基于啁啾光纤光栅的色散管理

本文通过数值仿真对基于啁啾光纤光栅的单信道的色散管理进行了研究，并在1500km的10Gb/s单信道传输系统中进行了实验验证.本文还通过分析啁啾光纤光栅引入的信道间随机时延差对交叉相位调制的抑制作用，发现了基于啁啾光纤光栅的多信道系统的色散管理的新的特点. 关键词： 光纤通信 色散补偿 啁啾光纤光栅     

优化调制格式实现2560 km低代价无误码传输

在单级调制器产生非归零码(NRZ)基础上,分析了利用双级调制器产生归零码(RZ)以及载波抑制归零码(CSRZ)的方法和特点。对非归零码,归零码和载波抑制归零码在以掺铒光纤放大器(EDFA)为单一的功率放大、以啁啾光纤光栅(CFBG)为色散补偿器的10Gb/s系统中的传输性能进行了计算机仿真并比较这三种调制码型的传输特性。同时在实际的2560km G.652光纤链路上利用上述三种调制格式以点对点形式进行了8×10Gb/s传输实验,通过适当控制线路的功率分配以及合理安排系统的色散补偿,实现了三种调制格式的无电中继条件下的零误码传输。计算机仿真和实际实验结果进一步表明,载波抑制归零码的采用有利于优化系统的传输性能,降低传输代价,载波抑制归零码在上述配置的实际传输系统中无误码传输2560km功率代价仅为2.5dB。     

40 Gb/s窄脉冲预啁啾归零码色散管理传输

通过数值计算的方法，对40Gb/s带有预啁啾和无啁啾的窄脉冲归零码在色散管理光纤链路中的传输特性进行了比较，计算发现，脉冲的预啁啾会与光纤的高阶色散共同作用，并增强高阶色散对传输的影响，只有在高阶色散得到很好补偿以后，窄脉冲带啁啾的归零码（CRZ）的传输特性才会好于无啁啾的归零码。对不同的入射脉冲条件和传输链路参量存在相应的预啁啾最佳值。     

利用均匀相位掩模板制作线性啁啾光纤光栅

理论上分析并从实验上验证了一种利用均匀相位掩模板写入啁啾光纤光栅的方法:将光纤弯曲,由于光纤离掩模板的距离不同从而使光纤光栅的周期轴向渐变,由此产生啁啾。分析了这种啁啾光纤光栅的谱特性和时延特性,同时也分析了由于光纤离掩模板的距离不同而引起的折射率调制变化给光纤光栅特性带来的影响。设计了一种石英曲面,利用其使光纤按照弯曲函数进行弯曲,然后进行紫外曝光制成了线性的啁啾光纤光栅。实验中制作的啁啾光纤光栅色散值为-1102 ps/nm,纹波为17ps。通过改变弯曲函数就可以实现利用一块均匀相位掩模板制作不同啁啾量的啁啾光纤光栅的目的,降低了啁啾光纤光栅的制作成本。     

基于啁啾光纤光栅的色散补偿器在超长距离密集波分复用系统中的应用

对啁啾光纤光栅在超长距离多波长传输系统中应用时所存在的问题进行了研究，主要分析了多波长级联的啁啾光纤光栅之间的串扰，并提出了利用相干长度法来抑制不同信道间啁啾光纤光栅串扰的方法.在此基础之上实现了基于光纤光栅色散补偿的8×10Gbit/s,1500km G.652光纤上的传输系统. 关键词： 光纤通信 色散补偿 啁啾光纤光栅     

16×10Gb/s啁啾光纤光栅色散补偿系统性能研究

运用啁啾光纤光栅法对在G.652光纤传输的16×10 Gb/s信号实现色散补偿数值模拟和研究,分析了入纤光功率、色散斜率以及啁啾光纤光栅色散补偿带宽对系统误码率的影响,结论是:入纤光功率在8～16 dBm之间时系统的性能较好;啁啾光纤光栅的色散补偿带宽对系统的影响较大;光纤的色散斜率对系统误码率有一定的影响.     

基于啁啾光纤光栅的掺Yb3+光纤激光器

啁啾光纤光栅可用于光纤色散补偿及脉冲压缩。该文从光纤光栅的耦合模方程出发，对中心波长为1053nm的啁啾光纤光栅进行了研究，数值分析了啁啾光纤光栅长度、耦合函数、啁啾系数、切趾技术等因素对啁啾光栅反射率、时延特性、色散特性、压缩特性的影响，并将结论应用于掺镱超短脉冲光纤激光器的设计，提出基于啁啾光纤光栅的全光纤环形腔连接方案。与其它非全光纤结构光纤激光器相比，这种结构具有更小的损耗和更高的效率。     

拉锥型啁啾光纤光栅滤波器的研究

本文主要对拉锥型啁啾光纤光栅滤波器进行详细的理论分析和实验研究. 结合传输矩阵法, 谐振理论和耦合模理论, 深入细致地分析了啁啾光纤光栅自身参数 (光栅长度, 折射率调制幅度, 啁啾系数), 拉锥参数和锥区损耗对拉锥型啁啾光纤光栅滤波器透射谱的影响, 并研究拉锥对啁啾光纤光栅各波长反射率影响. 在此基础之上进行相应的数值仿真及实验验证, 数值仿真与实验结果基本一致. 关键词： 光栅拉锥 啁啾光栅 传输矩阵法 滤波器     

连续线性温度梯度场对啁啾脉冲放大系统中啁啾光纤光栅的色散调节效应

利用啁啾光纤光栅的温度可调谐效应,提出了一种新型的色散补偿方法.该方法使啁啾光纤光栅处于一个连续的线性温度梯度场中,通过调节啁啾光纤光栅两端的温度差,改变其色散量,实现在以啁啾光纤光栅为展宽器和以体光栅为压缩器的超快激光系统中对输出脉宽的连续精密调节,并通过实验验证这一方法的可行性.实验结果表明:沿着啁啾光纤光栅应用连续的温度梯度场,当温差从0℃到50℃变化时,可以连续地调节啁啾光纤光栅的色散参数.展宽器和压缩器之间的色散失配可以通过调节线性温度场的温度梯度得到补偿,避免了繁琐的脉宽优化步骤.本文是以啁啾体光栅为压缩器的光纤啁啾脉冲放大系统中通过调节施加在展宽器上的连续线性温度场的梯度,实现对啁啾脉冲系统中的色散失配进行精密调制的技术方案.     

薄包层啁啾长周期光纤光栅的色散补偿

为了提高啁啾长周期光纤光栅(LPFG)光纤通信的色散补偿能力,提出了利用薄包层啁啾LPFG进行包散补偿的方法.首先介绍了根据传输信号确定啁啾LPFG的啁啾系数、光栅长度等参数的方法.然后利用上述方法设计了对光纤中传输的中心波长为1550 nm,带宽为0.2nm的信号进行色散补偿的薄包层啁啾LPFG.利用耦合模理论及传输矩阵法计算了约1m长的此种啁啾LPFG的色散,结果表明可以补偿该光信号通过46 km光纤所产生的色散.进一步分析了切趾函数、啁啾系数、交叉耦合系数等参数对薄包层啁啾LPFG色散的影响.     

Performance comparison for RZ-DPSK signal in DCF-based and CFBG-based dispersive transmission system

The impact of the phase noise induced by self-phase modulation and intrachannel nonlinear effect for return-to-zero differential phase-shift keying (RZ-DPSK) in long haul 40 Gb/s transmission systems where dispersion is compensated by chirped fiber Bragg grating (CFBG) is analyzed and numerical evaluated, and it is compared with what is derived from the conventional DCF-based phase-modulated system. Our work also provides a clear physical picture of how the transmission performance is affected by CFBG, which is instructive for further research on CFBG compensated phase-modulated formats.     

Influence of group-delay ripple on timing jitter induced by SPM and IXPM in systems with dispersion compensated by CFBG

An analytical expression was proposed to analyze the influence of group-delay ripple (GDR) on timing jitter induced by self-phase modulation (SPM) and intra-channel cross-phase modulation (IXPM) in pseudolinear transmission systems when dispersion was compensated by chirped fiber Bragg grating (CFBG).Effects of ripple amplitude, period, and phase on timing jitter were discussed by theoretical and numerical analysis in detail. The results show that the influence of GDR on timing jitter changes linearly with the amplitude of GDR and whether it decreases or increases the timing jitter relies on the ripple period and ripple phase. Timing jitter induced by SPM and IXPM could be suppressed totally by adjusting the relative phase between the center frequency of the pulse and the ripples.     

光纤光栅时延波动对传输系统性能的影响

对啁啾光栅的时延波动进行了详细的分析，建立了时延波动的简易模型和光栅的滤波函数。大量实验和计算表明，光纤光栅的时延纹波周期在0．01～0．1nm之间，并且在光纤光栅的阻带内，时延纹波周期随波长增大而逐渐增大。利用薛定谔方程对时延波动对系统的影响进行了仿真，得出了时延波动对系统的影响不仅与波动大小有关，而且还与时延波动周期有关，并用实验进行了验证。     

利用遗传算法优化线性啁啾光栅性能

针对制作町用于40 Gb/s全光色散补偿的宽带线性啁啾光栅时出现带内群时延纹波波动较大等问题.提出了一种通过设计和改变切趾函数的参量来优化线性啁啾光栅的新方法.该方法实现简单.只需根据需要设计具有不同滚降特性的切趾函数,同时利用遗传箅法来优化切趾参量.结合传输矩阵法经过200代获得了低带内时延纹波的线性啁啾光栅.数值结果验证了采取非对称分段切趾法在保持反射谱宽和平坦性的同时可以抑制带内群时延纹波的优越性.利用该方法制作了反射谱工作带宽为1.06 nm、时延纹波不超过45.60 ps、可用于大容量密集波分复用系统(DWDM)色散补偿的线性啁啾光纤光栅.     

Group-delay ripple correction in chirped fiber Bragg gratings

Group-delay ripple (GDR) introduced by systematic and random errors in chirped fiber Bragg grating fabrication is the most significant impediment to application of these devices in optical communication systems. We suggest and demonstrate a novel iterative procedure for GDR correction by subsequent UV exposure by use of a simple solution of the inverse problem for the coupled-wave equation. Our method is partly based but does not fully rely on the accuracy of this solution. In the experiment we achieved substantial reduction of the low-frequency group-delay ripple, from +/- 15 to +/- 2 ps, which resulted in dramatic improvement of the optical signal-to-noise-ratio system penalty, from 7 to less than 1 dB, for a chirped fiber Bragg grating used as a dispersion compensator in a 40-Gbit/s carrier-suppressed return-to-zero system.     

Fabrication of high quality chirped fiber Bragg grating by establishing strain gradient

To fabricate chirped fiber Bragg grating (CFBG) with high reflectivity and accurately controlled chirp profile with low cost, we develop the CFBG fabrication technique based on strain gradient: fabricating CFBG using fabricated fiber Bragg grating (FBG) by establishing strain gradient along the length of grating. We theoretically analyze the form of such CFBGs, and study the characteristics of gratings using piecewise-uniform approach. It is shown that increasing UV-induced index change or the length of the grating or both are the efficient ways to obtain high quality CFBG with high reflectivity and good reflection spectrum. The dispersion of this grating is decided by and varies inversely with the slope of the strain gradient along the length of the grating, not decided by UV-induced index change or by the length of grating. One can control the dispersion and the chirp profile by adjusting the slope of the strain gradient. Based on the theoretical analysis, we have fabricated CFBG whose reflectivity is maintained at 100% in a large range of strain gradients.     

An all-fibre multi-parameter sensor for composite structures based on a chirped fibre Bragg grating

An all-fibre multi-parameter sensor for composite structures based on a chirped optical fibre Bragg grating (CFBG) has been studied theoretically and experimentally. The principle of multi-parameters sensing with a single CFBG is based on that the centre wavelength and the FWHM (full width at half maximum) in the reflection spectrum of a CFBG vary linearly with the temperature and/or the axial stress. A wavelength matched optical fibre long period grating (LPG) and another wavelength matched reference CFBG (CFBGR) have been used to interrogate the signal of the sensor CFBG (CFBGS). The temperature and strain of the composite structure have been monitored real-time with one CFBG as a single sensor head. The temperature resolution of 0.12°C and the strain resolution of 1.1μ? for a composite structure have been realized in experiments. The experiment results agree well with the theoretical analyses.     

国产啁啾布拉格光纤光栅在飞秒激光系统中的应用

利用自行研制的啁啾布拉格光纤光栅(CFBG)刻写系统完成CFBG样品制作,成功应用于光纤锁模振荡器和啁啾脉冲放大(CPA)系统中。振荡器可输出19.4 nm带宽、18 mW平均功率激光,并可压缩至143 fs,经时域展宽、功率放大、时域压缩后,脉冲宽度可至264 fs。实验结果初步证明了国产CFBG在飞秒激光系统应用的可行性。     

Novel Optical Delay Line for Optical Coherence Tomography System

A novel all-fiber optical delay line for an advanced optical coherence tomography (OCT) system is proposed. Using the distributed reflectance characteristic of a chirped fiber Bragg grating (CFBG), the optical delay can be obtained without leaving the fiber that forms the system. The proposed delay line consists of a pair of identical CFBGs. The gratings are cascaded in reverse order to cancel the inherent wavelength dependency of CFBGs. Tunable optical delay is obtained by applying small strain on one of the CFBGs through an attached piezo actuator. The small displacement induced by the piezo actuator is amplified by a factor of up to 100 due to the distributed reflectance characteristic of the CFBGs. This principle and characteristics of the proposed optical delay line are analyzed in detail.     

Pulse-width tunable multi-channel NRZ-to-RZ conversion with duplicate output

We demonstrate multi-channel non-return-to-zero (NRZ) to return-to-zero (RZ) conversions with tunable output pulse-width and single-to-dual function, using a phase modulator and an array waveguide grating (AWG), which acts both detuned multi-channel filter and demultiplexer. Four-channel NRZ signals after transmission can be converted to eight-channel RZ signals with timing jitter and extinction ratio improvement. Further transmission and bit error ratio (BER) measurements for the converted RZ signal show a good performance compared with conventional one.