掺铒光纤放大器增益和噪声研究

文章首先介绍了掺铒光纤放大器(EDFA)的结构和工作原理,然后运用能级理论和激光原理,深入全面地分析了影响EDFA增益和噪声的主要因素,得出了EDFA增益和噪声与泵浦功率、泵浦方式、输入信号光功率和掺铒光纤长度等关系的一些重要结论,并且通过实验进一步验证了这些结论;提出了提高EDFA增益,减小噪声系数的方法;最后根据文中得出的结论,设计了一种高增益低噪声的C波段EDFA光路,该光路已经应用于工程实践中.     

Effect of pump laser noise on an erbium-doped fiber-amplified signal

The effect of pump laser noise on erbium-doped fiber-amplifier (EDFA) output was investigated using an optically pumped semiconductor laser (OPSL) as a high-power pump. Measurements included pump and amplified signal relative intensity noise (RIN) in frequency and time domains as well as gain spectral measurements and 10-Gb/s Q-factor tests, all under several levels of backreflection to the pump laser. Time-domain low-frequency noise (<50 kHz) was observed to increase with increasing backreflection. With 150-mW OPSL output power and -28 dB backreflection, temporal RIN was /spl sim/3.4% for the pump and /spl sim/2.2% for the amplified signal. At a maximum pump power of 450 mW, RIN was 1.4% and 1.1%, respectively. The measured Q-factor of 12.5 dB at 10 Gb/s showed less than 0.5-dB penalty compared to a back-to-back system measurement of 13 dB. Power budget and operating specifications of an OPSL-pumped multicoil EDFA were also evaluated.     

Erbium-doped optical fiber amplifiers pumped in the 660- and 820-nmbands

State-of-the-art erbium (Er)-doped optical fiber amplifiers (EDFA's) pumped in the 660- and 820-nm bands are described. We have demonstrated highly efficient EDFA's incorporating optimized 664- and 827-nm pump wavelengths and an Er-doped high numerical aperture (NA) fiber with thermally diffused expanded core (TEC) fiber ends. Gain coefficients of 3.8 and 1.3 dB/mW at respective wavelengths of 664 and 827 nm were achieved at a signal wavelength of 1535 nm. Noise figures of 3.1 and 4.1 dB at respective pump wavelengths of 670 and 827 nm were obtained at a signal wavelength of 1535 nm. A highly efficient Er-doped fiber amplifier module, in which an AlGaInP visible laser diode (LD) was used as the pump source, was successfully developed as a practical application of this technology. A maximum overall gain coefficient of 3.0 dB/mW was achieved at a signal wavelength of 1535 nm. The EDFA module realized a maximum overall signal gain of 33 dB at 1535 nm with a saturated output power of -1 dBm. A maximum saturated output power of 3.9 dBm was obtained at a signal wavelength of 1552 nm. The present EDFA design using a low-cost laser diode for optical disk memory use and a high NA Er-doped fiber has great potential for providing inexpensive, high-performance EDFA's     

掺铒光纤放大器的最佳光纤长度和增益特性

本文用三能级系统的速率方程建立了掺铒光纤放大器近似理论模型。在有激发态吸收时，各种泵浦波长下均获得了掺铒光纤的最佳长度。就增益随信号光及泵浦光光强的变化作了分析。通过对增益谱分析发现改变掺铒光纤长度可改变增益带宽，为掺铒光纤放大器在波分复用光纤通信系统中的应用提供了依据。     

S-band erbium-doped fiber amplifiers with a multistage configuration /sub e/sign, characterization, and gain tilt compensation

We report an S-band erbium-doped fiber amplifier (EDFA) with a multistage configuration in terms of its design, gain, and noise characteristics for various pump powers and input signal powers, the temperature dependence of the gain spectra, and gain tilt compensation for changes in input signal power and temperature change. We show that there is a tradeoff between low noise and efficiency in the S-band EDFA and describe the development of an S-band EDFA with a flattened gain of more than 21 dB and a noise figure of less than 6.7 dB. We also show that there is a change in the gain spectra with changes in the pump power and input signal power that is different from that observed in C- and L-band EDFAs, and that our EDFA has a temperature-insensitive wavelength. Furthermore, we develop a gain tilt compensated S-band EDFA that can cope with changes in input signal power and temperature.     

Gain control in L-band EDFAs by monitoring backward travelingC-band ASE

A novel and simple technique for gain flatness control is reported for gain shifted, long wavelength band (L-band) erbium-doped fiber amplifiers (EDFAs). Utilization of the backward traveling amplified spontaneous emission (ASE) in the C-band is analyzed with respect to controlling the gain tilt observed in the L-band when the total input power of the EDFA is changed. It is shown that a gain flatness of 0.6 dB/30 nm can be achieved over a dynamic range greater than 10 dB by using the backward traveling ASE power in the C-band as a monitor to adjust the copropagating pump power of the EDFA. The proposed technique eliminates the need to extract the output signals from the monitored ASE signal, demonstrating the suitability and simplicity of the proposed technique for wavelength division multiplexed applications     

Novel Gain Spectrum Control Method Employing Gain Clamping and Pump Power Adjustment in Thulium-Doped Fiber Amplifier

In this paper, we propose a novel method for controlling the gain spectrum of a thulium-doped fiber amplifier (TDFA) in the S-band. The conventional gain spectrum control method used for a silica erbium-doped fiber amplifier (EDFA) cannot be applied to TDFAs because of the complicated fluctuation of the TDFA gain spectrum. Our proposed method controls the gain spectrum by a combination of gain clamping and pump power adjustment. The algorithm for the method is as simple as that for the conventional EDFA gain spectrum control method. Furthermore, we describe a function for correcting the gain excursion generated by the incorporation of amplified spontaneous emission (ASE) at a signal monitoring photodiode (PD). We achieved a gain excursion of 0.35 dB against a total input signal power of 32 to 2 dBm.     

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。     

Analysis of channel addition/removal response in all-opticalgain-controlled cascade of erbium-doped fiber amplifiers

Application of the all-optical gain-controlled (AOGC) erbium-doped fiber amplifier (EDFA) for protection surviving channels in a multiwavelength network in which several EDFAs are cascaded is studied. The effects of addition and/or dropping of wavelength channels in a network comprising six concatenated EDFAs have been analyzed by numerical simulation. Only the first EDFA in the cascade is gain clamped using a ring laser configuration. A large-signal EDFA model which incorporates time variation numerical effects and the downstream propagation of signal and pump and downstream and upstream propagation of amplified spontaneous emission (ASE) has been used. In particular, the effects of relaxation oscillations from the gain-controlled EDFA on the surviving channel protection are investigated. It is shown that power excursions caused in an eight-channel wavelength division multiplexed (WDM) network by the loss/addition of 6 channels will be lower than 1 dB and free of relaxation oscillations if the gain-controlled EDFA is strongly inverted and the average normalized population density of the metastable level does not drop below 0.74     

New pump wavelength of 1540-nm band for long-wavelength-band erbium-doped fiber amplifier (L-band EDFA)

A long-wavelength-band erbium-doped fiber amplifier (L-band EDFA) using a pump wavelength source of 1540-nm band has been extensively investigated from a small single channel input signal to high-power wavelength division multiplexing (WDM) signals. The small-signal gain coefficient of 1545-nm pumping among the 1540-nm band is 2.25 times higher compared to the conventional 1480-nm pumping. This improvement in gain coefficient is not limited by the pumping direction. The cause for this high coefficient is explained by analyzing forward- and backward-amplified spontaneous emission spectra. The gain spectra as a function of a pump wavelength suggest that a broadband pump source as well as a single wavelength pump can be used as a 1540-nm-band pump. In the experiment for high-power WDM signals, the power conversion efficiency for 256 WDM channel input is 48.5% with 1545-nm pumping. This result shows more than 20% improvement compared with the previous highest value for the L-band EDFA. Finally, the 1545-nm bidirectionally pumped EDFA is applied as a second stage amplifier in an in-line amplifier of an optical communication link with a 1480-nm pumped first stage EDFA, in which the input power of the second-stage EDFA is +2.2 dBm. The power conversion efficiency yields a 38% improvement without noise figure degradation compared with the case of 1480-nm pumping.     

增益钳制掺铒光纤放大器特性研究

报道了一种新型基于环形激光腔的增益钳制掺铒光纤放大器。得到了较好的增益钳制效果和增益平坦度,利用980nm半导体激光器泵浦12m长掺铒光纤形成激光增益,观测到 30nm增益带宽。通过反馈1520nm 激光,在可变衰减器不同值测量了输入信号从- 40 ～10dBm的增益,其小信号增益被钳制在16dB。可为40个波分复用(WDM)信道波长提供增益钳制及平坦的放大功能。     

一种新型宽带EDFA及其实验研究

文章提出了一种基于三端口增益平坦滤波器、且在拓扑结构上不同于以往并行或串行结构的掺铒光纤放大器（EDFA）的新结构。理论模拟显示，同常规的并行结构EDFA相比，该新型结构在保证C波段EDFA性能的同时亦可将L波段掺铒光纤（EDF）用量减少48％以上，改善L波段泵浦效率55％以上。实验中，我们在C波段使用两只输出功率分别为106．9和109．6mW的980nm泵浦激光器，两段EDF的长度分别为8．5和9．6m，在L波段我们仅用1只80mW的1480nm泵浦激光器，EDF长度为19．8m。试验结果显示，在C＋L波段内得到的信号增益〉23dB，增益平坦度〈0．6dB，噪声指数在C和L波段内分别〈4．4dB和5.6dB。     

1477 nm LD泵浦掺铒光纤放大器的研究

报道了采用１４７７ｎｍ激光二极管（ＬＤ）泵浦的掺铒光纤放大器的实验结果。研究了放大器的增益和时域特性。对１５２０ｎｍ的信号光，获得了２３ｄＢ的增益，泵浦效率为２．２８ｄＢ／ｍＷ。低频脉冲信号经过放大器后未发生波形畸变。     

Polarization dependent gain in erbium-doped fiber amplifiers:computer model and approximate formulas

A computer model for polarization dependent gain (PDG) in Er-doped fiber amplifiers (EDFA) is presented. The model assumes that each erbium ion possesses an ellipsoidal gain surface and that all ion orientations are equally likely. By dividing the ions into subsets based upon orientation and computing the inversion of each subset in the presence of polarized pump and signal waves, the model predicts the dependence of the PDG induced by this polarization hole-burning (PHB) on the design of the EDFA, the signal degree and state of polarization (SOP), and the pump SOP. For moderate gain amplifiers (made from the same fiber) with the same gain peak wavelength and the same compression level, the magnitude of the PDG is nearly independent of the EDFA gain. Internal and random fiber birefringence are included to model real fibers. In fibers which cause the signal SOP to walk rapidly around the Poincare sphere, the PDG is reduced by a factor of 2/3 when compared with a linear polarization-maintained signal. Scrambled signals and partially-polarized saturating tones are also considered. Simple rules are derived for predicting the PDG of a given EDFA     

基于受激布里渊散射的可调谐多波长激光器

可调谐多波长布里渊掺铒光纤激光器将光纤中的SBS非线性放大同掺铒光纤的线性放大相结合得到室温稳定的多波长输出,具有波长间隔一致、线宽窄、功率谱相对平坦等优点。设计了一种基于光纤布拉格(FBG)反射的线性可调谐多波长布里渊掺铒光纤激光器。该线性腔激光器的一端利用光纤布拉格光栅作为反射镜,有效抑制了腔内自激模的影响,增加激光器输出波长数。布里渊泵浦信号进入布里渊增益介质之前经过掺铒光纤放大器的两次放大,降低了布里渊增益的阈值。该多波长激光器实现了1 530～1 560 nm之间30 nm可调谐范围的输出。在布里渊泵浦信号功率2 mW,980 nm泵源抽运功率60 mW情况下,1 540～1 554 nm范围内,获得了波长间隔0.088 nm的16个波长的输出。     

Performances of Erbium‐Doped Fiber Amplifier Using 1530nm‐Band Pump for Long Wavelength Multichannel Amplification

The performance of a long wavelength‐band erbium‐doped fiber amplifier (L‐band EDFA) using 1530nm‐band pumping has been studied. A 1530nm‐band pump source is built using a tunable light source and two C‐band EDFAs in cascaded configuration, which is able to deliver a maximum output power of 23dBm. Gain coefficient and noise figure (NF) of the L‐band EDFA are measured for pump wavelengths between 1530nm and 1560nm. The gain coefficient with a 1545nm pump is more than twice as large as with a 1480nm pump. It indicates that the L‐band EDFA consumes low power. The noise figure of 1530nm pump is 6.36dB at worst, which is 0.75dB higher than that of 1480nm pumped EDFA. The optimum pump wavelength range to obtain high gain and low NF in the 1530nm band appears to be between 1530nm and 1540nm. Gain spectra as a function of a pump wavelength have bandwidth of more than 10nm so that a broadband pump source can be used as 1530nm‐band pump. The L‐band EDFA is also tested for WDM signals. Flat Gain bandwidth is 32nm from 1571.5 to 1603.5nm within 1dB excursion at input signal of –10dBm/ch. These results demonstrate that 1530nm‐band pump can be used as a new efficient pump source for L‐band EDFAs.     

High-power EDFA applied in distributed optical fiber Raman temperature sensor system

In this paper, a high-power erbium-doped fiber amplifier (EDFA) for the temperature sensor system is theoretically designed and experimentally demonstrated. It consists of an erbium-doped fiber that is pumped bidirectionally with two 980-nm high-power laser diodes (LDs). At the EDFA input, an optical isolator (ISO) is used to ensure that the signal pulse transmits forward only. After that, a wavelength division multiplexer (WDM) is employed to combine the forward pump laser (980 nm) and incident optical pulse (1550nm) into the erbium-doped fiber for direct amplification in the optical domain. At the EDFA output, another WDM couples the backward pump laser (980 nm) into the erbium-doped fiber and outputs the amplified optical pulse (1550 nm) with an ISO followed to isolate the backscattering light. According to this structure, we carried out the experiment in the condition as follows. For 980 nm pump LD, the operating current is 590 mA, and the setting temperature is 25℃. For EDFA, the length of erbium-doped fiber is 12.5 m, and the power of 1550 nm input signal is 1.5 mW. As a result, the power of pump LD is 330 mW, and the power uncertainty is 0.5%. The power of EDFA output at 1550 nm is 300 mW, and the power uncertainty is ±3 mW.     

双波长全光自动增益箝制EDFA实验研究

提出了结构新颖的光纤环镜(FLM)全光自动增益箝制(OAGC)方案,进行了相关实验.通过控制抽运功率,调节腔内损耗和FLM,在环路内实现了波长为1 533.20 nm和1 559.05 nm的双波长激光振荡.对工作在透射式和反射式2种状态下的FLM,进行了信号波长为1 540 nm和1 550 nm的增益钳制实验.对于1 540 nm信号,在输入功率小于-14.88 dBm的范围内,增益波动ΔG＜0.3 dB;对于1 550 nm信号,在输入功率小于-16.51 dBm的范围内 ,增益波动ΔG＜0.1 dB.实验结果显示,FLM采用透射和反射方式均能达到增益箝制目的,而且得到的信号输出特性几乎一致,表明了这两种方案的等效性.     

宽带可调谐双频移多波长布里渊光纤激光器

提出了一种采用高非线性光纤作为布里渊增益介质 的双倍布里渊频移间隔的多波长布里渊光纤激光器(MW-BEFL)。激光器利用两个环形器构成 双倍频移结构,将奇数阶的斯托克斯信号隔离在腔内循环,仅有泵浦 信号和偶数阶的斯托克斯信号能够耦合输出,实现了双倍布里渊频移的多波长输出。激光器 腔内没有引入 任何的有源增益介质对斯托克斯信号进行放大,消除了腔内自激模的影响。激光器的调谐范 围由布里渊泵 浦的工作波长和掺铒光纤放大器(EDFA)的增益带宽决定。实验中,在布里渊 抽运 功率为0dBm、EDFA的输出功率为20 dBm的情况下,在1536~1605nm之间得到双频移间隔的多 波长输出,调谐范围是69nm。     

Highly efficient optical fibre amplifier pumped by a 0.8 mu m band laser diode

A highly efficient Er-doped fibre amplifier pumped by GaAlAs laser diodes is reported. Using a low Er-cluster content fibre with a high numerical aperture, the EDFA attains 39 dB signal gain for double LD pumping and 30 dB for single LD pumping at 1.536 mu m. A maximum gain coefficient of 1.3 dB/mW was achieved at the 0.827 mu m pump band.<>