Four-channel Wavelength Selective Switch Based on Vernier Second-order Microring Resonators with Asymmetric Coupling Regions

We propose and demonstrate a 4-channel wavelength selective switch based on four 2nd-order microring resonators (MRRs) on silicon-on-insulator substrate. Two ring cavities with different perimeters in each 2nd-order MRR are controlled independently by two thermal heaters. The fabricated MRR shows a free spectral region of 27.5 nm and a 3 dB bandwidth of 132 GHz. The extinction ratios are 16 dB and 20 dB at the through and drop ports, respectively. Through the asymmetric coupling design in the MRR, the group delay difference between its two output ports is 2.78 ps.