Variable focal length liquid crystal lens assembly and...

Details Variable focal length liquid crystal lens assembly and... Variable focal length liquid crystal lens assembly and...

1999-06-14

2001-11-13

Parker, Kenneth (Department: 2871)

Liquid crystal cells, elements and systems

Liquid crystal optical element

Liquid crystal lenses other than for eyewear

C349S084000

Reexamination Certificate

active

06317190

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to variable focal length lenses and in particular to a variable focal length, liquid crystal lens assembly.
2. Background Art
In the prior art, focus adjustment in an image sensing device such as video camera is made by moving lenses with a motor. The motor, complicated mechanisms required to move the lenses, and their power requirements make it difficult to implement these devices in small, lightweight applications.
Focus adjusting devices which use liquid crystal as a lens material, such as those disclosed in U.S. Pat. No. 4,037,929, can change focal length without deforming the lens. The lens uses small voltages to alter the refractive index of the liquid crystal and, thus, change the focal length of the lens. However, it is difficult to change the refractive index of the lens by more than about 20%, and the focal distance cannot be reduced sufficiently. Thus, an liquid crystal lens with greater focal length range is needed.
SUMMARY OF THE INVENTION
A lens assembly has a pair of polarized liquid crystal lenses. Each lens has pair of parallel glass plates that are separated by upper and lower glass substrates. A series of rectangular polymer films are symmetrically spaced apart between the two glass substrates. Both the substrates and the films are perpendicular to the glass plates. A semi-circular electrode is formed on each side of each piece of film to form a semi-cylindrical “stack” of film. The electrodes do not completely cover the film. Liquid crystal fills the space between each adjacent pair of the films. The films are coated and/or treated by an alignment process to predispose the liquid crystals to an alignment and rotation direction.
When a selected voltage is applied between adjacent ones of the electrodes, the liquid crystals are synchronously rotated to alter their refractive index to a desired value. Thus, when the layers of each lens are manipulated in unison, the bar code reader is able to adjust its focal length to read bar codes labels on media devices at various distances. For example, when the applied voltage is zero, there is no refractive index difference between the electrode portion and the non-electrode portion of the liquid crystal. Therefore, the focal length is infinite. Applying a voltage to the electrodes alters the refractive index of the liquid crystal and, thus, shortens the focal length of the lens assembly.


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