Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-03-23
2001-09-04
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S037000, C501S044000, C065S392000, C385S123000, C385S130000, C385S141000
Reexamination Certificate
active
06284685
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to light-induced refractive index changes in materials. More particularly, the present invention relates to a low temperature glass exhibiting light-induced refractive index changes.
BACKGROUND OF THE INVENTION
The term “photorefraction” has been used to describe the phenomenon where the refractive index of a material is altered upon exposure to light. Initially, the phenomenon was observed in a certain restricted class of crystalline materials that were photoconductive and exhibited large polar effects. An example of such a material is LiNbO
3
. There is also a version of this type of “photorefractive” behavior that can be obtained in organic polymeric materials. In these polymeric materials, the various photosensitive agents are added to the polymer in a guest-host format.
More recently, a new class of materials have been reported to exhibit significant “photorefractive” behavior. These materials are glasses in the family xSiO
2
—(1−x)GeO
2
. The origin of the effect in these materials is totally different from that of the ferroelectric crystals mentioned above. An excimer laser (193 nm and 248 nm) induces a refractive index change in these materials, and the refractive index change stems from large absorption changes originating from “defects” in the glass structure. Because the effect was originally discovered in a single mode optical fiber and, since the major application of the induced index change has been to fabricate phase gratings in the fiber, this “photorefractive” behavior is often referred to as “fiber Bragg gratings” in the technical literature. The effect has been reported to have been extended to other binary SiO
2
compositions such as P
2
O
5
, SnO, and Ce
2
O
3
. By far the largest induced refractive index change has been in the SiO
2
—GeO
2
system where values as large as 0.001 have been reported. The size of the refractive index effect may be increased in the SiO
2
—GeO
2
system by impregnating the glass with molecular hydrogen before exposure.
Tin-phosphorous oxyfluoride glasses are known and are disclosed in U.S. Pat. Nos. 4,314,031 and 4,379,070, which are relied upon and incorporated herein by reference. U.S. Pat. No. 4,314,031 discloses that tin-phosphorous oxyfluoride glasses desirably have a very low glass transition temperature, frequently below 100° C., yet still exhibit excellent resistance to attack by moisture at elevated temperatures. U.S. Pat. No. 4,379,070 discloses the use of tin-phosphorous oxyfluoride glasses as a matrix material for the support of photosensitive and electric-field-responsive polycyclic aromatic hydrocarbon compounds. Neither of these patents, however, discloses or suggests that tin-phosphorous oxyfluoride glasses exhibit a “photorefractive” effect or the use of tin-phosphorous oxyfluoride glass as a photorefractive material.
It would also be useful to provide a material that exhibits a “photorefractive” effect that could be doped with a variety of materials for altering the optical properties of the devices made from the material, including inorganic and organic dopants.
SUMMARY OF INVENTION
The present invention involves a tin-phosphorous oxyfluoride glass system that exhibits a large “photorefractive” effect by a mechanism different from either of the crystalline or silica-germania classes mentioned above. It has been discovered that exposure of tin-phosphorous oxyfluoride glass to light of a wavelength shorter than the absorption region of the glass for a sufficient amount of time shows little or no absorption changes, yet can exhibit refractive index changes greater than about 0.0004. A wide variety of devices may be fabricated from tin-phosphorous oxyfluoride glass which has been exposed to light of a wavelength shorter than the absorption region of the glass.
Accordingly, the present invention generally provides a device and a method of making a device comprising tin-phosphorous oxyfluoride glass which has been exposed to light for a time sufficient to change the refractive index the glass. Preferably the wavelength of the light is shorter than about 350 nm, which roughly corresponds to the absorption edge of the glass. The composition of the tin-phosphorous oxyfluoride glass may comprise, in weight percent on an elemental basis as calculated from the batch, about 20-85% Sn, 2-20% P, 3-20% O, 9-36% F, and at least 60% total of Sn+P+O+F. The composition may further include about 0-40% cation modifiers and about 0-20% anion modifiers. The glasses for making the devices of the present invention may further be doped with a optically nonlinear organic dye to alter the optical properties of the glasses.
In one aspect of the invention, the device may include an optical waveguide region. In another aspect of the invention, the device may include a periodic refractive index structure, such as a diffraction grating. Accordingly, the devices of the present invention may be formed into a variety of shapes, including planar and fiber forms. Gratings and waveguides may be formed by changing the refractive index of selected portions of the glass, which may be achieved by exposing the selected portion to light shorter than the absorption edge of the glass. For example, an optical interference pattern may be utilized to form a grating, or the glass may be selectively masked to provide a periodic refractive index structure in the glass.
Several important advantages will be appreciated from the foregoing summary. One advantage of the device and method of the present invention is providing a photorefractive device made from a glass material that has a low glass transition temperature and is resistant to moisture. The present invention also provides a photorefractive material that can be doped with wide variety of materials such as optically nonlinear organic dies, which can be used to dynamically alter the optical properties of the devices. Another advantage is the ability to form photorefractive devices into planar devices and fibers, including devices having gratings and/or core/clad structures for guiding light.
Additional features and advantages of the invention will be set forth in the description which follows. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
DETAILED DESCRIPTION
Reference will now be made in detail to the present preferred embodiment of the invention. The present invention provides a device and a method for making the same.
The device of the present invention comprises tin-phosphorous oxyfluoride glass, which has been exposed to light for a time sufficient to change the refractive index change of the glass. The light is preferably shorter in wavelength than 350 nm, which roughly corresponds to the absorption edge of the glass.
Reference is made to U.S. Pat. Nos. 4,314,031 and 4,379,070, for a more detailed understanding of processing of tin-phosphorous oxyfluoride glass compositions. As disclosed in those patents, tin-phosphorous oxyfluoride glasses can be made from conventional batch materials such as SnF
2
, P
2
O
5
, Sn
3
(PO
4
)
2
, SnO, NH
4
H
2
PO
4
, NH
4
PF
6
and Sn
2
P
2
O
7
and can be melted at temperatures not exceeding 600° C. Preferably, however, to provide glasses exhibiting the photorefractive effect, the compositions should be melted at temperatures below 450° C., and for some compositions, as demonstrated by the example, preferably below 400° C.
As also noted in the patents, the tin-phosphorous oxyfluoride glass system may include a variety of additional optional constituents including alkali metals, alkaline earth metals, group II metals such as zinc and cadmium, group II elements such as La, Ce, B and Al, group IV elements such as Pb, Zr, Ti, and Ge, group V elements such as Sb and Nb, group VI elements such as Mo and W, group VII elements such as Cl, Br and I, and group VIII metals such as Gd. Reference may be made to U.S. Pat. Nos. 4,314,031 and 4,379
Borrelli Nicholas F.
Boyd Robert W.
Radic Stojan
Tick Paul A.
Corning Incorporated
Group Karl
Short Svetlana
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