Efficient second harmonic generation of a Yb fiber-based amplified stimulated emission source

Efficient second harmonic generation (SHG) of ytterbium (Yb)-doped fiber-based amplified spontaneous emission (ASE) light with temporally low coherence is reported. A Yb-fiber ASE light with a tunable bandwidth was amplified in two power amplifier stages and was frequency-converted by a periodically-poled lithium tantalite waveguide. The second harmonic conversion efficiency of the ASE light achieved in the experiment was inversely proportional to the bandwidth, which was in very good agreement with theoretically calculated value using the self-convolution relationship of the power spectral density for nonlinear frequency conversion of low coherent light. The prospects for further improvement in nonlinear frequency conversion of the fiber ASE source will be discussed.