The Properties Of The PPLN Waveguide Based On Photorefractive Two-Wave Coupling And Cascaded Secondorder Nonlinear Effects

Based on quasi-phase matching and cascaded second-order nonlinear periodically poled lithium niobate (PPLN) has been widely applied in the parametric process, such as second harmonic generation, difference frequency generation, optical parametric oscillation, and all-optical switch, and the PPLN has an ideal tuning properties. In this paper, the property of all-optical switching and second harmonic generation are analyzed theoretically based on photorefractive two-wave mixing and cascaded second-order nonlinear effect in the PPLN waveguide with homocentric semicircle domain structure. Major contributions are as follows:Firstly, based on cascaded second-order nonlinear effect and photorefractive two-wave mixing of the same frequency gate wave and signal wave in the PPLN waveguide with the homocentric semicircles structure, the coupled mode equations that describe the evolution of three electric fields through the media are derived from the slowly varying envelope approximation with neglecting the depletion of the waves.Secondary, the dependency relationship between the second-order nonlinear coefficient and the duty ratio of PPLN crystal is deduced. The small signal solution of couple equations are given at phase matched. The output signal power curves versus the input gate power, interaction length and the angle between the gate wave and signal wave are given respectively.Then, based on solving the couple mode equations numerically, the dependence of the signal power on the gate power and the interaction length are given under different phase mismatch conditions such as the grating period, the crystal temperature and the gate wavelength.Finally, with the small signal, the normalized conversion efficiency of double-frequency versus the periodicity of grating, the temperature and the wavelength of fundamental frequency is studied, and the acceptances of polarized period, wavelength and temperature of the lithium niobate crystal are calculated. The property of second harmonic generation are analyzed numerically when the fundamental frequency has pumping depletion, and the dependence of the output second harmonic power and the second harmonic conversion efficiency versus input total power of fundamental waves are given.