WO2000070372A2

WO2000070372A2 - Jacketed fiber optic cable with improved light output

Info

Publication number: WO2000070372A2
Application number: PCT/US2000/013742
Authority: WO
Inventors: Jack Caruso
Original assignee: OPTIC-TECH INTERNATIONAL CORP
Current assignee: OPTIC-TECH INTERNATIONAL CORP
Priority date: 1999-05-19
Filing date: 2000-05-19
Publication date: 2000-11-23
Anticipated expiration: 2001-11-19
Also published as: WO2000070372A3; AU7050900A

Abstract

A fiber optic cable includes a plurality of fiber optic strands surrounded by a flexible jacketing that improves the quantity as well as the color quality of the light output. The jacketing composition includes at least one component that absorbs light in the invisible or nearly visible UV spectrum and, in response, emits light in the visible spectrum.

Description

JACKETED FIBER OPTIC CABLE WITH IMPROVED LIGHT OUTPUT

CROSS REFERENCE TO PROVISIONAL APPLICATION

This application is related to co-pending provisional application serial no. 60/134,842, filed May 19, 1999.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to improvements to fiber optic cable. More particularly, the present invention provides an improved fiber optic cable including jacketing manufactured from a flexible composition that improves the amount of visible spectrum light, as well as the color quality of the light, that is output from the cable .

2. Description of the Background Art Light emitting fiber optic cable containing a plurality of individual fiber optic strands is well known. One end of such cable is optically coupled to a light source, light is transmitted through the strands and is emitted from the other end. This other end of the cable may be optically and physically coupled to any of various light distribution appliances, such as optical lenses, down light fixtures, pool light fixtures, ground light fixtures, security-hardened light fixtures, general lighting fixtures, acrylic apparatuses such as display signs, point of purchase signs and displays. The cable can be coupled to the distribution appliance either by direct surface contact or by mechanically positioning the end an appropriate distance from a medium to be illuminated. This allows for light transmission onto or through a light permeable medium, such as opaque acrylic, transparent acrylic or clear acrylic.

Fiber optic cables can include a light-scattering feature to enhance the illumination emanating from the light -emitting end of the cable. For example, the plurality of individual strands can be separated or bunched or grouped together to alter the illuminating properties of the cable.

A wide variety of fiber optic materials are known, each exhibiting a unique set of light transmitting properties. However, many of these materials, especially fiber optic strands manufactured from glass, are relatively expensive. Due to the economics involved, they are for that reason not suitable for many commercial lighting applications. Poly (methyl methacrylate) ( "PMMA" ) based fiber optic strands have found wide use in commercial lighting applications because they present a reasonable balance of light transmitting properties, flexibility, and low cost to manufacture. Ideally, fiber optic strands would be capable of total internal reflection whereby no light would be lost via transmission through the walls of the strands. PMMA fiber optic strands exhibit a significant amount of loss due to light transmission (leakage) through the walls of the strands. The PMMA-based fiber optic cables sold for common commercial lighting applications typically include a black, PVC-based jacket that surrounds the bundle of PMMA strands. These black PVC-based jackets introduce a variety of drawbacks, however. First, because the fiber optic strands are not 100 percent efficient, a quantity of light is lost through the walls of the strands and interacts with the jacket. The traditional black-colored jacket tends to absorb much of this light; it is unable to return significant portions of the light to the fiber optic strands, thereby making an important contribution to the overall quantity of light loss from the cable. This light absorption phenomenon is known as albedo -- the extent of light loss to which an object reflects light, expressed as a number from 0 to 1, or as percentage from 0 to 100. A black object has an albedo of 0 or 0% while a white object has an albedo of 1 or 100%, with most objects falling in between these extremes. Further, the portion of the light that is returned to the strands after interacting with the jacket is undesirably color shifted into the green range due to its interactance with the jacket composition. This phenomenon makes it difficult to provide an emission of pure white light from the cable.

Previously known PVC jacketing compositions also are susceptible to damage from the high heat levels present in fiber optic lighting apparatus. The black PVC composition absorbs heat as well as light from the fiber optic strands. Heat can build up in the jacket, leading to damage to the system, for example by melting the jacket and/or the PMMA optical fibers. Heat absorption also can present hazardous situations. Metal halide illuminators typically used in fiber optic applications can generate large amounts of heat, and PMMA optical fibers can ignite if exposed to high heat. The heat resistance of a fiber optic illumination system is an important attribute of systems used in hazardous locations, such as in environments containing oxygen or a flammable gas, including hospital rooms, airliner fuel tanks, grain silos and fuel tankers .

Due to the characteristics of most flexible PVC compositions, PMMA optical fibers formed into light illuminating cables generate high levels of static energy (electricity) when encased in a PVC-based jacket. In a hazardous environment, static discharge can cause an explosive reaction. It is also known that flexible PVC compounds can be susceptible to self-ignition when subjected to high thermal energy, causing an immediate out-gassing of toxic fumes.

In view of the foregoing, PMMA optical fiber used in combination with a black flexible PVC jacket compositions has been limited to diameters of 0.75 mm. This small diameter minimizes the occurrence of hazardous conditions by lowering the mass of PMMA optical fiber relative to the mass of the black flexible PVC composition.

For the foregoing and other reasons, improvements to jacketed fiber optic cables have been desired. SUMMARY OF THE INVENTION

In one aspect, the present invention relates to improvements to jacketed fiber optic cables, wherein the jacket is manufactured from a flexible polymeric composition and includes at least one light -modifying component capable of absorbing light from the invisible or nearly visible UV spectrum and emitting light in the visible spectrum. Useful light -modifying components that function in this manner include optical brighteners (also known as fluorescent whitening agents) and halogenating agents.

In preferred embodiments the polymeric composition from which the jacketing is prepared includes a white pigment, an optical brightener and a halogenating agent that work synergistically to absorb invisible UV light that has been lost from the fiber optic strands and emit visible light that is returned to the strands and contributes to the quantity and color quality of the output light. The polymeric composition may advantageously include flame retardant, smoke inhibitor and anti-static components to further improve the properties and performance of the fiber optic cable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides fiber optic cables that include an improved jacketing prepared from a flexible, white polymeric composition. The jacketing of the present invention improves the quality and quantity of visible spectrum light that is emitted from fiber optic cable. Additionally, the jacketing exhibits excellent anti -static, heat resistance and flame retardant properties.

The jacketing can be prepared from any of a variety of known flexible materials. Flexible polymeric materials are preferred, including polyvinyl chloride, polyethylene, polypropylene. Polyvinyl chloride (PVC) compositions are particularly preferred. Formulations for flexible PVC compounds useful for the preparation of cable jacketing are well known in the art. Although a wide variety of flexible polymers, co-polymers and blends thereof are suitable for the preparation of cable jacketing, the invention is illustrated herein with specific reference to PVC-based formulations. The jacketing may be formed in situ over the optical fiber strands as is known in the art, a method that is desirable when large quantities of fiber optic cable are being manufactured. Preferred embodiments of the invention include jacketed fiber optic cables comprising a plurality of 1.0 mm diameter PMMA optical fibers.

The cable jacketing of the present invention should have an albedo of greater than about 0.5, preferably greater than about 0.8 and most preferably an albedo of about 1 (100%) . This is accomplished at least in part by the incorporation of one or more white pigments into the PVC formulation. White pigment preferably is present within the range of about 1 to about 10% by weight, based on the weight of the PVC compound. White pigments are well known in the art; typically they are oxides, hydroxides, carbonates, sulphates or sulphides of various metals including titanium (Ti) , zinc (Zn) , aluminum (Al) and barium (Ba) . Titanium dioxide is particularly preferred. Titanium dioxide additionally contributes to the desired high albedo of the jacketing material and to the overall increase in light output by imparting high reflectance to the internal walls of the jacket.

One aspect of the present invention relates to improvements to the quality and quantity of visible spectrum light that is output from end-emitting fiber optic cables. As noted above, fiber optic strands are not 100 percent efficient, and light loss through the walls of the strands can occur to varying degrees. While this light loss has presented problems in the prior art, the present invention takes advantage of this light loss by providing, in the jacketing composition, one or more components (referred to herein as "light-modifying components") that absorb the invisible and nearly- invisible ultraviolet (UV) portion of the spectrum, particularly light in the 250 - 400 nm spectrum, and convert this energy into the longer-wavelength visible portion of the spectrum. This longer-wavelength energy is returned to the strands in the form of light emitted by the light-modifying component (s) . In preferred embodiments, the light that is output by the fiber optic cable exhibits improved (whiter) color due to the interactance with the components of the jacketing material. Preferably, significant portions of the light emitted by the light-modifying component (s) is in the 400 to 525 nm spectrum. Additionally, the intensity of visible spectrum light is increased because some of the invisible UV light that would have been lost has been shifted into the visible spectrum and then returned to the fiber optic strands.

The shift from the invisible and nearly- invisible UV into the visible spectrum is accomplished by the presence of at least one optical brightening agent incorporated into the flexible jacketing. Optical brightening agents, also known as fluorescent whitening agents, are well known and have been used extensively in the textile, detergent, paper, synthetic fiber and plastics industries. These agents typically are organic compounds that are derivatives of stilbene, styryl derivatives of benzene and biphenyl , pyrazolines, bis (benzoxazol-2-yl) derivatives, coumarins and carbostyrils . These classes of optical brightening agents are fully described in the Kirk-Othmer Encyclopedia of Chemical Technology (1994), Vol. 11, pp. 227-241, the disclosure of which is incorporated by reference herein. The optical brighteners function by absorbing light from the UV spectrum, with typical absorption maxima falling in the range of about 300 to about 375 nm, and emitting light in the visible spectrum, with typical emission maxima falling into the range of about 400 to about 500 nm. Suitable optical whiteners can be exemplified by 1,4- distyrylbenzene, 2- (4-styrylphenyl) -5-phenyl-oxazol, 2,2- (2, 5-thiophendiyl) -bis (5- (1, 1-dimethylethyl) ) -benzoxazole, 1, 4-bis (5-phenyloxazolyle-2 ) -benzene and 5 , 6-bensocumarin- 3-carboxyl acid ethyl ester. The amount of organic optical whiteners can, according to the invention, be from about 0.001 to about 1 weight percent, based on the weight of the PVC (or other polymeric material) in the jacketing formulation. UVITEX OB, a well-known product of the Ciba-Geigy company, is a particularly preferred optical brightener for use in accordance with the present invention. The optically active ingredient in UVITEX OB is 2,2 '-(2,5- thiophenediyl) -bis- (5-tert-butylbenzoxazole) . UVITEX OB is a yellow crystalline powder having a melting point of 197°-203° C. The agent has an absorption maximum at 373 nm and an emission maximum at 435 nm, producing a cyan blue emission. Advantageously, UVITEX OB can be admixed with other additives during the preparation of the PVC (or other polymeric) formulation.

The formulation of the jacket composition may also include a halogenation agent that absorbs light in the UV spectrum and emits light in the visible spectrum. Xenon fluoride is a particularly preferred halogenation agent, and can be incorporated into the formulation in amounts ranging from about 0.00005 to about 0.001 percent, based upon the total weight of the product. Other suitable halogenation agents include Kr_θ5.

Preferred formulations for the jacketing material include both optical brightener halogenation agent light- modifying components. The absorption and emission spectra of the two components may overlap but, preferably, are not identical. Thus, when both components are present, the two agents can provide a cascade effect and work synergistically to improve the quantity and color quality of the light output by the fiber optic cable. UV energy outside of the visible spectrum that is emitted by the fiber optic light source interacts with the halogenation agent and is emitted as blue visible light. This light, in turn, is absorbed by the optical brightening agent and then emitted as higher wavelength light in a more desirable portion of the visible spectrum. The light that is returned to the fiber optic strands preferably has a color rendition index (CRI) of greater than 90, and most preferably a CRI of about 99.

The jacketing composition may also contain anti- flame, flame retardant, anti-smoke and anti-static agents to improve its physical characteristics and usefulness in a wide variety of contexts .

A particularly preferred formulation for a PVC-based jacketing composition according to the present invention is based upon a white-pigmented PVC molding composition, G-2190-AS-2731, available from the Gitto/Global

Corporation, Lunenberg, Massachusetts, USA, to which are added 0.00196690 percent by weight of UVITEX OB, 0.0001 percent xenon fluoride powder, 0.0000069 percent Violet ZIRS (a violet aniline dye), and 0.0277885 percent titanium dioxide. The G-2190-AS-2731 base polymer includes commercially available plasticizers, stabilizers, catalysts, anti-flame and anti-static agents.

Although the invention has been described in connection with certain preferred embodiments, it is not so limited. Variations to the formulations disclosed herein, within the scope of the invention, will be apparent to those skilled in the art.

Claims

What is claimed is:

1. A fiber optic cable, comprising a plurality of fiber optic strands surrounded by a flexible polymeric cable jacket, said cable jacket comprising at least one light -modifying component that absorbs light in the invisible or nearly invisible UV spectrum and, in response thereto, emits light in the visible spectrum.

2. The fiber optic cable according to claim 1, wherein said light -modifying component is an optical brightening agent.

3. The fiber optic cable according to claim 1, wherein said light-modifying component is a halogenation agent .

4. The fiber optic cable according to claim 1, wherein said cable jacket comprises an optical brightening agent and a halogenation agent.

5. The fiber optic cable according to claim 2, wherein said optical brightening agent absorbs light within a 250 to 400 nm spectrum and emits light within a 400 to 550 nm spectrum.

6. The fiber optic cable according to claim 2, wherein said optical brightening agent is 2,2'- (2,5- thiophenediyl) -bis- (5-tert-butylbenzoxazole) .

7. The fiber optic cable according to claim 3, wherein said halogenation agent is xenon fluoride.

8. The fiber optic cable according to claim 1, wherein said flexible polymeric cable jacket is comprised of PVC.

9. The fiber optic cable according to claim 8, further comprising white pigment and having an albedo of at least about 0.5.

10. The fiber optic cable according to claim 9, having an albedo of at least about 0.8.

11. The fiber optic cable according to claim 9, having an albedo of at about 1.0.

12. The fiber optic cable according to claim 1, comprising a plurality of PMMA fiber optic strands, each of said strands having a diameter of about 0.75 mm.

13. The fiber optic cable according to claim 1, comprising a plurality of PMMA fiber optic strands, each of said strands having a diameter of about 1.0 mm.