Design and performance analysis of a low-index-contrast cascaded multimode interference switch

The multimode interference (MMI) switch is a versatile component for photonic signal processing applications. A 4×4 silica-on-silicon (SOS) all-optical MMI switch design is presented in this paper. This structure is based on two cascaded 4×4 MMI couplers and phase compensation arms. First a 4×4 MMI coupler is designed using self-imaging principle and then it is optimized for minimum loss and uniformity using improved self-imaging principle, as weakly guiding features of SOS waveguides are different from the strongly guiding features considered in the self-imaging principle. BPM simulation is used to analyze the coupler structure. This optimized MMI couplers are then cascaded using phase compensation arms; from the calculation of relative phases of MMI sections the phase compensations are obtained. Numerical simulation results of the designed structure consequences a better device performance with a loss of 1.12dB and crosstalk level of less than -22dB.