关键词: polarization demultiplexers, wavelength-division-multiplexing, microring resonators

Abstract: A compact and fabrication friendly polarization demultiplexer (P-DEMUX) is proposed and characterized to enable wavelength-division-multiplexing and polarization-division-multiplexing simultaneously. The proposed structure is composed of a polarization-selective microring resonator in ultrathin waveguide and two bus channels in the silicon nitride-silica-silicon horizontal slot waveguides. In the slot waveguide, the transverse electric (TE) mode propagates through the silicon layer, while the transverse magnetic (TM) mode is confined in the slot region. In the designed ultra-thin waveguide, the TM mode is cut-off. The effective indexes of the TE modes for ultrathin and slot waveguides have comparable values. Thanks for these distinguishing features, the input TE mode can be efficiently filtered through the ultra-thin microring at the resonant wavelength, while the TM mode can directly output from the through port. Simulation results show that the extinction ratio of the proposed P-DEMUX for TE and TM modes are 33.21 dB and 24.97 dB, and the insertion losses are 0.346 dB and 0.324 dB, respectively, at the wavelength of 1551.64 nm. Furthermore, the device shows a broad bandwidth ($>100$ nm) for an extinction ratio (ER) of $>20$ dB. In addition, the proposed P-DEMUX also has a good fabrication tolerance for the waveguide width variation of $-20$ nm$\le \Delta w_{\rm g}\le 20$ nm and the microring width variation of $-20$ nm$\le \Delta w_{\rm r}\le $20 nm for a low insertion loss of $<0.75$ dB and low ER of $<-18$ dB.

Key words: polarization demultiplexers, wavelength-division-multiplexing, microring resonators