Abstract: An objective lens for recording data to and/or reproducing data from first and second optical discs. The objective lens is provided with at least one surface including a plurality of annular zones divided by steps. The steps has functions of phase shifting a wavefront of light passing through the plurality of annular zones so that a beam spot formed at a converging point of an average wavefront of the wavefront phase shifted by the steps is used for the first and second optical discs. The plurality of annular zones of the at least one surface includes at least one annular zone structure which includes first and second annular zone groups, each of which has at least three steps for phase shifting the wavefront in a first direction, and a first return step which is a step formed at a boundary between the first and second annular zone groups. The first return step phase shifts the wavefront in a second direction opposite to the first direction.

Abstract: There is provided an objective lens used for at least three types of optical discs when thicknesses are respectively represented by t1, t2 and t3, t1 as 0.6 mm, t2 is 0.6 mm and t3 is 1.2 mm. When numerical apertures for the first, second and third optical discs are respectively represented by NA1, NA2 and NA3, a relationship NA1>NA2>NA3 is satisfied. When the first and second optical discs are used, collimated light beams are incident on the objective lens. When the third optical disc is used, a diverging beam is incident on the objective lens. The following conditions are satisfied: ?0.02<f1×M1<0.02 * * * (1), ?0.02<f2×M2<0.02 * * * (2), and ?0.29<f3×M3<?0.19 * * * (3).

Abstract: An objective lens for an optical pick-up which is used to record data to and/or to reproduce data from at least three types of optical discs by selectively using one of at least three light beams having different wavelengths is provided. When thicknesses of a first, second and optical discs are represented by t1, t2 and t3, respectively, a relationship t1?t2<t3 is satisfied. When numerical apertures required for the first, second and third optical discs are represented by NA1, NA2 and NA3, respectively, a relationship NA1?NA2>NA3 is satisfied. The first, second and third light beams are incident on the objective lens as substantially collimated light beams, respectively. In this configuration, at least one of surfaces of the objective lens includes a first area for attaining the numerical aperture required for recording data to and/or reproducing data from the third optical disc, and a second area located outside the first area.

Abstract: There is provided an optical pick-up used for recording data to and/or reproducing data from at least three types of optical discs having at least two different thicknesses of cover layers. The optical pick-up includes light sources and an objective lens. A thickness t1 of a first optical disc, a thickness t2 of a second optical disc, and a thickness t3 of a third optical disc satisfy a relationship t1?t2<t3. A numerical aperture NA1 for the first optical disc, a numerical aperture NA2 for the second optical disc and a numerical aperture NA3 for the third optical disc satisfy a relationship NA1?NA2>NA3. Further, a first light beam for the first optical disc is incident on the objective lens as a converging light beam, and the second and third light beams for the second and third optical discs are incident on the objective lens as diverging light beams, respectively.

Abstract: An objective lens for recording data to and/or reproducing data from first and second optical discs. The objective lens is provided with at least one surface including a plurality of annular zones divided by steps. The steps has functions of phase shifting a wavefront of light passing through the plurality of annular zones so that a beam spot formed at a converging point of an average wavefront of the wavefront phase shifted by the steps is used for the first and second optical discs. The plurality of annular zones of the at least one surface includes at least one annular zone structure which includes first and second annular zone groups, each of which has at least three steps for phase shifting the wavefront in a first direction, and a first return step which is a step formed at a boundary between the first and second annular zone groups. The first return step phase shifts the wavefront in a second direction opposite to the first direction.

Abstract: An optical system of an optical pick-up for a plurality of types of optical discs with a corresponding plurality of light sources. A first coupling lens that is used at least for the first optical disc, and an objective lens that is used for the plurality of types of optical discs. A beam for the first optical disc emitted by the plurality of light sources passes through the first coupling lens and is incident on the objective lens as a diverging beam. The diverging beam being given spherical aberration by the coupling lens. When the objective lens shift occurs, a coma component relating to the spherical aberration of the diverging beam which is shifted with respect to the objective lens due to the shift of the objective lens is canceled by a coma generated by the objective lens and the cover layer of the first 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: There is provided an objective lens for an optical pick-up which is used to record/reproduce data to/from at least three types of optical discs. Thicknesses t1, t2 and t3 of cover layers of first, second third optical discs are t1?0.6 mm, t2?0.6 mm, and t3?1.2 mm. Numerical apertures NA1, NA2 and NA3 for the first, second and third optical discs satisfy a relationship NA1?NA2>NA3. When the first optical disc is used, a substantially collimated light beam is incident on the objective lens. When the second or third optical disc is used, a diverging beam is incident on the objective lens. With regard to magnifications M1, M2 and M3 and focal lengths f1, f2 and f3 of the objective lens for the first, second and third optical discs, the following conditions (1), (2) and (3) are satisfied: ?0.02<f1×M1<0.02??(1) ?0.10<f2×M2<?0.04??(2) ?0.29<f3×M3<?0.19??(3).

Abstract: An objective lens used for recording data to and/or reproducing data from a plurality of types of optical discs having different thicknesses of cover layers. The objective lens satisfies a condition 0.02<M2?M1<0.15, where M1 represents a magnification of the objective lens when recording/reproducing for a first optical disc is performed using the first light beam, and M2 represents a magnification of the objective lens when the recording/reproducing for a second optical disc is performed using the second light beam. Further, at least one of lens surfaces of the objective lens is provided with a diffracting structure having a plurality of annular zones configured to correct spherical aberrations for both of the first and second optical discs.

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 on which a beam having parallel light fluxes is incident includes a single element lens and a reflection suppressing coating formed on at least one surface of the single element lens. The reflection suppressing coating is formed such that the reflectivity across a radius of the objective lens exhibits a local maximal value, and the reflection suppressing coating is formed to achieve the following condition: 0.6<h1/hmax<0.95, wherein h1 denotes a distance between an optical axis and a position at which the reflectivity exhibits the local maximal value, and hmax denotes a distance between the optical axis and an outermost position of the effective diameter of the objective lens.

Abstract: There is provided an objective lens used for a plurality of types of optical discs having a front surface and a rear surface, each of which includes an inner region and an outer region. The outer region has a surface shape which suppresses a coma caused when a beam used for a first optical disc is incident thereon obliquely with respect to an optical axis of the objective lens. The inner region is configured such that, at a boundary position between the inner region and the outer region, the coma caused when a beam used for a second optical disc is incident on the inner region obliquely at a first angle with respect to the optical axis is less than the coma caused when the beam used for the second optical disc is incident on the outer region obliquely at the first angle with respect to the optical axis. Further, an inclination ?2A of the inner region and an inclination ?2B of the outer region of the rear surface satisfy a condition: ?2.5<?2B??2A<0.0??(1).

Abstract: An objective lens that satisfies conditions: ?0.02<f1×M1<0.02??(1) ?0.02<f2×M2<0.02??(2) ?0.29<f3×M3<?0.19??(3). At least one of lens surfaces of the objective lens includes a diffracting structure having a first region for converging the third light beam on a data recording layer of the third optical disc. The diffracting structure within the first region is configured such that a diffraction order at which diffraction efficiency of the first light beam is maximized is a sixth order, a diffraction order at which the diffraction efficiency of the second light beam is maximized is a fourth order, and a diffraction order at which the diffraction efficiency of the third light beam is maximized is a third order.

Abstract: A hand tool with an easy-to-grip holder portion allows a large amount of torque to be applied to the tool, so that the tool can be rotated stably and screws or the like can be easily and reliably fastened. A hand tool 1 includes a holder portion 2 from which a plurality of tools 10 can be selectively swung out for use. The holder portion 2 comprises two holder plates 3 and 4 disposed opposite to each other and spaced from each other, and three connecting axles 20 to 22 by which the two holder plates are connected. The two holder plates each include three protruding plate portions 6 extending from a plate center portion 5 in three directions. The three connecting axles are individually fixed to the three protruding plate portions. The plurality of tools are supported by the three connecting axles individually and swingably. The tools are capable of being accommodated within a distance S.

Abstract: There is provided an objective lens used for at least three types of optical discs. When thicknesses of a first, second and third optical discs are respectively represented by t1, t2 and t3, t1 is 0.6 mm, t2 is 0.6 mm, and t3 is 1.2 mm. When numerical apertures for the first, second and third optical discs are respectively represented by NA1, NA2 and NA3, a relationship NA1≧NA2>NA3 is satisfied. When the first and second optical discs are used, collimated light beams is incident on the objective lens. When the third optical disc is used, a diverging beam is incident on the objective lens. The following conditions are satisfied: −0.02<f1×M1<0.02 . . . (1), −0.02<f2×M2<0.02 . . . (2), and −0.29<f3×M3<−0.19 . . . (3). The objective lens includes a diffracting structure having a first region.

Abstract: An objective lens for an optical pickup has a single lens element. One surface of the objective lens is divided into a central area and a peripheral area, and a step providing a level difference along a direction of the optical axis is formed at a boundary therebetween. The step provides a phase shift between light passing through the central area and the peripheral area. The level difference is formed such that a thickness on the peripheral area side is greater than a thickness on the central area side at the boundary. In one case, the objective lens satisfies a condition: 0.83<hx/hmax<0.97, where hx is a radius of the boundary, and hmax is an effective radius defining a numerical aperture of the surface formed with the step.

Abstract: A single-element objective lens for an optical pick-up 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 to compensate for coma such that a characteristic of a change of spherical aberration due to a degree of divergence/convergence of the incident beam is comparable with respect to a characteristic of a change of spherical aberration due to variation of the cover layer so that the change of spherical aberration due to variation of the cover layer can be cancelled by the change of spherical aberration due to a degree of divergence/convergence of the incident beam.

Abstract: An optical pickup has a light source for emitting a plurality of laser beams with different wavelengths; and an objective lens for focusing the laser beams emitted from the light source on recording surfaces of plural types of information recording media. A diffractive lens structure is provided in a light path of the laser beam, the structure including ring zone areas divided by a plurality of phase steps for correcting a wavefront aberration of the laser beam, a diameter of an outermost phase step of the diffractive lens structure is smaller than a second largest effective diameter of effective diameters required for reproduction of the plural types of information recording media.

Abstract: There is provided an optical system of an optical pick-up for recording/reproducing data to/from at least two types of optical discs including a first optical disc and a second optical disc whose recording density is higher than that of the first optical disc. The optical system is provided with a light source unit for the first and second optical discs, an objective lens, and a photo detector. The optical system further includes an optical surface to satisfy compatibility between the at least two types of optical discs, the optical surface being located between the light source unit and one of the at least two type of optical discs. The optical surface has an inner region having a numerical aperture for the first optical disc, an outer region located having a numerical aperture for the second optical disc, and an intermediate region that is located within the outer region at a periphery of the inner region.

Abstract: An objective lens of an optical pick-up is formed to provide axial astigmatism corresponding to wavefront aberration of 0.01&lgr; [rms] or more when a shorter wavelength laser beam emitted by a first laser diode is converged on a first optical disc, and to provide coma so that its sign when the shorter wavelength laser beam is converged on the first optical disc will be opposite to its sign when a longer wavelength laser beam emitted by a second laser diode is converged on a second optical disc.