Photonic Generation of Chirped Microwave Pulses Using Superimposed Chirped Fiber Bragg Gratings

A novel approach to generating linearly chirped microwave pulses in the optical domain based on spectral shaping and linear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed system, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is spectrum-shaped by an optical filter that consists of two superimposed chirped fiber Bragg gratings (SI-CFBGs) with different chirp rates. The SI-CFBGs form a Fabry-Perot cavity with a cavity length linearly dependent on the resonance wavelength, thus a spectral response with an increased or decreased free spectral range is generated. A chirped microwave pulse with the pulse shape identical to the shaped spectrum is obtained at the output of a high-speed photodetector thanks to the frequency-to-time mapping in a dispersive device. The proposed technique is experimentally demonstrated, a linearly chirped microwave pulse with a central frequency of 15 GHz and a chirp rate of 0.0217 GHz/ps is experimentally generated.     

三角形谱啁啾光纤光栅在光栅传感系统中的应用

利用三角形谱啁啾光纤布拉格光栅（T-CFBG）的反射和时延特性,提出了一种新的基于相位检测的FBG解调方案。该方案由光强来确定传感器光栅反射波长的相位延迟角范围,由相位检测来确定在该范围的相位延迟角大小,两者结合给卅传感光栅的反射波长,因此具有更高精度和更大波长检测范围。实验制作了宽带宽具有三角形反射谱的T-CFBG,并对其用于传感解调予以了模拟分析。     

折射率啁啾调制光纤光栅性能研究

从耦合模理论出发,详细推导出平均折射率调制啁啾系数、初始位置平均折射率调制系数和啁啾光纤Bragg光栅(FBG)周期啁啾系数之间的对应关系,并进行了数值模拟和实验研究。结果表明：通过对平均折射率调制系数进行啁啾控制,可以利用一块相位掩膜版制作出不同色散补偿量的FBG。     

重叠写入啁啾光纤光栅型滤波器的研究进展

高性能的波分复用器是密集波分复用系统的核心器件之一,重叠写入啁啾光纤光栅型带通滤波器充分发挥了光纤光栅优良的波长选择特点,是一种低成本的新型全光纤波分复用器件.综合评述了各种不同结构的重叠写入啁啾光纤光栅型滤波器的工作原理、基本特点及其应用.     

啁啾布喇格光栅F-P传感器的优化设计

根据实际需要优化设计了一种基于啁啾布喇格光栅的本征型光纤法珀(F-P)传感器。对构成光纤F-P传感器的啁啾布喇格光栅的参数进行了优化设计,得到优化设计的光纤F-P传感器反射谱。实际制作了按照参数设计的啁啾布喇格光栅F-P传感器并进行了应变实验,实验结果表明,该方法设计的传感器应变测量精度高达±8με。     

Tunable All-Optical Microwave Filters Based on Fiber Loop and Chirped Fiber Bragg Gratings

All-optical microwave filters are important parts of fiber-optic microwave/millimeter wave processing systems. In this paper, two novel passive tunable all-optical microwave filters based on fiber loop and chirped fiber Bragg gratings (CFBGs) are demonstrated, where the frequency response of the both filters can be continuously tuned by adjusting the wavelength of the input light. The required free spectral range (FSR) of the filters can be obtained by carefully controlling the length of fiber loop and the positions of the CFBGs in the fiber loop. Experimental results prove the feasibility of the proposed filtering structures.     

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.     

Fabrication and Analysis of Chirped Fiber Bragg Gratings by Thermal Diffusion

We propose and demonstrate a fabrication method of chirped fiber gratings by a thermal diffusion process. The method could suggest a direction for a simple and cost‐effective implementation of chirped fiber grating‐based devices.     

不同切趾比例下啁啾光纤光栅的特性研究

对称切趾啁啾光纤光栅能够抑制反射旁瓣、平滑群时延曲线,但反射谱带宽利用率低.与对称切趾相比,非对称切趾光栅在保持群时延曲线基本不变的前提下,反射谱3 dB带宽提高了64.08%,同时群时延纹波振荡也得到了一定的抑制.利用升余弦函数对光栅的长波长端和短波长端进行了不同比例的切趾仿真,发现长波长端30%切趾、短波长端20%切趾能够有效地提高光栅的反射带宽,同时可将群时延纹波压低在±2 ps之内.     

平方型啁啾光纤光栅高阶色散补偿器的理论设计

对周期保持恒定,而其有效折射率大小随其长度按平方律变化的啁啾光 纤光栅提出了一个理论设计模型,从该模型出发,得到了光栅有效折射率分布函数与光栅色散量之间的关系,最后将该模型的计算结果与传输矩阵法的计算机模拟结果进行了比较,二者基本上一致。     

Bragg光纤光栅

详细阐述了光纤光栅的原理以及光纤光栅在光纤通信、光纤激光器、光纤放大器、光纤滤波器、光纤传感器和高速光纤通信系统中色散补偿方面的重要应用，并对线性啁啾Ｂｒａｇｇ光栅色散补偿技术进行了全面分析。     

Design of High-Channel-Count Multichannel Fiber Bragg Gratings Based on a Largely Chirped Structure

We propose a novel technique to design a high-channel-count, multichannel fiber Bragg grating (FBG) based on a largely chirped structure. The minimization of refractive-index modulation has been widely discussed in the previously demonstrated multichannel grating designs. The complexity of the grating structure, however, is also important from the point of view of practical fabrication. In this paper, the degree of grating complexity (DGC) is defined. We show that the DGC of a multichannel grating can be significantly reduced by designing a grating with a largely chirped structure. A detailed grating design process based on this technique is discussed, by which four multichannel gratings are designed and numerically studied, for applications such as periodic and nonperiodic spectral filtering, chromatic dispersion compensation and dispersion slope compensation. The proposed theory and examples show that different gratings with high-channel-count and multichannel responses can be designed and fabricated using a single commercially available phase mask, and all the gratings can be realized by a conventional FBG fabrication facility since the gratings have a low DGC with low index modulation.      

光栅参数对线性啁啾光纤光栅偏振特性的影响

研究了单模线性啁啾光纤光栅的偏振相关损耗特性。运用耦合模理论和传输矩阵分析法推出了反射光的偏振相关损耗,并模拟了光栅的反射谱和偏振相关损耗随光栅参数和双折射量的变化曲线。模拟显示双折射值的变化对啁啾光栅偏振相关损耗的影响非常显著, 尤其是在带边比较陡峭时。啁啾光栅的偏振相关损耗也受光栅的啁啾系数和调制深度的影响。这表明线性啁啾光栅的偏振相关损耗不光依赖光栅双折射量,还依赖其啁啾系数等其他参数。实验结果与理论模拟基本吻合。     

啁啾光纤光栅EDFA增益平坦滤波器的设计与制作

采用啁啾相位掩膜板和程控扫描曝光技术,在经过载氢增敏处理的普通单模光纤上制作出可以用于掺铒光纤放大器(EDFA)增益谱平坦化的啁啾光纤布喇格光栅(CFBG)型增益平坦滤波器(GFF),运用数值解析的方法得到曝光量曲线,并将之分解成曝光频率、曝光功率密度、光斑尺寸和光纤移动速度的曝光函数,按照曝光函数进行程控扫描曝光从而精确控制光栅的反射率.对制作的CFBG进行退火老化处理和温度补偿及保护封装,封装后GFF的温漂系数在-20～ 70 ℃内变化小于1 pm/℃,经平坦后的EDFA增益谱在30 nm带宽范围内,不平坦度＜±0.3 dB.根据不同的EDFA的ASE谱,可程控给出不同的曝光函数,以制作具有不同反射谱的CFBG型GFF.     

基于超结构光纤光栅的双边带编/解码器

分析了基于等效相移(EPS)技术的超结构光纤光栅(SSFBG)相位编/解码器的原理及特点,提出并实现了一种双边带编/解码器.该编/解码器在不改变光纤光栅长度的前提下,实现了+1级和+3级编解码谱的级联,并很好地继承了等效相移技术所具有的设计灵活、制作精度低和与波分复用(WDM)系统兼容能力强等诸多的优点.理论及实测数据仿真结果均表明,在光脉冲源匹配最佳的前提下,双边带编/解码器较传统等效相移编/解码器而言,使得基于该光纤光栅相位编/解码器的窄带相干光码分多址(OCDMA)系统的编解码性能提高了3 dB,通过对比分析得到其本质原因在于双边带编/解码器结构提高了其单位长度内携带的相位信息量.     

紫外写入移相光纤光栅

从耦合模理论出发分析了光致折变移相光纤光栅的基本特性,报道了采用紫外辐照制备移相光纤光栅的实验结果。     

啁啾光纤光栅法布里-珀罗传感器波分频分复用

实现了一种具有大容量复用潜力的啁啾光纤光栅(CFBG)法布里-珀罗(F-P)传感器复用系统。该传感器复用系统的建立基于波分频分复用方法,即中心波长相同的传感器利用腔长不同空间频率不同来实现空间频分的复用,采用不同中心波长的传感器阵列与频分复用方法相结合就可实现波分频分复用。描述了该光纤光栅法布里-珀罗传感器复用系统的结构、原理及应变实验结果。实验结果表明,该方法可以大大地提高光纤光栅法布里-珀罗应变传感器的复用能力,理论上可复用数百个光纤光栅法布里-珀罗应变传感器;实验中应变测量精度好于±10με,可满足大部分实际应用的要求。     

取样啁啾光纤光栅的时延抖动抑制

研究了用于多通道色散补偿器的取样啁啾光纤光栅时延抖动问题,分析了产生时延抖动的腔效应及抑制时延抖动的切趾技术,分析、比较了切趾前后取样啁啾光纤光栅的时延抖动情况,研究结果表明:取样啁啾光纤光栅的时延抖动与其折射率包络调制形成的外腔效应有关,与取样调制形成的多腔效应无关,对取样啁啾光纤光栅进行包络切趾能够有效地抑制时延抖动.     

Figure-of-Merit of Dispersion Compensating Devices Based on Chirped Bragg Gratings

A promising technology for chromatic dispersion compensation in fiber communication networks are modules based on chirped Bragg gratings (DCM). Imperfections in the Bragg grating, however, give rise to a noise-like ripple in the phase characteristics of the DCM, which causes extra system penalty. In this paper, we derive an analytic formula that calculates an upper bound of the eye-opening penalty caused by a DCM in a transmission link with no optical amplifiers and with a chirp free NRZ optical signal. The primary use of this formula is as a quickly calculated quality measure (figure-of-merit) of the phase ripple characteristics of DCMs. It is shown that the difference in as given by the formula and obtained from simulation calculations is considerable smaller than given by other formulas found in the literature.     

Formation Technologies of Fiber Bragg Gratings

The principle of fiber Bragg gratings(FBG)is briefly described.The formation technologies of FBG are systematically given and analyzed.In addition,the experiment is described in detail,e.g.,the phase mask method is used to write directly the period Bragg gratings into the Ge-doped single mode fiber with KrF excimer UV laser.The results of experiment are also presented and analyzed.