Broadband and compact polarization rotator-splitter based on adiabatic tapers and a 2 × 2 MMI coupler on the thin-film lithium niobate platform

We present a broadband and compact polarization rotator-splitter (PRS) implemented on the thin-film lithium niobate (TFLN) platform, utilizing two adiabatic tapers, a phase shifter and a general-interference-based 2 × 2 multimode interference (MMI) coupler. The device employs adiabatic mode conversion and multimode interference mechanisms to achieve mode conversion and polarization splitting within a compact length of 228 μm. Experimental results indicate that the fabricated device exhibits low insertion losses, with 0.2 dB for the TE 0 mode and 0.6 dB for the TM 0 mode at a wavelength of 1550 nm. Furthermore, the device demonstrates remarkable tolerance to fabrication variations within ±4 μm, highlighting its potential for practical implementations. This work paves the way for polarization-multiplexed transceivers, reconfigurable optical networks, and quantum photonic systems on thin-film lithium niobate platforms.