Reverse design of multifunctional cascade devices based on the adjoint method

In this paper, a 1×4 ultra-compact wavelength division multiplexing cascaded device(DMC) with an arbitrary splitting ratio based on adjoint topology optimization reverse design is proposed, which is approximately two orders of magnitude smaller than that of conventional waveguide devices. It can simultaneously perform wavelength demultiplexing, mode conversion, and arbitrary ratio power splitting. The DMC separates 1310 nm and 1550 nm wavelengths, converts the input light from fundamental transverse mode (TE0) to first-order transverse mode (TE1) and second-order transverse modes (TE2), and performs arbitrarily proportional power splitting of the converted higher-order light source. •An ultra-compact 1×4 DMC with an arbitrary splitting ratio based on adjoint method reverse design is proposed in this paper. It is located on a 220 nm thick SOI platform and simultaneously achieves wavelength demultiplexing, arbitrary proportional power division, and mode conversion.•Meanwhile, the footprint of the WDM and the arbitrary ratio splitter remains fixed, but the footprint of the bent waveguide is enlarged to 2.4 µm×2.4 µm. The widths of the input and output waveguides of the splitter are expanded to 0.9 µm. FDTD simulation results indicate that the device converts the TE0 mode to the TE1 mode.•In addition, the footprint of the WDM stays similar, with the increased footprint of the bent waveguide and arbitrary ratio splitter being 2.4 µm×3.6 µm and 4 µm×4.8 µm, respectively. Furthermore, the output waveguide width of the arbitrary ratio splitter is raised to 1.4 µm. FDTD simulation results indicate that the device will convert the TE0 mode to the TE2 mode.