OrbitFlySens - Optical manipulation of flying microparticles in the hollow core of a photonic crystal fiber by orbital angular momentum modes for innovative fiber sensing applications

传统的光纤传感器主要依赖于后向散射过程或传感器光纤中的离散传感元件，例如光纤布拉格光栅。研究项目OrbitFlySens追求一种基于在空心芯光纤中绕轨道运行的光捕获微粒的新型传感器概念。通过利用温度、压力、电场或杂质等物理量对粒子运动的影响，“飞行”微粒可以用作可移动的微传感器，原则上可以在一公里长的空心纤维上推进和光学读出。通过额外的轨道运动扩展先前轴向运动粒子的概念，将用于粒子定位的轴向运动与实际传感机构解耦。这可以提高μ m范围内的空间分辨率，更灵活的应用和电场的矢量确定。在项目过程中，HiFlySens在粒子的轴向定位和沿光纤运动的控制方面取得了优异的成绩。对于静止颗粒，在颗粒大小范围内完成了空间分辨率，对于移动颗粒，例如在温度测量高达200°C的情况下，在亚毫米范围内完成。可实现的传感器分辨率受到先前传感机制所需的轴向粒子运动的显着限制。因此，在OrbitFlySens项目中，轨道粒子运动应使用用于传感。为此，首次将激光束的轨道角动量（OAM）传递给空心芯光纤中的光悬浮粒子。针对研制轨道飞行粒子传感器的总体目标，提出了以下研究目标：(1)通过OAM光束在空心光纤中光捕获轨道粒子的理论研究，(2)OAM模式的生成和保留OAM的扭曲空心光纤的设计，(3)探索旋转检测方案，以测量光悬浮粒子的瞬时轨道频率及其在光纤中的位置，(4)轨道和轴向粒子轨迹的同时控制和测量。（五）传感应用的演示。两家项目合作伙伴计划继续HiFlySens项目的合作。所获得的知识以及在粒子定位（Schmauss）和空心芯纤维（Joly）方面的专业知识，将使HiFlySens的传感器概念扩展到10倍的空间分辨率。此外，该新原理还可以在平行于温度测量的情况下测量电场的方向、大小和相位。为了演示目的，构建了一个具有能源部门应用前景的温度和电场组合测量传感器并对其进行了表征。

Conventional fiber optic sensors rely mostly on backscattering processes or discrete sensing elements, e.g., fiber Bragg gratings, in sensor fibers. The research project OrbitFlySens pursues a novel sensor concept based on optically trapped microparticles orbiting in hollow core fibers. By exploiting the influence on the particle motion of physical quantities such as temperature, pressure, electric field or impurities along the hollow core fiber, the "flying" microparticles can be used as moveable microsensors that in principle can be propelled and read out optically over kilometer-long hollow core fibers. The extension of the previous concept of axially-moved particles by an additional orbital motion decouples the axial motion used for particle positioning from the actual sensing mechanism. This enables an improved spatial resolution in the µm range, a more flexible application and the vectorial determination of electric fields. In the course of the project HiFlySens excellent results have been achieved for the axial localization of particles and the control of their motion along the fiber. For stationary particles a spatial resolution in the range of the particle size was accomplished, for moving particles, for example in the context of temperature measurements up to 200°C, in the sub-mm range. The achievable sensor resolution is significantly limited by the axial particle motion required for the previous sensing mechanism. Therefore, within the project OrbitFlySens an orbital particle motion shall be used for sensing. For this purpose, the orbital angular momentum (OAM) of a laser beam will be transferred to an optically levitated particle in a hollow core fiber for the first time. For the overall goal of developing an orbiting flying particle sensor, the following research objectives are proposed: (I.) theoretical investigation of an orbiting particle optically trapped in the hollow core fiber by an OAM beam, (II.) generation of OAM modes and design of a twisted hollow core fiber that preserves OAM, (III.) exploration of a rotation detection scheme to measure the instantaneous orbital frequency of an optically levitated particle and its position in the fiber, (IV.) simultaneous control and measurement of the orbital and axial particle trajectories, and (V) demonstration of a sensing application. The two project partners plan to continue the cooperation of the HiFlySens project. The obtained knowledge as well as the expertise in particle localization (Schmauss) and hollow core fibers (Joly), will allow the sensor concept from HiFlySens to be extended with a 10-times enhanced spatial resolution. In addition, the novel principle also enables measurements of the electric field in terms of direction, magnitude, and phase in parallel to temperature measurements. For demonstration purposes, a sensor for combined temperature and electric field measurements with an application perspective in the energy sector is built and characterized.