An ultra-compact dual-channel multimode wavelength demultiplexer based on inverse design

Abstract An ultra-compact multimode wavelength demultiplexer (MWD) with a footprint of 3.6 × 2.4 μm2 was designed. Its size is approximately two orders of magnitude smaller than the size of the traditional waveguide-based device. Moreover, the designed demultiplexer is multifunctional, and can realize wavelength demultiplexing and mode conversion at the same time. This MWD splits light at the wavelengths of 1450 nm and 1550 nm and simultaneously converts the input light from the fundamental transverse electric (TE0) mode to the first-order transverse electric (TE1) mode. The direct binary search (DBS) algorithm was employed to simulate the design. The results show that the insertion loss of the demultiplexer is −1.26 dB and −0.82 dB for the upper channel (wavelength 1450 nm) and lower channel (wavelength 1550 nm), while the crosstalk values are maintained as low as −18.10 dB and −23.35 dB, respectively. Additionally, a similar structure can be expanded to several modes. Based on these advantages, this multifunctional photonics device is expected to be used extensively in advanced photonic integration circuits.