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     

Multichannel AM-VSB television signal transmission using anerbium-doped optical fiber power amplifier

The use of an erbium-doped optical fiber power amplifier in a multichannel amplitude-modulated vestigial-sideband CATV transmission system for potential subscriber loop applications is discussed. Using a color-center laser pump at 1.48 μm, a fiber-to-fiber gain of 11.5 dB (at 1.539 μm), which is 10 dB compressed from the small-signal gain, and a total system power margin of 15 dB were achieved. No intermodulation distortion was introduced by the fiber amplifier. The received video SNR of 40-46 dB was limited by the linearity of the distributed-feedback laser diode used     

Noise figure of erbium doped fiber amplifiers in the saturatedregime

We have made an experimental and theoretical study of the noise figure of an erbium doped fiber amplifier in the saturated regime. The saturated amplified spontaneous emission at the signal wavelength was measured using a very accurate pulsed source technique. We have quantified the noise figure dependence on compression, in excellent agreement with theory, to be less than 1.5 dB for a gain compression as high as 15 dB when the small signal gain was 26 dB, and the 1.48 μm pump power was 27 mW     

High-gain and high-efficiency diode laser pumped fiber amplifier at1.56 μm

Gain of an erbium-doped amplifier was optimized for operation at 1.56 μm, resulting in gains of up to 20 dB and slope efficiencies of 0.66 dB/mW. The amplifier is plug compatible with existing fiber networks. The gains of up to 20 dB were achieved using 1.48-1.49 μm laser diode pump sources with powers of 30 mW launched into the input of the system. The erbium-doped fiber used had an Er³⁺ concentration of roughly 30 p.p.m. in a GeO₂-Al₂O ₃SiO₂ host, and a core diameter of 7.0 μm     

28.3 dB gain 1.3 μm-band Pr-doped fluoride fiber amplifiermodule pumped by 1.017 μm InGaAs-LD's

A praseodymium (Pr)-doped fluoride fiber amplifier (PDFA) module that is pumped by strained quantum-well InGaAs laser diodes (LDs) is described. The amplifier module, consisting of a four LD pump configuration and a high NA Pr-doped fluoride fiber with low scattering loss, exhibits a maximum signal gain of 28.3 dB and a saturation output power of 6 dBm at a signal wavelength of 1.30 μm. It is shown to be the most promising module for the 1.3-μm-band optical amplifier     

2-Gbit/s signal amplification at λ=1.53 μm in anerbium-doped single-mode fiber amplifier

The gain, saturation power, and noise of an erbium-doped single-mode traveling-wave fiber amplifier operating at a wavelength λ=1.53 μm are characterized. In continuous-wave (CW) measurements amplification at 2 Gbit/s was demonstrated with up to 17-dB gain for 1×10^-9 bit error rate at 1.531 μm and a 3-dB full bandwidth of 14 nm. From the determination of the fiber-amplifier's output signal-to-noise ratio versus input signal power during data transmission, it was concluded that, with signal levels used here, signal-spontaneous beat noise limited the receiver sensitivity improvement. With the fiber amplifier acting as an optical preamplifier of the receiver, the best sensitivity was -30 dBm, obtained after installing a polarizer at the fiber amplifier output to reject half of the applied spontaneous emission power. This sensitivity was 6 dB better than without the fiber amplifier, proving that the fiber amplifier can be used as a preamplifier     

Multipass diode-pumped Nd:YAG optical amplifiers at 1.06 μm and1.32 μm

We have built two versions of a diode-pumped Nd:YAG amplifier using a compact multipass confocal geometry with a fiber-coupled input. This confocal geometry provided efficient power and high gain in a volume of approximately 100 cm³. When pumped with a commercially mature 2 W 809 nm laser diode, the 1.06 μm version produced 460 mW and a small signal gain of 51 dB. The 1.32 μm version produced 170 mW and a small signal gain of 29 dB. Such an efficient amplifier, especially at 1.32 μm would be useful as a power booster in fiber optic telecommunications     

Optimal pump wavelength in the4I15/2-4I13/2 absorption band for efficient Er3+-doped fiberamplifiers

The authors report the measured gain of a highly efficient erbium-doped fiber amplifier pumped at wavelengths between 1.46 and 1.51 μm. The optimal pump wavelength, λ_opt, was determined to be 1.475 μm. At this wavelength, the maximum gain coefficients for signals at 1.531 and 1.544 μm were 2.3 and 2.6 dB/mW, respectively. At λ_opt, high gains ranging from 32 dB at pump power P_p=20 mW up to 40 dB at P _p=80 mW were obtained. These modest pump powers are within the capabilities of currently available 1.48-μm diode lasers. The width about λ_opt for 3-dB gain variation exceeded 27 nm for P_p=10 mW and 40 nm for P_p >20 mW. With this weak dependence on pump wavelength, single-longitudinal-mode lasers do not have a significant advantage over practical Fabry-Perot multimode pump lasers     

Ultralong dispersion-shifted erbium-doped fiber amplifier and itsapplication to soliton transmission

Distributed, dispersion-shifted erbium-doped fiber amplifiers with doping concentrations as low as 0.1-0.5 p.p.m. (0.1-0.5×10^-4 wt.%) were fabricated and their grain characteristics studied for the purpose of soliton amplification. A 9.4-km dual-shape-core-type amplifier with a 0.5-p.p.m. concentration had a gain of more than 20 dB at 1.535 μm and 10 dB at 1.552 μm with a forward pumping configuration, and it could successfully amplify and transmit a 20-ps soliton pulse train at a 2.5-GHz repetition rate. The soliton transmission characteristics of an 18.2 km long fiber amplifier were studied using backward and forward pumping. It was found that A=1.5 soliton pulses with a pulse width of 20 ps could be amplified over 18.2 km at a repetition rate of 5 GHz, where soliton narrowing to 16 ps was observed     

1.4-μm-band gain characteristics of a Tm-Ho-doped ZBLYAN fiberamplifier pumped in the 0.8-μm band

The gain characteristics of a 1.4-μm-band thulium-holmium-doped ZBLYAN fiber amplifier are described. Signal gain is obtained over the whole 1.4-μm band for a pump power level of 73.5 mW. A maximum signal gain of 18 dB is achieved at a signal wavelength of 6.46 μm for a pump power of 150 mW at 0.79 μm. The noise figure is 5.6 dB in the signal wavelength region from 1.45-1.50 μm. From a comparison of the gain characteristics of thulium-holmium-doped ZBLYAN fibers and thulium-doped ZBLYAN fibers, it is proved that holmium ions play an effective role in increasing the gain and widening the gain spectrum     

Gain saturation properties of a polarization insensitivesemiconductor amplifier implemented with tensile and compressive strainquantum wells

The gain saturation properties of a 1.3 μm polarization insensitive semiconductor amplifier implemented with tensile and compressive strain quantum well active region are experimentally investigated in order to determine how well the amplifier maintains its polarization insensitivity in the saturation regime. The amplifier has unsaturated gain of 12 dB and in the saturation regime the maximum observed gain imbalance between TE and TM gains is 0.9 dB. The measured 3 dB saturation output power is 5 mW     

Performance of a distributed erbium-doped dispersion-shifted fiberamplifier

Continued improvements in the performance of a multi-kilometer, low-erbium-concentration fiber amplifier made by the modified chemical vapor deposition (MCVD) seed fiber method are discussed. Transparency for a -20-dBm signal at 1.55 μm and fiber length of 11.8 km was achieved with 20 mW of 1.48-μm copropagating pump power. The wavelength dependence of the gain for this signal level is reported, and the distribution in small signal gain along a 22-km length using an optical domain reflectometer (OTDR) was measured. Simulations are presented to show the effect of erbium concentration, input signal level, and pump power required for transparency of a 50-km span     

Compensation of Raman-induced crosstalk using a lumpedgermanosilicate fiber Raman amplifier in the 1.571-1.591-μm region

A new method to equalize power imbalance caused by Raman-induced crosstalk among optical channels is proposed using a lumped germanosilicate fiber Raman amplifier. Evolution of optical channels through the Raman amplifier was simulated using Raman frequency modeling, which theoretically predicted simultaneous amplification and power equalization. Experimentally, a gain band with negative slope in the range of 1.571-1.591 μm was achieved in a lumped Raman amplifier pumped by a broad-band laser diode centered at 1.467 μm. We demonstrated compensation of the Raman-induced crosstalk of 5 dB accumulated along 330 km of conventional single-mode fiber     

A high gain, high output saturation power Pr/sup 3+/-doped fluoride fiber amplifier operating at 1.3 mu m

A high net gain of 30.1 dB at 1.309 mu m and an output saturation of 13 dBm are obtained using a Pr/sup 3+/-doped fluoride fiber amplifier pumped at 1.017 mu m. The critical Pr/sup 3+/ concentration at which concentration quenching begins to occur was obtained by fluorescence lifetime measurement. The Pr/sup 3+/ concentration should be less than 1000 ppm to suppress the concentration quenching by cross relaxation. A high signal output power of 17.8 dBm was extracted from the Pr/sup 3+/-doped fluoride fiber. The Pr/sup 3+/-doped fluoride amplifier shows good potential for use in 13. mu m telecommunication systems.<>     

Optical amplification in Er3+-doped single-mode fluoridefiber

The amplification characteristics at around 1.5 μm of a 0.9-m-long, 1000-p.p.m Er³⁺-doped single-mode fluoride fiber are discussed. By using 1.48-μm laser diodes with 55-mW launched output as a pump source, a gain of 1.75 dB was obtained at 1.530 μm. A broad bandwidth of 40 nm was obtained, which may be suitable for wavelength-division multiplexing (WDM) system use     

Length dependence of the saturation characteristics in 1.5-μmmultiple quantum well optical amplifiers

The dependence on amplifier length of gain and gain saturation characteristics in 1.5-μm multiple-quantum-well optical amplifiers is reported. Gain measurements are presented for amplifiers with lengths of 200 μm to 1 mm, and a simple model is introduced which relates gain and saturation characteristics to the amplifier length. The 1-mm-long device has superb properties, with a gain of 25.2 dB and a saturation output power of 40 mW     

Gain characteristics of an Er3+-doped multicomponentglass single-mode optical fiber

Experimental results on gain characteristics of an Er³⁺-doped multicomponent glass single-mode optical-fiber amplifier are reported. This amplifier shows a gain spectrum with twin gain peaks of 1.535 and 1.543 μm, providing a broadened gain bandwidth. The apparent 6-dB gain bandwidth is 12 nm. Furthermore, the signal gain of 17 dB and 15-mW pump power is realized at a signal wavelength of 1.536 μm, and a signal gain coefficient of 1.4 dB/mW is achieved     

Polarization-insensitive optical amplifier withtensile-strained-barrier MQW structure

A new approach to achieving a polarization-insensitive semiconductor optical amplifier is presented. The active layer consists of a tensile-strained-barrier MQW structure that enhances TM mode gain. Polarization sensitivity below 0.5 dB is realized at a wavelength of 1.56 μm. A signal gain of 27.5 dB is obtained along with a saturation output power of 14 dBm. Deriving the refractive indices of well and barrier layers from both experiment and theory, we succeed in separation of the effect of the confinement factor and the gain coefficient. It is determined that TM mode gain enhancement in this structure is primarily due to the increase in the confinement factor     

Gain-shifted dual-wavelength-pumped thulium-doped fiber amplifierfor WDM signals in the 1.48-1.51-μm wavelength region

We constructed a gain-shifted dual-wavelength-pumped (1.05/1.56 μm) thulium doped fiber amplifier (TDFA) for wavelength-division-multiplexing (WDM) signals in the 1.48-1.51-μm, wavelength region. We obtained a gain of larger than 20 dB and a noise figure of less than 7 dB in the range from 1478 to 1505 nm. Amplifier saturated output power was +20.1 dBm with an optical-to-optical conversion efficiency of 9.1% for 12-channel WDM signals. We also obtained a successful bit error rate performance for signals modulated at 10 Gb/s when the gain-shifted TDFA was used in an optical preamplifier configuration. These results confirm the feasibility of using the gain-shifted TDFA as both a booster and an optical preamplifier in WDM networks     

Optimum position of isolators within erbium-doped fibers

An isolator is used as an amplified spontaneous emission suppressing component within an erbium-doped fiber. The optimum isolator placement is both experimentally and theoretically determined and found to be slightly dependent upon pump power. Improvements of 4 dB in gain and 2 dB in noise figure are measured for the optimum isolator location at 25% of the fiber length when the fiber is pumped with 60 mW of pump power at 1.48 μm