全光纤高功率柱矢量脉冲光产生与调控研究

Clindrical vector beam (CVB) with unique space vector light intensity and polarization distribution, has diverse applications. It is inevitable for development and applications of CVB to maximize its power and make its operation more convenient, while investigating its generation with high purity. This project aims to explore the generation, manipulation and amplification of CVBs from all-fiber high-power laser system. Firstly, through designing and fabricating of key taped few-mode fiber-based devices for mode control including mode-elective coupler and combiner, CVB fiber laser with higher-order mode oscillating will be set up. Moreover, based on the space separation of transverse mode manipulation and mode-locking control, mode-locked higher-order mode emission will be realized with high efficiency and high polarization purity. Secondly, based on the transmission theory of the high power CVBs in optical fiber, special optical fiber, i.e. total reflection microstructure fiber with nested microstructures in innermost ring air holes, which enables the transmission and amplification of high order modes, will be optimally designed and fabricated. This fiber should have large effective index difference for the degenerate modes of the LP11 mode, which will help us separate the CVBs from the LP11 mode. Thirdly, since the mode field intensity distribution of the cylindrical vector beams is a uniform ring, the mode field area is relatively larger with higher nonlinear threshold, and it has unique polarization characteristics, the cylindrical vector beam is very suitable for high power amplification. The project intends to adopt the master oscillator power amplifier scheme for the high power amplification of the cylindrical vector beams. This project will further deepen of the theory and technology of optical field manipulation in optical fibers, and open up a new idea for the regulation and amplification of high-order modes in optical fibers. All-fiber high power CVB pulsed laser has important application value in fields including information, chemistry, life and materials.

柱矢量光具有独特空间强度、偏振分布及多样化应用，研究其高纯度产生和调控的同时，使其功率最大化和操控最便化是发展必然和应用使然。本项目拟探索基于全光纤结构的高功率柱矢量脉冲光产生、调控和放大的方法和技术，核心思想是采用横模操控和纵模锁定空间分离的方法，解决同时实现高阶模振荡和锁模的难题，设计和制备较大模式间有效折射率差的特种光纤，更好地分离调控和放大各模式。研究内容包括设计和制备基于少模微纳光纤的模式调控关键器件，构建高阶模振荡柱矢量光脉冲光纤激光器；研究高功率柱矢量光在光纤中的传输放大特性，优化设计和制备微结构嵌套光纤，即对传统微结构光纤最里圈空气孔嵌套微结构；利用泵浦光模场匹配法，采用主振荡功率放大法实现柱矢量高功率高效放大。本项目是对光纤中光场调控理论和技术的进一步深化，为光纤中高阶模调控与放大开辟新思路。全光纤高功率柱矢量脉冲光在信息、化学、生命和材料等领域都有着重要应用价值。

柱矢量光是一种光的偏振态在横截面上呈现非均匀分布的新型结构光场，表现出不同于标量光场的一些新颖特性。由于其独特的光学特性，柱矢量光在超分辨显微成像、光学捕获、表面等粒子体激发、激光材料加工等应用方面具有显著优势。研究高纯度、高功率柱矢量光的产生是本项目的主要目的，基于光纤或光纤器件的结构光场产生具有结构简单、易于集成和成本低廉等优点，但仍然存在高效率模式调控关键光纤器件的制备和高阶模激光直接振荡等关键问题需要解决。.本项目围绕高纯度、高功率柱矢量高效产生的关键问题，研究了一种具有全光纤结构的高功率柱矢量锁模脉冲光产生和调控的方法和技术，具体包括设计和制备基于少模微纳光纤的模式调控关键器件，采用全少模光纤结构，构建了高阶模直接振荡的高效、高纯度柱矢量脉冲光纤激光器；研究柱矢量光在光纤中的传输放大特性，优化设计和制备能传输高阶模的特种光纤。.项目取得的结果包括：.1）.提出和研究了一种能直接产生高阶模的对称二模光纤耦合器，当二模拉锥光纤尺寸范围（即光纤锥腰部分的直径）大致介于26 μm和66 μm之间时，基模束缚在纤芯不发生耦合而高阶模式扩散至包层发生耦合。采用并行拉锥技术，保持两根二模光纤尺寸变化一致，得到了可以只输出高阶模式的二模光纤耦合器。.2）.研究了能同时实现波分复用和模式转换的波分复用-模式选择耦合器，并提出和研究了基于波分复用-模式选择耦合器的全少模锁模柱矢量光纤激光器。搭建了整个谐振腔全是由少模光纤构成的8字腔锁模光纤激光器，激光器内的所有器件均由少模光纤制作而成。最终获得了重复频率为3.51 MHz的锁模柱矢量脉冲，其信噪比为78 dB。柱矢量光束的纯度大于94%。.3）.探索了光子晶体光纤不同圈包层设计参数的改变对色散和限制损耗大小的影响，归纳总结为最内圈包层占空比与色散成正相关，外圈包层占空比与限制损耗成负相关的规律。引入微结构内包层和渐变扩大的外包层，这两个创新点分别有着改善色散和限制损耗的作用。对柱矢量光采用拉曼放大可以保持较高纯度。