Optical Distribution System Including Light Guide

This relates in general to light transmission and distribution systems comprising light guides and more particularly, to such a system in which the transmitting light guide serves as a primary light source.

For some years, optical fibers have been utilized in the prior art for transmitting optical energy from a source to a preselected destination with minimal energy loss along the transmission path. Accordingly, as described in detail in an article entitled The Fiber Light Guide by Alan G. Chenoweth, Vol. 29, No. 5, May 1976 of Physics Today, page 28 et seq., and in U.S. Pat. No. 3,641,332, issued to Franklin G. Reick and Michael Ebert, Feb. 8, 1972, for Fiber Optics Illumination System, the principal object of such systems is to practically eliminate the lateral diffusion of the optical rays from the core during course of light transmission. This is accomplished by forming the optical transmission core of a material which has a substantially higher index of refraction than the surrounding sleeve. This is enhanced, as disclosed in U.S. Pat. No. 3,641,332, supra, by interposing an annular layer of air between the core and the surrounding sleeve. The light from a source at one end of the optical fiber, or bundle of fibers, is totally reflected from the periphery back toward the center of the core, so that almost no energy is lost through the sidewalls of the transmitting fiber, and almost the entire light energy from the source is delivered to the selected destination at the other end. Thus, the sidewalls of the transmitting fiber or bundle of fibers, appear dark, and unable to function as a primary light source.

Line or strip sources of light are provided in the prior art by elongated tubes filled with rare gases, such as neon or argon. These are inexpensive to fabricate and install and require high voltages to operate.

Further, prior art safety signs and the like are fabricated using reflecting strips, which act as secondary sources of light. But none of the foregoing is fully satisfactory for safety or other utilitarian purposes, or for decorative purposes.

Accordingly, it is the principal object of the invention to provide a primary light source comprising a light guide in the form of a flexible rod or strip, bright along its length, which is simple and inexpensive to manufacture and install.

In accordance with the present invention such a light guide comprises a single optical transmission core of clear resinous plastic or the like, having a transparent or translucent sleeve which is shrink-fitted or otherwise tightly fitted around the periphery so as to substantially remove the air interface, and wherein the sleeve is designed to laterally disperse, diffuse, or refract through its sidewall a substantial component of light transmitted along the core from a source at one end. This causes the sleeve to have a bright appearance and to serve as a primary source of light.

In accordance with one modification, the surface of the core is scored with angular cuts or discontinuities at intervals along the length for the purpose of deflecting the traversing light beams outwardly through the sleeve. The inside surface of the tube may be etched or otherwise treated chemically or mechanically to cause light striking it to diffuse. Another device for providing discontinuities for deflecting light through the sleeve wall is by introducing air bubbles into the core material while it is still molten. In accordance with another modification, light is deflected outwardly from the core by reflective particles in the form of powder embedded in the material of the sleeve. In another form, the sleeve may comprise a material having an index of refraction which exceeds that of the core.

The source of light, which may either by steadystate or pulsating, such as a strobe light, may preferably comprise a tiny light bulb interposed into the end of the sleeve, immediately adjacent the end of the core, although the source or bulb may be located beyond the end of the light guide. For variation, color filters, or a color wheel may be interposed between the light source and the input end of the light guide, imposing preselected colors on the light diffused through the walls of the sleeve.

One method of forming a combination in accordance with the present invention is by providing a tube of radially expanded plastic, such as tetrafluoroethylene, manufactured by E. I. DuPont de Neymours under the trademark TEFLON (TFE), having a 2 to 10 percent fill, with reflective or refractive powders such as, for example, titanium dioxide (TiO.sub.2), or bismuth subcarbonate (Bi.sub.2 O.sub.3.CO.sub.3).sub.2.H.sub.2 O.

A thermosetting resin, which may, for example, comprise a liquid mixture of from 60-90% of allyl diglycol carbonate (CR39), with a 1.5 to 3.0 percent solution of isopropylpercarbonate (IPP), and the balance methyl methacrylate, is poured through a funnel into one end of the coil of tubing which is open at the other end, so that the liquid mixture flows down into the same by gravity. The coil is then transferred to a liquid bath, where the core is polymerized and substantially hardened by heating for a period of 12 to 24 hours at a temperature within the range 125 to 185 degrees Fahrenheit. The core material may be undercatalyzed in order for it to remain flexible. The tetrafluoroethylene sleeve may be shrink-fitted onto the polymerized core by heating the core and sleeve combination up to a temperature within the range, say, from 200 to 400 degrees Fahrenheit. In accordance with one embodiment the inner diameter of the enclosing sleeve is slightly less than the outer diameter of the core in order to impose a slight compression on the core and squeeze out any air remaining at the interface between the core and the sleeve.

Another alternative is to provide a sleeve consisting essentially of resins sold under the trademark AROCLOR (polychlorinated polyphenyls) which have indices of refraction ranging from 1.617 to 1.665, which is generally greater than that of the herein disclosed core materials which range around 1.5.

If shapes other than round are desired, such as elliptical, square, triangular, etc., the casing may be drawn through a die of the proper shape, in accordance with well-known extrusion practice.

The light guide of the present invention is adapted to be used for many applications. Because of its flexibility it can be used to form signs, both for utilitarian and decorative purposes, such as road safety signs, similar to the neon signs presently in use, and for line sources, both in and out of doors, for providing a soft, inexpensive light of any desired color over an extended area. The flexible rod light source of the present invention is also useful to light up strips on safety clothing, such as vests for traffic policemen, and for placement around the rims of vehicle wheels, or as the core of a rigid plastic rod, to be fastened to the rear of a bicycle, for safety purposes.

Other applications of the present invention, which are within the contemplation of this disclosure, are to surround meters on instrument panels and the like, and to surround mirrors and pictures, giving a uniform light around the edges.

The principal advantages of the light diffusing light guide of the present invention over prior art line sources are the simplicity and inexpensiveness of its manufacture, the ease with which it may be applied, and the many applications to which it is adapted.

These and other objects, features, and advantages will be better understood from a detailed study of the invention with reference to the attached drawings.

FIG. 1 is a longitudinal section of a light guide in accordance with the present invention showing the external sleeve shrunk tightly onto the inner light transmitting core so that air is substantially evacuated from the interface.

FIG. 2 is a schematic showing of a light beam from a light source passing down the core of a light guide shown in longitudinal section in accordance with the present invention, part being inwardly reflected, and part being refracted and/or reflected or diffused through the walls of the external sleeve.

FIG. 3 shows, in cross-section, a series of typical shapes into which the light guide of the present invention can be extruded.

FIG. 4A and 4B are longitudinal and cross-sectional showings in accordance with the present invention in which a series of cuts or discontinuities have been interposed through the sleeve into the surface of the inner core, to cause the light rays to be deflected outwardly.

FIG. 5 is a longitudinal sectional showing in accordance with the present invention in which particles of powder have been mixed into the matrix material of the sleeve to cause light from the core to be reflected, refracted or diffused outwardly.

FIG. 6 is a side elevation of a modification in accordance with the present invention in which a spiral marking has been etched or otherwise engraved onto the surface of the core to cause light to be deflected outwardly.

FIG. 7 is a longitudinal sectional showing of a further modification of the light guide of the present invention in which the inside of the sleeve has been either chemically or mechanically roughened to cause light from the core to be diffused or deflected outwardly.

FIG. 8 shows the process in accordance with the present invention of pouring a liquid mixture of core material into the sleeve.

FIG. 9A and 9B show the process of heat treating a coil of filled tubing in a heated bath for polymerizing the core of the light guide of the present invention.

FIG. 10 is an application of the light guide tubes of the present invention to a safety vest for traffice directors, miners, and other applications.

FIG. 11 shows a sign formed from a light guide in accordance with the present invention in combination with a pulsing device.

FIG. 12 shows a cane for the disabled, employing the light guide of the present invention.

FIG. 13 shows a bicycle having light guides in accordance with the present invention surrounding the inner periphery of the wheel rims; and a light guide in accordance with the present invention incorporated into a safety light rod attached to the rear of the bicycle.

FIG. 14 shows application of the light guide of the present invention to a meter dial in an instrument panel.

Whereas, as explained hereinbefore, the principal object of the prior art was to provide a light guide which delivers optical energy, substantially without loss, to a selected destination, the object of the present invention is to provide various embodiments of light guides, each of which outwardly deflects or refracts a substantial component of the light being transmitted along its core.

Referring to FIG. 1 of the drawings, there is shown in enlarged section, a flexible light guide 1 of the present invention in which a tube or sleeve 2 of a smooth, flexible transparent or translucent plastic material, is shrink-fitted onto a transparent, transmitting core 3, of transparent plastic or resinous material, so as to substantially eliminate any air interface between the core 3 and the sleeve 2. In at least one embodiment of the invention, the external sleeve has an index of refraction N.sub.2 which exceeds the index of refraction N.sub.1 of the core, so that total reflection does not take place. In other embodiments, the core or the sleeve are provided with discontinuities which outwardly diffuse or deflect a substantial component of the light traversing the core.

When any conventional light source 4 is disposed adjacent to one end of light guide 1, as shown in FIGS. 1 and 2 of the drawings, a substantial amount of light energy impinges on the adjacent end, and is transmitted along the core of the guide in a manner depending on the angle of incidence of the beam. A beam, designated 5a, which enters the core parallel to its principal axis will travel in a substantially straight path along the core without being reflected or refracted. A beam 5b, which enters the core at an angle i, is partially reflected at an angle r.sub.1, equal to the angle i, forming a beam 5c which passes in a zigzag path along the core 3. A component of beam 5b is also partly refracted through an angle r.sub.2 at the inner periphery of the sleeve 2, forming a beam 5d which passes out through the sleeve, and which is again refracted through an angle r.sub.3 at the outer periphery of the sleeve, to form an outwardly-directed beam 5e.

This tends to cause the sleeve 2 to appear bright, as a substantial proportion of the light from the source would be refracted outwardly, depending on the ratio of the indices of refraction and the angle of the incident light, as determined by the position of the source 4.

As shown in FIG. 3, it is contemplated that the cross-section of the light guide 1 need not be round, as shown in 6a, but can assume numerous different shapes such as square, triangular, elliptical, hexagonal, pentagonal, star-shaped, etc. as indicated in 6b-6g. This is achieved in accordance with well-known technology by passing the light guide casing through a die of the desired shape during processing. Pulsation or twisting may be applied during extrusion to achieve what is termed a "bellows" effect.

An alternative embodiment of the invention is shown in longitudinal and cross-section in FIGS. 4A and 4B of the invention in which a series of angular cuts 7 are interposed into the sleeve 2 of the light guide 1 along its length, and extended into the surface of the guide, forming discontinuities therein. Thus, beams 5g and 5h traversing the core 3 from the source 4, impinge on these discontinuities and are deflected outwardly through the sleeve 2, causing it to appear bright along its length. It is contemplated, for example, that the cuts taken at intervals along the core may be shaped, as shown in FIG. 4B. In order to provide substantially uniform brightness along the length of the light guide, the shaped cuts are made progressively larger as the longitudinal distance along the axis from the source increases, to reflect out a substantially larger percentage of the remaining light traversing the core at each cut.

Another device for achieving the same result is shown in FIG. 5 of the drawings, wherein the sleeve 2 comprises a matrix of plastic material which, during preparation, has been mixed with powdered reflecting material, such as certain types of metal oxides, to render it translucent. Beams 5i and 5j, for example, traversing the core 3 tend to strike the powder granules and are thereby deflected to pass out through the sleeve, thus causing the sleeve to appear bright.

Other devices for achieving this result are by etching or otherwise engraving a spiral strip on the surface of the core 3, prior to enclosing the same in the outer sleeve.

Another device is to "bleed in" bubbles or foreign materials through a needle into the inner core while the same is still in a viscous state, or by vigorously shaking up the core material before pouring it into the sleeve during processing.

Another technique in accordance with the present invention, illustrated by the longitudinal sectional showing of FIG. 7, comprises etching or taking other mechanical or chemical steps, such as treating with sodium naphthalene, to roughen the inner surface of the sleeve 2 before the core material is added.

The following is a typical numerical example for preparing a light guide in accordance with the present invention.

A tubular coil 12 of sleeve material, say 10 feet long, 3/16 inch outer diameter and 1/4 inch inner diameter, has a matrix consisting essentially of tetrafluoroethylene TFE, is filled with from 2 to 10 percent of reflecting metal oxide powder, having a average grain size of talcum powder, or the like.

The radially-expanded tubular coil 12 is filled with a viscous liquid core material, which, in the present example comprises the following formulation:

The liquid mixture 10 is then poured through a funnel into one end of the coiled tetrafluoroethylene sleeve 12, which is open at the other end. (See FIG. 8).

The coil 12 containing the liquid core material 3 is then mounted on a screen support 14a for a period of from 12-24 hours in conventional container 14 of a liquid bath 15, which is maintained at a temperature of 120 to 170 degrees Fahrenheit by a conventional heater 16, and which is constantly stirred by an impeller 17 driven by motor 18. This enables the core material to polymerize, forming a flexible thermoset transparent inner core.

In accordance with an alternative embodiment, the tubular coil 12 can be formed of a material having an index of refraction exceeding that of the core material. A suitable material for this purpose is a polychlorinated polyphenyl resin known by the trademark AROCLOR which has an index of refraction of about 1.6. Referring again to FIG. 2, when a sleeve of such a material is used, it is unnecessary to use filler materials or discontinuities in the sleeve 2 or the core 3 as a beam from the source 4 impinging on the inner wall of the sleeve 2 will be outwardly refracted through the sleeve.

Numerous applications are contemplated for use of the light guide of the present invention.

Referring to FIG. 10, there is shown a vest 19 which is particularly applicable to night-time operations, for use by traffic policemen and other directors of traffic, miners, and various types of sports persons, such as, for example, joggers and skiers. This may be formed of any of the materials used for such garments, cut to a conventional pattern adapted to slip over the head of the user, providing a highly visible front and back panel. A pair of vertical strips 21a and 21b, each about three inches wide are sewn or otherwise secured along their long edges, parallel to the lateral edges of the vest, in such a manner that in each case an inside vertically extending channel is provided between the strips and the backing material of the vest. Elongated light guides 23a and 23b, formed in accordance with any one of FIGS. 1-7 of the present invention, are respectively accommodated in the channels provided by each of strips 21a and 21b. The input ends of 23a and 23b are each connected to light source 22. This may comprise a pair of small 1/2 watt bulbs 22a and 22b secured in the respective ends of light guides 23a and 23b which are energized by means of a conventional battery. It is contemplated that for most applications light guides 23a and 23b are extended over the shoulders and down the rear of the vests. It is also within the contemplation of the present invention that a conventional pulsing device may be incorporated into the source 22 which causes the light bulbs 22a and 22b to flash on and off. The source 22 may be fitted into a small pocket provided for that purpose at the lower end of the vest 19.

Another application of the light guides of the present invention is for incorporation into various types of signs and indoor and outdoor line sources for both utilitarian and decorative illumination in the manner of neon, argon, and other gas-filled tubes used in the prior art for such purposes.

One illustration of such use is shown in FIG. 11 of the drawings, in which the light guide of the present invention is sufficiently flexible to form such letters as may be desired. In accordance with the alternative previously indicated, a conventional power source may incorporate pulsing means 25 connected to turn on and off the light source 26. In this embodiment, the light source may, for example, comprise a 1 to 1000 watt bulb, energized either by a battery or conventional source of power, which may either be fitted into the input end of the light guide forming the letters SIGN, or may be slightly spaced-apart therefrom. In the latter case, it may be desired to interpose a motor-driven color wheel 27 which would function to periodically change the color of the sign. For this application, it is contemplated that any of the light guides of the types disclosed in FIGS. 1-7 can be used.

Other applications of the light guides disclosed in any one of FIGS. 1-7 are shown in FIGS. 12, 13 and 14. FIG. 12 shows a cane 28 for the disabled in which, for example, battery operated light source is built into the upper end. Although a substantial portion of the light traversing the length of the cane is dissipated laterally, it is contemplated that a portion of the light will travel to the lower end 30, providing a lighted lower tip, for guidance purposes; and a portion of light would also be available at the upper end.

One of the most important applications of the invention is for safety lights for vehicles, which is illustrated by the bicycle of FIG. 13. A flexible light guide in accordance with the present invention is disposed around the inner periphery of the wheels. An additional light guide is interposed into a rigid tube of materials sold under the trademark LEXAN (polycarbonate), or similar material, vertically fastened to the rear of the vehicle. It is contemplated that all of these light guides will be lighted by small 1/2-10 watt bulbs, incorporated into the light guide sleeves, in each case.

They will be energized from a battery source 33 fastened to the frame or by an on-board generator. As an additional feature, the LEXAN tube including light guide 34 may terminate at its upper end in a lighted ball 34a, which may comprise a ball of transparent or translucent material similar to the core material.

It will be understood that similar safety lights in accordance with the present invention can be utilized for many different types of vehicles, such as automobiles, trains, ships, boats, aircraft, etc.

Another application of the invention is illustrated in FIG. 14, which shows the dial of a meter 35 with a light guide 36 in accordance with the present invention disposed around its inner periphery. It is contemplated that this can be energized by batteries, or another conventional source, at the rear of the dial or elsewhere, which energized one or more small light bulbs of, say, 1/10 to 1 watt, incorporated into the sleeve of the light guide.

Although a number of examples have been given of applications of the light guide of the present invention, it will be understood that the invention is not limited to the specific applications or forms set forth herein by way of example, but only by the scope of the appended claims.