A silicon TM mode multiplexer based on three waveguide directional coupler with subwavelength grating

In this work, a silicon TM mode multiplexer based on three waveguide directional coupler constructed by subwavelength gratings (SWG) is proposed. The working bandwidth is greatly increased by using the SWG waveguides and a mode block based on SWG is added to reduce the crosstalk. FDTD simulation results show that the insertion loss and crosstalk at 1550 nm are 0.7 dB and -35.9 dB respectively. Large working bandwidth of 270 nm (1400 nm similar to 1670 nm) can be achieved under the conditions of less than 3 dB insertion loss and -15 dB crosstalk. In addition, the fabrication tolerance of the proposed device is also investigated.