Fig. 1. Schematic of coupled waveguide system and E_z distributions under two modes. (a) Schematic of system; (b) E_z distributions

Fig. 2. Results under TE mode. (a) Momentum mismatch and phase compensation; (b) phase-matched bands; (c) spectral function; (d) conversion efficiency of FWM

Fig. 3. Flowchart of simulated annealing algorithm

Fig. 4. Simulated annealing optimization process. (a) Acceptance curve with iteration process of optimal value shown in inset; (b) comparison of phase matching before and after optimization; (c) comparison of spectral function

Fig. 5. Impact of propagation length on conversion efficiency. (a) Variation of FWM conversion efficiency with propagation distance; (b) FWM conversion efficiencies at propagation lengths of 3 mm and 5 mm

Fig. 6. Sensitivity analysis. (a) Parameters w and g; (b) parameter h

Fig. 7. Entanglement analysis result and photon flux density spectrum. (a) Schmidt coefficient with two-photon wave function for generation of photon pairs shown in inset; (b) photon flux density