Abstract:
An integrated multi-layer apparatus and method of producing the same is disclosed. The structure comprises an LED configured to emit first and second polarized light, and a polarizing layer configured to pass a first polarized light and reflect the second polarized light back to the LED, wherein the LED is further configured to randomly scatter the second polarized light reflected from the polarizing layer and redirect the scattered light back to the polarizing layer.

Description:
FIELD 
       [0001]    The present disclosure relates generally to the field of semiconductor light emitting devices, and more specifically, to polarization recycling optics for light emitting devices. 
       BACKGROUND 
       [0002]    Polarization of light is a property of waves which describes the orientation of the oscillations in the plane perpendicular to the wave&#39;s direction of travel. S and P polarization refer to the plane in which the electric field of a light wave is oscillating. The p-polarization refers to the polarization plane parallel to the polarization axis of the polarizer being used (“p” is for “parallel”). The s-polarization refers to the polarization plane perpendicular to the polarization axis of the polarizer. A linear polarizer, by design, polarizes light in the p-polarization. 
         [0003]    One useful application of a polarized light source is for a liquid crystal display (LCD). A LCD works by passing one polarization and blocking the other polarization. By tuning the degree of polarization at each pixel of the LCD, the amount of light exiting can be modulated to form a gray scale image. The LCD requires only one polarization of light to enter and one polarization of light to exit the system. This is accomplished typically with an input and output polarizer. Light sources emit light randomly in all polarizations. The job of the input polarizer is to eliminate the unwanted polarization of light. Thus, at least 50% of the light is lost by the first polarizer. If a polarized light source is available, then the system can before more efficient with the potential to eliminate the input polarizer. A light emitting diode with a polarized output would be a particularly attractive choice because, among other features, they consume less energy and have good conversion efficiency as compared to conventional light sources such incandescent and fluorescent lamps. 
       SUMMARY 
       [0004]    In one aspect of the disclosure, an integrated multi-layer apparatus including an LED configured to emit light having first and second polarized light, wherein the first polarized light has a different polarization from the second polarized light, and a polarizing layer configured to pass the first polarized light and reflect the second polarized light back to the LED, wherein the LED is further configured to randomly scatter the second polarized light and redirect the scattered light back to the polarizing layer. 
         [0005]    In another aspect of the disclosure, an integrated multi-layer apparatus includes an LED configured to emit light having first and second polarized light, wherein the first polarized light has a different polarization from the second polarized light, and a polarizing layer configured to pass the first polarized light and reflect the second polarized light back to the LED, wherein the LED further comprises a roughened surface and a back reflector. 
         [0006]    In yet another aspect of the disclosure, an integrated multi-layer apparatus includes light emitting means for emitting light having first and second polarized light, wherein the first polarized light has a different polarization from the second polarized light, and polarizing means for passing the first polarized light and reflecting the second polarized light back to the light emitting means, wherein the light emitting means comprises means for randomly scattering the second polarized light and means for redirecting the scattered light back to the polarizing reflector. 
         [0007]    In a further aspect of the disclosure, a method of emitting light from an integrated multi-layer structure having an LED and a polarizing layer, includes emitting light from the LED, the emitted light having first and second polarized light, wherein the first polarized light has a different polarization from the second polarized light, passing the first polarized light reaching the polarizing layer through the polarizing layer and reflecting the second polarized light reaching the polarizing layer back to the LED, randomly scattering the second polarized light reflected back to the LED, and redirecting the scattered light back to the polarizing layer. 
         [0008]    It is understood that other aspects of the present disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described only exemplary aspects of the disclosure by way of illustration. As will be realized, the disclosure includes other and different aspects and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and the detailed description are to be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various aspects of the present disclosure are illustrated by way of example, and not by way of limitation, in the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a cross-section view illustrating an example of an LED; 
           [0011]      FIG. 2  is a cross-section view illustrating an example of an integrated multi-layer apparatus; 
           [0012]      FIG. 3   a  is an illustration of an example of a multi-layer structure with a polarizing layer; 
           [0013]      FIG. 3   b  is an illustration of an example of another multi-layer structure with a polarizing layer; and 
           [0014]      FIG. 3   c  is an illustration of an example of yet another multi-layer structure with a polarizing layer. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The detailed description set forth below in connection with the appended drawings is intended as a description of various aspects of the present disclosure and is not intended to represent all ways in which the present disclosure may be practiced. The detailed description may include specific details for the purpose of providing a thorough understanding of the present disclosure; however, it will be apparent to those skilled in the art that the various aspects of the present disclosure may be practiced without these specific details. In some instances, well-known structures and components are summarily described and/or shown in block diagram form in order to avoid obscuring the concepts of the present disclosure. 
         [0016]    Various aspects of this disclosure will be described in terms of an integrated multi-layer apparatus. As used herein, an integrated multi-layer apparatus is intended to cover a structure having multiple layers. Each layer of the apparatus may itself comprise several layers or sub-layers. By way of example, an integrated multi-layer apparatus may include an LED layer having an active region sandwiched between two oppositely doped epitaxial layers all of which are formed on a growth substrate. A polarizing layer formed on the LED may include several layers of material deposited onto a substrate such as glass. In other words, the term “layer” used throughout this disclose does not necessarily denote a homogeneous layer of material. 
         [0017]    As those skilled in the art will readily appreciate, when a layer is referred to as being “on” another layer, it can be directly on the other layer or intervening layers may be present. For instance, the preceding reference to a polarizing layer on an LED does not preclude intervening layers between the two. In one configuration of a multi-layer apparatus discussed below, a refracting layer may be formed between the LED and the polarizing layer. This configuration may be modified by forming a beam shaping layer between the refracting layer and the polarizing layer. Alternatively, the apparatus may be formed with the polarizing layer between the refracting layer and the beam shaping layer. 
         [0018]    The “integration” of these layers into the apparatus means that the layers are formed together by suitable means, now known or later discovered. By way of example, the LED may be grown on a substrate and the polarizing layer may be adhered, bonded or otherwise applied to the LED, either directly or through an intervening layer (e.g., refracting layer). 
         [0019]    Various aspects of an integrated multi-layer apparatus are described herein with reference to cross-sectional view illustrations that are conceptual in nature. Various layers of the apparatus should not be construed as limited to the particular configuration shown in the drawings. By way of example, the “layers” of an integrated multi-layer apparatus are shown with discrete physical boundaries. However, in practice, a concentration gradient may exist across the physical boundaries between layers with the material from one layer penetrating the material of adjacent layers in either a controlled or random fashion. Thus, the layers illustrated in the drawings are conceptual in nature and their shapes are not intended to illustrate the precise shape of a layer of an apparatus and are not intended to limit the scope of the invention. 
         [0020]    Those skilled in the art will further appreciate that relative terms such as “top” or “bottom” (and similar terms) may be used herein to describe a relationship between layers. Notwithstanding the use of such terms, those skilled in the art will readily understand that the concepts presented throughout this disclosure are intended to extend to different orientations of an integrated multi-layer apparatus in addition to the orientation depicted in the drawings. 
         [0021]    Turning to  FIG. 1 , an LED with a vertical structure is shown. However, as those skilled in the art will readily appreciate, the various aspects presented throughout this disclosure are likewise applicable to other LED structures, as well as other light emitting semiconductors, now known or later discovered. Accordingly, any reference to a vertical structure LED is intended only to illustrate various aspects, with the understanding that such aspects have a wide range of applications. 
         [0022]      FIG. 1  is a cross-section view illustrating an example of an LED. An LED is a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred respectively as n-type or p-type semiconductor regions, respectively. A reverse electric field is created at the junction between the two regions, which cause the electrons and holes to move away from the junction to form an “active region.” 
         [0023]    The LED  10  is shown with an n-electrode  11  in contact with an n-type semiconductor layer  12  and a p-electrode  15  in contact with a p-type semiconductor layer  14 . A thermally and/or electrically conductive substrate  16  supports the LED  10  structurally. A back reflector  17  may be formed on the bottom of the substrate  16 . The LED may be fabricated using known processes with a suitable process being a fabrication process using chemical vapor deposition. The LED may be formed on a wafer and then singulated for mounting in a package. The growth substrate may remain as part of the singulated LED or the growth substrate may be fully or partially removed. 
         [0024]    When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, via the p-electrode  15  and the n-electrode  11 , electrons and holes are forced into an active region  13  and combine. When an electron combines with a hole, it falls to a lower energy level and releases energy in the form of light. If an incident angle of light at the interface between the n-type semiconductor layer  12  and the ambient air (or other encapsulating material) is greater than a critical angle in accordance with Snell&#39;s law, a portion of light generated inside the LED  10  device may get trapped inside the LED  10  due to total-internal-reflection (TIR). To increase the chance of light escaping from the LED, the n-type semiconductor layer  12  may be roughened. The roughened surface scatters the normal incident light in random direction and reduces the effects of TIR. The back reflector  17  may be provided at the bottom of the LED  10  for redirecting light emitted from the active region  13  back toward the top surface of the LED  10 . Alternatively, or in addition to, one or more the sides of the LED  10  may also have a back reflector. 
         [0025]      FIG. 2  is an abstract view illustrating an example of the functionality of an integrated multi-layer apparatus. The apparatus  99  includes a polarizing layer  100  on top of an LED  102  wherein the entire apparatus can be fabricated at an integrated circuit and/or at a wafer level. The LED  102  may be implemented as described above in connection with  FIG. 1 , or with some other suitable light emitting structure. The polarizing layer may include a thin-film polarizing reflector comprising several layers of material deposited onto a substrate (e.g., glass) by a physical vapor deposition process such as evaporative or sputter deposition or a chemical process such as chemical vapor deposition. An example of a polarizing reflector is manufactured by 3M under the trademark Vikuiti™ Dual Brightness Enhancement Films (DBEF). The LED  102  emits p-polarized and s-polarized light towards the polarization layer  100 . The polarizing layer  100  transmits the p-polarized light and reflects the s-polarized light back towards the LED  102 . The reflected s-polarized light gets randomly scattered by the roughened surface of the LED  102  so that a portion of light can be converted to p-polarized light (see  FIG. 1 ). The randomly scattered light is then recycled back up from the LED  102  by the back reflector (see  FIG. 1 ). The p-polarized recycled light then gets transmitted by the polarizing layer  100 . The remaining s-polarized light gets reflected and the recycling process is repeated. 
         [0026]      FIGS. 3   a - 3   c  are cross section views illustrating examples of various configurations for implementing an integrated multi-layer apparatus. Each example is shown with an LED  102 . The light emission profile from an LED is non-directional and typically assumes a “lambertian” like profile where light is equally emitted into all directions. However, in various configurations, the polarizing layer  100  may only have a limited angle of acceptance. For such cases, a refracting layer  104  of about 0.5 micron thick may be used to minimize high angle light emitted from the LED  102 . The refracting layer  104  has an index lower than the LED  102  and the polarizing layer  100 . The refracting layer  104  and polarizing layer  100  may be part of the same substrate or become a single component. The refracting layer  104  may be a material such as air or some other suitable material. Furthermore, the refracting layer  104  should be large enough to ensure no direct coupling between the LED  102  and the polarizing layer  100 . 
         [0027]    The refracting layer  104 , between the LED  102  and the polarizing layer  100 , may have the following properties. The index of refraction of the refracting layer  104  is less than the index of refraction of the LED  102  and the index of refraction of the polarizing layer  100 . In this configuration, the height of the refracting layer  104  is larger than 1 λ/nL to ensure no direct coupling between the LED  102  and the polarizing layer  100  takes place, where λ is the wavelength, and nL is the index of refraction of the refracting layer  104 . 
         [0028]    Turning to  FIGS. 3   b  and  3   c,  a beam shaping layer  106  may be used to ensure light that is not within the angle of acceptance of the polarizing layer  100  does not escape from the apparatus. The beam shaping layer  106  may be an optical element or filter that passes an angular range of incident light and reflects light falling outside the angular range due to TIR. The optical element may be formed by depositing several layers of material deposited onto a substrate (e.g., glass) by a physical vapor deposition process such as evaporative or sputter deposition or a chemical process such as chemical vapor deposition. An example of such an optical element is a periodic prism structure manufactured by 3M under the trademark Vikuiti™ Brightness Enhancement Film (BEF). Other optical elements that may be used include periodic structures formed with a number of lenses, mirrors, prisms, or other optical components, or any combination thereof. 
         [0029]    Referring to  FIG. 3   b,  the LED  102  is topped with a refracting layer  104 , and then the beam shaping layer  106  is placed on top of the refracting layer  104 . A polarizing layer  100  is then situated on top of the beam shaping layer  106 . 
         [0030]    In the structure shown in  FIG. 3   b,  light generated by the LED of  102  gets refracted through the refracting layer  104  with the high angular light getting reflected back by the beam shaping layer  106  through the refracting layer  104  to the LED  102 . Then the reflected light is randomly scattered by the roughened surface of the LED  102  and reflected by the back reflector (see  FIG. 1 ). The light reflected by the back reflector is recycled back up from the LED  102  through the refracting layer  104  to the beam shaping layer  106 . The recycling of light enables more light to pass through the beam shaping layer  106  to the polarizing layer  100 . At the polarizing layer, s-polarized light gets reflected back and later gets recycled back up. The p-polarized light gets emitted outwards which is expected to be of a brighter quality due to the recycling that was done by the beam shaping layer  106  and the polarizing layer  100 . The s-polarization and p-polarization may be interchanged with one another. 
         [0031]    Turning to  FIG. 3   c,  the LED  102  is topped with a refracting layer  104 , and a polarizing layer  100  is on top of the refracting layer  104 . A beam shaping layer  106  is then situated on top of the polarizing layer  100 . 
         [0032]    In the structure of  FIG. 3   c,  light generated by the LED  102  gets refracted through the refracting layer  104  to the polarizing layer  100 . At the polarizing layer  100 , p-polarized light is passed to the beam shaping optics layer  106  and s-polarized light is reflected back through the refracting layer  104  to the LED  102 . The reflected light is randomly scattered by the roughened surface of the LED and reflected upward by the back reflector (see  FIG. 1 ). The light reflected by the back reflector is recycled back up from the LED  102  through the refracting layer  104  to the polarizing layer  100 , where p-polarized light is passed to the beam shaping optics layer  106  and s-polarized light is reflected. The recycling of light in this fashion allows more light to pass to the beam shaping layer  106 . At the beam shaping layer  106 , high angle light gets reflected while light within a specified angular range gets emitted from the apparatus. Because of the refraction provide by the refracting layer  104 , more light should fall within the specified angular range of the beam shaping layer  106 . The light that is reflected by the beam shaping optics layer  106  gets recycled is much the same way as described earlier in connection with  FIG. 3   b.    
         [0033]    The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”