Fig. 1. Schematic diagram of external cavity mode, internal cavity mode, and VBG feedback bandwidth of semiconductor laser

Fig. 2. Relationship between volume Bragg grating diffraction efficiency and incident wavelength and incident angle. (a) Incident wavelength; (b) incident angle

Fig. 3. Schematic diagram of experimental device

Fig. 4. Laser output spectrum of the semiconductor laser before and after mode locked by VBG

Fig. 5. Output power characteristic curves of VBG external cavity semiconductor lasers

Fig. 6. Spectral analysis under different driving current conditions. (a) Spectrum of gain chip free-running; (b) spectrum of external cavity semiconductor laser with VBG

Fig. 7. Spectrum of external cavity semiconductor laser at different operating temperatures