Femtosecond second-harmonic generation in periodically poled lithium niobate waveguides written by femtosecond laser pulses

We present in this Letter the second-harmonic generation of femtosecond pulses in double-line-written waveguides fabricated in periodically poled lithium niobate (PPLN) with femtosecond laser pulses. In a 10-mm-long sample, a normalized conversion efficiency of 12.6% W−1 cm−2 has been achieved for 40 fs pump pulses with the wavelengths centered at 1550 nm. Simulation results show that in PPLN waveguides the FWHM of wavelength tuning curve for 40 fs pump pulses is 42 nm, which is 15 times of that for 40 ps pump pulses.