Fig. 1. Overall device structure. (a) Schematic of a tunable and non-volatile Y-junction photonic power splitter on a silicon-on-insulator (SOI) platform. In the diagram, the phase change material is depicted in red, silicon in blue, and silica substrate in gray. The top view of the device is shown in the top right, and the interface diagram focusing on the phase change material is shown in the bottom right. (b) Power ratio and (c) insertion loss (IL) between the upper and lower output ports of the 1300–1650 nm band with changes in the refractive index in the red region. In the figure, n represents the refractive index. This notation will be used consistently in the following discussion.

Fig. 2. Flowchart of the DBS algorithm. The phase change material is added to the initial structure, the FOM value and position are calculated and saved, the FOM value of the phase change material at different positions is sequentially calculated, and the FOM value and position are updated if there is an improvement in the FOM. The algorithm ends when all positions are calculated.

Fig. 3. Finite difference time domain (FDTD) simulation results at 1550 nm wavelength. (a) Optical fields of the phase change material at different positions with refractive indices of 1, 1.5, and 2.5, respectively. (b) Variations in the power ratio of different phase change material positions as a function of the refractive index. (c) Variation of IL with refractive index at positions numbered 8–9, 8–14, 9–17, and 9–19.

Fig. 4. FDTD simulation results. (a) Optical field diagrams of 1310 and 1550 nm lights at refractive indices of 1, 1.5, 2.5, and 3.5 of the phase change material. (b) Ratios of output power and (c) ILs of the upper and lower output ports after a Y-junction photonic power splitter for different wavelengths of light with continuously varying refractive indices.

Fig. 5. FDTD simulation results. (a) The optical field diagrams of 1310 and 1550 nm lights at radii of 50, 100, 200, and 300 nm. (b) Power splitting ratio and (c) IL when the radius of the phase change material is varied for a refractive index of the phase change material of 2.7. In the figure, r represents the radius. This notation will be used consistently in the following discussion.

Fig. 6. Simulation results of Sb₂S₃ material at 1550 nm wavelength. (a) The gradual phase change of 220 nm thick amorphous Sb₂S₃ (red) into crystalline Sb₂S₃ (green) at an incremental depth of 44 nm. (b) Power splitting ratios (red line) and ILs (blue line) at different phase change depths (crystalline Sb₂S₃ thickness). (c) Diagram of the optical field at 1550 nm for each degree of phase change. (d) The mode field at the section of the phase change material at each degree of phase change.

Fig. 7. (a) Ways of the Y-splitter cascade at the time of one split into two, the one split into four, and the one split into eight. (b) Optical field diagrams corresponding to one split into two, one split into four, and one split into eight. (c) Cascading numbers of single-point tunable Y-junction photonic power splitters to form a network can be used to construct a photonic neural network architecture by modulating the power splitting ratio to realize the weights between individual nodes.