一种可重构型相移光纤光栅传感系统

为了实现对相移型光纤光栅传感器回波光谱中相移幅度、位置的精确控制,提出了一种利用机械微应变控制相移光纤光栅传感器的方法。该方法采用千分尺螺杆、应变梁、相移型光纤光栅、解调仪等组成。通过千分尺螺杆完成微应变控制,由梁将应变传递给PSFBG,从而使回波光谱变化,最终,构建光谱偏移量与微位移Δy的函数模型。通过应力加载实验,结果显示拉伸与压缩可以使PSFBG产生正相移和负相移,相移拟合曲线是线性的,综合拟合斜率为0.9914。该系统可通过梁弯曲微应变实现对相移的连续调谐,相移的大小可通过改变负载位移实现线性控制。该方法简单、精度高、控制范围大且无源,具有一定的应用价值。     

机械写制π相移弯曲不灵敏光纤长周期光栅滤波器

采用2个交错放置的具有π相移的周期性刻槽板对弯曲不敏感光纤径向施力,形成了机械写制π相移长周期光栅(LPGs)滤波器。实验研究了压力和子光栅个数对π相移光纤光栅的光谱影响以及光栅的偏振相关损耗(PDL)。结果表明：两侧阻带的传输损耗由施加在光纤上面的压力决定,子光栅的个数决定π相移光纤光栅的通带宽度,但不影响通带中心波长;对LP13耦合模,当π相移个数从1增加到9时,滤波器通带带宽由8.2 nm增加到53.8 nm。LP13包层模具有最大PDL,其值约为6.86 dB。该方法制作的π相移长周期光纤光栅(LPFG)具有可重构性,结构简单,易于操作,在光纤通信和传感领域具有潜在的应用价值。     

基于长周期光纤光栅的可调谐光滤波器设计

分析了长周期光纤光栅(LPFGs)透射谱受外界环境折射率变化影响的特性及其原理,进而提出了一种新型的可调谐光滤波器的设计思路．并运用分段光栅的矩阵分析法对其进行了具体的计算。此种光滤波器具有滤波精度高、可实现滤波波长和深度单独、连续调谐及全光纤性等优点,滤波波长调谐范围可达15nm,衰耗深度调谐范围达9dB。     

光纤光栅声光调制特性分析

高频超声波在紫外写入的光纤布拉格光栅(FBG)上传播，产生的长周期超声光栅调制光纤光栅，形成光纤超声超结构光栅。利用模式耦合理论，分析了光纤超声超结构光栅的光谱特性，得出光纤超声超结构光栅的反射谱存在多个反射峰，其反射峰的波长间隔由超声波的频率决定。因此，可以通过改变超声波的频率，调节一阶反射谱的反射波长，从而实现宽调谐范围的快速波长可调滤波器。该滤波器与通常的声光可调滤波器相比，带宽更窄，调谐速度更快。     

分布式光纤光栅传感网络的复用解调技术

波长编码信号解调是实现光纤光栅多参量、多点分布式传感网络的核心技术之一。本文总结了光纤光栅传感信号解调的一般原理和技术难点，分类评述了常用解调方法的工作机理、特点和性能。同时，提出了一种新型的、用宽带光源和可调谐光滤波器(TOF)构成的可调谐窄带光源，对测量光栅阵列和参考光栅进行波长扫描，借助光电探测器和信号处理系统实现复用传感系统的解调技术。     

π相移光纤光栅制作方法的比较研究

介绍了目前最常用的两种制作相移光纤光栅的方法,即分步曝光法(或遮挡法)和相位掩膜板移动法,对比分析了两种方法引入相移的物理机制,并利用传输矩阵法理论模型,数值模拟了两种制作方法下的相移光纤光栅透射谱,并分别进行了分布反馈光纤激光器(DFB-FL)的对比实验。结果表明,分步曝光法制作相移光纤光栅时,相移量与光栅中无曝光段的长度及纤芯折射率调制量均有关,难以精确控制相移量的大小,并且存在偏振模竞争问题;而相位掩膜板移动法通过压电陶瓷直线微动台控制掩膜板和光纤相对位移,在光栅中引入相位变换,可以将相移量控制在0~2π范围之内,更容易实现π相移光栅的制作。     

光纤光栅外腔半导体激光器频率调谐技术研究

在分析了光纤光栅外腔半导体激光器(FBG-ECL)基本特性的基础上,调研了适用于该类型激光器的频率调谐方法,包括温度调谐法和应力调谐法,选取轴向应力调谐法改变光纤光栅的布拉格中心波长,进而实现频率调谐。利用压电陶瓷(PZT)来对光纤光栅施加轴向应力,通过调整PZT驱动电压值的大小来控制光纤光栅布拉格中心波长的变化量。实验结果表明,对于波长1550 nm的光纤光栅激光器,当PZT的驱动电压增加到126 V时,可实现 0.8 nm,即100 GHz的调谐范围以及每周期2 ms的调谐速度。     

基于F-P滤波器的光纤光栅解调技术研究

介绍了光纤光栅传感器的解调原理,设计并实现了一个基于可调谐F-P滤波器的光纤光栅波长解调系统.利用数据采集卡采集光纤光栅的光谱数据上传给计算机,用LabVIEW编写了对数据进行实时处理的软件.实验结果表明该系统有效可行,可以获得±0.3℃的测量精度,并具有对50个以上的光纤光栅传感器进行解调的潜力.     

基于游标原理的可调谐分布反射全光纤激光器

报道了一种新型全光纤离散可调谐分布反射(DBR)光纤激光器。光纤激光器为短腔结构,其有源区采用Er-Yb共掺单模光纤,有源光纤长度为6 cm。激光器采用两组级联光纤布拉格光栅(FBG)为反射腔镜,前腔镜各级联光纤布拉格光栅的布拉格波长间隔为1 nm,后腔镜为0.8 nm,利用游标原理,通过对前腔镜级联光纤布拉格光栅进行机械调谐,使前后腔镜各反射波长分别对准,实现了四个固定波长间隔为0.8 nm的离散调谐。这种光纤激光器具有波长调节准确,调谐速度快,成本低的优点,可用于作为多波长光纤传输系统的发射光源或系统检测光源,进一步增加级联光栅的组数可实现更大调谐范围。     

相移光纤光栅的反射谱特性分析

应用传输矩阵法对相移光纤光栅(FBG)的反射光谱特性作了详细的理论分析,给出了相应的数学模型,并进行了验证.结果表明,相移的引入导致光纤光栅反射谱产生分裂,分裂点波长与相移大小呈线性正比关系并具有用期性;分裂点反射率与相移位置、光栅中心波长之间具有一定的对称性,且符合双曲正切关系.     

Multiwavelength all-fiber ring laser using side-polished fiber comb filter and mechanically formed long-period fiber gratings

Multiwavelength all-fiber lasers to be operated at room temperature are demonstrated. A side-polished fiber comb filter and mechanically formed long-period fiber gratings (LPFGs) are used to generate colasing operation. By using the band suppression characteristics of the LPFGs to prevent the gain cross-saturation effect, simultaneous lasing of four-wavelength peaks is obtained.     

用于S波段光纤拉曼放大器增益平坦的长周期光纤光栅设计

根据实际所测得的S波段光纤拉曼放大器的信号增益谱,通过对长周期光纤光栅具体参数的选定,由两个长周期光纤光栅级联滤波的组合,可以使增益图谱在50 nm(1485-1535 nm)带宽内,增益平坦度达到±0.6dB以内.由三个长周期光纤光栅级联滤波组合,可以使增益图谱在49 nm(1490-1539 nm)带宽内,增益平坦度达到0.5 dB, 55 nm(1485-1540 nm)带宽内,增益平坦度达到1 dB.这对扩大长周期光纤光栅增益平坦滤波器的运用范围,扩大单泵浦S波段光纤拉曼放大器的有效增益带宽有着积极的意义.     

级联型长周期光纤光栅传输谱的研究

采用级联多个长周期光纤光栅的方法有效拓宽了长周期光纤光栅反射谱带宽.分析了LPFG透射谱的谐振峰的定位问题,并通过级联多段周期相同但长度和微扰不同的LPFG来形成一个级联型的长周期光纤光栅,然后通过使用传输矩阵的方法,对级联光栅的传输谱进行了数值分析.经过分析发现,如果适当地调整级联型长周期光纤光栅的各个参数如级联的段数以及各段的长度和微扰等值,则所得到的这个级联型长周期光栅的透射谱的有效带宽将显著地增大,其透射谱的形状也会发生显著改变.

Abstract：

An improved method of cascaded long-period fiber gratings (LPFGs) is proposed, which can effectively broaden the resonant spectrum bandwidth of LPFGs. The positioning of the resonance peak of transmission spectra in LPFGs was analyzed. A cascaded LPFG was obtained by cascading various LPFGs with the same period but different length and index perturbation. Transfer matrix method was used to numerically calculate its transmission spectrum, and it is found that the effective bandwidth will become wider and the shapes will correspondingly change if the related parameters in cascaded LPFG, such as the number of segments and length and index perturbations of each segment, are adjusted correctly.     

Synthesis of long-period fiber gratings with the inverted erbium gain spectrum using the multiport lattice filter model

This paper proposes an accurate modeling technique of concatenated long-period fiber gratings (LPFGs). The proposed technique is then applied to the synthesis of LPFGs for the erbium gain equalization using both the simulated annealing and the steepest descent minimization technique. A piecewise-uniform LPFG is theoretically synthesized according to the inverted gain spectrum of a commercially available erbium-doped fiber amplifier (EDFA) over the range of 1525-1570 nm. Sensitivity analysis of the designed structure is presented by Monte Carlo simulation with regard to the manufactured amplitude mask. To verify a synthesizing technique using the proposed modeling, the piecewise-uniform LPFGs for gain flattening of EDFA are fabricated and their spectra are also presented experimentally.     

Multiwavelength Raman fiber-ring laser based on tunable cascaded long-period fiber gratings

Multiwavelength Raman fiber lasers using intracavity tunable cascaded long-period fiber gratings (LPFGs) are discussed. The application of the cascaded LPFGs as a multichannel fiber filter for the multiple-wavelength generation is proposed and experimentally demonstrated. The characteristics of multiwavelength fiber-ring lasers can be controlled by changing the physical parameters of cascaded LPFGs such as the separation distance between the gratings, grating length, and number of gratings. The multiwavelength Raman fiber-ring laser with nine wavelength-division-multiplexing channels with 100-GHz spacing and 19 channels with 50-GHz spacing has been achieved by varying the physical parameters of cascaded LPFGs.     

三包层级联长周期光栅的传输谱特性

运用传输矩阵法对三包层级联长周期光纤光栅(LPFG)的传输谱特性进行分析,讨论了级联处光纤的长度、位置以及薄膜参数等对级联光栅传输谱的影响,并对级联长周期光栅和相移长周期光栅的传输谱进行了比较.结果表明两者传输谱在级联光纤长度较小或级联位置靠近光栅两端时具有较强的一致性;而在级联处光纤较长并且级联位置在中间时,两者表现出截然不同的特性,这一点和两包层级联光栅一致.另外,薄膜参数可以更灵活地调节传输谱衰减峰位置和峰值损耗的大小.     

Reduction of transmission spectrum shift of long-period fibergratings by a UV-preexposure method

We examined the photosensitivity and stability in an ultraviolet (UV)-preexposure method that locks the photosensitivity of refractive index by hydrogen loading in the fabrication of long-period fiber gratings (LPFGs). Photosensitivity and stability comparisons are made between the UV-preexposure method, a typical hydrogen-loading method, and a UV-exposure method without hydrogen loading. The UV-preexposure method can enhance the photosensitivity to induce effective refractive index modulations up to 1.6×10^-4, which is sufficient for fabricating LPFGs in a practical manner under the hydrogen-loading condition at a relatively low pressure of 2.9 MPa. The sensitivity is preserved in terms of the length of time at least over 10 000 h. The spectrum changes after the completion of the LPFG writing are more stable than under the typical hydrogen loading. Therefore, the proposed UV-preexposure method is one of the most useful techniques for fabricating precise and stable fiber gratings, because there are no free hydrogen molecules in the fiber when the fiber gratings are written     

Strain Characteristics of CO2-Laser-Carved Long Period Fiber Gratings

Unique strain characteristics of long period fiber gratings (LPFG) fabricated by a focused CO₂ laser beam carving periodic grooves on the fiber are investigated for the first time to our knowledge. Resonant wavelength, transmission attenuation, and polarization dependent loss (PDL) of the CO₂-laser-carved LPFG are found to depend strongly on the tensile strain applied, and their strain sensitivities are dependent on the depth of grooves and/or the initial refractive index modulation. The average strain sensitivity of resonant wavelength for LPFG is increased by 229 times and is up to -102.89 nm/mepsiv by means of carving periodic grooves on the fiber. When a stretching force is applied to the LPFG, the resonant wavelength can "blue" shift by -11.84 nm, the absolute value of peak transmission attenuation and the maximum PDL can be increased by 25.913 and 26.535 dB, respectively. The CO₂-laser-carved LPFG combines the features of the three types of LPFGs reported previously, i.e, the CO ₂-laser-induced LPFGs without physical deformation, the corrugated LPFGs fabricated by hydrofluoric acid etching, and the microbend-induced LPFGs. The mechanisms of refractive index modulation in the CO₂-laser-carved LPFGs under tensile strain are rather complicated and may be regarded as a combination of the stress-relaxation-, the groove-, the strain-, and the microbend-induced refractive index perturbations     

Multiwavelength fiber sources based on double-pass superfluorescentfiber sources

We demonstrate a new technique to generate a high-power multiwavelength fiber source (MWFS) by inserting cascaded long-period fiber gratings (LPFGs) in double-pass Er-doped fiber (EDF) superfluorescent fiber sources. 20 channels with extinction ratios larger than 10 dB can be obtained between 1525-1560 nm with appropriate EDF lengths. Though the total output power decreases due to the insertion of the cascaded LPFGs, the power in each channel for the proposed MWFS is larger than that obtained by using the spectrum slicing technique because of power redistribution. We also demonstrate that by using another LPFG in such a source to reduce the power variation among the desired channels. The wavelength stability of the source is shown to be determined by the cascaded LPFCs rather than by the EDF     

薄包层长周期光纤光栅的研究

报道了在薄包层光纤上用高频CO2激光脉冲写入的长周期光纤光栅(LPFG),并分析了该类薄包层LPFG横截面折射率的分布.结合LPFG的腐蚀实验,通过传输谱图的比较发现:较先写入光栅后腐蚀光纤包层的方法,先腐蚀光纤包层后写入光栅的方法更能有效地调整谐振波长.进一步研究发现薄包层LPFG对环境折射率的敏感度更高.