Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1991-01-31
1992-12-08
Howell, Janice A.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 55, 359 72, 359 84, 340784, G02F 1133, G02F 1135
Patent
active
051702711
ABSTRACT:
A shaped voltage pulse is applied to a polymer dispersed liquid crystal (PDLC) cell to control its transmission characteristics. The voltage has an initially high level that substantially exceeds the PDLC's threshold voltage. The initial voltage duration is relatively short, and is followed by a gradual reduction of the voltage to a level less than the threshold voltage within a given time frame; the voltage is preferably reduced at a generally exponential rate. Fast response is obtained by setting the initial voltage substantially above the voltage level that corresponds to the desired transmission level in the steady state; the voltage decays from its initial level so that the PDLC transmission actually peaks at the desired range. The shaped waveform forces the PDLC to operate on a hysteresis curve along which the reduction in transmission is delayed as the voltage decays, thereby increasing the cell's optical throughput. The invention is particularly applicable to liquid crystal light valves.
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Lackner Anna M.
Margerum J. David
Sherman Elena
Denson-Low W. K.
Duong Tai V.
Howell Janice A.
Hughes Aircraft Company
Leitereg E. E.
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