Large screen fiber optic display with high fiber density and method for its rapid assembly

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BACKGROUND OF THE INVENTION

1. Field of the Invention

Large Screen Displays (LSD's) can be defined as any dynamic display which can be viewed by more than one person and is at least two feet wide. The LSD market is diverse, with many differing products and technologies, each having certain strengths and weaknesses, competing to fill the needs of the end user. Applications requiring outdoor use in direct sunlight have traditionally been served best by CRT (Cathode Ray Tube) or LED (Light Emitting Diode) displays, while indoor applications may be served by video walls or front/rear projection systems. The CRT/LED systems, while very bright (typically 4-6 kcd/m.sup.2), are very expensive, and offer only marginally acceptable resolution. Moreover, they can only be viewed at a distance because of the need for the RGB (Red-Green-Blue) pixels to optically converge. Thus, they are not cost effective or suitable from resolution or minimum viewing distance criteria for indoor applications. Video walls are adequate for indoor use, but are bulky, not very bright (typically 250 cd/m.sup.2), and suffer from the appearance of mullions between each of the displays comprising the wall. Data projectors offer high resolution, yet, because of the constraints of projection systems, are not suitable for many applications. (Typically such a projector must be located several meters or more from the projection surface.)

Fiber optic LSD's offer substantial improvements over current CRT- and LED-based displays, due to their smaller depth, lighter weight, and elimination of sensitive and expensive electronic components on the surface of the display, while delivering superior resolution and adequate brightness for direct sunlight viewing. Because no RGB convergence is required in fiber optic displays, the minimum viewing distance is considerably less than that of CRT/LED displays.

Fiber optic displays are superior to video walls because they lack mullions, are brighter, more rugged, and are much thinner. Fiber optic displays have an advantage over projection systems in that the display is a "stand-alone" unit which can be easily moved and installed at almost any location.

Clearly, fiber optic displays have compelling advantages over competing technologies. Fiber optic displays, however, are not without shortcomings. In fabricating large displays (e.g., >100 inches diagonal), the cost of optical fiber becomes considerable. Installing and managing the large amount of optical fiber required for a large display (as many as 120,000 individual fibers for a six by eight foot display) is tedious, time-consuming, and, therefore, costly, inasmuch as each fiber must be cut to length, polished for optimum light transmission, individually inserted into the display and positioned precisely with respect to the display surface, and cemented into place. The opposite ends of the fibers must be arranged in ordered arrays and affixed into position as an input matrix. All of these procedures must be performed without damage to the fiber or its somewhat fragile cladding, in order to assure good light transmission through the fiber. Furthermore, the long, ordered fiber bundles are difficult to manage and susceptible to damage. These problems become particularly severe when designing immersive LSD systems, such as an interactive gaming environment. The purpose of this invention is to address and overcome these and other shortcomings in state-of-the-art manufacturing and assembling of fiber-optic based large screen displays.

This application is a continuation in part of application Ser. No. 09/482,290

2. Description of Related Art

Methods currently used for the manufacture and assembly of large fiber optic display screens are both time-consuming and labor-intensive since each fiber must be installed individually in the display surface and then routed to the input matrix. Furthermore, each fiber must occupy an assigned location in the input matrix, corresponding to an assigned location in the display, in order that an image projected onto the input matrix will be faithfully reproduced on the display. The time and labor required to assemble such displays results in a cost per square foot (of display surface) which is so high as to be essentially non-competitive with other display technologies, thereby effectively eliminating fiber optic displays from this marketplace, even though such displays have many other advantages over competing technologies.

Numerous attempts have been made to develop large screen fiber optic displays which can be manufactured and assembled efficiently and are, therefore, cost-competitive with other display technologies. Although improvements have been made, none of these attempts have been very successful.

U.S. Pat. No. 4,839,635 discloses a fiber optic display system in which optical fibers transfer an image from an input matrix to a display matrix. The display system of this invention is constructed from a large number of small blocks, and purports to be a system which is easily manufactured. However, detailed examination of the patent indicates primarily manual assembly of the many parts. For example, the fibers are handled individually to form groups of eight. A group of eight fibers is manually wrapped with metal foil tape to form a close-packed element of the input matrix while the opposite end of the group is manually disposed into a set of foam blocks which must be cemented together to secure the fibers at the display matrix. It is the purpose of our invention to replace most of these manual operations with machine operations.

U.S. Pat. No. 5,911,024 discloses an apparatus and method of assembly for a fiber optic image enlarger that operates in cooperation with a CRT display. The assembly described involves the formation of individual fibers with male and female ends, making it time consuming, even with automation, to construct a display. The display apparatus described is also costly in terms of the volume of fiber used.

U.S. Pat. No. 5,400,424 discloses a fabrication method for a fiber optic display by joining hexagonal modules with conical projections, each conical projection fixing a discrete optical fiber. The intent of the conical projections is to scatter ambient light in order to enhance the appearance of the display. No mention is made of the problems of fiber management. Moreover, the patent discusses techniques to improve the wide-angle characteristics of the display by making V grooves on each fiber end. Clearly, any manufacturing process that involves handling individual fibers will not be inexpensive or simple to manufacture.

U.S. Pat. No. 3,853,658 discloses a fiber optic image magnifier panel and method for manufacture. In this patent the fibers are threaded through a metal aperture plate. As with the previous patent, concepts for simple and repetitive fiber management are not discussed.

In U.S. Pat. Nos. 4,773,730 and 4,786,139 Sedlmayr discloses an optical light transfer apparatus and method for manufacture. This method entails piecing together multiple wedge-shaped modular fiber display screen devices with the use of many fastening items to form a large screen display. This method involves a high part count and considerable manual assembly, both of which result in a high-cost product.

In U.S. Pat. No. 5,376,201 Kingston discloses a more elegant manufacturing method: an apparatus for forming fiber optic magnification devices. This method involves the simultaneous fabrication of both an input matrix and a display matrix on a large drum, but using a single spool of fiber, which is very time-consuming. Furthermore, a large display requires a significant separation between the input and display matrices, requiring fiber optic cables of eight to ten feet or more in length. Using Kingston's method would require a drum of six or more feet in diameter to fabricate such cables. The drum itself would be a very costly tool.

U.S. Pat. No. 5,009,475 discloses a molded component in which are formed a plurality of in situ waveguides, preferably tapered. These components can be designed and assembled to function as an image enlarger. Two methods of light propagation are described. First, the authors propose creating hollow light guides and then "backfilling" the guides with an optical plastic or glass which has a higher index of refraction than the surrounding mold material. In practice this is difficult to do because of the long optical paths. Over the length of these optical paths, it is difficult to prevent the formation of bubbles and inhomogeneities in the light transmitting medium, resulting in significant optical losses. The alternative is to use hollow light guides coated with a reflective material. This method as well is difficult to manufacture, and is characterized by large light transmission losses.

BRIEF SUMMARY OF THE INVENTION

This invention discloses a large screen fiber optic display with high fiber density and novel methods for simplifying and thereby cost-reducing the manufacture and assembly of large screen fiber optic displays containing very large numbers of individual fibers, by installing and managing the fibers in subgroups (of approximately 10-100) and groups (of approximately 100-1000) rather than individually.

DESCRIPTION OF FIGURES

FIG. 1 is an illustration of two large screen displays (1, 2); a planar display (1) and a contoured display (2) with multiple curvatures.

FIG. 2a is an illustration of a group of flat fiber optic ribbon cables (4) with fiber optic connectors (6) installed at one end for quick connection to a display tile (3), and formed into an ordered array (5) at the other end to form a portion of the input matrix (13); for simplicity, only a representative sample of the totality of cables (4) and connectors (6) is illustrated. FIG. 2b is a cross-sectional view of a single ribbon cable (4) (subgroup of optical fibers) illustrating the fibers (7) embedded and secured in a planar (ribbon) configuration by the thin matrix adhesive (8). FIG. 2c is an alternative cross-sectional view of a single ribbon cable (4) (subgroup of optical fibers) illustrating the fibers (7) secured in a planar (ribbon) configuration by a two-part retention clip (22).

FIG. 3a is an illustration of an injection-molded display tile (3), with molded-in perforations to accept molded light guide arrays (11); FIG. 3b is an illustration of the interconnection between the display tile (3) and the input matrix (13), comprised of a group of molded light guide arrays (11), a group of optical fiber manifolds (20) consisting of arrays of fibers (7) on thin substrates (10), fiber optic connectors (6) (mating pairs), and a group of fiber optic ribbon cables (4) terminating in an ordered array (5) which forms a part of the input matrix (13); FIG. 3c is an end view of the ordered array (5) of optical fiber ribbon cables (4) formed into a portion of the input matrix (13); and FIG. 3d is a cross-sectional view through a molded light guide array (11) and display tile (3), showing the relationship of the optical fibers (7) to the light emitters (12).

FIG. 4 is an illustration of the back of a large screen display (1, 2), showing how the individual display tiles (3) are positioned and secured to form the viewing surface of the display (1, 2), and showing schematically the relationship of the video projector (18) and control computer (19) to the input matrix (13). (In an actual display the input matrix (13), video projector (18), and control computer (19) are located in an enclosure in the base of the display (1, 2).

FIGS. 5a,b defines coordinate systems for the display surface (1, 2) (5a) (viewed from the front) and the input matrix (13) (5b) (viewed from the input side) and illustrates how a typical display tile (3) on the display surface, having coordinates X.sub.d =j and Y.sub.d =k, is mapped to a corresponding ordered array of fibers (7) comprising a portion of the input matrix (13), having coordinates X.sub.m =n-j and Y.sub.m =k, where n is the total number of tiles (3) comprising the width of the display surface (1, 2).

DETAILED DESCRIPTION OF THE INVENTION

This invention comprises a method for the semi-automated manufacture and rapid, low-cost assembly of large screen fiber optic displays containing a very large number of individual fibers (thousands to hundreds of thousands, or more). Whereas the manufacture of state-of-the-art fiber-optic displays requires the manual installation of large numbers of individual, small optical fibers, this invention teaches automated and semi-automated methods for managing the fibers in subgroups of approximately ten to one hundred, and in groups or ordered arrays of approximately one hundred to one thousand, thus reducing the manufacturing and assembly labor by corresponding factors. The description of this invention, which follows, is facilitated by reference to the figures listed above.

The invention teaches a systematic method for the manufacture of large, ordered arrays of optical fibers by a) dividing the manufacturing process into several steps, some of which are fully automated and some of which are semi-automated for efficient, low cost mass production, and b) installing and managing the optical fiber in subgroups and groups rather than individually. The manufacturing steps are summarized below, and described in detail in subsequent paragraphs:

1. The automated manufacture of flat, multi-fiber ribbon cable (4) in continuous lengths;

2. The semi-automated (or automated) manufacture of flat, multi-fiber manifolds (20) to set the desired fiber pitch at the display surface and match this spacing to the fiber pitch of the ribbon cable (4);

3. The automated manufacture of molded arrays of light guides (12);

4. The manual or semi-automated insertion and locking of multi-fiber manifolds (20) into molded light guide arrays (11);

5. The automated manufacture of molded display tiles (3), perforated to accept arrays of light guides (11);

6. The automated manufacture of fiber optic interconnects (6) to join multi-fiber manifolds (20) to multi-fiber ribbon cable (4);

7. The automated attachment of fiber optic interconnects (6) to multi-fiber ribbon cable (4) and to multi-fiber manifolds (20);

8. The semi-automated formation of groups of flat optical fiber ribbon cables (4) into square (or rectangular) ordered fiber arrays (5);

9. The manual insertion of multi-fiber manifold (20) and light guide arrays (11) into molded display tiles (3);

10. The manual assembly of a plurality of identical display tiles (3) with light guide arrays (11) to form a display surface;

11. The manual engagement of fiber optic interconnects (6) which join multi-fiber ribbon cable (4) assemblies to multi-fiber manifold (20) and light guide arrays (11);

12. Formation of the input matrix (13);

13. Final assembly procedure.

Each of these manufacturing steps is discussed in detail below, with reference to FIGS. 1-5.

1. Automated Manufacture of Flat, Multi-Fiber Ribbon Cable in Continuous Lengths

An optical fiber (7) subgroup consisting of a planar, multi-fiber ribbon cable (4) is manufactured in continuous lengths using an automated multi-head cabling machine. The cabling machine is equipped with feeder spools of plastic (or glass) optical fiber (7), the number of spools corresponding to the number of fibers in the ribbon cable, typically 10-100. The cabling machine is also equipped with a multi-head die, the number of heads also corresponding to the number of fibers (7) in the ribbon cable (4), to guide each fiber (7) into its correct position in the cable (4). The fibers (7) are pulled into the die and guided into position on an UV-curable matrix (8), a continuous ribbon-like adhesive system which bonds together the fibers (7) and maintains the desired ribbon configuration. As the fibers (7) are guided onto the ribbon matrix (8), the matrix is immediately cured by a UV (ultraviolet) curing system, thus forming a continuous planar fiber ribbon cable (4) in which the fibers are separated only by a small amount of matrix adhesive (typically less than 25 micro-meters), that is, the fiber pitch (FP) is less than 25 micro-meters greater than the fiber diameter (FD) (FP and FD are illustrated in FIG. 2c). The continuous length of optical fiber cable (4) which can be manufactured is determined by the amount of fiber (7) on the spools, typically 6-9 km or more. Alternatively, in lieu of an adhesive matrix, the cabling machine may be designed to retain the fibers (7) in a planar, ribbon configuration by installing two-part retention clips (22) disposed systematically along the cable (4) length. FIG. 2c is a cross-sectional illustration of a ribbon cable (4) formed using retention clips (22). The two mating parts of the clip (22) are designed to snap together and interlock to capture the fibers (7) in a planar configuration. Since there is no adhesive matrix to separate the fibers (7) in this alternative construction, the fiber pitch (FP) is equal to the fiber diameter (FD). FP and FD are illustrated in FIG. 2c.

2. The Semi-Automated (or Automated) Manufacture of Flat, Multi-Fiber Manifolds

The function of the multi-fiber manifolds (20) is to adjust the fiber pitch from the tight spacing of the input matrix (13) and fiber ribbon cable (4) to the wider pitch required for the light guides (11) on the surface of the display tiles (3). There are at least two manufacturing options for the manifold configuration, involving somewhat different technologies: a) a continuation of the fiber ribbon cable (4), with separation, spacing, and arrangement of the individual fibers (7) into the manifold (20) configuration; b) a separate entity fabricated by cutting and affixing individual fibers (7) to a thin thermoplastic substrate (10), the fibers (7) being arranged in the desired manifold (20) configuration which is then fitted on one end with a fiber optic connector (6) and mated to the fiber ribbon cable (4), said cable (4) being fitted with a mating fiber optic connector (6). Although there are decided differences in how these two options would be manufactured, in the end the primary difference is that option (b) requires a multi-fiber connector (6) to join the manifold to the cable (4), whereas option (a) does not require a connector (6). The primary advantage to option (a) is lower parts cost, since fiber optic connectors (6) are not required; the primary disadvantage to option (a) is that each display tile (3) has a length of fiber optic cable (4) attached to it, making it more awkward to handle during assembly, and thus increasing assembly costs. Using option (b) only the manifolds (20) are attached to the display tiles (3) initially, making them much easier to handle during assembly. (The fiber optic cables (4) are connected following the assembly of all the display tiles (3). However the disadvantage of option (b) is the connector (6) requirement, adding thus to the parts cost.

The manufacturing process for option (a) consists of the following steps:

1) Working with one fiber ribbon cable (4) length at a time, and separating out the individual fibers (7). This can be done during the cable manufacturing process by separating the fibers (7) from the UV-curable matrix (8) for a short region along the cable (4), and repeating this separation at pre-selected intervals.

2) The cable length with fibers (7) separated at one end is guided into a precision fixture which positions and spaces all the individual fibers (7) according to the manifold (20) configuration.

3) A thin thermoplastic substrate (10) with adhesive (UV-curable or other type) on one side is placed into the precision fiber (7) fixture, at a pre-determined location designed specifically for the substrate, with the adhesive and substrate in contact with the fibers (7) in the fixture.

4) The adhesive is cured and the fiber manifold (20) with cable (4) attached is removed from the fixture. The fiber manifold (20) is now a fiber array secured by a thin thermoplastic or polyimide sheet.

5) The fiber manifold (20) is mounted in a second fixture having a cutting edge which cleaves all fibers (7) simultaneously.

6) The fiber manifold (20) is now ready for insertion into a molded lightguide array (11).

The manufacturing process for option (b) consists of the following steps:

1) Individual fibers (7) are cut to approximate length from a fiber spool and placed in a precision fixture which positions and spaces all the individual fibers (7) according to the manifold (20) configuration.

2) A thin thermoplastic substrate (10) with adhesive (UV-curable or other type) on one side is placed into the precision fiber fixture, in a holder designed specifically for the substrate, with the adhesive in contact with the fibers (7) in the fixture.

3) The adhesive is cured and the fiber manifold (20) is removed from the fixture. The fiber manifold (20) is now a fiber array secured by a thin thermoplastic or polyimide sheet.

4) The fiber manifold (20) is mounted in a second fixture having a cutting edge which cleaves all fibers (7) simultaneously.

5) The input end of the manifold (20) is also secured and cleaved, and then fitted with a multi-fiber connector (6) designed to mate with a connector installed on one end of the flat fiber optic ribbon cable (4).

Alternatively, for option (b), multi-head numerically-controlled machines are available which can lay any optical fiber circuit or pattern on an adhesive-coated polyester, polyimide, or other type of substrate (10). Subsequently the adhesive is cured to fix the fiber configuration and affix the fibers (7) to the substrate (10).

3. Automated Manufacture of Molded Arrays of Light Guides

A molded light guide array (11) is comprised of a linear (strip), square, rectangular or other regular, spaced array of individual light guides (12), or emitters (12), each light guide (12) designed to accept and terminate a single optical fiber (7). Typically the design of an individual light guide (12), including the optical fiber (7) interface and the emitting (12) surface, which is typically a lens, is carried out by optical ray tracing using computer software, a design method which is well-known to those skilled in the art. The functions of the light guide array (11) are several:

1) Each individual light guide (12) serves as the termination point for a single optical fiber (7), and holds the fiber (7) end securely in the desired position, without undue mechanical stress to the fiber (7);

2) The light guides (12) allow light emitted from each optical fiber (7) to diverge (the divergence half-angle being the arcsine of the numerical aperture of the fiber) and grow in spot size to a pre-selected value;

3) The emitting surface of each light guide (12) is either a convex lens, a fresnel lens, or some other type of lens or diffusing optical element which spreads the diverging light cone from each optical fiber (7) into a wide-angle cone, thus enabling viewing of the display (1, 2) from a wide angle.

4) The emitting surfaces may be tailored to distribute the light into a wide angle in the horizontal plane, but not in the vertical plane, or vice versa, depending on viewing requirements, or they may be tailored to achieve any other desired spatial distribution of the light, either symmetrical or asymmetrical. An asymmetrical light distribution may be designed, for example, to direct the light in relation to the disposition of viewing areas in front of the display (1,2), thus maximizing the display brightness where viewers are most likely located.

Although the light guide array (11) may be molded into any desired two-dimensional shape, the preferred embodiments are either a single linear (strip) array, or a double strip (two parallel rows). The single or double strip array is most compatible with subgrouping the optical fibers (7) via flat fiber ribbon cable (4), and with the insertion of fiber manifolds (20) into the light guide arrays (11) to terminate subgroups of optical fibers at the display tiles (3).

The injection-molded light guide arrays (11) are designed to attach to the display tiles (3) in a simple and straightforward manner, for example, by a "snap-in" mechanism, a near-interference fit, fast-cure epoxy or other adhesive, or a combination of these or other methods.

4. The Manual or Semi-Automated Insertion and Locking of Multi-Fiber Manifolds into Molded Arrays of Light Guides

The fiber optic manifolds (20) manufactured in Step 2 are inserted one-by-one into positioning slots molded into the linear light guide arrays (11), one manifold (20) into each light guide array (11) and, correspondingly, one fiber (7) terminating in each light guide (12), and "staked" into place using a periodic controlled mechanical deformation process which compresses the material of the light guide array (11) against the fiber manifold substrate (10), thus locking each fiber manifold (20) into its positioning slot and thereby securing both the entire array (11) and each individual fiber (7) in their respective positions. The staking process may be semi-automated using a staking machine. Alternatively the multi-fiber manifolds (20) may be secured using an adhesive or by a thermal fusion process. For small quantities this process may be pe