K. L. Walker

High-power Er-Yb-doped fiber amplifier with multichannel gain flatness within 0.2 dB over 14 nm

A high-power Er-Yb fiber amplifier for WDM applications has been constructed using a matched mid-stage gain shaping filter. Using precise measurements and careful design considerations, excellent gain flatness, with less than 0.2-dB variation, was obtained over a 14-nm spectral bandwidth. By simply adjusting the pump power to the amplifier, it was possible to maintain the flattened amplifier gain shape over a wide input signal power range from -11 dBm to 1 dBm. A low external noise figure of 5.2 dB at 1-dBm signal input and a high-output power up to 24.6 dBm has been measured.

Prediction of long-term hydrogen-induced loss increases in Er-doped amplifier fibers

Accelerated hydrogen aging tests have shown that Er-doped amplifier fibers of typical compositions react quickly with even trace levels of H/sub 2/, causing spectrally broad OH loss increases that influence signal and pump wavelengths. These loss increases have been noted in Er fibers made by different techniques and by different manufacturers. Loss increases at 1.55 mu m of 1 to 10 dB per 20-m device are predicted for nonhermetically coated fibers exposed to 0.001 atm of H/sub 2/ for 25 years at normal operating temperatures. These hydrogen induced losses can be prevented by using high-quality hermetic coatings to limit the H/sub 2/ that reaches the reactive fiber core.<<ETX>>

Gain peak wavelength measurements using a polarization scrambled fiber loop configuration

We present a quick and accurate method to measure the gain peak wavelength (GPW) of concatenated optical amplifiers in a long haul optical fiber communication system. This method utilizes a simple fiber-amplifier loop with polarization scrambling. We verify that the GPW of an amplifier is completely determined by the operating gain per unit erbium doped fiber length and changes linearly with compressed gain near 1.558 /spl mu/m. The data presented, indicates how the GPW can be controlled for a broad range of operating gains by adjusting the erbium fiber length. The temperature and pump power dependence of GPW were found to be negligible for typical undersea system amplifier conditions. The gain bandwidth for concatenated amplifier systems appears to be a function of compression not operating gain, implying that wavelength division multiplexing systems requiring a flattened gain response should take this into consideration.<<ETX>>

Measurement of erbium confinement in optical fibers: a differential mode-launching technique

We present a selective mode-launching technique to determine the confinement of erbium in optical fibers. The loss per meter, alpha(lm), of the individual LP(lm) modes (LP(01) and LP(11) at 980 nm) is measured, and the ratio gamma = alpha(01)/alpha(11) is related to the concentration of erbium in the core. We assume a Gaussian diffusion profile for erbium and relate the dependence of gamma on erbium confinement by using exact mode profiles. This technique uses only two sets of measurements and is independent of erbium concentration.

Dispersion precompensated, high-power Er-Yb linear amplifier with gain tilt optimization over 11 nm

In this paper, we describe a high-power Er-Yb codoped optical fiber amplifier with flat gain tilt characteristics and low noise figure with mid-stage dispersion-compensating-fiber (DCF). The amplifier has been tested with a 77 NTSC channel matrix box, and showed its full compatibility for the US standard for cable TV applications.

Gain-peak-wavelength measurements using a polarization-scrambled fiber-loop configuration

Design of optical communication systems based on concatenated erbium-doped fiber amplifiers (EDFAs) requires a good understanding of concatenated effects. For example, the gain- peak wavelength (GPW), determined by the autofiltering function of concatenated amplifiers,1-3 should be close to the minimum-dispersion wavelength of the fiber spans when the nonreturn-to-zero (NRZ) format is used. For long undersea systems the operating-signal wavelength window created by as many as a few hundred amplifiers will be very narrow. It then becomes critical to measure and control this GPW.

Annular erbium-ion distribution for ruggedized optical fiber amplifiers

We show that erbium ions placed in an annulus within the fiber core make 980-nm-pumped amplifiers insensitive to variations in pump power distribution among the spatial modes of the fiber and make 1480-nm-pumped amplifiers insensitive to variations in fiber parameters.

Measurement of Erbium Confinement in Optical Fibers : Differential Mode Launching Technique

Rare-earth doped single-mode optical fibers are extensively being used as optical amplifiers and fiber lasers [1,2]. One of the parameters that affects the performance of optical amplifiers is the degree of rare-earth confinement in the fiber core. Theoretical studies [3,4] have shown that varying degrees of erbium confinement lead to a variation in the gain, gain coefficient and optimal operational length of an optical amplifier. A practical evaluation of the erbium profile in an erbium doped fiber is a challenging task because of the small size of the fiber core. In the past, techniques for estimating erbium confinement have included an analysis of partially drawn thick (≈ 1 - 5 mm diameter) preforms, with an implicit assumption that the drawing process does not change the confinement parameter. Most quantitative chemical analysis techniques have been used for preform analysis. Specifically, secondary ion mass spectroscopy (SIMS) and electron probe microanalysis (EPMA) in conjunction with neutron activation analysis (NAA) and x-ray fluorescence (XRF) have been successful in quantitatively evaluating the erbium concentration and confinement in preforms [5]. The final draw of the preform into fibers with core diameters on the order of 4 µm leads to further diffusion of the erbium in the core and the analysis of preforms can tend to be inaccurate. Other methods currently being investigated for determining erbium confinement in fibers are near-field microscopy [6] and cathodoluminescence. In this paper, we present a novel diagnostic method that uses a differential mode launching technique.