Gain-clamping in two-stage L-band EDFA using an unwanted backward ase from second stage

A gain clamping technique for the long wavelength band erbium-doped fiber amplifier (L-band EDFA) is presented. It uses two circulators and a broad band fiber Bragg grating to route wasted backward C-band ASE from the second stage and launch it back into the input end of the first stage of a two-stage amplifier. The two-stage L-band EDFA has shown a small signal gain improvement of 5.7 dB compared to a single-stage amplifier with a slight noise figure degradation. By utilizing the wasted backward ASE, a L-band gain-clamped EDFA with high gain can be realized. Compared to the unclamped case, this gain-clamping technique is effective in reducing the total gain variation as small as 0.3 dB.     

The L-band EDFA of high clamped gain and low noise figure implemented using fiber Bragg grating and double-pass method

The L-band erbium-doped fiber amplifier (EDFA) of low noise figure and high clamped-gain using gain-clamped and double-pass configuration is presented in this paper. A total of five different configurations of EDFAs by reflection scheme with single forward pumping schemes are examined and compared here. Among these configurations, we first find the configuration of 1480-nm pumped L-band EDFA with optimum gain and noise figure value. To further minimize the gain variation, a fiber Bragg grating (FBG) with 1615-nm center wavelength and 1-nm bandwidth is determined and added in double-pass L-band EDFA. The gain variation and maximum noise figure of EDFA while channel dropping is investigated. As the number of channel dropping from 32 to 4, the L-band type-A EDFA keep the variation of gain within 2.9 dB and the maximum noise figure below 5 dB with each channel’s input power of −23 dBm.     

Gain-clamping techniques in two-stage double-pass L-band EDFA

Two designs of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) for gain clamping in double-pass systems are demonstrated and compared. The first design is based on ring laser technique where a backward amplified spontaneous emission (ASE) from the second stage is routed into the feedback loop to create an oscillating laser for gain clamping. The gain is clamped at 18.6 d B from -40 to -80 dBm with a gain variation of less than ±0.1 dB and a noise figure of less than 6 dB. Another scheme is based on partial reflection of ASE into the EDFA, which is demonstrated using a narrowband fiber Bragg grating. This scheme achieves a good gain clamping characteristic up to -12 dBm of input signal power with a gain variation of less than ±0.3 dB from a clamped gain of 22 dB. The noise figure of a 1580 nm signal is maintained below 5 dB in this amplifier since this scheme is not based on lasing mechanism. The latter scheme is also expected to be free from the relaxation oscillation problem.     

L-band EDFA 性能与增益光纤长度关系的分析

分析和模拟L_band EDFA的增益特性对其优化设计和实验有着重要的意义。基于Giles模型,数值模拟了L_band EDFA中的信号光、泵浦光和放大自发辐射(ASE)在一定泵浦功率下与铒光纤长度的关系;分析了L_band EDFA本征增益平坦的产生机理;数值模拟了小信号增益平坦特性。结果表明,在一定的泵浦功率下,如果在所选择的L_bandEDFA中铒光纤长度合适,则不需要任何平坦化处理就可以得到比较平坦的增益谱线。     

Study on EDFA Gain Tilt and Nonlinear Distortion in an AM-VSB CATV Optical Fiber Transmission System

1IntroduCtionAMVSB(~litUdemodulationwithvestigialsideband)CATVoPticalfibertrandriSSdrisystemiswidelyaPpliedduetocomplete1ycomatibilitywtthekistingCATVtechntheyandoccuPationaverynarrowband.Theopticalpowerbudgetofthesystemistoollttle(about5~8dBm)toreallzealDngdistancetransndssion,andoPticalmodulationdegreeisalsorestrainedinanarrowrangeinordertOguaranteethenonlinearrequlrementssinceitissensitivetOthenonlineardistortion.EDFAisintroducedintothesystemtoimProvetheopticalpoWrbudget.Indongs…     

Study on EDFA Gain Tilt and Nonlinear Distortion in an AM-VSB CATV Optical Fiber Transmission System

The gain tilt of the erbium-doped fiber amplifier (EDFA) and the nonlinear distortion in an AM-VSB CATV optical fiber transmission system with a cascade of EDFAs are analyzed. It demonstrates that the nonlinear distortion induced by the light source and the EDFA would be counteracted each other to a certain degree as long as the EDFA has a negative gain tilt. As a result,an optimal EDFA negative gain tilt is suggested as a solution to self-compensation of the nonlinear distortion.     

Low noise gain-clamped L-band erbium-doped fiber amplifier by utilizing fiber Bragg grating

A novel gain-clamped long wavelength band (L-band) erbium-doped fiber amplifier (EDFA) is proposedand experimented by using a fiber Bragg grating (FBG) at the input end of the amplifier. This designprovides a good gain clamping and decreases noise effectively. It uses two sections of erbium-doped fiber(EDF) pumped by a 1480-nm laser diode (LD) for higher efficiency and lower noise figure (NF). The gainis clamped at 23 dB with a variation of 0.5 dB from input signal power of -30 to -8 dBm for 1589 nm andNF below 5 dB is obtained. At the longer wavelength in L-band higher gain is also obtained and the gainis clamped at 16 dB for 1614 nm effectively. Because the FBG injects a portion of backward amplifiedspontaneous emission (ASE) back into the system, the gain enhances 5 dB with inputting small signal.     

Effect of injection of C-band ASE on L-band erbium-doped fiber amplifier

The effect of injecting conventional band (C-band) amplified spontaneous emission on the performance of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated. It uses a circulator and broadband fiber Bragg grating (FBG) to route C-band ASE from a C-band EDFA. Injection of a small amount of ASE (attenuation of 20 dB or above) improves the small signal gain with a negligible noise figure penalty compared to that of an amplifier without the ASE injection. A maximum gain improvement of 3.5 dB is obtained at an attenuation of 20 dB. At very large amounts of ASE injection (attenuation of 0 dB), the gain of the amplifier is clamped at 15.2 dB from ?40 to ?10 dBm with a gain variation of less than 0.3 dB. The saturation power is also increased from ?8 dBm (for without ASE injection) to 2 dBm (VOA=0 dB) with a slight noise figure penalty. These results show that the ASE injection technique can be used either for gain improvement or for gain clamping in L-band EDFA.     

低噪声、高增益的L -band EDFA的实验研究

针对传统的L-band EDFA的工作效率低,提出了一种基于单根光纤光栅、泵浦分配、两段级联的EDFA的新结构,其中的光纤光栅用来反射无用的后向C-band ASE.系统地研究了泵浦比例和光纤光栅波长对增益噪声指数的影响关系.最后经实验验证,得到了低噪声、高增益的L-band的EDFA.其在输入信号光（1570 nm）功率为-30 dBm及泵浦功率为70 mW时,增益为22.26 dB,增益噪声指数为4.96 dB.     

Simultaneously gain-flattened and gain-clamped erbium fiber amplifier

In this paper, we propose and demonstrate a simple erbium amplifier module based on an erbium-doped fiber amplifier (EDFA) and an erbium-doped waveguide amplifier (EDWA) in serial, having gain-flatted (GF) and gain-clamped (GC) functions simultaneously. In first proposed GF amplifier scheme, the maximum gain variation of 2.5 dB can be observed in the effective range of 1528 to 1562 nm and the entire gains are above 35 dB with the input signal power of ?30 dBm. Hence, we investigate second scheme by optical feedback method in the proposed fiber amplifier achieving gain-flattened (GF) and gain-clamped (GC) efficiencies simultaneously. Thus, the maximum gain variations of ±0.8 and ±1.8 dB can be obtained in the operating range of 1530 to 1564 nm, when the input signal powers are ?16 and ?40 dBm, respectively. Moreover, the dynamic gain profile can be adjusted and dynamic input power range is also measured based on the proposed GF and GC fiber amplifier.     

High gain double-pass L-band EDFA with dispersion compensation as feedback loop

We demonstrate an efficient double-pass L-band erbium-doped fiber amplifier (EDFA) incorporating chirped fiber Bragg grating (CFBG). The amplifier structure exploits the characteristics of CFBG to reflect the amplified signal back into the gain medium, filter out the recycled forward amplified spontaneous emission and block the residual 1480 nm pump power. The amplifier configuration has high gain and low noise figures as compared to double-pass EDFA using broadband mirror. The demonstrated amplifier has gain of more than 48 dB and low noise figure of less than 4 dB at low input signal power of −40 dBm.     

Optimizing the EDFA gain for WDM lightwave system with temperature dependency

The gain-flattened erbium-doped fiber amplifier (EDFA) is a key device for wavelength division multiplexing (WDM) modern optical network systems. A flat spectral gain EDFA has been achieved by controlling the doped fiber length and the pump power. The purpose of this paper is to study the variation of gain flattening over the temperature range from ?20 to +60 °C. The results obtained here indicate that gain flatness increases as temperature increases.     

长波段掺铒光纤放大器用掺铒光纤的设计考虑

本文分析了长波段掺铒光纤放大器(EDFA)的增益系数与Er³⁺离子浓度的关系.研制了铝共掺杂的高浓度掺铒光纤,以缩短长波段掺铒光纤的长度.用两级泵浦实现了L-波段EDFA.光纤放大器的掺铒光纤总长18m,在1570nm波长处的小信号增益为42.26dB,输出功率为17.5dBm.我们认为,较低的浓度淬灭效应归因于光纤中较高的A1掺杂浓度.当总的输入信号功率为-3dBm时,在1570至1600nm间的7路WDM信号的增益不平坦度仅为0.68dB..     

Enhancement of Gain in L-Band Bismuth-Based Erbium-Doped Fibre Amplifier Using an Un-pumped EDF and Midway Isolator

A hybrid L-band erbium-doped fibre amplifier (EDFA) with enhanced gain characteristic is demonstrated without a significant noise figure penalty. It uses a backward C-band amplified stimulated emission from both the ends of a bismuth-based EDFA system to pump an unpumped erbium-doped fibre (EDF) for gain enhancing. The maximum gain enhancement of 4.0dB is obtained at wavelength 1604nm with EDF length of 20m. The gain spectrum is reasonably fiat in this amplifier compared with the amplifier without an EDF. The gain varies from 27.4 dB to 30.2 dB at wavelength region 1564-1608 nm with incorporation of 20 m EDF. Noise figure also varies from 6.0 to 7.TdB at this wavelength region.     

Amplification enhancement of L-band erbium-doped fiber amplifiers by reflection scheme

A reflection L-band erbium-doped fiber amplifier (EDFA), which can effectively suppress and completely exploit the backward C-band amplified spontaneous emission (ASE) with a feedback reflection loop, is presented in this paper. The mechanism of the backward ASE secondary pumping effect is experimentally investigated in detail. Our experimental results have shown that, for a given input pump power, compared to the end-pumped EDFA, the gain and output power of the reflection EDFA can be improved considerably without paying much noise penalty. When the EDFA operates with flattened gain spectra, the gain is improved by about 7 dB with an extra noise penalty of about 1.2 dB, where the saturation output power is increased by 2.5–3.2 dB and which may also be made independent of the input signal power.     

Optimization of a Raman/EDFA hybrid amplifier based on dual-order stimulated Raman scattering using a single-pump

Based on dual-order stimulated Raman scattering (SRS) of a single 1395 nm Raman fiber laser in 75 km single mode fiber and its corresponding dispersion compensation module, a hybrid Raman/Erbium doped fiber amplifier (EDFA) for long wavelength band (L-band) amplification is realized by inserting a segment of EDF within the span. By comparing the performance of gain and noise in four hybrid amplifiers with different span configurations, we find that the distribution of the secondary L-band amplification obtained from the EDF along the link has a great influence on the performance of the hybrid amplifier. Both gain and noise performance of hybrid amplifier can be improved significantly by optimizing the location of the EDF. Moreover, we can extend the flat gain bandwidth from L-band to central wavelength band (C-band) plus L-band by recycling the residual first-order SRS to pump a segment of EDF with proper length.     

The amplified model of erbium-doped fiber amplifier (EDFA) with cross-phase modulation (XPM)

Based on the rate equations and the power propagation equations, the amplified model is obtained which considers the cross-phase modulation (XPM)-induced intensity fluctuation between pump power and signal power in erbium-doped fiber amplifier (EDFA). Simulation results show: a higher nonlinear coefficient and a stronger pump power cause a stronger XPM in EDFA. Before the optimal length of EDF, the intensity caused by XPM increases with the increasing length, but after the optimal length, the XPM presents saturation. A bigger nonlinear coefficient γ corresponds to a smaller optimal length and gain, and makes gain saturation more easy. XPM effect will decrease EDFA’s amplified efficiency.     

Gain and noise figure improvements in double-pass S-band EDFA

Double-pass short-wavelength band erbium-doped fiber amplifier (S-band EDFA) with enhanced gain and noise figure characteristics is demonstrated. It uses a broadband fiber Bragg grating (FBG) operating in conventional-band (C-band) region to reduce the C-band amplified spontaneous emission (ASE) in the amplifier system and thus increases the population inversion in the S-band region. The small signal gain is increased by about 2.7 dB for 1500 nm signal at pump power of 103 mW, compared with that of the conventional double-pass amplifier without the FBG. The corresponding noise figure is also improved by 0.5 dB.     

Broad-band EDFA gain flattening by using an embedded long-period fiber grating filter

An erbium-doped fiber amplifier (EDFA) gain flattening technique using an embedded long period grating (ELPG) is proposed. By bending the ELPG, due to different coupling strengths yielded from different bending curvatures, it can be used for both the static and dynamic gain flattening despite of the different pump currents of the EDFA. The experimental results demonstrate that the flattened gain region of 34 nm can be achieved within 1 dB ripple.     

高掺杂碲基EDFA增益噪声特性的数值模拟

采用四能级理论模型对高掺杂碲基EDFA进行了数值模拟,得出C波段和L波段EDFA的主要增益和噪声系数特性,C+L波段同时放大时,20 dB增益带宽达到85 nm.同时分析了铒离子高掺杂带来的上转换效应对放大增益和噪声性能的影响程度,C波段为4％,L波段为10％,当增大泵浦光功率时,影响程度会更小,采用两段级双向泵浦结构放大时影响仅为0.1％.