Fig. 1. Schematic diagram of initial structure. (a) Structure of 1×2 power splitter; (b) states of pixel units

Fig. 2. Three-dimensional structure diagram of devices based on different tangential platforms. (a) Z-cut lithium niobate thin film platform; (b) X-cut lithium niobate thin film platform

Fig. 3. Optimization process of inverse design algorithm

Fig. 4. Power splitters with 1∶1 spectral ratio designed based on Z-cut/X-propagation lithium niobate thin film platform. (a)‒(c) Structures of optimized devices with different design area sizes (L₁×L₂=2.86 μm×2.42 μm, 2.86 μm×2.86 μm, 2.86 μm×3.30 μm, in order); (d) electric field distribution of optimized device (L₁×L₂=2.86 μm×2.86 μm) at 1550 nm; (e) insertion losses of optimized devices at 1500‒1600 nm

Fig. 5. Power splitter with 1∶2 spectral ratio designed based on Z-cut/X-propagation lithium niobate thin film platform (L₁×L₂=2.86 μm×2.86 μm). (a) Structure of optimized device; (b) electric field distribution of optimized device at 1550 nm; (c) insertion loss and splitting ratio of optimized device at 1500‒1600 nm

Fig. 6. Power splitters with 1∶1 spectral ratio designed based on X-cut/Y-propagation lithium niobate thin film platform. (a)‒(c) Structures of optimized devices with different design area sizes (L₁×L₂=2.86 μm×2.42 μm, 2.86 μm×2.86 μm, 2.86 μm×3.30 μm, in order); (d) electric field distribution of optimized device (L₁×L₂=2.86 μm×2.86 μm) at 1550 nm; (e) insertion losses of optimized devices at 1500‒1600 nm

Fig. 7. Power splitter with 1∶2 spectral ratio designed based on the X-cut/Y-propagation lithium niobate thin film platform (L₁×L₂=2.86 μm×2.86 μm). (a) Structure of optimized device; (b) electric field distribution of optimized device at 1550 nm; (c) insertion loss and splitting ratio of optimized device at 1500‒1600 nm

Fig. 8. Mode distribution at input and output ports of optimized devices. (a) Z-cut, 1∶1; (b) Z-cut, 1∶2; (c) X-cut, 1∶1; (d) X-cut, 1∶2