Ultracompact polarization splitter–rotator based on an asymmetric directional coupler

An ultracompact polarization splitter–rotator based on an asymmetric directional coupler has been designed and analyzed. The device consists of one channel waveguide and one vertical slot waveguide, which couple to each other to form the asymmetric directional coupler. The coupling length is only 17.4 μm, and the polarization extinction ratio, with its largest value of 18 dB, is more than 15 dB in the operating wavelength range from 1515 to 1560 nm. The TM-to-TE conversion efficiency can reach up to 95% (0.02 dB) at 1550 nm wavelength.