High-performance dual-polarization mode-order converter in thin-film lithium niobate

Mode-order converters are crucial components in multimode optical transmission and switching systems. Thin-film lithium niobate (TFLN) has become a promising platform for scalable photonic integrated circuits due to its superior material properties. Here, we present a dual-polarization mode-order converter in TFLN to implement TE0–TE1, TE1–TE0, TM0–TM1, and TM1–TM0 mode conversion processes simultaneously. Numerical simulations show that it can achieve an insertion loss below 0.28 dB and a total crosstalk lower than −25.4 dB over a 300-nm bandwidth. Then, to the best of our knowledge, a TFLN-based dual-polarization mode-order converter has been experimentally demonstrated for the first time, with an insertion loss below 1.09 dB and a crosstalk of each input mode lower than −21.4 dB within the 1500–1600 nm wavelength range. Owning to the low loss, low crosstalk, broad bandwidth, and high fabrication tolerance, the proposed device offers a scalable and efficient solution for hybrid multiplexing in advanced photonic networks.