Frequency stabilization of multimode diode lasers with fiber Bragg gratings

We present the frequency stabilization of a multimode diode laser single emitter at 1074.8 nm by use of fiber Bragg gratings in a 105/125 $\mu$m NA 0.22 fiber that is spliced to the output fiber of the diode laser. At 25o C, the spectral full width at half maximum decreases from 4.6 nm in the free-running configuration to 1.1 nm using an FBG with a reflectivity of R=0.07, the thermal drift decreases from 2.12 nm/W to 0.45 nm/W. The optical output power at 10 A with frequency stabilization is 6.6 W compared to 6.7 W without FBG, hence the loss amounts to less than 3%. We compare the results for two different FBG-reflectivities and operate the diode laser at 25o C and 30o C. The FBGs are directly written into the multimode fibers with an ultra-fast laser (100 fs, 800 nm) and the phase mask technique.