Experimental comparison of 980 nm and 1480 nm-pumped saturatedin-line erbium-doped fiber amplifiers suitable for long-haul solitontransmission systems

The performances of 980-nm- and 1480-nm-pumped erbium-doped fiber amplifiers applicable to high-bit-rate, long-haul soliton transmission systems are compared. Depending on the system parameters and preferred pumping configuration, 980-nm pumping is likely to offer a noise figure advantage of between 1.0 and 1.5 dB. However, the tolerances on pump wavelength are significantly tighter around 980 nm than at 1480 nm     

Time-dependent modeling of erbium-doped waveguide lasers in lithiumniobate pumped at 980 and 1480 nm

We have developed a rigorous phenomenological model for analyzing rare-earth doped waveguide lasers. The model is based on time-dependent laser rate equations for an arbitrary rare-earth-doped laser host with multiple energy levels. The rate equations are coupled with the laser signal and pump photon flux equations that have time-dependent boundary conditions. The formulation results in a large and stiff set of transcendental and coupled differential equations that are solved using finite difference discretization and the method of lines. Solutions for the laser signal power, pump power, and populations of ion energy levels as functions of space and time are obtained for waveguide lasers. We have used the model to predict the CW characteristics and Q-switched performance of waveguide lasers in lithium niobate pumped by a 980-nm source. Our analysis shows that hole burning can occur in erbium-doped lithium niobate lasers because of the intensity variation across guided transverse modes. We have predicted that Q-switch pulse peak powers can exceed 1 kW with pulsewidths less than 1 ns. Moreover, we have compared the CW and Q-switched performance of 980-nm pumped waveguide lasers and 1480 nm pumped waveguide lasers. An analysis of the effects of host- and fabrication-dependent parameters on CW 980-nm pumped lasers is included. These parameters include cooperative upconversion, excited state absorption, doping concentration, excess waveguide loss, cavity length, and mirror reflectance values. We demonstrate good quantitative agreement with waveguide laser experimental data obtained in our laboratory and with results from the literature     

Characterization of erbium-doped fibers and application to modeling 980-nm and 1480-nm pumped amplifiers

Erbium-doped fibers are characterized using loss and gain coefficients, and one amplifier saturation parameter. With a large-signal amplifier model that resolves the amplified spontaneous emission spectrum, these easily measured parameters allow the fiber performance in 980-nm or 1480-nm pumped optical amplifiers to be assessed rapidly. In tests at 980-nm pump wavelength, good agreement between the theoretical and experimentally measured gains was obtained with amplifiers having either germano-silicate or germano-alumino-silicate core fibers.<>     

1480-nm pumped erbium-doped fiber amplifiers with optimized noiseperformance for AM-VSB distribution systems

Within analog video transmission systems, optical amplifiers have to display simultaneously good noise and output power performance because of the very stringent carrier-to-noise ratio requirements imposed by the AM-VSB modulation format. We show, theoretically and experimentally, that properly designed forward 1480-nm pumped erbium-doped fiber amplifiers can deliver +16 dBm saturated output power with noise parameter (n_sp/C_x) as low as 3.5dB. These amplifiers do not exhibit significant degradation of their noise performance when the input powers are as large as +3 dBm. These characteristics make 1480-nm pumped amplifiers suitable for AM-VSB transmission systems     

Noise characteristics of erbium-doped fiber amplifier pumped at 980nm

A noise figure of 2.9±0.4 dB, measured in a high-gain erbium-doped fiber amplifier for input signals in the range -35 to -15 dBm and for pump powers of >5.8 mW, is discussed. The spontaneous emission factor n_sp was 0.99±0.09 for input signals less than -15 dBm. These low figures are attributable to the optimized fiber design and the use of a pump wavelength of 980 nm, at which erbium operates as a true three-level system. These two factors contribute to the very low (~500 μW) pump threshold seen in fiber, which permits nearly complete inversion to be achieved for the low pump powers employed     

Pump wavelength independent gain with bidirectionally pumped alumino-silicate erbium-doped fiber amplifiers in the 800 nm pump band

Using a comprehensive computer model, it was shown that the effects of excited state absorption (ESA), in the 800 nm pump band, in alumino-phosphate-silicate (APS) erbium-doped fiber amplifiers (EDFAs) can be reduced significantly by using bidirectional pumping. If a band optimum length (BOL) is selected, a near optimum small signal gain (SSG) can be constant over broad pump wavelength regions due to the combined effects of ESA and ground state absorption (GSA). Hence, multilongitudinal mode, high power, reliable and inexpensive GaAlAs laser diodes can be used as pumping sources for EDFAs having SSG > 40 dB, noise figures of <4 dB, and output signal powers approaching 100 mW. These fibre amplifiers could be used as line repeaters, preamplifiers, and power amplifiers in different lightwave systems.<>     

980 nm 和1480 nm 抽运下铋基EDFA放大特性的比较研究

The population rate and power propagation equations are presented and solved to compare the amplification performances of bismuth-based Er3+-doped fiber amplifier (EDFA) pumped by 980-and 1480-nm lasers,respectively.In both single signal and coarse wavelength-division-multiplexing(CWDM)signals inputs,the 1480-nm pumped bismuth-based EDFA provides a larger signal gain than the 980-nm pumped one does,whereas the latter provides a relatively lower noise figure (NF).Comparative results indicate that the 1480-nm pumping scheme is more advantageous for bismuth-based EDFA regarding the band width and gain property.     

Proposal for an Er/sup 3+/-doped chalcogenide glass fiber upconversion laser operating at 980 nm and pumped at 1480 nm

We propose a novel fiber upconversion laser operating at 980 mn and pumped at 1480 nm, which will allow remote optical pumping of erbium-doped optical amplifiers. From the measured spectroscopy, we show Er/sup 3+/-doped gallium lanthanum sulphide glass to be a potential host for such a 1480-nm/980-nm upconversion laser. The small-signal gain is analyzed numerically and the lasing possibilities are discussed.     

The gain and optimal length in the erbium-doped fiber amplifierswith 1480 nm pumping

The approximate analytic expressions for the gain and optimal length of the 1480-nm-pumped erbium-doped fiber amplifier with an arbitrary dopant distribution are obtained when the saturation by amplified spontaneous emission (ASE) is neglected. Numerical calculations show that the values predicted from the analytic expressions of the maximal gain and optimal fiber length as functions of input signal and pump powers are very accurate for narrow dopant distributions confined to the center of the fiber core     

A widely tunable erbium-doped fiber laser pumped at 532 nm

A tunable erbium-doped fiber laser with a very wide continuous-tuning range (1522-1567 nm) is discussed. The wide tuning range was achieved using an aluminum/erbium-doped fiber; the aluminum codoping is known to broaden the gain spectrum substantially. The tunable fiber laser has a ring laser configuration utilizing an inline tunable etalon as the tuning element. Continuous tuning over 45 nm in the spectral range of 1522-1567 nm was achieved with 80 nW of pumping at 532 nm, using the second harmonic of a Nd:YAG laser as the pump source     

Operation of erbium-doped fiber amplifiers and lasers pumped withfrequency-doubled Nd:YAG lasers

An optical amplifier consisting of an erbium-doped germanosilicate fiber optically pumped at 532 nm is described. Negligible excited-state absorption at 532 nm allows efficient pumping, enabling a gain of 34 dB at 1536 nm to be obtained for only 25 mW of pump power. The pulsed pump source produces negligible noise on the small signal if the pump repetition rate is above 10 kHz. Pulsed laser operation is achieved by pumping a Fabry-Perot erbium-doped fiber laser with a frequency-doubled Q-switched Nd:YAG laser. Pulses of 0.9-W peak power and 280-ns duration at 1.538-μm were obtained     

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     

Characteristics comparison of Er-doped double-pass superfluorescent fiber sources pumped near 980 nm

The Er-doped superfluorescent fiber sources (SFS's) pumped near 980 mm in double-pass forward and backward configurations are compared for the first time. The results indicate that a double-pass backward SFS is superior to the forward counterpart in many aspects: higher output power at various lengths of erbium-doped fiber, better pump-power dependent mean wavelength stability, and larger linewidths at various fiber mirror reflectance.     

Spectral beam combining of a single-mode 980-nm laser array for pumping of erbium-doped fiber amplifiers

With a view to improve the power level and brightness of semiconductor pump lasers, we have resorted to a scalable implementation and achieved spectral beam combining through a low-quality-factor external cavity. For that purpose, a high-power single-mode laser array emitting up to 2.1 W at 3.2 A at 980 nm has been realized, which delivers 1.5 W in external cavity. A power of 0.66 W was finally coupled into the single-mode fiber, with a coupling efficiency of 44%. Pumping experiments of an erbium-doped fiber amplifier utilizing this laser have demonstrated efficiency and noise characteristics similar to what is usually obtained with conventional sources, with the noteworthy advantage of a lower gain excursion over the C-band.     

Analytical Expression of the Threshold Pump Power of Erbium—doped Fiber Laeers Pumped at 980 nm and 1480nm Wavelengths

The rate equations,which is suiable to erbium-doped fiber lasers pumped at 980 nm and 1480 nm wavelengths respectively,are investigated,and analytical ex-pressions of the threshold pump powers under two pump wavelengths are derived.As a result,some important parmeters can be quantitatively specified.     

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     

Analytical Expression of the Threshold Pump Power of Erbium－doped Fiber Lasers Pumped at 980nm and 1480nm Wavelengths

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Modulation instability in erbium-doped fiber amplifiers

The onset of modulation instability in erbium-doped fiber amplifiers (EDFAs) is studied through a stability analysis of the underlying nonlinear Schrodinger equation. The existence of gain in EDFAs lowers the threshold for modulation instability considerably compared with the case of undoped fibers. Modulation instability generates multiple pulses when a single pulse is amplified. It can also create multiple subpulses in mode-locked fiber lasers, a feature observed experimentally. Numerical simulations show that EDFAs can convert a continuous-wave optical signal into a train of high-repetition rate femtosecond pulses     

Comparison of forward and, bidirectional pumping at 805 and 819 nm in erbium-doped silica fiber amplifiers

Using an accurate and comprehensive computer model, 805-810 and 819-825 nm band pumping of erbium-doped aluminosilicate fiber amplifiers is compared. A comparison is made for both forward and bidirectional pumping over a wide range of pump powers. It is shown that 805-810 nm pumping is more efficient if bidirectional pumping is used, while 819-825 nm pumping is more efficient if only forward pumping is carried out.<>     

Evaluation of the 800 nm pump band for erbium-doped fiberamplifiers

Performs a comprehensive experimental and theoretical investigation of methods for overcoming the excited-state absorption (ESA), which is the main obstacle to efficient pumping of erbium-doped fiber amplifiers (EDFAs) at 800 nm. The effects of ESA on gain can be reduced at the cost of an additional noise penalty by adopting bidirectional pumping or by pumping in the long-wavelength tail of the ground-state absorption (GSA) band. The GSA and ESA cross-section spectra on the glass host material. One of the most promising hosts, fluorophosphate, is compared to Al/P silica in a detailed analysis based on a quantitative numerical model. It is predicted that 2-3 dB less pump power is required for the fluorophosphate EDFA. For Al/P-silica EDFAs, it is found that ~7-dB-higher power is required when pumping in the 800 nm band than for pumping at 980 and 1480 nm