Compact mid-infrared polarization rotator based on subwavelength grating with ultra-large broadband

To eliminate the polarization sensitivity issues in integrated photonic circuits based on a silicon-on-insulator (SOI) platform and improve the performance of the polarization diversity system, a large-bandwidth mid-infrared polarization rotator based on a sub-wavelength grating (SWG) combined with a single stair is proposed. It can achieve the conversion between the TM0 and TE0 modes through mode-hybridization by breaking the waveguide cross-sectional symmetry. The device structure parameters have been optimized, and its polarization rotation characteristics have been investigated using the finite-difference time-domain (FDTD) method. Simulation results reveal that at the central wavelength of 2.82 μm, the highest polarization extinction ratio (PER) can reach up to 40.75 dB, and the insertion loss (IL) is as low as 0.019 dB. The operational bandwidth (PER>10 dB) extends up to 800 nm (2.5 to 3.3 μm). Meanwhile, the device length is only 10.02 μm. In addition, tolerance analysis indicates that the device has good manufacturing tolerance. Owing to its compact footprint, high PER, and large bandwidth, the proposed PR has significant potential for application in mid-infrared photonics.