Thin-film lithium niobate waveguide polarizer with a high extinction ratio exceeding 40 dB

We demonstrate an integrated thin-film lithium niobate (TFLN) polarizer with a state-of-the-art polarization extinction ratio (PER) exceeding 40 dB. By employing cascaded 90° Euler-bend waveguides, the device ensures low-loss transmission of the fundamental transverse-electric mode while strongly radiating the transverse-magnetic mode. Numerical simulations project an ultrahigh PER over 80 dB and a low excess loss below 0.2 dB from 1500 nm to 1580 nm. Experimentally, we validate the device performance scaling across different cascaded configurations. The 2.5-unit device delivers a PER of 43 dB and an excess loss of 2.0 dB at 1550 nm, with PER > 40 dB over an 80 nm bandwidth. The 1-unit device delivers a PER of 30 dB and an excess loss of 0.8 dB at 1550 nm, while featuring a compact length of 186 μm. Our work provides a viable solution to robust on-chip polarization control for TFLN photonic integrated circuits.