非线性光纤布拉格光栅的飞秒激光制备及其低阈值全光开关的研究

The all-optical switch is a key component in the all-optical network. As a candidate of all-optical switch, fiber Bragg grating attracts more attentions. However, all-optical switch based on FBG meets the problem of high opening threshold power, which limits its application. To reduce opening threshold power of fiber Bragg grating optical switch, we propose the phase-shifted Bragg grating fabricated in high nonlinear glass optical fibers such as tellurate glass fibers, which is based on the high optical nonlinearity of materials as well as field enhancement effect in the phase-shifted Bragg grating. In view of the difficulty of fabricating FBG in high nonlinear glass fibers, the femtosecond laser micro-nano machining technique with phase mask is proposed to fabricate the phase-shifted FBG structure in the fibers. The main research content includes: (1) investigating field enhancement effect of nonlinear phase-shifted FBG and the propagation properties of ultrashort pulses in phase-shifted FBG. (2) clarifying the influence of field enhancement effect and nonlinear effect of phase-shifted FBG to its switch characteristics. (3) exploring the key technique of fabricating nonlinear phase-shifted FBG using femtosecond laser in high nonlinear glass optical fibers such as tellurate glass fibers. (4) reducing the opening threshold of switch and enhancing its extinction ratio by optimizing FBG periodic structure and phase shift parameters to strengthen the field enhancement effect of the devices. (5) optimizing the micro-nano machining parameters such as chirp of femtosecond laser pulses to control the nonlinear optical effect induced in the optical fibers, and finally realizing accurate control of laser induced mircostructures. The final goal is to develop the FBG all-optical switch, characterized by the threshold power less than 500 mW and the extinction ratio larger than 6.5 dB.

全光开关是全光网络中的关键器件。本项目针对光纤布拉格光栅(FBG)光开关开启阈值功率高的问题，提出在具有高光学非线性的碲酸盐等玻璃光纤中制备相移FBG结构，同时利用材料的高非线性和相移光栅的场增强效应降低开关阈值；针对在此类高非线性光纤内制作FBG所面临的加工困难的问题，提出利用飞秒激光相位掩模微纳加工技术制备相移FBG结构。主要内容包括：研究非线性相移FBG的场增强效应和超短光脉冲在相移FBG中的传输规律，掌握场增强效应及非线性效应对开关特性的影响；探索利用飞秒激光在碲酸盐等高非线性玻璃光纤内制作相移FBG的关键技术，通过优化相移FBG的周期结构和相移等参数增强器件的场增强效应，降低开关阈值，提高其消光比；通过优化飞秒激光脉冲啁啾等微纳加工参数调控激光与光纤相互作用的非线性效应影响，实现激光诱导微结构的精确控制，研制阈值功率低于500mW、消光比大于6.5dB的低阈值FBG全光开关器件。

全光开关是全光网络中的关键器件。本项目针对光纤布拉格光栅(FBG)光开关的开启阈值功率高的问题，提出在具有高光学非线性的碲酸盐等玻璃光纤中制备相移布拉格光栅结构，利用材料的高非线性以及相移光栅的场增强效应降低开关阈值；针对在碲酸盐等高非线性光纤内制作FBG所面临的加工困难的问题，提出利用飞秒激光微纳加工技术在具有高光学非线性的玻璃光纤中制备相移FGB结构。研究的主要进展和成果有：(1)研究了飞秒激光与石英及难加工材料SiC、GaN等材料相互作用的机理，利用飞秒激光在多种材料上制备出FBG，并分析了FBG的形成与材料带隙的关系。(2)探索了飞秒激光制备FBG的关键技术，利用飞秒激光相位掩模法结合扫描加工在高光学非线性光纤等特种光纤中制备了均匀FBG，不同布拉格波长FBG和相移FBG; 在FBG加工系统中增加斩波器和三维压电平台，降低加工中的热效应，拓展了成栅区域，提高了光栅的反射率，制备的FBG反射率在99%以上，带宽1nm左右。(3)研究了FBG的温度响应特性。利用飞秒激光相位掩模辐照结合光纤拉伸制备不同周期的布拉格光栅并构成准分布式高温传感器。标定了 FBG 的温度响应参数，实现了两点准分布式温度测量。(4)研究了FBG的非线性响应特性，在掺镱光纤中实现了0.22nm的光子带隙偏移，反射率调制度在10dB以上。通过980nm激光的泵浦在FBG带边可实现变化量最大为18.2dB（1548.6nm处）的共振吸收型全光开关。采用1064nm、脉宽为10ns的脉冲激光对实验中制备的FBG进行泵浦，得到互相位调制开关时间为10ns的开关信号，开关幅度约为42%。受基金资助，共发表在本领域著名国际SCI检索期刊14篇，核心期刊1篇，培养博士2名，另有在读研究生3名正参与本项目。