WO1999066355A2

WO1999066355A2 - Lighting fixture for fiber optics and method

Info

Publication number: WO1999066355A2
Application number: PCT/US1999/013901
Authority: WO
Inventors: Christopher F. Bragg
Original assignee: Fiberstars, Inc.
Priority date: 1998-06-19
Filing date: 1999-06-18
Publication date: 1999-12-23
Also published as: WO1999066355A3

Abstract

Lighting apparatus includes an elongated body of optical material forming an optical channel (5) having high refractive index, and is adapted to receive luminous flux (13) at one or both ends of the body for lateral emission of luminous flux at substantially uniform surface intensity per unit length of the channel. Discrete diffusive targets (15, 16, 17, 18) are disposed at aperiodically-spaced locations on a smooth interface of the channel with surrounding air to control the uniformity of diffused light per unit length laterally emitted from the channel. A computer-implemented calculation determines optimum orientations of discrete targets on the interfacing surface for substantially uniform intensity of laterally-emitted luminous flux per unit length from the optical channel.

Description

LIGHTING FIXTURE FOR FIBER OPTICS AND METHOD

Field of the Invention:

This invention relates to optical fiber lighting apparatus, and more particularly to apparatus and method for substantially uniformly laterally distributing illuminating light flux from a linear fixture coupled to a cable of optical fibers. Background of the Invention:

Numerous lighting applications require high-intensity illumination without infrared or ultraviolet radiation commonly associated with conventional filament or gas-discharge types of electrical light sources. Conventional fiber optic lighting apparatus usually obviates the undesirable infrared and ultraviolet radiation and is commonly employed to direct illumination from an end of an illuminated cable of optical fibers toward an object to be illuminated. However, such lighting apparatus also typically requires a lens system to distribute luminous flux from an end of an illuminated cable of optical fibers. Alternatively, other known lighting apparatus relies upon lateral emission of luminous flux from the optical fibers of an optical cable. Apparatus of this type is described in the literature (see, for example, U.S. Patent No. 4,763,948). Certain other lighting applications rely upon optical fibers to deliver luminous flux without infrared or ultraviolet radiation at a location that is remote from the light source. In such applications, it is commonly desirable to distribute luminous flux substantially uniformly along a linear segment of optical conduit in order to provide attractive, uniform lighting such as for display cases, work surfaces, perimeter accents, and the like, that are commonly accommodated by fluorescent or neon lights. Summary of the Invention:

In accordance with one embodiment of the present invention, an optical channel of optical material having an index of refraction greater than the index of refraction of air is illuminated from one or both ends and includes polished surfaces to inhibit lateral emission of luminous flux from within the channel into the surrounding air, except at selected distributed locations along the length thereof between the ends. Specific diffusively reflective targets are disposed in spaced relationships along a surface of the optical channel opposite locations therealong from which substantially uniform surface illumination per unit length is desired. Various patterns of targets that exhibit diffusive and reflective properties (i.e., DR targets) are arranged on the surface of an optical channel or light guide of diverse shapes and lengths to promote uniform or controlled lateral emission of luminous flux per unit length from the optical channel or light guide. A computer-implemented program computes the spatial positioning of the DR targets on a rear surface of the optical channel or light guide at locations opposite a front surface thereof from which substantially uniform luminous flux per unit length is desired. Description of the Drawings:

Figure 1 is a sectional view illustrating representative luminous ray traces within an optical channel;

Figure 2 is a sectional view illustrating representative luminous ray traces within an optical channel that includes discrete DR targets at spaced locations;

Figure 3 is a graph illustrating a theoretical distribution of output illumination from an elongated optical channel according to the present invention;

Figure 4 is a chart illustrating the calculations of areas and positions and relative brightness of DR targets according to the method of the present invention; Figure 5 is a graph illustrating actual output illumination from an elongated optical channel having DR targets disposed thereon at locations and with areas as illustrated in the chart of Figure 4;

Figure 6 is a flow chart illustrating the process according to the present invention; and

Figure 7 is a graph illustrating output illumination about the axis of an optical channel prepared according to the present invention. Detailed Description of the Invention:

In fiber optic lighting apparatus as described in the U.S. patent cited above, an optical channel is commonly formed of optical fibers that are arranged to emit luminous flux in lateral directions from illumination supplied at one or both ends of the optical fibers. Optional backside reflectors or diffusers and front side lenses may be employed to enhance the lateral emission of luminous flux from within the optical fibers. Additionally, scattering particles may be distributed uniformly along the lengths of each optical fiber to promote lateral diffuse emission of luminous flux through the sidewalls of the fibers. Lighting apparatus of these types commonly emit luminous flux laterally from each optical fiber and then require equipment external to the optical fibers such as back side reflectors to control the directionality of the laterally-emitted luminous flux.

With reference to the sectional view of Figure 1, there is shown an optical channel or light guide 5 of optical material such as glass or acrylic resin that extends linearly from an inlet port 6 that is optically coupled to an end of a fiber optic cable 7. Each unit length 8 of the surface of the optical channel subtends a decreasingly smaller angle, β, of luminous flux from the inlet port 6 at an end of the channel. Accordingly, the intensity of luminous flux emitted from the optical channel 5 per unit length 8 decreases non-uniformly with distance from the inlet port 6. In accordance with the embodiment of the present invention as illustrated in Figure 2, discrete diffusively reflective (DR) targets are disposed in spaced relationships at the interface of the optical channel 5 and surrounding air to provide aperiodic locations along the channel 5 at which luminous flux from within the channel is substantially laterally emitted through and along the channel to promote emission of luminous flux primarily perpendicularly from the surface of the channel. By establishing discrete, DR targets 15-18 (in contrast to continuous diffusive surface treatments), the uniformity of laterally- emitted luminous flux per unit length may be more readily controlled. Specifically, DR targets 15-18 ideally promote diffused rays that exhibit a cosine pattern of ray intensities measured with respect to the perpendicular to the diffusing surface, and not to the direction of an incident ray. This provides the advantage of altering the direction or angular orientation of incident light to an orientation for emission obliquely from the optical channel or light guide 5. In the pictorial illustration of Figure 2, ray traces 1, 2, and 3 are shown emanating from inlet port 6 at an illuminated end of the optical channel 5 within an angle 11 of illumination that is attributable to the numerical aperture of the illuminating optical fiber cable 7. Discrete DR targets 15-18 are shown distributed aperiodically along the length of the channel 5 and in contact with the optical surface at the interface of the material of the optical channel 5 with the surrounding air. The channel 5 is solidly formed of optical material (such as methyl methacrylate or lead-doped glass) having greater index of refraction than the index for air (index = 1.0), and the surfaces of the material optical are generally smooth and devoid of surface anomalies to assure maximum internal reflection and minimum scattering 9, 12 at the interfaces of the material with surrounding air. This assures retention of substantially all luminous flux 13 within the channel 5 at all locations along the length, except at locations relative to the DR targets 15-18. As illustrated in Figure 2, ray traces 1, 2, and 3 of luminous flux within the angle 11 of incident illumination (coupled through a smooth end wall of the channel) may internally reflect from smooth interfacing walls one or more times along the length of the channel 5, and may also reflect from a DR target 15, 16, 18 for lateral emission through an opposite surface. Other ray traces may traverse the channel 5 via multiple internal reflections at interfaces 9, 12 in combination with reflections at selected DR targets. Diffused luminous flux 19 from a discrete target is shown incident upon the interface ■ , surface at an angle greater than an angle for total internal reflection thereat, and some of such diffusively reflected luminous flux emerges from the wall of the channel 5 at locations within diffusion angles from the discrete DR targets 15, 16, 18. Discrete DR targets 16, 18 spaced at greater distances from the inlet port 6 receive incident luminous flux in combinations of flux that is internally reflected from interfaces, and that is diffusively reflected from discrete DR targets, and that is directly projected from the inlet port 6. Thus, the contributions to diffused luminous flux 19 from a given DR target is due to such total internal reflections, diffuse reflections, and projections of flux within the channel 5 and may be calculated according to the process embodiment of the present invention for each discrete target 15-18 as a function of position or distance from the inlet port 6. Each discrete target 15-18 may be varied in spacing relative to the inlet port in aperiodic array (with closer spacings at greater distances), or the diffusive targets 15-18 may vary in diffusively reflective properly (as, for example, by color variations, area of the target, or the like) as a function of distance from the inlet port 6, with greater ratio of disfuse-to-internally reflective areas or increased diffuse reflection at greater distances.

Alternatively, combinations of such variable parameters may also be used. Thus, by controlling one or more of the spacings, areal sizes, and reflectiveness of discrete DR targets 15-18 positioned along the length of the channel 5, the intensity of laterally-emitted luminous flux 19 per unit length may be rendered substantially uniform over the length of the optical channel 5. Additionally, such calculations of luminous flux intensity per unit length may be performed for illuminating flux supplied to the channel 5 from opposite ends thereof, with the results of the separate calculations for each end of illumination substantially superposed to yield more uniform intensity of laterally-emitted luminous flux per unit length of the channel 5 between illuminated ends thereof. Intermediate discrete DR target 20-22 may be spaced away from other discrete DR targets at aperiodic positions along the length of the channel as may be desired to further enhance uniformity of laterally-emitted luminous flux per unit length along the channel 5. The pattern of DR targets can thus be distributed to uniformly illuminate or to produce many non-uniform patterns of illumination, as desired. An optical channel 5 disposed to receive illuminating flux at only one end may include a DR target substantially covering the opposite other end. Discrete DR targets 15- 18 are spaced from each other to expose regions of surface walls of the channel 5 that interface with surrounding air to form refractive interfaces attributable to the difference of indices of refraction of the surrounding air and of the material forming optical channel 5. However, at each internal reflection 9, 12 of luminous flux at such interfaces, a small portion of the internal luminous flux traverses the interface and is laterally emitted from the channel 5 due, for example, to scattering in the acrylic material and to reflection off the front surface of the channel. In accordance with one embodiment of the present invention, a spectral or diffusive reflector 23 is disposed out of contact with a back surface of the channel 5 (on which the discrete DR targets 15- 18 are formed) in order to re-direct the light lost out the back of the channel to the back surface of channel 5 for passage therethrough and lateral emission from an opposite, or front surface of the channel 5. The discrete DR targets 15-18 may be formed as spots or strips on a smooth surface of an optical channel 5 using highly diffusively reflective material such as white paint or ink containing particles of barium sulfate or titanium dioxide in a binder. Such discrete DR targets 15-18 are illustrated and described as positioned in one dimension along the length of an optical channel (such as an acrylic rod of about V -inch square dimension), but it should also be understood that such targets may also be positioned at discrete 2-dimensional coordinate locations relative to an inlet port 6 of an optical channel 5 having substantial width relative to length. The process according to the present invention, described later herein, calculates 2-dimensional coordinates of diffusive targets based upon internal reflections from side walls and angular dependence of the transverse direction that are involved.

Referring now to Figure 3 and to the flow chart of Figure 6, there is shown a graph 31 of theoretical luminous intensity derived from a lighting apparatus of Figure 2 for which a body 5 of selected length, say one meter is mathematically segregated 41 into arbitrary units or divisions of resolution, say 500 or 1000 divisions, between the ends thereof. One facet (surface) of the body 5 receives a pattern of highly diffusively-reflective surface treatments 15-18, as previously described, that are capable of directing out of the body luminous flux from within the body. These diffusive-reflective regions or targets (DRs) are thus positioned within increments of area of the faceted surface which, for example, may be approximately 1 cm wide and 1 meter long, with resolution of 1000 divisions selected in the above example according to the process of the present invention, to yield 1 cm x 1 mm elements of area. The position of elements along the body are designated 43 by an array XN_(n), where n has integer values from 1 to the total number of elements of selected resolution, and each element may be considered as ON or OFF, depending upon whether such element(s) constitute a DR is, or not. In accordance with the process of the present invention, each element of area is assigned an identifier which designates 45 the element as a DR or as an unobstructed portion of the facet surface.

The radiance of each element identified as a DR is next calculated 47 with respect to its position relative to location of the input aperture 6 of the body 5, and to other DR's. This calculation assumes that luminous flux is well mixed or 'homogenized' within the body at each location of an element. In practice, this assumption can be enhanced in accuracy by including an entry or lead-in portion 4 of the body 5 adjacent the entry port 6, as shown in Figure 2. That is devoid of DR's to ensure more uniform luminous flux intensity within the body. "Well-mixed" luminous flux thus means that the intensity and angular distribution of luminous flux at all points in a cross-sectional plane of the body are substantially constant. A DR at this plane will be illuminated by a portion of luminous flux passing through the plane with a radiance determined by the area of the DR, and the numerical aperture (NA) of the optical fiber(s) that couple luminous flux to the entry port 6 of the body 5 (essentially, establishing the skew angle from the longitudinal axis of the body at which luminous flux is launched within the body). The total luminous flux passing through each such cross-sectional plane diminishes at each DR with distance away from the entry port and can be computed and stored for calculations of radiance 49 at each successive DR. From such succession of calculations along the length of the body 5 from the entry port 6, the areas (in increments of 1 mm, all 1 cm wide, for the example set forth above) and locations along the length of the body can be computed 51, as illustrated in the graph of Figure 4. This graph illustrates the computational results of the process according to the present invention by which the DR areas and locations along the length of the body are determined. Specifically, the DR's are represented by top segments 33 of the chart that are spaced approximately equally along the length of the body, but with different areas that generally increase with distance from the input end (near the origin). A desired far-field distribution of light flux, as indicated in the graph of Figure 3, can be selected and the pattern of luminous regions and the radiance of each region along the optical channel can be determined (on a scale of arbitrary units of radiance) according to the present invention. This graph illustrates the illuminance on a planar surface disposed at a constant selected distance away from the body 5 of the optical channel along the length thereof, and such surface may be mathematically divided into discrete regions for determining contributions of luminous flux thereto from each DR, assuming diffusely reflective luminous flux intensity from each DR. The intensity of illumination of the surface regions may thus be calculated, and may be subjected to a least squares fit to a desired output 55 in conventional manner, for example, as described in Numerical Recipes. The Art of Scientific Computing, Chapter 14, equations 14.1.1. and 14.1.2, Cambridge University Press (1986). The pattern of DR's, controlled by ON or OFF analogy, may be modified from initial determination, as illustrated in Figure 4, and recalculations 57 can be performed iteratively to yield substantially the desired illuminance.

Referring now to Figure 5, there is shown a graph 35 of actual data on illuminance in units of foot-candles on a planar surface disposed about 20 cm away from the body 5 of lighting apparatus. The body 5 is approximately 1/2" square and about 2 feet long, containing a pattern of DR's on one facet surface thereof, in an array as illustrated in Figure 4, and illuminated at one end by luminous flux supplied from a bundle or cable of optical fibers having a numerical aperture of about 0.51. It should be noted that the curve 35 of actual data in Figure 5 resulting from lighting apparatus fabricated according to the present invention closely resembles the theoretical luminous output illustrated by curve 31 of Figure 3. In addition, with reference to Figure 7, there is shown a pattern of illumination from lighting apparatus fabricated according to the present invention, in a plane normal to the elongated axis of the body 5, showing a confined pattern of illumination centered substantially about the angular orientation directly in front of the body. Similar patterns are obtained in other lateral planes at varying distances from the entry port 6, with some variations in the maximum luminous output indicated in such planes at locations along the axis of the body 5 between the ends thereof, with rear reflector 23 in place. From this graph, it should be noted that forward-directed lighting is achieved without the aid of lenses or focusing schemes disposed along the length of the elongated body 5.

For an optical channel disposed to be illuminated from opposite ends, the process of the present invention operates on a desired illumination pattern that is generally non-uniform with a decrease in luminous output as a function of increasing distance from an illuminated end. The luminous intensity at each DR is selectively decreased more with distance from the illuminated end than for a single-ended channel, and over essentially one half the total length of the channel. Then, the pattern of DR's is copied and inverted or assembled on the remaining one half length from the opposite end. The original pattern of DR's and its copy are thus connected co-linearly to form a complete pattern that is twice as long as the original pattern, but that extends between the ends and that is substantially symmetrical about the center of the channel between the ends thereof. Luminous flux that might have migrated to the end of each half-length pattern now adds to the luminous flux in the other half-length beyond the center for added intensity of luminous output over the entire length of the channel, substantially in excess of the luminous intensity attainable from two single- ended channels placed in close proximity.

Therefore, the method and apparatus of the present invention provide an illuminating fixture with intense luminous output and enhanced directionality from a source of luminous flux supplied to one or both ends of a linear optical channel.

Claims

What is claimed is:

1. Lighting apparatus for operation on luminous flux supplied thereto, lighting apparatus comprising: a body of optical material having an end oriented along a major axis, and being substantially transparent to luminous flux coupled thereto at said end, the body having a cross section normal to the major axis with dimensions in othogonal directions substantially smaller than a length dimension along the major axis of the body, the body including a major surface oriented along the major axis that is substantially devoid of surface anomalies from smooth; and a plurality of optical targets disposed on the major surface at spaced locations along the major axis from said end for diverting thereat out of the body luminous flux from within the body, said optical targets being arranged in a ratio of covered area to exposed area of the major surface per unit area thereof that varies with distance along the major axis from said end.

2. Lighting apparatus as in claim 1 in which said body includes an elongated rod of optically transparent material including said end and another end at an extreme of said length dimension, and said another end is disposed to receive luminous flux coupled thereto through optical fibers.

3. Lighting apparatus as in claim 2 in which the major surface of said body includes a length dimension along the major axis that is substantially larger than a lateral dimension thereof in a direction normal to the major axis, and said optical targets are disposed in spaced locations along the major surface as strips covering a selected portion of the lateral dimension.

4. Lighting apparatus as in claim 3 in which the body includes substantially rectangular cross section and the optical targets are disposed at spaced locations along a common major surface of the rectangular body as strips extending laterally substantially across the common major surface.

5. Lighting apparatus as in claim 1 in which the optical targets spectrally reflect luminous flux for emission laterally from the body.

6. Lighting apparatus as in claim 1 in which the optical targets diffusely reflect out of the body luminous flux from within the body.

7. Lighting apparatus as in claim 1 in which said ratio varies with distance from said end.

8. A method for forming an optical illuminator having an elongated body of transparent material for operation on luminous flux to be supplied to an end of the body, the method comprising: selecting an elongated portion of surface of the elongated body having a substantially aligned orientation for disposition thereon of optical targets; disposing a plurality of optical targets on the surface of the elongated body at spaced locations thereon to divert out of the body luminous flux from within the body from an area of each optical target that is selected in relation to distance from said end along an elongated dimension of the body, the spaced locations thereon between optical targets leaving exposed segments of the elongated portion of surface in a ratio of area of optical targets to area of exposed segments that varies with distance from said end.

9. The method according to claim 8 in which the elongated body includes another end remote in the elongated direction from said end for operation on luminous flux supplied to said end and to said another end, the method comprising: disposing a plurality of additional optical targets on the surface of the body at spaced locations thereon to divert out of the body luminous flux from within the body from an area of each additional optical target that is selected in relation to distance from said another end, the spaced locations between said additional optical targets leaving exposed segments of the elongated portion of surface in a ratio of area of additional optical targets to area of exposed segments that varies with distance from said another end.

10. The method according to claim 9 in which the plurality of optical targets and said additional plurality of optical targets are disposed on the surface of the elongated body at spaced locations thereon for which the ratio of area of optical target to exposed area varies as a function of the distance between said end and said another end.