Inverse design of an ultra-compact and large-bandwidth bent subwavelength grating wavelength demultiplexer.

Inverse design has attracted significant attention as a method to improve device performance and compactness. In this research, we employed a combination of forward design and the inverse algorithm using particle swarm optimization (PSO) to design a bent ultra-compact 1310/1550 nm broadband wavelength demultiplexer assisted by a subwavelength grating (SWG). Through the phase matching at 1550 nm and the phase mismatch at 1310 nm, we rapidly designed the width parameters of SWG in the forward direction. Then the PSO algorithm was used to optimize the SWG parameters in a certain range to achieve the best performance. Additionally, we introduced a new bent dimension significantly reducing the device length while maintaining low insertion loss (IL) and high extinction ratios (ERs). It has been verified that the length of the device is only 7.8 µm, and it provides a high ER of 24 dB at 1310 nm and 27 dB at 1550 nm. The transmitted spectrum shows that the IL values at both wavelengths are below 0.1 dB. Meanwhile, the 1 dB bandwidth exceeds 150 nm, effectively covering the entire O-band and C-band. This approach has been proven successful in enhancing performance and significantly reducing the device footprint.