Optical fiber for light amplifier

Details Optical fiber for light amplifier Optical fiber for light amplifier

1999-10-13

2001-08-07

Spyrou, Cassandra (Department: 2872)

Optical waveguides

Having particular optical characteristic modifying chemical...

Of waveguide core

C385S123000, C359S341430, C501S037000, C372S006000

Reexamination Certificate

active

06272277

ABSTRACT:

CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for OPTICAL FIBER FOR LIGHT AMPLIFIER earlier filed in the Korean Industrial Property Office on Oct. 13, 1998 and there duly assigned Ser. No. 42714/1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical fibers for use in a light amplifier, and more particularly, to an optical fiber for used in a light amplifier having an improved optical amplification efficiency.
2. Description of the Related Art
In general, in the manufacture of light amplifiers having a wavelength in the region of 1310 nm which is the zero dispersion wavelength of silica glass, neodymium ions (Nd
+3
) and praseodymium ions (Pr
+3
), which are used as rare earth elements, are implanted into the glass. However, using Nd
+3
causes the following problems.
In particular, the peak wavelength of fluorescence produced in the
4
F
3/2
→
4
I
13/2
transition, which occurs at a wavelength of 1.35 &mgr;m, is considerably removed from the zero dispersion wavelength. The intensity of fluorescence in the wavelength region of 1.3 &mgr;m is very weak compared to that of fluorescence emitted at other wavelength regions of 890 nm and 1064 nm in the
4
F
3/2
level. Also, the optical gain at wavelengths lower than 1.3 &mgr;m is significantly lowered, due to excited state absorption (ESA) at the
4
F
3/2
level.
In order to solve these problems, a method of using a fluoride-rich glass instead of silica glass as a base material has been suggested. However, this method does not achieve a great improvement in optical gain in the wavelength region of 1310 nm.
Meanwhile, in the case of using Pr
+3
, which is a rare earth element for use in doping glass, fluorescence emitted during the
1
G
4
→
3
H
5
transition can be used. Also, the transition probability at such levels is very high compared that at other levels, so that a high optical amplification efficiency is expected at the transition from
1
G
4
to
3
H
5
levels.
However, in the actual application of Pr
+3
, the energy gap between the
1
G
4
level and the
3
F
4
level, which is immediately below the
1
G
4
level, is as small as 3000 cm
−1
. Thus, in the case of using an oxide glass having a high lattice vibration energy (>800 cm
−1
), the probability of non-radiative transition of Pr
+3
excited to the
1
G
4
level due to multiple lattice vibration relaxation is greatly increased, thus lowering optical amplification efficiency.
To solve this problem, U.S. Pat. No. 5,379,149, to Snitzer et al., entitled GLASS COMPOSITIONS HAVING LOW ENERGY PHONON SPECTRA AND LIGHT SOURCES FABRICATED THEREFROM, discloses a method of using a germanium-galium-sulfur (Ge—Ga—S) glass as a base material. The patent in particular describes sulfur rich germanium-gallium-sulfur compositions doped with rare earth ions. Here, the lattice vibration energy of the Ge—Ga—S glass is smaller than that of a conventional oxide glass or fluoride glass, so that an improvement in optical amplification efficiency at the wavelength region of 1310 is anticipated.
K. Wei, Ph.D. dissertation, “Synthesis and Characterization of Rare Earth Doped Chalcogenide Glasses” Rutgers University (1994), pp. 71-79, also describes Ge—Ga—S glasses with excess sulfur relative to the stoichiometric composition line of Ge—S
2
—Ga
3
S
3
. Only sulfur rich compositions were studied because sulfur poor compositions were stated to be usually opaque. K. Wei has reported that when a Ge—S, As—S, or Ge—As(P,Sb)—S glass has a stoichiometric composition or contains more sulfur than in the stoichiometric composition, the degree of solubility of rare earth element with respect to such glass is no more than several hundreds of parts per million (ppm). Thus, in the case where excessive rare earth element is added, fine crystals are precipitated due to the clustering of rare earth ions, causing devitrification.
The described Ge—Ga—S glass compositions contain excessive sulfur (S) compared to the stoichiometric composition line of GeS
2
—Ga
3
S
3
, as shown in a phase diagram of Ge—Ga—S. Also, in the case of using Ge
25
Ga
5
S
70
glass which is a typical example of the composition, the solubility of Pr
+3
is relatively high compared to a Ge—S, As—S, or Ge—As(P,Sb)—S glass which has been adopted by a conventional method. However, if a high concentration of Pr
+3
is added, the energy transfer rate between ions is markedly increased due to clustering of Pr
+3
ions, so that the fluorescence lifetime at the
1
G
4
level is shortened, in addition to lowering the optical amplification efficiency.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved glass composition for an optical amplifier.
It is also an object of the present invention to provide a optical amplifier glass composition in which the solubility of Pr
3+
ions is high.
It is a further object of the present invention to provide an optical amplifier glass composition in which the distribution of Pr
3+
ions is uniform.
It is a still further object to provide an optical amplifier glass which is stable to crystallization.
It is a yet further object to provide an optical amplifier glass in which the absorption band of the Pr
3+
ion is shifted to a shorter wavelength.
It is another object of the present invention is to provide an improved optical fiber for use in a light amplifier.
It is yet another object to provide an optical fiber whose optical amplification efficiency is improved by suppressing the clustering of Pr
+3
ions in the case of adding a high concentration of Pr
+3
.
According to an aspect of the present invention, there is provided an optical fiber for use in a light amplifier, which is formed by doping a germanium-gallium-sulfur (Ge—Ga—S) glass containing less sulfur than a GeS
2
—Ga
2
S
3
stoichiometric composition line with a rare earth element or a transition metal, further comprising 0.1~10 atomic % of a halogen element based on the Ge—Ga—S glass.
Preferably, the amount of gallium is equal to or less than 10 mole-%, (or atom-%) and the amount of sulfur is less than 67 mole-%. If the content of Ga and S is outside the above ranges, the effect of increasing the optical amplification efficiency is negligible. Also, any rare earth element or a transition metal can be used without restrictions, and preferably, Pr
+3
is used as a rare earth element. The rare earth element may be implanted into the glass together with at least one of ytterbium (Yb), neodymium (Nd), holmium (Ho), erbium (Er), thulium (Tm), chromium (Cr) and manganese (Mn), thereby increasing optical amplification efficiency. In addition, light can be simultaneously amplified at multiple wavelength regions.


REFERENCES:
patent: 5351335 (1994-09-01), Ohishi et al.
patent: 5379149 (1995-01-01), Snitzer et al.
patent: 6148125 (2000-11-01), Hoe et al.
patent: 0 775 674 A2 (1995-03-01), None
patent: 6-342175 (1994-12-01), None
patent: WO97/03028 (1997-01-01), None
patent: WO98/01401 (1998-01-01), None

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