1.58-μm band gain-flattened erbium-doped fiber amplifiers forWDM transmission systems

This paper describes the amplification characteristics of gain-flattened Er³⁺-doped fiber amplifiers (EDFAs) by using 0.98-μm and 1.48-μm band pumping for a 1.58-μm band WDM signal. Silica-based Er³⁺-doped fiber (S-EDF) and fluoride-based Er ³⁺-doped fiber (F-EDF) have gain-flattened wavelength ranges from 1570 to 1600 nm and from 1565 to 1600 nm, respectively, and exhibit uniform gain characteristics with gain excursions of 0.7 and 1.0 dB, and the figure of merit of the gain flatness (gain excursion/average signal gain) of 3 and 4.3%, respectively, for an eight-channel signal in the 1.58-μm band. We show that 1.48-μm band pumping has a better quantum conversion efficiency and gain coefficient, and that 0.98-μm band pumping is effective for improving the noise characteristics. We also show that the EDFAs consisting of two cascaded amplification units pumped in the 0.98-μm and 1.48-μm bands are effective in constructing low-noise and high-gain 1.58-μm band amplifiers     

Design optimization for efficient erbium-doped fiber amplifiers

The gain and pumping efficiency of aluminosilicate erbium-doped fiber amplifiers (EDFAs) are analyzed as a function of guiding parameters and Er-doping profile for two pump wavelengths of λ _p=980 nm and λ_p=1.47 μm. Three designs of fiber-amplifier waveguides are considered: one with the same mode size as standard 1.5-μm communication fibers (type 1); one with the same mode size as standard 1.5-μm dispersion-shifted fibers (type 2); and one with mode size smaller than those of communication fibers (type 3). For the 1.47-μm pump, fundamental LP₀₁ mode excitation is assumed, while for the λ_p=980-nm pump, concurrent excitation of LP₁₁ modes is considered. It is shown that excitation of higher-order pump modes at 980 nm does not significantly affect the amplifier gain performance. The effect of concentrating the Er³⁺ doping near the center of the fiber core is shown to increase the amplifier gain coefficients by a factor of 1.5 to 2     

Power requirements for erbium-doped fiber amplifiers pumped in the800, 980, and 1480 nm bands

The authors examine relative merits of exciting Er³⁺ amplifiers at the three wavelengths for which high-power laser diodes are available at 800, 980, and 1480 nm. Model calculations are confirmed by a detailed experimental comparison of the power requirements for pumping in the 800-nm band and at 980 nm. To obtain comparable performance with respect to gain and noise figure, 7-8 dB more power is required when pumping in the 800-nm-band     

Improved gain performance in Yb3+-sensitized Er3+-doped alumina (Al2O3) channel opticalwaveguide amplifiers

Small-signal amplification in short, Yb³⁺-sensitized, Er³⁺-doped alumina (Al₂O₃) channel optical waveguides with high Er³⁺ concentrations is analyzed. Taking into account uniform up conversion, excited state absorption (ESA) from the Er³⁺ metastable level (⁴I_13/2 ), and Yb³⁺→Er³⁺ energy transfer by cross relaxation, the obtainable gain improvements compared to Yb³⁺ -free Er³⁺-doped Al₂O₃ optical waveguides are investigated. The amplifier model is based on propagation and population rate equations and is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that 5-cm long Yb³⁺/Er³⁺ co-doped Al₂O ₃ waveguides show 13-dB net signal gain for 100 mW pump power at λ_p=980 nm     

Modeling the gain degradation of high concentration erbium-dopedfiber amplifiers by introducing inhomogeneous cooperative up-conversion

The gain degradation of erbium-doped fiber amplifiers (EDFAs) with high erbium ion (Er³⁺) concentration at 1.48- and 0.98-μm pump wavelengths is modeled by introducing inhomogeneous cooperative up-conversion (IhCU). General formulas describing the gain degradation as a function of IhCU rate are obtained by solving rate equations for population probabilities in the relevant Er³⁺ energy levels. The experimental results, such as low gain for high Er³⁺ concentration, and higher saturated gain with counterpropagation than with copropagation pumping, which have not yet been explained theoretically, are qualitatively explained by this model. Good agreement between the measured and calculated gain is obtained. The gain degradation characteristics at 1.48- and 0.98-μm pump wavelengths are analyzed with this model. The advantage of counterpropagation pumping is determined qualitatively. The noise figure degradation is also evaluated     

A 980 nm pseudomorphic single quantum well laser for pumpingerbium-doped optical fiber amplifiers

The authors have fabricated ridge waveguide pseudomorphic InGaAs/GaAs/AlGaAs GRIN-SCH SQW (graded-index separate-confinement-heterostructure single-quantum-well) lasers, emitting at 980 nm, with a maximum output power of 240 mW from one facet and a 22% coupling efficiency into as 1.55-μm single-mode optical fiber. These lasers satisfy the requirements on efficient and compact pump sources for Er³⁺-doped fiber amplifiers     

Cascaded Two-Wavelength Lasers and Their Effects on C-Band Amplification Performance for Er3+-Doped Fluoride Fiber

In this paper, we report cascaded two-wavelength 853-nm (⁴ S_3/2rarr⁴I_13/2 transition) and 1533-nm (⁴I_13/2rarr⁴I_15/2 transition) lasing from Er³⁺-doped fluoride fiber pumped at 974 nm. The cavity for cascaded two-wavelength lasing is composed of two fiber ends with 4% Fresnel reflection. Its optical-to-optical efficiency is up to 26.6%. Its effects on C-band fiber amplifiers and green upconversion fiber lasers are discussed. A new way to get high efficiency and low noise C-band amplifier is suggested, i.e., a fluoride-based Er³⁺-doped fiber amplifier including 853-nm lasing cavity. Our simulated results show that such a new amplifier can enhance the signal gain greatly and break the limit of the saturated gain intensity for a normal amplifier     

Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

Cumulative waveform distortion in cascaded optical amplifierrepeaters for multigigabit IM/DD systems

An analysis was conducted of a cumulative pattern-dependent waveform distortion in cascaded semiconductor laser and Er³⁺-doped fiber amplifiers. At 2.5 Gb/s, cumulative waveform distortion limits the number of cascaded amplifiers to about 20 for the semiconductor amplifiers. The Er³⁺-doped fiber amplifier is relatively unaffected-over 100 stages can be cascaded. The Er³⁺ amplifier is seen to be the better choice for long-haul multigigabit systems     

Er–Yb Waveguide Amplifiers in Novel Silicate Glasses

A set of novel silicate glasses containing ZnO and co-doped with Er³⁺ and Yb³⁺ was designed as substrates for optical waveguide amplifiers. Characterized by exceptionally low up-conversion, minimum Er concentration quenching and high mechanical as well as chemical stability, the reported glasses can compete with phosphate-based materials typically used in the state-of-art active devices. Straight channel waveguides with propagation losses as low as 0.18 dB/cm were fabricated in these substrates using Ag⁺ hArr Na⁺ and K ⁺ hArr Na⁺ thermal ion exchange. Net on-chip gain values of 6.7 dB at 1537 nm were measured and a net fiber to-fiber gain of 5 dB was achieved when pumped at 976 nm. A six-level spatially resolved numerical model of an Er-Yb co-doped active waveguide was developed to analyze and optimize the amplifier performance. Modification of the rare-earth dopant concentration and the channel waveguide geometry was proposed to increase the gain figure and improve the overall amplifier efficiency.     

Erbium-doped glasses for fiber amplifiers at 1500 nm

Material-dependent properties influencing the performance of fiber amplifiers are reviewed together with the available data for Er³⁺ . The major glass types potentially useful in this application are considered and compared to silica. The topics addressed include quenching processes and the solubility of rare-earth ions, transition strengths and bandwidths at the 1500-nm gain transition, and the characteristics at the 800-, 980-, and 1480-nm pump bands. Aluminum is shown to be an extremely useful codopant for silica, improving its ability to dissolve rare-earth ions and providing desirable spectroscopic properties for Er³⁺. For some of the attributes considered, other glasses have advantages over Al silica, but only with respect to gain bandwidth and pumping performance at 800 nm is significantly better than expected from other glass compositions     

Optimum design of Er3+-Yb3+ codoped fibersfor large-signal high-pump-power applications

A comprehensive numerical fiber amplifier model has been used to optimize Er³⁺-Yb³⁺ codoped active fiber for maximum gain and quantum conversion efficiency (QCE) at large signal operation. The optimum cutoff wavelength of the LP₁₁ mode has been found to increase from 800 mm at low pump powers (≈50 mW) to 1400 mn at pump powers higher than 500 mW. While at low pump powers fibers with higher numerical aperture give higher QCE, at high pump levels better large signal performance is achieved with fibers having lower numerical aperture     

Er3+-doped fiber amplifier pumped by 0.98 μm laserdiodes

The performance of an Er³⁺-doped fiber amplifier pumped by 0.98 μm InGaAs laser diodes (LDs) is reported. By using a fiber with low Er³⁺ content and optimizing the fiber length, a maximum signal gain of 37.8 dB at 30-mW pump power was realized at a signal wavelength of 1.536 μm. A maximum gain coefficient of 1.9 dB/mW at 14 mW pump power was achieved. It was found that the fiber amplifier pumped by the 0.98-μm LDs is twice as efficient as that pumped by 1.48-μm LDs, from the viewpoint of both required fiber length and the attained gain     

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。     

铒铥共掺碲基质宽带光纤放大器研究

文章作者分析了铒铥共掺碲基质光纤放大器在980 nm泵浦下Er~(3+)-Tm~(3+)离子之间的能量转移过程,建立了速率方程和功率传输方程,并通过仿真得出了其放大增益随光纤长度和泵浦功率的变化规律.仿真结果表明:通过优化光纤长度和泵浦功率,该放大器可以在1 440～1 540 nm波段得到高达50 dB的平坦增益.     

The effect of pair-induced energy transfer on the performance ofsilica waveguide amplifiers with high Er3+/Yb3+concentrations

High-concentration Er³⁺/Yb³⁺ co-doped silica waveguide amplifiers are numerically analyzed. With optimized rare-earth concentrations the effect of Er³⁺/Er³⁺ ion-pairs can be neglected and each Er³⁺ ion can be assumed to be paired only to the surrounding Yb³⁺ ions. The rate-equations model includes uniform upconversion mechanisms from ⁴I_13/2 and ⁴I_11/2 erbium levels and an Yb³⁺ to Er³⁺ pair-induced energy transfer process. Numerical results demonstrate the possibility of fabricating short- and high-gain integrated optical amplifiers; it is shown that net gain as high as 3 dB/cm can be obtained     

两段级联掺铒光纤放大器的最佳光纤长度

基于Giles模型．研究了980nm和1480nm泵浦的两段级联掺铒光纤放大器(EDFA)的最佳光纤长度随泵浦功率和信号功率的变化关系，并与单段EDFA的最佳光纤长度进行了比较，在实用泵浦功率条件下，前者比后者长30％以上。     

EDFA中光隔离器的最佳位置

基于Giles模型,研究了980nm和1480nm泵浦的两段EDFA中光隔离器的最佳位置随泵浦功率和信号功率的变化关系。光隔离器的最佳位置在距EDFA信号输入端约1/3处。     

Gain and noise penalty for detuned 980 nm pumping or erbium-dopedfiber power amplifiers

The impact of altering the fiber length and pump wavelength on the gain and noise performance of erbium-doped fiber power amplifiers pumped in the 980-nm band is examined. A gain penalty of <0.5 dB was experimentally observed over an 18 nm pump wavelength range. Theoretical analysis indicates that increasing the numerical aperture (NA) from 0.15 to 0.25 significantly improves the tolerance for a given gain penalty but has little effect on the noise figure. For a given fiber length, the noise figure increases by 0.1 dB for each 3 nm the pump wavelength deviates from 979 nm