Nissan Motor Company Limited

Central Glass Company, Limited

Tomohisa Ishikawa

Yoshinori Akamatsu

Tsuyoshi Todoriki

Junichi Fukano

Masayuki Hori

A holographic display apparatus reconstructs an image by projecting a beam of a luminous source to a holographic sheet including a plurality of holograms. The holograms are arranged so that the central axes of images recorded in the holographic sheet are directed in a same direction, in the diverging direction, or in a converging direction. Additionally, each hologram has a first focal distance f1 (mm) and a second focal distance f2 (mm) which are in a relationship such that f1.ltoreq.f2/28+50 and f1&lt;f2.

Holographic display apparatus

The invention relates to a holographic display element which includes a reflection hologram and is attached to, for example, an automobile windshield so as to project light rays carrying images of display information onto the display element from a luminous source in the car. When external light such as sunlight coming is diffracted by the reflection hologram there is a possibility that visible light ranging from 570 nm (greenish yellow) to 780 nm (red) is diffracted into a certain range of angles in a horizontal plane and makes a strange impression on persons viewing the windshield from the outside. According to the invention another reflection hologram having different diffraction characteristics is superposed on the first hologram on the outer side in order that diffraction of visible light into the aforementioned range of angles may become inconspicuous. In one embodiment the second hologram diffracts light of 570-780 nm at angles outside the aforementioned range of angles thereby to prevent undesirable diffraction by the first hologram. In another embodiment the second hologram diffracts different wavelengths into the range of angles so that additive color mixing with visible light diffracted from the first hologram results in whitening of diffracted light or reduction in the excitation purity of diffracted light as viewed outside the vehicle.

Growing community of inventors

Matsusaka, Japan

Tomohisa Ishikawa