Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1988-09-14
1991-11-26
Miller, Stanley D.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
351 41, 359 99, 359 90, 359 93, G02F 113, G02C 0000
Patent
active
050677950
DESCRIPTION:
BRIEF SUMMARY
This invention concerns adjustable transparency eyewear, such as spectacles and visors. More particularly, the invention concerns spectacles equipped with liquid crystal means allowing the user to adapt the transparency of lenses to variation in external luminosity, even if sudden.
As is well known, whenever the external luminosity is suddenly reduced or increased, conventional sun-spectacles now in use have the deficiency of an annoying sensation of darkening or of dazzling, with an objective and sudden lessening of visual capacity, capable of causing substantial risks to the user.
An example of the foregoing is the effect on the driver of a car upon entering or exiting from a road tunnel.
There presently are available some sun spectacles, with lenses in photochromic glass, which effects at least a partial reduction of these difficulties. Actually said type of glass has the property of becoming absorbent, and therefore dark, under the action of light, and clear under conditions of reduced luminosity, thus allowing the production of lenses having the transparency thereof adjustable in an adequate manner, but not with that speed of intervention required and needed in special situations.
Actually the time of variation in the transparency should not exceed 1/10th of a second in order to minimize the referred to phenomena of darkening and of dazzling, while that typical of the photochromic glasses is in the order of several seconds.
Furthermore, with the photochromic glasses, it is impossible to operate directly upon the transparency of the lenses, since the latter depends directly on the quantity of light recently absorbed.
Other means are also known, capable of regulating the transparency of an opening, such as for instance the devices formed by two polarizers of plastic material, placed one upon the other and assembled in such a way as to be able to be relatively rotated, thus allowing adjustment of the transparency within wide limits. However, this apparatus is not suitable to being readily assembled in a pair of spectacles, since in order to effect the mechanical operation above described, there would be required a structure that is not the compact and light weight structure which is typical of spectacles.
The evolution of electronic technology in the field of display devices, used for the presentation of images, has led to the production of electrooptical; cells, as well as of similar contrivances which, in some special embodiments, are capable of rapidly adjusting the transparency thereof.
However, it is to be noted that, for the specific application of these cells to adjustable transparency lenses for spectacles, they should necessarily be able to satisfy the following requirements:
Adjustable transparency spectacles including liquid crystal cells are disclosed in WO 81/02795. In that disclosure, however, the lenses are provided with layers of polarization material.
To provide lenses for adjustable transparency spectacles, having the above referred to characteristics, the present invention uses liquid crystals cells of the dichroic type.
Cells of this glass are capable of causing variation of the transparency without any light diffusion, and without requirement the use of polarizers.
As a general rule, by dichroic cells is meant those in which the liquid crystal has dichroic properties. They mostly are derived from a small percentage of one or more dichroic dyes, whose molecules show an average alignment parallel to that of the liquid crystal holding them in solution.
The fundamental property of a dichroic element (material and/or substance) is that of absorbing light in a greater measure when the electric field of an incident electromagnetic wave (perpendicular to the direction of propagation and being oriented along the plane of polarization) is parallel to a characteristic direction thereof.
By dichroic ratio is meant the ratio between the maximum and minimum optical densities, which can be measured, under polarized light, parallel-wise and perpendicular-wise in reference to the characteristic direc
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White et al., "New Absorptive Mode Reflective Liquid Crystal Display Device", Journal of Applied Physics, vol. 45, No. 11, Nov. 1974, pp. 4718-4723.
Gharadjedaghi et al., "Mathematical Simulation of a Positive Contrast Guest-Host Display Using Nematic crolesteric Phase Change", J. Appl. Phys. 53(11), Nov. 1982, pp. 7306-7313.
Uchida et al., "Liquid Crystal Orientation on the Surface of Obliquely-Evaporated Silicon Monoxide With Homeotropic Surface Treatment", Japanese Journal of Applied Physics, vol. 19, No. 11, Nov. 1980, pp. 2127-2136.
Gianni Bulgari S.p.A.
Miller Stanley D.
Phan Trong
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