Fig. 1. Double asymmetric large optical cavity waveguide structure and refractive index distribution

Fig. 2. Schematic diagram of the high-order sidewall grating DFB semiconductor laser

Fig. 3. Reflection ability of sidewall gratings. (a) Effective refractive index of the fundamental mode undet different H and W; (b) κL versus w2 (w1=4μm)

Fig. 4. Lateral mode distributions of different sidewall grating structures. (a)‒(d) Mode distributions for various ridge widths at H=1.25μm; (e)(f) fundamental mode versus etch depth at W=4μm; (g)(h) first-order mode versus etch depth at W=4μm

Fig. 5. SEM images of the sidewall grating waveguide. (a) Top view with phase shift; (b) top view of the high-order sidewall grating; (c) etching cross-section

Fig. 6. Inverse external quantum efficiency versus cavity length

Fig. 7. Characteristics of FP laser. (a) PIV curve; (b) spectral characteristics

Fig. 8. Characteristics of high-order sidewall grating DFB laser. (a) PIV curves at different temperatures; (b) wavelength versus current and temperature; (c) spectra under various currents at 20 °C; (d) far-field pattern