用于光参量振荡器的准相位匹配晶体设计中非相位匹配非线性效应的考量
Consideration of non-phase-matched nonlinear effects in the design of quasi-phase-matching crystals for optical parametric oscillators
AI总结：
针对传统准相位匹配晶体光参量振荡器因寄生非相位匹配过程效率低的问题，提出九波耦合方程模拟全部非线性相互作用，优化设计非周期极化铌酸锂晶体，实现了50.6%的信号光转换效率，为相关晶体设计提供参考。
摘要：
飞秒光参量振荡器（OPOs）被广泛应用于超快非线性频率转换和量子信息领域。然而，传统基于准相位匹配（QPM）晶体的OPO存在大量寄生非相位匹配过程，会降低转换效率。本文中，我们提出九波耦合方程（NWCEs）来模拟QPM晶体中所有相位匹配和非相位匹配的相互作用，对传统的三波耦合方程（TWCEs）进行改进，尤其适用于高强度超短脉冲和结构复杂晶体的场景。我们探讨了如何设计QPM晶体的极化周期，以使给定OPO系统的信号光转换效率最大化。仿真结果显示，具有特定啁啾率的啁啾周期极化铌酸锂（CPPLN）基OPO的信号波转换效率高于周期极化铌酸锂（PPLN）基OPO，且证明了NWCEs能展现OPO腔内脉冲演化的更多细节。从CPPLN出发，通过修改晶体的畴长并利用动态优化算法优化OPO输出功率，可得到非周期极化铌酸锂（APPLN）设计方案。结果表明，采用合理设计的APPLN晶体时，由中心波长1030nm、脉冲宽度150飞秒、焦点处功率密度5 GW/cm²的飞秒激光泵浦的1600nm OPO，可实现高效输出，信号光转换效率达50.6%，高于PPLN的25.2%和CPPLN的40.2%。本文提出的方案将为OPO的非线性QPM晶体设计提供参考，并有助于理解OPO腔内复杂的非线性动力学行为。
英文摘要：
Femtosecond optical parametric oscillators (OPOs) are widely used in ultrafast nonlinear frequency conversion and quantum information. However, conventional OPOs based on quasi-phase-matching (QPM) crystals have many parasitic non-phase-matched processes which decreases the conversion efficiency. Here, we propose nine-wave coupled equations (NWCEs) to simulate all phase-matched and non-phase-matched interactions in QPM crystals to improve conventional three-wave coupled equations (TWCEs), especially for the situation of high intensity ultrashort pulses and complexly structured crystals. We discuss how to design the poling period of QPM crystal to maximize the conversion efficiency of signal light for a given OPO system. The simulation reveals that the OPO based on chirped periodically poled lithium niobate (CPPLN) with certain chirp rate has higher signal wave conversion efficiency than that of a PPLN, and demonstrates that NWCEs illustrates more details of the pulse evolution in the OPO cavity. Starting from a CPPLN, an aperiodically poled lithium niobate (APPLN) design is available by modifying the domain lengths of the crystal and optimizing the OPO output power via dynamical optimization algorithm. The results show that by using a properly designed APPLN crystal, a 1600nm OPO, when pumped by a femtosecond laser with 1030nm central wavelength, 150 femtosecond pulse duration and 5 GW/cm2 power intensity at the focus, can achieve very efficient output with a signal light conversion efficiency of 50.6%, which is higher than that of PPLN (25.2%) and CPPLN (40.2%). The scheme in this paper will provide a reference for the design of nonlinear QPM crystals of OPOs and will help to understand the complex nonlinear dynamical behavior in OPO cavities.
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