Beam combining optical element

Details Beam combining optical element Beam combining optical element

2000-03-20

2001-05-22

Mack, Ricky (Department: 2873)

Optical: systems and elements

Single channel simultaneously to or from plural channels

By partial reflection at beam splitting or combining surface

C359S742000

Reexamination Certificate

active

06236511

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to vehicle head-up display (HUD) systems, and more particularly, to a light-weight optical combiner which employs a Fresnel lens design.
BACKGROUND OF THE INVENTION
HUD systems typically are used in aircraft to provide pilots with information superimposed onto their forward field of view through the aircraft windshield. The information displayed may be data or symbolic images indicative of flight conditions such as the operating condition of the aircraft, environmental information or guidance information for use in bringing the aircraft to its destination. These images are presented in overlying fashion on the pilot's field of view so as not to interfere with the pilot's view of the background scene.
Although HUD systems may be useful in a variety of applications, known combiners are either undesirably thick and heavy for most applications, or are thin and undesirably highly curved. The thick combiners contain a pair of cooperative lens elements, at least one of which includes an embedded spherical surface coated with a spectrally reflecting thin film. The external surfaces of these thick combiners are flat so as to provide an undistorted view of the background scene. Thin combiners, on the other hand, typically employ a pair of spherical external surfaces, one of which carries the spectrally reflecting thin film. Thin combiners thus typically do not provide the necessary undistorted view of the background scene, especially when the combiner is thick enough to be adequately durable.
What is needed is an optical combiner which is thin and flat, but which contains sufficient optical power to present a collimated image on a relatively undistorted background scene.
SUMMARY OF THE INVENTION
Briefly, the invention concerns an optical combiner with a Fresnel lens having a Fresnel surface coated with a thin film spectrally selective reflective coating configured to reflect light within a first wavelength range, and transmit light within a second wavelength range. The optical combiner also includes a covering which covers the Fresnel surface and the reflective coating to provide a generally planar surface which is substantially parallel to a similarly planar exterior surface of the Fresnel lens. The covering may take the form of an optical adhesive (or of a second Fresnel lens) with an index of refraction which substantially matches the index of refraction of the Fresnel lens.
An optical system thus is provided for producing images and presenting them for observation in combination with an observer's visual exterior view of an outside world scene. The optical display system includes an image source providing an image carried by wavelengths of light propagating along an optical path toward an optical combiner positioned so that an observer can see the visual exterior view through the optical combiner and so that at least one of the wavelengths reflect off of the optical combiner to provide an image for observation by the observer. As indicated above, the optical combiner includes a Fresnel lens having a planar surface and a Fresnel surface opposite the planar surface, a reflective coating which coats the Fresnel surface of the Fresnel lens, and a covering which covers the reflective coating to provide a planar surface which is substantially parallel to the planar surface of the Fresnel lens. The reflective coating is configured to reflect light within a first wavelength range and to transmit light within a second wavelength range, and the covering is selected to have an index of refraction which substantially matches an index of refraction of the Fresnel lens.


REFERENCES:
patent: 3762809 (1973-10-01), Kato et al.
patent: 5625493 (1997-04-01), Matsumura et al.

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