Fig. 1. (a) Splicing two 1D PCs to excite the TIS. The refractive indices of dielectric layers are different in the 1D PC_L and 1D PC_R. (b) 3D scheme of the nonvolatile optical switch based on the tunable TIS. There are two different quasi-1D PCs on the left/right side of the ridge waveguide. The electric fields of the TIS are restricted near the interface between the quasi-1D PC_L and quasi-1D PC_R.

Fig. 2. Normalized electric field distributions of the ridge–slot cross-section (a), ridge cross-section (b), a_Sb2Se3 ridge cross-section (c), and c_Sb2Se3 ridge cross-section (d) of the ridge waveguide.

Fig. 3. (a)–(c) The band structure of the 1D PC (solid black curve) with parameters given by da=db=0.5Λ, where Λ is the length of the unit cell. (d)–(f) The Ey component distributions when kx=1 of different quasi-1D PC. (g) Simulated transmission spectrum of the 1D topological switch consisting of the two 1D PC structures. Resonance peaks are located in the center of the 1st gap, which correspond to the TIS. (h) Simulated transmission spectrum of the topological switch. The excitation wavelength corresponding to TIS is shifted by 0.8 nm. The topological switch has an IL of less than 0.5 dB and an ER of more than 16 dB.

Fig. 4. (a) Transmission spectra of 1D topological optical switch when the PCM is different crystalline states using the 3D FDTD simulation method. Due to the approximate conditions for the 1D PC_R period, the excitation wavelength corresponding to the TIS is shifted by 6.2 nm compared to the envisioned 1550 nm. The topological switch has an IL of less than 2 dB and an ER of more than 18 dB. (b), (c) Normalized electric field transmission of the 1D topological optical switch when the PCM is in the amorphous (b) and crystalline (c) state.

Fig. 5. Simulation results of the 1D topological switch with different defects. Simulated IL, ER, and wavelength of the exciting TIS with defects obtained by increasing or decreasing the air hole widths in the yellow region (a), the duty cycle of the PCM deposition length in a period (b), the PCM deposition width error (c), and the etching depth error (d).

Fig. 6. Schematic of the process flow for modulating nonvolatile optical switching using photonic crystal topological interface states.