为了制备高质量螺旋光纤器件，提出一种四电极电弧光纤加热的方法。基于磁流体动力学模型建立四电极电弧等离子放电的有限元仿真模型，研究了电极夹角、电极距离与施加电压对电弧放电温度场的影响。根据实际情况，进行了相应的温度场仿真计算，结果表明四电极电弧放电形成了较宽的恒温区，宽恒温区不仅有利于光纤应力的释放，同时减少了光纤偏移带来的影响。基于仿真结果，研制了四电极电弧放电的宽恒温区等离子热熔扭转加工系统，当系统中被加热光纤最高温度约为1 050 ℃时，被加热光纤轴向上的恒温区长度约为2.12 mm。用研制的系统制备了不同光纤与不同周期下的螺旋长周期光纤光栅，在波长1.21~1.3 µm，透射光谱的光强波动小于1 dB，光强平均值大于-1 dB；在波长1.3~1.35 µm，光强平均值大于-1 dB；最深的透射光谱波谷大于22 dB。为更进一步验证所研系统的性能，用单模光纤、偏芯光纤、偏双芯光纤制备了不同周期的螺旋光纤结构，结果显示加工得到的螺旋光纤结构的包层边界清晰且平直，无显著的螺纹结构；光纤中央芯无显著的螺旋加工痕迹；光纤偏芯光滑且连续。

为了实现对多芯光纤在光网络系统中的接续并评价连接效果，给出了一种多芯光纤活动连接器的制备方法，用光学连续波反射计和光学低相干反射计分别构建了多芯光纤活动连接器插入损耗和回波损耗测量系统。详细地分析了外在因素和端面质量对多芯光纤活动连接器插入损耗和回波损耗的影响，提出了多芯光纤活动连接器制备和对接时需要满足的三项质量控制条件：精准对芯、物理接触和不相对转动。所制备的多芯光纤活动连接器具有标准的LC型接口，采用三维轮廓仪对多芯光纤活动连接器端面的三维参数（顶点偏移、曲率半径和光纤凹凸度）以及粗糙度进行了表征。用构建的测量系统测得制备的四芯光纤活动连接器中所有纤芯通道实现了平均0.089 dB的低插入损耗和52.31 dB的高回波损耗。为多芯光纤活动连接器走向实际应用提供了制备方法和性能评价方案。

Vector bending sensing has been consistently growing in many fields. A low-cost and high sensitivity vector bending sensor based on a chirped long-period fiber grating (LPFG) with an off-axis micro helix taper is proposed and experimentally demonstrated. The grating is composed of several sections of single-mode fiber with gradually larger lengths, and the off-axis micro helix tapers with fixed lengths when they are fabricated by using the arc discharge technology. The large refractive index modulation in the micro-helix taper greatly reduces the sensor size. The total length of the sensor is only 4.67 mm. The micro-helix taper-based LPFG can identify the bending direction due to the asymmetric structure introduced by the micro helix. The experimental results show that the transmission spectra of the sensor have distinct responses for different bending directions, and the maximum bending sensitivity is 14.08 nm/m^-1 in the range from 0.128 m^-1 to 1.28 m^-1. The proposed bending sensor possesses pronounced advantages, such as high sensitivity, small size, low cost, and orientation identification, and offers a very promising method for bend measurement.

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.

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.