Femtosecond pulse second harmonic generation under large depletion conditions in long PPLN waveguides

Summary form only given. Efficient second-harmonic generation (SHG) of ultrashort optical pulses under the large group-velocity mismatch (GVM) condition may have interesting applications. As a parameter range largely unexplored experimentally, it has been shown recently that this process could lead to highly efficient generation of blue light and realization of an all-optical signal processing function. It was also demonstrated that, by using long periodically poled lithium niobate (PPLN) waveguides, a small-signal SHG efficiency as high as tens of percents per pJ can be realized for femtosecond pulses. Highly efficient SHG with very low average pump power could be possible and may find interesting applications. We study the femtosecond-pulse SHG process under the large depletion, large GVM condition and study the factors affecting the saturation of the conversion efficiency. We observed a maximum SHG efficiency of /spl sim/60%. In order to understand the factors that limit the SHG efficiency, we thoroughly analyzed the throughput fundamental signal. Strong spectral and temporal amplitude distortions of the pump were observed. Our simulations suggest that interactions between SHG, GVM and nonlinear spectral phase distortion are responsible for the observed spectral amplitude modulation in the pump spectrum. Spatially nonuniform distribution of phase velocity mismatch may also strongly, impact, the yield of the SHG process.