Compact Optical Polarization Rotators Based on an Asymmetric Silicon Waveguide

We design and compare two kinds of polarization rotators based on a partially etched waveguide: 1) the quadrate pattern and 2) the tapered pattern in the partially etched area. The devices are fabricated on a commercially available 200-mm silicon on insulator wafer with a 340 nm-thick top silicon and a 2 μm-thick buried dioxide. The tapered design realizes a polarization extinction ratio of ~ 13.3 dB for transverse-electric (TE)-transverse-magnetic (TM) rotation and 14.8 dB for TM-TE rotation, respectively. Compared with the quadrate structure, the tapered structure has an insertion loss reduction of ~ 2 dB for the TE-polarized input light and 1 dB for the TM-polarized input light without affecting the rotation efficiency in the wavelength range of 1525-1610 nm. Furthermore, the effects of the fabrication errors are analyzed and the results explain well the disagreement between the simulation and experimental results.