Abstract: An objective lens and optical pickup device that uses it is disclosed having an optical diffraction surface on its surface nearest a light source which may be switched in wavelength for either CD or DVD recording/replaying. The optical diffraction surface causes a selected wavelength beam to converge or diverge more than the other wavelength beam. Superimposed in a peripheral region of the diffraction grating is a step change in height (higher or lower) which causes destructive interference for light in the peripheral region for only one of the beams. In this way, an objective lens is provided that, with a simple and compact structure, enables a light beam to be converged accurately into a spot on a selected recording medium, despite the need to have the converged beam have different wavelengths and numerical apertures, depending on the recording medium used.

Abstract: An objective lens for converging two wavelengths of light to their predetermined positions is constituted by two or three lenses. Respective materials for forming adjacent lenses are chosen such that the respective refractive indices of adjacent lenses substantially equal each other with respect to only one of the two wavelengths of light, whereas the form of each lens surface is configured so as to suppress aberration in the objective lens as a whole.

Abstract: An objective lens for an optical recording medium comprises two lenses each having a positive refracting power disposed within a laser luminous flux having a wavelength of 360 to 450 nm outputted from a laser diode. The two lenses have at least one diffractive optical surface and at least one aspheric surface, and are set so as to have a total NA of at least 0.7.

Abstract: An achromatic beam shaping prism is disclosed which compensates for a fluctuation in oscillating wavelength of a semiconductor laser source of a recording type optical disc system using a single prism having a diffraction grating with a specified pitch so as to make the beam shaping prism achromatic. Two equations are given for specifying the pitch d or d′ of the diffraction grating, depending on whether the diffraction grating is applied to the output surface or the input surface of the prism, respectively.

Abstract: One surface of the substrate constituting a diffraction type lens is formed with a zone plate exhibiting a smaller converging action with respect to a first wavelength &lgr;1 of light and a greater converging action with respect to a second wavelength &lgr;2 of light, whereas the other surface is formed with a zone plate exhibiting a smaller converging action with respect to the second wavelength &lgr;2 of light and a greater converging action with respect to the first wavelength &lgr;1 of light. The substrate is transparent to the first and second wavelengths &lgr;1 and &lgr;2 of light. Each of the zone plates comprises concentric gratings having a stepped cross section.

Abstract: One surface of an objective lens is provided with a zonal part which acts such that the quantity of light having a wavelength of &lgr;1 is apparently canceled in the outer peripheral portion of the luminous flux due to an interference effect, whereas the quantity of light having a wavelength of &lgr;2 in the outer peripheral part is kept as it is. The zonal part has such a step that light supposed to pass a position corresponding to the zonal part if the zonal part does not exist and light passing a position at which the zonal part is formed if the zonal part exists generate therebetween a phase difference satisfying a predetermined conditional expression. The numerical aperture at a boundary position of the step has a value between two numerical apertures for the respective wavelengths &lgr;1 and &lgr;2.

Abstract: One surface of the substrate constituting a diffraction type lens is formed with a zone plate exhibiting a smaller converging action with respect to a first wavelength &lgr;1 of light and a greater converging action with respect to a second wavelength &lgr;2 of light, whereas the other surface is formed with a zone plate exhibiting a smaller converging action with respect to the second wavelength &lgr;2 of light and a greater converging action with respect to the first wavelength &lgr;1 of light. The substrate is transparent to the first and second wavelengths &lgr;1 and &lgr;2 of light. Each of the zone plates comprises concentric gratings having a stepped cross section.

Abstract: An objective lens for optical recording media is constituted by two or three lenses cemented together and used for recording or reproducing two kinds of optical recording media having respective thicknesses different from each other with two light beams having wavelengths &lgr;1 and &lgr;2 different from each other. The cemented face exhibits negative and positive refracting powers with respect to light beams having wavelengths &lgr;1 and &lgr;2, respectively, according to the wavelength-dependent difference in refractive index of materials constituting the respective lenses.

Abstract: An objective lens for a high-density optical recording medium, employed as an objective lens for an optical pickup for converging a luminous flux onto an optical recording medium, comprises, successively from the light source side, a first lens L1 made of a biconvex lens having at least one surface formed as an aspheric, and a second lens L2 made of a planoconvex lens having a convex surface directed onto the light source side, and satisfies the following conditional expressions (1) to (3): 0.588<&bgr;2≦0.676  (1) NA1≧0.45  (2) RMS1≦0.07&lgr;  (3) where &bgr;2 is the imaging magnification of the second lens L2; NA1 is the numerical aperture of the first lens L1; RMS1 is the RMS of the wavefront aberration of the first lens L1; and &lgr; is a reference wavelength.

Abstract: In a diffraction type optical pickup lens, at least one surface of a convergent lens is formed with such an aspheric surface that a luminous flux having a wavelength &lgr;1 is converged at a first predetermined position. At least one surface of the convergent lens is formed with a zone plate having such a wavelength selectivity that a luminous flux having a wavelength &lgr;2 is converged at a second predetermined position whereas the luminous flux having a wavelength &lgr;1 is transmitted therethrough as it is. The convergent lens is transparent to the luminous fluxes having the wavelengths &lgr;1 and &lgr;2.

Abstract: One surface of an objective lens is provided with a zonal part which acts such that the quantity of light having a wavelength of &lgr;1 is apparently canceled in the outer peripheral portion of the luminous flux due to an interference effect, whereas the quantity of light having a wavelength of &lgr;2 in the outer peripheral part is kept as it is. The zonal part has such a step that light supposed to pass a position corresponding to the zonal part if the zonal part does not exist and light passing a position at which the zonal part is formed if the zonal part exists generate therebetween a phase difference satisfying a predetermined conditional expression. The numerical aperture at a boundary position of the step has a value between two numerical apertures for the respective wavelengths &lgr;1 and &lgr;2.

Abstract: An objective lens for optical recording media is constituted by two or three lenses cemented together and used for recording or reproducing two kinds of optical recording media having respective thicknesses different from each other with two light beams having wavelengths &lgr;1 and &lgr;2 different from each other. The cemented face exhibits negative and positive refracting powers with respect to light beams having wavelengths &lgr;1 and &lgr;2 respectively, according to the wavelength-dependent difference in refractive index of materials constituting the respective lenses.

Abstract: An achromatic beam shaping prism is disclosed which compensates for a fluctuation in oscillating wavelength of a semiconductor laser source of a recording type optical disc system using a single prism having a diffraction grating with a specified pitch so as to make the beam shaping prism achromatic. Two equations are given for specifying the pitch d or d′ of the diffraction grating, depending on whether the diffraction grating is applied to the output surface or the input surface of the prism, respectively.

Abstract: An objective lens for converging two wavelengths of light to their predetermined positions is constituted by two or three lenses. Respective materials for forming adjacent lenses are chosen such that the respective refractive indices of adjacent lenses substantially equal each other with respect to only one of the two wavelengths of light, whereas the form of each lens surface is configured so as to suppress aberration in the objective lens as a whole.

Abstract: A diffraction type lens in an optical pickup apparatus for recording and reproducing two or more kinds of optical recording media is constituted by a substrate having one surface formed with a zone plate exhibiting a smaller converging action with respect to a wavelength &lgr;1 of light and a greater converging action with respect to a wavelength &lgr;2 of light, and the other surface formed with a zone plate exhibiting a smaller converging action with respect to the wavelength &lgr;2 of light and a greater converging action with respect to the wavelength &lgr;1 of light. The substrate is transparent to the wavelengths &lgr;1 and &lgr;2 of light.

Abstract: A zone plate having an aberration correcting function in a wavelength selecting manner and a diffraction grating substantially having a light shielding function in a wavelength selecting manner are formed, respectively, in a center region and a marginal region of a filter, whereby only a predetermined wavelength of light is converged or diverged by the zone plate and is diffracted sideways by the diffraction grating, whereby the luminous flux diameter of the irradiation light is changed while the aberration caused by a convergent lens is favorably corrected. The diffraction type filter 8A is constituted by a first region 11 comprising a central circular portion and a second region 12 comprising a marginal portion thereof. The first region 11 is provided with a zone plate 11A (diffraction grating formed like concentric circles) having such a wavelength selectivity that light at a wavelength of 635 nm is transmitted therethrough as it is and that light at a wavelength of 780 nm is converged thereby.

Abstract: A diffraction grating having a wavelength selectivity is disposed at a peripheral region of a filter, and only a wavelength of light whose luminous flux diameter is to be narrowed is diffracted sideways at the diffraction grating, whereby the luminous flux diameter of irradiation light is changed by a simple configuration without complicating an electric control system or restricting the direction of vibration of the irradiation light. On a glass substrate 10, a first region 11 having no diffraction grating 12A and a second region 12 having diffraction gratings 12A with a rectangular cross section are disposed. The second region 12 comprises linearly arranged diffraction gratings 12A each having a rectangular cross section. The thickness (height) of each diffraction grating 12A is set to such a value that the ratio of .+-.

Abstract: A diffraction grating with a wavelength selectivity having one sectional side formed like a step is disposed at a marginal region of a filter, and only a wavelength of light whose luminous flux diameter is to be narrowed is diffracted sideways at the diffraction grating, whereby the luminous flux diameter of irradiation light is changed by a simple configuration without complicating an electric control system or restricting the direction of vibration of the irradiation light, while reducing noise. Disposed on a glass substrate 10 are a first region 11 having no diffraction grating 12A, and a second region 12 having diffraction gratings 12A constituted by long protrusions arranged in parallel at a predetermined pitch, each protrusion being continuous in one direction and having one sectional side formed like a step.

Abstract: In an optical pickup apparatus which can be commonly used for a plurality of optical disks having different thickness values, thickness t of a optical transparent plane plate for thickness compensation is set by means of skew ray formula so that the amount of spherical aberration caused by the optical system is lowered, thus allowing accurate focusing for each of a plurality of optical disks having different thickness values. Spherical aberration S.A. is given by expression of S.A..ident.S'.sub.k -S'.sub.k0, wherein S'.sub.k is computed by expression of S'.sub.k =Ax.sub.k -(X'.sub.k /Y'.sub.k)Ay.sub.k. Here, by setting S'.sub.k -S'.sub.k0 =minimal value, the geometric thickness of the plane plate 8 can be determined.

Abstract: The surface of a lens for reading out an optical recording medium facing a light source is formed as a convex aspheric surface which is rotationally asymmetrical with respect to the optical axis and defined by a predetermined aspheric surface equation, whereby, even when a light beam having an astigmatic aberration is emitted from the light source, a signal surface of the optical recording medium can be irradiated with a light beam whose astigmatic difference has been favorably corrected, while the lens can be easily manufactured.