数值模拟分析了在周期域反转结构的铌酸锂光波导中的脉冲抽运波长转换过程, 通过对转换过程中光脉冲波形的演化分析, 讨论了抽运光和信号光同向和逆向两种注入方式对转换光脉冲波形的影响。研究结果表明在同向注入方式下由于倍频与差频效应是同时进行的, 群速度失配导致的走离效应使倍频光脉冲在波导内不断展宽, 遗传给差频转换时, 使转换光脉冲发生了波形畸变; 为防止转换脉冲发生畸变, 提出了采用单片光波导用抽运光和信号光逆向注入的方式, 将倍频与差频效应分开来, 二次非线性效应不再同时进行, 从而改善了转换光脉冲的波形畸变, 同时提高了转换效率。

A numerical simulation on wavelength conversion based on a periodically poled lithium niobate waveguide is presented. The evolution of pulses is exhibited and the walk-off between pulses is discussed to explore the influence of two different injecting modes that the pump wave and signal wave are injected from the same direction or from the reverse direction. The analysis results demonstrate that the second harmonic generation and the difference frequency generation are simultaneously realized in the same-direction-injected wavelength conversion, which widens the second-harmonic wave continuously because of the walk-off among the reactive pluses due to group-velocity-mismatch, and then the converted pulses produce waveform distortion in the subsequent difference frequency generation. The reverse-direction-injected wavelength conversion is proposed to avoid converted waveform distortion, and it is able to separate two processes of the second order nonlinear effect. It is expected to amend the waveform distortion of converted pulses as well as to improve the conversion efficiency.