利用SOA中FWM效应以及高非线性光纤中SPM实现40Gb／s信号的全光3R再生

通过半导体光放大器中的四波混频效应实现了全光3R再生方案中的波长转换，利用光脉冲在高非线性光纤中的自相位调制来获得40Gb／s全光3R再生信号，并使用Optisystem对其进行了仿真实验．结果表明，3R再生信号的质量得到了很好的提高．     

100Gb/s归零码信号的2R再生

本文提出了基于半导体光放大器(SOA)中的瞬态交叉相位调制(T-XPM)效应与交叉增益压缩(XGC)效应的全光2R再生方法, 同时研究了SOA中的T-XPM效应获得反逻辑码信号以及XGC 效应光开关门的特性, 实现了100 Gb/s归零码(RZ)信号的2R再生, 接收机灵敏度提高了1.7-2 dB; 对该方案中的反逻辑码对于再生效果的影响进行了量化研究, 并在C波段范围内研究了该再生方案的再生效果, 实现了覆盖1535-1555 nm的全光2R再生.     

40 Gb/s信号全光3R再生实验

提出一种新型40 Gb/s全光3R再生器方案。采用高精细度法布里-珀罗滤波器进行时钟提取。时钟提取前,通过高稳定光源对输入信号光波长变换实现信号光波长和法布里-珀罗滤波器梳状窗口对准;时钟提取后,接半导体光放大器(SOA)进一步消除时钟信号噪声。全光判决中,采用双半导体光放大器串联增大非线性性能,提高了判决门的响应速度。判决输出接窄带滤波器去除脉冲啁啾拖尾,减小码型效应。实验中,恶化40 Gb/s光脉冲信号通过全光3R再生器可以得到再生脉冲。输入恶化信号时间抖动大于5 ps,脉冲宽度大于16 ps,再生得到的信号时间抖动小于1.5 ps。再生信号相对于输入信噪比改善14 dB。连续稳定工作记录大于15 h。通过实验验证,这种全光3R再生器方案成功地实现了40 Gb/s信号的再生。     

10 Gb/s全光3R再生的研究

报道了对10Gb／s恶化数据信号的全光3R(再放大、再定时、再整形)再生的实验研究。针对利用基于半导体光放大器的注入锁模环形激光器进行时钟恢复时的码型效应问题,提出了利用梳状滤波器对信号进行预处理。利用这个技术极大的减小了由于码型效应造成的时钟信号的幅度和时间抖动,从恶化的数据信号中恢复出无码型效应的高质量光时钟脉冲。信号整形的关键是光判决门,性能良好的判决门可以进一步提高信号的消光比、减小抖动。研究了基于电吸收调制器的信号再整形。利用上述器件构成的3R再生器,实现了10Gb／s恶化信号的全光3R再生。     

基于信号抽运的光纤光参量放大的全光3R再生系统

本文研究了利用恶化信号作为抽运的光纤光参量放大效应(FOPA)进行全光判决的全光3R(再放大、再整形、再定时) 再生实验方案,理论上分析了在不同的抽运功率条件下时(分别对应"0"和"1"码)参量放大抑制噪声的不同机理,表明选用合理的实验参数可以同时对"0","1"码噪声进行抑制.实验中利用高Q值的法布里-珀罗(F-P)滤波器提取了均方根(RMS)抖动仅为180 fs的40 GHz时钟;完成了对40 bit/s的单波长恶化信号的全光判决实验,将恶化信号的信噪比从4.52改善为11.43.实验验证了理论分析的 关键词： 光纤通信 3R再生 光纤光参量放大 全光判决     

有源非线性光纤中光脉冲的再生特性研究

提出了一种利用有源非线性光纤同时实现信号放大和整形的方案.根据有源非线性光纤中导波光脉冲的四波混频耦合模方程,采用对称分步傅里叶算法计算了光纤中增益分布对系统输入输出功率转移函数的影响,并给出了一种基于功率转移函数的全光2R再生性能评价方法(可用功率转移函数曲线上的三个特征点来表征).分析了增益泵浦方式、增益大小以及光纤长度对数据泵浦四波混频2R再生性能(包括输入消光比、输出消光比、消光比提升以及饱和增益等)的影响.研究表明,在同向增益泵浦情形下,提高泵浦功率可以有效提高全光2R再生器的饱和增益特性,并且使空号/传号的输入阈值功率减小;增加光纤长度同样可以有效提高再生器的饱和增益,但它会增加空号/传号的输入阈值功率.上述结论可为基于有源非线性光纤的全光2R再生器研制提供理论指导.     

基于光纤光参量放大的异步双波长全光再生技术研究

本文提出了一种新型的多波长全光再生方案,利用相位时钟光纤光参量放大,并采用相邻信道偏振正交的方法,实现对由异步信源产生的双波长信号全光再生.理论分析了参量放大中的增益饱和现象用于幅度噪声抑制,以及利用相位时钟及后续色散实现对信号定时的机理.在这个基础上,对两个独立信源产生的异步双波长10Gbit/s信号进行再生实验,实验表明该方案有效的抑制了基于多波长3R再生系统中信道间的四波混频与交叉相位调制等非线性干扰.系统在单波长和双波长情况下分别将两路信号信噪比改善了至少6.5dB与4.5dB.误码率测试结果说明,与背对背测试结果相比,无论是在单波长还是双波长条件下,两路波长的信号经过再生后都实现了约2dB的接收机功率代价的改善.     

基于色散位移光纤中四波混频效应的2×40 Gb/s全光3R再生系统

利用色散位移光纤(DSF)中四波混频效应在闲频光波长处增益的指数增长特性及增益饱和特性,提出了一种基于恶化信号抽运的2×40Gb/s的双波长全光3R(再放大、再整形、再定时)再生实验方案。对再生原理做了理论分析和实验验证,完成了1550.92nm和1557.36nm两个波长上不同恶化信号的全光再生实验,将恶化信号的接收机灵敏度分别由-20.3dBm、-20.4dBm改善到-27.3dBm、-25.6dBm,灵敏度改善量为7.0dB和5.2dB。系统实验验证了理论分析的结果,对于解决波分复用(WDM)系统中多路信号的同时再生问题提出了一种可行的解决方案。     

相位调制信号的全光再生技术

介绍了差分相移键控信号的全光再生技术.研究了多进制相位调制信号的全光再生技术.对适用于正交相移键控和差分正交相移键控信号的全光再生器进行了仿真.研究结果表明,这种再生器可以显著抑制信号的幅度噪音和相位噪音,使40 Gb/s RZ差分正交相移键控系统在误码率为10-12条件下的传输距离延长至2 000 km以上.     

基于高非线性光纤中四波混频饱和效应的NRZ-DPSK和RZ-DPSK信号幅度再生实验

利用高非线性光纤中的四波混频饱和效应,实验展示了42.8 Gbit/s非归零差分相移键控（NRZ-DPSK）信号和归零差分相移键控（RZ-DPSK）信号的全光幅度再生.测量了NRZ-DPSK信号和RZ-DPSK信号经过高非线性光纤的功率传递曲线.在平均输入功率均为16 dBm的条件下,对两种调制格式的再生性能进行了比较.实验结果显示RZ-DPSK信号具有更好的幅度再生性能.     

Efficient across-frequency integration in short-signal detection

A series of experiments was performed on the influence of bandwidth on the masked threshold of brief deterministic signals in continuous broadband noise. The signal bandwidth is quantified by the number (n) of constituent 1/3-oct bands. For n increasing from 1 to typically 9, the masked-threshold level in the constituent 1/3-oct bands is found to decrease by 8 log(n). This integration rule is obtained when each of the 1/3-oct bands covered by the signal equally contributes to detection, i.e., that, for each of these 1/3-oct bands, the difference between signal level and the individual masked-threshold level is the same. It was found that this integration rule also applies to noncontiguous signal spectra and that it remains intact over a broad range of masker levels. Commonly, the masked threshold of compound signals (for instance, n frequency components with a spacing of typically 1/3 oct), relative to the masked threshold of single-component signals, has been described by a 5 log(n) integration rule. However, this rule was obtained for signal durations of typically 100 ms or more. For the present brief signals (typically 10 ms or less), the across-frequency integration is found to be more effective.     

The study of third harmonic demodulation in phase modulation optical heterodyne technique using optical resonator

With the technique of phase modulation optical heterodyne(PMOH), we detected the beat-frequency signal of the reflected wave from a F-P cavity. The frequency of the beat signal was three times of that of the modulation electric field, when the 3rd harmonic of the modulation electric field was used as the phase reference signal. The line shapes of the signal match those of the theoretical calculations, and the dispersion signal has good frequency-discrimination characteristic.     

Pulmonary resorption of inhaled gadobutrol in an animal model: usage to determine lung diffusion in MRI examinations

The aim of this study was to examine a pulmonary gadobutrol resorption after inhalation. An examination of 16 young swine, which were given different amounts of gadobutrol through inhalation, was performed. A measurement of the signal elevation in peripheral lung tissue as well as in the thoracic aorta was made using a T(1)-weighted FLASH-3D sequence in a 1.5 T magnetic resonance imaging (MRI) machine. Twenty minutes after gadobutrol application, a steep signal elevation in the aorta was reported, as well as a plateau phase after 45 min. The signal elevation in peripheral lung tissue after inhalation increased to a mean of 33.9%. The concurrent signal elevation of the abdominal aorta was 137.4%. The evaluation of an intravascular signal elevation after gadobutrol inhalation opens the possibility to evaluate and obtain lung diffusion with MRI.     

Longitudinal NMR and spin states in the A-like phase of 3He in aerogel

It was found that two different spin states of the A-like phase can be obtained in an aerogel sample. In one of these states, we have observed the signal of the longitudinal NMR, while, in the other state, no trace of such a signal was found. The states also have different properties in transverse NMR experiments. A longitudinal NMR signal was also observed in the B-like phase of ³He in aerogel. The text was submitted by the authors in English.     

Three-dimensional visualization of objects in scattering medium using integral imaging and spectral analysis

This paper presents a three-dimensional visualization method of 3D objects in a scattering medium. The proposed method employs integral imaging and spectral analysis to improve the visual quality of 3D images. The images observed from 3D objects in the scattering medium such as turbid water suffer from image degradation due to scattering. The main reason is that the observed image signal is very weak compared with the scattering signal. Common image enhancement techniques including histogram equalization and contrast enhancement works improperly to overcome the problem. Thus, integral imaging that enables to integrate the weak signals from multiple images was discussed to improve image quality. In this paper, we apply spectral analysis to an integral imaging system such as the computational integral imaging reconstruction. Also, we introduce a signal model with a visibility parameter to analyze the scattering signal. The proposed method based on spectral analysis efficiently estimates the original signal and it is applied to elemental images. The visibility-enhanced elemental images are then used to reconstruct 3D images using a computational integral imaging reconstruction algorithm. To evaluate the proposed method, we perform the optical experiments for 3D objects in turbid water. The experimental results indicate that the proposed method outperforms the existing methods.     

Investigation of magneto-optical effect in transverse magnetic field in He

The non-linear Voigt effect has been studied in He discharge under resonance laser interaction with the He transition. The range of non-linear signal existence was determined. The contribution of the lower and upper states to the overall signal was analyzed. The cross-section for depolarizing collisions with ground state He atoms was estimated for the 3³ D _2,3 He state. Received: 16 June 1998 / Received in final form: 14 December 1998     

The effect of modulation coherence on signal threshold in frequency-modulated noise bands

A series of four experiments was undertaken to ascertain whether signal threshold in frequency-modulated noise bands is dependent upon the coherence of modulation. The specific goal was to determine whether a masking release could be obtained with frequency modulation (FM), analogous to the comodulation masking release (CMR) phenomenon observed with amplitude modulation (AM). It was hypothesized that an across-frequency grouping process might give rise to such an effect. In experiments 1-3, maskers were composed of three noise bands centered on 1600, 2000, and 2400 Hz; these were either comodulated or noncomodulated with respect to both FM and AM. In experiment 1, the modulation was sinusoidal, and the signal was a 2000-Hz pure tone; in experiment 2, the modulation was random, and the signal was an FM noise band centered on 2000 Hz. The results obtained showed that, given sufficient width of modulation, thresholds were lower in a coherent FM masker than in an incoherent FM masker, regardless of the pattern of AM or signal type. However, thresholds in multiband maskers were usually elevated relative to that in a single-band masker centered on the signal. Experiment 3 demonstrated that coherent FM could be discriminated from incoherent FM. Experiment 4 gave similar patterns of results to the respective conditions of experiments 2 and 3, but for an inharmonic masker with bands centered on 1580, 2000, and 2532 Hz. While within-channel processes could not be entirely excluded from contributing to the present results, the experimental conditions were designed to be minimally conducive to such processes.     

垃圾渗滤液中溶解性有机物组分的三维荧光特性

运用三维荧光光谱技术研究了垃圾渗滤液中六种DOM组分的荧光特性。结果表明:类富里酸、类色氨酸和腐殖酸类物质是垃圾渗滤液DOM的主要组成,其中大量紫外区类富里酸物质的存在,是导致其可生化性差的主要原因。HOA含有较多紫外区类富里酸和较少可见区类富里酸,HIA正好相反;HIN组分主要包括紫外区和可见区类富里酸;HOB、HIB和HIN三种组分在各区域荧光信号都较强,包括HON组分在内,这四种组分荧光峰位置主要集中在类腐殖酸、紫外区类富里酸及可见区类富里酸三个区域;但不同组分的荧光强度差别较大,HOB和HIB在紫外区类富里酸有较强荧光强度,HIN在紫外区类富里酸、可见区类富里酸区域均有较强荧光强度;与这三者相比,HON在各位置的荧光信号中等;而HOA和HIA的荧光强度相对较弱,说明有机酸类物质的荧光特性较差。     

Measurement of the optical phase relation among subharmonic pulses in a femtosecond optical parametric oscillator

We observed the phase relation among subharmonic pulses generated by a femtosecond optical parametric oscillator (OPO). The ratio of the optical frequencies of the idler, the signal, and the pump pulses was set to 1:2:3. Under these conditions the wavelengths of the second harmonic of the signal pulse and the sum frequency between the pump and the idler pulses are the same. The beat signal between these two pulses represents the phase relationship among the pump, the signal, and the idler. The beat frequency varied when the cavity length of the OPO was changed.     

基于同步载波提取的光纤传感器相位生成载波解调方法

利用3×3耦合器和法拉第旋转镜等光学元件,构造了一个基于迈克尔逊干涉系统的光纤振动传感器.使用外调制的方法对传输光进行相位生成载波调制,并将该光纤振动传感器应用于长距离的安全监测中.通过对该传感器的干涉输出信号进行贝塞尔展开分析,发现干涉输出信号中含有与外调制所使用的载波频率相同的信号成分.因此,使用一个中心频率为载波频率且通带很窄的带通滤波器,可以同步地提取载波信号.同步提取的载波信号用于干涉输出信号的相位生成载波被动零差解调,可以得到作用于光纤振动传感器上的外界振动信号.本文提出了从输出信号中同步提取载波的方法,通过理论推导得出了该方法的可行性,并且通过软件仿真和实验验证了该理论的正确性.文中还对提取的载波受低频信号干扰,造成其幅度不稳定的现象进行分析并提出了解决方法.研究表明,同步载波提取法适用于相位调制器与干涉信号输出端距离较远,相位生成载波解调需要的同源载波获取较困难的情况.