Fully adiabatic polarization rotator-splitter based on thin-film lithium niobate platform

A Polarization Rotator-Splitter (PRS) based on thin-film lithium niobate (TFLN) is demonstrated in this work. The PRS consists of a partially etched polarization rotating taper and an adiabatic coupler, which enables the input TE₀ and TM₀ to be output as TE₀ from two ports, respectively. The fabricated PRS using standard i-line photolithography achieved large polarization extinction ratios (PERs) of > 20 dB across the whole C-band. Excellent polarization characteristics are maintained when the width is changed by ±150 nm. The on-chip insertion losses of TE₀ and TM₀ are less than 1.5 dB and 1 dB, respectively.