Analysis of distributed erbium-doped fiber amplifiers with fiber background loss

An accurate model for erbium-doped fiber amplifiers with fiber background loss applicable to the unsaturated gain regime is presented. Exact analytical solutions are derived for the output pump power, gain, and amplified spontaneous noise as a function of input pump power in the cases of unidirectional or bidirectional pumping. An exact relation is also derived between the pump threshold and the pump required for fiber transparency. Such expressions are particularly useful to model distributed fiber amplifiers and to determine the optimal fiber parameters corresponding to a given pumping scheme. As an example, the analytical solutions are used to study the pump power requirement for distributed fiber amplifiers unidirectionally pumped at 1.48 mu m, and to determine an optimum Er/sup 3+/ absorption coefficient.<>     

Optimum Er3+-doped fiber amplifier design for optical AMvideo signal distribution systems

An investigation into the transmission characteristics of erbium-doped fiber amplifiers for use in optical AM frequency division multiplexing (FDM) video distribution systems is reported. The output signal power and noise characteristics of erbium-doped fibers were measured for different fiber lengths and different pump powers. The experimental results confirm that there exists an optimum amplifier design which gives the maximum distribution number when the pump power and the required video quality are given     

一种新的优化喇曼掺Er混合光纤放大器结构

对于给定的非线性损伤，对喇曼／掺Er混合光纤放大器(HFA)结构进行优化，即优化光纤喇曼放大器(FRA)与掺Er光纤放大器(EDFA)的增益比和色散补偿光纤(DCF)长度比，得到一种最优HFA结构。分别比较了最优HFA、一般HFA、全FRA和全EDFA用作接收机前置放大器的噪声性能，以及用于多级链路在线放大器时系统所能到达的最大可传输距离。结果表明，最优HFA能提高系统性能。     

Noise reduction in long-haul lightwave all-amplifier systems

The overall gain of a chain of erbium-doped fiber amplifiers in a long-haul all-amplifier system would be automatically stabilized if each amplifier were operated slightly into saturation. However, with the required low level of amplifier output power which is imposed by nonlinearity in the transmission fiber, the resulting pump power becomes too low to effectively invert the gain medium of the amplifiers. Consequently, the amplifier output noise level becomes too high for proper system operation. This problem is solved by pumping the amplifiers harder so that a higher gain and higher output power are achieved. The excess gain is then counteracted by an appropriate value of post-amplifier loss. Because of the higher pump power in this case, the amplifier noise is reduced significantly. This technique is investigated theoretically, and experimental work that verifies it is reported     

Mining the optical bandwidth for a terabit per second

A significant part of optical-fiber capacity can be tapped now that optical amplifiers can boost many high-speed channels simultaneously. The erbium-doped optical fiber amplifier opened the floodgates to wide-bandwidth, all-optical schemes for multiplexing many wavelengths. Until the advent of the erbium-doped fiber amplifier, no practical all-optical amplifier existed. Optical signals were instead regenerated electronically to overcome the attenuation inherent in the silica fiber as well as other losses due to optical components along the line     

光纤长度优化的高功率铒镱共掺光纤放大器

为了研究不同增益光纤长度下1555nm高功率光纤放大器的输出功率,采用两级混合结构的方法,用掺铒光纤放大器和双包层铒镱共掺光纤放大器分别作为1级预放大器和2级主放大器。掺铒光纤放大器对信号光进行预放大,并提高放大器的信噪比;双包层铒镱共掺光纤放大器为主放大器,其双包层结构可以把更多的多模抽运光耦合进系统。对铒镱共掺光纤的最佳长度做了理论分析和实验验证,在信号光功率为10mW、掺铒光纤放大器的抽运功率为318.58mW、双包层铒镱共掺光纤放大器的抽运功率为11.71W、增益光纤长度为14m时,输出功率取得了2.11W的实验数据。在分析输出信号光谱时发现,L波段附近有放大自发辐射谱出现,这是选择的增益光纤过长导致的。结果表明,在光功率和信号光功率一定时,光纤放大器有一个最佳的光纤长度。这一结果对研究光纤放大器的高功率输出是有帮助的。     

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.     

Ultrawide 75-nm 3-dB gain-band optical amplification witherbium-doped fluoride fiber amplifiers and distributed Raman amplifiers

An extremely large 3-dB gain-bandwidth of 75 nm (1531-1606 nm) is achieved with a partially gain-flattened erbium-doped fluoride fiber amplifier and a distributed Raman amplifier. The Raman amplifier consists of a 85-km dispersion-shifted fiber (transmission fiber) and a practical 1505-nm Fabry-Perot laser diode pump. 9×2.5 Gb/s wavelength-division-multiplexing (WDM) transmission is successfully demonstrated using two 75-nm gain-band amplifiers as in-line and preamplifiers     

Spectral dependence of gain and noise in erbium-doped fiberamplifiers

A two-level model of the erbium-doped fiber amplifier is used to analyze the dependence of the amplifier gain saturation, saturated output power, and excess noise factor on pump and signal wavelengths. Measured data are presented confirming that the dependence of the gain, output saturation power, and noise of erbium-doped fiber amplifiers on the signal and pump wavelength can be described by simple equations derived from the model     

Propagation of signal and noise in concatenated erbium-doped fiberoptical amplifiers

Signal propagation and noise accumulation in lightwave systems using saturated optical amplifiers as repeaters are analyzed. Numerical simulations of amplified spontaneous emission in concatenated erbium-doped fiber amplifiers indicate that a reach beyond 10000 km is possible with a 1.55-μm system in the absence of fiber nonlinearities. Distributed optical amplifiers are shown to have low noise, but require higher pump power than lumped amplifiers. Three operating modes of an amplifier lightwave system are identified and their relative signal power efficiency and noise performance are described     

Inline amplifier transmission experiments over 4500 km at 2.5 Gb/s

An inline amplifier system was constructed with erbium-doped fiber amplifiers spaced at 100 km and 80 km intervals. The system transmits 2.5 Gb/s signals over 2500 km with continuous-phase frequency-shift-keying heterodyne detection and over 4500 km with intensity-modulation direct detection. With respect to amplifier output signal power levels, it is experimentally shown that there exists a dynamic range within which long-distance signal transmission can be achieved with only small receiver sensitivity degradation. The range's upper and lower limits are determined by fiber nonlinearities and amplifier noise characteristics, respectively     

A high-gain, high-output saturation power erbium-doped fiberamplifier pumped at 532 nm

An erbium-doped fiber amplifier with a high small-signal gain of 42 dB at the gain peak of 1536.4 nm, a pumping efficiency of 1.6 dB/mW, and an output saturation power of 10 dBm is obtained with a pump power of 60 mW at 532 nm using the second harmonic of a Nd:YAG laser as the pump source. These experimental results indicate that diode-laser-pumped mini-Nd:YAG lasers with intracavity frequency-doubling have an output power at 532 nm of 100-150 mW that can be of great interest for practical system applications using high-gain, high-output-power erbium-doped fiber amplifiers     

Design considerations for minimizing macrobending loss inerbium-doped fiber amplifiers

Step-index fiber designs which minimize macrobending loss in erbium-doped fiber amplifiers pumped at 980 and 1490 nm are discussed. An important consideration for the compact packaging of these amplifiers for field use is the minimum tolerable bend radius of the doped fiber for small extrinsic macrobending loss. Only small shifts in the peak value of the mode field of the fiber due to bending, such that the gain of the amplifier is essentially unaffected, are considered     

Rayleigh scattering effect on the gain efficiency and noise oferbium-doped fiber amplifiers

The effect of the internal Rayleigh scattering on the gain efficiency and noise of the erbium-doped fiber amplifier has been considered in detail. It is shown that excess background loss due to Rayleigh scattering at the signal and pump wavelengths dramatically reduces the optimum gain efficiency of either high NA, low-concentration or confined-dopant erbium-doped fibers. Distributed feedback due to Rayleigh backscattering, on the other hand, degrades the noise performance of high gain amplifiers considerably. In applications where high gain and low noise figure are required, increasing the fiber NA and dopant confinement above an optimum value are shown to increase the required pump power dramatically due to the deleterious effects of Rayleigh backscattering     

分布拉曼光纤放大的实验研究

采用符合ITU-T标准的G波段40信道波分复用(WDM)光源对分布式拉曼放大器(DRA)的特性进行了实验研究。对不同抽运方式及不同光纤长度的分布式拉曼放大器性能作了较为详细的报道。在抽运功率相同的条件下，选用50km单模光纤对比研究了不同抽运方式的拉曼放大器增益和噪声。通过对不同光纤长度的分布式拉曼放大器的实验研究发现，在较低抽运功率且输入信号功率较低的情况下，随着光纤长度增加，拉曼增益也增加，有效噪声系数减小。研究了分布式拉曼放大器对波分复用通信系统信噪比的改善，实验发现不同抽运功率下，拉曼放大器对系统信噪比的改善随抽运功率增加而增加，但是不成线性关系，而且最终会出现饱和。     

Distributed fiber Raman amplifiers with localized loss

Backward pumped C- and L-band distributed fiber Raman amplifiers are described, where discrete losses from 0-8 dB were added at various positions to examine the effect of localized loss. Below 3-dB additional loss, the overall optical performance degraded similarly, regardless of loss position in a hybrid Raman and erbium-doped fiber amplifier. Above 3 dB, the performance degradation worsened as the loss position became closer to the signal output. The spectral shape change of the fiber output against loss variation was made tolerable within /spl plusmn/0.4 dB simply by balancing the output power of L band with that of C band, unless the loss was close to pump input. The tolerance provides design flexibility for hybrid optical amplifiers and allows the use of fixed gain-flattening filters.     

Investigation of Transients in Single-Fiber Bidirectional Closed-Loop WDM Ring Network Using High-Power Gain Clamped EDWA

We investigate a transparent WDM ring network design immune to accumulated power transients where simultaneous bidirectional operation is achieved on a single fiber. This allows cost effectiveness, flexible traffic re-routing, and network operation. We demonstrate that add/drop of 15 out of 16 channels generate negligible $({≪ 0.15}~{hbox {dB}})$ power excursion on the surviving channel. These results have been obtained by using new high-gain erbium-doped waveguide amplifiers in an innovative gain-clamped configuration that allows bidirectional operation. The glass-on-silicon waveguide optical amplifiers are able to achieve a clamped flat gain of 15 dB on full C-band with up to 0-dBm input power. This is the highest output power ever reported for an erbium-doped waveguide amplifier. The amplifier can with almost identical performance operate with signals entering together from both ends or even from opposite ends. The gain properties of the amplifier are almost perfectly symmetric.      

Modeling of noise in erbium-doped fiber amplifiers in the saturatedregime

We have made a theoretical study of the noise figure of erbium-doped fiber amplifiers in the saturated regime. The noise figures of amplifiers subjected to specific gain and gain compression requirements were calculated for various amplifier lengths. The resulting noise figures together with the required pump and input signal powers map out all possible solutions given constraints on gain, compression, pump power, output signal power, and noise figure. In some cases, requirements on the output signal power prohibit any solutions. A way to solve this problem is the introduction of a post-amplifier loss. For this configuration, two possible solutions exist, which collapse into one solution at a certain critical loss, under which there exist no solutions. When the impact of amplified spontaneous emission is neglected in the model, only one solution is obtained, and the critical loss is much smaller than when the amplified spontaneous emission is included in the model. We conclude that amplified spontaneous emission generally has to be taken into account, even when the gain is as low as 10 dB, to accurately predict the noise performance of erbium-doped fiber amplifiers     

Long-haul coherent optical fiber communication systems usingoptical amplifiers

Studies on long-haul coherent optical fiber communication systems with in-line optical amplifier repeaters are made theoretically and experimentally. By theoretical calculation it was found that coherent systems can achieve wider dynamic range for an amplifier input power as compared with the intensity-modulation direct-detection (IM-DD) systems. The feasibility of such systems using traveling-wave semiconductor laser amplifiers (TWSLAs) and erbium-doped fiber amplifiers (EDFAs) was investigated, and 546 km, 140 Mb/s CPFSK transmission using TWSLAs and 1028-km, 560-Mb/s CPFSK transmission using EDFAs were successfully demonstrated     

ASE reflector-based gain-clamped erbium-doped fiber amplifier using an optical interleaver

We use a 50-GHz optical interleaver for the reflection of amplified spontaneous emission (ASE) to realize ASE reflector-based gain-clamped erbium-doped fiber amplifiers. The amplifier schemes can secure International Telecommunications Union Telecommunication Standardization Sector grids with 100-GHz channel spacing in the whole conventional band (C-band) for signal amplification gain-clamping characteristics including dynamic ranges lower than -7 dBm are successfully demonstrated.