Broadband and highly efficient integrated polarization rotator designed by topology optimization

Abstract

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 − 18 d B 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 − 18 d B , respectively, for a band ranging from 1500 nm to 1600 nm.

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“…specified footprints or structures) without manually tedious parameter adjustment works, saving massive resources. There are many reports on developments or improvements of nano-photonic devices using inverse design with various optimization algorithms [47][48][49][50][51][52][53][54][55][56][57][58][59][60], but only few studies about the applications of inverse design on nonreciprocal devices [61][62][63][64], which are normally based on magneto-optical effects. In this study, we introduce several magnetic-free nonreciprocal devices that avoid use of magneto-optical materials and magnets, which are difficult to be compatible with current semiconductor integration technology.…”