Signal-to-noise ratio in optical photodiode receivers

The SNR of a frequency-compensated optical receiver is derived, and the validity of the assumptions used in the derivation is analyzed. A compensating circuit having a wide range of application in video receivers is suggested.     

Four-wave mixing of incoherent light in a dispersion-shifted fiberusing a spectrum-sliced fiber amplifier light source

We investigate the FWM efficiency of incoherent light in a dispersion-shifted fiber (DSF) using a spectrum-sliced fiber amplifier light source. A theoretical model is provided to describe the FWM mechanism of incoherent light. The FWM efficiencies of coherent and incoherent light are compared theoretically and experimentally. Unlike the FWM of coherent light, the FWM signals of incoherent light are mostly generated by nondegenerate FWM regardless of the number of input signals. Thus, when two input signals are mixed, incoherent light has about 6 dB higher mixing efficiency than coherent light due to the difference in their degeneracy factor     

Impact of dispersion, PMD, and PDL on the performance of spectrum-sliced incoherent light sources using gain-saturated semiconductor optical amplifiers

The effects of chromatic dispersion (CD), polarization-mode dispersion (PMD), and polarization-dependent loss (PDL) on the intensity noise suppression of spectrum-sliced incoherent light sources achieved by using gain-saturated (GS) semiconductor optical amplifiers (SOAs) are investigated. Passing the spectrum-sliced incoherent light through SOAs, the excess intensity noise (EIN) originating from beating of spontaneous emission against itself can be greatly reduced. However, since the noise suppression is achieved by an elaborate balancing between numerous frequency/polarization components of light, thus, forming a high correlation between them, it is vulnerable to frequency/polarization-dependent optical phenomena. Through Q-factor and bit error rate (BER) measurements, this paper shows that CD, PMD, or PDL deteriorates the SOA-based noise suppression technique by breaking the correlation. Spectral analysis is also performed to investigate the frequency dependency of these effects. It is shown that CD and PMD negate the noise suppression giving rise to intensity noise from high frequencies, whereas there is no frequency dependence for PDL effects. Therefore, CD-, PMD-, or PDL-induced penalties for incoherent light sources using the SOA-based noise suppression technique are considerably greater than those produced by pulse broadening or distortion alone.     

Noise suppression of incoherent light using a gain-saturated SOA: implications for spectrum-sliced WDM systems

In this paper, we present an experimental and numerical study of semiconductor optical amplifier (SOA)-based noise suppression and its relevance to high-channel-density spectrum-sliced wavelength-division-multiplexed systems. We show that the improvement in signal quality is accompanied by spectral distortion, which renders it susceptible to deterioration in the presence of subsequent optical filtering. This phenomenon originates from the loss of intensity correlation between spectral components of the SOA output when the signal spectrum is altered. As a consequence, a design tradeoff is introduced between intensity noise and crosstalk in high-channel-density systems. These adverse effects can be overcome by optimized SOA design, resulting in a significant improvement in signal quality.     

光盘系统的信噪比、象差容限及伺服误差

采用脉冲响应函数方法,分析光盘存储系统中光学头存在各种象差及伺服误差时,对读出信号信噪比的影响,从而导出了各类光学头的象差容限及伺服要求。     

Coupling light from incoherent sources to optical waveguides

Spatially coherent laser light can be coupled into an optical waveguide with nearly 100 percent efficiency. However, coupling light from a spatially incoherent source to a waveguide can be frustrating. Here the author describes how to efficiently couple blackbody radiation to optical fiber waveguides. The same basic principles hold for other types of waveguides, such as integrated optic waveguides. Radiation emitted from other types of extended sources, such as surface emitting LEDs or ionized gases, can be efficiently coupled to waveguides using the same techniques     

Signal-to-noise ratio analysis of 100 Gb/s demultiplexing usingnonlinear optical loop mirror

This paper investigates experimentally and theoretically the signal-to-noise ratio (SNR) characteristics of 100 Gb/s all-optical demultiplexing using a nonlinear optical loop mirror (NOLM). The analysis takes into account two effects that degrade the SNR associated with NOLM demultiplexing. First is channel crosstalk originating from the leakage of nontarget channels. Second is the intensity fluctuations of demultiplexed signals caused by the combined effects of timing jitter and a profile of the switching window. Considering these two effects, power penalties associated with NOLM. Demultiplexing are theoretically evaluated using the conventional noise theory of an optical receiver followed by an optical preamplifier. Experimental results of bit error rate measurements for 100 Gb/s demultiplexing using three different NOLMs with different intrinsic crosstalk values, defined by signal transmittance in the absence of control pulses, show that the power penalties are in good agreement with the evaluation based upon our proposed analysis. It can be found from our investigation in demultiplexing from 100 to 10 Gb/s that intrinsic crosstalk of less than -25 dB, corresponding to a coupling ratio, K, of |K-0.5|⩽0.03, is required for the power penalty of less than 1 dB. The root-mean-square (rms) value of the relative timing jitter necessary for obtaining a sufficient timing tolerance width for combining control and signal pulses is determined     

Optimization of large-scale fiber sensor arrays incorporatingmultiple optical amplifiers. I. Signal-to-noise ratio

We report on optimizing the signal-to-noise ratio (SNR) of large-scale fiber sensor arrays employing erbium-doped fiber amplifier (EDFA) telemetry with respect to the number of sensors per rung, the number of amplifiers per array, and the coupling ratio between the fiber buses and the rungs. Broad optimum regions are found, providing design flexibility to minimize pump power requirements. Simulations predict that 300 sensors can be multiplexed on a fiber pair while maintaining a high sensitivity (1 μrad/√(Hz)) for all sensors with a moderate input pump power (<1 W)     

Green grooming in spectrum-sliced elastic optical path networks

With the continuous expansion in network scale and the rapid growth of Internet traffic, a high-capacity and power-efficient transport system is required. The Spectrum-Sliced Elastic Optical Path Network (SLICE) based on Orthogonal Frequency Division Multiplexing has been considered as a promising solution due to flexible spectrum provisioning. In a SLICE, compared with traditional components, the bandwidth variable transponder and cross-connects have higher power costs. So it is necessary to make a green footprint in this new networking framework. In this paper, we make a comprehensive study of green grooming in SLICEs, with the objective to save both spectrum and power consumptions. An Integer Linear Programming formulation with various SLICE constraints is presented for the optimization problem above. Under the large-scale network scenario, we also propose the auxiliary graph model which reflects spectrum/power usage, grooming policies implemented by adjusting link costs according to a comprehensive power consumption model, as well as a threshold-based spectrum reservation scheme. As a result, an efficient heuristic called green grooming algorithm is designed. The extensive simulation results demonstrate that our heuristic obtains near-optimal results and achieves a better performance in terms of spectrum and power efficiencies compared with benchmarks, under various topology structures.     

Signal-to-noise ratio in neuro activation PET studies

It has become commonplace to compare scanner sensitivity characteristics by comparing noise equivalent count rate curves. However, because a 20-cm diameter uniform phantom is drastically different from a human brain, these curves give misleading information when planning a neuro activation PET experiment. Signal-to-noise ratio (SNR) calculations have been performed using measured data (Siemens 921 scanner) from the three-dimensional (3-D) Hoffman brain phantom for the purpose of determining the optimal injection and scanning protocol for [ (15)O] labeled activation experiments. Region of interest (ROI) values along with the variance due to prompt (trues plus randoms) and random events were determined for various regions and radioactivity concentrations. Calculated attenuation correction was used throughout. Scatter correction was not used when calculating the SNR in activation studies because the number of scattered events is almost identical in each data acquisition and hence cancels. The authors results indicate that randoms correction should not be performed and that rather than being limited by the scanner capabilities, neuro activation experiments are limited by the amount of radioactivity that can be injected and the length of time the patient can stay in the scanner.     

Signal-to-noise ratio for lightwave systems using avalanchephotodiodes

An expression for the signal-to-noise ratio (SNR) at the output of an avalanche photodiode (APD) receiver is derived that includes the effects of photoinjected carriers, dark-generated carriers, and the receiver circuitry. It is found that the dark current alters both the magnitude of the SNR and the value of the mean multiplication where the SNR achieves its maximum value. The formula differs from the expression that is conventionally used (S.M. Sze, 1981) in that it makes use of different excess noise factors for photo-generated and dark-generated carriers     

光通信乘性噪声信道基于LDPC码的SNR估计方法

针对目前现有的信噪比(SNR)估计 方法不适用光通信中乘性噪声信道的问题,分析了乘性噪声信道下,SNR失配 对低密度奇偶校验(LDPC)码性能的影响,并通过仿真表明乘性噪声信道下 SNR精确估计的必要性。提出了一种基于量化的LDPC 码判决反馈的SNR估计方法,首先对接收到的光信号进行量化,利用 简化后的期望最大(EM)算法对量化后的SNR 进行一次粗估计,接着利用基于LDPC迭代译码的判决反馈结果对 SNR进行精估计。仿真结果表明,本方法能够在接收 信号的均值和噪声方差等参数未知情况下,能有效完成LDPC码迭代译码的辅助 工作;在误码率(BER)为10－5时,SNR估计后 ,LDPC码的译码性能距离理想情况下的译码性能,仅有约0.12dB以内损失。     

Piezoelectrically induced optical phase modulation of light insingle-mode fibers

Optical phase modulation induced in piezoelectric copolymer, vinylidene fluoride (73 mol.%)/trifluoroethylene (27 mol.%), coated single-mode fibers has been examined and analyzed from both experimental and theoretical aspects. High-sensitive phase modulation, which is more than four times as large as those of vinylidene fluoride/tetrafluoroethylene copolymer, is obtained over a flat response range from 10 kHz to 3 MHz. At frequencies below 7 kHz and higher than 6 MHz the optical responses are dominated by axial and radial resonances, respectively, of the fiber-jacket composite. The theoretical prediction on induced phase shifts at high frequencies is carried out based on radial vibration analysis and followed by the experimental results     

Intensity modulation of light transmitted in curved optical fibres

Coupled-mode theory is used to explain the intensity modulation of transmitted light which results from small changes in the radius of curvature. It is shown that the mode coupling induced by bends in small-V fibres introduces an uncertainty into light-transmission measurements.     

用EDFA提高激光雷达的信噪比

提出了掺铒光纤放大器(EDFA)应用于激光雷达接收系统光学前置放大器以提高雷达探测性能和作用距离的方法.回波信号功率是影响雷达探测分辨率的因素,它随着探测距离的增大而减小.讨论了光电检测前放大回波信号的技术,结合激光雷达回波信号的特点对EFDA主要应用特性(增益特性、噪声特性)进行理论分析.建立了雷达信号传输模型,讨论了大气消光与大气湍流对回波信号的影响.将PIN-FET用作光电探测,给出了没有采用光放大和采用EDFA光学前置放大情况下的信噪比.数值模拟结果显示,将EDFA用作激光雷达接收机极大地提高了雷达系统的信噪比,探测距离越远探测性能的改善越明显.     

Phase modulation to amplitude modulation conversion of CW laser light in optical fibres

We have measured the induced amplitude modulation of sinusoidally phase-modulated CW 1.5 ?m laser light propagating in a single-mode fibre. Amplitude modulation approaching 100% was observed for light phase-modulated at 4 GHz and transmitted through 50 km of fibre. PM-AM conversion produces a power penalty in coherent transmission systems.     

Signal-to-noise ratio enhancement of cardiac late potentials usingensemble correlation

An optimal one-weight filter is presented for the purpose of improving the signal-to-noise ratio of averaged ECG recordings in the analysis of late potentials. Based on a simple statistical model, the filter is estimated from the ensemble correlation of available beats. The correlation estimator is found by a maximum likelihood procedure in which the observed signal is assumed to have a Gaussian distribution. The performance of the optimal filter is studied in relation to an ensemble with individual or subaveraged beats     

Vibration-induced polarisation modulation of light guided in single-mode optical fibres

The polarisation state of the HE11-mode in a single-mode optical fibre with a fused silica core was varied by mechanical vibrations of the fibre. The accompanying amplitude modulation is suppressed in the experimental arrangement. The influence of the plane of the incident polarisation on the signal modulation is discussed. The measurements were made with both reflecting and nonreflecting fibre endfaces.     

机载可见-红外超光谱成像仪信噪比的估算

信噪比表征光谱成像仪的辐射响应,是与其图像质量密切关联的重要参数。对于机载超光谱成像仪,在保证光谱分辨率的同时,要求其信噪比达到数百量级。有别于单色相机,光谱成像仪的信噪比估算侧重于获得其工作波段内各波长处的信噪比值。仿真实际的拍摄条件,特别引入了入射狭缝对视场限制所引起的信噪比衰减,综合考虑平台高度、太阳高度角、地面反射率等环境因子,利用"中分辨率大气传输模型"建立光信号的大气传输模型。超光谱成像仪的工作波段覆盖可见、近红外范围,同时使用的两个探测器的噪声需分别予以计算。信噪比的估算可作为机载超光谱成像仪总体设计和参数确定的依据。     

激光测距中APD阵列探测信噪比分析

APD阵列可提高光子探测效率,然而在回波探测概率提高的同时提高噪声探测概率,因此需合理选择阵列单元数以提高探测信噪比。根据回波和噪声在距离门内的分布情况,结合光子探测概率,建立了盖革模式下APD阵列探测信噪比随阵列单元数的变化模型。讨论了回波光子数、背景噪声强度、回波在门控内位置、占空比等因素对探测信噪比的影响。分析结果表明,提高回波光子数、探测器占空比、轨道预报精度有助于增加APD阵列的探测信噪比;4元APD阵列适用于回波光子数小于0.1、门控内噪声光子数小于1的观测情况,而回波和噪声强度较强时,25元APD阵列能够取得相对较优的探测信噪比。建立的APD阵列探测信噪比模型有助于快速选择APD阵列单元数以达到较高探测信噪比。