Application of a Liquid Crystal Lens to an Optical Disc Memory Device

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An optical head shows a limitation of its miniaturization and highspeed accessions because of its mechanical control of an object lens for focus adjustment. The aim of this research project is applying a liquid crystal lens, of which focal length can be controlled by applying voltage, to an optical head.An axially symmetric nonuniform electric field is produced in a liquid crystal cell with a hole-patterned electrode, and radial distribution of refractive indices; that is, a liquid crystal microlens can be obtained by a molecular orientation effect in a nonuniform electric field. Optical properties and response properties of a homogeneously aligned or a hybrid-aligned liquid crystal microlens with an asymmetric electrode structure of a hole-patterned electrode and a flat electrode have been investigated. In the homogeneously aligned liquid crystal microlens with the asymmetric electrode structure, electrode structure, a disclination line which worsens the lens properties, is observed i … More n the direction perpendicular to the molecular orientation. Such a disclination line is eliminated by adopting a hybrid-aligned molecular orientation. However, the lens properties are not improved very much since a shifting effect of the lens center appears. Then more significant improvements can be expected by suppressing such deteriorating factors. Then, a homogeneously aligned liquid crystal microlens with hole patterns on both surfaces of the substrates is prepared and its optical properties are investigated. Concentrically circular and defect-free distribution properties of refractive indices can be obtained as a result of uniform tilt direction of the molecules; that is, some detrimental effects of lens properties in hitherto prepared lenses are eliminated and the lens properties are eceedingly improved. When a high voltage is suddenly applied across the microlens, the disclination lines appear immediately after the voltage is applied even if the liquid crystal microlens with the symmetrical electrode structure is used. The disclination lines does not disappear and it remains for a long period of time after voltage is removed.The response properties can be improved and the creation of the disclination lines can be suppressed by using a method of bias voltage application. The applied voltage is changed between the bias voltage and the target voltage. Then no disclination lines are observed, and the optical properties of the liquid crystal micro-lens and their reappearance can be improved. In addition, the response properties of the liquid microlens can be improved and the creation of the disclination lines can be suppressed by using the method of the bias voltage application. T disclination lines can be suppressed by using the method of the bias voltage application. Then a requirement for applying the microlens to the optical head today are seemed to be satisfied. requirement for applying the microlens to the optical head today are seemed to be satisfied.The possibility of application of the liquid crystal microlens to the optical head is discussed. Less