Large effective area erbium doped fiber optical amplifier

Details Large effective area erbium doped fiber optical amplifier Large effective area erbium doped fiber optical amplifier

2002-12-19

2004-04-06

Moskowitz, Nelson (Department: 3662)

Optical: systems and elements

Optical amplifier

Optical fiber

C359S337300, C359S341100, C359S342000, C372S006000, C372S040000, C385S127000, C501S042000, C501S097200

Reexamination Certificate

active

06717721

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an optical amplifier fiber or use in telecommunication systems and more particularly, an optical amplifier fiber having a large effective area and providing high absorption, linearity, and efficiency.
2. Technical Background
The continuous growth of bandwidth requirements in optical-based communication systems has resulted in a large demand for systems able to operate within several optical wavelength ranges including the S-band optical range, the C-band optical range, and the L-band optical range. The S-band is typically defined as the wavelengths between about 1465 nm and about 1525 nm, which lies below the C-band wavelength range which extends between about 1525 nm and about 1570 nm, which in turn lies just below the L-band wavelength range which extends between about 1570 nm and 1620 nm. In order to meet this explosive growth and demand for capacity in wavelength bandwidth in fiber optic transmission systems, system designers have begun to investigate those spectral regions lying beyond the conventional or C-band transmission band, including the aforementioned S-band and L-band wavelength ranges.
Erbium-doped fiber amplifiers are used to provide amplification in optical transmission systems, and particularly for deployment within those systems operating within the C-band wavelength range. Application of erbium doped fiber amplifiers within the telecommunication systems operating within the L-band wavelength range can be problematic in that lower excited-state population inversions are necessary to provide sufficiently flat gain spectra across the L-band wavelength range. Thus, longer lengths of fiber within the erbium-doped fiber amplifier or higher erbium concentrations therein are necessary to provide the same gain which would be provided within a given erbium doped fiber amplifier operating within the C-band wavelength range.
The longer lengths of fiber required in erbium doped fiber amplifiers utilized within the L-band wavelength range can result in a decrease in fiber efficiency and an increase in noise when compared with erbium doped fiber amplifier operating within the C-band wavelength range. Typically, the effective areas of erbium doped amplifier fibers are increased in an attempt to improve the “linearity” of the erbium doped fiber amplifiers. The reasoning for this approach has been that an increase in the effective area has the effect of enlarging the transverse optical power distribution in the fiber, thereby reducing the intensity of the optical power at any given point. This yields an erbium-doped fiber amplifier exhibiting a more linear material behavior. However, simply increasing the effective area of any particular erbium doped amplifier fiber by scaling the core diameter can have detrimental effects on optical performance including an increase in non-linear effects such as two-channel four-wave mixing. This is because the effective length of the deployed amplifier fiber may be increased in order to maintain absorption.
The spectroscopy of erbium within erbium doped fiber amplifiers operating within the L-band wavelength range thus poses several challenges with respect to designing the fiber amplifier to be used therein. These challenges include: (1) maximizing the effective area while simultaneously maintaining high absorption, (2) packaging amplifier modules with longer amplifier fibers required by the lower rate of gain while controlling fiber bend losses at longer wavelengths, (3) maintaining high absorption without significantly increasing concentration quenching, and (4) minimizing the intrinsically higher L-band noise figure.
SUMMARY OF THE INVENTION
This invention relates to an optical amplifier fiber that effects amplification of an optical signal within the L-band optical wavelength range. One aspect of the present invention relates to an optical waveguide amplifier fiber which comprises a core region having a relative refractive index &Dgr;
1
and an outer radius, the core region at least in part comprising Er
2
O
3
, and at least one other component selected from the group consisting of Al
2
O
3
, GeO
2
, Ga
2
O
3
, Ta
2
O
3
, P
2
O
5
, or a combination thereof; an inner clad surrounding the core region and having a relative refractive index percent &Dgr;
2
and an outer radius; and an outer clad surrounding the inner clad and having a relative refractive index percent &Dgr;
3
. The relative refractive index percentages and radii of the core region, the inner clad and the outer clad are chosen so that the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 &mgr;m to about 5.0 &mgr;m; the outer radius of the inner clad within the range of from about 3.8 &mgr;m to about 10.2 &mgr;m. The relative amounts of Al
2
O
3
and/or GeO
2
and/or Ga
2
O
3
within the core region, and the relative refractive index profile and percentages and radii of the core region, the inner clad and the outer clad are selected to provide an effective area of greater than or equal to about 38.6 &mgr;m
2
, more preferably greater than about 44.0 &mgr;m
2
, and most preferably greater than about 52.0 &mgr;m
2
at a wavelength of 1590 nm. Most preferably, the at least one other component comprises Ga
2
O
3
in combination with P
2
O
5
.
The amounts of Er
2
O
3
, Al
2
O
3
GeO
2
and Ga
2
O
3
within the core region, and the relative refractive index percent and radii of the core region, the inner clad and the outer clad are preferably selected to provide a pin array bending loss of less than or equal to about 0.11 dB, more preferably less than 0.09 dB, and most preferably less than 0.01 dB at a wavelength of 1590 nm.
The relative refractive index percent of the core region preferably increases linearly as the radius of the core region increases. The amplifier fiber also preferably exhibits an overlap factor of greater than or equal to about 50%, more preferably greater than about 70% at a wavelength of 1590 nm. In preferred embodiments, the amplifier fiber exhibits a step-index core.
Another aspect of the invention relates to an optical waveguide amplifier fiber which comprises a core region having a relative refractive index &Dgr;
1
and an outer radius, the core region at least in part comprising Er
2
O
3
, and at least one other component selected from the group consisting of Al
2
O
3
, GeO
2
, Ga
2
O
3
, Ta
2
O
3
, P
2
O
5
, or a combination thereof; an inner clad surrounding the core region and having a relative refractive index percent &Dgr;
2
and an outer radius; and an outer clad surrounding the inner clad and having a relative refractive index percent &Dgr;
3
. The relative refractive index percentages and radii of the core region, the inner clad and the outer clad are chosen so that the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 &mgr;m to about 5.0 &mgr;m; the outer radius of the inner clad within the range of from about 3.8 &mgr;m to about 10.2 &mgr;m. The amounts of Al
2
O
3
and/or GeO
2
and/or Ga
2
O
3
within the core region, and the relative refractive index percentages and radii of the core region, the inner clad and the outer clad are selected to provide an effective area of greater than or equal to about 38.6 &mgr;m more preferably greater than about 44.0 &mgr;m
2
, even more preferably greater than about 52.0 &mgr;m
2
, and most preferably greater than about 63 &mgr;m
2
at a wavelength of 1590 nm. Most preferably, the at least one other component comprises Ga
2
O
3
in combination with P
2
O
5
.
The amounts of Er
2
O
3
, Al
2
O
3
, GeO
2
and Ga
2
O
3
within the core region, and the relative ref

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