Second harmonic generation by femtosecond Yb-doped fiber laser source based on PPKTP waveguide fabricated by femtosecond laser direct writing

The frequency doubling of femtosecond pulses from an Yb-doped fiber laser source was demonstrated in a PPKTP waveguide fabricated by femtosecond laser direct writing. The PPKTP waveguide contains a fixed period of 8.9 μm and the feomtosecond fundamental pulses have a central wavelength of 1044 nm. A maximum SHG power of 406 mW was produced, yielding a conversion efficiency of 5.6%. Numerical simulations were carried out to investigate the property of frequency doubling for femtosecond pulses. The results show that the SHG process proceeds even the quasi-phase-matching (QPM) condition is not well satisfied, which is significantly different from that of “long” pulses or CW light and is accorded with the experimental results.