Comparative simulation of three types of 3-dB coupler using a Si wire waveguide

We have proposed a cross gap coupler (CGC), which has an X-junction with an internal mirror at the cross section. We compared the splitting properties of three types of 3-dB coupler using a silicon wire waveguide; a CGC, a directional coupler (DC), and a multimode interference (MMI) coupler. The wavelength dependences of these structures were simulated (or evaluated) by two-dimensional finite-difference time-domain (2-D FDTD) method. The CGC showed smaller wavelength dependence in comparison to the other types of coupler.