News Column

Patent Issued for Reduction of Intensity Ringing in Fluorescent Displays

September 3, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Ralli, Philip J. (Sudbury, MA), filed on September 13, 2012, was published online on August 19, 2014.

The patent's assignee for patent number 8809811 is Prysm, Inc. (San Jose, CA).

News editors obtained the following quote from the background information supplied by the inventors: "This specification relates to display screens and display devices.

"Electronic display systems are commonly used to display information from computers and other sources. Scanning beam display systems use screens containing fluorescent materials to emit light under optical excitation to produce images. In some embodiments, the optical excitation is provided by one or more scanning excitation laser beams. The fluorescent materials are arranged into periodic patterns of pixels or sub-pixels in a fluorescent layer of the display. When a particular pixel or sub-pixel of the fluorescent layer is irradiated by the excitation light from an excitation source (e.g., a scanning UV laser), the fluorescent materials in that particular pixel or sub-pixel emits visible light, and forms a corresponding pixel or sub-pixels of an output image. In some embodiments, different colored fluorescent materials are arranged into repeated patterns of parallel stripes in the fluorescent layer of the display. When a scanning laser beam is scanned across each fluorescent stripe, the footprint of the scanning laser beam on the fluorescent stripe defines the boundary of a respective sub-pixel in the output image. In operation, the intensity of the scanning laser beam is time-modulated according to the image information for each sub-pixel. As the scanning laser beams scan across the fluorescent stripes, the composite light emitted by the different colored fluorescent stripes form an image with the appropriate color and intensity in each image pixel."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "This specification describes a technique for reducing non-uniformity in image formation resulted from unintended intensity variability in the excitation light received by a fluorescent layer of a display device. In some embodiments, the technique also produces sturdy and scratch resistant screen layers at a relatively low cost.

"In one aspect, in some embodiments (A): a display screen includes a light-emitting layer configured to emit visible light in a first wavelength range under irradiation of excitation light in a second wavelength range distinct from the first wavelength range, the light-emitting layer having a first side facing a viewer side of the display screen, and a second side facing an excitation side of the display screen; an excitation filter layer disposed on the excitation side of display screen relative to the light-emitting layer, and configured to selectively reflect the visible light in the first wavelength range and transmit the excitation light in the second wavelength range; and an intermediate layer disposed between and adjacent to the light-emitting layer and the excitation filter layer, wherein the intermediate layer includes one or more first regions in contact with the light-emitting layer, and a second region separating the one or more first regions from the excitation filter layer, and wherein the second region has a bridging refractive index between a first refractive index of the one or more first regions and a second refractive index of the excitation filter layer.

"In some embodiments (B) of the display screen (A), the second region of the intermediate layer is a layer of glass; and the one or more first regions are one or more air gaps created by a plurality of stand-off elements separating the layer of glass from the light-emitting layer.

"In some embodiments (C) of the display screen (A), the second region of the intermediate layer is a layer of PET; and the one or more first regions are one or more air gaps created by a plurality of stand-off elements separating the layer of PET from the light-emitting layer.

"In some embodiments (D) of any one of the display screens (A-C), the plurality of stand-off elements are a plurality of supporting ridges; and the plurality of supporting ridges create a plurality of air gaps in a low-index layer separating the second region from the light-emitting layer.

"In some embodiments (E) of any one of the display screens (A-D), the light-emitting layer comprises a plurality of colored fluorescent stripes, and the plurality of stand-off elements are stripe dividers each separating an adjacent pair of colored fluorescent stripes in the light-emitting layer.

"In some embodiments (F) of any one of the display screens (A-C), the plurality of stand-off elements are a plurality of supporting pillars; and the plurality of supporting pillars create an air gap separating the second region from the light-emitting layer.

"In some embodiments (G) of any one of the display screens (A-F), the plurality of stand-off elements each extend through the intermediate layer and at least part of the light-emitting layer.

"In some embodiments (H) of any one of the display screens (A-F), the plurality of stand-off elements each extend between the light-emitting layer and the excitation filter layer.

"In some embodiments (I) of the display screen (A), the intermediate layer comprises a unitary structure having the bridging refractive index, the unitary structure having a flat first surface in contact with the excitation filter layer, and a ridged second surface in contact with the light-emitting layer, wherein one or more recessed areas on the ridged second surface of the unitary structure form the one or more first regions in the intermediate layer.

"In some embodiments (J) of any one of the display screens (A-I), the excitation filter layer is a coextruded multi-layer film stack configured to create a transmission resonance for the excitation light in the second wavelength range.

"In some embodiments (K) of any one of the display screens (A-J), the excitation filter layer is configured to create a transmission resonance for ultra-violet light of 405-415 nm wavelength.

"In some embodiments (L) of any one of the display screens (A-K), the second region in the intermediate layer reduces intensity variations in the excitation light transmitted through the excitation filter layer to the light-emitting layer that have resulted from manufacturing variability in the excitation filter layer.

"In some embodiments (M) of any one of the display screens (A-L), the excitation light is ultra-violet light of 405-415 nm wavelength.

"In some embodiments (N) of any one of the display screens (A-M), the first refractive index is approximately 1.0, the second refractive index is approximately 1.67, and the bridging refractive index is approximately 1.43.

"In some embodiments (0) of any one of the display screens (A-N), the second region in the intermediate layer has a thickness of approximately 5 microns and the bridging refractive index is approximately 1.4-1.5.

"In some embodiments (P) of any one of the display screens (A-O), the light-emitting layer is a fluorescent layer having a thickness of approximately ten times a thickness of the second region in the intermediate layer.

"In some embodiments (Q) of any one of the display screens (A-P), the one or more first regions in the intermediate layer each have a thickness of approximately 20 microns and the second region in the intermediate layer has a thickness of approximately 5 microns.

"In some embodiments of any one of the display screens (A-Q), the display screen further comprises a color filter layer on the viewer side of the display screen relative to the light-emitting layer, and the color filter layer comprises a periodic array of colored filter elements configured to transmit different colored light according to a predetermined sub-pixel pattern.

"In some embodiments (S) of any one of the display screens (A-R), the light-emitting layer is a fluorescent layer emitting broad-spectrum visible light under irradiation of the excitation light.

"In some embodiments (T) of any one of the display screens (A-S), the light-emitting layer is a fluorescent layer comprising a periodic array of colored fluorescent elements configured to emit different colored light according to a predetermined sub-pixel pattern when irradiated by the excitation light.

"In some embodiments (U) of any one of the display screens (A-T), the display screen further includes one or more viewer-side layers disposed on the viewer side of the display screen relative to the light-emitting layer, the one or more viewer-side layers including one or more of: a UV block layer, a contrast enhancement layer, and an outer protective layer.

"In some embodiments (V) of any one of the display screens (A-U), the display screen further includes an excitation source; and one or more excitation-side layers disposed on the excitation side the display screen relative to the excitation filter layer, the one or more excitation-side layers including one or more of: a Fresnel layer, a servo layer, a mechanical support layer, and an antireflection coating layer.

"In another aspect, a process for making a display screen includes: applying a coating layer to a first side of an excitation filter layer, the excitation filter layer configured to selectively reflect visible light in a first wavelength range and transmit excitation light in a second wavelength range distinct from the first wavelength range, wherein the coating layer has a bridging refractive index smaller than a refractive index of the excitation filter layer; after applying the coating layer, applying an adhesive layer to a second side of the excitation filter layer; after applying the adhesive layer to the excitation filter layer, laminating the excitation filter layer to a substrate by rolling the adhesive layer to the substrate; and after the laminating, disposing a light-emitting layer over the coating layer on the first side of the excitation filter layer, wherein the light-emitting layer is separated from the coating layer by a plurality of air gaps.

"Particular implementations of the subject matter described in this specification can be implemented to realize one or more of the following advantages.

"A low-index region inserted between a light-emitting layer (including a light-emitting fluorescent layer and an optional thin substrate) and an excitation filter layer of a screen creates enhanced coupling of the excitation light to the fluorescent layer and reduced loss of emitted fluorescent light into the excitation side of the screen. However, the enhanced coupling of excitation light into the fluorescent layer is accompanied by heightened sensitivity to the uniformity of the excitation filter layer and frequency stability of the excitation source. As a result, small non-uniformities in the excitation filter layer and frequency drifts in the excitation light source can result in visible artifacts (e.g., watermarks) and intensity non-uniformity in the output images of the display screen. Insertion of an index bridging region between the low-index region and the excitation filter layer reduces the sensitivity of the excitation coupling to the non-uniformities in the excitation filter layer and variability in the output frequency of the excitation source, leading to improved uniformity of display intensity without significant compromise in the excitation coupling efficiency.

"In addition, in some embodiments, an index bridging structure made of a single hard coat layer laminated onto the pre-made excitation light filter provides a simple, effective, and inexpensive solution to the intensity ringing problem. The hard-coated excitation filter layer can be used in an existing display assembly process without requiring significant modifications to existing assembly equipment and display components. Furthermore, various manufacturing techniques can be used to produce the index bridging structure, providing a flexible and economic solution adaptable for many different display manufacturing processes.

"In addition, the hard coat layer also protects the excitation light filter from being scratched or damaged during the manufacturing process, and improves the structural strength and integrity of the screen layers.

"The index bridging layer in conjunction with the adjacent screen structures increases the delivery of excitation energy from the excitation sources to the light-emitting fluorescent elements of the display, increases the uniformity of the excitation energy delivered to each light-generating fluorescent element, and reduces leakage of visible light from one light-generating fluorescent element into adjacent light-generating fluorescent element. As a result, screen contrast, brightness, and power efficiencies are improved.

"The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims."

For additional information on this patent, see: Ralli, Philip J.. Reduction of Intensity Ringing in Fluorescent Displays. U.S. Patent Number 8809811, filed September 13, 2012, 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=8809811.PN.&OS=PN/8809811RS=PN/8809811

Keywords for this news article include: Prysm Inc.

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Source: Journal of Engineering


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