Ultra-broadband mode (de)multiplexer based on a sub-wavelength engineered MMI coupler

We present an ultra-broadband two-mode de/multiplexer based on a multimode interference coupler with sub-wavelength grating waveguides, a symmetric Y-junction and a 90° phase shifter. Numerical simulations show insertion losses below 0.18 dB and crosstalk lower than −20.6 dB in a 300 nm wavelength range.