Patent
1980-04-15
1984-07-03
Arnold, Bruce Y.
350174, 350316, G02B 2714
Patent
active
044575793
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to an arrangement to reduce the influence from diffuse and direct reflections in a display device based on a source of light emitting in a narrow band where the image is regarded directly or through an optical system.
DESCRIPTION OF PRIOR ART
In fast aircrafts the pilot in certain situations cannot move the eyes from the field of view through the front window to the indicators which he must read because the aircraft during the time of reading will move too far. In order to render it possible for the pilot to read these indicators without reducing his attention to the outside view a semi-transparent mirror has been placed in the field of view through the front window. By means of this mirror symbols and indicator readings are reflected onto the field of view of the pilot so that he sees them clearly when the eye is focused on remote looking. An arrangement of this kind is usually called HUD, short for the English expression "head up display".
The symbols can for example be reflected from a cathode ray tube the display of which is projected through a lens system onto the semi-transparent mirror. As this mirror is planar the display will be in focus of the lens system. Sunlight accidentally passing the mirror towards the lens system will consequently be focused onto the display as a shining point which, however, does not essentially disturb the image.
Semi-transparent mirrors that are not wave-length selective have certain disadvantages when reflecting images onto a field of view since the transmission of incoming light and the reflection of the symbols are performed with low efficiency. Lately phase holograms have been used instead of such semi-transparent mirrors for reflecting symbols into the field of view of a pilot for example. Such arrangements are described for example in the Swedish Pat. No. 398 007 or the U.S. Pat. No. 3,915,548. Besides a high efficiency when reflecting and transmitting a hologram has the property that it also can refract the light in the same manner as lenses or spherical mirrors. In the above mentioned U.S. patent the hologram has been made in such a way that it works as a wave-length selective spherical mirror. Thus the exit pupil of the optical system will not depend on the dimensions of the lens system as in a conventional HUD-system, but it is possible to have a symbol presentation of remarkable size also when having a small dimension lens system. The lens system, the so called relay lens generates a virtual image of the symbol of the display unit in the focal plane of the spherical mirror enabling this image to be magnified as desired.
SUMMARY OF THE INVENTION
The contrast of the reflected symbol image, however, may be inferior as a diffuse reflection takes a large part of the field of view. This reflection also disturbs the transparency. In spite of the fact that the hologram performs a complicated filtering of incoming and reflected light the attenuation which is obtained is unsufficient. Sunlight can pass the hologram and fall towards the lens system which breaks the parallel sunlight towards a point in front of the display of the cathode ray tube. Consequently the display will be illuminated from this point and give a diffuse reflection which is thrown back via the lens system towards the hologram and further towards the observer who sees an unacceptable diffuse illumination of his field of view. There is a corresponding problem also in normal display units used for direct observation of a cathode ray tube where reflections are a big problem especially when they are to be used in sunlight.
According to the invention it is possible to reduce the influence of diffuse and direct reflections in a display device based on a light source emitting in a narrow band and the characteristics of the invention appear from the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described more in detail in connection with the accompanying drawing where FIG. 1 shows a display device with a semi-transparent mir
REFERENCES:
patent: 3454715 (1969-07-01), Larach et al.
patent: 3679297 (1972-07-01), Searle et al.
patent: 3915548 (1975-10-01), Oppittek et al.
Arnold Bruce Y.
Telefonaktiebolaget L M Ericsson
LandOfFree
Arrangement to reduce influence of diffuse and direct reflection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Arrangement to reduce influence of diffuse and direct reflection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Arrangement to reduce influence of diffuse and direct reflection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1627573