Fiber Bragg Gratings in Small-Core Ge-Doped Photonic Crystal Fibers

This paper reports fiber Bragg gratings （FBGs） inscribed in a small-core Ge-doped photonic crystal fibers with a UV laser and a Talbot interferometer. The responses of such FBGs to temper- ature, strain, bending, and transverse-loading were systematically investigated. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. The bending and transverse- loading properties of the FBGs are sensitive to the fiber orientations.

Analysis of Sampled Fiber Bragg Grating Based on the Photonic Crystal Theory

One of the most basic characteristics of photonic crystal is frequency band gap. When defects are introduced into the periodic photonic crystal, a number of defect modes appear in the stop band. In this paper, we exploit transfer matrix method based on photonic crystal theory, and assume the sampled fiber Bragg grating as one-dimensional dual photonic crystal with a large size defect. Characteristics of the sampled fiber Bragg grating are analyzed. Experimental results show that the sampled fiber Bragg grating has many reflective peaks. Its reflectivity, center wavelength, reflective peak intervals and band width all change with the grating parameters, including grating length, duty ratio of the material with high dielectric constant, and index modulation depth and period. Results agree with the conventional couple mode theory which can be used when analyzing other characteristics of the sampled fiber Bragg grating or applying it into practice.

On the Validity of the Effective Index Method for Long Period Grating Photonic Crystal Fibers

This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to study its limitations for various designs of LPG-PCFs. Results so obtained with the above method are compared with the corresponding values of multiple multipole (MMP) method results which points the range of validity and applicability of the improved effective index method to LPG-PCFs. It is shown that this method is excellent when the surrounding media is assumed to be air. However, it becomes less accurate when the fiber is immersed into a liquid with a refractive index close to that of the cladding.

The Design of Bending Long Period of Photonic Crystal Fiber Grating Sensors

The bending photonic crystal fiber grating sensor is an important role in underwater monitoring and fire alarm systems. It is studied that the resonant wavelength expression of bending long period photonic crystal fiber gratings is deduced, it is designed that a bending long period photonic crystal fiber grating sensor system, it is calculated in theory that between the bending long period photonic crystal fiber gratings sensor resonance wavelength and the grating period and the bending strain. The result is shown by calculating and analysing in theory, the grating curvature is increased by the increase of the bending strain of the grating, and the resonance wavelength of the grating sensor is drifted, the drift amount is increased, one in this grating, the drifted amount of the resonant wavelength is 0.014 nm.

Birefringent Bragg Gratings in Highly-Nonlinear Photonic Crystal Fiber

Efficient writing of Bragg gratings in 12-ring highly-nonlinear photonie crystal fibers is described. Experimental and numerical investigations are performed to reveal the optimum angle for coupling UV writing light to the core. Furthermore, we show that the formation of a strongly briefringent grating is at a particular angle of orientation.

基于布里渊动态光栅的高灵敏度保偏光纤多参量同时解调

为了实现基于保偏光纤在布里渊动态光栅的温度、快轴压力和慢轴压力同时解调,并克服传统压力传感灵敏度不足的缺点,提出了一种边孔型高灵敏度光子晶体光纤。利用有限元方法,研究了温度、快轴压力和慢轴压力与双折射频移、布里渊频移和布里渊线宽之间的关系,据此可实现多参量的同时解调。结果表明,该光子晶体光纤可以实现三参量的同时解调,且解调误差在1 MPa和1℃以内。快轴压力、慢轴压力和温度的误差均值分别为0.21 MPa、0.31 MPa和0.30℃,误差的标准差分别为0.15 MPa、0.21 MPa和0.21℃。在施加0~30 MPa的横向压力和0~100℃的温度时,该光子晶体光纤快轴方向上的压力灵敏度为-1.961 GHz/MPa,光纤慢轴方向上的压力灵敏度为1.356 GHz/MPa,其温度灵敏度为0.105MHz/℃。相较于目前最优结构的光子晶体光纤压力灵敏度提升了-957MHz/MPa。该传感器及解调方法适用于土木结构和大型机械在建造和使用过程中监测其内部所受温度和不同方向压力的变化。

Long Period Fiber Gratings Written in Photonic Crystal Fibers by Use of CO2 Laser

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.

Characterization of external refractive index sensitivity of a photonic crystal fiber long-period grating

Long-period gratings （LPGs） are fabricated in a photonic crystal fiber （PCF） using the symmetric point- by-point CO2 laser irradiation method to explore the sensitivity characterization of PCF-LPG. Numerical sim- ulation is used to guide the investigation. It is found that the refractive index （RI） sensitivity of PCF-LPG depends on the coupled cladding modes as well as the coupled resonance wavelength （RW） of the LPG. Experimental studies show that the longer the RW, the higher the RI sensitivity for the same cladding mode. At similar RWs, the lower the cladding mode, the higher the RI sensitivity of PCF-LPG.

Sensing Properties of Femtosecond Laser-Inscribed Long Period Gratings in Photonic Crystal Fiber

The use of near infrared, high intensity femtosecond laser pulses for the inscription of long period fiber gratings in photonic crystal fiber is reported. The formation of grating structures in photonic crystal fiber is complicated by the fiber structure that allows wave-guidance but that impairs and scatters the femtosecond inscription beam. The effects of symmetric and asymmetric femtosecond laser inscriptions are compared and the polarization characteristics of long period gratings and their responses to external perturbations are reported.

Long Period Gratings in Photonic Crystal Fibers

The authors review the recent advances in fabricating long-period gratings （LPGs） in photonic crystal fibers （PCFs）. The novel light-guiding properties of the PCFs allow the demonstration of novel sensors and devices based on such LPGs. The sensitivity of these PCF LPGs to temperature, strain and refractive index is discussed and compared with LPGs made on conventional single-mode fibers. In-fiber devices such as tunable band rejection filters, Mach-Zehnder interferometers are discussed.

基于结构性改变PCFG的制备工艺研究

研究了基于结构性改变的光子晶体光纤光栅的热激法制备工艺,理论分析了此种工艺的成栅原理,采用热传导理论和有限元法研究了制备过程中光子晶体光纤中的温度场分布,以及包层空气孔结构和激光参数对成栅效果的影响。研究结果表明,利用光子晶体光纤包层空气孔周期性塌缩可以形成光栅;采用两点热激法时,能够实现能量在光纤径向均匀分布,轴向近似于高斯分布;包层气孔结构加速了成栅过程,相同光斑尺寸下,光纤塌缩所需激光功率随气孔层数和气孔半径的增大而减小;最后,对包层空气孔结构为1层到7层的光子晶体光纤热激过程进行仿真,得到了空气填充率与所需激光功率的关系。此种光纤光栅从根本上克服了传统光栅热稳定性和长期稳定性不佳的问题,在光纤传感等领域具有较大的潜在应用价值。

Strain and Temperature Characterization of LPGs Written by CO2 Laser in Pure Silica LMA Photonic Crystal Fibers

This paper reports on the writing of long period gratings （LPGs） in a six-ring pure silica solid core, and large mode area photonic crystal fiber （fiber core diameter p = 10.1 μm） using a CO2 laser system, and the characterization of their strain and temperature sensitivities. Temperature and strain sensitivities in the order of-19.6pm/℃ and -88 pm/με, respectively, were obtained, which were comparable or surpassed values of the similar photonic crystal fiber （PCF）-based LPG or sensor configurations found in the literature.

基于布里渊动态光栅的横向压力传感器设计

设计了一种新型多层次结构的光子晶体光纤,其纤芯区域由大、小两种椭圆空气孔包围而成,而所有空气孔是沿y轴堆叠排布且关于x轴对称的。利用有限元法对该光纤的二维模型进行数值分析,在施加0~40 MPa的横向压力的情况下将温度的研究范围扩大到-100~100℃,在低温高压力的情况下计算不同温度和压力下的双折射频移以研究其温度和压力传感特性。研究表明,该光子晶体光纤的压力灵敏度可以达到1.021 GHz/MPa,其温度灵敏度为0.554 3 MHz/℃,与目前最优的具有“三明治”结构的光子晶体光纤设计的灵敏度为692 MHz/MPa的横向压力传感系统相比提高了328 MHz/MPa,适用于海底、土木等恶劣环境的高精度监测。

光子晶体光纤传感器的研究进展

简要介绍了光子晶体光纤的基本结构、导光原理和主要特性。依据传感机理将光子晶体光纤传感器分为4类:吸收型光子晶体光纤传感器、荧光光子晶体光纤传感器、干涉型光子晶体光纤传感器、光子晶体光纤光栅传感器,分别对其工作原理、结构、特点和研究进展进行了讨论。

膜层传输矩阵理论在布拉格光纤光栅分析中的应用

利用膜层传输矩阵理论研究折射率调制对布拉格光纤光栅传输特性影响.根据传输矩阵理论计算光栅折射率的调制幅度、光栅长度、调制方法等对布拉格光纤光栅的反射率、反射峰波长和半幅宽度的影响.结果表明:膜层传输矩阵理论与传统传输矩阵法、耦合模理论对布拉格光纤光栅特性分析结论一致;采用高调制长度、低调制幅度可以获得良好的布拉格光纤光栅反射峰,而反射主峰位置改变需用调整调制周期.实验和理论对比分析了主峰在1 550nm波长的布拉格光纤光栅反射峰情况,验证了该方法的可行性.与传统方法相比,膜层传输矩阵法计算公式简单、运行速度快,可应用于布拉格光纤光栅辅助设计.

弯曲长周期光子晶体光纤光栅传感器的研究

为了研究弯曲长周期光子晶体光纤光栅传感器谐振波长漂移量与光栅弯曲形变的关系,采用耦合模理论和计算机模拟方法进行了理论计算和仿真研究,推导出弯曲光子晶体光纤长周期光栅谐振波长表达式,设计了一般弯曲长周期光子晶体光纤光栅传感器系统模型,分析了弯曲长周期光子晶体光纤光栅传感器的基本工作原理,并计算了长周期光子晶体光纤光栅弯曲曲率、光栅有效折射率和谐振波长与弯曲应变的关系。结果表明,随着光栅弯曲形变的增加,光栅的曲率会增加,光栅传感器的谐振波长漂移量会增加,光栅每发生1με变化,光栅谐振波长的漂移量变化0.014nm。

高非线性光子晶体光纤中布拉格光栅的制作

采用相位掩模版法实验研究了高非线性掺锗光子晶体光纤中布拉格光栅的制作。实验中采用的光子晶体光纤的非线性系数约为12 W-1km-1,模场直径约为2.4 mm。分析了布拉格光栅的反射率随着曝光脉冲数的变化,随着曝光脉冲数的增加其反射率逐渐达到饱和,继续增加曝光量发射率开始下降。实验验证了可以在高非线性光子晶体中写入布拉格光栅,得到光栅的反射率为44.4%,这对于研究光纤布拉格光栅的非线性效应和应用具有重要意义。讨论了影响布拉格光栅写入效率的因素。

光纤光栅生物传感器的研究进展综述

本文介绍了光纤光栅生物传感器的传感原理,从光纤光栅新型结构的研究、可固定光纤表面的生物活性膜的研究以及应用研究三个不同的角度阐述了近年来光纤光栅生物传感器研究的进展情况,并分析目前该领域内面临的一些问题,对光纤光栅生物传感器的研究方向提出了一些建议。

光子晶体光纤光栅模式截止与高阶模的谐振条件

采用光束传播法研究了实心掺锗光子晶体光纤布拉格光栅(PCFBG)的模式截止特性。结果表明掺锗光子晶体光纤的归一化频率V与归一化间距Λ/λ和归一化孔径d/Λ有关。而且相对于纯硅的光子晶体光纤,其单模多模边界面向归一化孔径值较小的方向位移。并给出了在光子晶体光纤光栅中激发高阶谐振的条件:相位匹配条件、光栅区的电场交迭和关系不等式VPCF>π。

光子晶体光纤布拉格光栅慢光的研究

采用改进的全矢量有效折射率法和耦合模理论,研究了光子晶体光纤布拉格光栅长度、占空比、光栅周期与慢光的变化规律。结果表明当光栅长度和光栅周期不变时,随着包层空气孔占空比的增大,光栅的慢光峰值波长出现蓝移,且时延量逐渐减小;1.06 cm长的光子晶体光纤布拉格光栅可以产生约52 ps的线性时延;光栅长度越大,慢光时延量越大;优化结构参数,在光子晶体光纤布拉格光栅的时延谱的侧瓣附近会产生最大群速度为c/371的慢光峰。