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Waveguide-integrated reconfigurable nanophotonic devices are of importance for on-chip all-optical connection and flexible photonic circuits. In this paper, we propose inversely designed reconfigurable TE0-to-TE1 and TE0-to-TE2 mode converters based on digital metamaterials consisting of nanoscale silicon and non-loss phase change material Sb 2 Se 3 pixels. The design strategy combines finite element method, density method and method of moving asymptotes. Only 73 and 56 optimization iterations are taken to obtain the optimal digital metamaterials for targeted mode conversions. The footprints of ultra-compact functional regions are 0.92 and 1.04 square center wavelengths, respectively. TE0-to-TE1 and TE0-to-TE2 mode conversions with high transmission efficiency and output mode purity are realized with crystalline Sb 2 Se 3 , while TE0 mode directly pass through with amorphous Sb 2 Se 3. Meanwhile, by cascading these two mode converters, TE1-to-TE2 mode conversion is achieved as well. Moreover, the robustness of these designs is demonstrated by introducing random wrong pixels. • Reconfigurable mode order converters are inversely designed with pixelated Sb 2 Se 3 phase change material. • Highly efficient inverse design scheme combines finite element method, density model and method of moving asymptotes. • Footprints of functional regions are as compact as 0.92 and 1.04 square center wavelengths. • Performances of the reconfigurable mode converters are comparable and satisfactory. [ABSTRACT FROM AUTHOR]

The waveguide-integrated reconfigurable power splitting is of great importance for on-chip all-optical connection. Based on the combination of silicon and Sb-based phase change materials (PCMs), a series of ultra-compact reconfigurable power splitters is topologically designed. The footprints of the functional regions are kept less than 1.0λ2. The power splitting ratio between the output channels can be reconfigured through the amorphous and crystalline switching of Sb-based PCMs. We demonstrate Sb 2 Se 3 -based and Sb 2 S 3 -based digital metamaterials for the reconfiguration between power splitting ratio of 5:5 and power splitting ratios of 5:5, 6:4, 7:3, 8:2 and 9:1. The three-dimensional FDTD simulations show that the targeted power splitting ratio can be achieved with acceptable precision. Moreover, the robustness of design is validated by introducing pixel errors. • Reconfigurable power splitter is topologically designed with pixelated Sb-based phase change materials. • The reconfiguration between splitting ratio 5:5 and splitting ratios 5:5, 6:4, 7:3, 8:2 and 9:1 are achieved. • The topology design scheme combines finite element method, density model and MMA. • The footprint of the functional region is less than λ2. [ABSTRACT FROM AUTHOR]