强度调制的啁啾光纤光栅加速度传感器

设计了一种基于啁啾光纤布拉格光栅的新型加速度传感器,该传感器主要由矩形悬臂梁构成的传感机构和光纤光谱仪及光电探测器组成。导出了啁啾光纤布拉格光栅的反射谱带宽与加速度的关系;通过光谱仪检测啁啾光纤布拉格光栅反射谱的带宽或检测光电探测器输出的电压,即可获得加速度的大小。实验结果表明,该啁啾光纤布拉格光栅反射谱带宽及光电探测器输出的电压对温度变化不敏感,且在0~700m/s2测量范围内,反射谱带宽与加速度间具有良好的线性关系。由于反射谱带宽展宽造成了光纤布拉格光栅反射率的降低,因此光电探测器输出电压的线性响应范围只能达到0~35 m/s2,带宽和电压灵敏度分别达到0.005 6nm·m-1·s-2和0.785 6m V·m-1·s-2。     

光纤布喇格光栅沉降传感器

根据光纤布喇格光栅的光学传感原理,提出了一种基于悬臂梁及金属弹性膜片的光纤布喇格光栅沉降传感器结构,对其传感特性进行了实验研究.实验通过产生水的液位差来模拟地基沉降,分析结果显示,光纤布喇格光栅中心反射波长漂移对液位差呈现良好的线性关系,线性度高于0.999,灵敏度可达-2.11 pm/mm.通过改变悬臂梁厚度和有效长度,可以对传感器测量范围和灵敏度进行调整,以满足各种应用场合.综合实验结果,该传感器在桥梁、铁路地基等沉降监测方面具有重要意义.     

光纤布喇格光栅沉降传感器

根据光纤布喇格光栅的光学传感原理,提出了一种基于悬臂梁及金属弹性膜片的光纤布喇格光栅沉降传感器结构,对其传感特性进行了实验研究.实验通过产生水的液位差来模拟地基沉降,分析结果显示,光纤布喇格光栅中心反射波长漂移对液位差呈现良好的线性关系,线性度高于0.999,灵敏度可达一2.11 pm/mm.通过改变悬臂梁厚度和有效长...     

大啁啾光纤布拉格光栅的脉冲响应特性研究

脉冲堆积技术是高功率激光系统中产生任意种子脉冲的方案之一.该方案利用大啁啾光纤布拉格光栅的宽带特性来展宽宽带短脉冲,以满足脉冲堆积组件的需求.利用传输矩阵法模拟了大啁啾宽带光纤布拉格光栅的反射谱、时延曲线等特性.研究发现,光纤光栅的啁啾因子决定了色散量以及带宽的大小,但增加色散量的代价是降低了光纤光栅的带宽;光栅长度越长,反射带宽明显增加,但色散量变化不大.研究结果对高功率前端系统的设计具有一定的指导意义.     

光纤布拉格光栅自致啁啾效应的研究

根据耦合模理论,采用传输矩阵法分析了相位掩模法制作的光纤布拉格光栅的反射谱特性.设计了一种新的写制光纤光栅的光路,利用高斯激光光束写制出具有短波自致啁啾效应的切趾光栅(栅长0.015 m).对具有短波自致啁啾效应的光纤光栅进行了物理切割(剩余光栅的长度分别取0.007 m和0.0055 m),得到了一种新型的具有长波自致啁啾效应的光纤光栅.原本的自致啁啾光栅反射谱中旁瓣分布在短波长方向,而得到的新型自致啁啾光栅的反射谱中长波长方向的旁瓣更为明显.基于对光纤布拉格光栅自致啁啾效应的分析,提出一种新型类高斯切趾函数,以此函数对自致啁啾效应进行数值模拟,得到了与实验结果相一致的光谱图.     

基于啁啾光纤光栅的温度自补偿位移传感器

基于双三角结构的悬臂梁,提出了一种使用啁啾光纤光栅测定位移的方法.悬臂梁受到应力时引起刚性粘接在悬臂梁上的啁啾光栅反射谱带宽压缩,通过测量反射谱带宽进行位移的测量.该结构克服了位移测量时温度的交叉敏感问题,温度变化引起反射谱整体移动但不会改变带宽.测试结果表明该传感器具有较高精度、良好的线性和可重复性等优点.     

非对称单侧曝光切趾使啁啾光纤光栅获得优化性能

利用谐振理论对啁啾光纤光栅时延纹波和反射谱边瓣的形成原因进行了分析，研究了单侧曝光切趾方式中引入的非常数直流折射率调制分量对啁啾光栅特性的影响，阐明了切趾技术提高啁啾光纤光栅性能的作用机理，提出了一种能够使啁啾光纤光栅获得优化性能的切趾方法，该方法只需对光栅进行单侧曝光，实现简单. 关键词： 光纤布拉格光栅 切趾 群时延 反射谱     

光纤光栅传输矩阵研究

利用模耦合理论给出并分析了一般坐标系下相移布喇格光纤光栅中的传输矩阵及其特性,所给出的传输矩阵具有分段不变性,而且不能被分解为一个矩阵和一个相移矩阵的乘积.利用该传输矩阵可以研究均匀、相移、啁啾、超结构等光纤光栅及光栅的级联等.计算了相移光栅的反射谱和相移量的关系,以及两个光栅级联时的反射谱.结果表明,同样相移量时的反射谱和已有文献不同,两个光栅级联时,也不同于已有文献,各自的谐振波长与光栅的级联没有关系.     

三角形大带宽反射光谱光纤光栅的设计和制备

反射谱具有三角形形状的光纤光栅在光纤传感等领域中具有重要的应用前景。利用遗传算法设计出了产生三角形光谱分布的光纤光栅的耦合系数沿光纤的分布。计算表明,三角形光谱光纤光栅是可以实现的,其反射带宽可以通过光栅的啁啾量进行调节,常周期的三角光栅反射带宽小,变周期的三角光栅反射带宽大,其带宽同其啁啾量大致相等。实验中,采用光束扫描法制备了反射底宽为0．77nm三角形光谱的光纤光栅。     

保偏微结构光纤啁啾光栅折射率传感特性分析

将有限元法和传输矩阵法相结合,系统地研究了保偏微结构光纤(PM-MOF)啁啾布拉格光栅的折射率传感特性。仿真研究了光纤空气孔中充入不同折射率被测物时啁啾光栅的反射谱,结果表明随着被测物折射率的增加,反射谱的面积出现明显变化,由此得到了光栅反射谱面积与被测物折射率的关系。分析了中心孔直径、啁啾系数、切趾函数等光栅结构参数对反射谱的影响。分析表明由于光纤两个方向的偏振模对温度、噪声等干扰响应相似,因此利用两个偏振模式反射谱的相对变化进行监测能够有效地降低干扰,提高传感器的稳定性;其次,由于反射谱面积正比于光强,这一方法将光栅的光谱解调转化为光强解调,简化了解调系统,便于现场实时测量。研究结果为保偏微结构光纤光栅在折射率传感器及其生物传感器方面的应用提供了理论依据。     

Continuously spacing-tunable multiwavelength semiconductor-optical-amplifier-based fiber ring laser incorporating a superimposed chirped fiber Bragg grating

We investigate a flexibly tunable multiwavelength semiconductor-optical-amplifier-based fiber ring laser with continuous wavelength spacing controllability incorporating a superimposed chirped fiber Bragg grating (CFBG). The wavelength spacing of a superimposed CFBG can be continuously controlled by symmetrically modifying the chirp bandwidth of the grating with the specially designed apparatus. We achieve a wide and continuous tuning range of the wavelength spacing from 0.35 to 0.78 nm. The continuous tunability of the wavelength spacing is measured to be ~ +/-0.033 nm/mm. By controlling the reflection bandwidth of the tunable CFBG, we can independently adjust the number of lasing channels from 2 to 23 at the wavelength spacing of 0.51 nm.     

Detection of liquid-level variation using a side-polished fiber Bragg grating

A liquid-level sensor based on a side-polished fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor can detect height variation of liquids of arbitrary refractive index (RI). For liquids with RI lower than that of fiber core, liquid-level variation can be monitored by the peak power difference of the grating segments surrounded by the liquid and air. For liquids with RI higher than that of fiber core, liquid-level information can be obtained from the influence of the shortening of the effective length of the immersed grating segment upon the reflection spectrum.     

利用遗传算法优化线性啁啾光栅性能

针对制作町用于40 Gb/s全光色散补偿的宽带线性啁啾光栅时出现带内群时延纹波波动较大等问题.提出了一种通过设计和改变切趾函数的参量来优化线性啁啾光栅的新方法.该方法实现简单.只需根据需要设计具有不同滚降特性的切趾函数,同时利用遗传箅法来优化切趾参量.结合传输矩阵法经过200代获得了低带内时延纹波的线性啁啾光栅.数值结果验证了采取非对称分段切趾法在保持反射谱宽和平坦性的同时可以抑制带内群时延纹波的优越性.利用该方法制作了反射谱工作带宽为1.06 nm、时延纹波不超过45.60 ps、可用于大容量密集波分复用系统(DWDM)色散补偿的线性啁啾光纤光栅.     

An all-fibre multi-parameter sensor for composite structures based on a chirped fibre Bragg grating

An all-fibre multi-parameter sensor for composite structures based on a chirped optical fibre Bragg grating (CFBG) has been studied theoretically and experimentally. The principle of multi-parameters sensing with a single CFBG is based on that the centre wavelength and the FWHM (full width at half maximum) in the reflection spectrum of a CFBG vary linearly with the temperature and/or the axial stress. A wavelength matched optical fibre long period grating (LPG) and another wavelength matched reference CFBG (CFBGR) have been used to interrogate the signal of the sensor CFBG (CFBGS). The temperature and strain of the composite structure have been monitored real-time with one CFBG as a single sensor head. The temperature resolution of 0.12°C and the strain resolution of 1.1μ? for a composite structure have been realized in experiments. The experiment results agree well with the theoretical analyses.     

Fabrication of high quality chirped fiber Bragg grating by establishing strain gradient

To fabricate chirped fiber Bragg grating (CFBG) with high reflectivity and accurately controlled chirp profile with low cost, we develop the CFBG fabrication technique based on strain gradient: fabricating CFBG using fabricated fiber Bragg grating (FBG) by establishing strain gradient along the length of grating. We theoretically analyze the form of such CFBGs, and study the characteristics of gratings using piecewise-uniform approach. It is shown that increasing UV-induced index change or the length of the grating or both are the efficient ways to obtain high quality CFBG with high reflectivity and good reflection spectrum. The dispersion of this grating is decided by and varies inversely with the slope of the strain gradient along the length of the grating, not decided by UV-induced index change or by the length of grating. One can control the dispersion and the chirp profile by adjusting the slope of the strain gradient. Based on the theoretical analysis, we have fabricated CFBG whose reflectivity is maintained at 100% in a large range of strain gradients.     

一种通道数可变的光纤光栅梳状滤波器

利用级联长周期光纤光栅与具有宽带反射功能的啁啾光纤光栅,构成了一种反射型的光纤光栅梳状滤波器.由于光在输出前经过两次干涉滤波作用,所以该梳状滤波器的消光比与透射输出型(即反射前)相比,增加了一倍.而且,通过调节啁啾光纤光栅的反射带宽,可以改变滤波器输出信道的数目.实验中利用弹性梁弯曲的方法,获得了两个可调的光纤光栅梳状滤波器,其信道数可分别在1～5和3～9之间的奇数间调谐(如果改变啁啾光纤光栅的初始中心波长,也可以获得偶数信道间的调谐).     

国产啁啾布拉格光纤光栅在飞秒激光系统中的应用

利用自行研制的啁啾布拉格光纤光栅(CFBG)刻写系统完成CFBG样品制作,成功应用于光纤锁模振荡器和啁啾脉冲放大(CPA)系统中。振荡器可输出19.4 nm带宽、18 mW平均功率激光,并可压缩至143 fs,经时域展宽、功率放大、时域压缩后,脉冲宽度可至264 fs。实验结果初步证明了国产CFBG在飞秒激光系统应用的可行性。     

Synthesis of chirped apodized fiber Bragg grating parameters using Direct Tabu Search algorithm: Application to the determination of thermo-optic and thermal expansion coefficients

In this paper, Direct Tabu Search (DTS) is proposed to synthesize the physical parameters of a fiber Bragg grating (FBG) numerically from its reflection response. A reflected spectrum is being calculated by using the Transfer Matrix Method (TMM). Direct search based strategies are used to direct a tabu search. These strategies are based on a new pattern search procedure called Adaptive Pattern Search (APS). In addition, the well-known Nelder-Mead (NME) algorithm is used as a local search method at the final stage of the optimization process. Direct Tabu Search (DTS) is applied for reconstruction of a raised cosine chirped fiber Bragg grating (CFBG) and a Gaussian multi channel fiber grating. The method is then used to synthesize a CFBG from its reflectivity taken at different temperatures. It gives a good estimate of the thermal expansion coefficient and the thermo-optic coefficient of the fiber.     

Temperature-insensitive fiber Bragg grating dynamic pressure sensing system

Temperature-insensitive dynamic pressure measurement using a single fiber Bragg grating (FBG) based on reflection spectrum bandwidth modulation and optical power detection is proposed. A specifically designed double-hole cantilever beam is used to provide a pressure-induced axial strain gradient along the sensing FBG and is also used to modulate the reflection bandwidth of the grating. The bandwidth modulation is immune to spatially uniform temperature effects, and the pressure can be unambiguously determined by measuring the reflected optical power, avoiding the complex wavelength interrogation system. The system acquisition time is up to 85 Hz for dynamic pressure measurement, and the thermal fluctuation is kept less than 1.2% full-scale for a temperature range of -10 degrees C to 80 degrees C.