Self-injection-locked second-harmonic generation at 532 nm in high-Q Fabry-Perot micro-cavities

Based on the combination of DFB laser self-injection-locking (SIL) and external-cavity frequency-doubling, we have successfully demonstrated, for the first time to our knowledge, the self-injection-locked second-harmonic generation (SHG) at 532 nm by adopting the high-Q Fabry-Perot (FP) micro-cavities. With the DFB incident pump power of 79 mW at 1064 nm, the maximum output SHG power of 20.7 mW at 532 nm was achieved from the 11 mm long plane-concave FP external-cavity of 0.12 mL volume with the 10 mm long PPLN crystal. The corresponding output SHG efficiency of 26.2 % and the Q-factor of 56.5 M both exceeded all known SIL-SHG results reported, and the SIL SHG output power was one order of magnitude higher than the previous maximum of over 2 mW. The reliable SIL has been realized by utilizing the natural birefringence of the intracavity nonlinear crystal to provide laser feedback, and the intrinsic linewidth of the SIL pump laser at 1064 nm was about 30 Hz. Moreover, by replacing the PPLN crystal with the LN and KTP crystals, the output SHG power of 6.1 mW and 2.7 mW at 532 nm were respectively obtained with the Q-factors of 29.3 M and 27.6 M. Our new SIL-SHG design with the high-Q FP micro-cavity paves the way to a new type of the field-deployable ultranarrow-linewidth visible and near-visible lasers of low size, weight, and power (SWaP).