基于光致聚合物中自写型光波导光束自耦合的方法研究

A novel method for multi-mode fiber (MMF) laser beam cleanup is introduced based on the optically induced growth and interaction of self-written waveguides (SWWs) in a photopolymer material. The main contents of this research are arranged as follows: (1) we begin by reviewing the major photoreactions taking place during the photo-initiation process in a free radical photopolymer material. A set of rate equations was then derived, governing the temporal and spatial photosensitizer concentration distribution during SWWs formations. (2) According to the photochemical mechanisms, we analyze the nonlinear photo-absorptive effect during the photo-initiation processes. The time varying exposing light distribution is calculated by the wave equations and then used to iteratively estimate the evolving cross sectional refractive index and loss coefficient values. (3) Experimental validation was carried out to demonstrate that permanent optical waveguides can be self-written in a solid photopolymer material. The resulting waveguides formed can be used to guide different wavelengths. The experimental results and the numerical simulations are compared and good agreement is obtained. (4) When the light is introduced into a free radical photopolymerizable system from a MMF, the incident multichannel and structured beam shape can be caused to merge to form a single channel Gaussian like beam under specific exposure and material conditions, with the maximum transmittance efficiencies measured in the range from 65%. This work opens the door to studies involving self-developing laser beam cleanup and also to possible applications in photonic telecommunication systems and integrated optical devices.

针对激光从多模光纤耦合到单模光纤的问题，基于光波导在光致聚合物中生成过程中表现出的非线性特性和光子与分子之间的相互作用关系，创新的提出一种利用光束自生成光波导微结构作为光纤耦合元器件的方法。本课题的研究内容分为：（1）根据光化学反应机理，推导速率方程组，计算在光波导形成过程中光敏剂浓度在时间和空间的分布。（2）研究波导中光束能量的非线性吸收和调制，根据波动方程计算光强动态分布，然后同步反馈迭代，得到折射率和损耗系数的数值分布。（3）研究在固态聚合物材料中永久性光波导的制备方法，并对不同光谱条件下进行实验证明，分析对比获得的实验与理论结果。（4）在特定的光场能量和聚合物材料的条件下，分析多模光纤激光入射的光束整形过程，实现复杂微结构光波导自动合并成单模光波导通道，耦合效率达到65%以上。本项目研究开启了激光自激励作用实现光束操控的方法，可广泛应用于光通信系统和集成光学等领域。

本项目通过对光子传播和聚合物内部反应的研究，展开理论及实验的研究，最终实现在光致聚合物中自发激励产生的空间光波导，并将该结构的应用为光纤耦合器。项目首先对光致聚合物材料制备进行研究，解决光致聚合物材料的稳定性问题，优化改进固态光致聚合物材料制备方法。其次，从波动光学出发，建立仿真光子非线性吸收和非线性调制的理论模型，结合光致聚合物材料中单体分子链式反应的材料动力学原理，对光波导微结构形成的动态过程进行分析。第三，结合在光束方向上多模光纤入射的光束整形过程，实现复杂微结构光波导合并成单模光波导通道的自发耦合，并验证和测试耦合器件的性能指标。本研究从物理光学理论、实验验证和基础应用三大方面全方位开展工作，提高了激光自激励作用实现光束操控的能力，为微纳器件、集成光学平台的基础提供新方法，为未来生物医学领域和生命科学等涉及重大民生问题领域的基础科学探索奠定基础。