WO1995026519A1

WO1995026519A1 - A method of producing a photorefractive effect in optical devices and optical devices formed by that method

Info

Publication number: WO1995026519A1
Application number: PCT/AU1995/000177
Authority: WO
Inventors: Paul Lawrence Rossiter; Douglas Macfarlane; Peter Newman; John Javorniczky; Edward Eduardovich Tapanes
Original assignee: Monash University
Current assignee: Monash University
Priority date: 1994-03-29
Filing date: 1995-03-29
Publication date: 1995-10-05
Anticipated expiration: 1996-09-29

Abstract

A method for producing a refractive effect in an optical device and an optical device formed by the method are disclosed in which a material from which the device is to be formed is illuminated to induce solarisation involving a photoinitiated REDOX reaction in the material so that the material exhibits a permanent or quasi-permanent photorefractive effect. The mechanism of forming the photorefractive effect in the material relates to the photon induced oxidation of a species present in the material, either as a dopant, co-dopant or as a main component. The photo-oxidation of the species liberates an electron which, after a brief lifetime, usually finds a suitable repository by combining with some reducible species in the material. The method enables photorefractive effects to be produced in materials and, in particular, glass materials other than standard germanium-doped and silicon-based materials.

Description

A METHOD OF PRODUCING A PHOTOREFRACTIVE EFFECT IN OPTICAL DEVICES AND OPTICAL DEVICES FORMED BY THAT METHOD

This invention relates to a method of producing a photorefractive effect in an optical device, for example the production of in-situ refractive index gratings in waveguides, and to optical devices made by that method.

Optical devices are commonly used in industry and science and include waveguides such as optical fibres, lenses and other optical elements. Such optical devices are used in a variety of instruments and installations.

Waveguides, including optical fibres, are now in common use. Presently, there is a very high demand for sensors and systems which provide real-time, in-line analysis and monitoring of various chemical processes, environments, and the integrity of structures. Fibre optic sensors, in particular, are very promising for these applications because of their dielectric properties, their fine size, their ability to be remotely located and, in the case of intrinsic sensors, rapid response times. They also have particular advantages in hazardous environments. In addition, they have several clear advantages over existing conventional sensing techniques such as bulk optical analysis and measurements, poten iometrie electrodes, resistive foil gauges, piezo-electric transducers, and chemical batch analysis.

Industrial manufacturing processes, fabricated items, and engineering structures are usually not monitored in real¬ time because of the difficulties in incorporating the sensors into the sensing environment and because of the limitations of the sensors. Optical sensors overcome these difficulties by virtue of their inherent properties. In addition, optical processing systems are extremely fast and do not suffer from electro-magnetic interference, unlike their electronic counter-parts.

Silica-based optical fibres have been demonstrated to have photorefractive properties when doped with germanium. [Hill et. al., Applied Physics Letters, 32(10), 1978] Refractive index change due to ultraviolet (UV) irradiation induced generation of defect sites in germanosilicate glass preforms and optical fibres is well documented. [G. Meltz et. al.. Optics Letters, 14 (15), pp. 823-825, 1989] Early in the development of silica optical fibres for telecommunications a strong absorption band in the UV

(around 240 nm) was witnessed. It was later found that this absorption band could be photo-bleached by UV irradiation in the 240 nm region. The photo-bleaching effect was found to be associated with refractive index changes. The mechanism which induces the refractive index change in the germanium-doped silicates is thought to involve photon generated bond breaking (to generate defect sites termed E' centres) and bond relaxation as the defective system strives to approach equilibrium. [G. R. Atkins et. al. , IEEE Photonics Technology Letters, 4(1), pp. 43-46, 1992]

If the UV beam is in the form of an interference pattern a highly-ordered, three dimensional reflection/transmission or Bragg grating can be photo-'etched' or written permanently into the core of the fibre. [Morey et. al. , Optical Fiber Sensors, Springer Proceedings in Physics, Vol. 44, pp. 526-531, 1989] The Bragg gratings created by the periodic refractive index change have allowed silica optical fibres to act as in-situ narrowband filters. [Glenn, et. al. , US Patent 4807950, 1989] [R. Kashyap et. al., Electronics Letters, 26(11), pp. 730-732, 1990] The introduction of in-situ, narrowband reflection or transmission gratings in optical fibres has created exciting opportunities in a wide variety of applications with tremendous commercial potential. Some examples are: novel and practical fibre optic sensors, passive/active wavelength filters in wavelength multiplexed communications (ie., fibre-to-the-home) and sensor systems, frequency selective elements in passive/active fibre devices (instrumentation and laser tuning), signal detection and processing, optical pulse compression, dispersion compensation, and holography.

However, silica-based fibres are limited in operation to the visible and near IR region of the spectrum. This limitation has generated a strong interest in the development of glasses with a wider IR bandwidth (ie. for applications such as fluoride glass (IR) optical amplifiers and IR optical instrumentation) .

The object of the present invention is to provide a method for producing a photorefractive effect in an optical device made from materials other than standard germanium-doped silica-based materials.

The invention may be said to reside in a method for producing a photorefractive effect in an optical device, including the step of: illuminating a material from which the device is to be formed to induce solarisation involving a photo- initiated redox reaction in the material so that the material exhibits a permanent or quasi-permanent photorefractive effect.

The invention may also be said to reside in an optical device including: a body formed from an optical material; and a photorefractive effect in the optical material, the photorefractive effect being formed by illuminating the waveguide material to induce solarisation involving a photo-initiated REDOX reaction in the material so that the material exhibits a permanent or quasi-permanent photorefractive effect.

The mechanism of changing the refractive index of the material, that is forming the photorefractive effect in the material, relates to the photon induced oxidation of a species present in the material, either as a dopant, co- dopant or as a main component. The photo-oxidation of the species liberates an electron which, after a brief lifetime, usually finds a stable repository by combining with some reducible species in the material. The reducible species may also be added as a dopant or co-dopant or may be intrinsically part of the material composition. The overall process is therefore essentially a photo-initiated REDOX reaction within the material.

R+hv —> R⁺ + e^" O+e^" - O^"

Typical examples of solarisable materials include glasses containing Ce³⁺ and V³⁺ or Ce³⁺ and Cu²⁺ as reductant and oxidant respectively.

Thus, according to the preferred embodiment of the invention, the material is preferably an optically transmitting material, such as glass, which includes an oxidisable species either existing in the glass material or added as a dopant to the glass material and a repository species either present in the glass material or added as a dopant to the glass material.

Preferably the material is illuminated with electromagnetic radiation which is in the form of a preferred pattern, such as an interference pattern or is used to photo-etch the pattern generated by acousto-optical (or any other) means to induce the photorefractive effect in the material.

The oxidisable species and repository species must not only be capable of being involved in a REDOX reaction but must also produce a non-cancelling effect on refractive index when transformed by the REDOX reaction.

The host glass system maybe any amorphous material transparent over the wavelengths of interest, which is able to host the oxidant/reductant species. Alternately, one or more of the redox active species may be part of the host glass composition. Suitable amorphous hosts include:

i) oxide glasses including: silicates, borates, phosphates, fluorophosphates, aluminates, nitrates, and oxide glasses of Si, Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, Cd and/or transition metals.

ii) halide glasses including: fluoroberrylates, fluorozirconates, fluorohafnates, fluoroaluminates, fluoroindates, transition metal fluorile systems and glasses containing ZrCl₂, CdBr, Cdl, Hgl, Agl, AgBr, A1C1₃, AlBr₃, All₃ and/or Bi.

iii) Chalcogenide glasses including glasses based on As, Sb, Se, S, Te and/or Sb.

iv) Nitride and phosphide glasses.

v) Polymer glasses including: poly(methylmethacrylate) and acrylates and methacrylates generally, polymers based on poly(alkylene oxides), polycarbonates and non- crystalline polymeric materials generally.

vi) Molecular liquid based glasses including: glycerol, propylene glycol and other liquids capable of forming glasses at low temperatures. vii) Ioninσ glasses generally (not otherwise included above) including lithium acetate and lithium formate.

The photoredox mechanism may also be made operative in single crystal hosts and liquid crystalline materials.

The host glass system contains one or more of the following elements in an appropriate combination such that there is at least one oxidant species and at least one reductant species available:

S, Cl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, As, Se, Br,

Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Te, I, Ce, Pr, Sn, Sm, Eu, In, Tb, Tm, Yb, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, U, Ga and organic redox active species including: hydroquinone, quinones generally, radical stabilisers generally and organic reductants including ascorbates.

Preferably the photorefractive effect is used to form a refractive index grating in the material and preferably the optical device comprises a waveguide including an optical fibre, a lens or other optical element such as an optical sensor.

Examples of glass materials which may be used in the present invention include:

* In general any glass system having dopants added to it such that it is capable of being involved in a photo-redox reaction which produces a net change in refractive index.

* n-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

* Cu-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

* Ag-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

5 * Li-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-

20NaF mole percent) as the starting point fluoride glass.

* Cs-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point

10 fluoride glass.

* Ce-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

* V-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 15 20NaF mole percent) as the starting point fluoride glass.

* ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF mole percent) as the starting point fluoride glass doped with any combination of the above

20 mentioned dopan s.

* In-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

* Cu-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- 25 lOCsF mole percent) as the starting point fluoride glass.

* Ag-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

30 * Li-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

* Ce-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point

35 fluoride glass.

* V-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

* ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃-10CsF mole percent) as the starting point fluoride glass doped with any combination of the above

5 mentioned dopants.

* In-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point fluoride glass.

* Cu-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 10 20CsF mole percent) as the starting point fluoride glass.

* Ag-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point fluoride glass.

15 * Li-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-

20CSF mole percent) as the starting point fluoride glass.

* Ce-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point

20 fluoride glass.

* V-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point fluoride glass.

* ZBLACS20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20CsF mole 25 percent) as the starting point fluoride glass doped with any combination of the above mentioned dopants.

* Any of the ZBLAN or ZBLACs compositions containing the following co-dopants:

30 * Ce³⁺ and V^{3 +}

* Ce³⁺ and Cu^{2 +}

* Ce^{3 +} and Ag⁺

* Ce³⁺ and ln³⁺

* Ce³⁺ and Ti³⁺

35 * Ce³⁺ and Sn ⁺

* Pb²⁺ and V³⁺

* Pb^{2 +} and ln^{3 +} * Au³⁺ and V³⁺

* Au³⁺ and In³⁺

* As₂S₃ chalcogenide glass.

* Doped As₂S₃ chalcogenide glass. * As-S-Se chalcogenide glass.

* Doped As-S-Se chalcogenide glass.

* As-Ge-Se chalcogenide glass.

* Doped As-Ge-Se chalcogenide glass.

* Pb-doped (at lead concentrations below approximately 35 mol^*%) Si0₂ silica based glass due to interstitial Pb²⁺ and O^" defect centres.

* GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass.

* Pb-doped GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass.

* Calcium aluminate glasses (K₂0-Na₂0-CaO-Al₂0₃- Si0₂) .

* Neutron-coloured α-Al₂0₃ sapphire glass.

In a further aspect, the invention may also be said to reside in an optical device including or comprising a material selected from the materials disclosed in the preceding paragraph.

The preferred embodiment of the present invention will be further illustrated, by way of example, with reference to the following examples:

Example 1:

A glass block (10mm x 10mm x 4mm) was formulated to contain: ZrF₄, 60.78; BaF₂, 24.08; LaF₃, 5.41; A1F₃, 1.80; NaF, 5.73; CeF₃, 1.41; CuF₂, 0.79 weight percent. This glass was exposed to Ultraviolet/Visible (UV/Vis) light from an Osram Ultra-Vitalux 300W lamp for 32 hours.

After irradiation, the glass was found to have a refractive index of 1.5029 as compared to 1.5005 for the unirradiated glass.

Example 2:

As for Example 1 except that the dopants were CeF₃ and PbF₂ instead of CeF₃ and CuF₂, ie ZrF₄, 60.90; BaF₂, 24.013;

LaF₃, 5.42; A1F₃, 1.81; NaF, 5.75; CeF₃, 1.41; PbF₂, 0.59 weight percent and the refractive index after irradiation was 1.5004, as compared to 1.4993 before irradiation.

Example 3: As for Example 1 except that lnF₃ was also included, ie

ZrF₄, 60.14; BaF₂, 23.83; LaF₃, 5.35; AlF₃, 1.78; NaF, 5.67; CeF₃, 1.72; CuF₂, 0.85; InF₃, 0.65 weight percent and the refractive index after irradiation was 1.5045 as compared to 1.5031 before irradiation.

The conventional method of forming gratings in standard germanium-doped silica-based fibres typically produce a permanent refractive index change of no more than Δ^slO^-3 without irreparable damage to the glass or stability problems. This sets a serious limitation on the operating performance of devices made using the conventional method.

The method according to the present invention has provided substantial changes in refractive index and in the above examples a A. of 2.1 x 10^"3, 1.1 x 10^"3, and 1.4 x 10^"3 was provided.

Optical devices made by the method of the invention and optical devices according to the invention are useful in a wide variety of fields including spectroscopy and communications as optical signal detection, conditioning and processing devices, as well as strain and temperature • sensors in the optical sensing field and optical computing elements and optical memories in the computing field. Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method for producing a photorefractive effect in an optical device, including the step of: illuminating a material from which the device is to be formed to induce solarisation involving a photo- initiated redox reaction in the material so that the material exhibits a permanent or quasi-permanent photorefractive effect.

2. An optical device including: a body formed from an optical material; and a photorefractive effect in the optical material, the photorefractive effect being formed by illuminating the waveguide material to induce solarisation involving a photo-initiated REDOX reaction in the material so that the material exhibits a permanent or quasi-permanent photorefractive effect.

3. The method of claim 1, wherein the material is an optically transmitting material which includes an oxidisable species either existing in the glass material or added as a dopant to the glass material and a repository species either present in the glass material or added as a dopant to the glass material.

4. The method of claim 1 or claim 3 wherein the material is illuminated with electromagnetic radiation which is in the form of a preferred pattern or is used to photo-etch the pattern generated by acousto-optical means to induce the photorefractive effect in the material.

5. The method of claim 1 wherein the material is any amorphous material transparent over the wavelengths of interest, which is able to host the oxidant/reductant species.

6. The method of claim 1 wherein one or more redox active species are part of the material.

7. The method of claim 1 wherein the material is selected from the following group:

ii) halide glasses including: fluoroberrylates, fluorozirconates, fluorohafnates, fluoroaluminates, fluoroindates, transition metal fluorile systems and glasses containing ZrCl₂, CdBr, Cdl, Hgl, Agl, AgBr, A1C1₃, AlBr₃, A1I₃ and/or Bi.

iv) Nitride and phosphide glasses.

v) Polymer glasses including: poly(methylmethacrylate) and acrylates and methacrylates generally, polymers based on p.oly(alkylene oxides), polycarbonates and non- crystalline polymeric materials generally.

vi) Molecular liquid based glasses including: glycerol, propylene glycol and other liquids capable of forming glasses at low temperatures.

vii) Ioninc glasses generally (not otherwise included above) including lithium acetate and lithium formate.

8. The method of claim 1 wherein the material contains one or more of the following elements in an appropriate combination such that there is at least one oxidant species and at least one reductant species available:

S, Cl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, As, Se, Br, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Te, I, Ce, Pr, Sn, Sm, Eu, In, Tb, Tm, Yb, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, U, Ga and organic redox active species including: hydroquinone, quinones generally, radical stabilisers generally and organic reductants including ascorbates.

9. The method of claim 1 wherein the photorefractive effect is used to form a refractive index grating in the material and preferably the optical device comprises a waveguide including an optical fibre, a lens or other optical element such as an optical sensor.

10. The method of claim 1 wherein the material is selected from the following group: * Any glass system having dopants added to it such that it is capable of being involved in a photo-redox reaction which produces a net change in refractive index.

* In-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

* Cu-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass. * Ag-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-

20NaF mole percent) as the starting point fluoride glass.

* Li-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

* Cs-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

5 * Ce-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-

20NaF mole percent) as the starting point fluoride glass.

* V-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point

10 fluoride glass.

* ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF mole percent) as the starting point fluoride glass doped with any combination of the above mentioned dopants.

15 * in-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point f uoride glass.

* Cu-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point

20 fluoride glass.

* Li-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- 25 lOCsF mole percent) as the starting point fluoride glass.

* Ce-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

30 * V-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

* ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃-10CsF mole percent) as the starting point fluoride glass

35 doped with any combination of the above mentioned dopants.

* In-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent ) as the starting point fluoride glass .

* Cu-doped ZBLACS20 ( 53ZrF₄-20BaF₂-4LaF₃-3AlF₃ - 20CsF mole percent ) as the starting point

5 fluoride glass .

* Ag-doped ZBLACs20 ( 53ZrF₄-20BaF₂-4LaF₃-3AlF₃ - 20CsF mole percent ) as the starting point fluoride glass .

* Li-doped ZBLACs20 ( 53ZrF₄-20BaF₂-4LaF₃-3AlF₃ - 10 20CsF mole percent ) as the starting point fluoride glass .

* Ce-doped ZBLACs20 ( 53ZrF₄-20BaF₂-4LaF₃-3AlF₃ - 20CsF mole percent ) as the starting point fluoride glass .

15 * V-doped ZBLACS20 ( 53ZrF₄-20BaF₂-4LaF₃-3AlF₃ -

20CsF mole percent) as the starting point fluoride glass .

* ZBLACS20 ( 53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20CsF mole percent ) as the starting point fluoride glass

20 doped with any combination of the above mentioned dopants .

* Any of the ZBLAN or ZBLACs compositions containing the following co-dopants :

* Ce³⁺ and V³⁺ 25 * Ce³⁺ and Cu²⁺

* Ce³⁺ and Ag⁺

* Ce³⁺ and In³⁺

* Ce³⁺ and Ti³⁺

* Ce³⁺ and Sn⁴⁺ 30 * Pb²⁺ and V³⁺

* Pb²⁺ and In^{3 +}

* Au³⁺ and V³⁺

* Au³⁺ and In³⁺

* As₂S₃ chalcogenide glass .

35 * Doped As₂S₃ chalcogenide glass .

* As-S-Se chalcogenide glass.

* Doped As-S-Se chalcogenide glass. * As-Ge-Se chalcogenide glass.

* Doped As-Ge-Se chalcogenide glass.

* Pb-doped (at lead concentrations below approximately 35 mol^*%) Si0₂ silica based glass due to interstitial Pb²⁺ and 0^" defect centres.

* GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass.

* Pb-doped GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass. * Calcium aluminate glasses (K₂0-Na₂0-CaO-Al₂0₃-

Si0₂) .

* Neutron-coloured α-Al₂0₃ sapphire glass.

11. An optical device according to claim 2, wherein the material is an optically transmitting material which includes an oxidisable species either existing in the glass material or added as a dopant to the glass material and a repository species either present in the glass material or added as a dopant to the glass material.

12. An optical- device according to claim 2 or claim 11 wherein the material is illuminated with electromagnetic radiation which is in the form of a preferred pattern or is used to photo-etch the pattern generated by acousto-optical means to induce the photorefractive effect in the material.

13. An optical device according to claim 2 wherein the material is any amorphous material transparent over the wavelengths of interest, which is able to host the oxidant/reductant species.

14. An optical device according to claim 2 wherein one or more redox active species are part of the material.

15. An optical device according to claim 2 wherein the material is selected from the following group: i) oxide glasses including: silicates, borates, phosphates, fluorophosphates, aluminates, nitrates, and oxide glasses of Si, Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, Cd and/or transition metals.

iv) Nitride and phosphide glasses.

16. An optical device according to claim 2 wherein the material contains one or more of the following elements in an appropriate combination such that there is at least one oxidant species and at least one reductant species available: S, Cl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, As, Se, Br, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, Te, I, Ce, Pr, Sn, S , Eu, In, Tb, Tm, Yb, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, U, Ga and organic redox active species including: hydroquinone, quinones generally, radical stabilisers generally and organic reductants including ascorbates.

17. An optical device according to claim 2 wherein the photorefractive effect is used to form a refractive index grating in the material and preferably the optical device comprises a waveguide including an optical fibre, a lens or other optical element such as an optical sensor.

18. An optical device according to claim 2 wherein the material is selected from the following group: * Any glass system having dopants added to it such that it is capable of being involved in a photo-redox reaction which produces a net change in refractive index.

20NaF mole percent) as the starting point fluoride glass.

* V-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass.

5 * ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF mole percent) as the starting point fluoride glass doped with any combination of the above mentioned dopants.

* In-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- 10 lOCsF mole percent) as the starting point fluoride glass.

* Cu-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

15 * Ag-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

* Li-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point

20 fluoride glass.

* V-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- 25 lOCsF mole percent) as the starting point fluoride glass.

30 mentioned dopants.

* Cu-doped ZBLACS20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 35 20CsF mole percent) as the starting point fluoride glass.

* Li-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point

5 fluoride glass.

* Ce-doped ZBLACS20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point fluoride glass.

* V-doped ZBLACS20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 10 20CSF mole percent) as the starting point fluoride glass.

* ZBLACS20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20CsF mole percent) as the starting point fluoride glass doped with any combination of the above

15 mentioned dopants.

* Any of the ZBLAN or ZBLACs compositions containing the following co-dopants:

* Ce³⁺ and V³⁺

* Ce³⁺ and Cu ⁺ 20 * Ce³⁺ and Ag⁺

* Ce³⁺ and In³⁺

* Ce³⁺ and Ti³⁺

* Ce³⁺ and Sn⁴⁺

* Pb²⁺ and V³⁺ 25 * Pb²⁺ and In³⁺

* Au^{3 +} and V³⁺

* Au³⁺ and In³⁺

* As₂S₃ chalcogenide glass. Doped As₂S₃ chalcogenide glass.

30 * As-S-Se chalcogenide glass.

* Doped As-S-Se chalcogenide glass.

* As-Ge-Se chalcogenide glass.

* Doped As-Ge-Se chalcogenide glass.

* Pb-doped (at lead concentrations below

35 approximately 35 mol^**-ό) Si0₂ silica based glass due to interstitial Pb²⁺ and 0^" defect centres. * GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass. Pb-doped GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass.

* Calcium aluminate glasses (K₂0-Na₂0-CaO-Al₂0₃- Si0₂).

* Neutron-coloured α-Al₂0₃ sapphire glass.

19. An optical device including or comprising a material selected from the following group:

* Any glass system having dopants added to it such that it is capable of being involved in a photo-redox reaction which produces a net change in refractive index.

* In-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20 aF mole percent) as the starting point fluoride glass.

* Li-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20 aF mole percent) as the starting point fluoride glass. * Cs-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-

20NaF mole percent) as the starting point fluoride glass.

* Ce-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20 aF mole percent) as the starting point fluoride glass.

* V-doped ZBLAN20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20NaF mole percent) as the starting point fluoride glass .

5 * Cu-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃-

*» lOCsF mole percent) as the starting point fluoride glass.

* Ag-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point

10 fluoride glass.

* Li-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- lOCsF mole percent) as the starting point fluoride glass.

* Ce-doped ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃- 15 lOCsF mole percent) as the starting point fluoride glass.

20 * ZBLACslO (53ZrF₄-30BaF₂-4LaF₃-3AlF₃-10CsF mole percent) as the starting point fluoride glass doped with any combination of the above mentioned dopants.

* In-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 25 20CsF mole percent) as the starting point fluoride glass.

* Cu-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃- 20CsF mole percent) as the starting point fluoride glass.

30 * Ag-doped ZBLACs20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-

20CsF mole percent) as the starting point fluoride glass.

35 fluoride glass.

5 * ZBLACS20 (53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20CsF mole percent) as the starting point fluoride glass doped with any combination of the above mentioned dopants.

* Any of the ZBLAN or ZBLACs compositions 10 containing the following co-dopants:

* Ce³⁺ and V³⁺

* Ce³⁺ and Cu²⁺

* Ce³⁺ and Ag⁺

* Ce³⁺ and In³⁺ 15 * Ce³⁺ and Ti³⁺

* Ce³⁺ and Sn*⁺

* Pb²⁺ and V³⁺

* Pb²⁺ and In³⁺

* Au³⁺ and V³⁺ 20 * Au³⁺ and In³⁺

* As₂S₃ chalcogenide glass.

* Doped As₂S₃ chalcogenide glass.

* As-S-Se^' chalcogenide glass.

* Doped As-S-Se chalcogenide glass. 25 * As-Ge-Se chalcogenide glass.

* Doped As-Ge-Se chalcogenide glass.

* Pb-doped (at lead concentrations below approximately 35 mol%) Si0₂ silica based glass due to interstitial Pb²⁺ and O^" defect

30 centres.

* GPBZK (Ge0₂-PbO-BaC-2nO-K₂0) germanate glass. Pb-doped GPBZK (Ge0₂-PbO-BaO-ZnO-K₂0) germanate glass.

* Calcium aluminate glasses (K₂0-Na₂0-CaO-Al₂0₃- 35 Si0₂).

* Neutron-coloured α-Al₂0₃ sapphire glass.