Subwavelength grating based mode (de)multiplexerfor 3D photonic integrated circuits

A broadband three-dimensional (3D) mode (de) multiplexer [(De)MUX] is proposed based on the subwavelength grating (SWG) for 3D photonic integrated circuits (PICs). The proposed 3D mode (De)MUX consists of three SWG waveguides on two vertical layers. The coupling strength and operating bandwidth can be increased benefitting from both the subwavelength structure and offset between bus and access SWGs. The proposed 3D mode (De)MUX is optimized based on the 3D full-vectorial finite difference time domain method. The 1-dB bandwidths of the optimized device are over >300, 107, and 128 nm for demultiplexing TE0, TE1, and TE2 modes, respectively. The coupling lengths are only 5.0 and 1.75 µm for demultiplexing the TE1 and TE2 modes, respectively. The insertion losses are 0.12, 0.27, and 0.29 dB, respectively. The proposed 3D mode (De)MUX is also fabrication tolerant.