A hybrid high-gain double-pass erbium-doped fiber amplifier with dispersion compensation feedback loop

A new double-pass erbium-doped fiber amplifier (DP-EDFA) using chirped fiber Bragg grating (CFBG) is reported here showing a gain of 53.4 dB and noise figure (NF) of 5.36 dB. The proposed amplifier at the same time provides dispersion compensation through the use of CFBG.     

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     

Arbitrary chirped fiber Bragg gratings on application of filtering for optical communications

This paper presents an analysis of how to obtain narrow transmission band in the centre of the spectrum of the arbitrary chirped fiber Bragg grating (ACFBG). Grating chirp coefficient and refractive index profile are the critical parameters in contributing to performance of fiber Bragg grating. The reflection spectra and transmission band were analyzed with different refractive index profile. Apodization techniques are used to get optimized reflection spectra. The simulations are based on solving coupled mode equations by transfer matrix method that describes the interaction of guided modes.     

优化二元相位取样光纤布喇格光栅及对色散和色散斜率补偿的应用

利用粒子群算法对二元相位取样光栅的周期相位调制进行优化设计，在此基础上提出了基于二元相位取样光纤布喇格光栅的色散和色散斜率补偿技术.通过光栅周期啁啾可以调整每个信道的带宽，色散量由子光栅长度决定，调整取样函数的啁啾系数可以改变色散斜率，因此可以设计出用于波分复用系统的多信道色散补偿器件.     

Cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in dispersion compensated WDM transmission systems

The basic mechanism of cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in a periodically dispersion compensated transmission line has been investigated. Ordinary differential equations have been derived using variational analysis to estimate the phase fluctuation and the analytical result is verified by numerical simulations based on split-step Fourier method. We therefore explore the impact of different dispersion compensation maps on phase fluctuation for 10 Gb/s and 40 Gb/s WDM transmission systems. The effects of initial pulse spacing between channels, channel spacing and residual dispersion on phase shift have been studied. We find that cross-phase modulation induced phase fluctuation can be mitigated by proper adjustment of channel spacing and/or residual dispersion.     

A novel method of optimal apodization selection for chirped fiber Bragg gratings

Apodization is a crucial technology for improving the dispersion performance of fiber Bragg gratings (FBGs). In this paper, we focus on how to select an optimal apodization for chirped fiber Bragg gratings and demonstrate a novel apodization selection method capable of choosing the optimal apodization based on the relationship between the bandwidth change and variation in average group delay ripple (GDR). Compared with current approaches, the novel method can select an optimal apodization profile and parameter for FBGs easily and accurately. Two numerical experiments are used to demonstrate the advantages of this method, one exhibits the different performances of five different apodization profiles, the other evaluates the influence of FBG parameters such as grating length, period, chirp, and index change on the apodization performance.     

Analysis of dispersion compensation by chirped fiber grating in directly and externally modulated CATV systems

The dispersion compensation effect of the chirped fiber grating (CFG) is analyzed theoretically, and analytic expressions are derived for composite second-order (CSO) distortion in analog modulated sub-carrier multiplexed (AM-SCM) cable television (CATV) systems with externally and directly modulated transmitters. Simulations are given for the two kinds of modulations and for standard single mode fiber and non-zero dispersion shift fiber (NZDSF) systems. The results show that CFG could be used as a dispersion compensator in directly modulated systems, but its dispersion coefficient should be adjusted much more precisely than the externally modulated system. The requirements for the NZDSF system could be loosened much. It is proposed that directly modulated source may be used as a transmitter in CATV systems combined with tunable CFG dispersion compensator being adjusted precisely, which may be more cost-effective than externally modulation technology.     

折射率调制深度误差对切趾啁啾光纤光栅特性的影响

从耦合模方程出发,用一种矩阵方法分析了折射率调制深度误差对切趾啁啾布拉格光纤光栅传输特性的影响.结果表明:折射率调制深度误差的分布频率越高,光栅传输特性受到的危害越小;误差平均幅值越高,光栅传输特性的劣化程度越大.因此,在光栅的制作过程中,应注意避免和减小高幅值误差,并注意减少低空间频率分布的误差.     

Chirped Bragg光纤光栅的优化设计与优化指数

根据线性ChirpedBragg光纤光栅的一般原理 ,探讨了不同啁啾系数 ,准高斯耦合函数对Bragg反射光栅的反射率及色散补偿特性的响应。结果表明 :增大啁啾系数以及选取适当的准高斯耦合函数 ,在保证反射率较大的情况下 ,能有效地改善色散补偿特性。通过引入微波领域的“优化指数”这一概念 ,量化了色散补偿器的补偿能力。     

光栅不理想特性对不同调制码型的光传输系统的影响

分析了光纤光栅不理想特性的产生机理，对以啁啾光纤光栅为色散补偿器的10Gb/s光传输系统中，啁啾光纤光栅的不理想特性包括群时延纹波、反射纹波及光栅通带带宽对采用归零码(RZ)、非归零码(NRZ)以及载波抑制归零码(CSRZ)三种调制格式传输系统性能的影响进行了详细的数值分析和比较. 同时进行了基于光纤光栅色散补偿的1500km无误码传输实验，通过对啁啾光纤光栅由于不理想特性的差别而导致对实际传输系统不同信道性能影响的比较，进一步验证了仿真分析的正确性. 关键词： 光传输 啁啾光纤光栅 不理想特性 调制码型     

基于激光拍频实现啁啾光纤光栅色散的测量

以啁啾光纤光栅为例,研究了激光拍频的产生机制,并建立对啁啾光纤光栅色散的测量模型.详细阐述了系统结构和测量原理,并对测量结果和理论值进行了分析与比较,结果一致性较好.在频谱分析仪分辨率为2.5kHz的情况下,色散测量准确度可以达到0.1ps,啁啾光纤光栅色散的实际测量也证实了该系统的可行性,系统相对简单,测量准确度高,可为色散测量提供参考.     

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     

三角形谱啁啾光纤光栅的制备及其在光纤无线单边带调制系统中的应用

本文涉及一种三角形谱啁啾光纤光栅的制备以及其在光纤无线(radio over fiber,RoF)单边带调制系统中的应用.基于相位掩模法和变速度折射率调制,实验制备了底部变化范围1.9 nm、透射深度0—15 dB的三角形谱啁啾光纤Bragg光栅,利用其透射谱具有较大负向斜边,研究了其在RoF系统中的应用.方案仅使用一个三角形谱光纤光栅,实现了以下两种功能: 1)双边带调制信号到单边带调制信号转换; 2)降低信号的载波边带比(carrier-to-sideband ratio,CSR),提高接收灵敏度.并 关键词： 光纤通信 微波光子 光纤布拉格光栅 单边带调制     

A novel method to suppress the crosstalk of the system with dispersion compensated by fiber gratings

In this article, a novel method is proposed to suppress the nonlinear crosstalk of the system with dispersion compensated by several multi-wavelength fiber gratings. Random time delay is induced only between the adjacent channels to suppress the cross modulation effects and the four wave mixing effects simultaneously. Using this method, the system performance could be improved effectively.     

Remotely pumped hybrid double-pass L-band optical amplifier utilizing chirped fiber Bragg

This paper reported an investigation of remotely pumped double pass L-band amplifier with dispersion compensation technique. The proposed design used chirped fiber Bragg grating (CFBG) to reflect the amplified signal back into the active medium, compensate the effect of fiber dispersion and block the recycled forward amplified spontaneous emission (ASE) and the residual 1480 nm pump power. The characterization of the design was done experimentally. The gain is 37.5 dB and noise figure is 4 dB with best BER of 10⁻⁵² is achieved when the EDF is placed 150 km away from the transmitter and 48 km before the receiver terminal.     

A phase-shifted linearly chirped fiber Bragg grating with tunable bandwidth

We demonstrate a new method to broaden and adjust the transmission bandwidth of a phase-shifted linearly chirped fiber Bragg grating (PS-LCFBG) after its fabrication. A movable thermal head is used to heat the PS-LCFBG at a small contact point. The original ultra-narrow transmission bandwidth of the PS-LCFBG can be broadened due to both the presence of the passband peak caused by the thermally-induced temporary phase shift and the passband caused by the thermally-induced local Bragg wavelength shift. The transmission bandwidth of the new passband peak can be adjusted by changing the position of the thermal head. The transmission bandwidth of the PS-LCFBG can be broadened from <10 pm to 0.16 nm, and can be tuned from 0.16 to 1.05 nm.     

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.     

Lineshape and polarization mode dispersion of waves diffracted by apodized and chirped fiber Bragg gratings in reflection

The amplitude and phase of a light wave propagating in an apodized and chirped Bragg grating is given by the superposition of two orthogonal coupled wave functions that are the solution of a non-linear Riccati equation. An analytical solution, in the form of an integral transform, that predicts the amplitude, phase, and intensity profile of the light diffracted by grating, in which the local Bragg wavelength is asymmetric, and the forward and counter propagating modes are non-degenerate is presented. For even apodization and odd chirp the lineshape has an asymmetrical Gaussian form the result of mixing of the real and imaginary components of the apodized grating wave function. The effect of chirping is to shift the resonance wavelength, increase the grating bandwidth and polarization mode dispersion. The dependence of linewidth and dispersion on parameters that alter apodization and chirp after fabrication, is also discussed.     

Code synchronization based on lumped time-delay compensation scheme with a linearly chirped fiber Bragg grating in all-optical analog-to-digital conversion

We propose a novel lumped time-delay compensation scheme for all-optical analog-to-digital conversion based on soliton self-frequency shift and optical interconnection techniques. A linearly chirped fiber Bragg grating is optimally designed and used to compensate for the entire time-delays of the quantized pulses precisely. Simulation results show that the compensated coding pulses are well synchronized with a time difference less than 3.3 ps, which can support a maximum sampling rate of 151.52 GSa/s. The proposed scheme can efficiently reduce the structure complexity and cost of all-optical analog-to-digital conversion compared to the previous schemes with multiple optical time-delay lines.     

Timing jitter induced by intrachannel interactions in optical fiber communication systems using CFG as dispersion compensator

In this paper, a theoretical model is proposed for the analysis of timing jitter induced by intrachannel interactions in optical fiber communication systems using chirped fiber grating (CFG) as dispersion compensator. And for the first time, the impact of group-delay ripple (GDR) on timing jitter is taken into account in detail, theoretically and numerically. Results show that the GDR may increase or decrease the timing jitter of certain pair of adjacent pulses, deciding by the ripple parameters. The maximum influence will be obtained when ripple period is about 2/5 of the input pulse width. In practical systems, the GDR enhance the timing jitter for some adjacent pulses while reduce it for some other adjacent pulses, depending on the pulse pattern and the GDR parameters. In our simulation, the GDR guarantees a 3.04 ps increase of the standard deviation of the timing jitter.