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Title:
LIGHT FUNNEL
Document Type and Number:
WIPO Patent Application WO/2010/148389
Kind Code:
A2
Abstract:
A light funnel includes a transparent article having a first base surface, a second base surface, and a peripheral surface. The first base surface is characterized by a first surface area and the second base surface is characterized by a second surface area wherein the first surface area is greater than the second surface area. The light funnel further includes a reflecting coating disposed over the peripheral layer.

Inventors:
KUO, Pao, Kuang (6743 Johnathon Drive, Troy, MI, 48098, US)
Application Number:
US2010/039329
Publication Date:
December 23, 2010
Filing Date:
June 21, 2010
Export Citation:
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Assignee:
WAYNE STATE UNIVERSITY (4043 Faculty/Administration Building, Detroit, MI, 48202, US)
KUO, Pao, Kuang (6743 Johnathon Drive, Troy, MI, 48098, US)
International Classes:
H01L31/052; F24J2/06; F24J2/08
Attorney, Agent or Firm:
PROSCIA, James, W. et al. (Brooks Kushman, 1000 Town CenterTwenty-Second Floo, Southfield MI, 48075, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1. An article comprising: a transparent component having a first base surface, a second base surface, and a peripheral surface, the first base surface having a first surface area and the second base surface having a second surface area, the first surface area being greater than the second surface area and the peripheral surface having a cross section that defines a hyperbola; and a reflecting coating disposed over the peripheral layer.

2. The article of claim 1 wherein the transparent article comprises glass or plastics.

3. The article of claim 1 wherein the first base surface and the second base surface are substantially circular.

4. The article of claim 1 wherein the funnel is a light concentrator when light is incident on the first base surface and a light spreader when light is incident on the second base surface.

5. The article of claim 1 further comprising a photoactive device adjacent to at least one of the first or second base surfaces.

6. The article of claim 1 wherein the photoactive device comprises a device selected from the group consisting of a photodetector, a photovoltaic device, an optical imaging device, and a light emitting device.

7. An article comprising: a support; and a plurality of light funnels disposed in the support, each light funnel of a plurality of light funnels having: a transparent funnel-shaped article having a first base surface, a second base surface, and a peripheral surface, the first base surface having a first surface area and the second base surface having a second surface area, the first surface area being greater than the second surface area and the peripheral surface having a cross section that defines a hyperbola; and a reflecting coating disposed over the peripheral layer.

8. The article of claim 7 wherein the transparent article comprises glass or plastic.

9. The article of claim 8 wherein the transparent article comprises glass or plastic.

10. The article of claim 9 further comprising a photoactive device adjacent to the second base surface.

11 The article of claim 10 wherein the photoactive device includes a plurality of photoactive elements aligned to receive light from the plurality of light funnels.

12. The article of clam 11 wherein the photoactive device is a CMOS imaging device. 13 The article of claim 10 wherein the photoactive device emits light and includes a plurality of light-emitting elements that emits light into the plurality of light funnels.

14. The article of claim 13 wherein the light-emitting elements are light emitting diodes.

Description:
LIGHT FUNNEL

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] In at least one aspect, the present invention is related to an improved light concentrator and light spreader.

2. Background Art

[0002] The collection and manipulation of light is an important aspect of a number of imaging and alternative energy devices. In particular, the desire to develop and improve alternative energy sources is well established. Solar energy based technologies have been particularly desirable because of the lack of accompanying pollution. Solar cells and other photovoltaic devices are limited due to the low energy density of light incident on the Earth's surface. To address this issue, solar devices typically require a large collection area and/or the utilization of a solar concentrator. Currently, many solar collectors employ a lens system with rather small collection angles. Some solar energy systems employ technology that tracks the movement of the sun in order to compensate for the low collection angles and to optimize performance.

[0003] A typical imaging device typically includes a plurality of photocells for collecting the light necessary for imaging. CMOS technology has gained popularity in recent years in comparison with the traditional GaAs imaging devices in spite of the intrinsic less sensitivity and speed of the silicon photocells in comparison with GaAs ones. An advantage of CMOS imaging technology is its compatibility with the standard semiconductor processes, thereby reducing expenses as compared to GaAs processes. A second advantage is the ability to place control and switching circuits next to the photocells. This latter advantage provides increased flexibility in making sophisticated devices. However, the development of CMOS imaging technology suffers from several bottlenecks. The first is the fight for surface area between the main functions, light collection and circuitry. More sophistication in circuitry demands more surface area that cuts into the available area for light collection, which results in less sensitivity and speed. Another issue is the blooming effect.

[0004] LCD monitors are also pixel-oriented devices. An LCD pixel can change its optical property from transparent to partially transparent to opaque in milliseconds according to a control voltage. Therefore, it requires a uniformly lit background. This is provided by a large number of lights (LED) behind a diffusing layer. There is generally a trade-off between the density of LED's and the thickness of the diffuser. The diffuser makes the light going forward appear to be uniform, but also wastes a good part of the light in other directions

[0005] Accordingly, there is a need for improved technology for collecting, diffusing, or concentrating light.

SUMMARY OF THE INVENTION

[0006] The present invention solves one or more problems of the prior art by providing, in at least one embodiment, a light funnel. The light funnel of the present embodiment includes a transparent funnel-shaped article having a first base surface, a second base surface, and a peripheral surface. The first base surface has a first surface area and the second base surface has a second surface area wherein the first surface area is greater than the second surface area. The light funnel further includes a reflecting layer disposed over the peripheral layer. [0007] In another embodiment, a light concentrator/spreader comprising a plurality of light funnels is provided. The light concentrator/spreader includes a support and a plurality of light funnels disposed in the support. Each light funnel of the plurality of light funnels includes a transparent funnel-shaped article having a first base surface, a second base surface, and a peripheral surface. The first base surface has a first surface area and the second base surface has a second surface area. Characteristically, the first surface area is greater than the second surface area and the peripheral surface has a cross section that defines a hyperbola. A reflecting coating is disposed over the peripheral layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0009] FIGURE IA is a cross sectional view of the light funnel;

[0010] FIGURE IB is a top view of the light funnel;

[0011] FIGURE 2 is a cross sectional view of a light funnel with a multilayer reflecting layer;

[0012] FIGURE 3A is a cross sectional view of a light funnel coupled to a photoactive device that is substantially planar;

[0013] FIGURE 3B is a cross sectional view of a light funnel coupled to a photoactive device that is curved; [0014] FIGURE 4A is a schematic illustration demonstrating the modeling of a light ray using a modeling ellipse in the case of a ray that is not transmitted out of the second base surface;

[0015] FIGURE 4B is a schematic illustration demonstrating the modeling of a light ray using a modeling ellipse in the case of a ray that is transmitted out of the second base surface;

[0016] FIGURE 5 is a schematic illustration demonstrating that a light ray falling between the foci of the modeling ellipse cannot be modeled by the procedure of Figures 3A and 3B;

[0017] FIGURE 6 is a schematic illustration demonstrating the modeling of a light ray using a modeling hyperbola;

[0018] FIGURE 7 is a principle cross-section of the family of confocal ellipses and hyperbolae;

[0019] FIGURE 8 A provides a plot of the input solar energy as a function of time to a simulation of the collected solar energy for three different stationary solar collectors;

[0020] FIGURE 8B provides plots depicting the profile of the collected energy collected as function of time for three different stationary solar collectors;

[0021] FIGURE 9A is a cross section of a light concentrator/spreader incorporating a plurality of light funnels; and [0022] FIGURE 9B is a top view of a light concentrator/spreader incorporating a plurality of light funnels;

[0023] FIGURE 10 is a cross section of a light concentrator/spreader aligned to an imaging device;

[0024] FIGURE 11 is a cross section of a light concentrator/spreader aligned to a light emitting device; and

[0025] FIGURE 12 is a schematic illustration of a system using a light funnel to collect light from a weak light source.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0026] Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0027] Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, "parts of," and ratio values are by weight; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.

[0028] It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way.

[0029] It must also be noted that, as used in the specification and the appended claims, the singular form "a," "an," and "the" comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.

[0030] Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.

[0031] With reference to Figures IA and IB, a schematic illustration of a light is provided. The light funnel of the present embodiment operates as a light concentrator (collector) or spreader depending on which side light is incident on. Figure IA is a cross sectional view of the light funnel. Figure IB is a top view of the light funnel. Light funnel 10 includes transparent article 12 and reflecting layer 14. Transparent article 12 includes a first base surface 16, second base surface 18, and a peripheral surface 20. In a refinement, transparent article 12 is made from a transparent dielectric material. Suitable materials for article 12 include, but are not limited to, glass and plastics (e.g., polycarbonate, acrylic). The first base surface 16 has a first surface area and the second base surface 18 has a second surface area wherein the first surface area is greater than the second surface area. Reflecting layer 14 is disposed over peripheral surface 20. In this context, reflecting layer 14 reflects at least a portion of the incident light (e.g., visible light, near infrared light). In the variation depicted in Figures IA and IB, reflecting layer 14 typically includes a reflective metallic layer (e.g., silver, aluminum, etc). First base surface 16 and second base surface 18 may be of arbitrary shape (circular, hexagonal, square, etc.). In the variation depicted in Figures IA and IB, first base surface 16 is substantially circular characterized by a diameter di and second base surface 18 is substantially circular characterized by a diameter d 2 (e.g., di and d 2 are each independently between about 2 microns and 1 meter or more). Light funnel 10 is also defined by height hi (e.g., hi is between about 2 microns and 1 meter or more). In a variation of the present embodiment, peripheral surface 20 is describable by a section of a hyperbola as illustrated in Figure IA.

[0032] Still referring to Figures IA and IB, the light funnel 10 either concentrates or spreads out incident light. If light is incident from side 22, the light is concentrated when it emerges at side 24. If light is incident from side 24, the light is spread out as it emerges at side

22.

[0033] With reference to Figure 2, a schematic illustration of a variation utilizing a multilayer coating for reflecting layer 14 is provided. In this variation, reflecting layer 14 includes a plurality of layers. In the specific refinement depicted in Figure 2, reflecting layer 14 includes layers 26, 28, 30. [0034] With reference to Figures 3A and 3B, schematic illustrations demonstrate variations for coupling the light funnels to a photoactive device. In the variation of Figure 2A, photoactive device 42 is substantially planar. In the variation of Figure 2B, second base surface 18 is curved as is photoactive device 44. This coupling of curved surfaces allows effective coupling of light emerging from second base surface 18. In one variation, the photoactive device is a photovoltaic cell and the incident light collected is solar radiation.

[0035] With reference to Figures 4A and 4B, schematic diagrams illustrating a procedure for optimizing the shape of the light funnels set forth above are provided. The paths of the reflected light rays are iteratively determined as set forth below until the light either emerges from second base surface 18 or is reflected out through first base surface 16. In a variation of the present embodiment, peripheral surface 20 is describable by a hyperbola in cross section. In this variation, the hyperbolae are characterized by foci 62 and 64. Light ray 56 is incident on first base surface 16 with angle of incidence Al and angle of refraction A2. Refracted light ray 58 travels within transparent article 12. Generally, Al is less than A2 because the dielectric constant of transparent article 12 is greater than 1. The resultant path of light ray 58 is determined by reference to foci 62, 64. Ellipse 60 is constructed with reference to foci 62, 64. The parameters defining the ellipse are set such that the extension 66 of light ray 58 is tangent to the ellipse at point 68. Light ray 58 is incident on reflecting layer 14 at point 70. Reflected ray 72 is incident on reflecting layer 14 at position 80. The path of reflected ray 72 is determined by reference to the same ellipse 60. Specifically, the path of reflected ray 72 is such that extension 74 of reflected ray 72 is tangent to a point 76 on the ellipse. There is only one such point that can meet this criterion. It should also be appreciated that the modeling based on the current description is only applicable to rays that have extensions that do not fall between foci 62, 64. In Figure 4A, the light resulting from incident light ray 56 does not emerge from light funnel 10. Reflected light ray 72 is reflected at position 80 to form reflected light ray 82, which is incident on reflecting layer 14 at position 84. The path of reflected light ray 82 is again determined by reference to ellipse 50. Specifically, extension 86 of light ray 82 is tangent to a point on ellipse 60. In Figure 4B, reflected light ray 82 emerges from second base surface 18. [0036] It should be appreciated that the design analysis of Figures 4A and 4B can be extended to skew rays. In this case the relative ellipse for the analysis is defined by the intersection of the plane defined by the incident and reflected rays on surface 20 with the ellipsoid derived by rotating ellipse 76 about axis Li .

[0037] With reference to Figure 5, a schematic illustration demonstrating that a light ray falling between the foci of the modeling ellipse cannot be modeled by the procedure of Figures 4A and 4B is provided. Light ray 86 is incident on first base surface 16. Refracted light ray 88 impinges upon reflecting layer 14. Extension 90 of refracted light ray 88 is not tangent to any ellipse having foci 62, 64. Therefore, the methods of Figures 4A and 4B are not applicable to this case.

[0038] With reference to Figure 6, a schematic illustration of a procedure for optimizing the shape of the light funnels taking into consideration the situation of Figure 5 is provided. In this variation, model hyperbola 89 having branches 90, 92 is used. Focal point 62 is associated with branch 90 while focal point 64 is associated with branch 92. Light ray 94 is incident on base surface 14. Refracted ray 96 impinges on reflecting surface 14 at position 98. Extension 100 of refracted light ray 96 is tangent to branch 92. Reflected ray 102 is reflected in a direction such that extension 104 of light ray 102 is tangent to branch 90. Branch 90 is a mirror image of branch 90. This process continues as above until light is either reflected or transmitted from light funnel 10. It should be appreciated that the design analysis of Figure 6 can be extended to skew rays. In this case the relative hyperbola for the analysis is defined by the intersection of the plane defined by the incident and reflected rays on surface 20 with the surface derived by rotating hyperbola 89 about axis L 1 .

[0039] With reference to Figure 7, a principle cross-section of the family of confocal ellipses and hyperbolae is provided. Figure 7 allows visualization of the ellipses and hyperbolae that are involved in designing the light funnels of Figures 1-2. Moreover, the methods associated with Figures 4-7 allow these light funnels to be designed with a predetermined acceptance angle and concentration properties. The concentration of light will depend on the ratio of the area of base surface 14 to base surface 16. For example, the equation for a hyperbola is:

xW - y 2 /b 2 = 1

wherein the a is related to focal points 62, 64 and b is a number related to the shape of the hyperbola. Specifically, focal point 62 can be expressed in Cartesian coordinates as (a,0) and focal point 64 as (-a,0). A light funnel is constructed by specifying a desired acceptance angle and concentration. The methods associated with Figures 3-5 are used to determine a, b, the height of the light funnel and the positions of base surface 14 and base surface 16 relative to the hyperbola.

[0040] With reference to Figures 8A and 8B, simulated plots demonstrating the efficiency of the present invention are provided. Figure 8A provides a plot of the input solar energy as a function of time. In Figure 8 A a cross-section of the solar collector 106 used in the simulation is overlaid onto the plot as well as the effective target size 108. In the simulation, the solar collector 106 is oriented towards the sun's zenith. Figure 8B provides plots depicting the profile of energy collected as function of time (in hours relative to zenith) for three different stationary collectors. The simulations of Figures 8 A and 8B were performed using Mathematica commercially available from Wolfram Research located in Champaign, Illinois. The top curve is for a flat panel solar cell of radius 0.86. The middle curve is for a concentrated solar cell of the present invention of radius 0.17. The dimensions provided are relative. The bottom curve is for a concentrated solar cell of conventionally focusing means of radius 0.17. For each of the simulations using a concentrated solar cell, the concentration ratio is 25.4. The flat panel solar cell is set to have the same effective area. The energy collected by the solar collector of the present invention is 2.05 kilowatt-hour while the energy collected by the conventionally concentrated solar cell of the same area as used in this invention is 0.27 kilowatt- hour. The energy collected by the flat panel solar cell is 7.64 kilowatt-hour. It should be appreciated that these energy collection estimates are for a one-day period with a clear sky and an area of 1 meter squared. The collected solar energy does not take into consideration the efficiency of the solar cell. Significantly, the present invention shows considerable improvement over the conventionally concentrated solar cell. In the simulation for the solar collector of the present invention, the radius of the image of the solar cell as seen from the sun is 1, the radius of the opening of the cell is 0.86, and the radius of the solar cell is 0.17.

[0041] With reference to Figures 9A and 9B, a schematic illustration of a near monolithic light concentrator/spreader including a plurality of light funnels is provided. Figure 9A is a cross section of the light concentrator/spreader while Figure 9B is a top view. Light concentrator/spreader 110 includes a plurality of light funnels 112. Light funnels 112 are of the general design set forth above in Figures 1-7. The regions 114 between light funnels 112 are filled with a material to provide structural support. Advantageously, this material is the same material as used for transparent article 12 set forth above. The structure of light concentrator/spreader 110 is nearly monolithic since it is equivalent to a monolithic slab with a series of embedded thin reflecting layers. This design provides significant mechanical strength allowing the light concentrator/spreader to be integrated into roofs. In a variation of the present embodiment, light funnels 112 are packed to provide the highest density of such collectors. However, it should be appreciated that the 2-dimensional packing of the solar collectors is flexible. For example, a rectangular array could have been used instead of hexagonal, resulting in a less dense packing. Moreover, the first base surface (item 12 in Figure IB) could be shaped hexagonally, to eliminate the "dead zone" between adjacent cells to further improve the light collecting efficiency.

[0042] Still referring to Figures 9A and 9B, it should be appreciated that the present embodiment provides an array of light funnels. The dimensional scale of this array and the light funnels therein is completely unrestricted except by the length of the wavelength of light. Generally, to function properly, the dimensions of the light funnels are greater than the wavelength of light, which is of the order of a micron. If the size of a single funnel is sub- millimeter, then its enabling technology must be akin to that semi-conductor. In fact, a candidate for the main material of the funnels, optical quality polymer, is very similar to polymers widely used in semi-conductor devices. Therefore, there are many areas this invention can be used in semi-conductor applications.

[0043] With reference to Figure 10, a schematic cross section of the application of a plurality of light funnels to an imaging device is provided. Imaging device 120 includes a plurality of photoactive elements 122. Typically, the photoactive elements each define a pixel in the imaging device. Light concentrator/diffuser 124 is positioned adjacent to imaging device 120 such that the photoactive elements are aligned to receive light from the plurality of light funnels 126 through second base surface 18. Light funnels 126 are of the design set forth above in Figures IA and IB. If the pixel sized light funnels 126 are positioned over the photocells, one funnel per pixel, then all the light that falls on one pixel can be concentrated to a much smaller photocell, leaving more surfaces for circuitry in the imaging device 120. The resulting higher light intensity directed to the photocells provides improved signal-to-noise ratio which translates to better sensitivity and higher speed. Since the pixel size is of the order of tens of microns, this is still many times the wavelength. An additional advantage of the present design is that smaller photocell area implies that the photocells of different pixels are well separated from each other. This reduces the blooming effect of imaging devices. In this application, the light funnels used should have low concentration factor (e.g., 3 to 5) with large acceptance angle to accommodate the use of large aperture lenses. In a variation, imaging device 120 is a CMOS imaging device. In a refinement, photoactive elements 122 may be either silicon based photocells or GaAs photocells.

[0044] With reference to Figure 11 , a schematic cross section of the application of a plurality of light funnels to a light emitting device is provided. Light emitting device 130 includes a plurality of light emitting elements 132. Light concentrator/diffuser 124 is positioned adjacent to light emitting device 130 such that the light emitting elements 132 are aligned to introduce light into the plurality of light funnels 126 through first base surface 16. Light funnels 126 are of the design set forth above in Figures IA and IB. In the present embodiment, the light concentrator/diffuser 124 functions as a light spreader. In a variation of the present embodiment, light emitting elements 132 are light emitting diodes (LED). In the present embodiment, the light funnels direct most of the light into the forward direction in a controllable solid angle, making the dies appear to be a uniform source. Light funnels would not only make the LED dies appear to be a uniform source but also waste less light in unwanted directions. The end result is less power consumption and reduced working temperature. Moreover, since the light funnel works more efficiently, fewer LED's can be used, saving more power.

[0045] With reference to Figure 12, a schematic illustration of the application of a light funnel to the collection of a weak optical signal is provided. Weak light source 140 emits a weak light signal that is collected and concentrated by light funnel 142 onto photo-detector 144. Light funnel 142 is of the design set forth above in Figures IA and IB. In this variation, the light funnel is based on non-imaging optics which is very useful in a photo-detector used in collecting the very weak and diffuse fluorescent light produced by biological samples under light stimulation. The demands for high sensibility and short response time create a dilemma in the choice of the detector area. To increase the sensitivity, a large detector area is desirable. However, a large area would make the capacitance of the PN-junction large thus increasing the response time. An imaging type of light collector is not desirable because it limits the field of view. Advantageously, the non-imaging light collector of the present embodiment solves this problem without sacrificing field of view.

[0046] While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.