Fig. 1. Three-dimensional structure of SEDFB laser

Fig. 2. Cross-sectional sketch of SEDFB laser

Fig. 3. Schematic of grating structure and top transmission spectra of the second-order grating with or without λ/4 phase shift. (a) Schematic of grating structure; (b) top transmission spectra of the second-order grating

Fig. 4. Cross-sectional sketch of shallow ridge waveguide

Fig. 5. Variation curves of transverse refractive index difference and single-mode cut-off waveguide width with ridge waveguide depth H_r and spacer thickness H_s. (a) Transverse refractive index difference; (b) single-mode cut-off waveguide width

Fig. 6. Variation curves of coupling coefficient and optical confinement factor with ridge waveguide depth H_r and grating etching depth H_g. (a) Coupling coefficient; (b) optical confinement factor

Fig. 7. Schematic of the ridge waveguide structure. (a) Part of unetched grating; (b) part of etched grating

Fig. 8. Contour plots of optical confinement factor and coupling coefficient. (a) Optical confinement factor; (b) coupling coefficient

Fig. 9. Production process of SEDFB laser. (a) Fabrication of etching marks; (b) etching contact layer fabricated by wet method; (c) fabrication of surface grating; (d) fabrication of ridge waveguide structure; (e) fabrication of oxidation table; (f) oxidized aperture fabricated by wet oxidation method; (g) fabrication of upper electrode; (h) thinning and fabricating lower electrode

Fig. 10. SEDFB laser fabrication result diagrams. (a) SEM image of deeply etched ridge waveguide; (b) surface grating SEM image; (c) cross-sectional SEM image of oxidized aperture; (d) optical micrograph of SEDFB laser; (e) SEM image of SEDFB laser

Fig. 11. SEDFB laser static characteristic curves. (a) L-I-V curves of SEDFB lasers with different active region lengths; (b) spectra of SEDFB lasers under different injection currents

Fig. 12. Laser spectra. (a) Spectra of SEDFB laser at different TEC temperatures; (b) laser spectra with different first-order grating periods

Fig. 13. Simulation results of SEDFB laser light field. (a) Near-field pattern; (b) light field intensity along the longitudinal direction of the near field pattern; (c) far-field pattern

Fig. 14. Test results of SEDFB laser light field. (a) SEDFB laser output pattern; (b) test and fitting results of far-field divergence angle of SEDFB laser

Fig. 15. Measured small signal modulation responses of SEDFB lasers with different active section lengths. (a) 150 μm; (b) 50 μm