基于腔内几何相位调控的高性能光纤涡旋激光器研究

Vortex lasers can deliver vortex beams carrying optical orbital angular momentum (OAM) which hold great potential in various applications such as super-resolution imaging, optical micro-manipulation, laser micro-fabrication, optical communication and quantum information technology. However, most of the existent vortex lasers have several common drawbacks including low mode purity, inconvenient helicity control, difficulty in achieving high OAM, rather low efficiency and limited output power. Therefore, there is an urgent need for new principles and approaches to realize high-performance vortex lasers. This project proposes a novel scheme of vortex laser based on the combination of highly efficient fiber laser and highly flexible intracavity geometric-phase-manipulation technique. First, we develop the theoretical models describing the power characteristics and intra-cavity beam propagation of the laser. By analyzing the process of intra-cavity spin-orbital angular momentum conversion, we reveal the mechanism and related approaches of OAM control based on geometric-phase-manipulation. Then, we study the influence of cavity parameters and properties of geometric-phase-manipulation devices on the mode purity and explore new methods for vortex mode purification. Finally, we design and construct a high-performance fiber vortex laser employing the mode purification technique and geometric-phase-manipulation enabled OAM control, which has the capability of generating high-quality vortex beam with OAM as high as 100ℏ per photon. The above work will open up a new way to produce high-quality vortex beams and lay a solid foundation for high-performance vortex laser development and its practical application. Furthermore, our work will also provide new insights and useful approaches for the transverse mode control of lasers.

涡旋激光器能直接输出携带轨道角动量的涡旋光束，在超分辨成像、光学微操控、激光微加工、光通信和量子信息等领域有重要应用价值。目前的涡旋激光器普遍存在模式纯度不高、旋向控制不灵活、难以实现高轨道角动量、功率和效率偏低等问题，亟需探索新型高性能涡旋激光器相关原理和技术。本项目提出一种基于腔内几何相位调控的高光束质量高轨道角动量光纤涡旋激光器。首先，建立描述该激光器功率特性和腔内光束传输的理论模型；其次，通过分析腔内自旋-轨道角动量转换规律，阐明基于几何相位调控实现轨道角动量控制的机理和方法；然后，研究谐振腔参数和几何相位调控器件特性对模式纯度的影响，探索涡旋激光模式纯化技术；最后，结合模式纯化和轨道角动量控制，设计并实现输出轨道角动量达到100ℏ以上的高性能光纤涡旋激光器。以上研究为高质量涡旋光束的产生提供一种新的方案，推动涡旋光束在更多实际场合的应用，同时也为激光器横模控制提供新的思路和方法。

涡旋光因其能够携带轨道角动量而表现出许多独特的性质，具有广阔的应用前景。本项目围绕高质量涡旋光的制备及其轨道角动量调控开展研究，特别是针对目前研究仍较少的超高轨道角动量光束的制备方法与应用进行了探索,取得了以下进展和成果：1、提出并验证了级联和多通螺旋相位板、级联几何相位涡旋波片等新方案，实现了既灵活又高效的涡旋光束（或矢量涡旋光束）产生及其轨道角动量调控，研究表明几何相位调控方法具有产生大拓扑荷数涡旋光束的巨大潜力，实验上实现了100阶矢量和涡旋光束的制备。2、研究并改进了基于纯相位空间光调制器和计算全息技术的涡旋光束制备方法，在深入分析全息图编码方式的基础上，针对超高阶涡旋光束的特点，采用优化的复振幅调制方法，实现了拓扑荷数高达1400的拉盖尔-高斯涡旋光束制备，该拓扑荷数指标是目前用空间光调制器产生涡旋光的最高值。3、将交叉相位用于涡旋光束产生、调控与检测，首次提出高阶交叉相位的概念并进行了验证，利用交叉相位的特性分别实现了大拓扑荷数涡旋光的制备与拓扑荷数检测、涡旋光整形、奇点操控等功能，并且提出了两种新的模式纯度测量方法；4、拓展了涡旋光的应用，设计了利用叠加态涡旋光旋转多普勒效应进行物体转速探测的实验方案，探索了各种不同形式的涡旋光的探测效果以及频移和外差探测技术，结果表明高质量大拓扑荷数的涡旋光在目标角速度传感探测方面具有实际应用价值。