WO2007065002A1

WO2007065002A1 - High efficiency beam shaping illumination optical device for light emitting diode

Info

Publication number: WO2007065002A1
Application number: PCT/US2006/046253
Authority: WO
Inventors: Dongha Kim; Jongmin Wang; James F. Shanley
Original assignee: Dongha Kim; Jongmin Wang; Shanley James F
Priority date: 2005-12-03
Filing date: 2006-12-03
Publication date: 2007-06-07

Abstract

A beam shaping LED illumination optical device that is composed of a light pipe (8) and LED lens (14) is provided. Light beams that are emitted from an RGB LED light source (1, 2, 3) pass through a light pipe (8), then color combination and combined focusing occur. The light beams emitted from the light pipe produce a homogenous beam of light without any loss of light through the LED lens (14). This configuration makes it possible to produce an LED projection display system with high efficiency and a supercompact size.

Description

HIGH EFFICIENCY BEAM SHAPING ILLUMINATION OPTICAL DEVICE FOR LIGHT

EMITTING DIODE

Field of The Invention

The present invention relates generally to the field of projection systems, and, more specifically, to optical systems for digital light projection systems including LED light sources.

Background Of The Invention

Cell phone functions are now developing at an amazing speed. For example, it is possible to view a picture from the phone with a built-in camera capability as well as video display capability. However, the built-in display in a cell phone that displays pictures or videos is causing inconvenience due to its size limit. It is difficult to share information with others, and particularly, video screens have the problem of not displaying well.

A projection display in which information is not confined to within a cell phone but being projected into a large screen is now gaining much attention. In particular, when the light emitting diode (LED) light source becomes highly efficient, it is possible to produce a supercompact size projection display that uses LED as its light source thus becoming a strong alternate for use in a display that can be built into a cell phone.

However, in the currently presented supercompact projection displays that use LED light source, there are two major problems. First, its size is still too large to be built into a cell phone. To be built into a cell phone, system size should be smaller than 7cc, but those presented so far are much larger than that. Secondly, the light efficiency in the system is still very low. Not only does low light efficiency decrease the brightness of the display, but, in order to gain a brighter screen, it requires more electricity which makes its application to a portable display difficult where the electricity consumption should be minimized.

Problems of large size and low light efficiency are usually caused by an illumination optical system that plays a role of sending the light emitted from LED to a panel. That is, illumination optic devices presented nowadays combine three colors (red, green and blue) that are emitted from an LED to an X-CUBE, so the size is very large. In addition, the beam shape that is combined and moving toward the panel is oval which does not match the shape of the panel, which is usually a rectangle. Therefore, a huge amount of light loss occurs.

The technological task that the present invention wants to achieve is to combine light beams without using an X-CUBE, and to create a rectangular beam shape in order to provide an LED illumination optical device which creates a supercompact and highly efficient LED projection display system.

These and other advantages of the present invention will become more fully apparent from the detailed description of the invention hereinbelow.

Summary of the Invention

The present invention is directed to an illumination optical system for a digital light projection system, the illumination optical system comprising an LED array; wherein the LED array comprises a plurality of LEDs. The illumination optical system also comprises a light pipe positioned substantially adjacent to the LED array, wherein the light pipe includes an input end and an opposite output end, wherein the input end of the light pipe receives light emitted from the plurality of LEDs within the LED array and reflects the received light so as to provide substantially uniform and substantially focused light at the output end of the light pipe, and wherein the output end of the light pipe is narrower than the input end of the light pipe. The illumination optical system further comprises a concentrator lens that receives and concentrates the substantially uniform and substantially focused light from the light pipe to thereby form concentrated light having a predeteπnined shape at an output end of the concentrator lens.

Brief Description of the Drawings

For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein:

Figure 1 illustrates the configuration of a traditional LED illumination optical system.

Figure 2 illustrates the configuration of a LED illumination optical system of this invention, in accordance with a preferred embodiment of the present invention.

Figure 3 illustrates the configuration of a LED illumination optical system of this invention, in accordance with a preferred embodiment of the present invention.

Figure 4 illustrates the output beam shape that is produced by the LED illumination optical system of the present invention.

Figure 5 illustrates a cross-sectional side view of the configuration of the LED lens in the LED illumination optical system of the present invention.

Figure 6 illustrates a cross-sectional side view of the configuration of the LED lens in the LED illumination optical system of the present invention.

Figures IA-I C show 3D images of the LED lens in the LED illumination optical system of the present invention.

Figure 8 illustrates a cross-sectional view of the light pipe of the LED illumination optical system of the present invention.

Figure 9 illustrates the configuration of the LED chip arrangement at the bottom of the light pipe of the LED illumination optical system of the present invention.

Figures 1OA and 1OB show 3D images of the light pipe of the LED illumination optical system of the present invention.

Figure 11 illustrates the operation of an LED lens of the LED illumination optical system of the present invention.

Figure 12 illustrates the operation of an LED lens of the LED illumination optical system of the present invention. Detailed Description of the Preferred Embodiments

It is to be understood that the figures and descriptions of the present invention may have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements found in a typical projection system. Those of ordinary skill in the art will recognize that other elements may be desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. It is also to be understood that the drawings included herewith only provide diagrammatic representations of the presently preferred structures of the present invention and that structures falling within the scope of the present invention may include structures different than those shown in the drawings. Reference will now be made to the drawings wherein like structures are provided with like reference designations.

Figure 1 shows the structure of a traditional LED illumination optical system. Beams emitted from red (1), green (2) and blue (3) LEDs are reflected individually to an X-CUBE (4) that is prepared with dichroic coating and then enter into a light modulation element (5). As briefly described above, such structure uses an X-CUBE (4) for color combination and therefore the structural size is too large and the round shape of the output beam (6) causes significant light loss.

Figure 2 shows a cross section of the present invention. Light emitted from several LED chips (or matrix of LEDs) (7) passes through a cone-shaped light pipe (8). The individual red, green and blue light beams will be well combined as the light that passed through the light pipe (8) and will propagate as light that was generated from the apex of the light pipe (8). Among the light beams that propagate from the apex of the light pipe (8), those that have an angle larger than θ will cause a total internal reflection at the outer lateral side (9) of the LED lens (14) of this device and move upward, and those light beams that have an angle smaller than θ will undergo a change of their light path at the inner bottom (12) of the LED lens of this device and move upward as well. To improve the uniformity of the output beam, the path of light advance will be modified again at the top (13) of the LED lens (14) of this device at the end and advance upward. The LED lens (14) of this device varies depending of the desired shape of the final output beam (Figure 3). The LED lens 14 functions as a concentrator lens.

The light pipe (8) of this device not only performs color combination of several LED chips, but also creates the effect of light beams corresponding to each color as if they were emitted from one focal point, so there is no need to use a separate X-CUBE (4) for color combination as it was done in the previous devices (Figure 1), and it is possible to configure a single LED package (7) without using separate LEDs 1, 2, 3 for three colors. Therefore, the size of the illuminating optical device can be reduced significantly. In addition, using the cross-sectional structure of the LED lens (14) that continuously changes, makes it possible to have a beam shaping function that creates an output beam shape that is exactly or substantially identical to the panel shape. Thus, the light efficiency can be increased significantly.

In summary, the LED beam shaping optical system (15) of the present invention, is mainly composed of three parts to perform its function. The first is the part of the light pipe (8). Light pipe (8) plays a role of mixing light beams emitted from each LED chip (7) in a uniform manner, and making the light beams emitted from different LED chips appear as if they were emitted from one focal point. The second part is the outer lateral side (9) of the LED lens (14). Among the light beams that propagate from the light pipe (8), those light beams that have an angle larger than θ will pass through the inner lateral side (10) of the LED lens and will then be total internally reflected at the outer lateral side (9) of the LED lens and move along the Z axis, i.e., upward. The lateral side (9) shape that changes according to the angle of cross section creates the desired output beam shape. The third part is the inner' bottom (12) and top (13) of the LED lens (14). Light beams having an angle smaller than θ and propagating from light pipe (8) will enter into the inner bottom (12) of the LED lens (14), and then move upward again (Figure 3). At this time, to improve the uniformity of the final output beam, the light beams are modified at the top (13) of the LED lens (14). That is, the inner bottom (12) and top (13) of the LED lens play the role of making the uniformity of the output beam enhanced. The inner bottom (12) and top (13) of the LED lens that adjust the beam uniformity level can be a spherical surface, non-spherical surface, combination of spherical and plane surfaces, combination of non- spherical and plane surfaces, symmetrical surface, and non-symmetrical surface. The outer bottom side (11) of the LED lens is also illustrated.

An examination of detailed structure of the outer lateral side (9) of the LED lens (14) that makes an oval beam emitted from the light pipe (8) to a desired shape is explained here. For example, Figure 4 shows the configuration when the desired output beam shape is a rectangular structure (16) with a horizontal length of "a" and a vertical length of "b." Figure 5 shows the cross sectional structure of the LED lens (14) when it is cut to a plane that has an angle of φ corresponding to the Y axis. To design a parabola that changes according to the angle φ, three constants (1) should be determined first. The first one is the output beam shape (i.e. values a and b). The second one is the minimum angle θ of the light to be totally internally reflected, and the third one is the location of light source S (i.e. the apex of the light pipe).

When φ is determined based on the following equations, the R value will be determined (equations (2a) - (2b)). And when the R value is determined, the focal point distance FR of the parabola will be determined by the function of φ (equation 4). Once the focal point distance FR is determined, the equation of the parabola will be obtained. When the focal point FR of the determined parabola is applied to the light source position S, the cross section shape at the angle φ will be determined. a, b, θ, S = fixed constants (1)

R(φ) = b/cos(φ) (if φ < arc tan(b/a)) (2a)

R(φ) = a/cos(π/2-φ) (if φ > arc tan(b/a)) (2b)

U(φ) = R(φ)/tan(θ) (3)

From the equation of the parabola z = y /4FR,

Therefore, FR = R2(φ)/4(S + U(φ)) (4)

Figure 6 shows the cross section of the outer lateral side (9) of the LED lens (14) where R = a, that is φ = π/2. F_a is a focus when R = a. Figures IA-I C show 3D images of the outer lateral side (9) of the LED lens (14) that is drawn according to the calculation equation above.

Figure 8 shows the cross section of the LED chips (7) and of the light pipe (8). The light pipe (8) always meets the requirement of b < a because the end of its cone is cut to a plane vertical to the Z axis. As shown in the figure, light beams emitted from LED chips (7) are total internally reflected and the angle of reflection continues to become narrower. Once it reaches a point under which the condition of no more total internal reflection occurs, the light beams exit from the hole at the top part of the light pipe. Figure 9 is an illustration of the bottom part of light pipe (8) that is viewed from the top, and although 4 x 4 LED chips (7) are arranged here as an example, it is also possible within the scope of the present invention to have other arrangements (e.g. in a rectangular matrix) with a different number of LED chips (7), as well as a different non-square or non-rectangle layout. Figures 1OA and 1OB show a 3D structure of light pipe (8) that is made with such a method.

Figures 11 and 12 show the principle of operation of the inner bottom (12) and top (13) of the LED lens. Basically, the inner bottom (12) of the LED lens has a smaller angle than the angle θ, and it moves the light beams propagating from the light source location S upward and these light beams preferably fill up the space that the light beams reflected from the outer lateral side (9) of the LED lens cannot fill up. The top (13) of the LED lens plays the role of increasing the uniformity of the light beams that have moved upward. Like the outer lateral side (9) of the LED lens, the degree of curvature of the surfaces of the inner bottom (12) and top (13) of the LED lens can be changed according to the angle φ so that such function can be conducted well. Spherical surfaces, non-spherical surfaces, combination of spherical and plane surfaces, non-spherical and plane surfaces, symmetrical surfaces, and non-symmetrical surfaces are all possible.

The LED beam shaping illumination optical device of this invention that is composed of a light pipe and LED lens makes an RGB single package configuration possible and eliminates the need to use an X-CUBE for color combination so that the minimization of the LED projection display system size becomes possible. In addition, it converts the oval incident beam to the desired shape (for example, converting it into a rectangular shape which is the shape of a light modulation panel) so that maximization of the efficiency of the LED projection display system becomes possible.

In any of the embodiments described above, the light pipe may preferably be a solid comprising, for example, glass or plastic.

The contemplated modifications and variations specifically mentioned above are considered to be within the spirit and scope of the present invention.

Those of ordinary skill in the art will recognize that various modifications and variations may be made to the embodiments described above without departing from the spirit and scope of the present invention. For example, other colored LEDs may be employed for the LEDs instead of the red, green, or blue LEDs mentioned in the above embodiments. As another example, although total internal reflection is mentioned above with respect to the type of reflection performed by the light pipe, other types of reflection may be employed by the light pipe such as, for example, specular reflection (i.e. with the light pipe being hollow with a metalized surface or silvered glass). It is therefore to be understood that the present invention is not limited to the particular embodiments disclosed above, but it is intended to cover such modifications and variations as defined by the following claims.

Claims

What is claimed is:

1. An illumination optical system for a digital light projection system, the illumination optical system comprising: an LED array; wherein the LED array comprises a plurality of LEDs; a light pipe positioned substantially adjacent to the LED array, wherein the light pipe includes an input end and an opposite output end, wherein the input end of the light pipe receives light emitted from the plurality of LEDs within the LED array and reflects the received light so as to provide substantially uniform and substantially focused light at the output end of the light pipe, and wherein the output end of the light pipe is narrower than the input end of the light pipe; and a concentrator lens that receives and concentrates the substantially uniform and substantially focused light from the light pipe to thereby form concentrated light having a predetermined shape at an output end of the concentrator lens.

2. The illumination optical system of claim 1, wherein the light pipe is positioned directly in contact with the LED array.

3. The illumination optical system of claim 1, wherein the light reflected by the light pipe is performed by total internal reflection.

4. The illumination optical system of claim 1, wherein the concentrator lens comprises an inner lateral side, an outer lateral side, an inner bottom side, and a top side, wherein the substantially uniform and substantially focused light from the light pipe enters the concentrator lens through the inner lateral side and the inner bottom side, and wherein the concentrated light emerges from the concentrator lens via the top side.

5. The illumination optical system of claim 4, wherein the outer lateral side of the concentrator lens totally internally reflects a portion of the substantially uniform and substantially focused light from each light pipe.

6. The illumination optical system of claim 5, wherein the outer lateral side of the concentrator lens has a shape which is parabolic, and wherein the parabolic shape uses a center of the output end of the light pipe as a focal point.

7. The illumination optical system of claim 1, wherein the predetermined shape is rectangular.

8. The illumination optical system of claim 1, wherein the light pipe is hollow, and wherein the light reflected by the light pipe is performed by specular reflection.