Emmanuel Desurvire

Modeling erbium-doped fiber amplifiers

Erbium-doped fiber amplifiers are modeled using the propagation and rate equations of a homogeneous two-level laser medium. Numerical methods are used to analyze the effects of optical modes and erbium confinement on amplifier performance, and to calculate both the gain and amplified spontaneous emission (ASE) spectra. Fibers with confined erbium doping are completely characterized from easily measured parameters: the ratio of the linear ion density to fluorescence lifetime, and the absorption of gain spectra. Analytical techniques then allow accurate evaluation of gain, saturation, and noise in low-gain amplifiers (G >

High-gain erbium-doped traveling-wave fiber amplifier

Traveling-wave amplification of a λ = 1.53 μm signal with +22-dB gain is achieved at 295 K in an Er3+-doped single-mode fiber using a λ = 514.5 nm pump source. The optimum fiber length for maximum gain is determined experimentally. A limit in signal-to-noise ratio that is due to concurrent amplification of spontaneous emission is observed. By cooling the fiber to 77 K, the amplifier gain is increased to +29 dB as a result of depopulation of the lower laser level.

Amplification of spontaneous emission in erbium-doped single-mode fibers

Amplification of spontaneous emission (ASE) in erbium-doped single-mode fiber amplifiers operating at lambda =1.53 mu m is studied theoretically and experimentally. The ASE noise spectra obtained from the theory are found to be in excellent quantitative agreement with the experimental data. The observed changes in ASE spectral shapes under different population inversion conditions are also explained. The model may be used to evaluate the performance of erbium-doped fiber lasers as well as to assess the noise characteristics of erbium-doped fiber amplifiers as applied to wavelength-division multiplexing optical communications. >

Propagation of signal and noise in concatenated erbium-doped fiber optical amplifiers

Signal propagation and noise accumulation in lightwave systems using saturated optical amplifiers as repeaters are analyzed. Numerical simulations of amplified spontaneous emission in concatenated erbium-doped fiber amplifiers indicate that a reach beyond 10000 km is possible with a 1.55- mu m system in the absence of fiber nonlinearities. Distributed optical amplifiers are shown to have low noise, but require higher pump power than lumped amplifiers. Three operating modes of an amplifier lightwave system are identified and their relative signal power efficiency and noise performance are described. >

Transient gain and cross talk in erbium-doped fiber amplifiers

Transient gain saturation and recovery with 110-340-microsec time constants were observed in erbium-doped fiber amplifiers. This slow response reduces the effects of saturation-induced cross talk and intermodulation distortion associated with multichannel signal amplification. In a two-channel amplification experiment, negligible saturation-induced cross talk was measured at signal modulation frequencies >5 kHz. Increased suppression of saturation-induced cross talk was achieved through feed-forward compensation to reduce low-frequency gain fluctuations.

Gain saturation effects in high-speed, multichannel erbium-doped fiber amplifiers at lambda =1.53 mu m

Gain compression effects during multichannel signal amplification in an erbium-doped fiber amplifier at lambda =1.53 are investigated. A theory is presented that accurately models the observed amplified spontaneous emission spectra, signal gains, and saturation effects. Measurements of the gain dynamics show recovery times in the 1-ms range, indicating that the fiber amplifier is immune to interchannel interference over a wide range of bit-sequence rates. Simultaneous amplification of two signals modulated at 2 Gb/s shows low crosstalk penalty, attributable only to steady-state gain compression. This experiment demonstrates the potential of erbium-doped fiber amplifiers for application in wavelength-division-multiplexed communication systems. >

Study of the complex atomic susceptibility of erbium-doped fiber amplifiers

A study of the complex atomic susceptibility of erbium-doped fiber amplifiers operating near the 1.53- mu m transition (/sup 4/I/sub 13/2/-/sup 4/I/sub 15/2/) developed from a semiclassical theoretical description is presented. Expressions for the emission cross section sigma /sub e/( lambda ) and absorption cross section sigma /sub a/( lambda ) of erbium:glass as a quasi-three-level laser system with Stark-split sublevel manifolds are derived. The results are used to calculate the cross sections of aluminosilicate erbium-doped fibers at low temperatures (T=4.2, 77 K) and at room temperature. It is demonstrated that an expression for the gain coefficient of the fiber amplifier can be derived from the expression of the susceptibility. Using Kramers-Kronig relations, an expression for the refractive index change in the fiber is derived. The theoretical spectral gain profile of the fiber amplifier and concurrent refractive index changes are analyzed for different pumping regimes. >

Spectral gain hole-burning at 1.53 mu m in erbium-doped fiber amplifiers

Spectral gain hole-burning at lambda /sub 0/=1.53 mu m was observed in an erbium-doped fiber amplifier at temperatures between 4.2 and 77 K. The hole width was found to broaden with temperature for T>or=20 K according to a T/sup 1.73/ law. From the data, the room-temperature homogeneous linewidth associated with the 1.531- mu m transition in the /sup 4/I/sub 13/2/-/sup 4/I/sub 15/2/ laser system was determined to be Delta lambda /sub h/=11.5 nm for aluminosilicate fibers.<<ETX>>

Analysis of transient gain saturation and recovery in erbium-doped fiber amplifiers

An analysis of transient gain dynamics in erbium-doped fiber amplifiers is presented to provide a qualitative explanation of its time constants. The theory yields analytical solutions at the fiber amplifier input end, making it convenient to study the time dependence of gain saturation and recovery under changing input signal conditions. It is shown that, independently of the pump wavelength, gain saturation and recovery effects have long characteristic times (0.2-10.0 ms) which advantageously reduce saturation-induced crosstalk in the amplifier. The effect of saturation-induced gain modulation is found to vanish at signal frequencies above F=1 kHz, which is in good agreement with observed experimental results.<<ETX>>

Evaluation of 4 I 15/2 and 4 I 13/2 Stark-level energies in erbium-doped aluminosilicate glass fibers

Spectroscopic measurements of fluorescence and absorption in an erbium-doped fiber permit the evaluation of the Stark-level energies of the (4)I(15/2) and (4)I(13/2) manifolds in Er:glass. The data permit the allocation of the individual laser transitions associated with the room-temperature gain spectrum of erbium-doped fiber amplifiers operating near lambda = 1.53 microm.