提出基于双光束二氧化碳(CO2)激光的加热方法,设计并搭建了微锥型结构的长周期光纤光栅制备系统。该系统通过精确控制CO2激光功率、加热时间、光斑大小等实现均匀加热和光纤软化,通过高精度的步进电机控制光纤微型拉锥长度和拉锥比,以产生周期性的物理形变,制备出高精度(消光比>30 dB,插入损耗<1 dB)、光谱不退化的微锥型长周期光纤光栅(MT-LPFGs)。基于级联MT-LPFGs实现了宽带全光纤滤波器。实验结果表明,设计的双级联MT-LPFGs在30 dB消光比下实现了15 nm的宽带滤波,与单个光栅相比,其滤波带宽增加7.5倍;三级联MT-LPFGs在-25 dB带阻深度下能够实现25.2 nm的宽带滤波,该滤波带宽为单个光栅的12.6倍。最后,通过弯曲实验证明了级联光栅滤波器的弯曲容限为1.183 m -1。该滤波器具有精度高、制备简单、光谱不退化等优点,在宽带滤波方面有着重要应用。

基于四层光纤模型, 采用数值模拟方法, 研究了镀膜长周期光纤光栅的膜层折射率及厚度等参数对其传输谱特性的影响。结果表明, 随膜厚增加, 各包层模式有效折射率增大, 谐振波长向短波区漂移。当膜厚达到一定数值后, 有效折射率及谐振波长急剧变化, 长周期光纤光栅频谱出现模式转换现象, 模式跳变转折点对应最优薄膜厚度, 不同薄膜介质对应不同的最优膜厚, 研究对提高长周期光纤光栅传感器的敏感度具有重要的指导意义。

利用高频CO2激光单侧曝光技术及双芯光纤的非对称性, 设计并制作了一种长周期光纤光栅弯曲矢量传感器.成栅机理分析表明, 光纤边缘处嵌入的纤芯极大地增强了包层中的残余应力, 在CO2激光脉冲曝光时, 残余应力释放作用增强, 光栅质量更高; 同时, 双芯光纤的非对称结构以及CO2激光单侧曝光使得光纤器件对偏振非常敏感, 写制的光纤光栅在1 555.4 nm谐振波长处的偏振相关损耗高达20.8 dB.弯曲传感测试表明, 在0~1.235 m－1曲率范围内, 光纤光栅向+y方向弯曲时, 透射谱谐振峰波长向长波方向漂移, 灵敏度为2.37 nm/m－1; 光纤光栅向－y方向弯曲时, 谐振峰波长向短波方向漂移, 灵敏度为1.80 nm/m－1.该弯曲矢量传感器结构简单, 灵敏度高, 可广泛应用于道路、桥梁等建筑的安全检测.

Two promising post-treatment techniques, i.e. applying tensile strain and rising temperature, are demonstrated to enhance the mode-coupling efficiency of the CO₂-laser-induced long period fiber gratings (LPFGs) with periodic grooves. Such two post-treatment techniques can be used to enhance the resonant attenuation of the grating to achieve a LPFG-based filter with an extremely large attenuation and to tailor the transmission spectrum of the CO₂-laser-induced LPFG after grating fabrication.

Photonic crystal fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBFs). We presented the fabrication methods and applications of long period fiber gratings (LPFGs) written in these two types of photonic crystal fibers by use of a CO2 laser. A stain sensor with a high sensitivity was demonstrated by use of an LPFG written in solid-core PCFs. An in-fiber polarizer based on an LPFG was fabricated by use of a focused CO2 laser beam to notch periodically on a PCF. A novel LPFG was written in an air-core PBF by use of a CO2 laser to collapse periodically air holes in the fiber cladding.

提出了一种基于长周期光纤光栅(LPFG)载边比(CSR)连续可调的单边带调制光载无线通信(RoF)系统。其核心单元是由偏振控制器(PC)、偏振分束器(PBS)、两个平行的长周期光纤光栅和偏振合束器(PBC)构成的载边比调节单元。通过调节偏振控制器输出的偏振角度，就可以实现载边比的连续可调。进一步分析了调制指数、长周期光纤光栅透射率峰值和马赫曾德尔调制器消光比对载边比的影响。仿真结果与理论分析结果具有很好的一致性。经40 km标准单模光纤(SMF)传输后的仿真实验表明，当载边比由13.22 dB调节到5.4 dB后，系统灵敏度提高了5.7 dB。

通过模式耦合理论, 建立了基于长周期光纤光栅(LPFG)的二层圆光波导模型; 结合传输矩阵法, 仿真得到了外部介质折射率呈线性分布情况下LPFG的透射谱。仿真结果表明: 该结构下的LPFG透射谱特性强烈依赖于外部介质折射率梯度, 当外部介质折射率梯度升高, 透射谱的损耗峰深度逐渐降低, 损耗峰3dB带宽逐渐增加, 且增加量与折射率梯度的增加量呈较好的线性关系; 当外部折射率梯度由1.111 1×10-7 riu/mm增加到1.111 1×10-5 riu/mm时, 其梯度灵敏度可达到2.2×107 nm·mm/riu。这一结果使折射率梯度的高灵敏度测量成为可能, 为设计和制作基于LPFG的折射率梯度传感器提供了一定的理论依据,并有望用于生化反应中微小尺度下折射率呈梯度分布的液相介质的测量。

Based on the full vector complex coupled mode theory, a detailed analysis is made on the transmission spectrum characteristics of tilted long period fiber gratings. New transmission peaks are observed, which are located beside the long wavelength side of each transmission peak in the transmission spectrum of normal long period fiber gratings. The emerging transmission peaks are quite sensitive to both the grating tilted angle and the surrounding refractive index, and the corresponding relationship is discussed. Furthermore, a novel sensing characteristic is investigated about the tilted long period fiber gratings, which is related to the transmission resonant wavelength and peak amplitude.