Controllable liquid crystal layered Fresnel lens device
A liquid crystal optical device providing refractive Fresnel lens type element control over light passing through an aperture is provided. The device includes a layer of liquid crystal material contained by flat substrates having flat alignment layers; and an arrangement of electrodes configured to provide a spatially varying voltage distribution within a number of lensing zones within said liquid crystal layer. The arrangement of electrodes includes ring-shaped electrodes defining boundaries between Fresnel lensing zones. The liquid crystal optical device is structured to provide a spatial variation in the optical phase delay with an abrupt transition at a boundary between lensing zones to increase the effective aperture of the optical device.
1. An electrically controllable multiple zone gradient index lens comprising:
liquid crystal cells each having at least two layers of liquid crystal material each between a first alignment layer on a first substrate and a second alignment layer on a second substrate, wherein said liquid crystal cells are arranged over one another to act on both linear polarizations of light;
each liquid crystal cells having an electrode structure comprising a uniform transparent electrode on said first substrate and at least two ring-shaped electrodes on said second substrate,
wherein the electrode structure defines at least two lensing zones comprising a central lens formed by an inner electrode of said at least two ring-shaped electrodes and at least one Fresnel-type concentric band lens formed by at least one outer electrode of said at least two ring-shaped electrodes, said central lens having an aperture of at least about 2 mm and less than 4 mm in diameter and said at least one concentric band lens element each expanding a diameter of an aperture of said central lens by at least 1 mm to less than 3.5 mm; and
one of a weakly conductive layer and a high resistivity layer enclosing said at least two ring-shaped electrodes for distributing an electric potential over a lensing aperture and having at least one gap between lensing zones of said at least two lensing zones.
2. The liquid crystal optical device as defined in claim 1 , further comprising a driver circuit configured to provide drive signals to said arrangement of electrodes.
3. The device as defined in claim 2 , wherein the driver circuit is configured to provide a potential difference in electrical signals supplied to the electrodes of each lensing zone at one substrate, so that the electric field acting on the liquid crystal of each lensing zone is directed in part in a direction of the liquid crystal layer direction.
4. The device as defined in claim 1 , wherein the drive signal is an AC signal, and the potential difference is provided using a phase difference in said electrical signals.
5. The device as defined in claim 1 , wherein said layers of liquid crystal material are between about 25 mm to about 100 mm thick.