Study on high brightness fiber coupled diode laser through VBG (volume Bragg grating) beam combining

Brightness of single wavelength diode laser is limited to single chip and technology of beam space assembling. In order to improve the brightness of fiber coupled diode laser, two channels wavelength division multiplexing is employed to achieve power increased doubly but BPP (Beam Parameter Product) remained unchanged theoretically. According to Lang-Kobayashi rate equation and Lamb laser equation with external cavity feedback and coupled wave theory, method of spectral locking and Bragg diffraction has been established to support our optical and mechanical design. Laser operated at 976.5nm center wavelength is diffracting and 975.5nm center wavelength is transmitting through beam combing VBG, the spectrum of sub beam is locked to 0.3nm (FWHM), the combing spectrum is 976.5nm±1nm. The diffraction and transmitting efficiency are about 80%, 96% respectively. The power of beam combing can reached at about 800W, and the BPP is less than 15mm·mrad, which indicates that could be coupled to 200μm core diameter fiber, NA (Numerical Aperture) would be less than 0.15. The results could be benefit for high brightness pump source of fiber laser or direct LD (Laser Diode) applications.