Evolution of a narrowband exchange toward broadband

Today's telecommunications network is facing a continuing evolution, driven by the growing interest and demand for services requiring higher bandwidth and flexibility of transport. Replacing a narrowband switch fabric with a broadband switch fabric allows the operator to reuse existing narrowband hardware and software, while adding new capabilities such as SDH and ATM, making performance and capacity upgrades possible     

抗背景光干扰的双波长激光脉冲相关检测方法

针对激光脉冲相关检测易受背景光干扰影响的问题,提出了一种抗背景光干扰的双波长激光脉冲相关检测电路设计方案。设计了四路视场相同的探测单元,分别在其前面加装中心波长不同的窄带滤光片。当其中一个工作波长的威胁激光出现时,对应波长的两路探测器的输出与威胁激光信号和背景光响应,而另外两路探测器的输出则仅作为背景光响应,将它们分别对应相减后再进行相关处理,从而抑制各单元间相关背景光的干扰,同时实现对双波长激光脉冲的相关检测。实验结果表明:电路在实现对背景光干扰有效抑制的同时还能实现对双波长激光脉冲的相关检测,证明了设计方案的可实施性与有效性。     

变换域窄带干扰检测算法研究

基于数据链的应用背景,在直接序列扩频系统下,研究了不同变换域窄带干扰检测算法的基本原理,包括基于一、二阶矩的门限算法、K谱线法、条件中值滤波法及连续均值剔除算法。通过仿真对比了不同算法的干扰检测抑制性能。仿真结果表明,在几种干扰检测算法中,连续均值剔除算法对于典型窄带干扰的检测能力最优,能够实现干扰的快速实时检测处理。     

Absorption measurement of methane gas with broadband light source using fiber-optic sensor system

The absorption coefficient of methane is very important for measuring the concentration of methane.We theoretically analyzed the general expression of methane absorption coefficient for a given condition,at room temperature of 296K,and we simulated the relationship between the absorption and the wavelength of the light source.The experimental results we obtained are consistent with the simulation.The discrepancy between the experimental results and the simulation results is also discussed.     

Distributed sensing of polarization mode coupling in highbirefringence optical fibers using intense arbitrarily polarizedcoherent light

A polarization diversity detection system for location of polarization mode coupling has been studied both theoretically and experimentally for use with high birefringence fibers. Two complementary detectors are found to be sufficient for reliable operation of a pump-probe method based on the optical Kerr effect. Such a system is capable of locating any mode coupling point with arbitrary pump and probe polarization states when pump and probe polarization switching techniques are used to avoid signal fading. Experimental results are in good agreement with theory     

Capacity assessment of a cellular radio system using a narrowband multiuser detector

With a narrowband multiuser detector (MUD), multiple users can simultaneously share the same channel without using a bandwidth-expanding signature code when sufficient power differences at the receiver are maintained. In this paper, we assess the capacity gain that can be achieved in a hypothetical cellular system with centralized power control, using a narrowband MUD based on successive cancellation. The power-control algorithm is adapted to multiple users per channel in a cell. Simulation results are presented for two heuristic carrier-to-interference ratio-based channel-assignment schemes. The MUD allows for a substantial capacity gain due to a tighter packing of users in a channel. The observed gain compared with a conventional single user-per-channel system, ranges from 1.4 to 5 for cluster sizes C = 1 and 7, respectively.     

一种带环形器的双抽运掺铒光纤光源

把光纤环形器使用在掺铒光纤光源的结构中,得到C L波段的宽带光源.采用这种结构,通过调节三个激光二极管的控制电流到合适的数值,可以让输出光的功率提高到168.67mW(22.27dBm),带宽达到80.701nm(1525.112～1605.813nm).同时通过实验发现,研制的光源不仅有较高的功率,而且输出光平坦.     

Reference-free PRFS MR-thermometry using near-harmonic 2-D reconstruction of the background phase

Proton resonance frequency shift (PRFS) MR thermometry (MRT) is the generally preferred method for monitoring thermal ablation, typically implemented with gradient-echo (GRE) sequences. Standard PRFS MRT is based on the subtraction of a temporal reference phase map and is, therefore, intrinsically sensitive to tissue motion (including deformation) and to external perturbation of the magnetic field. Reference-free (or reference-less) PRFS MRT has been previously described by Rieke and was based on a 2-D polynomial fit performed on phase data from outside the heated region, to estimate the background phase inside the region of interest. While their approach was undeniably a fundamental progress in terms of robustness against tissue motion and magnetic perturbations, the underlying mathematical formalism requires a thick unheated border and may be subject to numerical instabilities with high order polynomials. A novel method of reference-free PRFS MRT is described here, using a physically consistent formalism, which exploits mathematical properties of the magnetic field in a homogeneous or near-homogeneous medium. The present implementation requires as input the MR GRE phase values along a thin, nearly-closed and unheated border. This is a 2-D restriction of a classic Dirichlet problem, working on a slice per slice basis. The method has been validated experimentally by comparison with the “ground truth” data, considered to be the standard PRFS method for static ex vivo tissue. “Zero measurement” of the gradient-echo phase baseline was performed in healthy volunteer liver with rapid acquisition (300 ms/image). In vivo data acquired in sheep liver during MR-guided high intensity focused ultrasound (MRgHIFU) sonication were post-processed as proof of applicability in a therapeutic scenario. Bland and Altman mean absolute difference between the novel method and the “ground truth” thermometry in ex vivo static tissue ranged between 0.069 °C and 0.968 °C, compared to the inherent “white” noise SD of 0.23 °C. The accuracy and precision of the novel method in volunteer liver were found to be on average 0.13 °C and respectively 0.65 °C while the inherent “white” noise SD was on average 0.51 °C. The method was successfully applied to large ROIs, up to 6.2 cm inner diameter, and the computing time per slice was systematically less than 100 ms using C++. The current limitations of reference-free PRFS thermometry originate mainly from the need to provide a nearly-closed border, where the MR phase is artifact-free and the tissue is unheated, plus the potential need to reposition that border during breathing to track the motion of the anatomic zone being monitored.A reference-free PRFS thermometry method based on the theoretical framework of harmonic functions is described and evaluated here. The computing time is compatible with online monitoring during local thermotherapy. The current reference-free MRT approach expands the workflow flexibility, eliminates the need for respiratory triggers, enables higher temporal resolution, and is insensitive to unique-event motion of tissue.     

Frequency domain detection of coherence multiplexed sensor signalsby using an optical loop with a frequency shifter

We describe a frequency domain detection scheme of coherence multiplexed sensor signals by using an optical loop with a frequency shifter. The optical path differences of the sensors are adjusted to integer-multiple of the loop length of the optical loop, and then the the sensor signals are multiplexed in the frequency domain, appearing at the integer-multiple of the working frequency of the frequency shifter. In the experiment, four Michelson-type sensors are successfully multiplexed with the sensitivities of about 2 mrad/√Hz. The sensitivities are also theoretically calculated which are in good agreement with the experimental results. The optimum design of the optical loop is also discussed     

狭缝光电池的光栅角度检测方法

提出了一种新颖的单光栅增量式角度检测方法。该方法采用狭缝光电池阵列按照一定的逻辑相位组合取代光栅副中的定光栅,通过码盘与狭缝光电池阵列相互配合完成计数操作。这样既回避了狭缝与码盘的间隙问题,又降低了增量式光电编码器对抖动的敏感程度和其相关零件的精度要求,进而提高了莫尔条纹对比度,增强了细分精度,最终增强了其计量精度和计量的稳定性。采用狭缝光电池阵列可以实现在工业级大间隙的高对比度、高计量精度的角度检测,并且可从整体上较大地提高光电编码器的系统鲁棒性。     

Gain clamping in two-stage L-band EDFA using a broadband FBG

A gain-clamped long wavelength band erbium-doped fiber amplifier (L-band EDFA) with an improved gain characteristic is demonstrated by simply adding a broadband conventional band (C-band) fiber Bragg grating (FBG) in a two-stage amplifier system. The FBG reflects backward C-band amplified spontaneous emission (ASE) from the second stage back into the system to clamp the gain. The gain is clamped at about 22.4 dB with a gain variation below 0.4 dB for input signal powers of -40 to -15 dBm. Compared with an unclamped amplifier of similar noise figure values, the small signal gain has improved by 2.4 dB due to the FBG which blocks the backward propagating ASE. At wavelengths from 1570 to 1600 nm, gain of the clamped amplifier varies from 19.4 to 26.7 dB. The corresponding noise figure varies by /spl plusmn/0.35 dB around 5 dB, which is not much different compared to that of the unclamped amplifier.     

InSAR中基于干涉图质量参数的相位展开

本文分析了二维相位展开算法的特点,探讨了基于干涉图质量参数的相位展开方法。按干涉图质量优劣排序,对InSAR干涉图进行相位展开,可以有效减小截断相位中无效点对相位展开结果的影响。文中给出了算法的详细描述,以及按干涉图质量参数排序进行相位展开的实验结果。     

Intermetallic phase detection in lead-free solders using synchrotron x-ray diffraction

The high-intensity, high-resolution x-ray source at the European Synchrotron Radiation Facility (ESRF) has been used in x-ray diffraction (XRD) experiments to detect intermetallic compounds (IMCs) in lead-free solder bumps. The IMCs found in 95.5Sn3.8Ag0.7Cu solder bumps on Cu pads with electroplated-nickel immersion-gold (ENIG) surface finish are consistent with results based on traditional destructive methods. Moreover, after positive identification of the IMCs from the diffraction data, spatial distribution plots over the entire bump were obtained. These spatial distributions for selected intermetallic phases display the layer thickness and confirm the locations of the IMCs. For isothermally aged solder samples, results have shown that much thicker layers of IMCs have grown from the pad interface into the bulk of the solder. Additionally, the XRD technique has also been used in a temperature-resolved mode to observe the formation of IMCs, in situ, during the solidification of the solder joint. The results demonstrate that the XRD technique is very attractive as it allows for nondestructive investigations to be performed on expensive state-of-the-art electronic components, thereby allowing new, lead-free materials to be fully characterized.     

一种双抽运结构C+L波段掺铒光纤宽带光源

介绍了一种结构简单、工作在C+L波段掺铒宽带光源。实验中用3dB宽带耦合器作为光纤反射镜,同时利用功率控制电路让光源输出光稳定,先用两个980nm二极管作为抽运源,将后向的C波段ASE重新引回光纤中,提高了抽运源的利用效率和光纤输出光的稳定性,优化掺铒光纤长度,获得了功率高达26.67mW(14.26dBm)的C+L波段ASE光输出,平均波长1550.887nm。之后采用一个980nm和一个1480nm的激光二极管,在输出相对平坦的情况下,得到了最高功率为23.23mW(13.66dBm),平均波长为1556.46nm的C+L波段ASE光输出,光纤环形镜的使用,不仅改善了光源的平坦度,并且大大提高了光光转化效率。     

强噪声背景下的信号检测方法研究

提出了一种利用高阶统计量对强噪声背景下的弱信号进行检测的方法。这种检测方法对加性噪声中的确定性信号以及非高斯信号均有效 ,且可以弥补似然比检测的不足。     

Stochastic object detection using its image with unknown parameters in the presence of background

A specific case where the image has the unknown area, regular component, and also the random component intensity has been considered. A maximum likelihood algorithm for the detection of stochastic image with unknown parameters was synthesized. Characteristics of the algorithm were obtained, and the impact of image characteristics and applicative background on the detection efficiency was analyzed.     

A coarse frequency offset estimation in an OFDM system using theconcept of the coherence phase bandwidth

We propose a new coarse frequency offset estimation algorithm in orthogonal frequency-division multiplexing systems, which performs robust operation in the presence of a symbol timing offset within an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed, and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. The proposed algorithm adapts the concept of the coherence phase bandwidth for the purpose of weakening the effect of the symbol timing offset     

Suppression of stimulated Brillouin scattering during transmission of high-power narrowband laser light in monomode fibre

A method is described for transmitting narrowband laser radiation over long lengths of monomode fibre at high power levels without suffering nonlinear attenuation due to stimulated Brillouin scattering. The technique could be applied to long-distance coherent optical data transmission.     

Integrated waveguide modulator using a LiNbO3TE&rlarr2;TM convertor for electrooptic coherence modulation of light

The authors report a wavelength independent TE-TM mode convertor used as a waveguide electrooptic modulator in a coherence modulated system. The modulation voltages thus obtained (20 V) are about 10 times lower than those previously reported in earlier coherence modulated devices. The modulator is a strip waveguide fabricated on Y-cut Z-propagation, Ti-indiffused LiNbO₃. When used in conjunction with a birefringent plate and polarizers, the modulator is shown to imprint on light a signal encoded into an optical delay greater than the source coherence length. Demonstration of the device is reported using a highly multimode laser diode at 820 nm     

混合遗传算法优化设计宽带加载螺旋天线

研究了遗传算法和模拟退火法相结合的方法来快速优化设计宽带加载螺旋天线.采用该算法对加载螺旋天线上的加载集总元件的值、加载位置以及匹配网络参数进行一体化优化设计.采用一种简单有效的方法来快速求解加载元件值和加载位置改变后的阻抗矩阵方程,提高了优化设计的效率.利用该方法成功地设计了两副宽带小型化加载螺旋天线.