Optical waveguides – Optical fiber waveguide with cladding – With graded index core or cladding
Reexamination Certificate
1999-07-29
2001-12-25
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
With graded index core or cladding
C385S037000
Reexamination Certificate
active
06334018
ABSTRACT:
FIELD OF INVENTION
The present invention relates to an optical means and to a method of producing optical means in the form of material or components that has a spatially varying chemical composition which enables the manufacture of optical material or components whose optical properties vary spatially. The method is well suited to create refractive index variations in optical material for the manufacture of optical waveguides, or for creating or generating periodic refractive index variations in different types of waveguides.
BACKGROUND OF THE INVENTION
It is known that the refractive index of germanium-doped, SiO
2
-based fibres (among others), can be changed by exposing the fibre to ultraviolet radiation within certain absorption intervals. The ultraviolet wavelengths used to create fraction index changes in holographic page-writing methods lie mainly within germanium-related absorption bands with a maximum at approximately 195 nm and approximately 240 nm, although other wavelength intervals have also been used, these latter wavelength intervals normally requiring much longer exposure times, however. It is possible to produce with holographic page-writing methods periodic refractive-index variations, so-called Bragg gratings, that function as wavelength selective mirrors or filters, with several applications within, e.g., telecommunications and laser or sensor applications.
Fibre gratings are described in the document “Fibre Gratings”, Physics World, October 1993, Philip ST. J. Russell et al, pp. 41-46, and also in PCT publication WO 94/00784.
Although the actual process lying behind these index changes has not been fully established, it is generally considered that germanium defects—the concentration of Ge
2+
(c.f., for instance, U.S. Pat. No. 5,157,747, Atkins et al) is the main reason for the resultant photosensitivity. The photosensitivity of a material is, e.g., its ability to change its refractive index upon given exposure to electromagnetic radiation. Although the photosensitivity of fibre can be enhanced in many different ways, the method used is still highly dependent on the use of wavelengths of approximately 195 nm and approximately 240 nm. Sensitivity to ultraviolet light can be enhanced by doping with more GeO or GeO
2
and/or B
2
O
3
.
U.S. Pat. No. 5,500,031, Atkins et al, teaches a method of increasing the refractive index of glassy material, by applying heat in conjunction with hydrogen sensitization. Such increases in refractive index are not temperature-stable at temperatures above 600° C. This patent specification teaches solely a method that is aimed at causing chemical reactions to take place over the space of time of some seconds and for temperatures higher than 500° C., and not to cause diffusion of material that has diffused into the material or of doping substances in the material. In order to cause diffusion, the material is heated to temperatures of from 800 to 1100° C. and over much longer times, for instance over minutes or hours.
It has been possible to increase the photosensitivity of certain fibres or waveguides, by diffusing hydrogen thereinto.
SUMMARY OF THE INVENTION
One object of the present invention is to provide optical means, and a method that uses optical material that has spatially varying optical properties, and also a method of manufacturing such optical material. The optical properties of an optical material are greatly influenced by the chemical composition of the material, which enables a spatial change of its optical properties to be obtained by spatially changing its chemical composition. The method is well suited for generating a spatially varying refractive index, and also in obtaining variations in the non-linearities and/or the electro- or magneto-optical properties of the optical material.
A change in the spatial chemical composition of an optical material means that gate writing will no longer be dependent on the wavelengths of 195 nm and 240 nm respectively, since the photosensitivity no longer depends on germanium defects that are related to these wavelengths.
To this end, the present invention provides an optical means which has a spatially varying chemical composition. The means has diffused therein mobile substances that have taken part in at least one chemical reaction in said means or in parts of said means, by supplying energy through electromagnetic radiation, via optical writing or by subjecting said means to predetermined temperature changes.
Further predetermined temperature changes in said means have caused diffused substances that have not taken part in the reaction to diffuse out from or through said means, and that predetermined temperature changes achieved by changing the energy supply via exposure to electromagnetic radiation, or temperature changes generated by some other form of energy, have caused the substance to diffuse out of said means or within said means, therewith changing the chemical structure and optical properties in this region. This results in a means that has a spatially varying chemical composition and spatially varying optical properties.
In one embodiment of the invention, said means is produced by a combination of or by repetition of at least two of the steps of diffusing mobile substances in said means, supplying energy via optical writing, and predetermining temperature change for diffusion of the substances into said means.
It is also a means for conducting electromagnetic radiation.
In one embodiment of the invention, variations in refractive index have been achieved via the steps of diffusing mobile substances into the means, supplying energy by exposing said means to electromagnetic radiation, via optical writing or by predetermined temperature changes, and predetermined temperature changes for diffusion of mobile substances that have not reacted chemically, and predetermined temperatures for diffusing said substances out of said means or within said means.
In another embodiment, spatially varying optical properties have been achieved in said means via the steps of diffusing mobile substances therein, supplying energy by exposing said means to electromagnetic radiation via optical writing or predetermined temperature changes, predetermined temperature changes for diffusion of mobile substances that have not reacted chemically, and predetermined temperature changes for diffusion of substances in said means.
The present invention also relates to a method of producing a spatially varying chemical composition in optical means by
diffusing at least one mobile substance in said means;
inducing at least one chemical reaction between the diffused substance or substances and the optical means, by supplying energy through the medium of electromagnetic radiation via optical writing or by raising the temperature to a predetermined value;
changing the temperature of the means to a predetermined temperature level, therewith causing diffused substances that have not participated in said chemical reaction to diffuse out of or within said means; and
changing the temperature of said means to a predetermined temperature level by changing the energy supply via exposure of the means to electromagnetic radiation, or by some other form of energy supply, so that the substances will diffuse out of said means or within said means, therewith resulting in a chemically varying means having varying optical properties.
Alternatively, the method comprises a combination of or a repetition of these steps.
In one embodiment of the inventive method, the optical means includes fluorine, and either hydrogen, nitrogen or oxygen, or combinations thereof, is diffused into said optical means, therewith resulting in a higher concentration of hydroxyl groups that react with fluorine to form hydrogen fluoride, which can be readily caused to diffuse out of said means or within said means.
In another embodiment of the inventive method, the optical means includes halogens, and hydrogen, nitrogen, oxygen or a combination thereof are diffused into said optical means, therewith resulting in a higher concentration of hy
Birch Stewart Kolasch & Birch, LLP.
Sanghavi Hemang
Telefonaktiebolaget LM Ericsson
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