Broadband and highly efficient integrated polarization rotator designed by topology optimization

Being a fundamental block for systems that utilize polarization-diversity schemes, such as coherent transceivers, polarization rotators allow the conversion of polarization states. In this work, we present an ultra-compact efficient silicon polarization rotator designed via an inverse design method. By optimizing a topology based on the adjoint method, we designed polarization rotators for several combinations of lengths and widths. Simulation results show that the best optimized device presents a polarization conversion loss of 0.67 dB and cross talk of -18dB for a central wavelength of 1550 nm. These results were achieved for a 7 µm long and 1.2 µm width device. Furthermore, the high coupling efficiency and low cross talk were achieved for a bandwidth exceeding 100 nm. The polarization conversion loss and cross talk were maintained below 0.82 dB and -18dB, respectively, for a band ranging from 1500 nm to 1600 nm.