Antimony oxide glass with optical activity

Details Antimony oxide glass with optical activity Antimony oxide glass with optical activity

1999-04-08

2002-06-25

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S041000, C501S042000, C501S043000, C501S050000, C501S052000, C501S054000, C501S056000, C501S055000, C501S057000, C501S058000, C501S059000, C501S064000, C501S065000, C501S066000, C501S068000, C501S069000, C501S070000, C501S072000, C501S073000, C501S078000, C359S341430, C359S343000

Reexamination Certificate

active

06410467

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to antimony oxide-containing glass compositions and, more particularly, to optically active antimony oxide-containing glasses that are optically active by being doped with a rare earth element; their use in optical amplifying devices and optical amplifying devices incorporating these compositions; and methods for making the glass compositions of the invention. As used herein, the term “optically active” refers to a rare earth doped glass capable of stimulated emission for amplifying a light signal when the glass is excited by a suitable pumping source.
2. Technical Background
Recently, transparent materials capable of efficient frequency upconversion, in particular, various rare earth ion-doped fluoride glasses and crystals, have received much attention because of their potential use in blue or green solid state lasers. Single mode optical fibers doped with low levels of rare-earth ions can be drawn from fluoride glasses, bringing about highly efficient blue or green upconversion fiber lasers. Unfortunately, heavy metal fluoride glasses suffer certain undesirable attributes that have restricted their applications. Most notably, heavy metal fluoride glasses exhibit poor resistance to devitrification. Mimura et al. discusses the crystallization problems heavy metal fluoride glasses, one example of which is referred to as ZBLAN, and the light scattering problems resulting therefrom. The susceptibility of heavy metal fluoride glasses to devitrification generates problems in making large preforms. Crystallization in the preform causes difficulties during the formation of optical fibers by commonly used methods. Heavy metal fluoride glasses are quite prone to inhomogeneous nucleation, which leads to crystallization at the core and cladding interfaces during the drawing of the optical fiber. The resulting crystals in the fibers cause serious light scattering losses.
Devitrification of the heavy metal fluoride glasses is aggravated when ions necessary to impart differences in indices of refraction to the core and cladding are added to the glass composition. Additional doping, for example, with rare earth metal ions, also tends to reduce the stability of the glass. As a consequence of those problems, research has focused on finding additives to a base fluoride glass composition that will reduce the tendency of the glass to devitrify and to increase the chemical stability thereof. In addition, the preparation of fluoride glasses requires that the glass forming components be reheated at high temperatures. Furthermore, these glasses cannot be melted in air but require a water-free, inert gas environment.
Most oxide glasses such as, for example, silicon dioxide, are easier to prepare, more chemically and mechanically stable, and more easily fabricated into rods, optical fibers, or planar waveguides than are fluoride glasses. Unfortunately, because of their higher phonon energy, silica glasses are very inefficient for infrared upconversion. Addition of even small amounts of oxides into fluoride glasses to improve their stability significantly quenches their upconversion luminescence.
One author describes a class of infrared (“IR”) upconversion materials prepared from classical glass-forming oxides (SiO
2
, GeO
2
, P
2
O
5
, etc., containing PbF
2
and rare earth oxides). These materials show an efficiency nearly twice as high as a LaF
3
:Yb:Er phosphor, but, because they are inhomogeneous and include both a glassy phase and a crystalline phase containing large (ca 10 &mgr;m) embedded crystals, they are not transparent.
Another reference describes transparent oxyfluoride vitroceramics (also called glass ceramics) containing oxides of high phonon energy like SiO
2
and AlO
1.5
but showing IR to visible upconversion that are more efficient than fluoride glass. A reported typical composition consists essentially, expressed in terms of mole percent, of: SiO
2
, 30; AlO
1.5
, 15; PbF
2
, 24; CdF
2
, 20; YbF
3
, 10; ErF
3
, 1. Heat treatment of that composition at 470° C. causes the formation of microcrystallites, which are reported not to reduce the transparency of the body. It is further asserted that the Yb
3
+and Er
3+
ions are preferentially segregated from the precursor glass and dissolved into the microcrystals upon heat treatment. The microcrystallites are reported to be about 20 nm in size, small enough that light loss from scattering is minimal. The upconversion efficiency of their products is said to be about 2 to 10 times as high as that measured on the precursor glass and other fluoride-containing glasses. However, the crystals that are formed in the reported glass have a cubic lattice structure, which limits the concentration of some of the trivalent rare-earth elements that can be incorporated into the glass ceramic. Another problem with these materials is that their formulation requires cadmium, a carcinogen whose use is restricted. Furthermore, the reported glass-ceramic does not appear to have a broad, flat emission spectrum required for some optical amplifier applications.
Rare earth-doped glasses have found frequent use for the fabrication of light-generating and light-amplifying devices. For example, Snitzer describes a laserable glass comprising a host material that contains a fluorescent trivalent neodymium ingredient. Desurvire et al. describe an optical amplifier comprising a single mode fiber that has an erbium-doped core. da Silva et al. describe an apparatus and method for flattening the gain of an optical amplifier that utilizes an erbium-doped silica fiber having a germanosilicate core. Bruce et al. describe an erbium-doped planar optical device whose active core includes a mixture of oxides such as lanthanum and aluminum oxides. The inclusion of antimony oxide in glasses for optical devices is also reported. One reference describes a glass for use in waveguides that contains 50-75 mol % SbO
1.5
.
For the construction of efficient optical amplifiers, there remains a need for new, readily prepared glasses that display an optimal combination of gain flatness and breadth. This need is well met by the glass of the present invention.
SUMMARY OF THE INVENTION
The present invention is directed to an optically active glass containing Sb
2
O
3
and up to about 4 mole % of an oxide of a rare earth element. All constituents listed herein are expressed in mole percentages on an oxide basis. An undoped, nonactive base glass may consist essentially of Sb
2
O
3
. Its active form may consist essentially of Sb
2
O
3
and up to about 4% RE
2
O
3
, where RE is a rare earth element. A glass comprising Sb
2
O
3
and up to about 4% RE
2
O
3
can preferably include 0-99% percent SiO
2
, 0-99% GeO
2
, and 0-75% (Al
2
O
3
or Ga
2
O
3
). In addition, any of the glass compositions described herein may contain up to 10 mole % B
2
O
3
substituted for an equivalent amount of Sb
2
O
3
.
Although the glass of the present invention is highly desirable because it can be fabricated in air using standard melting techniques and batch reagents, when the glass contains about 90% or more of Sb
2
O
3
it is formed by the techniques of splat quenching or roller quenching. The glass composition of the present invention exhibits a gain spectrum with excellent breadth and flatness characteristics and can be readily modified for specific optical amplifier applications.
Further in accordance with the present invention is an optical energy producing or light-amplifying device, in particular an optical amplifier, that comprises the glass of the invention. The optical amplifier can be either a fiber amplifier or a planar amplifier, either of which may be of a hybrid (composition) construction.


REFERENCES:
patent: 2918382 (1959-12-01), King et al.
patent: 3677960 (1972-07-01), Ishiyama
patent: 3714059 (1973-01-01), Shaw et al.
patent: 4239645 (1980-12-01), Izumitani et al.
patent: 4248732 (1981-02-01), Myers et al.
patent: 4962067 (1990-10-01), Myers
patent: 5274728 (1993-12-01), Tran
patent: 5283211 (1994-02-

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