also improves the extinction ratio. The optimized demultiplexer, with a compact length of 42.8 μm, exhibits exceptionally low insertion losses of 0.36 dB and 0.22 dB, in addition to high extinction ratios of 33 dB and 16 dB for the 780 nm and 1550 nm channels, respectively. The 0.5-dB bandwidths exceeding 70 nm for both wavelengths.