少模光纤中飞秒光场的时空调控及传输特性研究

The temporal properties of femtosecond optical fields are focused on shape, duration, and peak power of pulses, while the spatial properties pay attention to polarization, phase, and intensity of traversal distributions. The temporal modulation and spatial modulation of optical fields are two hot spots in the academic world, but the combined temporal-spatial modulation is a new emerged research area. For temporal-spatial modulated optical fields, the coupling mechanism, propagation behavior, and evolution mode in fiber still remain unclear. Based on temporal-spectral Fourier transformation and fiber coupled-mode theory, this project aims to establish a combined physical model for describing temporal-spatial modulated optical fields in few-mode fibers, propose the corresponding experiment system to generate such types of optical fields, and investigate the nonlinear evolution behaviors of the optical fields in fibers. To achieve these, the following studies will be carried out: (1) Construct spectral transform function between traditional pulses and complex pulses, modulate the intensity of spectrum as well as the distribution of phase using the diffraction grating and programmable liquid crystal modulation array, and finally obtain ultrashort pulses with arbitrary temporal profiles. (2) Investigate the coupling mechanism between the fundamental mode and high-order modes in few-mode fiber gratings and fiber tapers, and explore a way to generate vector beams and vortex beams with complex temporal distributions. (3) Establish the propagation model of temporal-spatial modulated optical fields in fibers, and investigate the nonlinear propagation behavior of the optical fields. The obtained results will not only help to get a new understanding of multi-dimensional modulation about optical fields, but also provide experimental and theoretical supports for the long-distance propagation and application of temporal-spatial modulated optical fields.

飞秒光场时域特性体现为脉冲的形状、持续时间和峰值功率，而空域特性体现为光场横向的偏振、相位和强度分布。光场时域和空域调控是学术界高度关注的两个研究热点，但时空联合调控起步较晚，尤其是光纤中时空光场的耦合机理、传输行为和演化方式尚不明晰。本项目以时-频域傅里叶变换和光纤模式耦合理论为基础，构建少模光纤中光场时空联合调控的物理模型并提出实验方法，研究该类光场在光纤中非线性演化的方式和机理。拟开展以下研究：①构建传统脉冲与复杂脉冲之间的频域变换函数，利用衍射光栅和可编程液晶阵列调控光场的频谱和相位，获得任意时域分布的超短脉冲；②研究少模光纤光栅、拉锥光纤中基模与高阶模式耦合的机理，探索光纤中复杂时域分布矢量、涡旋光场的产生方法；③建立时空光场在少模光纤中传输的物理模型，研究其非线性演化行为。相关研究成果将有助于人们在光场多维控制方面获得新的认识，并为长距离传输和应用时空光场提供实验和理论支持。

飞秒光场时域特性体现为脉冲的形状、持续时间和峰值功率，而空域特性体现为光场横向的偏振、相位和强度分布。光场时域和空域调控是学术界高度关注的研究热点，但时空联合调控起步较晚，尤其是光纤中时空光场的耦合机理、传输行为和演化方式尚不明晰。本项目以光场时-频域傅里叶变换和光纤模式耦合理论为基础，构建了少模光纤中飞秒光场时空联合调控的物理模型并提出了相应的实验方法，研究该类光场在光纤中非线性演化的方式和机理。项目开展的主要工作包括：①对少模光纤中矢量模式特性进行了分析，提出了光纤激光器中产生柱矢量光束和涡旋光束的方法，基于长周期光纤光栅、错位熔接光纤和拉锥耦合光纤等器件进行了实验验证；②通过在光纤谐振腔中引入群延迟调控，实现了多波长同步锁模激光输出，揭示了脉冲的形成及演化过程；③通过在腔外施加三阶相位，将高斯脉冲调控为艾里脉冲，所得脉冲形具有多级旁瓣；④提出了包含色散、非线性和双折射效应的相位匹配理论，在光纤激光器中引入保偏光纤控制脉冲的传输特性，分别获得双折射管理孤子和互异矢量脉冲。该项目培养研究生7名，发表主流学术论文20篇，包括Nature Communications、Light: Science & Applications、Advanced Photonics各1篇，被SCI引用近200次。2篇论文入选ESI高被引论文，1篇论文获得陕西省自然科学优秀学术论文二等奖。