Bragg gratings in multimode and few-mode optical fibers

Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 μm is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 μm in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed     

温度及应力变化对光纤光栅布喇格波长的影响

着重讨论温度对光纤光栅的稳定性和反射谱的影响。分析了温度变化引起光纤光栅布喇格波长漂移的机理,为提高光纤光栅稳定性,对布喇格波长的温度漂移进行应变补偿。     

基于光纤光栅F-P腔的一种新颖传感系统的理论研究

在对光纤光栅F-P腔的反射光谱特性进行理论分析的基础上,提出了一种基于弱反射率、长腔长光纤光栅F-P腔的新颖的传感系统,分析了两种适用于该系统的有效解调方法。讨论了系统参数对传感器性能的影响和系统的优化设计原则。理论研究表明,这种新颖的传感系统可实现温度的精确测量,具有很高的可靠性。     

Transmission Characteristics of Sagnac Loop with Fiber Bragg Grating

A transmission filter composed of a Sagnac loop and a fiber Bragg grating is studied in detail.It is found that the transmission spectrum of this filter is the splitting of the reflection spectrum of the fiber Bragg gratings.The filter can behave as a multiple-passband filter when the fiber Bragg grating is strong and as a single-band filter when the fiber Bragg grating is weak.Very narrow transmission filters can be obtained in this way.     

正十边形光子晶体光纤布拉格光栅传感特性的研究

研究了正十边形对称结构光子晶体光纤布拉格光栅(PCFBG)特性,分析了不同空气孔层数以及不同占空比对布拉格光栅反射谱的影响.在此基础上,对正十边形光子晶体光纤光栅的传感特性进行了研究.研究表明:随着温度的增加,该光纤光栅的反射谱谐振波长明显向长波方向偏移;随着应力的改变,光纤光栅的反射谱谐振波长变化趋势不明显.该光栅具有对温度敏感,对应变不敏感的特点.这种空气孔排列为正十边形对称结构的光子晶体光纤光栅有望应用在光子晶体光纤光栅的传感领域中.     

An optical sensing system for the concentration of methane based on fiber Bragg gratings

Based on a special catalyst and fiber Bragg gratings (FBGs), an optical sensing system is proposed to measure the concen- tration of methane. The temperature of the catalyst rises rapidly as the concentration of methane increases, and hence it can be detected by an FBG-type sensor through monitoring the wavelength shift of the reflection spectrum. The experimental results show the good performances of our system, such as the high resolution and temperature stability.     

Investigation on reflection spectr a of chirped and phase-shifted fiber Bragg gratings

The characteristics of chirped and phase-shifted fiber Bragg gratings have been investigated by the use of transfer matrix formulation. While the characteristics of a chirped and phase-shifted fiber Bragg grating are the same as those of non- chirped one in some important aspects, both the reflection and transmission windows of a chirped and phase-shifted fiber Bragg grating can be broadened in a wide range. Therefore, chirped and phase-shifted fiber Bragg gratings will have applications in WDM or DWDM optical communication systems. The work in this paper can be used to design the new devices based on chirped and phase-shifted fiber Bragg gratings.     

带宽为O.84 nm色散补偿100 km以上线性啁啾光纤Bragg光栅的研制

本文用传输矩阵法分析了啁啾Ｂｒａｇｇ光纤光栅的反射谱特性及时延特性,同时给出了用１４２ｍｍ长相位掩模板和扩束技术研制的色散补偿线性啁啾Ｂｒａｇｇ光纤光栅的反射谱特性及传输实验结果．实验研制的线性啁啾Ｂｒａｇｇ光纤光栅样品带宽为０．５６~０．８４ｎｍ,可实现对普通光纤色散补偿１００ｋｍ以上．     

光纤光栅反射波长移动研究

提出并实验了一种探测光纤光栅波长移动的新方法。该方法用一组与各个传感光纤光栅的参数对应相同的光纤光栅作为滤波元件,用抖动倍频的方法跟踪传感光纤光栅的反射光谱的峰值点,同时采用高分辨率的光栅尺作为系统的读出设备,彻底消除了压电陶瓷的非线性性及滞后性带来的误差,从而得到高精度的测量结果。     

光纤光栅反射波长移动研究

提出并实验了一种探测光纤光栅波长移动的新方法.该方法用一组与各个传感光纤光栅的参数对应相同的光纤光栅作为滤波元件,用抖动倍频的方法跟踪传感光纤光栅的反射光谱的峰值点,同时采用高分辨率的光栅尺作为系统的读出设备,彻底消除了压电陶瓷的非线性性及滞后性带来的误差,从而得到高精度的测量结果.     

Characteristics of Bragg Gratings in All-Solid Photonic Bandgap Fiber

We report on fiber Bragg gratings in all-solid photonie bandgap fiber that was composed of a triangular array of high-index Ge-doped rods in pure silica background with fluorine-doped index-depressed layer surrounding the Ge-doped rod. Fiber Bragg gratings were photowritten with 193 nm ArF excimer laser and characterized for their response to strain, temperature, bending, and torsion. These gratings couple light from the forward core mode to not only backward core mode but also backward rod modes. This results in multiple resonance peaks in the reflection spectrum. All resonance wavelengths exhibited the same temperature and strain response with coefficient similar to that of Bragg gratings in standard single-mode fiber. The strength of the resonance peaks corresponding to the backward rod modes showed high sensitivity to bending and torsion.     

用光功率计测量应力变化

主要用实验数据简要叙述光纤Bragg光栅(FBG)的反射谱功率与应力的变化成线性关系,并介绍一种用光功率计测量应力变化的装置,它能够通过测量FBG的反射谱功率较准确地测出应力。     

弱非周期性相位取样啁啾光栅的优化方法

取样光栅可以同时对多个信道进行滤波或色散补偿，所以在波分复用(WDM)系统中有广泛的应用，其中周期相位取样光栅是一种很有前途的设计方法，但周期取样的方法会使取样光栅的所有信道具有相同的色散补偿能力。提出设计弱非周期性相位取样啁啾光栅的优化方法，通过引入一组与信道色散补偿量有关的啁啾控制参数，可使不同信道的色散补偿量存在差异。运用该方法设计出弱非周期的取样光栅后，可用传输矩阵法来模拟该光栅的复反射谱，结果显示通过调整啁啾控制参数，可方便地控制不同信道的色散补偿能力，从而能实现对光纤链路色散与色散斜率的同时补偿，而且取样函数的幅度值的起伏则被完全消除。     

折射率非线性调制的双重光纤光栅特性

利用耦合模理论 ,系统分析了双重光纤光栅在折射率深度调制或非线性调制情况下的光谱特性。结果发现 ,在折射率非线性调制情况下 ,双重光纤光栅具有规则的多波长反射特性 ,同时 ,其反射光谱中的二次谐波也变得非常强 ,因此 ,它是一种实现多通道波分复用器、分插复用器及多波长激光器等的潜在技术。     

L波段掺铒光纤放大器的增益平坦滤波器设计

EDFA的增益平坦化是WDM系统中的重要问题．用成本低、插损小的光纤光栅实现该功能是一项有吸引力的方案，采用剥层法设计了基于啁啾光栅的增益平坦滤波器。基于时间因果律的剥层算法将光纤光栅看成一个分离的模型，由一系列长度为△的复反射器所组成，每个反射器的后端耦合系数都可由它的前端耦合系数递归地求出，从而能快速、精确地反演出光栅的耦合系数函数。啁啾光栅的目标反射谱由理想的增益平坦滤波器透射谱获得，利用与反射谱群时延有关的常数α可控制光栅的长度，α取值为0．0024cm。时，对应的光栅长度为3．5cm。用剥层法反演出耦合系数函数后，又通过解Riccati方程模拟了合成光栅的透射谱。数值模拟结果显示理想透射谱与合成光栅透射谱之间的峰峰值误差小于0．1dB．并且在工作带宽范围内，透射谱群时延的变化量小于0．6ps，表明该滤波器对系统没有额外的色散影响。     

白光干涉法测量光纤布喇格光栅反射谱

为了实现光纤布喇格光栅反射谱的低成本测量,采用白光干涉技术搭建了一套结构简单的反射谱测量装置,利用该装置进行了实验,对所采集的干涉信号进行了数据处理,获得了光纤布喇格光栅的反射谱,光谱分辨率达到3pm,并对所测反射谱的光谱分辨率进行了理论分析.结果表明,利用该装置测得的反射谱具有良好的光谱分辨率,通过增加测量量程可以进一步提高光谱分辨率.     

Fabrication of High Quality Broadband Type IIA Chirped Fiber Bragg Gratings

Chirped fiber Bragg gratings have found many applications in optical communication and sensing systems. High quality filters based on chirped fiber Bragg gratings with reflection bandwidth of 2.6 and 32nm and high reflectivity are demonstrated experimentally with 2 and 4cm long phase masks, respectively. These filters with flat reflection band and high reflectivity are achieved by writing type IIA chirped Bragg gratings.     

一种计算光纤布拉格光栅谱特性的新方法

使用微波网络模型对光在光栅中的传播过程进行建模,给出了在光栅微波网络模型中的光场传输矩阵,并阐明了这种传输矩阵与传统分段光栅模型中的传输矩阵的关系;结合改进的有效折射率分析方法,提出了一种计算光纤光栅谱特性的新方法.该方法对应的MT矩阵很简洁且数值模拟的精度很高.     

New structure for multipoint temperature-independent strain sensing system employing optical power detection scheme

A new structure of multipoint temperature-independent strain sensing system with dual fiber Bragg gratings as sensors is proposed. An optical switch is employed to bridge between the detection site and multiple far ends where fiber Bragg grating sensors are located. A voltage divider is used in the proposed optical power detection scheme to resolve the measurement instability caused by the power fluctuation of the light source in a long term and the nonflat spectrum of the light source. This new detection scheme is demonstrated to have a measurement linearity and resolution of ±0.25% and 0.4 μS, respectively.     

采用高斯波形近似的干涉型光纤光栅法布里-珀罗传感系统的可见度分析

两光纤布拉格光栅(FBG)的光谱失配会使其构成的光纤法布里-珀罗(FFP)传感系统的干涉条纹可见度降低,从而影响探测性能。基于弱反射率FBG反射谱的高斯波形近似,推导了光谱失配引起的可见度变化表示式。实验测量了干涉型FFP传感系统的可见度曲线,对理论分析进行了验证。研究表明,反射谱旁瓣对光谱失配引起的可见度变化有重要影响。从光谱匹配的角度,采用高斯切趾光栅的FFP传感系统优于普通均匀光栅的系统。