LAUSR

Abstract. A compact vertical coupler is proposed and optimized based on the multi-phase matching for three-dimensional (3D) mode (de)multiplexing [(De)MUX]. The multi-phase matching conditions can be achieved for the operating TE2, TE1, and TE0 modes of the subwavelength grating-based waveguide. The coupling strength can be significantly increased due to the subwavelength structure. The proposed 3D mode (De)MUX is optimized by utilizing the 3D full-vectorial finite difference time domain method. The optimized mode (De)MUX can achieve the coupling lengths of only 0.25 and 1.75  μm for demultiplexing TE1 and TE2 modes. The insertion losses of the TE2, TE1, and TE0 modes are only 0.25, 0.27, and 0.13 dB, respectively, and 3-dB bandwidths are calculated to be 364, 203, and >300  nm, respectively.