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     

Efficient optical amplifier using a low-concentration erbium-dopedfiber

A gain coefficient of 3.8 dB/mW was achieved for an erbium-doped fiber amplifier pumped by a 1.48 μm laser diode. The main reasons for the improvement are high NA (0.23) and low concentration (43 p.p.m.). Pump-to-signal energy conversion efficiency was 18% at 3 dB gain compression. A decrease in saturation power with increasing erbium concentration was also demonstrated. In high-concentration fiber, fluorescence at 0.98 μm due to cooperative upconversion was detected. These results indicate that several kilometers of distributed fiber amplifier with high gain and high output saturation power could be possible, because the absorption coefficient at 1.48 μm is still two orders higher than the background loss in the 43 p.p.m. fiber     

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     

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     

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     

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     

Gain monitoring of erbium-doped fiber amplifiers by detectingspontaneous emission

Gain monitoring by detecting the spontaneous emission (SE) emitted by 0.98-μm laser diode (LD) pumped erbium-doped fiber amplifiers was investigated using three erbium-doped fibers (EDF's) with different absorption coefficients at 1.55 μm (α). Unfavorable 0.98-μm scattered light was observed and removed by an optical filter. The minimum gain accuracy was less than ±0.21 dB for EDF-b (α=1.5 dB/m) with launched pump powers (P_p) from 10 to 30 mW. The minimum gain reproducibility over a 9-h period was ± 0.015 dB for EDF-a (α=3.3 dB/m) at P_p=20 mW     

Upconversion pumped thulium-doped fluoride fiber amplifier andlaser operating at 1.47 μm

A 1.064-μm band upconversion pumped Tm³⁺-doped fluoride fiber amplifier and a laser both operating at 1.47 μm are investigated in detail. The two devices are based on the ³F ₄→³H₄ transition in a trivalent thulium ion, which is a self-terminating system. When pumped at 1.064 μm, the amplifier has a gain of over 10 dB from 1.44 to 1.51 μm and a low-noise characteristic. Also, the fiber laser generates a high-output power of over 100 mW with a slope efficiency of 59% at around 1.47 μm. These levels of performance will be important for optical communication systems     

Experimental studies on wavelength division bidirectional opticalamplifiers using an Er3+-doped fiber

This paper presents a novel structure of an Er³⁺-doped fiber amplifier capable of bidirectional operation through the wavelength division multiplex method. The idea is to combine an Er³⁺-doped fiber, pump devices, optical isolators, and wavelength selective couplers so that two lightwaves having different wavelengths pass each proper isolator. The suitable structure was determined from experimental studies on several basic amplifier configurations. Optical gains of more than 25 dB were attained in both wavelength regions of 1.533 μm and 1.55 μm. Successful bidirectional operation of the amplifier was confirmed by means of a 2.488-Gbit/s-signal transmission experiment     

Stimulated Raman amplification of 1.6-μm-band pulsed light inoptical fibers

A synchronous Raman fiber amplifier is proposed which is pumped at a wavelength around 1.55 μm by output pulses from an erbium-doped fiber amplifier. This arrangement achieves an output optical peak power exceeding 200 mW and a 3-dB net gain bandwidth of 33 nm around 1.66 μm. The Raman fiber amplifier is useful for 1.6-μm-band OTDR as it can be used in live maintenance of optical transmission networks     

Asymmetric fiber microlenses for efficient coupling to ellipticallaser beams

It is demonstrated that it is possible to fabricate asymmetric hyperbolic microlenses directly on the ends of single-mode optical fiber to enhance the fiber's coupling to elliptical laser beams. The lenses, with controlled eccentricity ratios, are made by micromachining the end of the fiber with a pulsed CO₂ laser, as the fiber is directed by computer control about the focussed laser beam. Coupling efficiencies of 84% (-0.74 dB) have been realized with single transverse mode lasers at a wavelength of 0.98 μm having an approximately 3 to 1 beam ellipticity. With multitransverse-mode lasers at 1.48 μm having similar ellipticities, the asymmetric lenses demonstrate a 2-dB increase in coupling efficiency over symmetric hyperbolic microlenses. The authors have coupled about 120 mW from such a 360 mW laser, used to pump erbium-doped fiber amplifiers, into single-mode fiber     

Ultrawide-band La-codoped Bi/sub 2/O/sub 3/-based EDFA for L-band DWDM systems

The demonstration of a 253-cm-long lanthanum-codoped Bi/sub 2/O/sub 3/-based erbium-doped fiber which provides gain of greater than 20 dB and noise figure less than 6.7 dB to 142 dense wavelength-division-multiplexing channels simultaneously over an extended wavelength range of 58 nm from 1554 to 1612 nm is reported. The 3-dB (gain of 17-20 dB) bandwidth of the erbium-doped fiber amplifier is 54 nm when it is pumped with 350 mW of 1480-nm light. The power conversion efficiency of the fiber is about 54%.     

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.<>     

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.<>     

Femtosecond soliton transmission characteristics in an ultralongerbium-doped fiber amplifier with different pumping configurations

The transmission characteristics of femtosecond optical solitons in an 18.2 km-long erbium-doped fiber amplifier (EDFA) have been investigated in detail by changing the pumping configuration. With backward pumping, a lossless transmission of 440 fs solitons at 1.55 μm has been realized with a pump power of 16 mW. The output pulsewidth is determined by the spectrum modified by the soliton self-frequency shift. In a bidirectional pumping configuration, 440-fs soliton pulses have been transmitted for a total pump power of 38 mW, where the output pulse width is determined by the original 1.55 μm spectrum. Although a femtosecond soliton is very weakly trapped in the EDFA-gain bandwidth of 1.55 μm and the soliton self-frequency shift inevitably occurs, the femtosecond pulse component still exists at 1.55 μm, and a pulse can be successfully transmitted with a gain of 11 dB and very little pulse broadening     

Compact and highly efficient fiber amplifier modules pumped by a0.98-μm laser diode

Highly efficient and small-size erbium-doped fibers with a gain coefficient of 4.9 dB/mW and a strained quantum-well-type InGaAs laser diode with a lasing wavelength of 0.98 μm as a pumped light source. As a result, the module 4×6×1.5 cm, realized a maximum net gain of 33 dB with an electricity consumption of only 175 mW, which corresponds to a drive current of 80 mA. The module consists of four individual components: a pumping laser diode submodule, a wavelength-division-multiplexing-type fiber coupler, a polarization-insensitive optical isolator, and an erbium-doped single-mode fiber coil     

A novel compensating light injection configuration for gain-clampedEDFA's

A novel compensating light injection configuration for gain-clamped erbium-doped fiber amplifier (EDFA's) is proposed. The compensating light is backward injected from the end of the first stage of the amplifier and then reflected by a grating at the amplifier input end. Very wide input dynamic range (0.5 μW-500 μW) with less than 1 mW of compensating light and low noise penalty (<0.5 dB) is demonstrated     

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     

A 3.3-V 800-nVrms noise, gain-programmable CMOSmicrophone preamplifier design using yield modeling technique

A 3.3-V CMOS low-noise gain-programmable microphone amplifier with a high-impedance balanced input is presented. The preamplifier allows gains from 20 to 35 dB to be set by software control in 1-dB steps with 0.05-dB accuracy. Typical measured V_OS is 0.8 mV, V_OS drift is 1 μV/C, input-referred p-weighted noise is 0.8 μV _rms and total harmonic distortion (THD) is -70 dB. The active area is about 350 mils², and power consumption is 1.7 mW at 3.3-V supply and 2.9 mW at 5-V supply. These results have been obtained through an intensive use of the yield modeling technique for yield-performance optimization during the design phase, and by applying a common-centroid cross-coupled strategy to the layout of all the ideally matched MOS transistors in the input stage     

Erbium-doped fiber amplifier pumped in the 950-1000 nm region

The pump wavelength dependence of the gain of an erbium-doped fiber amplifier pumped in the wavelength region 950-1000 nm is discussed. It is found that efficient gain at 1.557 μm, between 25 and 28 dB for 17 mW of launched pump power, can be obtained for any wavelength pump in the range 965-985 nm. The optimum length of erbium fiber needed is found to vary as a function of pump wavelength. The gain as a function of signal wavelength is also investigated at these pump wavelengths