Effect of span loss increase on the optically amplifiedcommunication system

In optical fiber communication systems using Er³⁺ doped fiber amplifiers operating in their compression region, the optical signal power is known to be restored by the self-healing effect in the case of the span loss increase. In this paper, the influence of such excess loss on the system transmission performance is experimentally and numerically investigated from the point of view of the system signal-to-noise ratio and Q-factor. The results show that the system SNR is not completely recovered although the signal power is restored after several stages of amplifiers and that there exists the residual degradation of the system SNR. Through a 5.3 Gb/s data transmission experiment over 3000 km, the transmission penalty due to the excess span loss is confirmed to be decided by this residual degradation of the system SNR. The obtained results can be used for system design and a plan of maintenance for the optical amplifier communication system     

Degradation of the MIMO channel capacity due to additional noises of amplifiers

It is theoretically well known that a multiple input multiple output (MIMO) system can offer higher channel capacity than a conventional wireless system. The MIMO capacity is increased as a function of signal‐to‐noise ratio (SNR) and a number of antenna elements at both the transmitter and receiver. To realize MIMO capability in practical use, the implementation of all electronic devices is necessary to be considered. Amplifiers become the most common devices assembled at the transmitter and receiver with the purpose of overcoming the power loss in the wireless channel. High power amplifier (HPA) and low noise amplifier (LNA) are the special types of amplifiers that are compulsory for the transmitter and receiver, respectively. Both devices have the same function to provide the reliable power gains while adding as little noise as possible. For a MIMO system, the channel capacity sensitively grows as a function of SNR. Therefore, the changes in SNR due to HPA and LNA definitely degrade the system capacity. In this paper, the degradation due to both devices is investigated by taking the gain and noise figure of these amplifiers into account. The new formula of MIMO channel capacity including amplifier characteristics is originally proposed. The results indicate the remarkable consideration on using amplifiers as they may degrade the capacity up to 26%. This can be the guideline for MIMO researchers to spare the capacity margin caused by the additional noises of amplifiers. Copyright © 2008 John Wiley & Sons, Ltd.     

Transmission of many WDM channels through a cascade of EDFA's inlong-distance links and ring networks

We analyze the transmission of many wavelength-division-multiplexed (WDM) channels through a cascade of erbium-doped fiber amplifiers (EDFA) in both long-distance links and ring-based networks. For a megameter long-distance system, optimal operating conditions are found for achieving a high signal-to-noise ratio (SNR) per channel with as small an SNR differential as possible between 20 WDM channels spaced 0.5 nm apart. Critical issues addressed in this paper include: (a) the non-uniformity of the EDFA gain with wavelength: (b) the link loss between amplifiers; (c) the small-signal gain per amplifier; and (d) the input signal power     

Transmission of Analog Video and Digital Signals Over Analog-Repeatered Coaxial Lines

The transmission of digital telephony or data, alone and together with analog video, over analog-repeatered coaxial-cable lines is discussed. Expressions for the total random noise power and the signal-to-noise ratio (SNR) are derived. These expressions include the effects of thermal noise and the intermodulation distortion due to nonlinearity in the analog repeater amplifiers. The dependence of the SNR on system parameters, particularly the signal level and the repeater spacing, for systems that carry digital telephony, video, or both, is discussed and its implications on system design are noted.     

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。     

A study of green wavelength-division multiplexed optical communication systems using cascaded fiber bragg grating

This paper studies the performance analysis of wavelength-division multiplexed optical communication systems (WDM). First, flat-gain erbium doped fiber amplifiers (EDFAs) are seriously needed to obtain proper and equal amplification of all channels. Such amplifiers can be designed by intrinsically modifying the host material or extrinsically using proper filters. In this research, we benefit from both the intrinsic and extrinsic methods to achieve sharp flat EDFA output gain using cascaded fiber Bragg gratings (FBGs). Second, the performance of our technique has been evaluated through calculating the bit error rate (BER) and signal-to-noise ratio (SNR) of a WDM system embedded with the reported EDFA flattening system. The parametric simulations of the FWHM of FBGs, SNR, optical power and the transmission distance have shown a noticeable improved performance. Sending data via an optical WDM system will be proven from comprehensive simulations to achieve high quality signal transmission spectrums, increased transmission distances and low power consumption. By extension, the reported design using cascaded FBGs can also be generalized to equalize the gain of any arbitrary profile.     

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.     

Location optimization and distribution of polarization-mode dispersion compensators using polarizers

This paper investigates the benefits of using compensators with either linear or elliptic variable polarizers in order to mitigate the effects of polarization-mode dispersion (PMD) in high-speed optical fiber transmission systems. Such compensators are characterized by only one or two degrees of freedom and the optical average power of the compensated signal is used as a monitor signal, which simplifies the control algorithm. We maximize the tolerable differential group delay for the compensated system with two different approaches. In the first, we optimize the position of the compensator along the transmission line. In the second, we distribute a number of compensators through the transmission line. The attenuation of the optical signal, caused by the use of polarizers in the PMD compensators, induces additional noise in amplified systems. We assess the impact of this impairment and show that the noise enhancement is limited in systems with erbium-doped fiber amplifiers operating in gain saturation.     

A CMOS low-distortion fully differential power amplifier withdouble nested Miller compensation

A four-stage fully differential power amplifier using a double-nested Miller compensated structure is presented. The multiple-loop configuration used results in a lower harmonic distortion, at least in the audio band, compared to conventional three-stage amplifiers with nested Miller compensation. Design criteria and stability conditions for good stability of amplifiers using a multiple- (greater than two) loop topology are presented. The amplifier operates with a single power supply which has a minimum value of 3 V. With a 5-V supply, power dissipation is 10 mW and total harmonic distortion (THD) is -83 dB for a -V_p-p differential output signal at 10 kHz and a load of 50 Ω. With an 8 Ω load and for a 10-kHz, 4-V _p-p output signal, THD is -68 dB. The chip area is 0.625 mm ² in a 1.5-μm single-poly, double-metal, n-well CMOS technology     

Digital Predistortion for Envelope-Tracking Power Amplifiers Using Decomposed Piecewise Volterra Series

Due to dynamic changes of supply voltage, envelope-tracking (ET) power amplifiers (PAs) exhibit very distinct characteristics in different power regions. It is very difficult to compensate the distortion induced by these amplifiers by employing conventional digital predistortion techniques. In this paper, by introducing a new piecewise Volterra model based on a vector threshold decomposition technique, we first set several thresholds in the input power level according to the PA characteristics, and decompose the input complex envelope signal into several sub-signals by using these thresholds. We then process each sub-signal separately by employing the dynamic deviation reduction-based Volterra series, and finally recombine them together to produce the predistorted output. Experimental results show that by using this new decomposed piecewise digital predistorter model, the distinct characteristics of the ET system at different signal power levels can be accurately modeled, and thus, the distortion, including both static nonlinearities and memory effects, caused by the amplifier nonlinear behavior can be effectively compensated.     

Theoretical analysis of system limitation for AM-DD/NRZ opticaltransmission systems using in-line phase-sensitive amplifiers

This paper shows the theoretically derived performance of single channel, amplitude modulation/direct detection optical transmission systems using in-line optical phase-sensitive amplifiers (PSA's). The calculations take into account the degradation of the signal-to-noise power ratio (SNR) and intersymbol interference (ISI) due to the distortion of transmitted signal pulses. The SNR is analyzed by considering not only amplifier noise and fiber loss but also noise enhancement by four-wave mixing in the transmission fiber. The ISI is estimated by eye-pattern degradation of the transmitted signal numerically calculated using the nonlinear Schrodinger equation. The regenerative repeater spacing of in-line PSA systems limited by SNR and ISI can be expanded by approximately 3 to 10 times that of in-line EDFA systems, in the case of |D|⩽0.1 ps/mn/km dispersion fiber systems transmitting a 40-Gb/s signal     

基于XGM的SOA波长变换器噪声特性分析及实验研究

本文将半导体光放大器的ASE噪声功率引入到SOA分段动态模型,得到随SOA长度变化的ASE噪声功率,并讨论了偏置电流、泵浦光功率、SOA长度对变换性能影响.理论计算结果表明,大的偏置电流有利于提高消光比(ER)和信噪比(SNR);对于长度一定的SOA和一定的偏置电流,泵浦光功率存在最佳值;SOA长度存在信噪比最佳值.我们对2.5Gbit/s SDH信号进行了XGM方式波长变换,实验结果与理论分析一致.     

Turbo decoding of concatenated channel coding and trellis shaping for peak power controlled single-carrier systems

Trellis shaping (TS) has found its application in the peak power control of band-limited single-carrier signals. Our recent work has demonstrated that a well-designed TS can control the symbol transitions such that the output signal has almost constant envelope, which significantly alleviates the linearity requirement of power amplifiers. Compared to transmission without constellation shaping, however, the TS involves signal constellation expansion exclusively for peak power control. Therefore, unlike trellis coded modulation (TCM) that increases the minimum Euclidean distances (MED), the TS decreases the MED, thus incurring the increase in signal-to-noise power ratio (SNR) required for achieving a certain error rate. In this letter, in order to overcome this drawback, we propose a serial concatenation of coding and shaping together with an effective decoding algorithm that utilizes the memory effect (i.e., error correcting capability) of the shaped symbols. The achievable performance of the proposed system is analyzed in terms of the average mutual information. The simulation results demonstrate that the iterative decoding of the proposed concatenated system with outer convolutional codes and inner trellis shaping offers a significant performance gain.     

Gain equalization of EDFA cascades

Investigates the impact of wavelength-dependent erbium-doped fiber amplifier (EDFA) gain spectrum on multichannel direct-detection lightwave transmission systems employing multiple amplifiers. An analysis is presented which quantifies the constraints imposed by received power imbalance, signal-to-noise ratio (SNR), and receiver sensitivity on an EDFA cascade. Expressions are derived which relate the system constraints to the EDFA gain imbalance, bit rate, number of channels, and receiver dynamic range. Results demonstrate that when four-wave mixing (FWM) is compensated in an 11-channel system, received power imbalance can impose a significant constraint on transmission distance when the EDFA gain imbalance is greater than 1 dB or when bit rate is less than 1.8 Gb/s. In addition, performance of the preemphasis gain equalization technique is studied for multichannel systems employing APD or p-i-n/FET direct-detection optical receivers. Simple expressions are derived which can be used to quantify the increase in transmission distance obtained when employing preemphasis equalization. Results indicate that equalization of the received power spectrum can provide a two- to four-fold increase in the transmission distance when using APD receivers, compared to a one- to two-fold improvement with p-i-n/FET receivers. Analytic results are compared with results obtained by proven simulation methods and found to be in good agreement     

Single-channel operation in very long nonlinear fibers with opticalamplifiers at zero dispersion

The author investigates, by means of computer simulations, the performance of a very long, single-channel optical fiber system operating very close to the zero-dispersion wavelength of the fiber. Fiber losses are compensated by optical amplifiers. The optical signal is filtered after each amplifier, is passed through a final optical filter prior to square-law detection, and is finally filtered electrically. It is found that such a system does not work well if the fiber dispersion is strictly constant and if the carrier wavelength of the modulated signal coincides with the zero-dispersion wavelength of the fiber. As a result, the optical signal spectrum spreads to many times its initial width so that power is lost in the optical filters and the signal-to-noise ratio is degraded by the need for admitting a wider band of noise to the receiver     

Design techniques for cascoded CMOS op amps with improved PSRR and common-mode input range

Internally compensated CMOS op amps have been widely used in sampled-analog signal processing applications over the past several years. However, the popular two-stage op amp suffers from poor AC power supply rejection to one of the power rails. Two circuits are presented that overcome the power-supply rejection ratio (PSRR) problems of the earlier amplifier: one for virtual ground applications such as switched-capacitor integrators, the other for buffer applications requiring wide common-mode input range. Small signal analysis is developed for the open-loop and PSRR responses of the two amplifiers. In addition, design guidelines are suggested and test results are presented.     

Error floors in the satellite and land mobile channels

In a satellite mobile channel (SMC) and land mobile channel (LMC) because of fading and nonlinear power amplifiers, constant envelope modulation and noncoherent detection methods may outperform other schemes. It is shown how to compute the error floor for four noncoherent digital communication systems in satellite and land mobile channels. Differential phase shift keying (DPSK) with differential phase detection (DPD) or frequency shift keying (FSK) with DPD, limiter discriminator integrator detection. (LDID), or limiter discriminator detection (LDD) are studied. The error floor is the residual error probability when SNR is infinity, i.e. the error probability in the system is limited by the error floor. The error floor is computed as a function of Doppler frequency, modulation index, and ratio of powers in the specular and diffuse signal components for DPSK-DPD, FSK-DPD, FSK-LDID and FSD-LDD systems     

A 10 Gb/s AlGaAs/GaAs HBT high power fully differential limitingdistributed amplifier for III-V Mach-Zehnder modulator

High power, high frequency linear distributed amplifiers are available commercially which provide high power single-ended drive capability from a single-ended source. The signal source can be either analog or digital. Such amplifiers must have stringent gain and phase response requirement over a wide bandwidth in order to maintain good eye quality of the signal. A limiting amplifier, with less stringent bandwidth requirement than analog amplifiers, can be used to amplify pure digital signal source. The purpose of this paper is to present a high power, fully differential limiting distributed amplifier operating at 10 Gb/s. The amplifier has been fabricated with both AlGaAs/GaAs and InGaP/GaAs heterojunction bipolar transistor (HBT) processes. The amplifier is designed to drive any 50 Ω system. In particular, this amplifier is intended to drive a III-V Mach-Zehnder modulator     

Lossless wide-band reflective star coupler using erbium-doped fiberamplifiers

A wide-band 64-port amplified reflective star coupler (ARSC) using eight fiber amplifiers and only four pump laser diodes is demonstrated. The loss of this ARSC can be fully compensated from 1530 mn to 1565 nm due to its double-pass amplification process. The power margin increment of 21.7 dB with the power penalty of 1.3 dB and the cross-channel power penalty of 2 dB are achieved in a 1.7 Gb/s system experiment. This ARSC technology makes the star coupler cost-effective to be used in many larger wavelength division multiple access networks     

一种多频外辐射源雷达信号相参处理方法

拓展照射源个数,增加可利用的信号功率以改善系统的检测性能,是外辐射源雷达的一个重要发展方向.本文以调频广播外辐射源雷达为背景,研究了基于多个电台信号的多频外辐射源雷达相参处理技术.从信号模型出发,推导了各匹配输出的表达式,分析了各信号间的相位关系及影响信号相参合成的各种因素;信号处理过程中进行相位补偿,实现了多信号的相...