Inverse asymmetrical ridge taper polarization splitter–rotatorcovering optical fiber communication band from O to U

A novel on-chip ultra-broadband polarization splitter-rotator (PSR) based on an inverse asymmetrical ridge taper coupler is proposed by using evanescent coupling between two straight waveguides with gradual ridge widths. The two ridge-widths decrease inversely to realize mode hybridization between fundamental transverse magnetic (TM0) mode and fundamental transverse electric (TE0) mode, which effectively expands the bandwidth. The structural parameters are optimized by utilizing the frequency-domain finite-difference and eigenmode expansion method. The results show that efficient polarization splitting and rotating are simultaneously achieved with a broad operating bandwidth from 1250 nm to 1750 nm and a high polarization conversion efficiency of more than 95%. The insertion loss is below 0.05 dB and 0.2 dB over the bandwidth for TE0 and TM0, respectively. To the best of our knowledge, the PSR achieves the broadest bandwidth up to 500 nm (covering all the optical fiber communication O-, E-, S-, C-, L-, and U-bands) for the first time