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A Polarization Splitter and Rotator Based on a Partially Etched Grating-Assisted Coupler

A fabrication-tolerant mid-infrared silicon polarization splitter and rotator (PSR) based on a partially etched grating-assisted coupler is proposed. The design of the partially etched structure allows to use different cladding layers, such as SiO2, to make the device compatible with the metal back-end of line process. Moreover, by using the grating-assisted coupler, the device is no longer limited by the precise requirement of the coupling length and strength as those in its counterparts based on directional couplers. The simulation results show that the PSR can work over a wide spectral range of 50 nm around the mid-infrared wavelength of 2.5 μm with the typical transverse electric (TE) to transverse magnetic (TM) polarization conversion efficiency of 96.83%, the conversion loss of -0.97 dB, and the polarization crosstalk of -21.48 dB. The TM-to-TM through insertion loss is around -0.76 dB. The effects of the fabrication errors are analyzed. The numerical simulation results demonstrate that the device has a good fabrication tolerance larger than 45 nm.