Detailed design analysis of erbium-doped fiber amplifiers

When pumping the erbium-doped fiber amplifier at 0.98 and 1.48 mu m, the optimum cutoff wavelength for step profiles with arbitrary numerical aperture is shown to be 0.80 and 0.90 mu m, respectively. The use of a confined erbium profile can improve the gain coefficient up to 45%. The index raising co-dopant is shown to be very significant for the gain coefficient when pumping at 0.98 mu m.<>     

Gain and noise performance of fibre amplifiers operating in new pump configurations

New configurations of erbium-doped fibre amplifiers have been investigated for the 0.98 mu m and 1.48 mu m pump wavelengths. A doubling of the gain coefficient has been predicted for reflective type amplifiers at the cost of a noise figure increase of 1.5 dB.<>     

Feasibility demonstration of low pump power operation for 1.48 mu m diode-pumped erbium-doped fibre amplifier module

An optimisation of the erbium-doped fibre greatly improves the 1.48 mu m pumping efficiency. The amplifier exhibits 26.2 dB fibre gain for 8 mW launched pump power and 20.2 dB gain for only 5.2 mW pump power, giving an outstanding 3.9 dB/mW gain coefficient.<>     

Temperature dependence of signal gain in Er3+-dopedoptical fiber amplifiers

Temperature-dependent signal gain characteristics at signal wavelengths of 1.536 and 1.552 μm in Er³⁺-doped optical fibers with a temperature range of -40 to 80°C are reported for 0.98 and 1.48 μm pumping. The temperature dependences of signal gain strongly depend on fiber length, pump wavelength, and signal wavelength. The fiber length at which signal gain temperature insensitivity occurs is found for the amplification of a 0.98-μm-pump-1.536-μm-signal, a 0.98-μm-pump-1.552-μm-signal, and a 1.48-μm-pump-1.536-μm-signal. It is confirmed theoretically that the temperature dependences result from linear changes in the fluorescence, and absorption cross sections at the signal and pump wavelengths, and a shift in the effective pump wavelength     

Laser diode pumped Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fluoride fiber amplifiers operating at 1.3 mu m

Both Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped singlemode fibres with high numerical apertures are pumped by laser diodes with InGaAs/GaAs strained quantum well structures. A net gain of 5.2 dB is obtained from Pr/sup 3+/-doped fluoride fibre pumped by laser diodes operating at 1.1017 mu m and a net gain of 3.2 dB is obtained from Pr/sup 3+/-Yb/sup 3+/-codoped fibre pumped by laser diodes operating at 0.98 mu m. The pumping efficiency difference between Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fibre is discussed.<>     

Comparative study on temperature-dependent multichannel gain andnoise figure distortion for 1.48- and 0.98-μm pumped EDFAs

Temperature dependence of multichannel gain flatness and noise figure (NF) was compared for different pump wavelengths of 1.48 and 0.98 μm on silica-based erbium-doped fiber amplifiers (EDFAs) through measurement-based numerical simulation. Owing to its temperature sensitive pump emission cross section, the 1.48-μm pumping showed greater temperature sensitivity (maximum 0.75-dB gain flatness distortion with 0.57-dB average gain level shift, 0.3-dB NF variation for 25°C change) than the 0.98 μm pumping (maximum 0.5-dB gain flatness distortion with 0.015-dB average gain level shift, 0.05-dB NF variation for 25°C change). However, it was also found that distortion ripple spectra mainly coming from the changes of signal cross sections and asymmetric gain temperature dependence necessitate compensation techniques in the EDFA link, irrespective of pump wavelength     

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     

Highly efficient optical fibre amplifier pumped by a 0.8 mu m band laser diode

A highly efficient Er-doped fibre amplifier pumped by GaAlAs laser diodes is reported. Using a low Er-cluster content fibre with a high numerical aperture, the EDFA attains 39 dB signal gain for double LD pumping and 30 dB for single LD pumping at 1.536 mu m. A maximum gain coefficient of 1.3 dB/mW was achieved at the 0.827 mu m pump band.<>     

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     

Mutual signal gain saturation in Er/sup 3+/-doped fibre amplifier around 1.54 mu m wavelength

Signal gain saturation characteristics of a 1.48 mu m wavelength laser diode pumped Er/sup 3+/-doped fibre amplifier are experimentally investigated for two signal channels amplified around the gain peak wavelengths of 1.535 mu m and 1.551 mu m. The degree of gain saturation is uniquely determined by the total output power when the signal wavelengths are closely positioned. This feature is not suited to two-channel amplification for widely spaced wavelengths.<>     

Highly efficient integrated optical fibre amplifier module pumped by a 0.98 mu m laser diode

A small fibre amplifier module pumped by a 0.98 mu m LD has been fabricated. Using a low erbium content fibre with a 4.9 dB/mW gain coefficient, the module attained 33 dB gain at 1.535 mu m with only 80 mA drive current.<>     

30 dB optical net gain at 1.543 mu m in Er/sup 3+/ doped fluoride fibre pumped around 1.48 mu m

A 30 dB optical net gain and 12 dBm maximum output power for -1 dBm signal input have been measured at a signal wavelength of 1.54 mu m with an erbium doped ZBLAN fibre pumped at 1.47-1.48 mu m. The results confirm the great potential of ZBLAN fibres for hosting rare earth ions to generate optical amplification. The discussion points out the parameters to be studied to improve the fibre amplifier performance.<>     

Noise characteristics of Er3+-doped fiber amplifierspumped by 0.98 and 1.48 μm laser diodes

Measured noise characteristics of Er³⁺-doped optical fiber amplifiers pumped by 0.98- and 1.48-μm laser diodes (LDs) are reported. The noise figures estimated from the beat noise between signal and spontaneous emission are 3.2 dB for pumping by 0.98-μm LD and 4.1 dB for pumping by 1.48-μm LD. The beat noise between spontaneous emission components and the spontaneous shot noise for the 0.98-μm pumping are lower than those for the 1.48-μm pumping     

Lanthanum codoped erbium fibre amplifier

A lanthanum codoped erbium fibre amplifier (La-Er/GeO/sub 2//SiO/sub 2/) has been investigated by comparing such an amplifier with Al-Er/GeO/sub 2//SiO/sub 2/ and Er/GeO/sub 2//SiO/sub 2/ EDFAs. A gain of more than 35 dB at a wavelength of 1.535 mu m was obtained for 1.48 mu m pump power of 35 mW, which was the highest gain among them. The gain spectral profile was moderately flattened at around 1.552 mu m and the gain peaks at 1.535 and 1.552 mu m shifted 0.5-1 nm towards the shorter wavelength region.<>     

Efficient erbium-doped fibre amplifier pumped at 820 nm

The highest gain coefficients of 0.86 dB/mW at 1.552 mu m and 0.72 dB/mW at 1.534 mu m are realised at a pumping wavelength of 822 nm by using an erbium-doped fibre with a relative refractive index difference as high as 1.67%, a low intrinsic loss, and an erbium ion concentration of 210 p.p.m. The gains at 1.552 mu m reach 25 and 30 dB for launched pump powers of 30 and 40 mW, respectively.<>     

High-power 0.98 mu m GaInAs strained quantum well lasers for Er/sup 3+/-doped fibre amplifier

High-power GaInAs strained quantum well lasers with an emission wavelength of 0.98 mu m, suitable for Er/sup 3+/-doped fibre amplifier pumping, have been fabricated. A threshold current of 15 mA and a peak output power as high as 85 mW have been obtained for the ridge waveguide structure with AR/HR facet coating. Highly efficient pumping for the 1.536 mu m signals has been confirmed.<>     

Analysis of distributed erbium-doped fiber amplifiers with fiber background loss

An accurate model for erbium-doped fiber amplifiers with fiber background loss applicable to the unsaturated gain regime is presented. Exact analytical solutions are derived for the output pump power, gain, and amplified spontaneous noise as a function of input pump power in the cases of unidirectional or bidirectional pumping. An exact relation is also derived between the pump threshold and the pump required for fiber transparency. Such expressions are particularly useful to model distributed fiber amplifiers and to determine the optimal fiber parameters corresponding to a given pumping scheme. As an example, the analytical solutions are used to study the pump power requirement for distributed fiber amplifiers unidirectionally pumped at 1.48 mu m, and to determine an optimum Er/sup 3+/ absorption coefficient.<>     

Erbium-doped fibre amplifiers with an extremely high gain coefficient of 11.0 dB/mW

A gain coefficient of 11.0 dB/mW is obtained using 0.98 mu m laser diode pumped erbium-doped fibre amplifiers with a low erbium concentration of 81 p.p.m. and a high relative refractive index difference of 1.88%.<>     

Highly efficient Er-doped fibre amplifiers pumped in 660 nm band

High gain coefficient in an erbium-doped fibre amplifier, 3.8 dB/mW at 1.536 mu m and 2.3 dB/mW at 1.552 mu m, is achieved for a pump wavelength of 664 nm by using an erbium-doped fibre with a high numerical aperture of 0.285 and thermally-diffused expanded core fibre ends. The gain at 1.536 mu m reaches 30 and 35 dB for launched pump powers of 10 and 15 mW, respectively.<>     

100 dB optical path loss transmission system experiment employing two linear optoelectronic repeaters

Linear optoelectronic amplification is investigated as an economic option for the provision of sufficient optical gain for fibre transmission systems of several hundred km lengths. Experimental results are presented demonstrating a system span capability in excess of 100 dB at 420 Mbit/s and 1.55 mu m wavelength with two intermediate linear repeaters. Extensions of the technique to higher line-rates and larger numbers of repeaters are discussed.<>