Fig. 1. Structure of slot waveguide. (a) Two-dimensional schematic of horizontal slot waveguide; (b) three-dimensional schematic of horizontal slot waveguide.

Fig. 2. Distribution of normalized |E (x, y)| in slot waveguide with the Si guiding layer height h_g = 200 nm, width w = 300 nm, and slot height h_s = 40 nm. (a) TM mode profile at 1530 nm; (b) TM mode profile at 1480 nm; (c) TE mode profile at 1530 nm; (d) TE mode profile at 1480 nm. The white arrows represent the directions and amplitudes of the electric field in the xy plane.

Fig. 3. Simulation results for varying h_s from 10 to 120 nm. (a) Effective refractive indices n_eff of the TM/TE mode at 1530 nm and 1480 nm; (b) confinement factors Γ_s of the TM/TE mode at 1530 nm and 1480 nm; (c) normalized power density I_norm of the TM/TE mode at 1530 nm and 1480 nm.

Fig. 4. Optimization of width and height of the Si layer with a 40 nm thick slot. (a) Field confinement factors Γ_s as a function of single silicon layer height h_g and waveguide width w. (b) Normalized power density I_norm as a function of single silicon layer height h_g and waveguide width w. The white dashed lines in (a) and (b) are the boundaries of the n_eff (TM) > n_eff (TE) condition; only the domains below these lines are valid. The white dots in (a) and (b) denote Γ_s = 29.17% and I_norm = 24.31 µm⁻², respectively, at the positions of h_g = 200 nm and w = 300 nm.

Fig. 5. Energy-level transitions for the Er³⁺-doped four-level system (pumped by 1480 nm).

Fig. 6. Simulated gain characteristics of the designed slot waveguide amplifier. (a) Gain versus propagation distance for different pump powers. (b) Gain versus pump power for different amplifier lengths. For both situations, the signal power is assumed to be 0.01 mW.