Design and Fabrication of Fiber Bragg Gratings With V-Shaped Dispersion Profile

We propose a new type of fiber Bragg grating (FBG) with a V-shaped dispersion profile. We demonstrate that such V-shaped FBGs bring advantages in manipulation of optical signals compared to conventional FBGs with a constant dispersion, e.g., they can produce larger chirp for the same input pulsewidth and/or can be used as pulse shapers. Application of the proposed V-shaped FBGs for signal prechirping in fiber transmission is examined. The proposed design of the V-shaped FBG can be easily extended to embrace multichannel devices     

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 linearly tapered fiber Bragg grating for dispersion slope compensation

We demonstrate that linearly tapered fiber Bragg gratings (FBGs) display nonlinear group delay under strain or stress. The nonlinear group delay of the tapered FBG is analyzed theoretically. Experimental results show a good agreement with the analysis. We are the first to find that linearly tapered FBGs can be used in dispersion slope compensation.     

光纤光栅埋入后温度、应变解耦分析

光纤光栅传感器在现实应用中的一个主要问题是温度和应变的交叉敏感问题.介绍了光纤双光栅同步测量温度和应变的原理,设计了一个光纤双光栅温度、应变测量系统,对光纤双光栅的温度和应变传感性能进行了实验研究,结果表明光纤双光栅具有多参量同时测量的能力.     

Power penalties due to in-band and out-of-band dispersion in FBG cascades

We measure the in-band dispersion penalty in a cascade of five 50-GHz low-dispersion linear-phase fiber Bragg gratings (FBGs) and compare the results with conventional apodised FBGs. At the 0.5-dB power penalty level, the usable bandwidth of a single linear-phase FBG (40 GHz) is twice as wide as that of a conventional apodised FBG (19 GHz). The bandwidth-utilization factor of a single linear-dispersion grating is 89%, while for the five-grating cascade, it is 76%. To our knowledge, these are the highest values reported to date for cascaded optical devices. The corresponding factors for the conventional gratings are 53% and 31%. We also measure the additional penalty on a dropped channel caused by a cascade of five adjacent-channel gratings. The bandwidth narrowing due to the adjacent-channel FBGs is 6 GHz both for linear-phase and conventional FBGs, giving a usable bandwidth of 34 GHz (linear-phase) and 13 GHz (conventional).     

大模场面积双包层光纤光栅模式特性研究

分析了在大模场面积双包层光纤(LMA-DCF)上刻写光栅的技术要求和难点,采用相位掩模法在20/400μm的LMA-DCF上刻写了高反射率光纤布拉格光栅。针对大模场光纤中存在高阶模的可能性,通过调整单模光纤(SMF)入射光场和LMA-DCF芯径的相对偏移量,对LMA-DCF光栅中的传输模式特性进行了理论分析和模拟计算,并在实验研究中测量了偏移量不同时光栅的反射谱,观测到了相应的LP01模和LP11模的模场光斑分布。对LMA-DCF光栅的几种光谱测试方法进行了对比研究,分析了各种方法的优缺点。研究结果将为LMA-DCF光栅在高功率激光系统中的应用提供依据和参考。     

提高制作光纤光栅时飞秒激光光斑质量的方法

由于光纤自身固有的圆柱形结构,在飞秒激光逐点刻写光纤布拉格光栅过程中会产生柱透镜效应,使得聚焦光斑呈长条状,对刻写光栅结构产生不利影响。基于几何光学原理分析了产生长条状光斑的原因,并提出了一种有效地改善聚焦光斑质量的方法。实验中,将待写光纤夹在玻璃板之间并填充折射率匹配液,运用800 nm钛蓝宝石飞秒激光通过50×显微物镜聚焦在双包层光纤内,单脉冲曝光后得到了直径为1.5μm圆形光斑,方法简单,易于操作。光斑质量的提高扩展了飞秒激光在光纤微细结构制作中的应用。     

一种同时测量温度和应变的光纤光栅传感器

报道了一种新型实用的用单根光纤布拉格光栅(FBG)实现温度和应变分离传感的技术。当光纤光栅一部分包层直径变小时，整个光栅可以看成由两个周期相同但直径不同的子光栅连接而成。理沦分析和实验都证实了这两个子光栅具有相同的温度敏感性和不同的应变敏感性．由此实现光纤光栅传感器中温度和应变两参数的分离测量，而且这两个子光栅的中心波长间距可以直接测量应变大小．温度变化不影响所测量的应变值。实验中光栅的一部分包层直径被HF酸腐蚀到82μm．获得了两子光栅应变响应系数分别为0．00201nm/με．0．000858nm/με，二峰间距的应变响应系数为0．00116nm／με．二峰的温度响应系数均为0．01nm/℃的测量结果．依据这些结果可以对温度和应变进行同时分离测量。     

Photodarkening and photobleaching in fiber optic Bragg gratings

A photobleaching effect is reported which reduces the broadband losses induced by the single-pulse writing of fiber Bragg gratings (FBGs). A primary application of the optical FBG reflector is as arrays of wavelength-encoded sensing elements for detecting mechanical strain. Instrumentation is being developed to interrogate >100 point sensors along a single fiber with FBGs and detectors operating in the 790-820 nm band. In this paper, we describe broadband absorptions induced by writing single-pulse FBGs which would impose a 10 dB power penalty with as few as 40 serialized FBGs. We have reduced these photo-induced losses more than seven-fold (measured near 800 nm) using a photobleaching process which minimally affects the FBG's reflectivities. After treatment, optical losses are sufficiently low to allow the interrogation of hundreds of FBGs along a single fiber. Photodarkening and photobleaching are measured in gratings prepared by single laser pulses, and by multiple pulses with and without hydrogen loading. Parasitic loss following photobleaching is lower for single-pulse FBGs operated near 800 nm than for FBGs written with multiple pulses in hydrogen loaded fibers and operated near 1300 nm     

40-nm-wide tunable fiber ring laser with single-mode operationusing a highly stretchable FBG

We demonstrate a 750-Hz linewidth single-mode erbium-doped fiber (EDF) ring laser with wide tunability using a widely tunable fiber Bragg grating (FBG). The stable single-mode operation is realized by using the FBG as a narrow wavelength-selective element and 4 m of unpumped EDF as a saturable absorber in the cavity. The 40-nm continuous tuning range of 1522-1562 nm is achieved using a highly stretchable FBG that exhibits a filter tuning range of over 52 nm. The grating is prepared with chemically stripped deuterium-loaded fiber to eliminate degrading factors for the grating strength, thereby achieving the wide tunability. The tuning range represents a 3.5-fold increase in wavelength tuning over previous use of FBGs     

All-Fiber Q-Switched Erbium-Doped Fiber Ring Laser Using Phase-Shifted Fiber Bragg Grating

We propose a unique all-fiber Q-switched erbium-doped fiber ring laser. It consists of a phase-shifted fiber Bragg grating (FBG) and an apodized FBG reflector. By using the piezoelectric transducer (PZT) to periodically stretch the apodized FBG and detune it with the phases-shifted FBG, the cavity loss of the fiber ring laser is switched between high and low states to achieve Q-switching. This Q-switched fiber laser has advantages of narrow spectral bandwidth, stable oscillation wavelength, and the repetition rate of the Q-switched pulses can be double of the PZT modulation frequency. A numerical model is developed and presented to simulate and analyze this FBGs-based Q-switched fiber ring laser with consideration of the dynamic response of FBGs during Q-switching. We experimentally demonstrate 10 and 20 kHz Q-switching operation with 10 kHz PZT modulation frequency. The experimental result is similar to the simulation result.     

Arbitrary-Order Ultrabroadband All-Optical Differentiators Based on Fiber Bragg Gratings

We introduce a general approach for designing ultrabroadband arbitrary-order all-optical (all-fiber) time differentiators based on the use of fiber Bragg gratings (FBGs). Specifically, we numerically demonstrate that an Nth-order time differentiator can be implemented using a single specially apodized highly dispersive linearly chirped FBG operated in transmission. A concatenated reflection phase-shifted FBG is also required for implementing any odd-order differentiator. Our numerical simulations show that accurate and efficient time differentiation of optical signals with bandwidths up to a few hundreds of gigahertz can be realized using readily feasible FBG structures.     

一种新型具有温度补偿功能的光纤光栅交流电流互感器

为了消除温度对实现电流测量的影响,提出了一种具有温度补偿 功能的光纤Bragg光栅(FBG)交流电流互感器。利用两个FBG和超磁致伸缩材料(GMM)组成的 传感单元分别放置在两个相邻对称的铁磁回中,并加上两个方向相反的直流偏置磁场,利用 匹配检测方法对两只FBG进行解调,实现交流的测量。测量结果表明,在温度的影响下,系 统的静态工作点几乎未发生变化,在线性区测得最大电流为93.78A , 可获得1.68%的满量程精度。这种FBG电流传感器不仅可以测量交流电 流,也可以实现直流电流的测量。     

UV-Inscribed Optical Fiber Gratings in Mid-IR Range and Their Laser Applications

We have UV-inscribed fiber Bragg gratings (FBGs), long-period gratings (LPGs), and tilted fiber gratings (TFGs) into mid-IR 2m range using three common optical fiber grating fabrication techniques (two-beam holographic, phase mask, and point-by-point). The fabricated FBGs have been evaluated for thermal and strain response. It has been revealed that the FBG devices with responses in mid-IR range are much more sensitive to temperature than that in near-IR range. To explore the unique cladding mode coupling function, we have investigated the thermal and refractive index sensitivities of LPGs and identified that the coupled cladding modes in mid-IR range are also much more sensitive to temperature and surrounding medium refractive index change. The 45 tilted fiber gratings (45-TFGs) as polarizing devices in mid-IR have been investigated for their polarization extinction characteristics. As efficient reflection filters and in-cavity polarizers, the mid-IR FBGs and 45-TFGs have been employed in fiber laser cavity to realize multi-wavelength 2 m Tm-doped CW and mode locked fiber lasers, respectively.     

Generation of Power-Efficient FCC-Compliant UWB Waveforms Using FBGs: Analysis and Experiment

In this paper, we design, analyze, and demonstrate experimentally U.S. Federal Communications Commission (FCC)- compliant power-efficient ultrawideband (UWB) waveforms generated by optical pulse shaping. The time-domain pulse shape is written in the frequency domain, and a single-mode fiber performs the frequency-to-time conversion. The waveform is inscribed in the frequency domain by the fiber Bragg grating (FBG). A significant challenge for this approach is elimination of an unwanted, positive rectangular pulse superimposed on the desired waveform. Our innovative use of balanced photodetection eliminates this pedestal, assuring compliance with the FCC mask at low frequency. Three UWB pulses with duration of 0.3,0.6, and 1.2 ns are designed and tested experimentally. Whereas an excellent match between the optimized and measured pulses is achieved for the simpler, shorter duration waveforms, the noise in the fabrication process of FBGs limits the generation of the more complex, longer duration waveforms.     

光纤光栅应力传感器信号检测中双值问题的研究

介绍了采用匹配光纤布拉格光栅解调法(detector FBG)进行强度解调的基本原理，选择反射谱与传感光纤布拉格光栅(sensor FBG)反射谱部分重叠的解调光栅，通过探测解调光栅反射光强的变化进行解调。对这种光栅匹配解调法引起的反射光功率与应力为高斯函数而不是线性对应的问题——双值问题进行了研究，提出了一种新颖的多档光栅并联解调的解决方案，选择并联解调光栅的中心波长和带宽，从而实现所传感的应力与探测到的光功率之间的线性对应，并建立理论模型进行了模拟，从理论上进行了公式推导。最后以两档光栅并联解调为例，用实验证明了该方案切实可行，同时达到的传感范围为522με，测量精度为2．6με。     

飞秒激光脉冲刻写光纤布拉格光栅的研究进展

介绍了利用飞秒激光器刻写光纤布拉格光栅的三种基本方法:全息干涉法、相位掩模板法、直接逐点刻写法.讨论了飞秒激光制作光纤布拉格光栅的主要作用机制.详细论述了这三种方法的特点、规律及最新研究进展,并总结了飞秒激光制作的光纤布拉格光栅呈现出来的独特性质.