宽带大动态射频光传输技术

宽带大动态的射频光传输链路是微波光子技术应用的基础。针对射频光传输对链路高动态范围的应用需求,分别介绍了多频点副载波复用数字预失真和多源非线性数字后补偿两种失真线性化技术的原理及其研究进展,这两种方法能较好地抑制信道间的交调失真和信道内的三阶交调失真。同时,将全光下变频技术引入到接收链路中,通过充分利用相位调制线性特性的优势,分析了基于相位调制及相干解调DSP处理的大动态光载射频传输系统,实验得到的宽带射频信号光传输系统的无杂散动态范围达到了128.8 dB.Hz2/3。     

光载无线通信链路拉格朗日乘子线性度优化

非线性失真是影响光载无线通信链路无杂散动态范围和工作带宽的主要因素.通过结合射频功率比、偏振复用和偏置控制技术,针对分布式天线系统,构建了一种大动态范围和跨倍频程带宽多通道光载无线通信链路.利用拉格朗日乘子法对所提链路进行线性度优化建模,得到了射频输出功率、偏振入射角和射频功率比之间的最佳折衷,从而在抑制三阶交调失真和二阶谐波失真的基础上,实现了链路线性度的最优化.仿真和实验结果验证了所提方案的有效性和可行性.     

一种高线性度的全双工光载射频系统

本文提出了一种高线性度的全双工光载射频系统.该系统克服了下行链路三阶交调失真与周期性功率衰落的影响,同时对上行链路进行波长重用,简化了基站的成本和复杂度,实现了高线性度的全双工光载射频系统.实验结果表明,与基于单个马增调制器的常规系统相比,本系统下行链路中三阶交调失真得到明显抑制,克服了光纤色散引起的功率衰落,系统无杂散动态范围提高17dB,宽带信号的星座图和误差矢量幅度改善明显,另外,上行链路可以实现稳定的波长重用及宽带信号传输.     

实现光载无线电系统三阶交调抑制的新方案

光载无线电(Ro F)系统是近年来光通信研究的一个热点。抑制三阶交调从而增大无杂散动态范围(SFDR)是Ro F系统优化的重要内容。为了提高Ro F系统的动态范围,提出了一种基于光纤光栅陷波器和可调延迟线(TDL)抑制三阶交调的新方案。在对该方案理论分析的基础上,进行了实验验证。实验结果表明,该方案能有效抑制三阶交调,系统的SFDR提高了10.5 d B,且具有结构简单易实现、器件成本低的优势。     

高线性波分复用模拟光链路的设计及实现

面向多路射频模拟信号的高线性传输需求，基于强度调制-直接探测的原理，提出了基于波分复用技术的模拟射频光传输方案；利用高线性度模拟直调半导体激光器、波分复用器、模拟光电探测器，设计了基于微波光子技术的波分复用射频光传输链路，该链路具有低串扰、低失真、链路增益可调等性能。利用该链路进行了直调激光器、驱动控制电路、射频光发射模块和光接收模块的样机研制。对所研制出的样机进行了实验测试。测试结果表明：通道增益可在-30～10 dB调谐，通道内基波与二次谐波抑制比高于50 dB，相邻及非相邻通道间射频串扰均低于60 dB，相位一致性在±5°以内。针对不同的信号输入功率，在线调整链路增益，改善链路的信噪比或非线性失真效应。设计和研制的样机可用于低频段射频信号的光纤传输。     

一种-16 dB ~12 dB增益范围的高线性度PGA设计

可编程增益放大器广泛应用于射频接收通道,起中频放大、驱动模数转换器的功能.基于电阻反馈运放设计的可编程增益放大器具有动态范围大、线性度高的特点.文中采用互补金属氧化物半导体工艺设计实现了一种基于全差分运放和衰减器的宽范围、高线性度可编程增益放大器.测试结果表明增益变化范围为-16dB～12dB,步进为1 dB,输出1 dB压缩点大于10 dBm@60 MHz,输出三阶交调点大于26 dBm@60 MHz.     

基于HBT工艺的低三阶交调失真射频放大器优化设计

针对宽带大信号容量无线系统对低三阶交调失真射频放大器的迫切需求,从放大器偏置点优化和片上散热优化两个方面研究了基于HBT工艺的低三阶交调失真射频放大器优化设计方法。分析了达林顿复合结构射频放大器交调特性与直流偏置点的关系,给出了放大器最佳三阶交调直流偏置点。提出了一种优化散热的输出级分散布局电路结构,减小了片上温升带来的三阶交调性能恶化。应用提出的优化设计理论方法,基于2μm AlGaAs/GaAs HBT工艺,设计了一款工作于0.05～1 GHz的低三阶交调失真射频放大器。测试结果表明,该放大器实现了42.1 dBm的输出三阶交调点,三阶交调与1 dB压缩点之比达到了21.2 dB。     

UHF大功率收发前端设计

射频收发前端电路是无线收发信机的重要电路之一,它对整个系统的噪声系数,动态范围等关键指标起决定性作用。文中具体分析了射频前端电路在无线通信系统中的重要性、射频收发前端的组成、工作原理、接收和发射部分的设计难点和重点。对关键技术指标进行了优化设计。设计了思维简洁、电路控制速度快的UHF大功率射频收发前端,并对方案进行试验改良。通过实验结果表明,该电路噪声系数达到3.2 dB,接收通道增益达到30 dB。发射通道输出功率≥40 dBm,三阶交调≤-18 dBc,试验结果达到预期目标。最后结合实际测试曲线,对实验结果进行进行了分析,并对现有方案提出了改进。     

分布式反馈激光器调制特性研究

为了深入了解分布式反馈激光器（DFB）的发光机理与调制特性,通过理论分析和实验对DFB的调谐特性进行了研究。得到FITEL和JDS Uniphase两款激光器调制电流与输出中心波长的对应关系和两种确定系数不同的拟合方程,证明了这两款DFB激光器在实际应用中存在非线性关系。结果表明,FITELFRL15DCWD-A82激光器的3dB带宽与驱动电流幅值关系为3.715pm/mA;该调制结果优化了该激光器的可用相干长度,并验证了驱动信号频率变化不影响3dB光谱宽度。对DFB激光器低频调制特性的定量分析结果可为相干检测系统驱动电路设计提供实验依据。     

抑制空间行波管三阶交调失真的信号注入技术

为了抑制空间行波管非线性特性产生的交调失真,本文通过理论分析、计算机仿真和实验验证,分别研究了谐波、交调和混合信号注入技术对空间行波管三阶交调（IM3）分量的抑制情况。实验结果表明：IM3注入技术能够得到25.2 dB的IM3最大抑制量,明显大于谐波注入技术的12.7 dB,两者对IM3失真分量的抑制效果都很良好,且就窄带空间行波管而言IM3注入技术比谐波注入技术更具优势。通过进一步仿真实验,证明双IM3注入技术可以在两个IM3频率处分别产生46 dB和53 dB的最佳抑制量,且混合注入谐波和交调信号也能最大抑制36.9 dB。     

Continuous-wave frequency synthesis of a laser diode based ondiscrete-time negative frequency feedback. I. Experiment

The absolute frequency synthesis of a distributed-feedback (DFB) laser diode (LD) is demonstrated by use of a loss-compensated optical ring circuit with a frequency shifter and a frequency-stabilized master laser system containing an acetylene (¹³C₂H₂ ) absorption cell. A lightwave from the master laser is modulated into a pulse and circulated around the ring to shift its frequency in the 0~100 GHz range. A continuous-wave from the DFB LD is mixed with a recirculated pulse with a desirable reference frequency, and their beat frequency is counted in order to obtain the error signal. The absolute frequency of the DFB LD is locked to the reference frequency based on discrete-time negative frequency feedback control for the injection current. The accuracy of the absolute frequency was experimentally confirmed to be within a few MHz for an averaging time of 1 s and an operation time of 1 hour     

Coherent self-heterodyne Brillouin OTDR for measurement ofBrillouin frequency shift distribution in optical fibers

Time domain reflectometry of spontaneously Brillouin scattered lightwaves in a single-mode optical fiber is demonstrated with a coherent self-heterodyne detection system employing a recently proposed frequency translator, a DFB laser diode, and erbium-doped fiber amplifiers. Since the probe pulse frequency is up-converted by the translator by an amount approximately equal to the Brillouin frequency shift, the self-heterodyne beat frequency can be reduced to a sufficiently low frequency in the IF band. The system enables one-end measurement of the Brillouin frequency shift distribution in optical fibers with a single way dynamic range (SWDR) of 16 dB and a frequency resolution of 5 MHz for a spatial resolution of 100 m     

Intensity noise suppression and modulation characteristics of a laser diode coupled to an external cavity

Static and dynamic properties of a GaAlAs laser diode with an external cavity (1.5-50 cm) have been studied experimentally, it is found that the optical feedback induced intensity noise is strikingly suppressed by 30 dB when a single frequency oscillation is realized with good phase matching. The threshold of modulation depth, over which intensity noise increases abruptly, has been measured as a function of the modulation frequency in a range of 10-400 MHz. It has the maximum at about 40-70 MHz and increases with the decrease of the external cavity length. On the basis of the compound cavity model the phase and gain conditions for the single frequency oscillation are discussed and the threshold modulation depth is calculated, which is shown to be in good agreement with the experimental results.     

Numerical simulation of intensity and phase noise from extracted parameters for CW DFB lasers

A self-consistent numerical approach is demonstrated to analyze intensity and phase noise from experimentally extracted parameters for a continuous-wave distributed feedback (DFB) laser. The approach takes into account the intrinsic fluctuations of the photon number, carrier number, and phase. Values for the parameters appearing in the rate equations are extracted from the measured relative intensity noise spectra and linewidth of the laser. The simulation of the frequency spectra of intensity and phase noise of the DFB laser are performed by fast Fourier transform and exhibit good agreement with experimental results. The model presented here can readily be extended for the purpose of system simulations.     

Fundamental Thermal Noise in Distributed Feedback Fiber Lasers

A detailed analysis of fundamental thermal frequency noise in distributed feedback fiber lasers (DFB FL) is presented. An expression relating the laser frequency noise spectrum to the spectrum of thermal (temperature) fluctuations in the fiber, accounting for the nontrivial DFB FL mode shape, is derived. A new expression for the thermal fluctuation spectrum of single-mode optical fiber is derived which predicts high-frequency thermal noise 3 dB higher than previously published results. Theoretical predictions are compared against experimental measurements for a well characterized DFB FL. Anomalous 1/f noise at low frequency is discussed     

外部光注入分布反馈激光器的非线性动力学特性

实验研究了外部光注入分布反馈(DFB)激光器的非线性动力学行为,并给出了其输出特性随注入光强度和频率失谐量变化的动力学特征图.实验结果表明,激光器的动力学行为对外部的微扰十分敏感;在不同外部光注入条件下,激光器可以呈现出单周期、倍周期、多周期以及混沌等多种非线性动力学特征;在注入光强度和频率失谐量变化空间存在三个复杂动力学区域;激光器表现出的复杂动力学行为总是与周期行为有关;当激光器处于复杂动力学区域时,其频谱为连续谱,在连续谱上存在多个明显的峰,所对应的频率定义为特征频率,特征频率的大小不随注入光的强弱以及频率变化.     

基于分布反馈激光器的局部放电监测系统研究

电力设备的局部放电监测是发现设备的绝缘缺陷、维护电网安全运行的重要手段。文章基于分布反馈(DFB)激光器线宽窄、噪声低、相干长度长等优点，设计了一种用于局部放电监测的振动传感系统。系统采用粘接在悬臂梁上的DFB激光器作为传感头，利用光纤迈克尔逊干涉仪将DFB激光器波长变化转换为干涉仪的输出光强变化，采用相位生成载波(PGC)算法进行局部放电信号解调。设计并仿真分析了悬臂梁的振动响应特性，得到其一阶谐振频率为876 Hz。研究了迈克尔逊干涉仪臂长差与系统灵敏度的关系。实验选取脉冲点火器作为局部放电源进行放电检测，验证了系统用于局部放电检测的可行性。结果表明，该系统能够检测到800～900 Hz放电信号，灵敏度可达-74.67 dB re rad/Pa。     

Two-electrode DFB laser filter used as a wide tunable narrow-bandFM receiver: tuning analysis, characteristics and experimental FSK-WDMsystem

Characteristics of a two-electrode DFB laser filter are studied both theoretically and experimentally. Using a matrix analysis of spontaneous emission, a continuous tuning range of 6.7 Å is achieved by changing both net field gains of the two electrodes. A total discontinuous tuning range of over 10 nm comprising alternating mode jumps and continuous tuning range of 4 Å are measured experimentally. The laser filter presents a FWHM bandwidth of 5 GHz which depends on the optical input power. In addition, it is demonstrated that a DFB laser filter can act as a frequency discriminator/photodetector, i.e., a narrow-band FM receiver, with a uniform bandwidth of 1.5 GHz. Using the two-electrode DFB laser for both transmitter and receiver, a two-channel FSK-WDM transmission system utilizing the discontinuous tuning range is reported. The advantage of such a device is the simplicity as compared to the heterodyne technique     

Wide Temperature Range Operation of a 1.55-$mu$m 40-Gb/s Electroabsorption Modulator Integrated DFB Laser for Very Short-Reach Applications

We present the uncooled operation of a 1.55- mum 40-Gb/s InGaAlAs electroabsorption modulator (EAM) integrated distributed-feedback (DFB) laser within a temperature range of 95degC (-15degC to 80degC ). To the best of our knowledge, this is the largest temperature range reported so far for such a 40-Gb/s EAM integrated DFB laser. We designed the EAM to operate at high speed by reducing the electrical parasitics, and we achieved a 3-dB frequency bandwidth of over 39 GHz for an EAM length of less than 150 mum. We demonstrated a 2-km single-mode fiber (SMF) transmission at 40-Gb/s over a wide temperature range of -15degC to 80degC by adjusting only the bias voltage to the EAM while keeping the modulation voltage swing constant at 2.0 V when the temperature changed. We achieved a dynamic extinction ratio of over 8.2 dB and a 2-km SMF transmission with a power penalty of less than 2 dB over a wide temperature range.