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This paper presents an overview of self-imaging principle used in MMI couplers and also explains the application of multimode waveguide as an optical switch. The application of MMI coupler to realize a 2times2 optical switch has been explained by varying the refractive indices of various regions of MMI section by only 1-2% and the switch is found to exhibit 2-10% loss for various coupling states at different power inputs. Then the basic 2times2 switch is exploited in design of 4times4 Benes switch. Benes switch is used as it is suitable for large switches requiring fewer SOAs which make it a good candidate for further use in higher order switches. Simulation results are shown. Power coupling losses occurring in 4times4 switch are compensated using minimum number of SOAs with low input injection current of the order of 10-20 mA.