Broad-band erbium-doped fiber amplifier with double-passconfiguration

We demonstrate a broad-band silica-based erbium-doped fiber amplifier (EDFA) with double-pass configuration. The signal gain and noise figure are obtained more than 24 dB and less than 6 dB, respectively, for 1526-1562 nm and 1569-1605 nm. The same signal gain can be achieved with 53% less pump power and 45% shorter erbium-doped fiber length, compared to a conventional parallel type EDFA. Furthermore, the noise figure and power conversion efficiency are improved for the wavelength range     

基于光纤环形镜的L-波段掺铒光纤放大器增益的提高

提出了一种基于光纤环形镜作为反射器的反射式L-波段掺铒光纤放大器(EDFA)结构。光纤环形镜不但可以反射后向放大自发辐射(ASE)作为二次抽运源，而且还可以反射信号，使信号得到二次放大。当抽运功率为115mW时。在1570～1605nm波长范围内，反射式L-波段掺铒光纤放大器的平坦小信号增益达到29．14dB，与前向抽运方式L-波段掺铒光纤放大器相比(保持平坦性不变)。增益提高了5．33dB。分别输入波长为1580nm和1600nm的信号，反射式L-波段掺铒光纤放大器的饱和输出功率为7．63和7．6dBm．与前向抽运方式L-波段掺铒光纤放大器相比分别提高了2．98和3dB。     

980 nm和1480 nm LD混合泵浦两段级联掺铒光纤放大器实验研究

采用两段级联掺铒光纤、９８０ｎｍ和１４８０ｎｍＬＤ混合泵浦方式，实验分析比较了内插光隔离器和内插光隔离－耦合环光路结构掺铒光纤放大器（ＥＤＦＡ）的增益、噪声系数和输出功率特性。研制出内插光隔离－耦合环的ＥＤＦＡ，在信号波长１５５３．５ｎｍ处，小信号增益为４２．８ｄＢ，噪声系数为４．４ｄＢ，输出功率为１５．２ｄＢｍ。     

High-gain coefficient long-wavelength-band erbium-doped fiberamplifier using 1530-nm band pump

A 1530-nm band has been studied as a pump wavelength for the long-wavelength-band erbium-doped fiber amplifier (L-band EDFA). The pump source is built using a tunable light source and cascaded conventional-band (C-band) EDFA. The L-band EDFA uses a forward pumping scheme. Within the 1530-nm band, the 1545-nm pump demonstrates 0.45-dB/mW gain coefficient, which is twice better than that of conventional 1480-nm pumped EDFA. The noise figure of the 1530-nm pump is at worst 6.36 dB, which is 0.75 dB higher than that of the 1480-nm pumped EDFA. Such high-gain coefficient indicates that the L-band EDFA consumes low power     

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.     

Study on noise characteristic of gain-clamped erbium-doped fiber-ring lasing amplifier

A simplified method to estimate the noise figure of the optically gain-clamped erbium-doped fiber amplifiers (EDFA's) is proposed. The simulation results indicate that the population inversion level at the signal input end dominates the noise performance of the entire amplifier. For a gain-clamped EDFA with ring-lasing configuration, the effects on the noise figure of the amplifier by the distributions of the pumping and lasing powers as well as the lasing wavelength are analyzed theoretically. The suggested noise-optimum configuration is co-pumping and co-traveling lasing oscillation at 1531 nm. Near quantum limit internal noise figure of 3.6 dB is achieved in the experiments under the best arrangement. The experiment results show perfect accordance with the theoretical analysis.     

Comparison between regenerative-feedback and cofeedback gain-clamped EDFA

The erbium-doped fiber amplifier (EDFA) with regenerative feedback is compared with the cofeedback scheme. Without the bandpass filter, the injected signal experiences regenerative amplification and results in a higher signal gain. Such an above-threshold regenerative amplifier also exhibits a lower noise figure due to a higher inversion for the transition corresponding to the signal wavelength of 1550 nm. A near quantum-limited noise figure of 3.1 dB is achieved at the maximum pump power of 134.5 mW, showing nearly complete inversion at the EDF input end in the regenerative-feedback scheme. A low (<10/sup -10/) bit-error rate has been achieved with saturation input signal power above -12 dBm.     

On the Temperature-Dependent Gain and Noise Figure Analysis of C-Band High-Concentration EDFAs With the Effect of Cooperative Upconversion

We present an efficient temperature-dependent analysis to study the effect of cooperative upconversion on the temperature-dependent gain (TDG) performance of the C-band erbium-doped fiber amplifier (EDFA) at high-concentration. The influence of cooperative upconversion on the TDG is examined by using a set of temperature-dependent rate and light propagation equations. In the analysis given, the amplified spontaneous emission (ASE), as well as the excited state absorption (ESA) are also considered. In the forward pumping configuration at a signal wavelength of 1547 nm and in the temperature range of - 40degC to + 80degC, the variations of the TDG and the noise figure (NF) are about 1.7 and 0.9 dB, respectively. Numerical analysis results show that, with 260-mW/1480-nm pump power, an erbium-doped fiber amplifier having a doping concentration of 4.4 times 10²⁶ ion/m³ and optimum length of 9.2 cm may reach a signal gain of 44.6 dB and a noise figure of 3.9 dB at room temperature.     

Gain clamping in two-stage L-band EDFA using a broadband FBG

A gain-clamped long wavelength band erbium-doped fiber amplifier (L-band EDFA) with an improved gain characteristic is demonstrated by simply adding a broadband conventional band (C-band) fiber Bragg grating (FBG) in a two-stage amplifier system. The FBG reflects backward C-band amplified spontaneous emission (ASE) from the second stage back into the system to clamp the gain. The gain is clamped at about 22.4 dB with a gain variation below 0.4 dB for input signal powers of -40 to -15 dBm. Compared with an unclamped amplifier of similar noise figure values, the small signal gain has improved by 2.4 dB due to the FBG which blocks the backward propagating ASE. At wavelengths from 1570 to 1600 nm, gain of the clamped amplifier varies from 19.4 to 26.7 dB. The corresponding noise figure varies by /spl plusmn/0.35 dB around 5 dB, which is not much different compared to that of the unclamped amplifier.     

Gain enhancement in L-band loop EDFA through C-band signal injection

Gain enhancement provided in L-band erbium-doped fiber amplifier (EDFA) with loop configuration and through C-band signal injection is experimentally demonstrated and compared with conventional single-stage L-band EDFA design. Significant backward amplified spontaneous emission suppression in C-band and pump conversion efficiency increase in L-band were observed for varying C-band seed signal wavelength and power levels. Gain and noise figure (NF) performance of loop design L-EDFA is compared with the conventional bidirectionally pumped single-stage L-EDFA design. Gain and NF measurements in the loop configuration have resulted in an up to 9.5-dB increase in gain and up to 2.6-dB degradation in NF at a moderate signal wavelength of 1585 nm.     

Double-pass L-band EDFA with enhanced noise figure characteristics

A new double-pass long wavelength band erbium-doped fiber amplifier with enhanced noise figure characteristics is demonstrated by adding a short length of forward pumped erbium-doped fiber (EDF) in front of a double-pass amplifier. Compared with the conventional double-pass amplifier, the new amplifier provides noise figure improvement of about 0.8 to 6.0 dB over the flat-gain region from 1568 to 1600 nm. Since the optical circulator prevents the amplified signal and backward amplified spontaneous emission from propagating into the EDF, the population inversion of the input part of the amplifier is hardly affected by the intense lights, therefore, the noise figure could be kept low. The new double-pass system has achieved a flat-gain output at about 33.5 dB, which is 13.5 dB higher than that of the single-pass system with gain variation less than 1.3 dB at the flat-gain region. The noise figure varies from 5.9 to 6.6 dB in this region.     

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.     

Characteristics of regenerative erbium-doped fibre ring amplifier

A study is presented into the dynamic characteristics of a unidirectional regenerative erbium-doped fibre ring amplifier at below laser threshold. A considerable improvement in gain and noise figure performance was observed due to the suppression of amplified spontaneous emission in the regenerative amplification process. It was found that lower feedback power provides higher optical gain. An optical signal of -33.5 dB was found to experience a gain of ⩾35 dB at and near the resonance wavelength using 1% feedback by an optical fibre coupler for an optical pump (1480 nm) power as low as 10 mW     

Hybrid fiber amplifiers consisting of cascaded TDFA and EDFA for WDM signals

The detailed gain characteristics of hybrid fiber amplifiers that consist of cascaded thulium-doped fiber amplifiers (TDFAs) and erbium-doped fiber amplifiers (EDFAs) are reported. The experimental results showed that the hybrid amplifiers have gains of over 20 dB with the bandwidth of more than 80 nm in the wavelength range between 1460 and 1560 nm. The low noise figure (NF) below 7 dB was obtained in 1460-1540 nm when placing a TDFA in the first stage followed by an EDFA and in 1480-1560 nm when placing amplifiers in a reversed order. The gain of TDFA and EDFA was optimized for minimizing the gain variation ratio (GVR=(maximumgain-minimumgain)/minimumgain: in the unit of decibels) of the hybrid amplifiers, and it could be minimized to less than 0.4 for the amplifiers that have gain in the wavelength region from 1460 to 1537 nm. The gain-equalization technique was applied, and the hybrid amplifier that had an average gain of 20 dB, a gain excursion of less than 2 dB, an output power of 14.5 dBm, and an NF of less than 7 dB in the 77-nm gain band was achieved.     

反射式L波段掺铒光纤放大器增益与噪声指数改善

提出了一种改善反射式L波段掺铒光纤放大器增益和噪声指数的方法,即在放大器的输入端插入一泵浦源,通过提高信号输入端的粒子数反转率实现提高增益和降低噪声指数的目的.通过仔细调整两个泵浦源的输出功率,与单泵浦结构相比,在相同条件下,在1565～1615 nm波长范围内,小信号增益提高了1.5～9.9 dB,噪声指数下降了1.3～9.4 dB.     

A low-noise and gain-flattened amplifier composed of a silica-based and a fluoride-based Er/sup 3+/-doped fiber amplifier in a cascade configuration

We propose a novel low noise and gain-flattened Er/sup 3+/-doped fiber amplifier (EDFA) with a cascade configuration for wavelength division multiplexing (WDM) signals. In this configuration, a 1480-nm pumped fluoride-based EDFA is joined to a 980-nm pumped silica-based EDFA through an optical isolator. By adjusting the silica-based Er/sup 3+/-doped fiber length in the silica-based EDFA, we realized an excellent flat gain EDFA with a gain excursion of less than 0.9 dB and noise figure of 5.7/spl plusmn/0.2 dB, and a low noise EDFA with a noise figure of 5/spl plusmn/0.2 dB and a gain excursion of less than 1.4 dB, for 8 channel WDM signal in the 1532-1560-nm wavelength region.     

Low-noise intelligent cladding-pumped L-band EDFA

We present results on a low-cost cladding-pumped L-band amplifier based on side pumping (GTWave) fiber technology and pumped by a single 980-nm multimode diode. We show that simultaneous noise reduction and transient suppression can be achieved by using gain clamping by a seed signal (/spl lambda/=1564 nm). In the gain-clamping regime, the amplifier exhibits 30-dB gain over 1570-1605-nm spectral band with noise figure below 7 dB. The noise figure can be further reduced to below 5 dB by utilizing a low power single-mode pump at 980 nm. The erbium-doped fiber amplifier is relatively insensitive to input signal variations with power excursions below 0.15 dB for a 10-dB channel add-drop.     

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.     

Er^3＋/Yb^3＋共掺光纤放大器小信号放大特性

基于速率方程,文中研究了双包层Er^3＋/Yb^3＋共掺光纤放大器小信号放大时的放大特性和噪声特性。结果表明：双包层Er3＋/Yb3＋共掺光纤放大器对波长为1550nm的小信号具有良好的放大特性,反向泵浦,当泵浦功率超过2W时,放大增益可超过60dB;同时,该放大器对C波段的小信号亦具有良好的放大特性,其3dB增益带宽达到54nm。该研究进一步表明双包层Er^3＋/Yb^3＋共掺光纤放大器在C波段具有良好的噪声特性,小信号放大时,噪声系数接近于EDFA的噪声极限。     

Low-noise extended L-band phosphorus co-doped silicate EDFA consisting of novel two-stage gain-flattened gain blocks

A novel low-noise extended L-band silicate erbium-doped fibre amplifier (EDFA) is proposed, consisting of two novel gain-flattened gain blocks for wavelength-division multiplexing (WDM) signals from 1562.2 to 1619.6 nm. Each gain block consists of three isolated phosphorus/ alumina co-doped silicate EDFs, an intermediate embedded gain flattening filter (GFF), a short wavelength pump laser diode, and a pump bypass and/or a recycle path. The proposed EDFA, which uses only three pump laser diodes, has achieved noise figures as much as 6.1 dB lower than those realised by an earlier EDFA, when its intermediate optical attenuator has large signal losses and the input signal power is low.