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.     

WDM用增益平坦的高增益低噪声双段级联掺铒光纤放大器

给出了设计波分复用(WDM)用高增益、低噪声和宽带宽增益平坦的双段级联掺铒光纤放大器(EDFA)的一般步骤和方法.通过优化设计各种参量,研制出了一台高增益、低噪声和宽带宽增益平坦的双段级联EDFA样机,实现了从1524.8～1561.4 nm共36.6 nm带宽内±0.325 dB的平坦增益,0 dBm输入时,饱和输出功率大于15 dBm的高功率输出;噪声指数低于5 dB.     

混合泵浦两段级联掺铒光纤放大器实验研究

基于内插隔离－耦合环两段级联新结构，采用９８０ｎｍ与１４８０ｎｍ激光二极管混合泵浦方式，研制出在１．５５μｍ波段兼具高增益，大功率，低噪声九特性的掺铒光纤放大器。     

Gain-clamped two-stage L-band EDFA with a FBG laser in second stage

A gain-clamped two-stage L-band EDFA is demonstrated by simply incorporating two different FBGs on both side of EDF in the second stage. It forms a FBG laser at 1560 nm to clamp the gain in the system. The gain is clamped at about 16.5 dB with gain variation of less than 1.0 dB at dynamic range up to −10 dBm. A flat gain is obtained over 30 nm of wavelength range from 1568 to 1598 nm with a gain variation of less than 1.1 dB. At the flat region, the noise figure varies from 5.0 to 5.8 dB, which is slightly higher compared to those of unclamped amplifier. The advantage of this technique is that the FBG laser does not disturb the WDM signals in the flat gain region.     

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.     

Investigation of the optical gain and noise figure for multi-channel amplification in EDFA under optimized pump condition

We present the results of an investigation of optical gain and noise figure for simultaneous multi-channel amplification of an erbium doped fibre amplifier (EDFA) under optimized pump condition. Different pump configurations with varying input signal levels show interesting features on gain flatness. In the experiment, population inversion along the fibre length which determines the gain-spectra and noise characteristics of the amplifier is adjusted through optimized fibre length and injected pump power in order to minimize the gain-tilt at C-band. It is observed that bi-directional pumping manifests the best combination of low noise and high gain of EDFA which are useful as in-line repeaters in WDM network. We obtain 30 ± 1.5 dB intrinsically flat small signal gain from 1538 nm to 1558 nm band of wavelength with noise figure <4 dB for 16-channel simultaneous amplification in a single stage EDFA without gain flattening filter.     

Optimization of gain flattened C-band EDFA using macro-bending

Optimization of gain flattened C-band erbium-doped fiber amplifier (EDFA) using a macrobending method with an improved gain flatness and bandwidth is demonstrated. The optimization for gain flatness and bandwidth was achieved by varying the bending radius and the length of the doped fiber. In the optimized condition, the gain saturation effect as well as the energy transfer from shorter wavelengths to longer wavelengths resulted in a flattened and broadened gain profile in the C-band region. The amplifier was optimized to a 9 m long erbium-doped fiber (EDF) with erbium ion concentration of 1100 ppm and bending radius of 6.5 mm. The gain variation of the EDFA is obtained within ±1 dB over 25 nm bandwidth of C-band region.     

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.     

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.     

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.     

High-gain and low-noise-figure erbium-doped fiber amplifier employing dual stage quadruple pass technique

A high-gain and low-noise-figure (NF) erbium-doped fiber amplifier (EDFA) was demonstrated utilizing a new technique called the dual-stage quadruple pass (DSQP) with filters. An efficient amplification occurs at the signal wavelength of 1550 nm when it travels along the DSQP amplifier. The highest gain of 62.56 dB with a low noise figure of 3.98 dB was achieved for an input signal power of −50 dBm and pump powers of 10 and 165mW in the second and first stage amplifiers respectively.     

Bidirectional-pumped L-band erbium-doped fiber amplifier with pump distribution technique

A dual-stage erbium doped fiber amplifier (EDFA) having a flat gain wavelength response throughout L-band transmission window is presented. By applying pump power distribution technique, the pump power is distributed to two different stages with different length of EDF depending on the coupling ratio. By controlling these two parameters, gain of 19.1 dB with small gain variation of less than 0.5 dB and a noise figure of less than 10.5 dB are achieved in this architecture using bidirectional pumping. However, when another 3 dB power coupler is added to split the pump power equally at the second stage in bidirectional, a better noise figure of less than 7.5 dB was obtained. Comparison with a conventional single-stage optical amplifier was made in order to validate the performances of this dual-stage EDFA.     

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.     

Limitation in the intrinsic method of EDFA gain optimization for 32 × 40 Gbit/s WDM systems

The gain flattening of the erbium doped fiber amplifier (EDFA) is one of the most important aspects in the EDFA which the gain is wavelength dependent. For the first time the limitation of EDFA gain optimizing for a 32-channel wavelength division multiplexing (WDM) systems is investigated and reported in this paper. In a 32-channel WDM system the most favorable flatness gain achieved was 23.16 ± 1.51 dB with an average noise figure of 5.70 dB. This outcome proposes that the method does not achieve a uniform spectral gain in a 32-channel WDM system that incorporates a bandwidth of around 25 nm. Based on the simulation results the intrinsic optimization of EDFA causes the poor SNR and peak signal power with great variation over a transmission distance of 480 km single mode fiber.     

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.     

Gain clamping in double-pass L-band EDFA using a broadband FBG

A highly efficient gain-clamped L-band EDFA with improved noise figure characteristic is demonstrated by simply adding a broadband C-band FBG in double-pass system. The combination of the FBG and optical circulator has created laser in the cavity for gain clamping. By adjusting the power combination of pumps 1 and 2, the clamped gain level can be controlled. The amplifier gain is clamped at 28.1 dB from −40 to −25 dBm with a gain variation of less than 0.5 dB by setting the pumps 1 and 2 at 59.5 and 50.6 mW, respectively. The gain is also flat from 1574 nm to 1604 nm with a gain variation of less than 3 dB. The corresponding noise figure varies from 5.6 to 7.6 dB, which is 0.8 to 2.6 dB less than those of unclamped amplifier.     

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.     

Low noise double pass L-band erbium-doped fiber amplifier

A new double pass long wavelength band erbium-doped fiber amplifier with enhanced noise figure characteristics is demonstrated. The noise figure is improved by about 2.6 dB with the incorporation of broadband conventional-band fiber Bragg grating (FBG) in between the two segments of erbium-doped fiber. By incorporating both the pre-amplifier and the FBG, the noise figure is further improved, which varies from 4.0 to 5.0 dB in the flat gain region from 1570 to 1600 nm. The gain varies from 32.0 to 33.4 dB within this region. The new amplifier with high gain and low noise figure can be useful as an inline amplifier in a wavelength division multiplexing transmission system.     

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.     

Hybrid flat gain C-band optical amplifier with Zr-based erbium-doped fiber and semiconductor optical amplifier

An efficient gain-flattened C-band optical amplifier is demonstrated using a hybrid configuration with a Zirconia-based Erbium-doped fibre (Zr-EDF) and a semiconductor optical amplifier (SOA). The amplifier utilizes a two-stage structure with a midway isolator to improve flat gain characteristic and reduce noise figure. At input signal power of −30 dBm, a flat gain of 28 dB is obtained from wavelength region of 1530 to 1560 nm with gain variation of less than 4 dB. The noise figure is maintained below 11 dB at the flat-gain region. This amplifier has the potential to be used in the high channel count dense wavelength division multiplexing system due to its simplicity and compact design.