Integrated Hybrid Mode-Wavelength Demultiplexers Based on Cascaded Digital Metamaterials

High-dimensional multiplexing technology is of importance in the on-chip photonic interconnections and challenging to design within ultracompact footprint. Herein, high-dimensional demultiplexers are proposed and demonstrated to enable wavelength-division and mode-division simultaneously. The functional regions of digital metamaterials are obtained by inverse design individually and are cascaded to work as high-dimensional demultiplexers. The gradient-based inverse design is carried out with an efficient method combining finite-element method, density method, and method of moving asymptotes. The performances are simulated by 3D finite difference time domain with silicon-on-insulator configuration. The proposed demultiplexer with four-channel has ultracompact footprint of 4.1 × 3.65 μm². Its average transmission efficiency is 38.7% and contrast ratios are higher than 13.0 dB. Besides, the proposed demultiplexer with six-channel has a footprint of 4.55 × 5.55 μm². Its average transmission efficiency is 24.3% and contrast ratios are higher than 11.8 dB.