Abstract: A single-element objective lens is employed in an optical pick-up. The objective lens directs an incident light beam to a data recording surface of an optical disc through a cover layer to form a beam spot thereon. A numerical aperture of the objective lens is 0.7 or more. The objective lens is configured such that a characteristic of aberration which is generated due to decentering of surfaces of the objective lens is substantially comparable to a characteristic of aberration due to an inclination of an optical axis of the objective lens and an inclination of a central axis of the light beam incident on the data recording surface of the optical disc with respect to the optical disc.

Abstract: An image reading system includes an imaging optical system for forming an image of an object, the optical system including at least one refractive lens and a diffractive grating blazed at a predetermined wavelength, an aperture stop positioned close to the diffractive grating, main image sensors for receiving the images of respective color components, and a flare compensating unit for compensating the image signals input from the main image sensors to eliminate flare components due to unnecessary order diffractive light.

Abstract: Disclosed is an objective lens of an optical pick-up that includes a refractive lens and a diffractive lens structure that is formed as a large number of concentric ring areas having minute steps in an optical axis direction at the boundaries therebetween. The lens surface of the objective lens is divided into a high NA exclusive area for a DVD only, and a common area that is surrouned by the high NA exclusive area. The diffractive lens structure in the common area changes the spherical aberration in the undercorrected direction as the wavelength of the incident laser beam increases. The diffractive lens structure formed in the high NA exclusive area has a smaller wavelength dependence of a spherical aberration than that formed in the common area, and is designed such that a spherical aberration at the short wavelength is adequately corrected for the thin cover type optical disc.

Abstract: A coma compensating element has two refraction surfaces. The refraction surfaces provide, as a whole, no aberration with respect to rays perpendicularly incident thereon, while the refraction surfaces provide coma with respect to rays obliquely incident thereon.

Abstract: A beam shaping optical system which is provided with a first wedge prism having two refractive surfaces defining a first principal section, and a second wedge prism having two refractive surfaces defining a second principal section that is parallel to the first principal section, wherein a reference ray of light forms incident angles at each of the refractive surfaces of the prisms satisfying the following condition (1): &LeftBracketingBar; ∑ j = 1 L ⁢ α j &RightBracketingBar; < 0.020 .

Abstract: When it is intended to realize a lens having a large NA with one lens, an adjustment precision between both surfaces of the lens is very strict. Accordingly an objective lens having an NA of 0.8 or more was usually realized by two lenses. However, a working distance is small, and collision of the objective lens with a disc is apt to occur. A coma corrector for compensating coma caused by decentering of both surfaces in realizing the high NA lens with one lens is added. However, in this case, astigmatism occurs when the objective lens decenters from the coma corrector relatively accompanied with a tracking operation. The objective lens and the coma corrector are fixed to a mirror barrel so as to be unified with each other, and driven by a two-dimensional lens actuator. With such a constitution, decentering of the objective lens and the coma corrector does not occur, and hence astigmatism does not occur.

Abstract: Disclosed is a refractive-diffractive hybrid lens that includes a refractive lens having at least one aspherical surface, and a diffractive lens structure having a plurality of concentric ring-shaped steps that are formed on at least one lens surface of the refractive lens. The refractive lens and the diffractive lens structure are designed such that a change of the spherical aberration due to a change of the refractive index becomes small. That is, the refractive lens is designed to correct a coma and to reduce the change of the spherical aberration due to the variation of the refractive index, and the diffractive lens structure is designed to correct the residual spherical aberration. The refractive lens is a single biconvex lens, and at least one surface is aspherical. The diffractive lens structure generates a negative spherical aberration to reduce the ratio of a change of the spherical aberration to a variation of the refractive index.

Abstract: Disclosed is an objective lens of an optical pick-up that converges light beams of two different wavelengths onto recording layers of optical discs of two different standards, respectively. The objective lens includes a refractive lens having a positive power and a diffractive lens structure formed on one surface of the refractive lens. The diffractive lens structure has a plurality of concentric ring areas with minute steps at the boundaries therebetween. The diffractive lens structure maximizes the diffraction efficiency of the third order diffracted light at the shorter wavelength and maximizes the diffraction efficiency of the second order diffracted light at the longer wavelength. This enables the diffractive lens structure to correct the chromatic aberration at the respective wavelengths with keeping high diffraction efficiency.

Abstract: An objective lens for an optical pick-up has a refractive lens element provided with a diffraction lens structure on at least one surface thereof. The diffraction lens structure has a plurality of annular zones. The objective lens is capable of converging at least two beams having different wavelengths on at least two types of optical discs having different data recording densities, respectively. The objective lens is partitioned into a common area through which a beam with a low NA passes, and an exclusive high NA area which is designed to converge a beam with a high NA. The boundaries of the annular zones formed on the exclusive high NA area are designed independently from boundaries obtained from an optical path difference function so that the beam with the high NA is converged substantially on a certain point and the beam with the low NA is diffused.

Abstract: A diffraction optical element is configured such that a plurality of annular zones having minute steps extending in a direction of the optical axis therebetween are formed on a base element.

Abstract: An optical head for an optical disc drive is provided with a first laser diode that emits a shorter wavelength laser beam, a second laser diode that emits a longer wavelength laser beam, and an objective lens for converging the beams emitted by the laser diodes on the data recording surface of the optical disc. Each of first and second surfaces of the objective lens is rotationally symmetrical, and a rotational axis of the first surface and a rotational axis of the second surface are arranged to be deviated from each other.

Abstract: Disclosed is an objective lens of an optical pick-up that converges light beams of two different wavelengths onto recording layers of optical discs of two different recording densities, respectively. The objective lens includes a refractive lens whose one surface is divided into a common area through which a light beam of a low NA, which is necessary and sufficient for an optical disc having low recording density, passes and a high NA exclusive area through which a light beam of a high NA, which is necessary only for an optical disc having high recording density, passes. A diffractive lens structure is formed in both the areas. The diffractive lens structure in the common area maximizes the diffraction efficiency of the first order and that in the high NA exclusive area maximizes the diffraction efficiency of the second or third order at the wavelength corresponding to the optical disc having high recording density.

Abstract: An objective lens includes a refractive lens having a positive refractive power, and a diffractive lens structure having a plurality of concentric ring-shaped steps that are formed on a lens surface of the refractive lens. The objective lens is a biconvex plastic lens having first and second aspherical surfaces. The diffractive lens structure has such a wavelength dependence that at least two diffracted beams having different wavelengths with the same diffraction order form appropriate wavefronts for at least two kinds of optical discs having cover layers of different thickness, respectively. Further, the diffractive lens structure has a predetermined power at any points in a middle ring area that is concentrically arranged about the optical axis at a middle range of the radius of the refractive lens.

Abstract: An optical disc drive using either one of a first disc (e.g., DVD) and a second disc (e.g., CD), is provided with a first laser diode that emits a shorter wavelength beam, a second laser diode that emits a longer wavelength beam, an objective lens, and a driving unit that holds and rotates the optical disc. The optical axis of the objective lens is inclined relative to a normal to the optical disc. The first laser diode is located at a first position so that the coma, which is caused when the first laser beam is converged on a data recording surface of the first disc, is minimized, and the second laser diode is located at a second position so that the coma, which is caused when the second laser beam is converged on a data recording surface of the second disc, is minimized.

Abstract: Disclosed is an optical disc apparatus that is adapted for DVD, CD and CD-R. The optical system includes a laser module and an objective lens that converges a divergent laser beam emitted from the laser module onto information layers of optical discs. The laser module is provided with a pair of emission points that are in close proximity to each other, and a pair of light receiving elements. A focusing mechanism moves the objective lens so that the beam spot follows an information layer of the optical disc. The objective lens is provided with the diffractive lens structure to have a wavelength dependence such that the spherical aberration varies in response to the change of the wavelength. Thereby, the variation of the spherical aberration due to the change of the thickness of the cover layer can be canceled by changing the wavelength.

Abstract: A single element objective lens for an optical disc drive converges a laser beam, which is emitted by a laser source, on a data recording surface of an optical disc through a protective layer of the optical disc. One surface of the objective lens is divided into a central area including an optical axis thereof and a peripheral area surrounding the central area. The peripheral area is provided with a diffraction lens structure formed by a plurality of concentric annular zones including minute steps. The central area is a continuous surface having no stepped portions. The diffraction lens structure compensates for variation of converging characteristic of the objective lens due to a change of a temperature.

Abstract: An optical system for an optical head of an optical disc drive is capable of using first and second discs, protective layer of the second disc being thicker than that of the first disc, a data density of the second disc being lower than that of the first disc. A light source selectively emits first and second laser beams having first and second wavelengths, respectively. An objective lens converges the first and second beams on the first and second discs, respectively. The second beam is incident on the objective lens as diverging light, and the first beam is incident on the objective lens as a beam of which degree of divergence is smaller. A diffraction lens structure is formed in the high NA exclusive area, which compensates for aberrations of a portion of the first laser beam, and causes aberrations to a portion of the second laser beam passed therethrough.

Abstract: An objective lens for an optical head converges a first laser beam having a relatively short wavelength and a second laser beam having a relatively long wavelength on first optical disc (DVD) and a second optical disc (CD), respectively. A protective layer of the first disc is thinner than a protective layer of the second optical disc. The objective lens is compensated for astigmatism with respect to the first beam, which is incident on the objective lens as an off-axis beam at a predetermined incident angle, by providing on-axis astigmatism corresponding to wave front aberration greater than or equal to 0.01&lgr; (rms), and the objective lens is configured such that the coma is compensated better in a case where the first laser beam is converged on the first optical disc than in a case where the second laser beam is converged on the second optical disc.

Abstract: The objective lens is a biconvex plastic lens having first and second surfaces which are both aspheric. The objective lens is divided into an inside area which is inside of a circle of an effective diameter of the objective lens and an outside area which is outside of the circle of the effective diameter. A diffractive lens structure having a plurality of concentric ring-shaped steps is formed in the inside area. A surface of the outside area is continuous with no steps and corresponds to a macroscopic base curve of the inside area. The objective lens has a gap of a spherical aberration between the inside area and the outside area.

Abstract: In coupling a part or component of synthetic resin mounted on a vehicle and a threaded member capable of detachably engaging with the part, the part is provided with a retaining portion for retaining at least a portion of the threaded member against rotation relative to each other, and a claw construction means capable of disengageably engaging with the threaded member so as to inhibit the separation of the threaded member from the retaining portion. With this coupling structure, the operation of molding a part of synthetic resin for a vehicle having a threaded member integrally incorporated therein can be carried out easily and a labor-saving is achieved in the operation. Further, the recycling of parts defectively formed or the like can be promoted.