Controlled diffraction efficiency far field viewing devices

Details Controlled diffraction efficiency far field viewing devices Controlled diffraction efficiency far field viewing devices

2000-09-27

2002-09-17

Spyrou, Cassandra (Department: 2872)

Optical: systems and elements

Holographic system or element

Head up display

C359S009000, C359S022000, C359S024000, C359S025000, C359S567000, C351S051000

Reexamination Certificate

active

06452699

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to controlling the brightness of light patterns created by a hologram. More specifically, this invention balances the brightness of a far field holographic light pattern and the clarity of a scene when viewed through a far field viewing device.
2. Background Information
Holograms of many different types have become commonplace in modern society. They are used as ornaments and as novelty items, as well as security devices on credit cards. A hologram is a pattern recorded on a substrate that provides a predetermined light diffraction effect.
There are many different types of holograms that are differentiated from one another by their optical properties and behavior. Most of the commonly seen holograms depend upon reflection of light from the hologram to the observer's eye. Less commonly seen are transmission type holograms wherein light passes through the hologram.
When an observer looks through a far field hologram at a scene that contains compact bright points of light, the observer sees holographic diffracted light patterns associated with each bright point location. We define this unique form of display holography as a far field viewing application. Far field viewing devices are made up of physical apertures (or frames) and far field holograms combined in a way designed for viewing a scene and superimposing holographic light patterns around each compact bright point of light in the scene.
Referring to
FIG. 1
, a far field viewing device containing of a far field hologram
10
mounted in a frame
12
is illustrated. The far field viewing device is placed in front of an observer's eye
14
. The observer's eye
14
looks through far field hologram
10
mounted in frame
12
at a scene containing at least one bright compact source of light
16
. Each point in the scene is viewed through a utilized hologram area
18
. Schematic depictions of a tree and a star represent scene elements
20
that the observer wants to see in sharp focus.
Examples of far field viewing devices include the eyeglass device containing far field holograms as described in U.S. Pat. No. 5,546,198, as well as far field holograms mounted in windows. Ordinarily, a human observer looks through a far field device. Additionally, far field devices can also be incorporated into film-based or electronic image capture devices, such as still or motion cameras.
An example of an algorithm for calculating computer generated holograms is described by Gallagher and Liu. See N. C. Gallagher and B. Liu, “Method for Computing Kinoforms That Reduces Image Reconstruction Error” Applied Optics, v. 12, pp.2328-2335 (1973). The output of the algorithm is a set of numerical values. Each value corresponds to the desired complex transmittance at a different spatial location on the physical hologram. The resultant data set is used to drive any of a variety of fabrication methods which impose the desired transmittance values onto a physical substrate. There are a number of methods for producing a physical computer generated hologram from a set of date. These are summarized in the textbook MICROOPTICS [editor Hans P. Herzig, published by Taylor and Francis, London 1997] in chapters 4 and 5. An original hologram can be used as a master and copied or replicated using a variety of techniques as discussed in chapter of 7 of Herzig's MICROOPTICS.
Referring to
FIG. 2
, an idealized view of the overall scene as seen through an ideal far field viewing device is illustrated. The ideal view contains a well-focused representation of scene elements
220
in addition to a desired diffracted light pattern
222
produced by light diffracted by the far field hologram adjacent a bright compact source of light
216
. In the example, the hologram has been tailored to diffract the light pattern in the form of letters spelling the word “NOEL”.
FIG. 2
shows only one bright compact point of light to keep the illustration simple. In the case where many such sources of light are present, the desired diffraction pattern will surround each bright compact source of light.
A salient aspect of far field viewing applications that is different from most display hologram applications is that the observer is encouraged not to focus all of the attention on the holographic diffracted light pattern. Instead, the observer focuses on an overall scene in a unique combination with the holographic diffracted light patterns at each bright point source of light present in the scene. Accordingly, it is important for the viewing device to present a clear image of the scene while also presenting bright holographic light patterns.
It is also desirable for a far field viewing device to have a loose tolerance for the distance between the observer's eye and the hologram so that the viewer is not forced to maintain a particular position relative to the far field viewing device.
Additionally, it is desirable for the hologram in a far field viewing application to be capable of producing relatively large diffracted light patterns containing fine spatial detail.
The problem of balancing the clarity of the scene and the brightness of the holographic light patterns is not common in display holography. In most applications of display holography, the hologram is designed to diffract as much of the light as possible to create the brightest possible holographic reconstruction. Such a hologram is said to have high diffraction efficiency. The push in the industry is directed to design methods and fabrication processes that maximize the diffraction efficiency of display holograms since most applications of display holography call for maximum brightness in the holographic reconstruction.
Referring to
FIG. 3
, a view through a high diffraction efficiency far field hologram is illustrated. The scene elements appear as blurred images
324
when viewed through a far field transmission hologram having a high diffraction efficiency.
FIG. 3
also shows that such a far field hologram also produces an undesired diffracted light pattern
326
, symmetrically disposed about a bright compact light source
316
in the form of a mirror image of desired diffracted light pattern
322
.
In contrast, our goal for far field viewing applications is to attain a diffraction efficiency that is often considerably less than the diffraction efficiency produced by standard methods for designing and fabricating holograms. When a highly efficient far field hologram is used in a far field viewing application, the diffracted light patterns are bright but the scene appears blurred. This effect on the view of the scene is much like looking through a light diffusing piece of shower glass, and it is undesirable since viewing, not obscuration, is desired. On the other hand, when the hologram has low diffraction efficiency the scene observed through the hologram appears well focused, but the holographic light patterns surrounding the point sources of light in the scene are not sufficiently bright.
Whereas the prior art provides no way to simultaneously maximize the scene clarity and the brightness of the holographic light patterns, we recognize that the diffraction efficiency of the hologram should be chosen to strike an optimum balance between the un-diffracted energy and the energy in the desired diffracted light pattern. The optimum diffraction efficiency can depend on the nature of the desired holographic pattern as well as the expected scene characteristics. Thus, flexible and simple control in achieving the desired diffraction efficiency of the hologram is needed.
One broad approach to the problem of reducing diffraction efficiency would be to start with an established method that produces high diffraction efficiency and to modify the approach to obtain reduced diffraction efficiency. The need for intentionally reducing diffraction efficiency of a far field hologram in a controlled manner has not been recognized in the prior art. In contrast, we have made it a goal to increase the amount of un-diffracted light by re

Affiliated with

Also associated with

Rating

Controlled diffraction efficiency far field viewing devices does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Controlled diffraction efficiency far field viewing devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Controlled diffraction efficiency far field viewing devices will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2823654