外调制微波光子链路性能研究

针对外调制方式工作的微波光子链路,建立了链路的小信号分析模型,理论仿真了调制器输入光功率及调制器直流偏置点对链路增益、噪声系数和线性动态范围的影响。理论仿真与实验结果表明,适当增大调制器输入光功率以及使调制器工作在最佳线性偏置点,可提高链路增益和线性动态范围,同时降低链路噪声系数。该研究为优化外调制微波光子链路性能提供了有益参考。     

外调制微波光传输链路性能优化研究

微波光传输链路(MWPL)具有损耗小、容量大、重量轻、抗干扰能力强等优点,已在军事、雷达、无线通信等领域得到广泛应用.决定微波光传输链路性能的参数主要有链路增益、噪声系数和动态范围.文章首先通过建模分析,推导出了增益和噪声系数的关系,研究了微波光传输系统噪声系数的各种影响因素.通过仿真与实验验证表明,合理的调节调制器输入光功率,可提高链路增益,同时降低链路噪声系数,优化传输链路的性能.     

基于光纤干涉仪的相位调制器半波电压的测量

基于相位调制干涉仪解调微波光链路的数学模型 ,提出了通过链路的S21增益峰值计算得到相位调制器半波电压的方案。 实验表明,此方法测得的相位调制器半波电压和厂家提供的数据相符合。把测得的相位调制 器半波电压应用在实际的光链路系统,增益仿真曲线和实验结果也相吻合 。在实验中,实现调制信号相位-幅度转换的光纤干涉仪由2个保偏 耦合器加特定跳线构成。实验结果表明,本文方案是一种结构简单、操作容易且具较高实 用价值的相位调制器半波电压测量方法。     

宽带多频段微波光子链路性能研究

覆盖C、Ku、Ka三个频段的多频段微波光子系统链路性能受自频段三阶交调失真、不同频段间二次谐波和二阶交调失真以及电光调制器半波电压变化的影响.分析了不同频段内干扰信号,得到了链路性能优化时调制器直流偏置电压,讨论了不同输入射频功率时各频段主要干扰信号.     

长距离传输中毫米波光链路性能的分析

建立了毫米波长距离光传输链路增益和噪声系数模型,分析了外调制器工作点对链路增益、噪声系数等的影响;计算了长距离传输中色散效应对链路增益的影响;推导分析了激光器相对强度噪声、散弹噪声、EFDA自发辐射噪声对链路噪声系数的函数关系。通过控制调制器工作点等技术手段优化了链路的增益和噪声系数指标,对毫米波光链路工程设计和应用提供了理论指导。     

两段级联宽带碲基掺铒光纤放大器特性研究

利用四能级结构速率方程组和光功率传输方程组,研究了在碲基掺铒光纤(EDTF)中内插一个光隔离器、形成两段级联的碲基掺铒光纤放大器(EDTFA)后对EDTFA性能的改善.结果表明,在给定泵浦方式、泵浦功率、纤芯掺杂浓度和输入信号功率条件下,两段级联EDTFA可以有效的抑制光纤中反向传输放大自发辐射(ASE)噪声,降低反转粒子数的消耗,从而提高信号增益、输出功率,并且降低了噪声系数.对不同光纤长度和光隔离器内插在光纤中不同位置的研究表明,当光纤为最佳长度和光隔离器在最佳位置处时,可使短波长信号增益增加10 dB,噪声系数减小1 dB,并进一步增加了放大带宽以及功率转换效率.     

基于激光相控阵原理的相位调制器半波电压测量方法

半波电压是电光相位调制器的一个重要指标, 针对现有半波电压测量方法存在的测量误差大、测量装置复杂等问题, 提出了基于激光相控阵光束扫描原理的半波电压测量方法.通过理论分析, 得到了远场主光束的偏移量和相位调制器半波电压的关系表达式.搭建了12 全光纤激光相控阵光路, 对铌酸锂波导相位调制器的半波电压进行了实验测量, 改变相位调制器的加载电压, 记录多幅远场光强分布图, 通过求平均值减小测量误差, 而且根据远场光强分布的变化得到了相位调制特性曲线.结果表明, 该方法测量装置简单, 不仅可以精确地测量半波电压, 还可以对相位调制线性度进行分析, 具有重要的工程应用价值.     

射频光传输雷达接收链路的系统优化

在雷达指标体系中,探测距离和目标分辨能力是其中的重要参数。而噪声系数（NF）和接收链路的压缩动态范围（CDR）则影响着这两个指标。随着射频光传输（ROF）在雷达接收链路中应用的推进,除了对光链路本身的探讨外,还需扩展到接收链路中微波和光波的协同分析。因此,将其中的微波前级放大、射频光传输（ROF）、微波后级放大进行耦合,普适性地探讨接收链路CDR和NF。例如,当光链路噪声功率谱密度为?164 dBm/Hz,光链路增益?20 dB时,可设计前级放大41 dB。在这种情况下,接收链路CDR_1dB达143 dB·Hz,噪声系数为4.15 dB,能够同时满足探测距离和目标分辨的要求。对外调制光链路而言,调制器的半波电压可选择在2.0~5.8 V之间,实现性能和成本的平衡。分析从系统角度出发,探讨了基于ROF的接收链路,能够满足雷达功能要求,同时,也为接收链路中电器件和光器件的设计提供了依据。     

高饱和电流光电探测器在低噪声系数和高增益RoF光链路中的应用

研究了光载无线通信(RoF)链路中掺Er3+光纤放大器(EDFA)对链路噪声系数(NF)和增益的影响,同时采用自制的具有高响应度、高饱和功率特性单载子传输光电探测器(UTC-PD)作为链路光电转换器件,在不以NF为代价的同时使得链路增益性能获得大幅提升。实验表明,对于由LD、马赫-曾德调制器(MZM)、EDFA、光滤波器(OBPF)和UTC-PD组成的RoF光链路,在LD输出功率为17dBm、UTC-PD的输出平均光电流为60mA时得到最低链路NF为30.3dB,相比不含EDFA的基本链路在LD输出光功率同为17dBm时的NF略小0.4dB;同时链路增益高达15.5dB,相比基本链路大幅提升了41.3dB。     

一种低驱动功率的ADP调制器

本文提出了一种四块晶片组合的 ADP 45°x(y)切调制器的设计方案。与常用的二晶片组合的ADP 45°x(y)切调制器相比,其显著优点是不但可以获得低的半波电压,而且驱动功率可以成倍地降低。该器件已研制成功,其调制性能如下:6328(?)时,半波电压100伏,消光比大于200∶1,100%调制时驱动功率15瓦/兆赫。     

X波段单片集成低噪声接收子系统

报道一种新型 X波段 0 .2 5 μm PHEMT全单片集成低噪声子系统。该子系统由开关衰减电路、采样检波电路和低噪声放大器三部分组成。开关插入损耗仅 0 .5 d B,放大器噪声系数小于 1 .5 d B。当开关控制电压为-2 V,输入电平 <-7d Bm时 ,此系统相当于一个低噪声放大器。在 8.5～ 1 0 .5 GHz频率内 ,整个系统增益大于2 4d B,噪声系数小于 2 .0 d B,输入输出 VSWR<1 .5 ;但当输入电平 >-7d Bm时 ,采样检波电路开始工作 ,打开主放大器前的开关衰减器 ,限制输入功率进入 LNA。输入功率越大 ,反射越大。在开关控制电压为 +2 V时 ,无论输入功率多大 ,开关关闭通道     

All silica S-band double-pass erbium-doped fiber amplifier

Double-pass (DP) and single-pass (SP) erbium-doped depressed cladding fiber amplifiers designed for S-band operation are evaluated under changes of the input optical power, pumping power, and fiber bending radius. The DP configuration employs the usual combination of a circulator and a Faraday rotator mirror while the SP is based on the copropagating scheme. The amplifiers were characterized in terms of gain and noise figure. It is demonstrated that the DP topology shows much improved gain performance compared to the SP configuration although the noise figure is slightly degraded by counterpropagating amplified spontaneous emission.     

Influence of reflected light on erbium-doped fiber amplifiers foroptical AM video signal transmission systems

Investigates experimentally the influence of reflected light on an erbium-doped fiber amplifier for use in optical AM frequency-division multiplexing (FDM) video distribution systems when reflection points exist before and after the amplifier. It is found that amplifier distortion is not affected by reflected light but that the signal gain and the noise figure of the fiber amplifier degrade with increased reflectivity. Gain was decreased by 3 dB when reflectivity after the amplifier was -12 dB. It was theoretically and experimentally clarified that the noise figure degradation was related to the internal reflection of the erbium-doped fiber, in addition to the reflection before and after the fiber amplifier. This internal reflection is caused by input signal light scattered within the erbium-doped fiber     

Experimental study on noise characteristics of a gain-saturatedfiber optical parametric amplifier

A fiber optical parametric amplifier (OPA) has a unique saturation property such that, with increase in signal input, the signal output power increases, reaches a peak level, then decreases. Around the output peak condition, a negative feedback mechanism works to suppress intensity fluctuations in the signal output. This paper experimentally studies noise characteristics of such a gain-saturated fiber OPA. Two kinds of incident signals are injected into a fiber OPA. One is intentionally fluctuated light with large excess noise and the other is excess-noise-free (or shot-noise-limited) light. It is demonstrated that the noise suppression has an effect both on the excess noise and on beat noise due to amplified spontaneous emission generated inside the amplifier     

An optical power equalizer based on one Er-doped fiber amplifier

A device which exhibits zero or slightly negative differential optical gain over a broad input power range is demonstrated. The scheme is based upon saturation enhancement by bidirectional signal input in an Er-doped fiber amplifier. Power equalization of better than 1.2 dB over a 14-dB dynamic input power range is achieved at the 1530-nm signal wavelength. The noise figure penalty due to the equalization is below 3 dB as evaluated by a device simulation     

光纤干涉系统光学湍流测量原理及其偏振噪声问题的分析

光纤干涉仪具有测量精度高、探测灵敏度大等优点,可用于直接测量大气湍流折射率起伏.首先简要介绍了光纤Mach-Zehnder干涉仪的光学湍流测量原理,描述了低双折射单模光纤中光束偏振态变化诱导的偏振信号衰落现象,并通过偏振态的邦加球分析和详细的公式推导,得出了干涉仪可见度和相移噪声的关系式.结果表明:控制输入光偏振态与干涉仪本征向量之间的夹角在零度左右,可有效地抑制偏振噪声,最后给出了偏振控制器实现偏振控制的原理,为构建稳定的光学湍流测量光纤干涉系统提供了科学依据.     

Demodulation of low-level broad-band optical signals with semiconductors

A simple approach to the problem of detection of optical signals with semiconductors leads to a general understanding of the performance. It shows that the low impedance level of broad-band circuits prevents high efficiency conversion of the incident power. Because of this, the envelope detector has a signal-to-noise ratio (SNR) which is determined by the noise of the following amplifier. As in radio communication, addition of a coherent optical signal from a local oscillator can increase SNR; however, for optical signals the limiting value of the noise figure is determined by the shot noise of the conversion current. Comparison with the limiting SNR expected from a photo-emission detector reveals no important distinction between them for frequency conversion. The unit which uses material with the higher quantum conversion efficiency will have the possibility of better SNR. For envelope detection, the photo emitter can be far superior to the photoconductive detector. The two cases of a photovoltaic and a photoelectromagnetic solid-state device are analyzed and general expressions as well as numerical examples given for the design parameters. The devices are comparable both in dimensions and performance.     

The Quantum Theory of Optical Pulses Amplification

The propagation of optical signals in optical fiber amplifier is treated with fully quantum mechanics method in this paper. The micro-Hamiltonian of the system with nonlinear effect is derived by combining spatial mode and temporal mode, and propagation equation of optical pulses in a optical fiber amplifier is derived with dispersion relation. The characteristic parameters such as gain, output power and noise figure of the amplifier are analyzed and their quantum mechanics formulas are obtained.     

掺铒光纤放大器双向放大特性

建立了掺铒光纤放大器（ＥＤＦＡ）双向放大传输的方程，通过数值模拟计算，分析了掺铒光纤长度、泵浦功率的变化对增益、噪声系数的影响；研究了ＥＤＦＡ的正反向增益和噪声系数特性；给出了增益、正反向系数与输入信号功率的关系曲面。     

MMIC compatible lightwave-microwave mixing technique

The work presented here concerns the mixing of a microwave signal with a modulated optical signal in a MESFET. A brief theoretical analysis of the mixing mechanism is given in terms of the input signal parameters and device characteristics. Experimental results for the IF response of the MESFET as a function of RF frequency, incident optical power, optical modulation depth and gate bias voltage are shown. The IF response and the noise figure of the MESFET below 700 MHz were smaller than those of a p-i-n detector/Schottky mixer combination