Inverse-Designed Compact Six-Mode (de)Multiplexer via Subwavelength Gratings

Based on the inverse-designed cascaded subwavelength grating structures, a six-channel compact mode (de)multiplexer is proposed and experimentally verified. The distribution of subwavelength gratings for each mode channel is optimized via a particle swarm optimization algorithm to enable high-efficiency mode conversion and rapid mode coupling. Moreover, different mode channels are engineered for direct cascading without adiabatic tapering transitions, which significantly reduces the device footprint. Our designed six-channel mode (de)multiplexer exhibits low insertion loss and crosstalk across the 1500-1600 nm wavelength range, as well as ultra-short coupling lengths ranging from 8.0 to 14.6 μm for TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub>-TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> mode channels. Measured performance indicates that all mode channels achieve peak insertion loss below 0.88 dB and crosstalk below -12 dB. Furthermore, the device has been verified through simulations to exhibit high fabrication tolerances. These compact components provide an alternative approach for enabling high-capacity and dense-integrated on-chip mode-division multiplexing circuits.