polarization insensitive 40-channels 100 GHz spacing fold-back planar Echelle grating mux/demux for photonic integrated wavelength selective switches

We present and numerically demonstrate a novel polarization insensitive (PI) 40-channels 100 GHz spacing fold-back planar Echelle grating (PEG) multiplexers/ demultiplexers (Mux/Demux) to realize the compact 1×2 crossing-less photonic integrated wavelength selective switch (PIC-WSS). The PI operation is achieved by a polarization splitter to feed the TE mode and TM mode into the PEG via two waveguides with different incidental angles so that the diffracted optical signals (two different modes) combine at the same PEG’s output waveguide. By optimizing the design of the different inputs/outputs angles combinations and sharing the same blazed angle, a single compact PI PEG with fold-back configuration can simultaneously operate as twice Demuxes and Muxes. The single fold-back PI PEG’s footprint is only 40 mm2. The numerical results show that 40-channels 100 GHz spaced PI fold-back PEG owns < 2.4 dB insertion loss, <-60 dB cross-talk, zero polarization dependent wavelength shift (PDWS), 0.3 dB polarization dependent loss (PDL), < 0.5 dB loss variation and < 0.01 nm wavelength shift between Mux and Demux.