Silicon TM-mode multiplexer based on bridged subwavelength grating

Abstract

A silicon TM-mode multiplexer (MUX) is proposed by using the bridged subwavelength grating (BSWG) based three-waveguide coupler. The dispersion engineering can be enabled by using the BSWG structures, resulting in enhanced strength of the mode coupling, thereby significantly improving the bandwidth and fabrication tolerance. The proposed mode MUX for handling the TM0 and TM1 modes is optimized by using the three-dimensional full-vectorial finite difference time domain (3D-FV-FDTD) based band-structure and propagation calculations. The numerically simulated results show that the optimized mode MUX is with a compact coupling length of 18.75 μm, a low insertion loss of 0.5 dB, and an ultra-low crosstalk of -36.4 dB at the wavelength of 1550 nm. An ultra-broad bandwidth of 500 nm can be achieved for the crosstalk < -15.0 dB. The 1 dB and 3 dB bandwidths are over 310 nm and 500 nm, respectively. The deteriorations of the insertion loss and crosstalk are less than 0.2 dB and 5.3 dB with a width error of ± 50 nm.