Simple model of optical amplifier chains to evaluate penalties inWDM systems

A simple model to evaluate the penalty due to amplifier gainshape in a wavelength division multiplexing (WDM) optical system is proposed. The model requires only knowledge of the overall gain of the amplifier chain for all channels and provides signal-to-noise ratio (SNR) penalties for given launched powers. It also provides the input power distribution required for SNR equalization, and the associated SNR penalty, by solving an eigenvalue/eigenvector problem. The penalty predicted by the model agrees well with recent field measurements on a transoceanic cable. The model can also be applied to predict the gainshape of the amplifier chain from a measurement of the output noise spectrum with no input signal. The capacity of a long amplifier chain can thereby be determined from the receiving terminal only     

Study of PMD and PDL Equalization Via a Nonunitary FIR Lattice Filter

We study a novel configuration and synthesis algorithm for equalization of polarization-mode dispersion (PMD) alone and combined with polarization-dependent loss (PDL) using a nonunitary optical lattice filter (NU-OLF). The NU-OLF is a generalization of a previously studied unitary lattice filter (U-OLF) for PMD equalization. Comparison of the improvement in the noise loaded PMD/PDL-induced eye closure, for typical optical signal-to-noise ratio values, shows that a NU-OLF is always superior to a U-OLF of the same order and it offers a significant advantage over a U-OLF with the same number of degrees of freedom in the equalization of PMD in the presence of PDL.     

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.     

An optical power equalizer based on one Er-doped fiber amplifier

A device which exhibits zero or slightly negative differential optical gain over a broad input power range is demonstrated. The scheme is based upon saturation enhancement by bidirectional signal input in an Er-doped fiber amplifier. Power equalization of better than 1.2 dB over a 14-dB dynamic input power range is achieved at the 1530-nm signal wavelength. The noise figure penalty due to the equalization is below 3 dB as evaluated by a device simulation     

EDFA-based DWDM lightwave transmission systems with end-to-end power and SNR equalization

An approximate analysis is presented which can be used to predict the performance of power and signal-to-noise ratio (SNR) equalization schemes when applied to dense wavelength-division multiplexing (DWDM) lightwave systems employing erbium-doped fiber amplifier (EDFA) cascades. Expressions are provided which relate the maximum number of amplifiers, EDFA gain imbalance, bit rate (R/sub b/), transmitter power, receiver dynamic range and number of channels. The relative advantages of these two equalization strategies are quantified by comparing the maximum number of amplifiers allowed by each scheme. It is shown that, while SNR equalization represents, on balance, the more desirable equalization strategy for future EDFA-based DWDM lightwave transmission systems, under certain conditions power equalization may be a better choice. When employing an APD receiver, for instance, power equalization can support 1.9 times more amplifiers than SNR equalization. However, when employing the more conventional preamplified PIN/FET receiver, SNR equalization can support 1.7 times more amplifiers than power equalization.     

Polarization dependent loss induced gain ripple statistics inerbium-doped fiber amplifiers

A Monte-Carlo model is used to simulate the wavelength-dependent polarization dependent loss (PDL) statistics and PDL induced gain-ripple statistics for a chain of concatenated optical elements in an erbium-doped fiber amplifier (EDFA). Simulations indicate that unlike polarization-mode dispersion (PMD), the quadrature sum of PDL overestimates the mean of the PDL distribution. We show that EDFA total PDL variance scales linearly with the individual component PDL variance. Moreover, the relative impact of PDL on the gain ripple is reduced in the presence of the PDL independent gain ripple in the EDFA     

Penalties in long-haul optical amplifier systems due topolarization dependent loss and gain

The impact of polarization dependent gain (PDG) and polarization dependent loss (PDL) in long-haul optical amplifier systems is studied by means of a power analysis accounting for PDG, PDL and polarization mode dispersion (PMD) in the saturation regime of the erbium-doped fiber amplifiers (EDFAs). System penalties are characterized in terms of mean values and standard deviations. Mean penalties on the bit-error-ratio (BER) are directly related to PDG. BER fluctuations are found to be greatly enhanced when PDG and PDL are combined. The impact of PMD is dependent on the values for PDG and PDL     

Effects of signal power control strategies and wavelength assignment algorithms on circuit OSNR in WDM networks

Software-defined networking is enabling wavelength-division multiplexed (WDM) networks to be programmable down to individual components. While taking into account typical gain and noise figure profiles of erbium-doped fiber amplifier (EDFA) components, the authors consider a number of signal power control strategies and compare their performance in terms of achievable lightpath optical signal-to-noise ratio (OSNR). These strategies are applied network-wide to concurrently control the gain of each individual amplifier and the signal power equalization at each reconfigurable optical add/drop multiplexer. Simulation and (in part) experimental results show that the lightpath OSNR is affected by three factors: the EDFA gain control strategy, power equalization strategy and wavelength assignment (WA) algorithm. A trade-off between lightpath average OSNR and OSNR variance across the WDM channels is also noted. Experimental work is conducted using a five-node meshed WDM network testbed proving both feasibility and effectiveness of a coordinated use of signal power control strategies and WA algorithms.     

Optimization of pump and signal powers for wavelength converters based on FWM in semiconductor optical amplifiers

We investigate the effect of input pump and signal powers on the noise performance and intersymbol interference (ISI) in a frequency-converter based on four-wave mixing (FWM) in a semiconductor optical amplifier. We demonstrate that there is an input pump power at which the noise figure of the frequency converter is a minimum, and a corresponding input signal power for which the output signal-to-noise ratio (SNR) is a maximum. We report bit-error-rate measurements which show that there is a trade-off between maximizing the output SNR, and minimizing intersymbol interference in the SOA. Consequently, the power penalty incurred in the frequency conversion can be minimized by careful selection of the input signal power. We show that power penalties of less than 1 dB are achievable.     

Noise characteristics of dual-pump fiber-optic parametric amplifiers

The noise figure (NF) properties of an undepleted and lossless dual-pump fiber-optic parametric amplifier (FOPA) are theoretically and numerically investigated. The theoretical study takes into account the noise characteristics of the two pump waves that are considered to have parallel polarization states for gain maximization. It is shown that noisy pump waves degrade the amplifier's NF, especially when the amplifier is operating at high gain values and when the input signal is high. The theoretical observations are validated by Monte Carlo numerical simulations, and the agreement between them is excellent. Finally, a comparative study concerning the noise characteristics of dual-pump and single-pump FOPAs is performed.     

OXC节点级联的信噪比计算

文章给出了计算OXC级联信噪比的一般解析模型,并针对“信号功率均衡”和“总功率均衡”两种方案进行了研究,分析了在这两种特定情况下系统的信噪比特性。同时还给出了OXC中输入EDFA和输出EDFA特性对系统信噪比的不同影响,得出了在设计OXC时对输入EDFA和输出EDFA优化设计的原则。     

光纤Raman放大器

本文介绍了Raman放大的机理、泵浦源及泵浦方式,分析了FRA的设计原则、增益均衡的各种方法、噪声及Raman串扰等问题,提出了可行的方案。     

热释电BST薄膜红外探测器噪声分析及前置放大电路设计

针对热释电红外探测中微信号放大时的低信噪比问题,在分析热释电红外探测器及前置放大电路噪声来源的基础上,提出了一种热释电红外探测前置放大电路.电路仿真表明,文中所设计的前置放大电路具有低频特性好、高信噪比、高增益的特点,能有效放大微弱信号.     

Calculation of penalties due to polarization effects in a long-haulWDM system using a Stokes parameter model

We derive a Stokes parameter model to calculate the penalties due to the combination of polarization mode dispersion (PMD), polarization dependent loss (PDL), and polarization dependent gain (PDG) in long-haul, dense wavelength division multiplexed (WDM) systems. In this model, we follow the Stokes parameters for the signal and the noise in each channel instead of following the full time domain behavior of each channel. This approach allows us to determine the statistical distribution of penalties with up to 10⁵ fiber realizations and 40 channels. We validate this model to the extent possible by comparison to full numerical simulations. Using this model, we find that the interaction of PMD and PDL is the major source of penalties and that the effect of PDG is negligible in WDM systems with more than ten channels     

Gain equalization of EDFA's with Bragg gratings

Flat-gain amplifiers are needed to ensure proper amplification of every channel in wavelength-division-multiplexed communication systems. Such amplifiers can be realized by combining a precisely tailored filter with an erbium-doped fiber amplifier (EDFA). In this letter, we show that Bragg gratings can lead to accurate EDFA gain equalization. Reflection and transmission gratings have been used to demonstrate gain equalization over 32 nm with excursion inferior to ±0.1 and ±0.3 dB, respectively. A maximum 0.04-dB noise-figure penalty results from this process. By extension, Bragg gratings could also equalize the gain of any arbitrary gain profile, over any arbitrary bandwidth     

SINR analysis of FFH/OFDM over frequency selective Rayleigh fading channel

Fast frequency hopping/orthogonal frequency division multiplexing (FFH/OFDM) has been previously proposed to achieve frequency diversity over frequency selective channels. However, the performances of the FFH/OFDM scheme have been usually calculated using simulations over empirical channel models in earlier works. The main aim of this paper is to theoretically expose the diversity of the FFH/OFDM signal over statistical models, specifically Rayleigh distributed, for frequency selective fading channels. In order to achieve this aim, we first derive the decision variables and the signal‐to‐interference noise ratios of the FFH/OFDM signal at the output of minimum mean square error and zero forcing receivers. For various levels of quadrature amplitude modulation used in FFH/OFDM, the performances are calculated and validated via simulations. The results show that FFH/OFDM in case of zero forcing equalization does not provide any diversity gain even over a frequency selective channel. However, in case of minimum mean square error equalization, it brings significant diversity gain at high signal‐to‐noise ratio (SNR) values with the rise of number of sub‐carriers. Moreover, the FFH/OFDM with four quadrature amplitude modulation scheme provides better performance than that of the conventional OFDM even at low SNR values, as well as a significant diversity gain at high SNR values. Copyright © 2016 John Wiley & Sons, Ltd.     

双向时分复用光纤时间传递链路噪声分析

研究分析了双向时分复用(BTDM)光纤时间传递链路 的主要噪声及产生机理,建立了基于BTDM光纤时间传递 的链路噪声模型。仿真分析了激光器强度噪声、光放大器增益与个数、接收机带宽等对BTDM 光纤时间传 递接收信噪比(SNR)的影响。结果表明,BTDM光纤时间传递 接收SNR在光放大器达到最优增益时最大,且最 大SNR随光放大器个数的增加而增加并趋于稳定;相同长度光纤链路,光放大器个数越多 ,在一定范围 内,激光器相对强度噪声对BTDM光纤时间传递链路接收SNR 影响更大,接收机带宽对BTDM光纤时 间传递接收信号抖动的影响越小;BTDM光纤时间传递接收SNR随定时信号前 光持续时间的增加而减小,并趋于WDM方案的SNR。     

Noise in Orthogonally Pumped Fiber-Optical Parametric Amplifiers

The noise figure (NF) of a fiber-optical parametric amplifier, driven by pumps with orthogonal polarizations, is quantified experimentally. It is shown that this amplifier has a signal-polarization-dependent gain, with a corresponding polarization-dependent NF. The polarization dependence of the NF is particularly large when higher input-signal powers are amplified, in which case pump-induced noise dominates. At lower input-signal powers, the NF is less dependent on the input polarization, but increases closer to the lower-frequency pump     

波分复用系统的光信噪比与代价测试方法探讨

本文通过分析光放大器噪声的成分,指出了波分系统中在OSNR表象一致的情况下光放大噪声与ASE噪声的差异,以及这种差异在检测系统传输性能时所造成的影响,并设计了相关的代价测试实验系统。通过对实验数据的分析,指出了进行与系统OSNR代价相关的性能测试时如何获得真实系统参数的办法。     

猫眼逆向调制激光通信接收放大电路的设计

猫眼逆向调制激光通信由于通信速率高,回波信号微弱,对接收放大电路提出了低噪声、高增益和宽带宽的严格要求。首先分析了猫眼逆向调制激光通信链路模型和信噪比对误码率的影响。然后,根据系统设计指标分析了电路的带宽、增益和噪声限度等性能参数;在此基础上设计了由跨阻放大模块和增益可变主放大模块构成的接收放大电路。最后,计算了电路的总噪声,并对电路的响应特性进行了仿真。该接收放大电路的带宽达到140 MHz,信号增益大于70 dB,总噪声电流约为1.34×10~(-7)A。结果表明,该设计能满足系统后续的数据处理要求。