Illumination fiber optic ribbon

An illumination fiber optic ribbon includes optically-transmissive fibers which are adjacent to each other. At least two of the optically-transmissive fibers are twisted together to form a twisted segment. Where the two optically-transmissive fibers are not twisted forms a non-twisted segment. The twisted segments and non-twisted segments alternate along the length of the ribbon. Bends are disposed along the twisted segment and are formed by twisting adjacent optically-transmissive fibers. A light source is connected to one or both ends of the optically-transmissive fibers. The light source emits a light flux into the ribbon so that light emits from the bends in the twisted segment.

FIELD OF THE INVENTION

The present invention relates to fiber optic cables used for illumination. In particular, the present invention relates to an illumination fiber optic ribbon with alternating twisted segments from which light is emitted and non-twisted segments for better connection to a light source.

BACKGROUND OF THE INVENTION

Fiber optic cable is often used to transmit light in the longitudinal direction of the cable from one end of the cable to the other end. Fiber optic cables can also be made to transmit light radially away. Such radial light transmission is often used for area lighting, such as around swimming pools, walkways, signs, safety lighting, or decorative accent lighting. Fiber optic cables are often used instead of electrical cables because fiber optic cables require only one light source and the light source's electrical power can be at a distant location.

Such fiber optic cables use special methods of manufacture, such as inclusion of actinically-sensitive dyes or other light-scattering materials to enhance the radial transmission of light. Other approaches avoid special manufacturing methods by bundling a large number of individual fibers together or by bundling groups of wound fibers together. The bundling is not cost efficient and wastes emitted light since light from central fibers is blocked by outer fibers.

Additionally, known fiber optic cables do not provide a simple and efficient mechanism for connecting the fibers to a light source so that the maximum amount of light is sent into the cable and not reflected back to the light source or refracted away from the cable. Cable installers must unwind the cable and laboriously connect individual fibers to the light source. Additionally, known cables do not provide an efficient way to sever the cable to a desired length and then provide a labor-saving way to connect the severed end to a light source so that the maximum amount of light is accepted into the cable.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the invention to provide an illumination fiber optic ribbon with alternating twisted segments from which light is emitted and non-twisted segments for optimal connection to a light source. The ribbon can be severed at one of the non-twisted segments and still provide optimal connection to the light source.

One embodiment of the present invention provides an illumination fiber optic ribbon. The ribbon includes optically-transmissive fibers disposed adjacent to each other, at least two of the optically-transmissive fibers being twisted together to form a twisted segment and the at least two optically-transmissive fibers being parallel to one another to form a non-twisted segment, the twisted and non-twisted segments alternating along a length of the ribbon; bends disposed along said twisted segments, the bends formed by the twisting of adjacent optically-transmissive fibers; and at least one of the non-twisted segments being capable of connection to a light source disposed at one or both ends of the optically-transmissive fibers, the light source emitting a light flux into the twisted and non-twisted segments of the optically-transmissive fibers so that light therefrom is emitted from the bends along the twisted segments.

Another embodiment of the present invention provides an illumination fiber optic ribbon. The ribbon includes optically-transmissive fibers disposed adjacent to each other, at least two of the optically-transmissive fibers being twisted together to form a twisted segment and the at least two optically-transmissive fibers being parallel to one another to form a non-twisted segment, the twisted and non-twisted segments alternating along a length of said ribbon; bends disposed along the twisted segments, the bends formed by the twisting of adjacent optically-transmissive fibers; at least one of the non-twisted segments being capable of connection to a light source disposed at one or both ends of said plurality of optically-transmissive fibers, the light source emitting a light flux into the twisted and non-twisted segments of the optically-transmissive fibers so that light therefrom is emitted from the bends along the twisted segments; and a sheath substantially enclosing the optically-transmissive fibers.

Yet another embodiment of the present invention provides a method of manufacturing an illumination fiber optic ribbon. The method of manufacturing includes the steps of: disposing a plurality of optically-transmissive fibers adjacent to one another; twisting adjacent optically-transmissive fibers in a portion of a length of the ribbon to form a twisted segment; forming a plurality of bends at a cladding on each of said plurality of optically-transmissive fibers by the twisting; providing a non-twisted segment in a portion of the length of the ribbon in which adjacent optically-transmissive fibers are not twisted; and alternating the non-twisted segments with the twisted segments.

Yet another embodiment of the present invention provides an illumination fiber optic ribbon. The illumination fiber optic ribbon includes optically-transmissive fibers disposed adjacent to each other, at least two of the plurality of optically-transmissive fibers being twisted together to form a twisted segment and the at least two optically-transmissive fibers being parallel to one another to form a non-twisted segment, the twisted and non-twisted segments alternating along a length of the ribbon; bends along the twisted segment formed by the twisting of adjacent optically-transmissive fibers, the bends per unit length increasing as the length of the ribbon increases; and at least one of the non-twisted segments being capable of connection to a light source disposed at one or both ends of the optically-transmissive fibers, the light source emitting a light flux into the twisted and non-twisted segments of optically-transmissive fibers so that light therefrom is emitted from the bends along the twisted segments.

Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1-16, the present invention relates to a fiber optic ribbon100that transmits light from a light source to a distant area to provide illumination. Light preferably emits along the sides of the ribbon100and not merely at its ends to provide a greater illumination area. Portions of the ribbon100from where light is emitted, e.g. twisted segment104a, alternate with portions of the ribbon100where light is conserved, e.g. non-twisted segment106a, so that multiple areas may be illuminated while minimizing loss of light in transmission between areas. The ribbon100may be thin and compact. The thin and compact construction expands the potential locations where the ribbon100can be used. The construction of the ribbon100also simplifies the coupling of the ribbon100to a light source so that the maximum amount of light enters and is emitted by the ribbon100.

Referring toFIG. 1, the illumination fiber optic ribbon100is shown. The illumination fiber optic ribbon100may include a plurality of optically-transmissive fibers102with a plurality of bends116in twisted segments104aand104bfrom where light is emitted and a sheath110. The optically-transmissive fibers102transmit light. The cross-sectional shape of the optically-transmissive fiber102can be of any shape and dimension. The length of the optically-transmissive fibers102is determined by the requirements of each particular application, such as the area to be illuminated or the distance to the light source. If the area to be illuminated is broad or if the area to be illuminated is at a great distance, then a longer length of fiber102may be required.

Referring toFIG. 2, a sectional view of the optically-transmissive fiber102with a representative bend116is shown. Each optically-transmissive fiber102is composed of a core204and a cladding202that substantially surrounds the core204. Preferably, the core204and the cladding202are made of a substantially optically-transparent material. The cladding202causes light to travel away from the cladding202and towards the core204such that light206travels generally in the longitudinal direction of the core204. In one exemplary embodiment, an index of refraction of the core204differs from an index of refraction of the cladding202so that light206is reflected towards the core204and away from the cladding202, and thus, the light206travels generally in the longitudinal direction of the core204. Preferably, the optically-transmissive fibers102are made of polymethylmethacrylate (PMMA), plastic, glass, or other similarly substantially optically-transparent materials.

In the twisted segments104aand104bof the ribbon100, the twisting of the optically-transmissive fibers102causes bends116in the cladding202of the individual fibers102. Due to the bends116in the cladding202, the index of refraction of the cladding202is altered. The change in the index of refraction of the cladding202affects a critical angle of light or the angle at which the light208can be directed back to the core204. The change in the critical angle of light allows the light208to emit through the bend116. In alternate embodiments, the change in the index of refraction of the cladding202may be caused by distortions in the cladding202instead of by bending the cladding202. The distortions in the cladding202may be caused chemically or mechanically. The cladding202may also be disrupted to allow light208to emit.

As best seen inFIGS. 1 and 3, the optically-transmissive fibers102lie adjacent to one another to form the ribbon100for transmitting light. The number of optically-transmissive fibers102lying adjacent to each other may be increased or decreased to increase or reduce the size of the ribbon100.

The ribbon100includes alternating twisted segments, such as segments104aand104b, and non-twisted segments, such as segments106a,106b, and106c. The twisted segments104aand104binclude at least two adjacent optically-transmissive fibers102twisted together. Preferably, all of the optically-transmissive fibers102are twisted into pairs at the twisted segments104aand104b. Portions where the adjacent optically-transmissive fibers102are not intertwined, that is parallel, form the non-twisted segments106a-106cwhich may alternate with the twisted segments104aand104b. Although only two twisted segments104aand104band three non-twisted segments106a-106care illustrated, the ribbon100may have more than two twisted segments104aand104band more than three non-twisted segments106a-106c, or only a single twisted segment and single non-twisted segment. Preferably, at least one non-twisted segment, such as106aor106c, is disposed at one or both ends of the ribbon100to facilitate connection to a light source302. The light source302provides light. It may be an electrically-powered light source, a solar-powered light source, or a natural light source.

The light208provided by the light source302can attenuate as the length of the ribbon100increases. However, in certain applications, the attenuation in light208may be undesirable. Thus, to compensate for the attenuation in the light emitted from the ribbon100as its length increases, the bends116per unit length of the ribbon100can be increased as the length of the ribbon100increases. As described above, the twisting of optically-transmissive fibers102causes bends116in the cladding202of each fiber102, and the bends116allow light208to be emitted. Accordingly, by increasing the twisting of optically-transmissive fibers102, the number of bends116per unit length of the ribbon100can be increased which allows more light208to be emitted from the ribbon100. Referring toFIG. 11, a plan view of an illumination fiber optic ribbon1100is shown. In ribbon1100, the twisted segment1104bmay have more twisting of adjacent optically-transmissive fibers102than twisted segment1104a. Thus, more light can be emitted from twisted segment1104bthan twisted segment1104a. Because the bends116are formed by twisting adjacent optically-transmissive fibers102, more twisting results in the twist lay length becoming shorter or tighter. The number of bends116per unit length can be increased progressively by increasing the twisting of fibers102progressively, or the number of bends116per unit length can be increased in stepped increments by increasing the twisting of fibers102in stepped increments.

Referring toFIG. 4, for maximum transmission of light along the optically-transmissive fiber424, a light ray has to enter within a specified optimum acceptance angle402of the optically-transmissive fiber424where an acceptance angle is measured from a longitudinal axis416of the optically-transmissive fiber424. The optimum acceptance angle402is also known as the maximum acceptance angle. Previously, an optically-transmissive fiber424may have been coupled to the light source418such that not all light rays were within the optimum acceptance angle402. For instance, light ray408enters the optically-transmissive fiber424at an angle414relative to the longitudinal axis416. The angle414is greater than the optimum acceptance angle402so that a portion of light ray408is able to escape through the cladding420. As light ray408proceeds through the optically-transmissive fiber102, additional portions of light ray408are able to escape through the cladding420so that light ray408attenuates as it travels through the optically-transmissive fiber424. Light rays, such as404and406, that enter the optically-transmissive fiber424at an angle equal to or less than the optimum acceptance angle402transmit through the optically-transmissive fiber102without escaping through the cladding420. Light ray404enters the optically-transmissive fiber102at an angle412equal to the optimum acceptance angle402measured relative to the longitudinal axis416and reflects to travel in a direction substantially parallel to the longitudinal axis416of the optically-transmissive fiber424. Another light ray406enters the optically-transmissive fiber424at an angle410smaller than the optimum acceptance angle402measured relative to the longitudinal axis416. Light ray406travels longitudinally through the optically-transmissive fiber424by being repeatedly reflected towards the core422by the cladding420.

The optimum acceptance angle402is determined by a numerical aperture of the optically-transmissive fiber424. The numerical aperture is a value that can be readily found by one skilled in the art for a particular optically-transmissive fiber424. The numerical aperture is defined as the square-root of the difference of the squares of the index of refraction for the core and the index of refraction for the cladding or √(index of refraction of the core)2−(index of refraction of the cladding)2. The numerical aperture is also the sine of the optimum acceptance angle402or sine (optimum acceptance angle402). Therefore, to find the optimum acceptance angle402for a particular optically-transmissive fiber424, find the inverse sine or arcsine of the numerical aperture, a value readily obtained for a particular optically-transmissive fiber424. The optimum acceptance angle402derived from the numerical aperture is relative to the longitudinal axis416of the optically-transmissive fiber424.

Referring toFIG. 5, for the ribbon100, the optically-transmissive fibers102may be positioned for connection to the light source518so that light rays will be within the optimum acceptance angle502. Substantially all the light rays, such as light ray504and506, from the light source518are within the optimum acceptance angle502. A light ray504that enters the optically-transmissive fiber102at an angle512equal to the optimum acceptance angle502measured relative to the longitudinal axis516reflects to travel in a direction substantially parallel to the longitudinal axis516of the optically-transmissive fiber102. A light ray506that enters the optically-transmissive fiber102at an angle510smaller than the optimum acceptance angle502measured relative to the longitudinal axis516travels longitudinally through the optically-transmissive fiber102by being repeatedly reflected towards the core204by the cladding202.

Referring toFIG. 6, the non-twisted segment106aof the ribbon100may be positioned for connection to multiple array light sources618so that the light rays from the light sources618are within the optimum acceptance angle502of the optically-transmissive fibers102. The light source618may be a multiple array planar light source as depicted. Since the optically-transmissive fibers102in the non-twisted segment, such as106a, are substantially parallel to one another, several optically-transmissive fibers102may be positioned for connection to the light source618so that light rays therefrom will be substantially within the optimum acceptance angle502. Only two pairs of optically-transmissive fibers102are shown inFIG. 6for clarity. However, the number of pairs depicted is not meant to be limiting to the invention. The ribbon100may have one pair of optically-transmissive fibers102or a multitude of pairs of optically-transmissive fibers102.

As shown inFIG. 7, the ribbon100may be provided on a reel702. On such longer lengths of ribbon100with several non-twisted segments alternating with several twisted segments, a desired smaller length of ribbon100may be provided by severing a non-twisted segment, such as106b, and still provide an efficient connection to the light source at the optimum acceptance angle.

As shown inFIG. 1, the sheath110substantially encloses the optically-transmissive fibers102. The sheath110may include panels112and114forming the sides of the ribbon100. Alternatively, the sheath110may have only one panel leaving the fibers102exposed on the opposite side. The sheath110can be made of a substantially transparent material, reflective material, opaque material, or a combination of such materials. For example, the substantially transparent material may be MYLAR, TEFLON, a polymer such as TEDLAR, a plastic material such as polyvinyl chloride, or other similarly transparent material. The reflective material may be aluminum foil, MYLAR, MYLAR composite, titanium oxide (TiO2), white reflective paint, or any other substantially reflective material. The opaque material can be polyester film, plastic film, polypropylene, polyethylene, polyvinyl chloride (PVC), vinyl, TEFLON, or another substantially opaque material. The combination of substantially transparent and substantially reflective material is preferably used when only one side of the ribbon100provides illumination to an area, e.g., when the ribbon100is positioned on a floor or a wall. The substantially transparent portion of the sheath110is positioned toward the area to be illuminated, and the substantially reflective portion of the sheath110is provided on the side away from the area to be illuminated, e.g., the floor or the wall. The light emitted from the side of the ribbon100away from the area to be illuminated is reflected back by the substantially reflective portion of the sheath110to maximize the light for illumination.

Referring toFIGS. 8 and 9, the sheath110may be coupled to the optically-transmissive fibers102. The coupling can be by bonding, lamination, extrusion, and other similar processes. Preferably, the sheath110is coupled to the optically-transmissive fibers102by an adhesive, such as a polyester adhesive. In one embodiment, the sheath110is coupled to both the twisted segments104aand104band the non-twisted segments106a-106c. Also, prior to coupling, the optically-transmissive fibers102may undergo corona etching. Corona etching is a process where the optically-transmissive fibers102are disposed between electrodes that provide an electrical discharge or “corona” onto a surface210(shown onFIG. 2) of the optically-transmissive fibers102. The electrical discharge increases the surface tension of the surface210so that the surface210is more receptive to the adhesive film.

InFIG. 8, the coupling of the twisted section104bto the sheath110is shown. The optically-transmissive fibers102are coupled at substantially the same center-to-center distance from each other. They can also be coupled to the sheath110at different center-to-center distances. Other twisting segments, such as104a, are also coupled to the sheath110similar to the coupling between the twisting segment104band the sheath110described above.

InFIG. 9, the coupling of the non-twisted segments106bto the sheath110is shown. Similar to the twisted section104b, the optically-transmissive fibers102are coupled at substantially the same center-to-center distance from each other. They may also be coupled to the sheath110at different center-to-center distances. As an example, by locating optically-transmissive fibers102at substantially the same center-to-center distance from each other, the ribbon100can be connected to a planar array light source that requires the optically-transmissive fibers102to be in the same centerline plane with each fiber102being equidistant with an adjacent fiber102. Also, other non-twisted segments, such as106aor106c, are coupled to the sheath110similar to the coupling between non-twisted segment106band the sheath110.

Substantially all of the optically-transmissive fibers102in the non-twisted segments, such as end segment106a, can be simultaneously positioned since all the optically-transmissive fibers102are coupled to the sheath110. That way, all of the fibers102of the non-twisted segment106amay be positioned for light to enter at the optimum acceptance angle of the optically-transmissive fibers102to facilitate connection of the fibers102to the light source302.

In another embodiment, as seen inFIG. 10, a ribbon1000includes a sheath1010that is substantially similar to ribbon100, except the sheath1010is coupled only to the twisted segments and not the non-twisted segments such that the fibers102of the non-twisted segments1002are loose. The coupling of the twisted segments to the sheath1010is similar to the coupling described above for twisted segments106aand sheath110. By not coupling the optically-transmissive fibers102of the non-twisted segments1002to the sheath1010, an installer can sever the ribbon1000at the non-twisted segment1002and group the optically-transmissive fibers102for connecting to a non-planar array light source as desired, such as at the optimum acceptance angle.

Referring toFIG. 3, a plan view of the illumination fiber optic ribbon100is shown. Preferably, one of the non-twisted segments, such as106a, is connected to the light source302. When the ribbon100is connected to the light source302, the light flux from the light source302is transmitted into the optically-transmissive fibers102. By using the non-twisted segment106athe optically-transmissive fibers102may be positioned into the optimum acceptance angle of the optically-transmissive fibers102for connection to the planar array light source. Since there are no bends116in the non-twisted segments106a-106c, when the light flux is transmitted through the non-twisted segments106a-106c, no light emits and so the light flux is conserved for illumination. When the light flux is transmitted through the twisted segments104aand104b, some of the light from the light flux is emitted from the bends116.

Referring toFIG. 12, a perspective view of an alternate embodiment of an illumination fiber optic ribbon1200is shown. The portion of the fiber optic ribbon1200shown has a ferrule120. The ferrule120may be provided at one end or both ends of the fiber optic ribbon1200. In the preferred embodiment, optically-transmissive fibers102in a non-twisted segment106b-106cwhere the fibers102are not coupled to the sheath110are gathered to form a substantially circular bundle which is then inserted into the ferrule120. In alternate embodiments, the fibers102can be gathered to form a non-circular bundle.

The ferrule120allows the ribbon1200to be coupled to an illuminator (not shown). The ferrule120accurately aligns the fibers120to the illuminator. The ferrule120also protects the stripped ends of the optically-transmissive fibers120. The ferrule120can be made of glass, plastic, metal, ceramic material, combinations of the aforementioned, or any other suitably rigid material. In the preferred embodiment, the ferrule120is made of a metal, such as aluminum or steel.

The shape of the ferrule120is determined by the mating receptacle of the illuminator. The illuminator can be a metal halide illuminator, a quartz halogen illuminator, a light emitting diode (LED) illuminator, or any other suitable light source. Illuminators are commercially available from Fiberstars, Inc. or DiCon Fiberoptics, Inc. Referring toFIGS. 13 and 14, alternate embodiments of the ferrules220and320are shown. InFIG. 13, the ferrule220has a generally tubular shape that can be received by an LED illuminator made by DiCon Fiberoptics, Inc. InFIG. 14, the ferrule320has a shape that can be inserted into a metal halide illuminator made by Fiberstars, Inc.

The ribbon1200can also have a wrapping124as shown inFIGS. 13-14. The wrapping124bundles and keeps the fibers102together during manufacture. The wrapping124is preferably a tube of predetermined length that can be slipped over the fibers102and then heated to shrink around the fibers102. In the preferred embodiment, the wrapping124does not substantially extend into the ferrule220or320.

Referring toFIGS. 15 and 16, cross-sectional views of the ferrules220and320are shown. After the fibers102are bundled together in a substantially cylindrical bundle, the fibers102are inserted into a substantially cylindrical bore224or324of the ferrules220or320. The bore224and324also has a ring222and322machined internally within the bore224and324. The ring222and322has a diameter slightly larger than the diameter of the bore224and324. During manufacturing of the ribbon1200, the ferrule120,220, or320and the fibers102may be heated. Because the ferrule material and the materials used for the components of the fibers102(such as a covering protecting the core202and the cladding204) do not expand at the same rate when heated, the ring222or322provides stress relief by allowing components of the fibers102to thermally expand into the ring222or322. Also, the expansion of the components of the fibers102into the ring222or322couples the fibers102to the ferrule120. In one exemplary embodiment, the ring222or322is located approximately a quarter of the overall length of the ferrule220or320away from the front of the ferrule220or320and has dimensions of approximately 12.7 mm (approximately 0.50 inches) in width and approximately 1.27 mm (approximately 0.050 inches) in depth. Also, the wrapping124does not substantially extend into the ferrule220or320.

A method for manufacturing the illumination fiber optic ribbon100begins with placing optically-transmissive fibers102adjacent to one another in generally the same plane. As described previously, the number of optically-transmissive fibers102can be varied in order to achieve the required size. Next, adjacent optically transmissive-fibers102are twisted for a predetermined portion of their respective lengths to form at least one twisted segment104aor104b. By twisting the adjacent optically-transmissive fibers102into pairs, bends116are formed from which light is emitted. In alternate embodiments, the cladding202may be distorted mechanically, chemically, or by other similar processes that affect the index of refraction of the cladding202. The cladding202may also be disrupted to allow light emission. Next, non-twisted segments106a,106b, and106care provided where the optically-transmissive fibers102are not twisted. Next, the twisted segments104aand104band non-twisted segments106a-106care alternated. Finally, the number of bends116per unit length may be increased as the length of the ribbon100increases. As discussed above, increasing the number of bends116per unit length can compensate for the attenuation of light as the length of the ribbon100increases. By providing more bends116per unit length, more light can be emitted from the ribbon100.

The sheath110may be coupled to both the twisted segments104aand104band non-twisted segments106a-106c. Alternatively, the sheath110may be coupled only to the twisted segments104aand104b. The light source302can be disposed at one end of the optically-transmissive fibers102and coupled to a non-twisted segment106a. A second light source (not shown) may be coupled to the opposite end of the ribbon100such as at segment106c. Corona etching the plurality of optically-transmissive fibers102may be done prior to coupling the optically-transmissive fibers102to the sheath110, preferably before placing optically-transmissive fibers102adjacent to one another.

To manufacture a ribbon1200with ferrules120, the optically-transmissive fibers102of a non-twisted segment106a-106cwhere the fibers102are not coupled to the sheath110are gathered together to form a bundle. Then, preferably the wrapping124is placed over the ends of the fibers102. The wrapping124is cut to a predetermined length, and preferably the length of the wrapping124is such that it does not substantially extend into the ferrule120. The fibers102are approximately cut to length with, preferably, scissors. A ferrule120of predetermined shape is placed on the cut fibers102. The fibers102are then sheared, preferably by a hot knife, at a distance extending from the front of the ferrule120by approximately 1.27 mm (approximately 0.050 inches). The shape of the ferrule120is determined by the mating receptacle of the light source302. The ferrule120and the fibers102are placed in an oven to couple the ferrule120to the fibers102. The cut ends of the fibers102are then polished to a glass-like finish.

As apparent from the above description, the present invention provides an illumination fiber optic ribbon. Optically-transmissive fibers are placed adjacent to each other to form a generally flat ribbon. Twisting adjacent optically-transmissive fibers forms twisted segments which alternate with non-twisted segments where adjacent optically-transmissive fibers are not twisted. The twisting of adjacent-optically transmissive fibers forms bends from which light is emitted. The number of bends may increase as the length of the ribbon increases. A sheath may substantially surround the optically-transmissive fibers.

Accordingly, when a light source is coupled to one end of the optically-transmissive fibers, the light source emits a light flux into one end of the optically-transmissive fibers. The light flux then emanates from the bends to provide illumination.