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Optical Fiber Communication Conference

Pump-mediated inhomogeneous effects in EDFAs and their impact on gain spectral modeling

Michael J. Yadlowsky, Leslie J. Button

Published Nov 27, 2002• 7 citations

Abstract

Summary form only given. Recently it has been shown that small changes in pump wavelength within the 980-nm pump band change the shape of the gain spectrum of erbium-doped fiber amplifiers (EDFAs). These gain variations can be as large as 3 dB in a typical line amplifier and cannot be explained by the well known homogeneous model for EDFAs. Pump-induced gain changes must be accounted for in multiwavelength amplifiers and systems operating over the pump-wavelength-sensitive short-wavelength portion of the erbium gain band. In this paper, we compare the impact of pump-mediated inhomogeneities on the gain spectra of EDFAs pumped in the 1480- and 980-nm pump bands. We find that the shape of the EDFA gain spectrum is less affected by changes in pump wavelength in the 1480-nm band, and show that in both cases the dynamic gain tilt function (DGTF) is relatively insensitive to changes in pump wavelength. The latter indicates that inversion-induced gain changes can be predicted from a (measured) DGTF despite pump band and some signal band inhomogeneities. We present fluorescence line narrowing measurements that explain these results and suggest a physical mechanism for 980-nm band pump-mediated inhomogeneities.

DOI: 10.1109/ofc.1998.657182

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Gain-difference spectra are used to show that 980-nm band pump wavelength changes can significantly effect spectral-hole burning (SHB) in erbium-doped fiber amplifiers (EDFAs). Gain measurements made using a number of different signal and pump wavelengths help to characterize the underlying inhomogeneous spectral properties of EDFAs and a framework for modeling these effects is presented. Despite the difficulty of obtaining the needed subpopulation specific cross section spectra, this model can be used to explain seemingly anomalous changes in the gain spectra of EDFA as a result of changes in signal or pump wavelength.

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Chinese Optics Letters•Jan 1, 2011•1 citation

Summary form only given. Recently it has been shown that small changes in pump wavelength within the 980-nm pump band change the shape of the gain spectrum of erbium-doped fiber amplifiers (EDFAs). These gain variations can be as large as 3 dB in a typical line amplifier and cannot be explained by the well known homogeneous model for EDFAs. Pump-induced gain changes must be accounted for in multiwavelength amplifiers and systems operating over the pump-wavelength-sensitive short-wavelength portion of the erbium gain band. In this paper, we compare the impact of pump-mediated inhomogeneities on the gain spectra of EDFAs pumped in the 1480- and 980-nm pump bands. We find that the shape of the EDFA gain spectrum is less affected by changes in pump wavelength in the 1480-nm band, and show that in both cases the dynamic gain tilt function (DGTF) is relatively insensitive to changes in pump wavelength. The latter indicates that inversion-induced gain changes can be predicted from a (measured) DGTF despite pump band and some signal band inhomogeneities. We present fluorescence line narrowing measurements that explain these results and suggest a physical mechanism for 980-nm band pump-mediated inhomogeneities.

Gain-difference spectra are used to show that 980-nm band pump wavelength changes can significantly effect spectral-hole burning (SHB) in erbium-doped fiber amplifiers (EDFAs). Gain measurements made using a number of different signal and pump wavelengths help to characterize the underlying inhomogeneous spectral properties of EDFAs and a framework for modeling these effects is presented. Despite the difficulty of obtaining the needed subpopulation specific cross section spectra, this model can be used to explain seemingly anomalous changes in the gain spectra of EDFA as a result of changes in signal or pump wavelength.

This paper reports the measurement and analysis of signal power-induced changes in the refractive index spectrum of an aluminosilicate erbium-doped fiber amplifier (EDFA). For a constant 980 nm pump power of 11 mW, a 1553 nm signal power of 4.6 mW caused a peak-to-trough change in refractive index of (3.8/spl plusmn/0.4)/spl times/10/sup -8/ across the EDFA gain spectrum. A Kramers-Kronig transform of the signal-induced change in absorption coefficient agreed well with the measured change in refractive index. This result conflicts with the behavior of the system predicted by a homogeneously broadened two-level model and suggests limitations in the representation of the Er/sup 3+/:glass system by a discrete set of homogeneously broadened transitions.

Rapid development of optical fiber amplifiers, and more especially of the erbium-doped fiber amplifiers (EDFA) during the last decade, has benefited from extensive work on the configuration of the system itself: determination of pump wavelength, pumping configuration, improvement of noise performance, etc. However, less effort have been dedicated to study the interaction that influences the spectral profile of the gain bandwidth and particularly the relation between the glass composition and the spectroscopy of erbium. Here, we report a systematic determination of key parameters responsible for the global profile of the gain bandwidth: stark splitting, homogeneous broadening, and inhomogeneous broadening. The correlation between these parameters and the glass structure from one part and the behavior of the EDFA in amplification regime from another part is discussed. The quasiregular crystal-field splitting of tellurite and fluoride glasses is found to correlate well with the flatness of the gain profile. Moreover, the low-temperature homogeneous bandwidths extrapolated to room temperature can be correlated to the saturation spectral hole widths measured in the amplification regime.

In this paper, we investigate the effects of complex energy transfer dynamics and Gaussian profiles on the gain and noise figure performance of erbium-doped fiber amplifiers (EDFAs) with high doping concentration. We use a two-level system to study the complex energy transfer dynamics that comes from the homogeneous up-conversion (HUC) and the pair-induced quenching (PIQ). In our model, the system is stimulated by a pump source at the wavelength of 1480 nm and operated with a signal source at the wavelength of 1560 nm. Assuming a uniform distribution of erbium ions in the fiber core, we approximate the fundamental mode distributions by Gaussian profiles which are commonly used to calculate the mode radius or spot size. Using the numerical calculations and analysis of the rate and power propagation equations for a two-level model under consideration, the most advantageous Gaussian profile is determined as the Whitley mode radius to obtain a high-gain and a low-noise figure per unit length of silica-based fiber amplifiers. The effects of the number of ions per cluster and the percentage of ions in clusters on the calculated gain and noise figure are compared for several pump powers. Results are discussed to achieve a desired gain and noise figure performance, and compared with the available experimental data to verify the feasibility of the model.

Spectral hole burning (SHB) effects in a gain-flattened erbium-doped fiber amplifier (EDFA) are demonstrated to be significant in the presence of large signal power around the 1530-1532-nm wavelength range. These are the first effects reported in a setup employing equivalent power level distribution of 40 channels ranging from 1530 to 1561 nm. To explain this, the introduction of a new local population variable into the laser equation is required to support the original inversion ratio that is determined by the pump lasers. In the analysis section, spectroscopic parameters and high signal powers are considered to be other contributing parameters to the change in the gain characteristics. An improvement to this theoretical basis is suggested by implementing mathematical modeling to validate similarities between the gain shape of simulation to that obtained in the experiment.