Study Of Spectrum Stabilization Of Laser Diode Array With Volume Bragg Grating

Due to the small size, high efficiency and easily integrated, etc., laser diode array(LDA) have applied in many fields such as communication, medical laser, research anddevelopment, pumping solid-state lasers and others. Because of the drawback such aswide line-width and central wavelength drifts with temperature, the further developmentin industry R&D and pumping other lasers is restricted. Theoretical and experimentalstudy of wavelength stabilization and line-width narrowing of external-cavity laser diodearray based on volume Bragg grating (VBG) has been studied in this thesis. Theinfluence of spectral selectivity and peak diffraction efficiency of VBG with differentgrating parameters, such as thickness, period and refractive index modulation, isanalyzed with Kogelnik coupled-wave theory. The operating characteristics of external-cavity LDA such as output line width and threshold gain are analyzed with rate equations.The results show that the operating characteristics are influenced by the reflectivity ofVBG and LDA front facet. The spectral stabilization and photon density of the externalresonator is proportional to the reflectivity of Bragg gratings, but inversely proportionalto the reflectivity of the LDA front facet. The spectral linewidth is obviously narrowedand the the threshold of the LDA is decreased with the external Bragg grating resonator.The spectral stabilization and spectral narrowing experiment with the external-cavity LDA with volume Bragg grating was studied. The influence of fast-axis-collimation on coupling efficiency was studied with ray-tracing method. The resultsindicate that the central wavelength of LDA was locked efficiently and line-width wasnarrowed sharply under the effect of VBG external-cavity. For808nm LDA, an outputpower of24.8W is obtained with the linewidth down to0.18nm, which corresponds to the efficiency of82.6%. For852nm LDA, an output power of20.54W is obtained withthe linewidth down to0.17nm, which corresponds to the efficiency of86.6%.Thedependence of of spectral characteristics of external cavity LDA with the reflectivity ofVBG was studied. The results show that the increasing of VBG reflectivity can inhibitthe intra-cavity mode, enhance the spectral contrast and narrow the line-width, whilethe slope efficiency of the external LDA was reduced. Combined the experimental resultsand theoretical analysis, the VBG reflectivity between25%and35%is suitable forhigh external-cavity efficiency and excellent spectral characteristics.