Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Utility Patent
1997-06-03
2001-01-02
Henry, Jon (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S033000, C359S034000
Utility Patent
active
06169613
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to holographic optical devices, and particularly to devices which include a plurality of holographic optical elements (HOEs) carried by a common light-transmissive substrate. The invention is capable of being implemented in a large number of applications. Described below, for purposes of example, are the following implementations: division multiplexing/ demultiplexing systems; compact holographic displays; compact holographic beam expanders and compressors; and holographic visor or head-up displays.
Recently, there have been significant advances in optical fibers technology for telecommunication systems. One of the proposed methods to exploit more efficiently the high potential bandwidth of optical fibers is by wavelength division multiplexing (WDM). With this technique, a large number of communication channels can be transmitted simultaneously over a single fiber. During the last decade, various systems for implementing WDM have been proposed, including systems based on birefringent materials, surface relief gratings, Mach-Zender interferometry, and waveguides. Unfortunately, these proposed systems generally suffer from low efficiencies or from a strict limitation on the number of channels.
Another proposed approach is to use a thick reflection hologram as described in N. Moslehi, P. Harvey, J. Ng and T. Jannson, Opt. Lett. 14,(1989) 1088. However, the necessity to use a conventional aspheric lens for collimating and/or focusing the light waves makes the system bulky and space consuming. Furthermore, a single holographic element is very sensitive to the signal's wavelength which usually depends strongly on temperature. One application of the present invention described below enables wavelength division multiplexers/ demultiplexers to be constructed having advantages in the above respects.
The invention also enables improved holographic displays to be constructed. Since its inception three decades ago, there has been significant progress in the area of display holography. Indeed, it has become so popular as to play an important role in advertising, packaging and even in art. Yet, the current form of display holograms has some severe drawbacks. The necessity to use a readout light source that must be located at some distance from the hologram, in order to illuminate its whole surface, makes the holographic display systems bulky, space consuming, and sometimes inconvenient to use. Another drawback is that the transmitted part of the readout wave, which is not diffracted by the holograms, usually bothers the observer.
Recently, there have been several proposals, based on edge-illuminated holograms for constructing compact displays that overcome the above drawbacks. The salient feature of these proposals is to reconstruct the holograms with a readout wave which enters the hologram substrate through a polished edge so as to reach the emulsion at a large angle of incidence. Unfortunately, the necessity to enter the is comprised of an array of points whose geometry at readout differs from that at recording. As a result, the imaged array contains aberrations that decrease the image quality. In addition, it is often necessary to record the HOEs at a wavelength that differs from the readout wavelength. This is particularly true when the readout wavelength is not suitable for recording the HOEs. Such a wavelength shift introduces additional aberrations.
Another problem, which is usually common to all types of diffractive optical elements, is their relatively high chromatic dispersion. This is a major drawback in applications where the light source is a CRT which is not purely monochromatic.
Recently several new designs were proposed for improving the performance of holographic lenses. These designs, which only deal with single HOEs, compensate for the geometric and chromatic aberrations by using nonspherical waves rather than simple spherical waves for recording. However, they do not overcome the chromatic dispersion problem.
The present invention may also be used for designing and recording HOEs for visor displays in which both the aberrations and chromatic dispersions are minimized. It is particularly advantageous because it is very compact and can be readily incorporated even into optical systems that have specialized configurations
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
According to a broad aspect of the present invention, therefore, there is provided a holgraphic optical device, comprising: a light-transmissive substrate; a first holographic optical element carried by the substrate; and a second holographic optical element carried by the substrate laterally of the first holographic optical element; characterized in that at least one of the holographic optical elements is a complex diffraction grating that can handle a multiplicity of plane waves and/or spherical waves arriving from a range of angles, and/or having a range of wavelengths.
As indicated earlier, one application of the invention is as a novel wavelength division multiplexer/demultiplexer, in which the device serves for the transmission of optical signals of a plurality of channels of different wavelengths between (a) a plurality of optical transmission paths, one for each channel, and (b) a single optical transmission path for all the channels. In this application, the holographic optical elements include: a single hologram aligned with the single optical transmission path and having a plurality of holographic optical elements, one for each of the channels; and a plurality of holograms, each aligned with one of the plurality of optical transmission paths and having a holographic optical element for the channel of the respective path.
In further described applications of the invention, the first holographic optical element is constructed to convert an input beam of light into a diverging spherical wave at a high off-axis angle such that the wave propagates by total internal reflection towards the second holographic optical element to illuminate the second holographic optical element and to emerge from the substrate by means of the second holographic optical element. In one such application, the second holographic optical element is a display hologram illuminated by the internally reflected light from the first holographic optical element so as to reconstruct a three-dimensional image.
According to additional applications of the invention, the first and second holographic optical elements are both holographic lenses. These lenses may be constructed such that the lateral dimensions of the light beam emerging from the substrate at the second holographic lens is either a magnification, or a de-magnification, of the lateral dimensions of the light beam entering the substrate to the first holographic lens, so as to provide a beam expander or compressor which can be used with both monochromatic light as well as polychromatic light.
A still further application of the invention described below is a holographic visor display or head-up display. In this application, the first holographic optical element collimates the waves from each data point in a display into a plane wave that is trapped inside the substrate by total internal reflection, and the second holographic optical element constitutes the complex diffraction grating and diffracts the plane waves into the eye of an observer.
REFERENCES:
patent: 3970357 (1976-07-01), Moraw et al.
patent: 4235442 (1980-11-01), Nelson
patent: 4248093 (1981-02-01), Andersson et al.
patent: 4249744 (1981-02-01), Bromley
patent: 4367876 (1983-01-01), Kotoyori
patent: 4407564 (1983-10-01), Ellis
patent: 4624462 (1986-11-01), Itkis
patent: 4671603 (1987-06-01), McQuoid et al.
patent: 4711512 (1987-12-01), Upatnieks
patent: 4768853 (1988-09-01), Bhagavatula
patent: 4866694 (1989-09-01), Korth
patent: 4946253 (1990-08-01), Kostuck
patent: 4998787 (1991-03-01), Caputi et al.
patent: 5013047 (1991-05-01), Schwab
patent: 5061027 (1991-10-01), Richard
patent: 5082286 (1992-01-01), Ryan
patent: 5101460 (1992-03-01), Richard
p
Amitai Yaakov
Friesem Asher Albert
Shariv Isaac
Henry Jon
Ladas & Parry
Yeda Research & Devel Co., Ltd.
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