Abstract:
A system and method are disclosed employing a dielectric mirror layer, highly reflective at wavelengths below a cut off but highly transparent at wavelengths above the cut off, is placed within a display assembly. This dielectric mirror layer creates a very efficient reflecting cavity for a portion of a Light Emitting Diode (LED) pumping spectrum. Accurate dielectric filter tuning allows an increased portion of the pumping spectrum to be converted to desired wavelength spectrum and also raise the luminance ratio of the display to a useful value for display applications. Variable and active tuning of the cut off wavelength value functions to optimize system performance.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to display methods and layers of display systems. More particularly, embodiments of the present invention relate to a system and method for employing a quantum dot nano crystal layer within a display assembly for increased spectrum conversion from a broad spectrum of ultraviolet (UV) energy to a visual wavelength. 
     BACKGROUND OF THE INVENTION 
     Nano crystals or Quantum dot emissions may be uniquely tuned in wavelength outputs and possess very high conversion efficiencies. These properties may be potentially useful for display applications. Traditional implementation of nano crystals may use a blue Light Emitting Diode (LED) as a pump source. The blue LED pump source allows a portion of the blue wavelength to be converted to green and red wavelengths but also to be used as the emission source for the blue light projected from the Liquid Crystal Display (LCD). One drawback of the technology is that some of the blue LED pump emission spectrum will pass through the conversion layer in an unconverted state and the luminance ratio of the display being biased towards the pumping spectrum. 
     Polarization recycling filters offer some level of light recycling to increase efficiency. The concept being to recycle a portion of the energy that was not converted in a single pass through the nano crystal. 
     Another attempt at increasing the conversion of the pump wavelength has been incorporation of the nano crystals in a diffusing medium thus increasing the effective path length of the light. This diffusing medium does increase overall conversion but also suffers from losses into the backlight cavity. 
     Consequently, a need exists for an effective system and method for increasing spectrum conversion of an blue LED pump. 
     SUMMARY OF THE INVENTION 
     Accordingly, an embodiment of the present invention is directed to a system for efficient conversion of light through a display assembly, comprising: a light source configured to emit a light spectrum, a quantum dot nano crystal layer adjacent to the light source, the quantum dot nano crystal layer configured for conversion of the light spectrum from a first wavelength to a second wavelength, a dielectric mirror layer adjacent to the quantum dot nano crystal layer, the dielectric mirror layer more distal from the light source than the quantum dot nano crystal layer, the dielectric mirror layer configured for reflection of a first portion of the emitted light spectrum toward the quantum dot nano crystal layer, the dielectric mirror layer further configured for transmission of a second portion of the emitted light spectrum, and the quantum dot nano crystal layer is further configured for conversion of the reflected first portion of the emitted light spectrum from a third wavelength to the second wavelength. 
     An additional embodiment of the present invention may provide a system where first portion of the emitted light spectrum and the second portion of the emitted light spectrum reflected by the dielectric mirror layer are constant or are actively controlled via an external input. 
     An additional embodiment of the present invention may provide a system where the first wavelength spectrum is shorter than the second wavelength spectrum, the second wavelength is visible and the first wavelength equals the third wavelength. 
     An additional embodiment of the present invention may provide a system where the first portion is visible blue and the second portion is visible red and visible green and the quantum dot nano crystal layer and the dielectric mirror layer are configured to convert an emitted spectrum from one of: a blue light emitting diode light source, a white light emitting diode light source and an ultraviolet light source. 
     An additional embodiment of the present invention may provide a method for efficient conversion of light through a display assembly, comprising: emission of a light spectrum from a light source, conversion of the light spectrum from a first wavelength to a second wavelength by a quantum dot nano crystal layer adjacent to the light source, reflection of a first portion of the emitted light spectrum toward the quantum dot nano crystal layer by a dielectric mirror layer adjacent to the quantum dot nano crystal layer, the dielectric mirror layer more distal from the light source than the quantum dot nano crystal layer, transmission of a second portion of the emitted light spectrum by the dielectric mirror layer, and conversion of the reflected first portion of the emitted light spectrum from a third wavelength to the second wavelength by the quantum dot nano crystal layer. 
     An additional embodiment of the present invention may provide a method for efficient conversion of light through a display assembly, comprising: means for emission of a light spectrum, means for conversion of the light spectrum from a first wavelength to a second wavelength, means for reflection of a first portion of the emitted light spectrum toward the quantum dot nano crystal layer, the reflection means occurs after the conversion means, and means for transmission of a second portion of the emitted light spectrum, wherein the conversion means is further configured for conversion of the reflected first portion of the emitted light spectrum from a third wavelength to the second wavelength. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
         FIG. 1  is a diagram of a system for efficient conversion of light energy through a liquid crystal display assembly illustrative of an embodiment of the present invention; 
         FIG. 2  is a diagram of a system for efficient conversion of light energy through an embedded liquid crystal display assembly illustrative of an embodiment of the present invention; 
         FIG. 3  is a diagram of a system, configured proximal within a display assembly, for efficient conversion of light energy through the display assembly of a light emitting diode illustrative of an embodiment of the present invention; 
         FIG. 4  is a diagram of a system for efficient conversion of light energy through a compact display assembly of a light emitting diode illustrative of an embodiment of the present invention; 
         FIG. 5  is a graph of normalized spectral radiance of a pump emission over wavelength exemplary of an embodiment of the present invention; 
         FIG. 6  is a graph of spectral radiance reflected back into a cavity exemplary of an embodiment of the present invention; 
         FIG. 7  is a graph of dielectric filter transmission spectrum exemplary of an embodiment of the present invention; 
         FIG. 8  is a graph of exemplary spectrum transmitted by an embodiment of the present invention; and 
         FIG. 9  is a flow chart of a method for efficient conversion of light energy through a display assembly illustrative of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     The following description presents certain specific embodiments of the present invention. However, the present invention may be embodied in a multitude of different ways as defined and covered by the claims. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. 
     Embodiments of the present invention are directed to a system and related method for employing a quantum dot nano crystal layer within a display assembly for increased spectrum conversion from a broad spectrum of UV energy to a visual wavelength. However, skilled artisans will recognize additional spectrum conversion techniques function within the scope of the present invention. 
     In one embodiment of the present invention, systems herein may control, from a narrow to a broad spectrum, the wavelengths of conversion from UV to visible. Further, a single pass through a material may be insufficient to convert a desired amount of light with the nano crystals. Embodiments herein may convert additional energy through reflection into a cavity for “multiple passes” for reconversion by the nano crystal to a visible wavelength. 
     In embodiments, systems herein may preferably employ a UV source, a UV filter blocking all UV, followed by a layer of quantum dot nano crystals for accepting a broad wavelength band and converting to a more sharply defined band of desired wavelength to increase transmissivity of an LCD at the desired wavelength. 
     One embodiment of the present invention may comprise a desired layer of quantum dot nano crystals including blue nano crystals, green nano crystals, and red nano crystals enabling a display of one gamut of desired colors. One sharply defined band of desired wavelength may include a visual wavelength band. 
     Some embodiments of the present invention may include a filtering concept including selecting a specific wavelength of light. This selection may be a mechanical process in manufacture selectively controlling a specific wavelength which remains stationary during operation. This specific wavelength of light may then be physically filtered by layered elements of embodiments herein. 
     Additionally, embodiments of the present invention may actively and dynamically control the specific wavelength during operation. Elements of the present invention may function to actively alter a targeted specific wavelength or band for inclusion or exclusion from the desired emission. 
     Referring to  FIG. 1 , a diagram of a system for efficient conversion of light energy through a liquid crystal display assembly illustrative of an embodiment of the present invention is shown. System  100  may comprise a display assembly  102  backlight with an associated chassis. A LED Printed Wiring Board (PWB)  104  with an associated light source  110 . The light source  110  may preferably be one of white, royal blue and UV emitting a pump spectrum of light  112 . 
     A quantum dot nano crystal layer  120  may convert shorter wavelength light from pump spectrum  112  to a longer wavelength light including visible blue  128  while allowing visible red  124  and visible green  126  to pass. However, not all light may be converted by the quantum dot nano crystal layer  120  leaving a portion  122  of the light remaining unconverted. System  100  may efficiently reconvert this unconverted portion  122  of light through reflection and re-excitation of the quantum dot nano crystal layer  120 . 
     A dielectric mirror layer  130  may reflect the unconverted portion  122  of light back into the cavity as a reflected portion  132 . The dielectric mirror layer  130  may function as an interference filter for recycling UV light back into the cavity. The reflected portion  132  may then excite the quantum dot nano crystal layer  120  and be reconverted to a desired wavelength red  134 , green  136 , and blue  138 . Some of the reflected portion  132  may also continue back to the LED PWB  104  and be reflected for further transmission  142 . System  100  may be configured with a specific dielectric mirror layer  130  allowing red  124  and green  126  to pass unreflected through the dielectric mirror layer  130  while a portion of the blue  128  is reflected. 
     In some configurations of System  100 , a specific dielectric mirror layer  130  may allow a portion of the blue  128  of greater luminance and phototropic eye response to pass through the dielectric mirror layer  130  while reflecting a reflected portion  132  of the blue  128  to which the nano crystals within quantum dot nano crystal layer  120  may specifically respond. This reflected portion  132  may include a specifically targeted wavelength for desired reflection and conversion of a shorter wavelength from the source to a longer wavelength visible by a user. The blue  128  forms one portion of light the dielectric mirror layer  130  may be tuned to a specifically targeted wavelength to reflect. 
     System  100  may function independent of the physical geometry of associated layers. System  100  may employ a cavity  106  between quantum dot nano crystal layer  120  and dielectric mirror layer  130  to conform to display geometry constraints. Since wavelengths of targeted light bands are relatively small, the function of system  100  may be independent of cavity size  106 . 
     Diffuser plate  140  forms the rear of a well-known LCD stack  150  for transmission of each of the first portion of red  124 , green and  126  blue  128  and reconverted portion red  134 , green  136  and blue  138 . 
     In on embodiment, a UV light source excites a plurality of colors within quantum dot nano crystal layer  120 . Within the quantum dot nano crystal layer  120 , blue nano crystals emit blue, red nano crystals emit red, and green nano crystals emit green for a desired gamut of color spectrum transmission. 
     Referring to  FIG. 2 , a diagram of a system for efficient conversion of light energy through an embedded liquid crystal display assembly illustrative of an embodiment of the present invention is shown. Preferably, one embodiment of the present invention may include a pixelated (e.g., red, green and blue pixel elements, etc.) quantum dot nano crystal layer  220  aligned with a Thin Film Transistor (TFT) substrate  250  and a front pixel mask substrate  254  embedded within the LCD optical stack  150 . In this embodiment, placement of the dielectric mirror layer  130  may function best at the top of the LCD optical stack  150 . In addition, a secondary, pixelated dielectric light rejection filter  252  may be placed on the bottom of TFT substrate  250  to enhance color purity. 
     In this configuration, system  200  may employ select quantum dot material within pixelated quantum dot nano crystal layer  220  (one element with red material, one element for green, etc.). System  200  may then apply the pixelated dielectric light rejection filter  252  to properly recycle each wavelength band for each pixel element. 
     System  200  may increase transmissivity of the display assembly  102  employing pixelated quantum dot nano crystal layer  220  to convert wavelengths from shorter to longer. As before, dielectric mirror layer  130  may reflect unconverted portion  122  to reflected portion  132  for reconversion to visible red  134 , visible green  136  and visible blue  138 . 
     System  200  may efficiently reconvert this unconverted portion  122  of light through reflection and re-excitation of the pixelated quantum dot nano crystal layer  220 . 
     In addition, system  200  may employ specific coatings which may respond to outside stimuli offering a level of control of the transmissivity. Such specific coatings may include manufactured layers embedded within dielectric mirror layer  130 . 
     Referring to  FIG. 3 , a diagram of a system, configured proximal within a display assembly, for efficient conversion of light energy through the display assembly of a light emitting diode illustrative of an embodiment of the present invention is shown. One embodiment of the present invention may include a quantum dot nano crystal layer  120  configured proximal with the dielectric mirror layer  130  above an LED light source  110 . Pump spectrum  112  emits from LED light source  110  and enters and excites quantum dot nano crystal layer  120 . Quantum dot nano crystal layer  120  may convert shorter wavelength light from pump spectrum  112  to a longer wavelength light including visible blue  128  while allowing visible red  124  and visible green  126  to pass. 
     System  300  may employ a cavity  106  within which pump spectrum  112  may travel before reaching quantum dot nano crystal layer  120 . Reflected portion  132  of blue  128  may excite quantum dot nano crystal layer  120  for reconversion to one of visible spectra  134 ,  136 ,  138 . 
     The recycling and conversion may occur within the display assembly  102  over a plurality of passes. For example, on a first pass, dielectric mirror layer  130  of system  300  may allow a specific amount of light to transmit as visible  124 ,  126 ,  128  while a specific portion  132  is reflected. This reflected portion  132  may 1) excite quantum dot nano crystal layer  120  for reconversion to visible  134 ,  136 ,  138 , and 2) is reflected within cavity  106  as an additional pass through quantum dot nano crystal layer  120  for conversion to visible. The recycling and conversion may continue over many passes until pump excitation is exhausted. 
     Referring to  FIG. 4 , a diagram of a system for efficient conversion of light energy through a compact display assembly of a light emitting diode illustrative of an embodiment of the present invention is shown. System  400  may include LED PWB  104 , light source  110 , quantum dot nano crystal layer  120  and dielectric mirror layer  130  configured proximal within display assembly  102 . 
     Referring to  FIG. 5 , a graph of normalized spectral radiance of a pump emission over wavelength exemplary of an embodiment of the present invention is shown. Systems  100  through  400  may employ an exemplary white light source  110  emitting a pump spectrum  112 . As shown in graph  500 , a peak  510  of white radiance is indicated at approximately 450 nm. While an exemplary white light source pump curve is indicated with a peak radiance near 450 nm  510 , additional colors of light source may function within the scope of the present invention. For example, a blue LED in multiple wavelengths and UV LED light sources are contemplated as functional within the scope of the present invention. 
     Referring to  FIG. 6 , a graph of spectral radiance reflected back into a cavity exemplary of an embodiment of the present invention is shown. Systems herein may employ a specific dielectric mirror layer  130  tuned to reflect a specific wavelength band with a specific cut-off wavelength of light back toward the quantum dot nano crystal layer  120  for recycling and further conversion. As graph  600  indicates, this targeted wavelength  610  may be specifically tuned to maximize performance of quantum dot nano crystal layer  120  for reconversion and further transmission as visible red  134 , green  136  and blue  138 . Here, an exemplary 450 nm is tuned to reflect back toward quantum dot nano crystal layer  120  for reconversion. 
     As previously indicated, systems  100  through  400  may actively target a desired wavelength for reflection back toward quantum dot nano crystal layer  120 . This active control of a targeted wavelength may dynamically increase performance of the overall display assembly  102 . For example, a specific wavelength of blue  128  may be targeted for reflection and reconversion for a specific display configuration. An exemplary 470 nm may be the desired and therefore targeted wavelength for reconversion for a specific display quality. Alternatively an exemplary 440 nm may be the desired and therefore targeted wavelength for reconversion for an additional specific display quality. As reflected portion  132  may be targeted, transmission spectrum through dielectric mirror layer  130  may also be targeted. 
     Referring to  FIG. 7 , a graph of dielectric filter transmission spectrum exemplary of an embodiment of the present invention is shown. As graph  700  indicates, transmission spectrum of dielectric mirror layer  130  may be indicated as all levels above an exemplary specific cut-off wavelength, here approximately 450 nm  710 . At specific wavelengths of transmission, systems  100  through  400  may maintain control of transmission spectra as well as reflected spectra. 
     Referring to  FIG. 8 , a graph of exemplary spectrum transmitted by an embodiment of the present invention is shown. One exemplary level of transmitted spectrum radiance may be derived from a combination of spectrum emitted by a source pump ( FIG. 5 ) and spectrum not filtered by Dielectric Filter ( FIG. 7 ). For example, a multiplication of pump spectrum by dielectric filter transmission spectrum may yield a portion of spectrum actually transmitted ( FIG. 8 ). As shown in graph  800 , a peak  810  indicated near approximately 460 nm may be the targeted transmission spectrum for a specific display characteristic. 
     System  100  may be specifically configured for application within a plurality of display systems. For example, one embodiment of the present invention may be specifically configured for, without limitation, application within a projection display system while another embodiment of the present invention may be configured for a heads up display system. 
     Referring to  FIG. 9 , a flow chart of a method for efficient conversion of light energy through a display assembly illustrative of an embodiment of the present invention is shown. Method  900  begins at step  902  with emission of a light spectrum from a light source, and, at step  904  with conversion of the light spectrum from a first wavelength to a second wavelength by a quantum dot nano crystal layer adjacent to the light source, and, at step  906  with reflection of a first portion of the emitted light spectrum toward the quantum dot nano crystal layer by a dielectric mirror layer adjacent to the quantum dot nano crystal layer, the dielectric mirror layer more distal from the light source than the quantum dot nano crystal layer, and, at step  908  with transmission of a second portion of the emitted light spectrum by the dielectric mirror layer, and, at step  910  with conversion of the reflected first portion of the emitted light spectrum from a third wavelength to the second wavelength by the quantum dot nano crystal layer. 
     CONCLUSION 
     Specific blocks, sections, devices, functions, processes and modules may have been set forth. However, a skilled technologist will realize that there are many ways to partition the system, and that there are many parts, components, processes, modules or functions that may be substituted for those listed above. 
     While the above detailed description has shown, described and pointed out the fundamental novel features of the invention as applied to various embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the system illustrated may be made by those skilled in the art, without departing from the intent of the invention. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears, the invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.