Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1996-10-28
1998-06-09
Nelms, David C.
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359265, 359268, 359275, 359245, 349 33, 310321, G02F 103, G02F 115, H01L 4104
Patent
active
057644020
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a control system for an optical cell (also called a light valve).
An optical cell may be formed by sandwiching a layer of sensitive material between two parallel plates of rigid, generally transparent sheet material, each plate having an electrically conducting surface layer facing the sensitive material. Examples of constituents of the sensitive material include suspended particles, liquid crystals and a layer of electrochromic material.
By applying or not applying an electric potential across the facing plates the constituents can be switched between a state in which light can pass and a state in which light is absorbed, scattered or reflected.
Optical cells, including optical cells having a control system according to the invention, can be used in mirrors or in glazing panels for vehicles or buildings so as to provide variable light transmission. For example they can be used as a glazing panel adjustable between an opaque and clear condition to limit solar transmission or to conceal the interior of a room or vehicle to provide privacy therein. They can be used in a vehicle sun-visor or sunshine roof panel or on an aircraft porthole.
The control system of the invention is particularly well suited for use with an optical cell used in a rear-view mirror of a motor vehicle, and is described herein largely with reference to that application.
The use of an optical cell in a rear view mirror is known for example from French patent specification FR 2 366 958 (Brisard Gerard) so as to provide a rear-view device in which the reflectivity varies as a function of the degree of dazzle. Traditional vehicle rear-view mirrors with an anti-dazzle feature, often called "prismatic" mirrors, have a "day" position and a "night" position, the mirror position being changed manually by the vehicle driver between the day and night positions. In the day position the degree of luminous reflectivity from a rear-view mirror is required to be high, generally greater than 50%. In the night position the reflectivity is limited to 12% or less, often about 4%, in order to avoid dazzling of the driver by fights such as the headlights of following vehicles.
Optical cells offer a rear-view mirror with the possibility of automatic adjustment according to the incident light conditions, adjusting from day to night positions and vice versa and to intermediate variations between those limits, thereby giving advantages in terms of convenience and safety. The cell is located adjacent and parallel to the reflective surface of the mirror and in the line of sight between the reflective surface and the vehicle driver. The cell thus provides a variable level of light reflection from the mirror to the driver. In one preferred configuration the reflective layer is provided by one of the electrically conducting layers being a material which is also reflective.
The level of light transmission or reflection through the optical cell is adjusted by the control system, which is activated by the external conditions. The control system is desirably housed alongside the optical cell so as to form a combined unit therewith. Traditional control systems have however been of a bulk which has made for difficulties in miniaturising any unit of which they have formed a part.
An object of the present invention is to provide a control system for an optical cell which can be conveniently accommodated adjacent to the cell.
According to the invention there is provided a control system for an optical cell, which system comprises a first circuit supplied by a low voltage power source and including an oscillator and a primary winding of an induction coil and further comprises a secondary circuit which includes the optical cell and a secondary winding of the aforementioned induction coil, characterised in that the secondary circuit is a resonant circuit which includes the inductance of the secondary winding and the optical cell, and the induction coil provides a weak coupling between the primary and secondary windings.
The control system of the inventi
REFERENCES:
patent: 3991416 (1976-11-01), Byles et al.
patent: 4212513 (1980-07-01), Gravel
patent: 5189547 (1993-02-01), Day et al.
Thomas Jean-Fran.cedilla.ois
Vezin Pierre
Glaverbel
Lester Evelyn A.
Nelms David C.
LandOfFree
Optical cell control system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical cell control system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical cell control system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2207669