Spectral Characteristics of Femtosecond Pulses Propagation in Periodically Poled Lithium Niobate via Cascaded Quadratic Nonlinearity

Characteristics of spectral shift and spectrum broadening of femtosecond pulses propagation in periodically poled lithium niobate via cascaded quadratic nonlinearity are investigated. Amount of spectral broadening is obtained analytically from coupled equations including Kerr-like term. Multipeak spectra with the typical self-phase-modulation-like characteristics were obtained experimentally using 40-fs pulses with a spectral width of 60 nm at 1550-nm band. The spectral blue and red shifts as large as 50 nm were observed with a large phase mismatching Δk = 95 mm^-1. The simulated spectra confirmed the experimental measurement.