海底光缆在线监测与相干光时域反射仪技术

对应用相干OTDR(optical time-domain reflectometer,光时域反射仪)于实用的海底光缆在线监测问题进行了讨论,对相干OTDR的技术作了论述,并就应用相干OTDR对海缆监测时,对监控信道性能进行了分析.最后给出了对海缆出一些故障时COTDR的计算机仿真探测结果.     

Fiber Impairment Compensation Using Coherent Detection and Digital Signal Processing

Next-generation optical fiber systems will employ coherent detection to improve power and spectral efficiency, and to facilitate flexible impairment compensation using digital signal processors (DSPs). In a fully digital coherent system, the electric fields at the input and the output of the channel are available to DSPs at the transmitter and the receiver, enabling the use of arbitrary impairment precompensation and postcompensation algorithms. Linear time-invariant (LTI) impairments such as chromatic dispersion and polarization-mode dispersion can be compensated by adaptive linear equalizers. Non-LTI impairments, such as laser phase noise and Kerr nonlinearity, can be compensated by channel inversion. All existing impairment compensation techniques ultimately approximate channel inversion for a subset of the channel effects. We provide a unified multiblock nonlinear model for the joint compensation of the impairments in fiber transmission. We show that commonly used techniques for overcoming different impairments, despite their different appearance, are often based on the same principles such as feedback and feedforward control, and time-versus-frequency-domain representations. We highlight equivalences between techniques, and show that the choice of algorithm depends on making tradeoffs.      

Optimum Gaussian Filter and Deviated-Frequency-Locking Scheme for Coherent Detection of MSK

Predetection Gaussian bandpass filtering effect on the coherent detection of minimum-shift-keying (MSK) is theoretically anlayzed on the basis of the worst signal pattern which brings the maximum intersymbol interference. The optimum 3 dB-down bandwidth (B)-bit duration (T) product of the Gaussian bandpass filter is proved theoretically to beBT = 0.5887, which degrades the requiredE_{b}/N_{0}(signal-energy-per-bit to noise-power-density ratio) only by 0.14 dB from that of antipodal coherent PSK using differential encoding. The degradations due to the phase errors of reference carrier and decision timing and the frequency drift of the received input signal are also shown. In addition, an alternative coherent detection using the reference carrier having the frequency deviated from the center frequency by the frequency deviation, which is called the deviated-frequency-locking scheme, is presented, and its error-rate performance is proved to be substantially identical with that of the conventional center-frequency-locking scheme.     

基于相干激光雷达的激光微多普勒探测

利用相干激光雷达探测目标微动特性技术是一种以单频激光为光源,用外差探测的方式实现对低速、低频多个运动物体进行微多普勒信息提取和识别的技术.以波长为1.064 μm的窄线宽单块激光器为光源,发射激光经过模拟长距离传输的4 km的光纤延迟,照射到以扬声器的发声单元和电动平移台为目标的微动物体上,目标反射的激光会聚进入单模光纤,参考光与信号光通过3 dB光纤合束器线性耦合进入同一根光纤,并在探测器表面进行相干.用于接收相干信号的探测器的接入方式为光纤输入,带宽为3.5 GHz.利用时间-频率域联合描述的方法对数/模(A/D)采样后的数据进行分析.在4 km光纤延迟时,本系统最低探测速度为0.5 mm/s,速度分辨率达到毫米每秒量级,频率分辨率达到千赫兹量级.利用微多普勒信息探测技术,实现了探测物体表面的微动状态信息和识别运动状态的目的.     

光通信系统中前置跨阻放大器的研究和设计

本文介绍了前置跨阻放大器在光通信中光接收机上的应用及其发展方向，提出了一种新型的前置跨阻放大器电路结构，即在普通跨阻结构上适当地加了有源反馈的电路结构，并对它们进行了理论分析，最后用BSIM3v3模型，0．35μm工艺，Cadence仿真器工具对它们进行仿真，结果很好，带宽从lGHz增加到2．15GHz。     

相干纤维束及其在我国的应用

本文主要介绍多组分玻璃光纤相干纤维束的特性及其在我国的应用。     

采用PMD-QPSK和相干检测技术在G.652光纤上实现超长距离传输

给出了SMF-28 ULL超低损耗光纤的特点,列出了其与普通G.652光纤相关参数的对比;介绍了利用SMF-28 ULL超低损耗光纤进行超长距离传输试验的情况,并对试验结果进行了讨论。     

Four-Wave Mixing Between Coherent Signal and Incoherent Pump Light in Nonlinear Fiber

We report an experimental and theoretical investigation of the four-wave mixing (FWM) process between a coherent signal light and an incoherent pump light in a highly nonlinear fiber. In the experiment, two main phenomena are observed: 1) the peak power of the spectrum of the coherent signal light decreases along the fiber rather than be amplified; 2) the spectrum of the coherent signal is broadened. A theory of the FWM process between incoherent pump and coherent signal is proposed by considering the incoherence of the pump which has amplitude and phase fluctuations. The theoretical results agree with the experimental results.     

First-Order All-Pass Filter Canonical in the Number of Resistors and Capacitors Employing a Single DDCC

In this work, a voltage-mode canonical first-order all-pass filter is presented. The filter contains only a single resistor, a single capacitor, and a single differential difference current conveyor (DDCC). No passive component-matching constraints are required. A complementary metal oxide semiconductor CMOS implementation of a DDCC is given to simulate the proposed circuit with a Spice simulation program whose results illustrate the high performance of the circuit.     

Continuous and Damped Vibration Detection Based on Fiber Diversity Detection Sensor by Rayleigh Backscattering

An optical fiber vibration sensor based on a polarization diversity scheme has been developed to study structural vibration properties under external disturbance. The polarization diversity scheme has improved signal-to-noise ratio (SNR) by over 13 dB with capability of detection frequency of sub-hertz to tens of kilo- hertz. The minimum dynamic strain we have detected is 3 nepsiv, and the SNR of the sensor is >37 dB without any averaging. For the first time, Rayleigh backscattering has been utilized to detect continuous and damped vibration generated by a piezo fiber stretcher and vibrating cantilever with a frequency range of sub-hertz to 16 kHz. We also use this sensor and polarization analyzer to characterize the polarization state change and phase shift of the piezo fiber stretcher in transmission and Rayleigh backscattering up to kilohertz frequency, both results agrees quantitatively.     

等效凹槽滤波器及其在无源相关定位雷达中的应用(英文)

归一化最小均方误差(NLMS)算法被广泛应用于无源相干定位(PCL)雷达系统的直达波和多径干扰对消。该文提出NLMS干扰对消器与雷达模糊函数结合可以等效为凹槽滤波器,该滤波器在雷达模糊函数平面中的零多普勒处产生一个凹槽。分析显示凹槽的宽度和深度与NLMS算法的步长密切相关。文章分析了凹槽对PCL雷达目标检测的影响,结果显示宽的凹槽会使PCL雷达系统的目标检测性能恶化。文章进一步提出了非均匀归一化最小均方误差(Non-uniform NLMS, NNLMS)算法,该算法能有效抑制具有多普勒频率的杂波,并且能有效降低雷达模糊函数的底噪。该算法引进了步长矩阵,利用该矩阵可以实现在不同的距离单元产生不同宽度的凹槽,每个距离门的凹槽宽度取决于杂波干扰的能量和多普勒频率。与传统NLMS相比,NNLMS算法可以实现更快的收敛速度,试验结果验证了该算法的有效性及优越性。      

Position Effect of Spectral Filter on Properties of Highly Chirped Pulses in an All-Normal-Dispersion Fiber Laser

Numerical studies on the position effect of spectral filter (SF) in an all-normal-dispersion fiber laser are presented in this paper. The dependence of the available bandwidth range of the SF on its position in the laser cavity is investigated. Our simulation results suggest that the output pulses with high energy and strong peak power can be obtained when the SF with an appropriate spectral bandwidth is placed at the optimal positions in the laser cavity.     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

相干检测中的能量守恒与信噪比分析

对光通信相干检测原理中两个容易引起误解的问题进行了深入分析。一是零差接收机的光耦合器输入输出能量不守恒现象,指出这是因为混频方案默认信号光和本振光频率和相位完全同步,提供了隐形的"锁相增益"。二是纠正了经典文献将外差接收机噪声带宽设为符号率一半的错误,证明了外差检测中频信号和基带信号的信噪比相对零差检测基带信号的信噪比分别低6dB和3dB。     

Linear Fiber Impairments Mitigation of 40-Gbit/s Polarization-Multiplexed QPSK by Digital Processing in a Coherent Receiver

To provide higher capacity networks, 40-Gb/s transmission systems are under active development and their cost is on the way to be competitive with the one of 410 Gb/s. However, their lower tolerance to linear and nonlinear fiber impairments remains a major drawback for field deployment. To address the issue of linear impairments, coherent detection of multilevel formats with polarization division multiplexing appears as a promising solution by reducing the symbol rate to 10 Gbaud. Indeed, such coherent based systems have already demonstrated an improved tolerance to optical noise and an interesting capability to compensate for large amount of chromatic dispersion. In this paper, the tolerances to narrow optical filtering, chromatic dispersion, and polarization mode dispersion are investigated with coherent detection of 10-Gbaud quadrature phase shift keying (QPSK) with and without polarization division multiplexing. Moreover, the efficient mitigation of these linear impairments by digital processing in a coherent receiver is demonstrated in an ultralong haul transmission (4080 km) of 40-Gb/s QPSK polarization multiplexed data.     

Design and Performance of an Adaptive Filter in Fiber Optical Pressure Sensors

In this paper, a compensation model based on the signal channel and the reference one is established. Then an electronic adaptive filter is performed using one-step residual error for the optical fiber pressure sensor. In our realization we employ only one parameter to be tracked by adaptive filter. Thus a real-time processing is obtained.     

Optimum Threshold Signal Detection in Broad-Band Impulsive Noise Employing Both Time and Spatial Sampling

This paper investigates the optimum detection of a weak signal, where this signal is dominated by broad-band impulsive noise. It has been suggested that by using a form of space diversity reception (many receiving sites), it would be possible to "look between the large noise pulses" and thereby detect a signal well buried in the noise. In this paper we obtain and determine the performance of the locally optimum (or threshold) detector for any form of interference and apply these results to an example case of atmospheric noise for the single receiver case and for the diversity case of many receivers. Substantial improvement or processing gain can be obtained with one receiver with substantial, but less, additional improvement obtainable by then going to many additional receivers.     

Acoustooptic Coherent Mode Coupling in Polarization-Maintaining Fiber and Its Application as a Variable-Polarization-Dependent Loss Element

In this letter, we investigate coherent acoustooptic coherent mode coupling from the LP₀₁ core mode to LP_1m cladding mode of a polarization-maintaining fiber (PMF) induced by two acoustic gratings. We show narrowband variable attenuation along either birefringent axis of the PMF by varying the relative phase between the two acoustic gratings. By launching two acoustic gratings at different frequencies, variable attenuation and low crosstalk along either birefringent axis within the acoustooptic coupling bandwidth are demonstrated     

光纤激光相干合成中倾斜波前控制的研究进展

相干合成是获得高功率、高光束质量激光输出的有效方法之一。在光纤激光相干合成中,各路激光的活塞相差、倾斜波前和光束拼接方式直接影响合成光束的质量。各个单元光束波前的倾斜误差对合成的效果有重要影响,因而倾斜波前控制具有重要的意义。详细介绍了液晶空间光调制器、高速倾斜镜和光纤自适应准直器等常用的倾斜控制器件,对比目前用于倾斜波前控制的不同方案,分析了各方案的优缺点。并对光纤激光相干合成中倾斜波前主动控制的发展进行了总结和展望。     

双通道光纤通信波分复用滤光片的设计与模拟

讨论了在采用薄膜干涉方法分（合）波时,其中的关键器件－薄膜干涉滤光片的设计和镀膜监控误差模拟,主要介绍了一个波分复用双通道薄膜干涉滤光片的设计原理、设计过程、滤光片的性能及影响因素分析。并进行了假定监控误差下的镀膜过程的模拟。