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Patent Issued for Wavelength Plate, Light Emitting Element, and Image Display Device Using the Light Emitting Element

September 3, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Katayama, Ryuichi (Tokyo, JP), filed on January 12, 2011, was published online on August 19, 2014.

The assignee for this patent, patent number 8807769, is NEC Corporation (Tokyo, JP).

Reporters obtained the following quote from the background information supplied by the inventors: "There has been offered an image display device that uses a light emitting diode (LED) as a light emitting element. The image display device of this type is configured by including a plurality of LEDs for respectively emitting lights of red , green (G), and blue (B) colors, an illumination optical system into which the lights from the plurality of LEDs enter, a light bulb including a liquid crystal display panel into which the lights from the illumination optical system enter, a color synthesis prism for synthesizing the lights of the respective colors from the light bulb, and a projection optical system for projecting the lights from the color synthesis prism onto a projection screen.

"In the image display device thus configured, to increase the luminance of a projected image, it is required to prevent light loss as much as possible in an optical path from the light emitting element to the projection optical system.

"Among the aforementioned components, the liquid crystal display panel and the color synthesis prism are polarization-dependent. To achieve high efficiency of the optical system, therefore, the light emitting element advisably emits linearly polarized light.

"As the light emitting element for emitting linearly polarized light, a light emitting element that includes a polarizer, a wavelength plate, and a reflection layer can be employed.

"As a light emitting element that includes the polarizer, the wavelength plate, and the reflection layer, there is an element that reflects the light reflected by the polarizer on the reflection layer via the wavelength plate, and that changes a polarizing direction again via the wavelength plate to enter the light into the polarizer, and an element that enters the light into first and second polarizers through which polarized lights orthogonal to each other are passed, that provides a phase difference to the light passed through one of the polarizers by the wavelength plate to change the polarizing direction, and accordingly that emits the lights passed through the first and second polarizers as linearly polarized lights made uniform in a polarizing direction.

"In the light emitting element thus configured, the wavelength plate for changing the polarizing direction is important. Generally, the wavelength plate has a narrow permissible range of incident angles to function as the wavelength plate, and thus widening the incident angle permissible range of the wavelength is one of the important factors for improving the performance of the light emitting element.

"Patent Literature 1 (JP2001-51122A) discloses, for the purpose of providing a birefringent element tat is industrially manufacturable at low costs, and that exhibits large birefringence having an optical axis within a plane, and is permitted a large opening area with a small optical path length, a periodic structure that is a z-axis direction multilayer structure including two or more types of transparent members whose refractive index in three dimensional orthogonal coordinates x, y and z: a shape of a layer as a stacking unit for each transparent member having a periodic concave-convex structure in an x axis direction and a periodic or nonperiodic concave-convex structure of a length uniform or larger than that in the x axis direction and in a y axis direction, and layers being stacked in a z axis direction by repeating the shape at each period shorter than a first Bragg condition in the z direction. By entering light to this periodic structure vertically or obliquely to an xy surface, and providing a phase difference between a polarized wave having an electric field component in the x direction and a polarized wave having an electric field component in the y direction, the periodic structure is used as a phase plate.

"Patent Literature 2 (WO2004-113974A1) discloses, for the purpose of expanding the operation band of a polarization separation element and increasing incident angle tolerance, a configuration for gradually changing a stacking period in the z direction with respect to the configuration disclosed in Patent Literature 1."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "Problems to be Solved by Invention

"According to the invention described in Patent Literature 2, the stacking period in the z direction is gradually changed. However, since the stacking period for the used wavelength is used as the polarization separation element, the stacking period is defined to be located in a band gap for polarized light (TE polarized light) parallel to the longitudinal direction of the concave-convex structure, and is located in a band for polarized light (TM polarized light) vertical to the longitudinal direction of the concave-convex structure. As a result, the stacking structure cannot be used as a wavelength plate.

"The present invention provides a wavelength plate capable of achieving high incident angle tolerance, a light emitting element capable of emitting linearly polarized light within a wide angle range, and an image display device that can achieve high light use efficiency.

"Solution to Problems

"According to the present invention, a wavelength plate in which a high refractive index layer and a low refractive index layer are alternately stacked, each layer having a concave-convex structure the period of which is equal to or shorter that a wavelength in one direction within a plane, includes, as periods in the thickness direction of the high refractive index layer and the low refractive index layer:

"a first period defined so that a used wavelength can belong to the first band of a photonic band structure; and

"a second period defined so that the used wavelength can belong to a wavelength side longer than the center wavelength of the second band of the photonic band structure.

"According to the present invention, a light emitting element having the aforementioned wavelength plate includes:

"a light emitting layer for emitting light;

"a polarizer and the wavelength plate arranged on an exit surface side with respect to the light emitting layer; and

"a reflection layer disposed on a side opposite the exit surface with respect to the light emitting layer.

"According to the present invention, an image display device uses the light emitting element of the aforementioned configuration.

"Effects of Invention

"In the wavelength plate configured as described above, incident angle tolerance can be increased. Thus, the light emitting element using this wavelength plate can emit linearly polarized light within a wide angle range, and the image display device using this light emitting element can achieve high light use efficiency."

For more information, see this patent: Katayama, Ryuichi. Wavelength Plate, Light Emitting Element, and Image Display Device Using the Light Emitting Element. U.S. Patent Number 8807769, filed January 12, 2011, and published online on August 19, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8807769.PN.&OS=PN/8807769RS=PN/8807769

Keywords for this news article include: Light Bulb, Electronics, NEC Corporation.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


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Source: Electronics Newsweekly


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