Fig. 1. Flowchart diagram of reverse design method

Fig. 2. Initial layout diagram of terahertz demultiplexer. (a) Initial three-dimensional structure; (b) top view of structure; (c) section view of waveguide structure

Fig. 3. Optimized structure and electric field intensity distribution of terahertz demultiplexer. (a) Top view of device; (b) electric field intensity diagram of 0.500 THz frequency for terahertz wave incident from Port1; (c) electric field intensity diagram of 0.417 THz frequency for terahertz wave incident from Port1; (d) electric field intensity diagram of 0.500 THz frequency for terahertz wave incident from Port2; (e) electric field intensity diagram of 0.417 THz frequency for terahertz wave terahertz incident from Port3

Fig. 4. Spectrum diagram of terahertz demultiplexer at two output ports. (a) Before bandwidth optimization; (b) after bandwidth optimization

Fig. 5. Schematic of initial layout of terahertz grating coupler. (a) Three-dimensional structure diagram of device; (b) top view of device; (c) symmetrical section view of device

Fig. 6. Optimized structure of grating coupler. (a) Variation curve of objective function value with number of iterations; (b) grating structure diagram after continuous optimization; (c) local magnification map after continuous optimization; (d) local magnification map after discrete optimization

Fig. 7. Discrete optimization structure and simulation results of grating coupler. (a) Optimized structure of terahertz grating coupler; (b) electric field intensity distribution diagram