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.     

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.     

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.     

High gain L-band erbium-doped fiber amplifier with two-stage double-pass configuration

An experiment on gain enhancement in the long wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated using dual forward pumping scheme in double-pass system. Compared to a single-stage single-pass scheme, the small signal gain for 1580 nm signal can be improved by 13.5 dB. However, a noise figure penalty of 2.9 dB was obtained due to the backward C-band ASE from second stage and the already amplified signal from the first pass that extracting energy from the forward C-band ASE. The maximum gain improvement of 13.7 dB was obtained at a signal wavelength of 1588 nm while signal and total pump powers were fixed at -30 dBm and 92 mW, respectively.     

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.     

双向掺铒光纤放大器的特性分析

讨论了双向掺铒光纤放大器的结构方案,利用考虑放大的自发辐和北员耗影响的双向掺铒光纤放大器稳态放大速率方程模型分析的增益与掺铒光纤长度、输入信号光功率、帛运光功率及抽运方式等参数之间的关系,研究了单向和双向等功率抽运下正反向噪声系数随正反向信号光输入功率的变化行为。     

L-Band掺铒光纤放大器的优化设计

提出了泵浦分配两段级联,并利用前向ASE推动下一级EDF工作的L-Band放大器的新结构.基于Giles模型并考虑了ASE噪声的影响,运用数值模拟算法系统分析了泵浦光功率分配和铒光纤分配比例对这种EDFA性能的影响.最后优化得到高增益且增益谱平坦的L-Band EDFA,其在输入信号光功率为-20 dBm时,在1571～1608 nm范围内,增益值高达35 dB,增益偏差小于1 dB.     

L-band all-optical gain-clamped EDFA by utilizing C-band backward ASE

By using an optical circulator and C/L-band wavelength division multiplexer to recycle the C-band backward ASE, an L-band gain-clamped erbium-doped fiber amplifier is presented. We have experimentally studied the static gain clamping property of this amplifier. As the ASE feedback attenuation is set to 0, the gain at 1585 nm can be clamped at 18.84 ± 0.26 dB within dynamic range of 25 dB and the critical power reaches about −15.09 dBm. The gain variation and saturated output power at 1585 nm for 0 dB attenuation are 1 dB lower and 2.17 dB higher than those for 30 dB attenuation, which indicates that the L-band EDFA gain can be effectively clamped via the ASE injection technique.     

带光隔离器的掺铒光纤放大器性能分析

本文通过速率方程对带光隔离器的掺铒光纤放大器(EDFA)的性能进行了理论分析.由于光隔离器有效地抑制了反向传输的放大自发幅射(ASE),从而改善了掺铒光纤放大器的增益、噪音系数和输出功率等性能,分析结果表明光隔离器加在最佳位置时,可使小信号增益提高约5dB,噪音系数降低约1.6dB.     

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.     

Dynamic-performance characterization of C-band EDFA using ASE-power peak-selective feedback gain-clamping

We propose and demonstrate a C-band Erbium-doped fiber amplifier (EDFA) using amplified spontaneous emission (ASE) power peaking-selective and feedback to achieve highly stabilized and wide dynamic range gain clamping performances. The gain of 16.20 ± 0.13 dB is obtained with the input signal power dynamic range of 30 dB and the maximum noise figure (NF) was 6.6 dB with the input signal power from −35 to −10 dBm. To investigate the gain variation for the probe signals, we applied a saturation tone signal to simulate 16-channel DWDM signals as it is added (dropped) into (from) EDFA. The gain variation of the proposed scheme at a appropriate ring-cavity loss (VOA = 5 dB) is less than 0.13 dB for the input signal power from −35 to −5 dBm and wavelength from 1530 to 1564 nm.     

基于长周期光纤光栅滤波器的掺铒光纤放大器理论和实验研究

从理论和实验上研究了带有高频二氧化碳激光写入的低成本长周期光纤光栅（LPFG）掺铒光纤放大器（EDFA）.结果表明,单波长和多波长EDFA的性能都可以通过在掺铒光纤（EDF）中插入长周期光纤光栅用作自发辐射噪声（ASE）滤波器或增益平坦器来提高性能.优化设计了带LPFG噪声滤波器的线放EDFA,与没有LPFG噪声滤波器相比,线放的噪声和小信号增益分别被减小和提高了约0.5 dB和7 dB。通过在多波长EDFA的EDF中插入一个LPFG增益平坦滤波器的方法,获得了1.5 dB的增益平坦度,与没有LPFG平坦器相比,EDFA的噪声被减小了0.1 dB,增益被提高了1 dB.     

有源循环式光脉冲复制系统的输出特性研究

改进并验证了一种基于有源循环光纤延迟线的模拟光脉冲信号复制技术.实验系统采用低增益掺铒光纤放大器补偿循环损耗.进行了光脉冲信号复制的仿真和实验,在掺铒光纤放大器增益为6.774 dB,光滤波器－3 dB,带宽为0.8 nm时,测得第500个复制光脉冲的信噪比为31 dB.仿真和实验结果表明,选用小增益掺铒光纤放大器可以实现低于3 dB的噪音系数,降低掺铒光纤放大器的放大自发辐射噪音并提高输出脉冲序列的信噪比,有望成为提高光脉冲复制器性能的一种新方法.在系统中插入窄带光滤波器等手段也是改善信噪比的有效措施.     

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.     

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.     

一种结构新颖的L波段掺铒光纤激光器

提出了一种结构新颖的L波段环形腔掺铒光纤激光器。用掺铒光纤作为增益介,采用980nm激光器作为前向抽运源,利用起偏器和偏振控制器获得L波段激光,利用光环形器将后向的放大自发辐射再引入铒光纤的前端,重复利用。当抽运功率为103mW时得到了阈值功率约为23．87mW,输出功率达6．34mW的激光输出,斜率效率约为8．05％,与没有重复利用后向放大自发辐射谱的掺铒光纤激光器做比较,该结构对L波段掺铒光纤激光器的性能有明显的提升作用。对于长度不合适的铒纤,在没有重复利用后向放大自发辐射谱时没有获得激光输出;而在利用后向放大自发辐射后,在阈值功率约为88mW时得到了激光输出,从而很好地证明了上述结论。     

Characteristics of low noise hybrid fiber amplifier

The characteristics of hybrid fiber amplifier (HFA) are investigated. HFA is composed of three stages: short-length EDFA pre-stage, DCF Raman amplifier, and power boosting EDFA. HFA has low noise figure, high output power, and also wide input power dynamic range. Gain control method of HFA is presented experimentally, and the transient gain excursion is suppressed to less than 0.5 dB at 3 dB channel add-drop. HFA can be used as line amplifier in optical transmission link even combined with distributed Raman amplifier due to wide input power dynamic range. The transmission performance of HFA is better than EDFA by more than 1.0 dB of Q-factor in 720 km SMF transmission.     

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.     

Ultra-broadband amplified spontaneous emission source by using heterogeneous optical amplifier

In this work, we propose and experimentally investigate an ultra-broadband amplified spontaneous emission (ASE) light source with 113.8 nm bandwidth (1446.2 to 1560.0 nm) by using a cascaded two-stage optical amplifier, which is consisted of semiconductor optical amplifier (SOA, 1st stage) and erbiumdoped fiber amplifier (EDFA, 2nd stage), when the output intensity is above ?35 dBm/0.01 nm. And, the EDFA only uses a 3 m long erbium-doped fiber (EDF) with a 27 mW pumping power and SOA is driven at 200 mA bias current. Moreover, the proposed amplifier also can provide a broadband gain amplification of 114 nm in the wavelengths of 1464.0 and 1578.0 nm with the noise figure distribution of 6.8 to 8.1 dB.     

小信号脉冲抽运时掺铒光纤自发辐射的研究

自发辐射(ASE)是掺铒光纤放大器(EDFA)的重要噪声源,对于由EDFA构成的光纤激光器有重要影响。理论与实践证明,它与抽运方式紧密相关,所以研究脉冲抽运时掺铒光纤(EDF)的自发辐射有重要的学术价值。同时,脉冲抽运对于EDFA锁模激光器的研究也有一定意义。从理论和实验两方面研究了小信号脉冲抽运时,抽运脉冲宽度和幅度对于EDF的自发辐射特性的影响,得到了小信号抽运时输出ASE噪声平均值的近似解析解。研究发现,小信号脉冲抽运时输出信号的幅度与抽运脉冲的宽度成正比。这个新现象可用于脉冲宽度的全光检测。