π相移光纤光栅对超声波致非均匀应变场的传感特性

π相移光纤光栅用于水中超声传感时,超声波沿光纤轴向入射和垂直光纤入射时的传感波形及幅度显著不同。针对这一现象,本文建立了基于光学传递矩阵的光纤光栅声传感理论模型,计算了超声波分别沿轴向和沿垂直方向入射时π相移光纤光栅中的非均匀应变场分布,进而分析了光谱偏移,揭示了两种入射角度下π相移光纤光栅的传感特性与声传播导致的应变场分布相关,并通过实验进行了验证。结果表明,两种入射角度产生的不同的非均匀应变场分布对π相移光纤光栅的传感特性影响明显。超声波垂直入射时的传感波形和幅度均优于轴向入射,且π相移处对传感有显著作用。当入射位置远离π相移处时,垂直入射的响应也明显降低。本研究可为π相移光纤光栅超声传感的机理分析提供参考。     

Fiber Bragg grating sensor for petroleum hydrocarbon leak detection

A novel type of fiber optic Bragg grating sensor for petroleum hydrocarbon leak detection is presented. The sensor structure includes attached to the fiber a polymer member, which reversibly expands in hydrocarbon presence and strains the fiber section with the Bragg grating inside. A shift of the grating Bragg wavelength due to fiber strain is more than 2 nm for 20-min gasoline influence, which significantly exceeds a shift due to possible environmental temperature variation.     

光纤布拉格光栅型全光纤声光调制器的特性研究

将光纤光栅的傅里叶模式耦合理论应用于光纤布拉格光栅型全光纤声光调制器的理论分析中. 与现有的分析方法相比, 该模型算法简单、 求解容易, 能够快速有效地获得调制器的传输特性. 基于该模型, 理论分析了超声波频率及声致应变幅度对调制器特性的影响. 仿真结果表明, 该调制器反射谱的主反射峰与次反射峰的波长间隔与超声波频率成正比, 反射峰的反射率随着声致应变幅度的改变而发生周期性的变化. 另外, 在同一声致应变幅度下, 低频超声波调制的光栅反射中存在更多的次反射, 光栅反射能量的周期性变化更加明显. 实验中, 使用频率为885.5 kHz的超声波对光纤布拉格光栅进行调制. 实验结果与仿真结果相一致.     

Simultaneous Measurement of Temperature and Refractive Index of Liquid Using Cladding-Etched Double-Core Fiber Bragg Grating

Abstract

This study proposed and demonstrated a fiber Bragg grating sensor for simultaneous detection of the temperature and refractive index of a liquid. The fiber Bragg grating is composed of three index layers: an inner core, an outer core, and a cladding. The cladding was etched for evanescent wave coupling between the outer core mode and an external liquid. The Bragg wavelength of the inner core mode is used for obtaining temperature data, while the refractive index for the liquid was determined by using the difference between the Bragg wavelength of the inner core mode and that of outer core mode.     

Wavelength-spacing-tunable multichannel filter incorporating a sampled chirped fiber Bragg grating based on a symmetrical chirp-tuning technique without center wavelength shift

We propose and experimentally demonstrate a simple and flexible scheme for a wavelength-spacing-tunable multichannel filter exploiting a sampled chirped fiber Bragg grating based on a symmetrical modification of the chirp ratio. Symmetrical bending along a sampled chirped fiber Bragg grating attached to a flexible cantilever beam induces a variation of the chirp ratio and a reflection chirp bandwidth of the grating without a center wavelength shift. Accordingly, the wavelength spacing of a sampled chirped fiber Bragg grating is continuously controlled by the reflection chirp bandwidth variation of the grating corresponding to the bending direction, which allows for realization of an effective wavelength-spacing-tunable multichannel filter. Based on the proposed technique, we achieve the continuous tunability of the wavelength spacing in a range from 1.51 to 6.11 nm, depending on the bending direction of the cantilever beam.     

光纤光栅的温度补偿

提出了一种简单、小型的光纤光栅温度补偿器件，将光纤光栅粘贴在具有负热膨胀系数的材料上，实现了光纤光栅的温度补偿。该器件在-20～44℃温度范围内光栅波长变化0.08m，是未补偿光纤光栅的1／8。     

非线性二次曝光法制作三角形光纤Bragg光栅

提出了一种利用非线性二次曝光技术制作三角形光纤Bragg光栅的新方法.该方法只使用普通Bragg位相模板,采用两次曝光技术,通过控制光纤光栅的本地谐振波长和反射率,达到控制光纤光栅谱形的目的.第一次直接对光纤曝光,用来控制光纤光栅谐振波长;第二次通过位相模板曝光,用来控制光纤光栅的反射率.考虑到光敏光纤感光特性曲线的多项e负指数变化规律,按照"分步写入光纤光栅设计软件"进行曝光分布设计,利用"分步曝光光纤光栅写入系统"进行曝光控制,使用信息产业部第46研究所生产的DCS-01型光敏光纤,得到了线性范围1.24 nm、反射率为0～64%的三角形光纤Bragg光栅.三角形光纤Bragg光栅作为光纤光栅传感解调器件,在光纤传感领域具有重要应用价值.     

光纤光栅反射谱对非均匀应变的展宽响应

光纤布拉格光栅在非均匀应力场作用下，其纤芯折射率及光栅栅距都将产生非均匀变化，本文给出了光纤光栅与非均匀应变场的相互作用模型，建立了反射谱对非均匀应变的响应关系。并给出了线性应力场的实验结果。     

聚合物封装的高灵敏度光纤光栅温度传感器及其低温特性

介绍了一种新型的光纤光栅温度传感器。这种光纤光栅温度传感器使用了特殊的工艺将光纤布拉格光栅封装于一种热膨胀系数较大的有机聚合物基底中 ,使得传感器的温度灵敏性比裸光纤光栅提高了 12 .3倍 ,其温度灵敏度系数KT 达到 82 .6 9× 10 -6/℃。在 - 80～ 0℃的低温度范围内 ,对这种新型光纤光栅温度传感器的反射谱进行了测量。研究了这种新型光纤光栅温度传感器的低温特性 ,并与裸光纤光栅和铝基封装的光纤光栅进行了比较 ,结果表明这种新型的光纤光栅温度传感器具有很好的低温响应特性。     

光子晶体理论应用于光纤布拉格光栅的研究

将光纤布拉格光栅近似为一维光子晶体，研究光栅的能带结构和光学传输特性。利用平面波展开法对光子晶体进行理论研究，将研究方法移植到光纤布拉格光栅上，并对其进行数值分析，得到光栅的传输特性。研究表明，光栅反射谱有多个反射峰，峰值中心频率是基频的整数倍，而且峰值处存在光子带隙，反射峰带宽对应光子带隙宽度，中心频率和带宽随光栅长度、高介电常量材料占空比、调制深度而变化。结果与传统的耦合模理论一致。     

Continuous recording of ultrasonic velocity by laser Bragg diffraction

A method for improving the measuring accuracy of ultrasonic wave velocities in a liquid sample is given. This utilizes the Bragg diffraction angle. Continuous recording of the ultrasonic velocity for a continuously varying sample temperature is also described. An analogue of the Czerny-Turner mount in the grating monochromater is used for the determination of the angle of diffraction. A frequency modulated ultrasonic wave produces an oscillating photo-electric signal from a diffracted light component incident on a photo-multiplier tube. Using this signal, the peak point in the intensity distribution of the component is determined with extremely high accuracy. Applying the phase-sensitively detected output of this signal to a servo motor which drives the angle of a plane mirror (replacing the grating in the Czerny-Turner mount), gives automatic tracking of the angle of diffraction. This in turn allows the possibility of continuous recording of the velocity dispersion as a function of sample temperature.     

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.     

Tunable and reconfigurable microwave filter by use of a Bragg-grating-based acousto-optic superlattice modulator

We present an all-optical novel configuration for implementing multitap transversal filters by use of a broadband source sliced by fiber Bragg grating arrays generated by propagating an acoustic wave along a strong uniform fiber Bragg grating. The tunability and reconfigurability of the microwave filter are demonstrated.     

Fiber Bragg grating interrogator using edge filtering technique with microbend loss error mitigation

This paper presents an edge filtering technique based interrogator for fiber Bragg grating sensors with microbend attenuation compensation system. The interrogator uses reference fiber along with the fiber in which the grating is inscribed to mitigate the effect of microbend attenuation in determining the Bragg wavelength of the sensor.     

40Gb/s光时分复用传输光纤光栅补偿色散研究

用精密扫描掩模法写入宽阻带啁啾光纤光栅,掩模板背面两端各10％长度处镀有按4阶高斯函数透过率的膜,写入的啁啾光栅的时延纹波最大值为20ps。为减少写入光纤光栅的偏振模色散,研制了新的低偏振模色散光纤光栅补偿写入法。采用补偿写入法前的平均微分群时延为9．1406 ps;采用补偿写入法后的平均微分群时延为0．1521 ps。并利用低偏振模色散光纤光栅对40Gb／s光时分复用系统在普通G．652光纤传输122km的色散进行了补偿实验,功率代价为1．5dB。     

Nondestructive imaging of a type I optical fiber Bragg grating

Nondestructive images of refractive-index variation within a type I fiber Bragg grating have been recorded by the differential interference contrast imaging technique. The images reveal detailed structure within the fiber core that is consistent with the formation of Talbot planes in the diffraction pattern behind the phase mask that had been used to fabricate the grating.     

Stable Dual-Wavelength Oscillation of an Er-Doped Fiber Ring Laser at Room Temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23 nm and mutually orthogonal polarization stages was achieved by utilizing the polarization hole-burning effect. An amplitude variation of less than 0.7 dB over an 80 s period was obtained for both wavelengths.     

Stable Dual-Wavelength Oscillation of an Er-Doped Fiber Ring Laser at Room Temperature

We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23 nm and mutually orthogonal polarization stages was achieved by utilizing the polarization hole-burning effect. An amplitude variation of less than 0.7 dB over an 80 s period was obtained for both wavelengths.     

Dynamic strain monitoring by wavelength locking between two fiber Bragg gratings fiber sensing system

We demonstrated a fiber sensing system using the method of wavelength locking of two identical fibers Bragg gratings (FBG) to interrogate the wavelength shift by directly measuring the intensity of the reflection from the sensing Bragg grating. The light source of the fiber sensing system is an EDFA fiber ring laser pumped by a 980 nm laser diode and a narrow bandwidth fiber Bragg grating for the filter of the ring laser resonator. The wavelength shift is converted to the intensity deviation of the reflection from the sensing FBG under strain variation, and is able to achieve real-time sensing of the dynamic strain sensing in civil engineering. The characteristics and key factors to maintain stability of the dynamic strain sensing system are discussed.     

高双折射光子晶体光纤中均匀布拉格光栅的特性

研究了具有高双折射的光子晶体光纤(HB PCF)中均匀布拉格光栅(FBG)的光谱特性。利用紧凑的超格子模型,对光子晶体光纤的传输特性进行分析,研究正向传输和反向传输的模式之间的耦合规律,从而研究写入光子晶体光纤中的均匀布拉格光栅的特性。首先给出具有C6v对称性的零双折射光子晶体光纤中光纤布拉格光栅的布拉格波长λB随光纤结构参量的变化规律;然后分析一种高双折射光子晶体光纤中的光纤布拉格光栅的光谱特性,高双折射使两个不同偏振态的反射峰分开较大;最后分析了一种常用的双模双折射光子晶体光纤中光纤布拉格光栅的光谱特性,LP01模和LPe11模的两个偏振态对应的反射谱都由于高双折射而分开。