Gain flattened distributed fiber Raman amplifiers

An S band and a C band distributed fiber Raman amplifiers (DFRAs) with flattened gain and compensated dispersion have been studied and implemented with 1427 nm and 1455 nm mono-wavelength fiber Raman lasers as the pumped sourcesrespectively. The gain of single-wave pumped S band and C band can reach 10 dB and 15 dB respectively. And a 50 nmgain flattened width was successfully obtained by using a chirp fiber Bragg grating (CFBG) gain flattened filter with gainripple of ±0.6 dB. The C band DFRA has been applied to CDMA wireless communication system successfully.     

Gain and noise figure of GaAs transferred-electron amplifiers at 34 GHz

Experimental results obtained from supercritical c.w. GaAs transferred-electron reflection amplifiers at about 34 GHz are reported. Gains in excess of 20 dB have been observed with typical (gain)?×bandwidth products of 1.0?1.5GHz. The best noise figure is 18 dB, and this parameter is shown to be sensitive to the doping profile. The output power for 1 dB gain compression is typically 2.5?3.0 mW.     

Gain saturation spectrum of backward-pumped broad-band Raman amplifiers

The gain saturation of optical amplifiers due to changes in wavelength-division-multiplexed channel loading is characterized using a technique that determines the saturation effect on each channel. This channel gain saturation (CGS) measurement is applied to a broad-band backward-pumped Raman amplifier and used to study how the CGS spectral tilt is controlled by the relative contributions of the pump-to-pump and channel-to-channel interactions. The CGS is also used to measure the gain dependence on the channel add-delete pattern.     

A simple algorithm for gain spectrum adjustment of backward-pumped distributed fiber Raman amplifiers

In this letter, a simple algorithm for the gain spectrum adjustment of backward-pumped distributed fiber Raman amplifier (B-DFRA) is demonstrated both theoretically and experimentally. It is shown that the change in pump power and corresponding change in gain spectrum are approximately related through a linear matrix, while the elements of the matrix can be easily measured. Feasibility of this algorithm is approved by experiment: a gain ripple of less than 1.2 dB across the C + L band is achieved during net gain adjustment from -15 dB to -9 dB of a 160-channel B-DFRA by varying the launched power of four pumping LDs.     

多泵浦拉曼光纤放大器增益均衡的研究

基于受激拉曼散射原理,根据传输方程,用数值解法计算了单泵浦输入时的拉曼光纤放大器的增益;在此基础上,计算了多信道信号输入时,多泵浦拉曼光纤放大器的增益,并和文献的实验结果做了比较;用遗传算法优化泵浦参数以实现多泵浦拉曼光纤放大器的增益均衡。 1     

Gain saturation in fiber Raman amplifiers due to stimulatedBrillouin scattering

The effects of stimulated Brillouin scattering (SBS) on Raman gain are explored. Measurements of gain in a fiber Raman amplifier show a saturation at low gain levels. Experimental data and a theoretical model are presented, demonstrating that this saturation is due to pump depletion by SBS. This effect also leads to Raman gain fluctuations arising from mode partitioning in a multimode pump laser. Two ways to avoid the deleterious effects of SBS on the performance of Raman amplifiers are suggested. One is to use a multimode semiconductor laser with a modal linewidth of the order of a few hundred megahertz, which leads to a strongly reduced Brillouin gain coefficient. The second approach is to use very short pump pulses in a backward configuration     

反射式L波段掺铒光纤放大器增益与噪声指数改善

提出了一种改善反射式L波段掺铒光纤放大器增益和噪声指数的方法,即在放大器的输入端插入一泵浦源,通过提高信号输入端的粒子数反转率实现提高增益和降低噪声指数的目的.通过仔细调整两个泵浦源的输出功率,与单泵浦结构相比,在相同条件下,在1565～1615 nm波长范围内,小信号增益提高了1.5～9.9 dB,噪声指数下降了1.3～9.4 dB.     

Spectral noise figure of Er3+-doped fiber amplifiers

The erbium-doped fiber amplifier noise figure spectrum and its evolution under various pumping regimes is analyzed. The analysis shows that noise figures in the range ±0.15 dB around the 3-dB quantum limit are possible within a spectral band of 50 nm. This demonstrates the possibility of quantum-limited amplification for broadband wavelength-division multiplexed (WDM) signals     

De-embedding the noise figure of differential amplifiers

Many radio-frequency circuits use differential topologies, whereas the instruments to evaluate them are inevitably single ended. Taking into account noise correlations, this work extends Friis' well-known equation for the noise figure of a cascade of two-ports to the case of three-ports, such as baluns, which surround a differential amplifier during measurements. The amplifier gain and noise figure may be accurately de-embedded with single-ended measurements on the cascade and on the baluns. The new formulas are experimentally validated     

Gain transients in copumped and counterpumped Raman amplifiers

Gain transients in both copumped and counterpumped distributed Raman amplifiers were investigated as a function of signal launch power, fiber type, and surviving signal wavelength for the first time. We found that gain transients are much more pronounced in a copumping scenario than in a counterpumping scenario for the same operating conditions. We also found that the dependency of gain transients on signal launch power, fiber type, and surviving channel wavelength follows the pump-depletion theory. A simple transient suppression technique with better than 0.2-dB ripple capability was also demonstrated.     

Noise figure of erbium-doped fiber amplifiers in saturatedoperation

We have developed a simple electrical noise figure measurement technique for the characterization of optical amplifiers. By subtracting the results of noise measurements at identical detected power levels made with and without the amplifier present, we are able to achieve an accuracy of ±0.3 dB in measured noise figure. Using this technique we obtain an excellent agreement between electrically and optically measured noise figures for two 98O-nm-pumped, copropagating erbium-doped fiber amplifiers (EDFA's) operating in saturation     

Impact of pump OSNR on noise figure for fiber-optical parametric amplifiers

Electrical measurements of the noise figure of a fiber-optical parametric amplifier are presented and compared with optical measurements. The transfer of pump noise by four-wave mixing was clearly demonstrated. A numerical model was developed to simulate the transfer of pump noise and validated by these measurements. Using this model, we determine, for practical systems, a minimum required pump optical signal-to-noise ratio of 65 dB.     

Measuring gain and noise figure of erbium-doped fiber amplifiers using a broad-band source and a transmission filter

We report a unique low-cost technique for measuring gain and noise figure (NF) in erbium-doped fiber amplifiers using a broad-band amplified spontaneous emission source and a transmission filter, by extracting the slope and intercept of output power spectral density versus input power spectral density at filter edges. The required filter depth is 30 dB. Discrepancies of /spl les/0.3 dB are found between gain or NF obtained from this technique and those measured using conventional spectral-interpolation technique employing multiple lasers at 100-GHz spacing across the C-band.     

Amplified spontaneous Raman scattering in fiber Raman amplifiers

Amplified spontaneous Raman scattered light power in forward and backward Raman amplifiers is theoretically and experimentally studied under the assumption of the constant Raman gain coefficient in the bandwidth of an optical filter. On the basis of the results, the power ratio of the amplified signal to amplified spontaneous scattering is discussed. As a result, it is clarified that the effect of amplified spontaneous Raman scattering on the signal to noise ratio for backward Raman scattering is larger than for forward Raman scattering.     

Experimental gain and noise figure performance of distributed MESFET amplifiers

The noise figure and gain characteristics of lossless and lossy MESFET distributed amplifiers have been theoretically investigated by various workers. In the letter, in order to support previously reported theoretical results, the experimentally measured noise figure and power gain performance of two-stage and five-stage hybrid microwave distributed amplifiers employing MESFETs are presented. The measured results are compared to theoretically obtained values and found to be in reasonable agreement over most of the band.     

Analytical model for Raman noise figure in dispersion-managed fibers

We derive an exact and a closed-form approximate analytic formula for effective lumped Raman noise figure in backward-pumped dispersion-managed fibers (DMFs) of arbitrary topology. Within the single-pump small-signal amplification model, important effects such as unequal loss coefficients at pump and signal wavelengths or splice loss for the pump and the signal between the DMFs' sections are taken into account. Theoretical results agree well with the noise figure measured in a symmetric DMF. The developed approach can be used to optimize the noise performance of DMFs.     

一种测量光纤喇曼放大器增益的方法

根据喇曼放大器的增益和噪声的定义,提出一种独特的低成本的测量噪声和增益的方法.该方法是用一个梳状滤波器对宽带ASE信号进行调制,并在输入和输出信号的凹陷的较陡处进行取点,从而得出某个局部的输入和输出信号的线性关系,进一步计算出光纤喇曼放大器的增益和噪声系数.对该方法进行了数值模拟,以便进一步阐明测量原理.     

喇曼光纤放大器的几项关键技术

喇曼光纤放大器具有优越的宽带性能 ,是现代宽带通信的较理想放大器。它的实用化得益于一些关键性技术的发展。对喇曼光纤放大器的最新发展进行了研究 ,对其中的关键性技术进行了分析、对比 ,以期有利于今后的实用化研制工作     

光纤拉曼放大器的优化设计

文章介绍了一种设计多波长泵浦光纤拉曼放大器（FRA）的方法以及怎样用此方法实现需要的增益曲线。利用这种方法仿真实现了增益接近20dB、平坦度小于0.2dB的拉曼放大器，它与现有的拉曼放大器相比具有更平坦的增益曲线。     

Amplified spontaneous Raman scattering and gain in fiber Raman amplifiers

The spectrum of amplified spontaneous Raman scattering and gain in a fiber Raman amplifer has been calculated analytically as a function of distance and pump power. The model used makes no assumptions on the magnitude of the gain and considers the pump nondepletion region. From the results, the on/off ratio has been calculated and is found to have a variation with length that depends on frequency detuning. An enhancement in on/off ratio is also found for small fiber lengths but at limited gain. The use of a narrow-bandpass optical fiber leads to quite different behavior of the on/off ratio than for the unfiltered case.