Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2000-06-30
2001-04-03
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S022000, C359S024000, C359S618000, C349S201000, C349S202000, C353S030000, C353S031000
Reexamination Certificate
active
06211976
ABSTRACT:
RELATED APPLICATIONS
This application claims priority to U. S. Provisional Application No. 60/100,218, entitled “Holographic Illumination System,” by inventors Milan M. Popovich and Jonathan D. Waldem, filed Sep. 14, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to illumination systems, and particularly to light sources in video projection displays.
2. Description of the Related Art
Projective display systems are a growing technology in the market of televisions and digital monitors. Projective displays use images focussed onto a diffuser to present an image to a user. The projection may be done from the same side of the diffuser as the user, as in the case of cinema projectors, or from the opposite side. The image is typically generated on one or more “displays”—a miniature LCD device that reflects or transmits light in a pattern formed by switchable pixels. The LCD displays are generally fabricated with microelectronics processing techniques. Each pixel in the display is a region whose reflective or transmissive properties can be controlled by an electrical signal. In an LCD display, light incident on a particular pixel is either reflected, partially reflected, or blocked by the pixel, depending on the signal applied to that pixel. In some cases, LCD displays are transmissive devices where the transmission through any pixel can be varied in steps (gray levels) over a range extending from a state where light is substantially blocked to the state in which incident light is substantially transmitted. More recently, displays have also been constructed from micro-electromechanical devices (MEMs) that incorporate small movable mirrors. The mirrors, one or more at each pixel, control whether or not light is reflected into an output direction.
When a uniform beam of light is reflected from (or transmitted through) a display, the beam gains a spatial intensity profile that depends on the transmission state of the pixels. An image is formed at the LCD by adjusting the transmission (or gray level) of the pixels to correspond to a desired image. This image can be imaged onto a diffusing screen for direct viewing or alternatively it can be imaged onto some intermediate image surface from which it can be magnified by an eye-piece to give a virtual image, as for example in a wearable display.
The displays are generally monochromatic devices: each pixel is either “on” or “off” or set to an intermediate intensity level. The display typically cannot individually control the intensity of more than one color component of the image. To provide color control, a display system may use three independent LCD displays. Each of the three LCD displays is illuminated by a separate light source with spectral components that stimulate one of the three types of cones in the human eye. The three displays each reflect (or transmit) a beam of light that makes one color component of a color image. The three beams are then combined through prisms, a system of dichroic filters, and/or other optical elements into a single chromatic image beam.
Another method of generating a full color image, which eliminates the problems of combining the beams from three separate displays is to sequentially illuminate a single monochromatic display that is updated with the appropriate primary color components of the image.
The displays can be configured as arrays of red, green, and blue pixels that are illuminated by white light with arrays of color filters being used to illuminate each pixel with the appropriate color. However, generating a color image in this manner will reduce image resolution since only one third of the pixels are available for each primary color.
A significant part of the design considerations for these systems involves the choices of light sources and provisions for effective control over the relative intensities of the light sources. This control is required to allow effective color balancing during initial calibrations as well as during operation.
Holograms essentially generate predetermined wavefronts by means of diffractive structures recorded inside hologram mediums. A hologram may be used to reproduce the effects of a particular optical element, such as a lens or a mirror. In certain cases, where complex optical operations are not being reproduced, “holographic optical elements” (HOEs) may be based on simple diffraction gratings. These HOEs may be far easier and less expensive to produce than their glass counterparts, especially when the optical element is complicated or must meet stringent tolerances. HOEs can be compact, lightweight and wavelength specific which allows more flexibility in designing optical systems. HOEs may be used to replace individual optical elements, groups of elements and in some cases entire systems of conventional optical components.
SUMMARY OF THE INVENTION
Holographic optical elements (HOEs) can be used in systems and methods for providing illumination and for projecting images. The HOEs may be electrically switchable HOEs, whose diffractive properties can be controlled. In one embodiment, a switchable HOE can be gradually and reversibly switched from a diffracting state to a transmitting state by an applied electrical field.
Described herein is a method of combining light from two or more different illumination sources. The method includes illuminating a reflective or transmissive-type holographic optical element (HOE) with light from the first illumination source. The HOE diffracts light from the first illumination source into an output direction. This output direction may be an image display (or “video display”) or any other object that needs to be illuminated. Light from the second illumination source is transmitted through the HOE (either because it is of the wrong color or has the wrong incidence angle) and onto a reflective optical element, which reflects the light back through the HOE and into the same output direction as the first illumination source.
The reflective optical element may also implemented as a holographic element, making it a second HOE. Additionally, the reflective HOE and/or the reflective optical element may be a switchable HOE. Further, one or both of these devices may also be used to compensate for aberrations in a an image projected in the light or to otherwise modify spatial profiles of the light. The first and second illumination sources may be used to provide light of different colors.
Also described is an illumination system comprising an HOE and a reflective optical element. The HOE is configured to diffract light from a first light source into an output direction. The reflective optical element is disposed so that light from a second light source passes through the HOE and onto the reflective optical element. The reflective optical element reflects light from the second light source into the same output direction.
The reflective optical element may be a second HOE that diffractively reflects light from the second light source into the output direction. One or both of the elements may be a switchable HOE, and one or both of them may be used for aberration correction or for beam-shaping.
This disclosure further describes a projection system that uses two or more HOEs to combine two or more colors of light from two or more different light sources. The system includes a first light source for a first color of light, a second light source for a second color of light, an image display (such as a reflective or transmissive LCD display or a MEMS display, for example), and a first and a second HOE. The first HOE is mounted between the image display and the first light source, and is configured to provide the first color of light from the first light source to the image display and from the image display into an output direction. Similarly, the second HOE is mounted between the image display and the second light source, and is configured to provide the second color of light from the second light source to the image display and from the image display into the same output direction.
Each HOE preferably us
Popovich Milan M.
Storey John J.
Waldern Jonathan D.
Boutsikaris Leo
DigiLens Inc.
Skjerven Morrill & MacPherson LLP
Spyrou Cassandra
LandOfFree
Holographic projection system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Holographic projection system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Holographic projection system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2508509