Compact and broadband polarization splitter-rotator on thin-film lithium niobate minimized with the fast quasi-adiabatic algorithm.

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Polarization splitter-rotators (PSRs) are crucial for on-chip polarization-division multiplexing (PDM) systems. Here, we design and experimentally demonstrate a compact and broadband PSR based on adiabatic mode evolution on a thin-film lithium niobate (TFLN) platform. A novel, to the best of our knowledge, quasi-adiabatic algorithm is proposed to minimize the device size. The fabricated PSR, with an adiabatic waveguide length of only 0.4 mm, exhibits an insertion loss of <0.64 dB and a polarization extinction ratio of >20 dB over a 122-nm bandwidth.