补偿走离角时产生的相位失配及其补偿方法

Phase Mismatch Generated in Walk-Off Compensation and Its Compensation Method

在非线性频率变换中,常用级联晶体补偿走离角。然而在KTiOPO4晶体级联倍频实验中发现,当其中一块晶体沿通光轴旋转180°时,倍频转换效率急剧降低。理论分析表明,当一块晶体旋转180°后,其有效非线性系数正负号发生改变,等效于在级联晶体之间产生了大小为π的相位失配量,使倍频转换效率降低。提出了利用空气色散补偿该相位失配量的方法,相较于使用波片的相位失配量补偿方法,具有结构简单、温度稳定性好、无插入损耗和成本低等特点。实验结果表明,利用空气色散可以补偿相位失配量,消除单块晶体旋转对晶体级联倍频效率的影响,验证了理论分析的正确性以及空气色散补偿方法的可行性。

Crystal cascading is widely used for the compensation of walk-off angles in the nonlinear optical frequency conversion process.However,it is discovered that the conversion efficiency dramatically decreases when one of the cascaded crystals is rotated by 180° along the optical axis in the second harmonic generation experiment based on KTiOPO4 crystal cascading.The theoretical analysis indicates that the crystal rotation of 180° changes the sign of the effective nonlinear coefficient,which is equivalent to the generation of a phase mismatch ofπand thus the second harmonic generation conversion efficiency decreases.A method based on air dispersion is proposed for the compensation of phase mismatch,which is characterized by simple configuration,solid temperature stability,low insert loss and low cost if compared with those for the compensation method based on wave plates.The experimental results show that the phase mismatch is compensated by air dispersion and the influence of crystal rotation on second harmonic generation conversion efficiency is eliminated.The validity of the theoretical analysis and the feasibility of the compensation method based on air dispersion are demonstrated.