数字滤波器的选择和设计

本文结合带通滤波器的设计实例，介绍了用MATLAB设计、实现IIR数字滤波器的方法，并分析了硬件实现中的数据处理。     

F—P干涉滤波器及其在光纤通信系统中的应用

对Ｆ－Ｐ干涉滤波器及春在光纤通信系统中的应用进行了研究。对Ｆ－Ｐ干涉滤波器的原理特性进行了分析，导出了传递函数的普遍形式，对滤波器的参数进行了设计和测量，并对精细度的测量进行了修正。研究了用滤波器产生变换限制脉冲的方法，导出了获得变换限制脉冲所需的滤波器优化带宽。分析了采用滤波器来抑制光通信系统中的放大器自发辐射噪声。     

基于FPGA的FIR滤波器的设计与实现

分析了FIR滤波器的结构特点和基本原理，基于Matlab用窗函数法对FIR滤波器进行设计，并在Sireulink中进行系统仿真。最后，在FPGA中实现并利用SignalTap Ⅱ逻辑分析器对设计进行测试验证，测试结果与仿真结果一致。     

RF滤波器对DS—CDMA系统性能的影响

在无线通信系统特别是扩频通信系统中，其发射信号必须限定在一定频段，并遵守一定的无线频率资源管理规定，以防干扰别人，因而发射机必须用滤波器；同样，接收机为了抑制镜像干扰和带外噪声也需采用镜像滤波器各频滤波器。这些滤波器都对相关器的输出产生了不同程度的影响。本文主要是分析一些滤波器参数在这些影响中所起的作用，以便选取适当参数的滤波器。     

RF滤波器对DS─CDMA系统性能的影响

在无线通信系统特别是扩频通信系统中，其发射信号必须限定在一定频段，并遵守一定的无线频率资源管理规定，以防干扰别人，因而发射机必须用滤波器；同样，接收机为了抑制镜像干扰和带外噪声也需采用镜像滤波器和中频滤波器。这些滤波器都对相关器的输出产生了不同程度的影响。本文主要是分析一些滤波器参数在这些影响中所起的作用，以便选取适当参数的滤波器。     

不同阶数的FIR数字滤波器的DSP实现

在分析了FIR数字滤波器主要特点的基础上，采用最大误差最小化准则的等波纹迫近法，来设计FIR数字滤波器。然后通过Matlab程序设计语言中Remez函数扣Remezord函数计算FIR数字滤波器的系数，并基于美国德州仪器公司生产的TMS320C5402芯片的数字信号处理功能，应用DSP汇编语言编程实现了该滤波器，使不同阶数的FIR数字滤波器都可以用Matlab所得到的结果来修改DSP程序中的数据子程序。     

微波介质陶瓷在介质滤波器上的应用

移动通信用天线滤波器应具有尺寸小，频率稳定，插入损耗低等特点。研究了ＢａＯ－Ｎｄ_２Ｏ_３－ＴｉＯ_２系介质材料的组成对其介电性能的影响，并分析了影响插入损耗的各个因素。在此基础上用掺Ｂｉ_２Ｏ_３的ＢａＯ－Ｎｄ_２Ｏ_３－ＴｉＯ_２系材料作介质试制出天线滤波器，测试了滤波器的性能，测定表明所制造的天线滤波器性能能够满足移动通信机的要求。     

基于TMS320F240的数字滤波器的设计

介绍了FIR数字滤波器的原理，叙述了怎样用TMS320F240实现FIR实时数字滤波器，并给出了程序流程。     

分数阶线性相位滤波器的设计与实现

文中讨论了一种基于内点算法的分数阶线性相位滤波器的设计方法。从分数阶全极点低通滤波器传递函数的一般形式出发，推导了（1+α）阶和（2+β）阶线性相位滤波器传递函数的合理结构，进而对分数阶滤波器的相频特性优化问题进行建模和求解，得出了一种具有线性相位特性的分数阶滤波器，并对滤波器进行了稳定性分析和频域分析。结果表明所分析的滤波器均稳定并且有良好的相频特性，此外相比于整数阶滤波器，分数阶滤波器群延时的步阶更为精细。基于分数阶电容还设计了（1+α）阶和（2+β）阶滤波器的有源电路，其中分数阶电容用Foster-I型RC网络进行近似。最后对（1+α）阶和（2+β）阶滤波器有源电路进行了实测，测试结果与电路理论上的幅相频率特性之间的误差在可接受范围内。     

基于GUIDE进行Butterworth滤波器的分析

用GUIDE开发了“Butterworth滤波器的分析”的图形用户界面，只要从键盘上输入Butterworth滤波器的阶数和截止频率，就可以绘制出Butterworth滤波器的幅频特性图、单位阶跃响应图、Bode图和计算出它的各种性能指标，使Butterworth滤波器的分析变得更加简单、快捷。     

A comparison between optical SSB transmitter-filter in a full-duplex radio-on-fiber transport system

We present the investigation of the fiber Bragg grating (FBG) filter as an optical single sideband (SSB) filter at the receiving site. A comparison is made with an alternative optical SSB generation technique using optical SSB transmitter. The function of the optical SSB filter is employed to replace the optical SSB transmitter, not only to select the appropriate wavelength but also to suppress the fiber dispersion effect. Using simple FBG filter as an optical SSB filter in full-duplex radio-on-fiber (ROF) transport systems is a very attractive option, as it is passive and potentially low cost.     

Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique

A new technique to generate and distribute a wide-band continuously tunable millimeter-wave signal using an optical external modulator and a wavelength-fixed optical notch filter is proposed. The optical intensity modulator is biased to suppress the odd-order optical sidebands. The wavelength-fixed optical notch filter is then used to filter out the optical carrier. Two second-order optical sidebands are obtained at the output of the notch filter. A millimeter-wave signal that has four times the frequency of the microwave drive signal is generated by beating the two second-order optical sidebands at a photodetector. Since no tunable optical filter is used, the system is easy to implement. A system using an LiNbO/sub 3/ intensity modulator and a fiber Bragg grating filter is built. A stable and high spectral purity millimeter-wave signal tunable from 32 to 50 GHz is obtained by tuning the microwave drive signal from 8 to 12.5 GHz. The integrity of the generated millimeter-wave signal is maintained after transmission over a 25-km standard single-mode fiber. Theoretical analysis on the harmonic suppression with different modulation depths and filter attenuations is also discussed.     

基于应变的多模光纤可调谐光纤滤波器设计

可调谐光纤滤波器技术是波分复用系统的关键技术之一,对于发展全光通信网络和光纤传感具有极其重要的意义。提出了一种基于大芯径的多模光纤可调谐带阻滤波器,其制作方法是将包层/纤芯直径为125/105μm的特种多模光纤通过单模光纤接入光纤系统,实现单模-多模-单模(SMS)光纤结构,并使一端单模光纤与多模光纤熔接,另一端只是共轴对接而不焊接。在多模干涉原理的基础上,利用该结构对应变的敏感性实现可调谐光滤波。该可调谐滤波器的调制和解调借助于放大自发辐射(ASE)宽谱光源和光谱分析仪(OSA)实现。详细给出了该滤波器的理论仿真分析,并实验证实了该方案的有效性。     

新型光纤光栅梳状滤波器设计

基于马赫—曾德尔(M—Z)干涉仪和光纤光栅Sagnac环,设计出高反射率和大反射带宽的光纤光栅梳状滤波器。模拟仿真了滤波器的输出特性。在工艺允许范围内,设计出反射带宽达5nm,反射率接近100%的梳状滤波器。所设计的梳状滤波器可以在光纤传感和通信领域中获得广泛的应用。     

基于高精细度光纤滤波器的双波长光纤激光器

提出了基于高精细度光纤环形滤波器的双波长窄线宽光纤激光器结构.在单波长光纤激光器的基础上,增加保偏光纤布拉格光栅(PM-FBG)和高精细度的光纤滤波器.其中保偏光纤布拉格光栅作为激光器的波长选择元件,可产生两个波长的激光输出.高精细度的光纤滤波器由两个光耦合器和一段弱抽运的掺铒光纤构成,掺铒光纤产生的增益和光纤时延使滤...     

Optimization of the frequency response of a semiconductor opticalamplifier wavelength converter using a fiber Bragg grating

Cross-gain modulation in a semiconductor optical amplifier (SOA) is one of the simplest techniques for all-optical wavelength conversion. However, the finite gain recovery time of the semiconductor optical amplifier causes distortion and pattern dependence at high bit rates. Here we show that filtering the output of a semiconductor optical amplifier wavelength converter with the transmission edge of a fiber grating filter improves its frequency response. The grating sharpens the transition between the bits by converting the phase modulation at the edge to useful amplitude modulation. We determine the filtering condition that produces the optimum frequency response and reduces bit-pattern dependence for nonreturn-to-zero (NRZ) data. For small modulation, the apparent frequency response increases by the linewidth enhancement factor α_H of the SOA. In this case, pattern dependence is eliminated completely by the fiber grating filter. For large modulation, pattern dependence can be substantially reduced, but not completely eliminated. We show that after spectral filtering, the residual pattern dependence of an SOA depends only on modulation depth. For a given SOA, we find the optimum grating for minimum conversion penalty at 12 Gb/s for a wide range of operating parameters. Using a fiber grating filter reduces the required optical power for conversion in a semiconductor optical amplifier     

可调谐光纤F-P线性滤波器的设计与分析

光纤滤波器在光纤通信和光纤传感领域发挥着重要的作用。本文基于光学薄膜干涉理论设计了一种用于光纤传感的可调谐F-P线性滤波器,该滤波器由两端面相对的入射光纤与出射光纤构成,两光纤端端面分别镀有反射光纤薄膜。该F-P干涉腔改善了传统F-P腔的透射率响应特性,有助于提高滤波器的线性度和线性范围。本文采用光学薄膜干涉矩阵分析法对该滤波器的透射率响应关系进行了计算与分析,并得出该FP滤波器的结构参数。设计结果表明,这种新型线性滤波器具有线性度好、线性范围宽和线性区间可调的优点。     

An optical filter of adjustable finesse using an amplified fiberring resonator

We consider an optical filter constructed from a simple ring resonator with two electro-optical directional couplers and a fiber amplifier in the ring. By adjusting the coupling coefficient of the electro-optical directional couplers, the finesse of this optical filter can be controlled over a specified range. The variation in the insertion loss of the optical filter can be overcome by adjusting the gain of the fiber amplifier simultaneously. This paper analyzes theoretically the performance of the optical filter, as a function of the coupling coefficient of the electro-optical directional coupler and the gain of the fiber amplifier. We also show that it is possible to design an optical filter of wide adjustable finesse by changing only the coupling coefficient of the electro-optical directional couplers, leaving the gain of the fiber amplifier unchanged. This simpler method results only in a slight change in the insertion loss if an appropriate condition is chosen. The filter will be useful in coherent optical systems, where the bandwidth of the optical filter needs to be appropriately adjusted under varying biasing and signaling conditions, or as an optical discriminator with an adjustable Q-factor     

A New Optical Fiber Line Testing Function for Service Construction Work That Checks for Optical Filters Below an Optical Splitter in a PON

In this paper, we propose a new function for construction work undertaken to install optical fiber lines for services in a passive optical network (PON). This paper describes a novel measurement technique designed to check for optical filters located in front of an optical network unit in branched optical fiber regions in PONs with outside optical splitters. The purpose is to determine whether an optical fiber is ldquoliverdquo or ldquounused.rdquo The features of our proposed technique are the use of test lights operating at two different wavelengths and a nondestructive macrobending technique. By comparing the difference between the reflected powers of the two wavelengths, we can determine the presence of a filter at the end of a fiber line. Furthermore, we describe an enhanced estimation analysis method that uses two photodetectors installed symmetrically in the detection part and an analysis procedure for detecting only a test light reflected from the fiber end. We also demonstrate the performance of the enhanced analysis method experimentally and confirm that it can be employed to detect an optical filter installed at the end of an optical fiber line.     

Tunable microwave photonic filter based on a fiber ring and erbium-doped fiber amplifier

The tunable microwave photonic filter based on a fiber ring and erbium-doped fiber amplifier （EDFA） was proposed. By introducing a section of erbium-doped fiber （EDF） into the fiber ring, the loss of the signal can be compensated by the EDFA gain through adjusting the pump power. This can largely increase the number of the effective sampling taps, and then improve the performance of the microwave photonic filter notably. When the pump power was set to be 42.7 roW, a microwave bandpass filter with the 3-dB bandwidth of 0.15 MHz, the Q factor up to 100 and extinction ratio up to 20 dB was achieved. By employing a tunable optical delay line in the above fiber ring, a tunable microwave photonic filter has been realized through tuning the length of the optical delay line. The proposed tunable microwave photonic filter can fred great applications in microwave signal processing and ROF system.