Patent Publication Number: US-2011057557-A1

Title: Projection led module and method of making a projection led module

Description:
FIELD OF THE INVENTION 
     The present invention relates to a light emitting diode module, and more particularly, to a projection light emitting diode module for emitting polarized light. 
     BACKGROUND OF THE INVENTION 
     Advances in high-brightness light emitting diodes (LED) have created opportunities for the use of LED in different lighting technologies, including pico projectors. Light from the LED is projected onto a micro-display, such as a liquid crystal display (LCD), liquid crystal on silicon (LCoS) or digital micro-mirror device (DMD). One challenge of the pico-projector technology is that the light is typically polarized in LCD or LCoS applications. However, in polarizing LED light, a large part of the light source is wasted since one polarization state is absorbed, scattered, and/or blocked. Additionally, existing pico projectors may include a large number of separate components, resulting in a higher cost and larger device size. 
     Therefore, existing projection LED modules have these and other limitations. Accordingly, there is a need for an LED module that solves these and other shortcomings. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a projection light emitting diode (LED) module for converting LED light to polarized light and emitting the polarized light is disclosed. The LED module includes a reflective polarizer positioned in a light emission path of the LED light, wherein the reflective polarizer is configured to polarize the LED light, and the reflective polarizer further transmits first polarization state light and reflects second polarization state light; and a polarization conversion element bonded to the reflective polarizer, the polarization conversion element positioned between the LED light and the reflective polarizer, wherein the polarization conversion element coverts the second polarization state light to desired polarization state light. 
     According to another embodiment of the present invention, a projection light emitting diode (LED) module for converting LED light to polarized light and emitting the polarized light is disclosed. The LED module includes a substrate, one surface of the substrate defining a reflecting cup; an LED chip bonded to the substrate, the LED chip configured to emit a light beam; a reflective polarizer positioned in a light emission path of the light beam, wherein the reflective polarizer polarizes the light beam and transmits first polarization state light and reflects second polarization state light; and a polarization conversion element located on the substrate, the polarization conversion element positioned between the LED chip and the reflective polarizer, wherein the polarization conversion element is configured to convert the second polarization state light to desired polarization state light, and wherein the bonding of the polarization conversion element to the substrate defines an air gap adjacent to the LED chip, wherein the air gap is configured to narrow the light beam. 
     According to yet another embodiment of the present invention, a method of making a projection light emitting diode (LED) module is disclosed. The method includes the steps of providing a substrate, one surface of the substrate defining a reflecting cup; bonding an LED chip bonded to the substrate, the LED chip configured to emit a light beam; positioning a reflective polarizer in a light emission path of the light beam, wherein the reflective polarizer polarizes the light beam and transmits first polarization state light and reflects second polarization state light; and positioning a polarization conversion on the substrate between the LED chip and the reflective polarizer, wherein the polarization conversion element coverts the second polarization state light to desired polarization state light, and wherein the bonding of the polarization conversion element to the substrate defines an air gap adjacent to the LED chip. 
     Still other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the invention are described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the spirit and the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective, cross sectional view of a light emitting diode (LED) module, in accordance with an embodiment of the present invention. 
         FIG. 2  is a side, cross sectional view of the LED module showing light reflection paths, in accordance with an embodiment of the present invention. 
         FIG. 3A  is a side, cross sectional view of the LED module showing a spherical reflector shape, in accordance with an embodiment of the present invention. 
         FIG. 3B  is a graph illustrating LED position and reflection path for the spherical reflector shape, in accordance with an embodiment of the present invention. 
         FIG. 4A  is a side, cross sectional view of the LED module showing a parabolic reflector shape, in accordance with an embodiment of the present invention. 
         FIG. 4B  is a graph illustrating LED position and reflection path for the parabolic reflector shape, in accordance with an embodiment of the present invention. 
         FIG. 5A  is a side, cross sectional view of the LED module showing an elliptical reflector shape, in accordance with an embodiment of the present invention. 
         FIG. 5B  is a graph illustrating LED position and reflection path for the elliptical reflector shape, in accordance with an embodiment of the present invention. 
         FIG. 6  is an LED module production process flow, in accordance with an embodiment of the present invention. 
         FIG. 7A  is an exploded, perspective view of a first example LED module, including a compounded frame mount, in accordance with an embodiment of the present invention. 
         FIG. 7B  is a side, cross sectional view of the first example LED module shown in  FIG. 7A , in accordance with an embodiment of the present invention. 
         FIG. 8A  is an exploded, perspective view of a second example LED module, including a LED chip on an MCPCB, in accordance with an embodiment of the present invention. 
         FIG. 8B  is a side, cross sectional view of the second example LED module shown in  FIG. 8A , in accordance with an embodiment of the present invention. 
         FIG. 9A  is an exploded, perspective view of a third example LED module, including a commercial LED package, in accordance with an embodiment of the present invention. 
         FIG. 9B  is a side, cross sectional view of the third example LED module shown in  FIG. 9A , in accordance with an embodiment of the present invention. 
         FIG. 10A  is an exploded, perspective view of a fourth example LED module, including a commercial LED package, in accordance with an embodiment of the present invention. 
         FIG. 10B  is a side, cross sectional view of the fourth example LED module shown in  FIG. 10A , in accordance with an embodiment of the present invention. 
         FIG. 11A  is an exploded, perspective view of a fifth example LED module, including a commercial LED package, in accordance with an embodiment of the present invention. 
         FIG. 11B  is a side, cross sectional view of the fifth example LED module shown in  FIG. 11A , in accordance with an embodiment of the present invention. 
         FIG. 12  is a perspective view of a sixth example LED module, including a compounded frame mount without the lens, in accordance with an embodiment of the present invention. 
         FIG. 13  a perspective view of a seventh example LED module, including a commercial LED package without the lens, in accordance with an embodiment of the present invention. 
         FIG. 14A  is a side cross sectional view of a projection system including the LED module, according to an embodiment of the present invention. 
         FIG. 14B  is an exploded, perspective view of the projection system shown in  FIG. 14A , according to an embodiment of the present invention. 
         FIG. 15  is a schematic diagram illustrating the LED module and generated light paths, according to an embodiment of the present invention. 
         FIG. 16  is a distribution plot showing the beam angle of the LED module, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings where, by way of illustration, specific embodiments of the invention are shown. It is to be understood that other embodiments may be used as structural and other changes may be made without departing from the scope of the present invention. Also, the various embodiments and aspects from each of the various embodiments may be used in any suitable combinations. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
     Generally, embodiments of the present invention are directed to an LED module that provides a polarizing system, a light recycling system, a condenser system, and thermal management. The LED module may be used to provide polarized light output without necessarily having an extended polarizing device in liquid crystal on silicon (LCoS) and liquid crystal display (LCD) projection systems. The light recycling system includes reflection and conversion of a first polarization state to the second polarization state. With the recycling system, more than half of the light from the light source LED chip can be outputted, thereby enhancing the optical efficiency and increasing the output brightness of a system incorporating the LED module. Additionally, embodiments of the present invention may generate a narrower viewing angle and a lower thermal resistance. 
     Referring now to the figures,  FIG. 1  is a perspective, cross sectional view of a light emitting diode (LED) module  100 , in accordance with an embodiment of the present invention. The LED module  100  includes a plurality of layers to provide a polarizing system, a light recycling system, a condenser system, and thermal management. The LED module  100  includes an LED chip  102  bonded on a substrate  104 . A cup  106  is formed by the substrate  104 . The cup  106  may have a reflector or reflective layer on the surface of the cup  106 . Therefore, the cup  106  or the reflector on the surface of the cup  106  may be referred to as a reflecting cup. A quarter wave plate (QWP) layer  108  is formed over the LED chip  102  on the substrate  104 . A reflective polarization layer  110  is positioned on the QWP layer  108 . A lens  112  is applied over the reflective polarization layer  110  and may also further enclose the LED module  100 . According to an embodiment of the present invention, an air gap  114  is formed between the LED chip  102  and the QWP layer  108 . 
     The reflective polarization layer  110  is configured to transmit first polarization state light and reflect the second polarization state light back toward the substrate  104 . The reflective polarization layer  110  may be any suitable type of polarizer such as, for example, a wire grid polarizer or a multilayer optical stack film. The QWP layer  108  is a polarization conversion element, or polarization shifter, that converts the second polarization state into a desired polarization state. The desired polarization state is effectively similar to the first polarization state. Therefore, once the second polarization state light has been converted into the first polarization state light, the light is transmitted by the reflective polarization layer  110 . Suitable QWP layers  108  are known to those of skill in the art. 
     The air gap  114  may be provided to narrow the beam angle as light from the LED chip  102  is reflected into the QWP layer  108 . Without the air gap  114 , or if the air gap is filled with silicone or epoxy, the beam angle of the light emitted from the LED chip  102  may be larger than that provided using embodiments of the present invention. With the air gap  114 , the beam angle is narrower and the resulting emitted light is more focused, as shown in  FIG. 15-16 . 
     The LED chip  102  may be any suitable LED device, such as either a single LED chip or a multi-chip LED. The substrate  104  is any suitable substrate for carrying an LED chip, such as silicon, ceramic, metal core printed circuit board (MCPCB), or other circuit board, where improved heat dissipation by reducing the thermal resistance between the LED chip  102  and the outside is desired. The lens  112  is any suitable lens such as, for example, PMMA, epoxy, glass, and etc. 
     In operation, the LED chip  102  emits light having both p-polarization and s-polarization. The reflective polarization layer  110  allows p-polarized light to be emitted through the lens  112  and reflects s-polarized light back toward the substrate  104 . If s-polarized light is translated a quarter wavelength twice, then it is converted into p-polarized light. Therefore, when s-polarized light passes through the QWP layer  108  a first time when emitted from the LED chip  102 , and after reflection by the reflective polarization layer  110 , the s-polarized light is reflected by the cup  106  and passes through the QWP layer  108  a second time. After passage through the QWP layer  108  the second time, the s-polarized light is converted into p-polarized light and is then emitted through the lens  112 . The emission of the p-polarized light that is converted from s-polarized light increases the total light output and energy of the LED module  100 . 
     According to one embodiment of the present invention, the first polarization state light is p-polarized light, the second polarization state light is the s-polarized light, and the desired polarization state light is p-polarized light that has been converted from s-polarized light to p-polarized light. 
       FIG. 2  is a side, cross sectional view of the LED module  100  showing light reflection paths, in accordance with an embodiment of the present invention. A legend shows the various types of light being passes through the LED module  100 . Referring to one example light path, LED light  200  is emitted from the LED chip  102 . A part of the LED light  200  is emitted through the reflective polarization layer  110  as p-polarized light  202 . A part of the LED light  200  is reflected back as s-polarized light  204 . The s-polarized light  204  is circularly reflected as once shifted light  206  and then as twice shifted light  208  before being emitted from the reflective polarization layer  110  as p-polarized light  210 . 
     One advantage of embodiments of the present invention is that both large angle and small angle light is reflected out of the LED module  100 . The configuration of the LED chip  102  and the shape of the cup  106  with reflector may reflect both large angle and small angle light, thereby increasing the amount of light emitted by the LED module  100 . 
     Referring now to  FIGS. 3A to 5B , three different cup shapes and associated LED chip position and reflection path graphs are illustrated. The surface of the cup has a reflector to increase the reflection of the light from the LED chip. By choosing a position of the LED chip that complements the reflector shape, an increased amount of light can be emitted from the LED module  100  by considering the light path of light reflected by the particular cup shape. In conventional LED packages, the shape of the substrate is not configured for optimal reflection. By specifically configuring the shape of the substrate and the position of the LED chip on the substrate, a recycled light path can be controlled and predetermined similar to the original light path so that a greater amount of light is recycled and can pass through the projection. If the recycled light path is not similar to the original light path, even the reflected light is recycled but it can not pass through the projection system because the projection optical design is based on the original LED chip position and size. 
       FIG. 3A  is a side, cross sectional view of the LED module showing a spherical reflector shape, and  FIG. 3B  is a graph illustrating LED position and reflection path for the spherical reflector shape. A reflector  306  is located on the substrate  104 , the substrate  104  or the reflector  306 , or both the substrate  104  and the reflector  306 , having a generally spherical shaped curve. The LED chip  302  is located on the surface of the substrate  104 . Recycled light rays  325  are reflected by the reflective polarization layer  310 , and then the reflector  306 , and a chip image  330  is formed generally at a location that would be the center of the sphere shaped curve. 
       FIG. 4A  is a side, cross sectional view of the LED module showing a parabolic reflector shape, and  FIG. 4B  is a graph illustrating LED position and reflection path for the parabolic reflector shape. A reflector  406  is located on the substrate  104 , the substrate  104  or the reflector  406 , or both the substrate  104  and the reflector  406 , having a generally parabolic shaped curve. The LED chip  402  is located generally at the vertex of the reflector  406 . Recycled light rays  425  are reflected by the reflector  406  and passed through the reflective polarization layer  410  substantially orthogonally. A chip image  430  is formed generally at a location that would be the focus of the parabolic reflector. 
       FIG. 5A  is a side, cross sectional view of the LED module showing an elliptical reflector shape, and  FIG. 5B  is a graph illustrating LED position and reflection path for the elliptical reflector shape. A reflector  506  is located on the substrate  104 , the substrate  104  or the reflector  506 , or both the substrate  104  and the reflector  506 , having a generally elliptical shaped curve. The LED chip  502  is located at a first focus of the elliptical shape, proximate to the reflector  506 . Recycled light rays  525  are first reflected by the reflective polarization layer  510  towards the LED chip  502  and then reflected at a second part of the reflector  506 , then forming a chip image  530  generally at a location that would be a second focus of the elliptical shape. 
       FIG. 6  is an LED module production process flow, in accordance with an embodiment of the present invention. In a first step, a substrate  104  is provided, the substrate  104  having a cup formed into the surface, and an LED chip  102  is provided. Then, the LED chip  102  is attached to the substrate  104  by LED and wire bonding. In one embodiment, after the LED and wire bonding, a silicon  602  filling process may be included. In another step, the reflective polarization layer  110  and the QWP layer  108  are joined. The QWP layer  108  and the reflective polarization layer  110  are then placed on the substrate  104 . The lens  112  covers the reflective polarization layer  110  and the QWP layer  108  then is joined to substrate  104 , thereby forming the LED module  100 , in accordance with an embodiment of the present invention. The LED module  100  may then be surface mounted, for example, onto a MCPCB or PCB  600 . While these process steps are described in a particular order, other fabrication orders and processes may be used. Therefore, the above steps illustrate one example fabrication process. 
     Referring now to  FIGS. 7A to 10B , examples of LED modules made in accordance with embodiments of the present invention are illustrated in described. The description with reference to  FIGS. 1 to 6  similarly applies to the examples shown and described with reference to  FIGS. 7 to 10 . 
       FIG. 7A  is an exploded, perspective view of a first example LED module, including a compounded frame mount, in accordance with an embodiment of the present invention. Three separate components are provided and combined to form an LED module  700  including: (1) an LED chip  702  formed on a substrate  704 ; ( 2 ) a QWP layer  708  and a reflective polarization layer  710  bonded together; and (3) a lens  712 . The lens  712  maybe be a combination of a lens with a lens cube defining a hollow on one side of the lens  712 . The reflective polarization layer  710  and the QWP layer  708  may be positioned in the hollow, and then the lens  712  together with the QWP layer  708  and the reflective polarization layer  710  are joined to the substrate. 
       FIG. 7B  is a side, cross sectional view of the first example LED module shown in  FIG. 7A , in accordance with an embodiment of the present invention. A reflective cup  714  is shown formed in the substrate  704 . The lens  712  surrounds the substrate  704  when joined to for the LED module  700 . 
       FIG. 8A  is an exploded, perspective view of a second example LED module  800 , including a LED chip on a MCPCB  850 , in accordance with an embodiment of the present invention. The mounting of the LED chip  802  direct on the MCPCB  850  may result in for lower thermal resistance. Three separate components are provided and combined to form an LED module  800  including: (1) an LED chip  802  direct bonded on a MCPCB  850 ; ( 2 ) a QWP layer  808  and a reflective polarization layer  810  bonded together; and (3) a lens  812 . The lens  812  maybe be a combination of a lens with a lens cube defining a hollow on one side of the lens. The reflective polarization layer  810  and the QWP  808  layer may be positioned in the hollow, and then the lens together with the QWP layer  808  and the reflective polarization layer  810  are joined to the MCPCB  850 . 
       FIG. 8B  is a side, cross sectional view of the second example LED module shown in  FIG. 8A , in accordance with an embodiment of the present invention. A reflective cup  852  is shown formed in the MCPCB. The lens  812  surrounds the QWP  808  layer and reflective polarization layer  810  when fixed on the MCPCB  850 . 
       FIG. 9A  is an exploded, perspective view of a third example LED module  900 , including a commercial LED package, in accordance with an embodiment of the present invention. Two separate components are provided and combined to form an LED module  900  including: (1) a QWP layer  908  and a reflective polarization layer  910  bonded together, and (2) a lens  912 . The LED module  900  may then be sealed onto any suitable, commercial available LED package  950 . In one embodiment, the LED package  950  includes a reflective cup configured in accordance with embodiments of the present invention to provide increased reflection of light from the LED chip. In another embodiment, the LED package  950  is a multi-LED package, such as an RGB LED package. 
       FIG. 9B  is a side, cross sectional view of the third example LED module shown in  FIG. 9A , in accordance with an embodiment of the present invention. The LED module  900  is shown sealed to the LED package  950 . 
       FIG. 10A  is an exploded, perspective view of a fourth example LED module, including a commercial LED package, in accordance with an embodiment of the present invention. Two separate components are provided and combined to form an LED module  1000  including: (1) a QWP layer  1008  and a reflective polarization layer  1010  bonded together, and (2) a lens  1012 . The LED module  1000  may then be sealed onto any suitable, commercial available LED package  1050 . In one embodiment, the LED package  1050  includes a reflective cup configured in accordance with embodiments of the present invention to provide increased reflection of light from the LED chip. 
       FIG. 10B  is side, cross sectional view of the fourth example LED module shown in  FIG. 10A , in accordance with an embodiment of the present invention. The LED module  1000  is shown sealed to the LED package  1050 . The LED package  1050  includes wires  1052  for electrical coupling with a circuit for operation. 
       FIG. 11A  is an exploded, perspective view of a fifth example LED module, including a commercial LED package, in accordance with an embodiment of the present invention. Two separate components are provided and combined to form an LED module  1100  including: (1) a QWP layer  1108  and a reflective polarization layer  1110  bonded together, and (2) a lens total internal reflection (TIR) lens  1112 . The LED module  1100  may then be sealed onto any suitable, commercial available LED package  1150 . In one embodiment, the LED package  1150  includes a reflective cup configured in accordance with embodiments of the present invention to provide increased reflection of light from the LED chip. 
       FIG. 11B  is side, cross sectional view of the fifth example LED module shown in  FIG. 11A , in accordance with an embodiment of the present invention. The LED module  1100  is shown sealed to the LED package  1150 . The LED package  1150  includes wires  1152  for electrical coupling with a circuit for operation. 
       FIG. 12  is a perspective view of a sixth example LED module, including a compounded frame mount without the lens, in accordance with an embodiment of the present invention. The LED module  1200  includes an LED chip  1202  bonded on a substrate  1204 , a QWP layer  1208  and a reflective polarization layer  1210  affixed together. Then the QWP layer  1208  with the reflective polarization layer  1210  affixed on the substrate  1204  to seal the LED Chip  1202 . 
       FIG. 13  a perspective view of a seventh example LED module, including a commercial LED package without the lens, in accordance with an embodiment of the present invention. A QWP layer  1302  and a reflective polarization layer  1304  are affixed together. The QWP layer  1208  with the reflective polarization layer  1210  can then be affixed onto any suitable, commercial LED package  1308  with a generally flat package surface for emitting light. 
     Referring to  FIGS. 14A and 14B ,  FIG. 14A  is a side cross sectional view of a projection system including the LED module, and  FIG. 14B  is an exploded, perspective view of the projection system illustrated in  FIG. 14A , according to an embodiment of the present invention. The LED module  1406  is bonded to an MCPCB  1408 , and a heat sink  1410  is attached to the back side of the MCPCB  1408  so that the heat from the LED chip in the LED module  1406  can be dissipated. Then the LED module  1406  and the MCPCB are coupled to a housing  1404 . Several optical components  1402  may be positioned in the optical path and secured by the housing  1404  and cover  1420 . An LCoS panel  1400  is attached to the housing  1404  opposite to the LED module  1406 . Some projection lenses  1412  may be positioned in a cylinder  1422  which can slide within the housing for adjusting the focus. The light rays emitted from LED module  1406  transmit through the optical components  1402  then reach the LCoS panel  1400 . After reflected by the LCoS panel  1400  and optical components  1402 , the light rays transmit through the projection lenses  1412  and then are projected out of the projection system. Due to polarizing and light recycling, the LED module  1406  can increase the total light output and energy of the projection system when compared to conventional projection systems. 
       FIG. 15  is a schematic diagram illustrating the LED module  700  and generated light paths, according to an embodiment of the present invention. The light paths, some of the light paths labeled with reference number  1500 , are shown having a narrower light angle when compared to convention light modules where an air gap is not provided. 
       FIG. 16  is a distribution plot showing the beam angle of the LED module, according to an embodiment of the present invention. In the distribution plot, in order to match with the projection optical path, the beam angle is configured to 55°. For different projection optical engine, the beam angle of the LED module  700  can be changed to match with the projection optical engine by modify the lens shape, the reflective polarization thickness, the QWP thickness and the air gap thickness. 
     Embodiments of the present invention include a reflective polarization layer and a QWP layer inside of or under the lens. Therefore, embodiments of the present invention may permit smaller LED module design having similar brightness or increased brightness when compared to larger devices. Similarly, the beam angle is similar or improved when compared to larger devices. Embodiments of the present invention can also be used with a large output angle while maintaining a high level of efficiency. 
     While the invention has been particularly shown and described with reference to the illustrated embodiments, those skilled in the art will understand that changes in form and detail may be made without departing from the spirit and scope of the invention. For example, while specific component types have been indicated, other similar and suitable alternatives may also be used. Additionally, while embodiments of the present invention are well suited for use in LED micro-projectors and pico projectors, embodiments of the present invention may also be used for any other suitable applications. 
     Accordingly, the above description is intended to provide example embodiments of the present invention, and the scope of the present invention is not to be limited by the specific examples provided.