Two-mode de/multiplexer based on multimode interference couplers with a tilted joint as phase shifter.

A novel design of a two-mode de/multiplexer (DE/MUX) based on multimode interference (MMI) couplers is presented. Instead of the phase shifter (PS) in the shape of a narrow strip waveguide, which needs tight design and fabrication requirements, a tilted joint is used as a PS in the proposed device, so that the effects of the fabrication errors of the PS on the performance of the device can be reduced greatly. Simulations show that while the size of the device is as small as 39.54 μm, which is more compact than other MMI-based DE/MUX, the fabrication tolerance is larger than ±25  nm. Within the entire C-band wavelength range, the de-multiplexing crosstalk of the device is lower than -28  dB and the insertion loss is below 1.0 dB.