Performance analysis of high-density WDM systems using Raman amplification

The applications of Raman amplifiers as repeater amplifiers or post-transmitter amplifiers in a high-density WDM system are theoretically investigated. There exists an optimum pump power which results in maximum amplifier gain. The result shows that amplifier gains up to 50 dB and 20 dB are achievable for use as a repeater and a post-transmitter amplifier, respectively.<>     

Gigahertz analog repeater for fiber optic delay lines

A gigahertz analog fiber optic repeater is used to extend the achievable delay time for radar delay line applications. The repeater consists of a silicon avalanche photodiode (APD), a wide-band amplifier, and a GaAlAs laser diode transmitter. This repeater has an optical gain of 14.5 dB, a 42 dB electrical dynamic range, and a noise figure of approximately 6.5 dB. The frequency response is flat within ±2 dB over the frequency range from 10 MHz to 1.3 GHz. The nanosecond pulse fidelity is such that the subtraction between input and output pulses is 20 dB below the pulse amplitude.     

Monolithic integrated amplifiers for 400 Mbit/s optical repeater

Introduction of monolithic integrated circuit technology to high bit rate optical repeater is studied. Monolithic integrated amplifiers are realised for a 400 Mbit/s optical repeater such as a preamplifier, AGC amplifier and postamplifier, using advanced silicon bipolar process technology. An equalising amplifier with four monolithic amplifiers got 66 dB maximum gain, 35 dB variable gain and 350 MHz band-width with 550 mW power consumption.     

Design of N-way distributed Doherty amplifier for WCDMA and OFDM applications

A novel three-way distributed Doherty power amplifier with an extended efficiency range for WCDMA or OFDM repeater or base-station applications is presented. This distributed Doherty amplifier consists of one main amplifier and two peaking amplifiers. To achieve high efficiency at a high back-off power, the peaking amplifier structure is based on the dual-fed distributed amplifier form. The 2140 MHz measured results of the three-way distributed Doherty amplifier yielded an 11 dB power gain, with 39.5% power added efficiency at 9.5 dB back-off power     

Gallium-nitride microwave Doherty power amplifier with 40 W PEP and 68% PAE

A 40 W gallium-nitride microwave Doherty power amplifier for WCDMA repeater applications is presented. The main amplifier and peaking amplifier are implemented using two 20 W PEP GaN HEMTs. Performance is evaluated for broadband gain, power efficiency and adjacent-channel-power-ratio (ACPR). Experimental results of the GaN Doherty amplifier yielded a power gain of over 11 dB from 1.8 to 2.5 GHz, 68% power added efficiency at 40 W peak power. Good linearity performance of -48 dBc ACPR is obtained at a peak-to-average ratio of 9.8 dB.     

高效率高线性度功率放大器的设计与实现

基于对传统两路Doherty功放存在的问题分析,文中对其结构进行改进,提出了一种新颖的非对称结构。该非对称结构采用相同的功放管,通过变换漏极与栅极电压分别对主辅功放进行负载牵引和源牵引以达到不同的饱和输出功率,从而实现更高的功率回退。基于该理论,结合互调对消技术和多谐波双向牵引技术设计并实现了应用于工作频段为2.57～2.62GHz的TD-LTE直放站功率放大器。在饱和输出功率回退9dB的平均输出功率处,功率附加效率(PAE)为38%,5MHz和10MHz偏移量的相邻信道功率比(ACPR)分别为-41dBc和-50dBc,实测结果显示Doherty功放的参数性能良好,满足TD-LTE直放站要求的同时验证了设计方案的正确性。     

Field demonstration of coherent transmission system with diode-pumped erbium doped fibre amplifiers

Reports a field demonstration of 622 Mbit/s DPSK and FSK coherent transmission over 200 km of installed single mode fibre. Diode-pumped erbium doped fibre amplifiers were used as both power amplifiers and repeaters. System loss budgets of more than 68 dB were achieved with an intermediate amplifier repeater gain of 16.5 dB. Both systems incorporated fully automated endless polarisation control.<>     

Laser diode pumped Er3+-doped fiber amplifier in a 565Mbit/s DPSK coherent transmission experiment

A laser-diode-pumped erbium-doped fiber amplifier, exhibiting 9-dB gain, has been operated as an in-line optical repeater in a 565-Mb/s coherent optical communications system. A sensitivity penalty of 0.4 dB was observed when the amplifier was positioned 35 dB away from the receiver, thus indicating a system improvement of 8.6 dB. By progressively reducing the coupling loss between amplifier and receiver, the noise figure of the contradirectionally pumped amplifier was calculated to be 5.4 dB, a value which is consistent with simple noise theory     

A channel-number insensitive erbium-doped fiber amplifier withautomatic gain and power regulation function

The design scheme for an erbium-doped fiber amplifier (EDFA) with automatic channel-by-channel gain and power regulation function is discussed with much emphasis on the pump power control scheme and the requirement for feedback circuitry. Based on both wavelength and time-resolved simulation technique, an amplifier repeater employing novel high-speed automatic gain control (AGC) and automatic level control (ALC) functions is designed and implemented. The AGC and ALC scheme can suppress the transient power fluctuation of a surviving channel caused by adding or dropping all other channels less than 0.45 dB and keep output power constant over 9-dB input power range     

5 Gbit/s, 233 km optical fiber transmission experiment employingfive semiconductor laser amplifiers

A directly modulated 1.519-μm distributed-feedback laser signal was transmitted over 233 km of single-mode fiber consisting of dispersion shifted fiber and conventional step-index fiber to minimize the dispersion penalty. The power penalty after the transmission was 0.25 dB. The results show the effectiveness of an optical amplifier repeater system for high-speed long-haul fiber optic transmission     

Noise figure monitoring of optical amplifiers via backwardamplified spontaneous emission

A new configuration of an optical amplifier is proposed that provide in-service noise figure (NF) monitoring. It is difficult to determine the NF of traditional optical amplifiers in operation because the amplified spontaneous emission (ASE) power cannot be measured separately from the output signal power. The proposed technique measures the NF from the backward ASE power. The discrepancy between the NF measured from forward ASE (using the traditional technique) and backward ASE (proposed technique) is found to be less than 1.0 dB at input powers below -6.2 dBm. A prototype optical amplifier is successfully used as a linear repeater, in a 10 Gbit/s 200 km transmission experiment     

Amplification Effect on Rayleigh Scattering and SBS in 25 km Distributed Fiber Raman Amplifier

The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fibers Raman amplifier have been researched. The signal source is a tunable narrow spectral bandwidth （〈10 MHz） ECL laser and is pumped by the tunable power 1427.2 nm fiber Raman laser. The Rayleigh scattering lines are amplified by fiber Raman amplifier, and Stokes stimulated Brillouin scattering lines are amplified by fiber Raman amplifier and fiber Brillouin amplifier. The SBS lines total gain is a production of the gain of Raman and the gain of Brillouin amplifier. In experiment, the gain of SBS is about 42 dB and the saturation gain of 25 Ion G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.     

G652光纤中背向自发拉曼散射的增益特性

讨论了背向自发Raman散射脉冲在自生分布式G652光纤Raman放大器中传输的增益特性。实验发现，反Stokes Raman（ASR）和Stokes Raman（SR）自生分布式脉冲光纤Raman放大器的阈值抽运峰值功率是25．4W和18．0W。在入射功率为52W时，ASR和SR的增益分别为5．0dB和8．6dB。放大的反Stokes和Stokes背向自发Raman散射光时域反射（OTDR）曲线上放大的阈值时间位置随激发功率的增高前移并具有规律性。放大的ASR背向自发散射强度受光纤温度调制，具有温度效应，已应用于远程分布光纤Raman温度传感器系统。     

Observation of equivalent Rayleigh scattering mirrors in lightwavesystems with optical amplifiers

Experimental and theoretical studies that indicate that Rayleigh scattering acts as an equivalent mirror which can generate high levels of multiple reflection noise in lightwave systems employing optical amplifiers are discussed. The relative intensity noise can be calculated as a simple function of the amplifier gain and the ratio of total backscattered to incident power in the fibers. In high-speed digital systems, this noise limits the maximum usable repeater gain to less than 20 dB, unless optical isolators are employed     

Broadband GaN HEMT push-pull microwave power amplifier

We report a broadband, linear, push-pull amplifier that utilizes GaN-based HEMTs grown on SiC substrates. The high power density capabilities of these devices can be enhanced by the high efficiency achievable with push-pull operation. Good amplifier performance is facilitated by use of a new low-loss balun that is implemented with three symmetric coupled lines and which showed insertion loss of less than 0.5 dB per balun. The bias was injected through the baluns, thereby simplifying the amplifier design and reducing loss associated with dc decoupling capacitors. Using two 1.5 mm HEMTs with 0.35-μm gate length, a push-pull amplifier produced a small-signal gain of 8 dB at 5 GH2, a 3 dB bandwidth of 3.5-10.5 GHz, and a PAE of 25%     

Linearization of CMOS Broadband Power Amplifiers Through Combined Multigated Transistors and Capacitance Compensation

We present the development of a device-level linearization technique and its applications in broadband power amplifiers (PAs). The proposed topology firstly combines derivative transconductance superposition method and gate capacitance compensation technique, and creates a "sweet region" for suppressing third-order intermodulation (IM3) without the penalty of large power consumption. The effectiveness of the proposed technique has been demonstrated through a fully integrated distributed amplifier. The experimental results in 0.18-mum RF CMOS technology show that IM3 is improved by 11 dB. The achievable power-added efficiency is up to 25%, which is the highest among the broadband CMOS PAs reported thus far. The amplifier achieves a measured 3-dB bandwidth of 3.7-8.8 GHz, and a gain of 8.24 dB. The amplifier only consumes 154-mW dc power, and the measured saturation power (P_sat) is 19 dBm.     

最大中继距离的光网络传输工程设计方法

介绍了最大中继距离的光传输系统设计模型，比较了最坏值设计法、联合设计法和统计设计法三类最大中继距离的光传输系统设计方法的特点，给出了实际可以达到的要生段距离的具体计算方法及其在自愈网、波分复用系统、光放大器、无源光网络及有源光网络工程应用中需要进行的附加修正。     

用记忆型 BP 神经网络实现 HPA 预失真的算法研究简

在分析宽频带CMMB直放站高功率功放(HPA）特性的基础上,提出了一种可分离处理功放记忆效应和非线性的延时神经网络（FIR-NLNNN）模型。该模型以实数延时神经网络（RVTDNN）为基础,用Levenberg-Marquardt（LM）优化算法确定神经网络系数,在模型中新增参数w0,给出了LM算法的修改公式。接着在预失真神经网络系统中引入Bayesian机理消除LM算法的过拟合现象,构建CMMB数字直放站的间接学习预失真器,拟合HPA的非线性和记忆效应。结果表明：RVTDNN和FIR-NLNNN 2种预失真器均能显著提高系统性能,降低邻信道功率比30 dB左右。在保持均方误差（MSE）小于10?6的情况下,FIR-NLNNN结构的网络参数比RVTDNN结构减少了近50%,迭代过程中的乘法和加法次数约降低75%。     

A highly stable low-RIN hybrid Brillouin/erbium amplified laser source

We demonstrate a low-noise all-fiber hybrid Brillouin/erbium amplified source consisting of a Brillouin/erbium fiber laser with a subsequent Brillouin amplifier to boost the power and reduce the noise. The same single-mode fibers used in the fiber laser and the amplifier lead to the same amount of Stokes frequency shifts in spite of the environmental variation, ensuring stable Brillouin amplification. The hybridly amplified source features temperature insensitivity, low noise, potentially high power, and low cost. The relative intensity noise of the hybridly amplified source is /spl sim/10 dB lower than that of the erbium-doped fiber amplifier (EDFA)-based source at radio frequencies >200 MHz due to the filtering characteristics of the Brillouin amplification. Compared with an EDFA amplified fiber system, the spurious-free dynamic range of an analog transmission system employing such a laser source is improved by 7.7 dB owning to the lower RIN.     

Noise and error rate performance of semiconductor laser amplifiers in PCM-IM optical transmission systems

Applications of semiconductor laser amplifiers in intensity modulated digital optical transmission systems were studied theoretically. An optical linear amplifier repeater between electronically regenerating terminal repeaters and an optical linear preamplifier in front of a photodetector in an electronically regenerating repeater are discussed. Both traveling-wave type and Fabry-Perot cavity type laser amplifiers are considered. The noise and error rate performance in these systems are evaluated using formulations for semiconductor laser amplifiers. The mean and variance in the optical amplifier output photons calculated by the photon master equation [1] is used to obtain the worst case variance in the equalized output voltage [2] for these systems. The required receiving power reduction from direct detection scheme by a preamplifier system and the repeater spacing expansion between two electronically regenerating terminals by an optical linear amplifier repeater system are delineated.