光纤作为量子信道的性能

本文研究光纤作为量子信道在密波分复用时模式间非线性干扰造成的信道噪声的性质 ,和光纤量子信道在该噪声下的经典容量 .用位移算符方法计算量子噪声的累加 ,同时建立了有衰减和噪声时的信道的量子模型 .本文论证如果干扰是各其他模式独立而均等的贡献的叠加 ,信道噪声是热辐射噪声类型的 ,并求出了在给定参数的情况下的经典容量     

Incoherent in-band crosstalk induced power penalty in amplified WDM networks: a comparative study using Gaussian and chi-squared probability density functions

An analytical expression for power penalty (PP) from the formula for bit-error rate is derived by employing saddle point approximation in the chi-squared probability distribution function. This theory differs from the earlier ones in that it takes into account the dominant signal-amplified spontaneous emission beat noise applicable for optically pre-amplified systems. Imperfect extinction ratio accounting for higher power penalties is also considered in the analysis. Results have been compared with the available experimental results for a low number of crosstalk sources and an excellent agreement has been found. Although Gaussian probability density function (pdf) is simple to analyse, PP calculated from this pdf for a low number of crosstalk sources fails to match with the experimental results.     

光互联网中新型双向OXC的串扰分析

本文基于光纤布喇格光栅和光环行器提出了2×2双向光交叉连接器光串扰分析模型.分析了基于新型模型的相干串扰与非相干串扰的原理、特性以及它们对系统性能的影响.我们采用蒙特卡洛方法进行仿真实验,仿真结果表明,新型双向光交叉连接器的相干串扰将随着波长数的增加而增加且具有较小的功率代价特性.这种新型的双向光交叉连接器通过级联可扩展到N×N的波长路由.它在未来的全光网络中有较好的应用前景.     

Comparative analysis of wavelength-multiplexed photonic-sensor networks using fused biconical WDMS

Three networks based on fused biconical wavelength division multiplexers (WDMs) and fiber Bragg gratings (FBGs) are theoretically and experimentally demonstrated for photonic-intensity-sensor multiplexing. The aim of replacing standard couplers for WDMs in the power division process is to reduce power losses and improve the robustness of the systems to FBG wavelength shifts. The different network topologies are analyzed both in terms of power budget and crosstalk noise, considering the multiplexing of two fiber-taper displacement sensors. The configuration with one detector for each sensor and the corresponding FBG at the detection end is proven to be the best topology in terms of crosstalk, doubling the peak-isolation value of the WDMs employed and yielding a 37.4 dB optical signal-to-noise ratio for a two-sensor network. Regarding power losses, the optimum configuration locates the FBGs at the sensor heads, thus improving power budget and avoiding additional couplers at the detectors. Both topologies are expanded to multiplex four sensors, with crosstalk identified as the critical factor in these networks. With this limiting parameter, the first configuration has been determined as the most suitable for multiplexing a high number of sensors.     

Self-seeded reflective semiconductor optical amplifier based optical transmitter for up-stream WDM-PON link

A novel up-stream transmitter for wavelength division multiplexed-passive optical network (WDM-PON) using a self-seeded reflective semiconductor optical amplifier (RSOA) was proposed. The RSOA was self-seeded by an amplified spontaneous emission itself using a fibre Bragg grating without an additional optical source. The side mode suppression ratio of self-seeded output signal and the extinction ratio were ~28 and 8.1 dB, respectively. Required power for 10^-9 BER at 622 Mb/s was about -28 dBm and the power penalty after 20 km transmission was <2 dB for 30 nm range of wavelength     

A transmission length limit for space division multiplexing in step-index silica optical fibres

ABSTRACT

By solving the power flow equation, we investigate the influence of mode coupling on space division multiplexing capability of three multimode step-index silica optical fibres with a different strengths of mode coupling. Results show that mode coupling significantly limits the length of these fibres at which the space division multiplexing can be realized with a minimal crosstalk between the neighbour optical channels. This is most pronounced in silica optical fibres with the strongest mode coupling. The two and three spatially multiplexed channels in the investigated step-index silica optical fibres can be employed with a minimal crosstalk up to the fibre lengths of few hundred of meters and few tens of meters, respectively. These lengths are much shorter than kilometer lengths at which these fibres are usually employed without space division multiplexing. Such characterization of optical fibres should be considered in designing an optical fibre transmission system for space division multiplexing.     

基于噪声信号和改进VMD的滚动轴承故障诊断

受运行环境及传递路径影响,滚动轴承声音信号中包含有强背景噪声和较大的非周期性瞬态冲击成分,导致轴承故障特征提取困难.文中提出一种基于自适应变分模态分解(AVMD)的滚动轴承噪声信号故障诊断方法.该方法首先根据不同的信号自适应地确定模式数和惩罚因子,利用优化参数的VMD对原始信号进行分解,得到多个本征模式分量;然后计算各...     

Flat broadband wavelength conversion based on cascaded second-harmonic generation and difference frequency generation in segmented quasi-phase matched gratings

Bandwidth enhancement and response flattening of wavelength conversion based on single-pass and double-pass cascaded second harmonic generation and difference frequency generation were investigated in segmented quasi-phase matched (QPM) gratings. It is shown that the signal and pump bandwidths are both efficiently widened by increasing the segment number of the QPM grating and optimising the poling period of each segment. The ripple on the matching response is also very small. The conversion bandwidth in a 3-cm-long three-segment waveguide reaches 150–160?nm, which is over the whole conventional band and long-wavelength band. Larger signal bandwidth can be obtained with a little response flatness penalty and conversion efficiency penalty, which can be compensated by increasing the input pump power. Compared with a sinusoidally chirped optical superlattice device, a wavelength converter based on the segmented gratings has higher conversion efficiency, broader bandwidth and better pump-wavelength tolerance, and is easier to fabricate in practice.     

Performance of burst-mode receivers for optical digital pulse position modulation in passive optical network application

A DC coupled burst-mode receiver for digital pulse position modulation (DPPM) is proposed for the first time. An analysis of the potential performance benefits of using such a receiver configuration in the upstream of a passive optical network is given. An optical pre-amplifier is assumed. Bit error rate expressions are derived and the performance is evaluated in terms of sensitivity and threshold acquisition penalty. Results are compared with a DC-coupled on?off keyed non-return-to-zero burst-mode receiver, and it is seen that DPPM?s continuous mode sensitivity advantage (about 8 dB for the optimal case) is only reduced to 7.7 dB when overhead preamble is restricted to 12 bits and 6 dB when restricted to 6 bits. Thus, if necessary, DPPM can almost recover its sensitivity advantage by a trade off with preamble length. As such DPPM can potentially offer an increase in optical network unit numbers by a factor of 4 or, alternatively, an increase in range of around 20 km.     

Inviscid instability of an unbounded shear layer: effect of surface tension, density and velocity profile

The inviscid temporal stability analysis of an unbounded shear layer of two fluids of different density is investigated. Two background velocity profiles are considered: the piecewise-linear profile and the more realistic error-function profile. The disturbance kinetic energy is analyzed to physically understand the mechanism that causes instability. The surface-tension effect is investigated extensively. Surface tension is found to destabilize the neutrally stable waves that exist when surface tension is absent. This surface-tension-induced unstable mode is generally weaker than the dominant mode and extremely less evident when the density and/or viscosity difference increases. Short-wavelength instability is observed with a background viscosity jump at the interface. A comparison between the two velocity profiles is presented. The piecewise-linear profile does not match the more realistic results obtained with the error-function profile in the short wavelength range, especially in nonhomogeneous shear-layer flows; however, the phase-speed results are in a good agreement with those of the error-function profile.     

In-band optical signal-to-noise ratio monitoring method based on high-resolution polarization analysis and induced differential group delay

We report on an in-band optical signal-to-noise ratio monitoring technique for wavelength division multiplexed channels. Our proposal relies on the different degree of polarization between the signal (highly polarized) and the noise (not polarized). Using this principle, we divide the signal under test into two orthogonal polarization components and induce a differential group delay via a controlled birefringence apparatus that produces a wavelength-dependent shift of the polarization state of the signal. After a linear polarizing filter, high-resolution spectral analysis allows measurement of the amplified spontaneous emission noise level. The method is tested by experimental measurements of a 40 Gbit/s differential phase-shift keying channel showing very good performance.     

Use of an additive noise to transfer spatial information from a laser to a stimulated Raman beam

A spatial signal cannot be converted from a laser wavelength to a stimulated Raman scattering wavelength if the laser intensity is too weak to obtain the stimulated Raman. The addition of high intensity spatial noise can help the Raman excitation if averaging occurs in the nonlinear system to restore the spatial signal. In order to have a sufficient quality of spatial information transfer, optimization of the noise intensity dependent on the signal intensity must be carried out. A model based on this idea is studied.     

宽带铋基掺铒光纤放大器增益及噪声特性研究

利用Er3 离子四能级结构速率方程组和光功率传输方程组,数值模拟了铋基掺铒光纤放大器(EDFA)的增益及噪声特性,模拟结果与实验报道结果取得了很好的一致。同时,详尽地分析了增益及噪声特性与光纤长度、泵浦功率和输入信号功率的关系,优化了放大器的性能,从理论上得出一个20dB增益带宽达76nm、噪声系数接近4dB的铋基EDFA。研究表明了铋基掺铒光纤放大器适合用作于现代DWDM系统中C L波段的光纤放大器。     

The bipenalty method for arbitrary multipoint constraints

In finite element (FE) analysis, traditional penalty methods impose constraints by adding virtual stiffness to the FE system. In dynamics, this can decrease the critical time step of the system when conditionally stable time integration schemes are used by introducing spurious modes with high eigenfrequencies. Recent studies have shown that using mass penalties alongside traditional stiffness penalties can mitigate this effect for systems with a one single‐point constraint. In the present work, we extend this finding to include systems with an arbitrary set of multipoint constraints. By analysing the generalised eigenvalue problem, we show that the values of spurious eigenfrequencies may be controlled by the choice of stiffness and mass penalty parameters. The method is demonstrated using numerical examples, including a one‐dimensional contact–impact formulation and a two‐dimensional crack propagation analysis. The results show that constraint imposition using the bipenalty method can be employed such that the critical time step of an analysis is unaffected, whereas also displaying superiority over the mass penalty method in terms of accuracy and versatility. Copyright © 2012 John Wiley & Sons, Ltd.     

Gain-clamped erbium-doped fibre amplifier for wavelength division multiplexed systems

Abstract

Amplification of multiwavelength signals by an erbium-doped fibre amplifier (EDFA) is becoming critical, due to the proliferation of wavelength division multiplexed systems. However, when a standard EDFA is employed, dissimilarities between signal gains may prove unacceptable. Thus, a novel gain-clamped EDFA is proposed here to tackle the issue of gain tilt, a measure of maximum gain difference. The suitability of the configuration is then investigated through a numerical model, which is developed based on the standard EDFA and fibre laser models.     

Gain improvement in a dual-stage S-band EDFA by filtration of forward C-band ASE

Gain improvement in a dual-stage S-band erbium-doped fiber amplifier (S-band EDFA) is demonstrated using a broadband fiber Bragg grating (FBG) operating in the conventional-band (C-band) region or a C-band/S-band wavelength division multiplexing (WDM) coupler which filters out the forward C-band amplified spontaneous emission (ASE) in the amplifier system, thus increasing the population inversion in the S-band region. The gain for the amplifier with the WDM coupler increases by about 8.5 dB with an input signal power of ?40 dBm, compared to that of the conventional dual-stage amplifier. The gain improvement varies from 4.0–9.2 dB at a wavelength region between 1480 to 1512 nm without a significant noise figure penalty.     

基于排气噪声的柴油机失火故障诊断

通过计算机和声传感器采集排气噪声,研究九种工况下柴油机排气噪声的频谱规律。通过对柴油机排气噪声信号功率谱分析,提取二个参数来表征排气噪声的频谱规律。对这两个参数在各工况下的值进行了详细的分析后,发现这两个参数在失火工况下有较大的变化,故对这两个参数确定相应的阈值来诊断失火故障。通过编写相应的故障诊断程序,输入排气噪声样本和对应的转速后即可判断出失火故障。这种方法具有非接触,操作简单,成本低的特点。     

集合经验模态分解的稳健滤波方法研究

为了消除野值和噪声信号对观测数据的影响,给出一种基于集合经验分解的具有稳健性的滤波算法：首先用滑动中值滤波算法剔除原始数据中的野值,然后采用集合经验模态分解算法,抑制数据中的噪声。数值仿真和实际工程应用表明,该方法不仅能剔除野值,抑制信号中的噪声,提高信噪比,还能够有效消除模态混叠问题,将被测信号中不同的频率成分独立分解在不同的固有模态函数中,从而得到更清晰的时频分布,有利于实际数据处理中的信号分析和故障诊断。     

Large area double p–i–n heterostructure for signal multiplexing and demultiplexing in the visible range

Results on the use of a double a-SiC:H p–i–n heterostructure for signal multiplexing and demultiplexing applications in the visible range, are presented.Modulated monochromatic beams together (multiplexing mode), or a single polychromatic beam (demultiplexing mode) impinge in the device and are absorbed, accordingly to their wavelength, giving rise to a time and wavelength dependent electrical field modulation.Red, green and blue pulsed input channels are transmitted together, each one with a specific transmission rate. The combined optical signal is analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that in the multiplexing mode the output signal is balanced by the wavelength and transmission rate of each input channel, keeping the memory of the incoming optical carriers. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing regaining the transmitted information. An electrical model gives insight into the device operation.     

Optimal due date quoting for a risk-averse decision-maker under CVaR

This study investigates a due date quoting problem for a project with stochastic duration, taking the decision-maker’s risk attitude into consideration. The project profit is defined as the difference between the price and the cost that is comprised of production cost and earliness–tardiness penalties. In this situation, the due date determination has to be modelled as a stochastic optimisation due to stochastic duration. Conditional value at risk is thus employed as a performance measure to describe the decision-maker’s risk attitude. In fixed price contract, when the unit production cost is not smaller than the unit penalty on earliness, the optimal due date increases with the increase of the degree of a decision-maker’s risk aversion, the unit penalty on delay, and the decrease of the unit penalty on earliness. Besides, when the price is proportional to the due date and the slope is no bigger than the unit penalty on tardiness, the optimal due date is smaller than the result in fixed price. This is because high price for a short due date encourages a decision-maker to quote a small due date. Further, we compare the optimal due date in different parameter setting where the penalty coefficient of earliness is negative or zero, which means there is reward or no penalty on earliness, respectively. Finally, a case study is conducted to validate the effectiveness and efficiency of the proposed model.