粒子群优化算法用于光纤布拉格光栅综合问题的研究

提出了一种新的光纤光栅综合技术,将光纤光栅的传输矩阵法与粒子群优化算法(PSO)结合起来,得到了一种光纤光栅综合问题的全新方法。通过调整粒子群优化算法的相关参数,我们可以得到适合需要的反射谱。与其它光栅综合算法相比,该方法具有简单,收敛速度快等优点,同时该技术具有普遍性,还可以用于其它类似的综合问题。     

Synthesis method based on genetic algorithm for designing EDFA gain flattening LPFGs having phase-shifted effect

We propose a new synthesis method based on the genetic algorithm for the design of erbium-doped fiber amplifier gain flattening filters. Our genetic algorithm iterates starting with the long period fiber gratings structure constructed by inserting the phase-shifted long period fiber gratings in the middle of the structure, for the more accurately matched spectrum to the desired erbium-doped fiber amplifier gain flattening filter. To verify a synthesizing technique using the proposed algorithm, we have synthesized the long period fiber gratings structures according to the inverted gain spectrum of a commercially available erbium-doped fiber amplifier over the entire 1525–1570 nm range, theoretically. We have also obtained the synthesized structure was more accurate than the structure without phase-shifted section.     

Optimization of Phase Shifted Long-Period Fiber Gratings for Multiband Rejection Filters

A new approach for designing multiband rejection filters is proposed based on the optimization of a periodically phase-shifted long period fiber grating (LPG). The validity of the method is demonstrated by performing simulations for the typical cases. It is shown that using the proposed synthesis method, spectral position, and bandwidth of the each reflection band can be controlled by varying the grating length and the phase shifting period. In addition, a desired number of rejection bands within the transmission spectrum can be generated using a phase-shifted LPG with an optimized phase shifting series. Furthermore, a number of unwanted rejection bands can easily be removed from the transmission spectrum by optimizing the phase shifting series.      

Reconstruction of chirped fiber Bragg grating parameters and phase spectrum using two thermally modulated intensity spectra and a genetic algorithm

This study presents a synthesis method for reconstructing the multiple parameters such as grating position, length, period profile, refractive index modulation, and phase response of a chirped fiber Bragg grating (FBG) and its phase spectrum using two thermally modulated reflection intensity spectra and a genetic algorithm. In the proposed approach, the FBG parameters are determined using the genetic algorithm and are then used to reconstruct the phase response. The advantages of the proposed method include its simplicity, low cost, and nondestructive nature. Furthermore, the proposed method does not require a prior knowledge of the sign of the chirp of the grating period distribution of FBGs.     

提高光纤光栅传感器测量精度的研究

在实际应用中,光纤光栅传感器的测量精度受到噪声,成本等因素的制约。为了实现低成本的高精度光纤光栅传感器系统,提出了对光纤光栅反射谱采用自适应阈值小波消噪和B多节点样条拟合插值算法的处理技术,并通过实验和仿真得出自适应阈值小波消噪,有效提高了系统的信噪比,在相同采样精度下拟合插值处理前波长检测的误差为0.01nm,处理后误差为0.0017nm,误差降低了一个数量级。实验结果证明该方法不但可以有效降低噪声带来的读取误差,而且提高了测量Bragg波长漂移量的分辨率,从而实现高精度地测量温度、应变等外界参量。     

Influences of writing-beam size on the performances of dispersion-free multi-channel fiber Bragg grating

Analysis for the influences of writing-beam size on the performances of a dispersion-free multi-channel fiber Bragg grating (FBG) is presented. It is found that the writing-beam size strongly affects the response of this kind of grating and would make the grating spectrum considerably distorted once the beam size of the UV light is too large to form the complex index-modulation pattern within the fiber core. A novel design method has been proposed to compensate this beam-size effect and a nine-channel dispersion-free FBG with identical spectrum response has been obtained. This compensation method could decrease the tolerance for the demand of small writing-beam size and can be easily extended to the design and fabrication for most of the other complex FBGs.     

串扰感知的空分弹性光网络频谱转换器稀疏配置和资源分配方法

针对大容量多芯光纤空分复用弹性光网络(SDM-EON)中芯间串扰导致业务传输质量下降和阻塞率上升的问题,该文提出了节点稀疏配置频谱转换器降低芯间串扰的路由纤芯频谱分配方法。该方法根据网络中节点中介中心性稀疏配置频谱转换器。在业务路由阶段,设计综合考虑光路负载和节点频谱转换能力的光路选择的权重方法;为了降低串扰,在纤芯频谱分配阶段,设计纤芯分组和频谱分区分配方法;最后,针对串扰较大的业务,采用频谱转换以降低业务串扰和改善带宽阻塞率。仿真结果表明,所提算法能有效地提高频谱利用率,降低因芯间串扰导致的带宽阻塞率。     

On a Pitch Alteration for Speech Synthesis Systems

Speech synthesis can be classified into waveform coding, source coding, or hybrid coding by the synthesis method. Among these, waveform coding is especially suitable for high-quality speech synthesis. However, synthesis techniques using syllable or phoneme unit is not desirable since it fails to separate the excitation and the formant part to handle speech. Therefore, there is a need for a pitch alteration method to apply in synthesis using waveform coding. This study proposes a pitch alteration method that uses spectrum scaling after flattening the spectra by a sub-band linear approximation to minimize the spectrum distortion. A comparison with LPC (Linear Predictive Coding), Cepstrum and lifter function is presented to show the better performance of the proposed method. Estimation method seeks each of the distributions of the flattened signal and measures the degree of the flattened spectrum Signal, which is normalized, so the highest point amounts to zero, and the distribution of the signal, whose average is zero, is calculated. The results are presented by the spectrum distortion rate to estimate the performance of the proposed method. The average spectrum distortion rate kept below the average 2.12%, showing the proposed method’s superiority in comparison with the other existing approaches.

Novel Gain Spectrum Control Method Employing Gain Clamping and Pump Power Adjustment in Thulium-Doped Fiber Amplifier

In this paper, we propose a novel method for controlling the gain spectrum of a thulium-doped fiber amplifier (TDFA) in the S-band. The conventional gain spectrum control method used for a silica erbium-doped fiber amplifier (EDFA) cannot be applied to TDFAs because of the complicated fluctuation of the TDFA gain spectrum. Our proposed method controls the gain spectrum by a combination of gain clamping and pump power adjustment. The algorithm for the method is as simple as that for the conventional EDFA gain spectrum control method. Furthermore, we describe a function for correcting the gain excursion generated by the incorporation of amplified spontaneous emission (ASE) at a signal monitoring photodiode (PD). We achieved a gain excursion of 0.35 dB against a total input signal power of 32 to 2 dBm.     

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。     

Synthesis of long-period fiber gratings with the inverted erbium gain spectrum using the multiport lattice filter model

This paper proposes an accurate modeling technique of concatenated long-period fiber gratings (LPFGs). The proposed technique is then applied to the synthesis of LPFGs for the erbium gain equalization using both the simulated annealing and the steepest descent minimization technique. A piecewise-uniform LPFG is theoretically synthesized according to the inverted gain spectrum of a commercially available erbium-doped fiber amplifier (EDFA) over the range of 1525-1570 nm. Sensitivity analysis of the designed structure is presented by Monte Carlo simulation with regard to the manufactured amplitude mask. To verify a synthesizing technique using the proposed modeling, the piecewise-uniform LPFGs for gain flattening of EDFA are fabricated and their spectra are also presented experimentally.     

非均匀应变场中光纤布拉格光栅的数值分析

当非均匀应变场作用在光纤布拉格光栅（FBG）上时，由于FBG周期和有效折射率在沿FBG长度方向都为变量，所以会导致光谱形状的变化。采用耦合模理论和龙格库塔的方法可以准确地分析非均匀应变场中的FBG光谱特性，其缺点是收敛速度慢；而传输矩阵法虽然可以大大提高收敛速度，但是由于忽略了非均匀应变场的变化梯度，在分析变化率较大的非均匀应变场时与龙格-库塔方法相比准确度较差，通过改进适用于分析非均匀应变场的FBG等效周期，既保留了传输矩阵分析FBG的快速收敛性，又保证了分析准确性。     

基于高斯函数的光谱叠加信号处理仿真研究

针对重金属离子敏光纤传感器阵列光谱信号叠加引起的多种离子浓度测量误差较大的问题,采用高斯函数对重金属离子敏光纤传感器阵列信号进行建模。在利用Matlab对光纤传感器阵列光谱叠加信号进行分离和相对误差分析的基础上提出了一种误差修正的方法。从仿真结果可知,这种算法可以减小由于重金属离子敏感膜的离子间干扰引起的光谱重叠误差,为实际光纤传感器阵列的制作和光谱信号处理提供了理论依据。     

光纤Bragg光栅的优化设计

提出了一种优化设计变迹啁啾光纤Bragg光栅的方法。在优化设计过程中，利用四阶五阶Runge-Kutta方法来计算光纤光栅的反射谱，利用非线性最小二乘法来对光纤Bragg光栅的啁啾和变迹参数进行优化，以获得不同反射谱要求下的变迹啁啾光纤Bragg光栅的最佳参数。     

双泵浦光纤参量放大器光纤长度的选取研究

文章研究了在采用高非线性光纤的光纤参量放大器中,光纤长度的选取对增益谱性能的影响,结果表明,在其他参数固定不变的情况下,光纤长度选取的不同会在很大程度上改变增益谱的形状.最后,文章提出一种最佳光纤长度的选取方法,并通过数值模拟验证了该方法能有效地改善增益性能.     

Novel algorithm for synthesis of fiber gratings

A novel algorithm for the synthesis of fiber gratings is presented.For the first time we propose an effective optimal approach to construct a coupling coefficient function by employing 4th-order Runge-Kutta (R-K) analysis method for calculating the reflection spectra of fiber gratings.The numerical results show that with this proposed method, some required optical filters have been yielded with better features compared with other methods such as Gel'Fand-Levitan-Marchenko (GLM) algorithm.In addition, the performance of different interpolation functions particularly utilized in our algorithm, including linear-type, spline-type, and Hermit-type, are discussed in detail.     

C+L波段掺铒光纤被动锁模激光器

提出并证明了一种宽光谱被动锁模掺铒光纤激光器,为光学频率梳和光纤飞秒脉冲的产生奠定了基础。该激光器基于非线性偏振旋转的锁模机理,同时在大的正常色散区合理地将C波段和L波段掺铒光纤结合,确保激光器具有C+L波段的增益谱覆盖。当泵浦功率为350mW时,脉冲稳定的以基频4.32MHz运转,3dB带宽为60nm,20dB覆盖了1522~1630nm,实现了增益带宽内光谱的完全覆盖。这种利用增益拼接加宽光谱的方法可以有效避免光谱成分的非线性相位噪声,并且有利于进一步压窄脉冲。     

波长扫描型布里渊光时域反射仪

布里渊光时域反射仪(BOTDR)是一种具有广泛应用前景的分布式光纤传感器。对于特定的入射波长,自发布里渊散射光的布里渊频移与温度和应变成线性关系,通过测量光纤沿线布里渊频移分布可实现温度或应变的分布式传感。布里渊功率谱扫描是BOTDR获取布里渊频移的常用手段,已有光频差扫描与电频扫描两种方式。基于布里渊频移对波长的依赖性,提出一种波长扫描型BOTDR。采用可调谐激光器作为光源,通过扫描入射光波长,来获取布里渊功率谱,该方法兼具光频差扫描与电频扫描的优点。实验证明了该方法的可行性,对23.4km光纤进行测量,实现了5m的空间分辨率与2.2℃的温度测量精度。     

基于图像功率谱的激光散斑评价方法

激光散斑在相干光成像、全息术、多模光纤通信、计量等领域具有重要的应用。为了对激光散斑进行评价,提出一种在频域采用散斑图像功率谱谱宽作为激光散斑评价的方法,设计了一种基于光纤振动的功率谱散斑评价实验装置。采用0.5W,532nm激光作为光源,通过电压驱动音圈电机振动光纤对激光散斑进行控制,利用CCD图像采集卡采集图像后,分别采用散斑图像的对比度方法和功率谱方法对不同驱动电压下的散斑图像进行了分析评价。结果表明,功率谱方法具有较高的灵敏度及较宽的评价范围。     

一种新的高重频宽带相干激光雷达系统研究

该文提出一种新的同时具有高重复频率和大带宽性能的相干激光雷达系统。该系统基于IQ调制器正交调制技术与带宽合成信号处理技术,使得系统能够同时满足大带宽和高重复频率的要求,解决了传统激光雷达宽带信号调制速度慢的问题。该系统能够生成高重频、大带宽的相干线性调频激光雷达信号,在高分辨距离成像、(逆)合成孔径激光雷达成像、距离分辨的振动测量等方面,具有重要的应用价值。文中阐述了宽带高重复频率调制的原理和方法、基于微波域频率步进的带宽合成信号处理方法,并进行光纤环路实验和自由空间实验。作为演示,该激光雷达系统获得了16.7 kHz重复频率、6 GHz带宽,实现了优于2.5 cm距离向分辨率成像及远距离运动目标逆合成孔径激光雷达成像。实验结果证明了该系统与方法的有效性。