基于局域相位匹配的特殊光束非线性模式转换  

Nonlinear Mode Conversion of Special Beams Based on Local Quasi-Phase-Matching

作　　者：陈欢 吴淦 孙旭辉 马艺冰 陈涌创 汪称龙 王童 姚依正 高冰 吴浩 陆蓉儿 张超[1,2] 秦亦强[1,2] Chen Huan;Wu Gan;Sun Xuhui;Ma Yibing;Chen Yongchuang;Wang Chenglong;Wang Tong;Yao Yizheng;Gao Bing;Wu Hao;Lu Ronger;Zhang Chao;Qin Yiqiang(National Laboratory of Solid State Microstructures,Nanjing University,Nanjing 210093,Jiangsu,China;College of Engineering and Applied Sciences,Nanjing University,Nanjing 210093,Jiangsu,China;School of Physics,Nanjing University,Nanjing 210093,Jiangsu,China;Department of Physics,Nanjing Tech University,Nanjing 211816,Jiangsu,China)

机构地区：[1]南京大学固体微结构物理国家重点实验室,江苏南京210093 [2]南京大学现代工程与应用科学学院,江苏南京210093 [3]南京大学物理学院,江苏南京210093 [4]南京工业大学物理系,江苏南京211816

出　　处：《光学学报》2023年第14期195-202,共8页Acta Optica Sinica

基　　金：国家重点研发计划(2022YFA1405000,2022YFA1205100);国家自然科学基金(12274214,91950103,11874214,12004177);江苏省自然科学基金(BK20200701);江苏省高等学校重点学科建设项目(PAPD)。

摘　　要：提出一种能够同时实现拉盖尔高斯光束倍频和模式转换两种功能的光学超晶格。首先,通过局域相位匹配原理设计得到了实现以上功能所需的超晶格结构函数。不同于常规的多通道周期或啁啾结构,采用局域相位匹配原理得到的是一种具有弯曲畴的超晶格结构,理论上可以减少相差并提高转换效率。其次,讨论了正反两种模式的超晶格结构,两种结构均可以实现非线性模式转换,但正向结构效果更佳。最后,对不同角向指数的拉盖尔高斯光束的模式转换过程进行数值模拟,观察转换得到的厄米高斯光束图像,验证了两种光束模式指数的关系。模拟结果表明,这样设计不仅能够实现不同特殊光束之间的相互转换,而且将倍频和模式转换两种功能集为一体,使得器件更加紧凑。该结构有望推进非线性模式转换器的研究。Objective In recent years,photon orbital angular momentum,as a new degree of freedom,has attracted wide attention.The LaguerreGaussian(LG)beam is a commonly used orbitalangularmomentum(OAM)beam and is widely studied.Among a large amount of research,the mode conversion of LG beam attracts much attention from researchers.It is found that an LG beam can be converted into a HermiteGaussian(HG)beam with the help of cylindrical lenses.In addition,the nonlinear beam shaping technique can change the condition of phase matching in the nonlinear process to realize wavefront modulation,and harmonic waves with shaped wavefronts can be achieved by this technique during nonlinear optical processes.By combining these hot topics,we propose a novel mode conversion method for special beams in nonlinear processes,and the local quasiphasematching(LQPM)theory is employed to design the required optical superlattice(OSL).The function of mode converters is concentrated on the superlattice structure,and the phasematching condition is satisfied in the nonlinear mode conversion.Methods LQPM is used to design the OSL structure required by the nonlinear mode conversion process.Different from the conventional quasiphasematching(QPM)method in the reciprocal space,the LQPM is a nonlinear beam manipulation theory in real space.According to the principle of LQPM,the OSL structure function for the nonlinear mode conversion of LG beams can be obtained.The domain structure shows a curved boundary,and the function of cylindrical lenses is integrated into the OSL.Matlab software is used to carry out numerical simulations for the nonlinear mode conversion process.The finitedifference method is employed in the numerical simulation process to calculate the field distribution in the twodimensional OSL.The field distribution and intensity curves of the secondharmonic wave after nonlinear mode conversion are obtained.It can be found that the designed OSL structure shows positive results on both mode conversion and frequency doubling.Result and Discussions I

关 键 词：涡旋光 模式转换 倍频 弯曲畴 局域相位匹配 

分 类 号：O436[机械工程—光学工程]