相移光纤光栅透射光谱特性研究

基于模耦合理论,利用传输矩阵法系统地分析了相移光纤光栅的透射谱特点.结果表明,相移光栅可在透射谱阻带中打开线宽极窄的一个或多个透射窗口,通过对相移光栅在不同相移量、不同位置、不同相移个数、不同kL值时的传输光谱特性进行分析研究,得到了影响其透射率以及其线宽和位置的主要因素.这些结果将对相移光纤光栅在滤波、波分复用、光纤激光器和光纤光栅传感系统的实际制作及应用有重要的指导意义.     

基于相移布喇格光纤光栅的折射率传感实验研究

利用图解法求解光纤特征方程,获得腐蚀过程和传感过程中光纤光栅的光谱特性,设计了光纤光栅的部分腐蚀方案,采用氢氟酸溶液腐蚀制作相移布喇格光纤光栅。对光纤光栅进行部分腐蚀,将形成相移光纤光栅。根据相移光纤光栅的特性,讨论了利用反射光光强解调的方式,该方式具有结构简单且对温度不敏感的优点。     

三层亚波长光栅结构的透射特性

设计了一种具有三层结构的亚波长金属光栅,采用时域有限差分（FDTD）法对所设计的三层光栅结构进行仿真计算．与单层金属光栅相比,这种三层的光栅结构具有更好的滤波效果,其透射光谱中峰值可达77％,且能很好地抑制高波段的透射率．分析了各几何参数对所设计的光栅结构透射特性的影响,尤其是对透射光谱中0值位置的影响．结果表明0值位置主要受光栅缝宽、介质层高度和介质折射率的影响,而与金属层光栅的高度无关．其影响规律为偏振滤波器的设计提供了参考．     

分布式光纤拉曼放大器研制的进展

对分布式光纤拉曼放大器研究的历史、基本原理、优化设计以及现状和进展进行了讨论.对S波段的色散补偿型分布式光纤拉曼放大器以及采用光纤拉曼激光器作为抽运源,在前向抽运和后向抽运条件下,对5kmDCF-50kmG652光纤色散补偿型分布式光纤拉曼放大器增益光谱和噪声谱进行了研究.设计和制作了光纤光栅的增益平坦滤波器,取得了较好的增益平坦效果.FRA-1型分布式光纤拉曼放大器在校园网进行了应用试验,取得了较好的试验效果.     

L波段掺铒光纤放大器增益钳制及提高特性研究

报道了一种新型980nm激光二极管（LD）泵浦高增益的掺铒光纤放大器（EDFA）．通过加入中心波长为1550nm光纤光栅（FBG）可以明显提高增益，并分析了增益钳制的原理．实验得到其增益比无FBG结构EDFA提高8dB，并得到了小信号输入时增益25dB的有效钳制．     

利用光纤光栅测量加速度的方法研究

提出了一种基于长周期光纤光栅(LPFG)弯曲特性的加速度传感方法.传感系统采用悬臂梁结构,LPFG粘贴于悬臂梁的上表面,将悬臂梁的自由端受力产生的梁体弯曲转变成长周期曲率的变化,来监测光栅谐振谱的幅值和波长变化.并在系统中加入布拉格光栅(FBG),利用其反射特性记录固定波长处长周期光栅谐振谱的变化,然后将其转化为加速度...     

光纤拉曼放大器现状的研究

拉曼放大器以其能放大任意波长、有较宽的增益谱、较低的等效噪声指数和较好的增益平坦度等,使其成为理想的光纤放大器。它是通过受激拉曼效应实现光放大,同时存在前向泵浦、后向泵浦和双向泵浦三种结构。并能与EDFA进行配合使用,得到性能更好的光放大器。为光纤通讯传输能力升级、光纤放大方案优化的最佳选择。但同时它也存在泵浦功率要求高、增益均衡和偏振相关增益等问题还有待解决。     

基于级联光栅温度补偿的溶液浓度测量研究

为解决长周期光纤光栅(LPG)折射率测量时的温度交叉敏感问题,利用布喇格光纤光栅(FBG)对环境折射率不敏感的特点,将其与长周期光纤光栅(LPG)级联,构成具有温度补偿的折射率传感方案。实验结果表明：随着温度的变化级联光栅的两个透射谐振波长都有线性变化,而改变溶液折射率时只有一个透射谐振波长改变。因此,可以利用级联光栅对折射率和温度双参量进行同时测量,补偿因温度变化产生的测量误差。     

光纤光栅应用于梳状滤波器和光分插复用器(OADM)的研究

研究了光纤光栅在梳状滤波器和光分插复用器(OADM)中的应用特性。基于传输矩阵法对Sinc取样光栅反射谱进行分析,分析了取样光栅长度、折射率调制深度和取样周期等光栅参数对Sinc取样光栅反射谱的影响规律。根据各参数对Sinc取样光栅反射谱的影响规律构造了4种反射率高、反射峰间隔均匀及谱宽稳定的Sinc取样光栅梳状滤波器,为梳状滤波器的设计与制作提供了新思路、新技术。用OptiSystem软件对光纤Bragg光栅型光分插复用器进行了仿真研究。研究表明,经过光纤光栅光分插复用器后,下载和除了下载的光谱峰值基本为-4dBm,下载的功率也基本是均衡的。     

基于长周期地震动记录的SDOF体系能量谱探讨

为分析长周期地震动作用下结构的能量反应谱及其影响因素,本文从1985年墨西哥8.1级地震、1999年台湾集集7.6级地震和2003年日本十胜冲8.0级地震记录库中,选取了36条具有可靠长周期信息的强震记录,以此作为输入,采用能量谱面积归一的方法,首先对单自由度体系的弹性能量谱进行了分析,建议了适用于长周期地震动的简化三段式输入能量谱。在此基础上,讨论了延性系数、阻尼比对弹塑性能量谱的影响;给出了通过调整长周期地震动弹性能量谱参数来确定长周期地震动弹塑性能量谱的方法,并与长周期地震动弹塑性能量谱的拟合结果进行了比较,验证了上述方法的可行性。最后,通过分析长周期地震动累积滞回耗能与弹塑性输入能量之间的比值关系,给出了长周期地震动累积滞回耗能比值谱的计算公式。     

A comparison of wavelength dependent polarization dependent lossmeasurements in fiber gratings

We have measured wavelength dependent Polarization Dependent Loss (PDL) in chirped fiber Bragg gratings for dispersion compensation, grating filters for wavelength add/drop multiplexing and long period gratings for EDFA gain flattening. The PDL is measured in devices used in reflection and in transmission by applying the Jones matrix method, the Mueller matrix method and the polarization scanning method. A comparison of the experimental results and an analysis of the sources of errors are presented     

Mechanism and characteristics of asymmetrically phase-shifted corrugated long-period fiber grating fabricated by burning fiber coating and etching cladding technology

In this letter, a new phase-shifted corrugated long-period fiber grating (PS-CLPFG) manufacture method is proposed based on burning the fiber coating and etching cladding method. We analyze the effect of phase amplitude, locations, and numbers on transmission spectrum. A proof-of-concept experiment is performed, and a good agreement of theoretical analysis and experiment results is obtained. In addition, a relative easier method to control band-pass and band-rejection characteristics is reached. Moreover, the obvious sidelobes in the passband of multiple-π PS-CLPFG can be effectively suppressed.     

Refractometric sensor based on a phase-shifted long-period fiber grating

A refractometric sensor based on a phase-shifted long-period fiber grating written by electric-arc discharges is presented. Transmission and reflective configurations for refractive index measurements are studied. It is observed that the reflective topology permits better performance compared with the transmission one, which is the approach normally utilized in the context of long-period fiber sensing. The resolution achieved in the measurement of refractive index enables the application of this sensing head structure in demanding situations, such as the measurement of the level of salinity of water.     

Reconstruction of long-period fiber gratings from their core-to-core transmission function

In order to reconstruct the structure of a long-period grating, both the complex core-to-core transmission function and the complex core-to-cladding transmission function should be known. However, in practice, only the core-to-core transmission function of the grating can be measured. We demonstrate theoretically the reconstruction of long-period gratings from only the core-to-core transmission function. The reconstruction is performed by extracting the complex core-to-cladding transmission function of the grating from its core-to-core transmission function. Generally, the extraction is not unique; however, we show that by writing an additional grating in cascade to the interrogated grating, a unique reconstruction can be obtained. In weak long-period gratings, only the amplitude of the core-to-core transmission function is needed to reconstruct the grating. The results of our work can enable the experimental reconstruction of long-period gratings from their transmission function as well as the development of novel distributed sensors.     

Coherent tunnelling adiabatic passage in optical fibres using superimposed long-period fiber gratings

Abstract

In this paper, we present the optical analogue of stimulated Raman adiabatic passage (STIRAP) technique for three level atomic system in optical fibre geometry. Considering linearly polarized modes of an optical fibre, it is shown that using a pair of superimposed long-period gratings with peak refractive index perturbation varying spatially along the propagation axis, light can be transferred adiabatically from one core mode to another core mode via an intermediate cladding mode which itself does not get appreciably excited; thus acting like a dark mode. We compare the transmission spectrum of superimposed long-period gratings involved in adiabatic transfer with the transmission spectrum of conventional long-period grating. The analogue output is further analysed for its tolerance to the changes in the ambient refractive index, temperature and other fabrication parameters.     

All-fiber dynamic gain equalizer based on a twisted long-period grating written by high-frequency CO2 laser pulses

A novel dynamic gain equalizer for flattening Er-doped fiber amplifiers based on a twisted long-period fiber grating (LPFG) induced by high-frequency CO(2) laser pulses is reported for the first time to our knowledge. Experimental results show that its transverse-load sensitivity is up to 0.34 dB/(g.mm(-1)), while the twist ratio of the twisted LPFG is approximately 20 rad/m, which is 7 times higher than that of a torsion-free LPFG. In addition, it is found that the strong orientation dependence of the transverse-load sensitivity of the torsion-free LPFG reported previously has been weakened considerably. Therefore such a dynamic gain equalizer based on the unique transverse-load characteristics of the twisted LPFG provides a much larger adjustable range and makes packaging of the gain equalizer much easier. A demonstration has been carried out to flatten an Er-doped fiber amplifier to +/-0.5 dB over a 32 nm bandwidth.     

Transfer-matrix method based on a discrete coupling model for analyzing uniform and nonuniform codirectional fiber grating couplers

A simple and efficient transfer-matrix method based on a discrete coupling model is presented to analyze uniform and nonuniform fiber grating couplers between copropagating core and cladding modes. Uniform and piecewise-uniform long-period gratings were fabricated by a point-by-point arc discharge technique. Their measured transmission spectra were compared with the transmission spectra calculated by the presented method.     

Transfer-matrix approach based on modal analysis for modeling corrugated long-period fiber gratings

A transfer-matrix method is developed for modeling a corrugated long-period fiber grating. Cladding-mode resonance in such a corrugated structure can be controlled by the applied tensile stress based on the photoelastic effect. A first-order vectorial perturbation expansion is used to derive the mode fields of the two basic regions under the strain-induced index perturbation. Because the etched cladding radius is much smaller than the unetched radius, the effect of the corrugated structure on cladding modes cannot be treated as a small perturbation. Thus the conventional coupled-mode theory is inadequate for the modeling of such a structure. Based on a self-consistent mode-matching technique, mode coupling within the corrugated structure can be described by a set of transfer matrices. We apply the formulation to the calculation of the transmission spectra of a corrugated long-period grating and compare the calculated with the experimental results. The transfer-matrix approach is found to account well for the features of the transmission spectra of the corrugated long-period gratings.     

Ultra-widely tunable long-period holey-fiber grating by the use of mechanical pressure

We report an ultra-widely tunable long-period holey-fiber grating, which combines the wide-range single-mode behavior and transverse strain sensitivity of the holey fibers with the advantages of mechanically induced long-period fiber gratings. We obtain a versatile widely tunable long-period holey-fiber grating with attractive transmission spectral characteristics for optical communications, fiber-based amplifiers, and lasers. The mechanically induced long-period holey-fiber grating shows a continuous tuning range over 500 nm, more than 12 dB depth notches with less than 0.75 dB out-of-band losses, and bandwidth control from 10 to 40 nm.     

Real-time wavelength reuse based on Bragg trans-reflection for dynamic reference frequency and data transfer in Datacom

ABSTRACT

We experimentally demonstrate the first VCSEL-based all-optical wavelength reuse technique with reconfigurable fibre Bragg grating add and drop multiplexer. EDFA gain saturation and Bragg trans-reflection effect on a single FBG are respectively, adopted for full-duplex reference frequency and data transfer. A 1550 nm energy-efficient VCSEL is modulated with 1.7?GHz clock signal and transferred downstream over 26.6?km fibre OLT attain a phase noise stability of ?54.01 dBc/Hz at 10?kHz offset frequency. A saturated EDFA is exploited to optically reduce the peak-to-peak voltage of the incoming downstream RF, allowing for wavelength reuse with 10?Gbps upstream data. A 1.57 dB transmission penalty is incurred over the transmission fibre. An all-passive OADM is developed exploiting Bragg trans-reflection at 1549.45?nm. The reflected wavelength is routed over another 24.7?km fibre network attaining an extinction ratio of 6.1?dB and a SNR of 5.8?dB. This work provides an all-optical technique for routing and spectral management in flexible networks.