High brightness narrow linewidth blue laser diodes with fiber output

Chip on sub-mount chips are used as minimum emitting units of blue laser diodes, whose original power is about 7 W at a current of 4 A. Littrow-configuration plane diffraction gratings positioned at every slow axis collimation are employed to achieve spectral locking; the diffraction angle, groove density, and diffraction efficiency of the gratings are designed to be about 70°, 4242 lines/mm, 20%, respectively. Optical feedback appears along with a slow axis; therefore, the linewidth can be reduced to 0.15 nm (full width at half magnitude) compared to 3 nm in the free running condition. The spectral tuning ranges from 440.5 to 444.5 nm with a total of 4 nm through tuning the azimuth angle of gratings. Based on a “7 + 7” step design, through space stacking and polarization combining, a power of more than 60 W is obtained; the laser radiation is coupled into a fiber with 50 μm core diameter, numerical aperture less than 0.17, and a beam parameter product of about 4 mm mrad. The spatial and spectral brightness can reach at 42.1 MW/cm2/sr and 2.8 PW/cm3/sr separately.