Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-01-22
2004-08-17
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S200000
Reexamination Certificate
active
06778246
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical lenses and, more particularly, to liquid crystal switchable lenses with electrically adjustable focal lengths, and related fabrication and control methods.
BACKGROUND OF THE INVENTION
In many applications, such as imaging systems, display systems, optical memory systems and optical communication systems, it is desirable for the focal length of the lens system to be adjustable. In conventional lens systems, the lenses are designed to focus light by varying the thickness of a uniform refractive index medium over an aperture. The phase delay is generally graded in a parabolic shape across the aperture. Currently, adjustment of such conventional lenses are made in most systems by mechanical movement, with the lenses having static indices of refraction. This mechanical movement, however, is usually bulky, slow and expensive. Additionally, in high-power microscope systems the working distance is very short, which makes it easy to damage expensive lenses and samples being viewed when trying to mechanically adjust the focal length of the lens.
To remedy the problems associated with mechanically adjustable optics, liquid crystal (LC) switchable lenses with electrically adjustable focal lengths have been developed to provide adaptive optics, which directs light in real time without mechanical motion of bulky optics. For example, LC switchable lenses, such as micro-lenses, LC active lenses and LC modal lenses, are electro-optical devices that utilize a refractive index graded over the aperture of the lens to bring light into focus. In this regard, micro-lenses use a pair of hole-patterned electrodes to grade the refractive index over the aperture. LC active lenses connect a lens with a two-dimensional liquid crystal phase modulator with an electrode matrix. And LC modal lenses are driven by an AC voltage applied to the cell boundary. Generally, LC lenses have several advantages over mechanically adjustable optics, such as light weight, fast speed, simple control, low power consumption, high reliability, low cost and the ability to simulate different lens configurations, such as spherical and cylindrical lenses as well as Fresnel lenses, for example.
One type of LC switchable lens uses two tandem cells with orthogonal linear electrodes to control the refractive index of the lens. In these lenses, the surface of the lens is treated so that the liquid crystal molecules align homogeneously in either the “x” or “y” direction. If the preferred direction is in the “x” direction, only light polarized in the “x” direction will be affected, and visa versa. A single lens of this type of configuration, however, can only emulate a cylindrical lens. And due to the polarization sensitivity of the lens, to obtain a true spherical lens that can focus random plane polarized light, four cells of this configuration are required instead of two. Thus, to simulate spherical lenses, these type of LC lenses require two cells for each linear polarization. Additionally, because cells are never identical, two cells cannot be driven with the same voltages, which further complicates the operation of these lenses.
SUMMARY OF THE INVENTION
In light of the foregoing background, the present invention provides a liquid crystal adaptive lens (LCAL) with closed-loop electrodes and related fabrication methods and control methods. The closed-loop shape of the electrodes enables the electrodes to provide radial variation in the refractive index of the LCAL. Thus, the LCAL is capable of focusing linearly polarized light with just one cell. Additionally, because one cell can focus linearly polarized light, a single controller can drive the cell with one set of control voltages.
According to one aspect of the present invention, a liquid crystal adaptive lens (LCAL) comprises a reference plate, a liquid crystal layer disposed in electrical communication with the reference plate, and a plurality of closed-loop electrodes disposed in electrical communication with the liquid crystal layer. The closed-loop electrodes are adapted to receive a variable control voltage such that the refractive index of at least a portion of the liquid crystal layer is adjustable such that light passing through the liquid crystal layer is capable of having its phase modulated across the aperture of the liquid crystal layer.
To provide radial variation in the refractive index across at least a portion of the liquid crystal layer the closed-loop electrodes can be disposed in a concentric circular pattern. And to provide the variable control voltage to the closed-loop electrodes, the LCAL can further include at least one pair of conductors in electrical contact with at least two closed-loop electrodes, and at least one connector electrically connecting at least two closed-loop electrodes and each conductor of a respective pair of conductors. The closed-loop electrodes can also be evenly spaced from one another such that a voltage drop between each adjacent closed-loop electrode is equal when the variable control voltage is applied across the pairs of conductors. Additionally, the pairs of conductors can have a resistivity less than a resistivity of a respective connector.
In one embodiment, the closed-loop electrodes comprise at least one subset of closed-loop electrodes. In this embodiment, each pair of conductors are in electrical contact with a respective subset of closed-loop electrodes, and each connector electrically connects each closed-loop electrode of a respective subset of closed-loop electrodes and each conductor of the respective pair of conductors. As such, the LCAL can emulate a Fresnel phase profile with each subset of closed-loop electrodes comprising a Fresnel zone. In this regard, to reduce overall aberration, a phase delay in each Fresnel zone can be equal.
According to another aspect of the present invention, a method of fabricating a liquid crystal adaptive lens comprises begins by forming the pairs of conductors upon a substrate, and thereafter depositing an insulating layer upon the pairs of conductors and the substrate. Next, the closed-loop electrodes are created on the insulating layer such that at least one closed-loop electrode is in electrical contact with each conductor. For example, the closed-loop electrodes can be created by depositing a layer of electrically conductive material upon the insulating layer and thereafter forming the layer of electrically conductive material into the plurality of closed-loop electrodes. In a further embodiment, creating the closed-loop electrodes can include forming at least one connector between at least two closed-loop electrodes. After the closed-loop electrodes are created, a layer of liquid crystal is then deposited upon the plurality of closed-loop electrodes, and the reference plate is secured upon the layer of liquid crystal.
In another embodiment, the closed-loop electrodes are created by forming at least one pair of electrically conductive vias within the insulating layer such that the vias are in electrical contact with a respective pair of conductors. And then the closed-loop electrodes are produced such that at least one closed-loop electrode electrically contacts each via. In this regard, the electrically conductive vias can be formed by first forming an etch mask defining at least one opening upon the insulating layer. Then, at least one hole is etched within the openings, with the holes extending through the insulating layer such that at least a portion of the at least one pair of conductors is exposed. Finally, an electrically conductive material is deposited within the holes such that the electrically conductive material electrically contacts the pairs of conductors.
The present invention also provides an LCAL system that comprises an LCAL, such as that described above, and an auto-focusing subsystem capable of adjusting the variable control voltage to the LCAL to thereby adjust a refractive index of at least a portion of the liquid crystal layer of the LCAL such that light passing through the liquid cr
Kowel Stephen T.
Nordin Gregory P.
Sun Yi
Alston & Bird LLP
Chung David
Kim Robert H.
University of Alabama in Huntsville
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