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Using a novel design approach, high-performance large-port-count switches based on cascaded multimode interference (MMI) couplers are shown to be feasible in low-index-contrast materials. This approach combines the transfer matrix method, optimization of the MMI dimensions, and mode propagation analysis (MPA) for calculation of phase shifts. 1×4, 1×8, 1×16, and 1×32 switches are designed, with insertion losses of 1 dB and crosstalk as low as -31.7 dB. Also, it is shown that this approach can balance the losses for different switch states.