空间光调制器模拟锥透镜法是目前最为广泛使用的产生完美涡旋光的方法，但是该方法无法调控光束环宽，为了解决这个问题，提出了使用傅里叶空间相位计算全息法产生、调控完美涡旋光。通过理论分析和实验测量证明，改变编码相位可以实时调控完美涡旋光的光环半径、环宽和拓扑荷数。该方法光路简单，产生的光束质量高，且光路只需进行一次调整，操作简便。另外，该方法还具有通用性强的优点，可用于产生各类变形完美涡旋光。实验产生了不同参数的椭圆形完美涡旋光，实验测量结果与理论结果吻合得很好。因此，傅里叶空间相位计算全息法是一种简便、通用、实用性更强的完美涡旋光产生、调控方法。

We propose a high-sensitivity bidirectional torsion sensor using a helical seven-core fiber taper embedded in multimode fiber (MHSTM). Sensors with different taper waists and helical pitches are fabricated, and their transmission spectra are obtained and analyzed. The waist and length of the sandwiched seven-core fiber are finally determined to be 68 µm and 3 mm, respectively. The experimental results show that the clockwise and counterclockwise torsion sensitivities of the proposed sensor are 2.253 nm/(rad/m) and -1.123 nm/(rad/m), respectively. When tapered waist diameter reduces to 48 µm, a superior torsion sensitivity of 5.391 nm/(rad/m) in the range of 0–4.24 nm/(rad/m) is obtained, which is 46 times as large as the traditional helical seven-core fiber structure. In addition, the MHSTM structure is also relatively stable to temperature variations.

理想完美涡旋光束是一种光强分布不随拓扑荷数的改变而改变的特殊光束，与普通涡旋光束相比，其可以大幅提升在微粒操纵、光纤传输等方面的应用效率。为了探究完美涡旋光束的自由空间传播特性，利用汉克变换详细计算并分析了拓扑荷数、初始面光环半径以及环宽度对其衍射特性的影响，发现完美涡旋光束不具备无衍射特性，光环会随着衍射距离的增加而展宽并逐渐向贝塞尔函数转变。当初始面光环半径增加或环宽度减小时，衍射效应增强，其中环宽度的影响要大于光环半径。与前两者相比，拓扑荷数对衍射效应的影响较小。研究结果对完美涡旋光的进一步应用提供了有益的理论参考。

In this paper, a novel liquid level sensor with ultra-high sensitivity is proposed. The proposed sensor is configured by a slice-shaped composite long period fiber grating (SSC-LPFG). The SSC-LPFG is prepared by polishing two opposite sides of a composite multimode–single-mode–multimode fiber structure using a CO2 laser. The method improves the sensitivity of the sensor to external environment. Based on the simulation calculation, a liquid level sensor with a length of 3 mm is designed. The experimental transmission spectrum agrees well with the simulation result. The experimental results show that the sensitivity reaches 7080 pm/mm in the liquid level range of 0–1400 μm in water. The temperature sensitivity is 24.52 pm/°C in the range of 20°C–90°C. Due to the ultra-high sensitivity, good linearity, and compact structure, the SSC-LPFG has potential application in the field of high-precision liquid level measurement.

为了提高具有亚波长结构的圆对称艾里光束的自聚焦特性，将光束的工作波长扩大至太赫兹波段，并在频谱空间中分别加入高通和带通滤波进行调控。对两种滤波效果进行对比发现，通过滤波函数的参数变化可以控制空间频谱的分布，从而对光束的传播特性进行调制。当选取合适的参数时，焦斑尺寸减小，焦点强度增加，突然自聚焦特性会大幅增强，同时可实现焦点位置的控制。比较两种调制方法后发现，带通滤波后的光束拥有更好的自聚焦特性。

We propose and investigate a compact optical fiber sensor that aims to measure the torsion in both amount and direction with high sensitivity. This sensor is configured by a triangular-prism-shaped long-period fiber grating, which is fabricated by the high frequency CO2 laser polished method. The unique design of the triangular-shaped structure breaks the rotational symmetry of the optical fiber and provides high sensitivity for torsion measurement. In preliminary experiments, the torsion response of the sensor achieves a good stability and linearity. The torsion sensitivity is 0.54 nm/(rad/m), which renders the proposed structure a highly sensitive torsion sensor.

A novel phase-shifted long-period fiber grating (PS-LPFG) for the simultaneous measurement of torsion and temperature is described and experimentally demonstrated. The PS-LPFG is fabricated by inserting a pre-twisted structure into the long-period fiber grating (LPFG) written in single-mode fiber (SMF). Experimental results show that the torsion sensitivities of the two dips are ?0.114 nm/(rad/m) and ?0.069 nm/(rad/m) in the clockwise direction, and ?0.087 nm/(rad/m) and ?0.048 nm/(rad/m) in the counterclockwise direction, respectively. The temperature sensitivities of the two dips are 0.057 nm/°C and 0.051 nm/°C, respectively. The two dips of the PS-LPFG exhibit different responses to torsion and temperature. Simultaneous measurement of torsion and temperature can be implemented using a sensor. The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed, and hence this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.