Abstract: An aberration correction element is disposed between first to third laser light sources and an objective lens, first and second laser lights emitted from the first and second laser light sources are incident upon the aberration correction element in the form of parallel lights, and a third laser light emitted from the third laser light source is incident upon the aberration correction element in the form of a divergent light.

Abstract: An optical information recording medium (1) is composed of a pit recording area (2), wherein various control information is recorded by a prepit, and a user recording area (3) having a guide groove formed in a groove format, and a phase depth for the prepit and the groove are approximately the same wherein the phase depth is less than or equal to ?/10, wherein ? is a wavelength for reproducing light source. A recording/reproducing apparatus (4) for the optical information recording medium (1) includes decoding means (12) for decoding information by detecting a tangential push-pull reproduced signal from the prepit recording area (2) and detecting an aggregated signal from the user recording area (3).

Abstract: Disclosed is such an optical pickup controlling an aberration even if optical axes of an objective lens and another optical system are shifted from each other.

Abstract: When a wavelength having the same value as a reference wavelength Al of a first laser light is set to a designed wavelength ?, a diffractive optical element has: an inner circular side irregular diffraction pattern portion, in which a plurality of irregular portions in which a height of a convex portion is set to approximately 1?-fold of the designed wavelength ? with respect to a concave portion are repeated, being formed in an annular shape in an inner circular area having a predetermined diameter for the correction of a spherical aberration generated due to a difference in substrate thickness between first and second optical recording mediums centering on a central point through which an optical axis runs while gradually changing a pitch of the irregular portions in a radial direction toward the outer circular side; and an outer circular side tiered diffraction pattern portion which is intended to improve a chromatic aberration with respect to the first laser light by forming in an annular shape in an oute

Abstract: First and second phase function curves are respectively obtained based on first and second phase functions with a wavelength having the same value as a reference wavelength ?1 of a first laser light being determined as a designed wavelength ?, a phase shift element then has an inner circular side tiered phase difference pattern portion formed in annular shapes in an inner circular area on one surface thereof based on the first phase function curve and an outer circular side tiered phase difference pattern portion formed in annular shapes in an outer circular area outside the inner circular side tiered phase difference pattern portion based on the second phase function curve.

Abstract: A phase shift element has a tiered phase difference pattern portion, in which an inner circular side tiered phase difference pattern portion is continuously connected with an outer circular side tiered phase difference pattern portion based on a phase function curve obtained by a single phase-function with a wavelength having the same value as a reference wavelength ?1 of a first laser light being determined as a designed wavelength ?, formed in annular shapes on one surface thereof. A tier pitch of tiers of the inner circular side tiered phase difference pattern portion is set to a height corresponding to a phase difference of substantially 1? and, on the other hand, a tier pitch of tiers of the outer circular side tiered phase difference pattern portion is set to a height corresponding to a phase difference of substantially m? (where m is a natural number which does not include 0) or a height corresponding to the phase difference of substantially m? by changing a value of m for each step.

Abstract: An aberration correction element is disposed between first to third laser light sources and an objective lens, first and second laser lights emitted from the first and second laser light sources are incident upon the aberration correction element in the form of parallel lights, and a third laser light emitted from the third laser light source is incident upon the aberration correction element in the form of a divergent light.

Abstract: When an extra-high density optical disc, a DVD having a recording density lower than that of the extra-high density optical disc, a CD having a recording density lower than that of the DVD, and a combined optical recording medium in which the extra-high density optical disc, DVD, and CD are appropriately combined and integrally stacked are selectively recorded or reproduced by an objective lens whose numerical aperture (NA) is set to 0.75 or more, the objective lens satisfies the following expression: t<a·f+b wherein t: an axial thickness of the objective lens, f: a focal distance of the objective lens, a: a coefficient, and b: a constant, and the coefficient a and the constant b satisfies that a=2.02, b=?1.94; a=2.08, b=?1.84; or a=2.11, b=?1.77.

Abstract: After diffracting laser light by a diffraction grating to separate the light into three beams of a 0-order light and ±1st order lights, the three beams are enlarged by a beam shaping/PBS synthesizing prism to shape an elliptic light intensity distribution thereof into a substantially circular light intensity distribution. In this case, it is assumed that a direction for enlarging diameters in shaping the three beams into the substantially circular light intensity distribution by the beam shaping/PBS synthesizing prism is an x-axis and an axis crossing a plane including the x-axis and an optical axis at right angles is a y-axis. At this time, the diffraction grating is formed along an xy-plane including the x-axis and the y-axis, and an angle formed by the xy-plane and the optical axis is set to a predetermined angle other than a right angle so that the grating formed along the xy-plane is substantially parallel to the x-axis.

Abstract: There is disclosed an optical pickup device including: a blue semiconductor laser which emits a first laser light having a wavelength of 450 nm or less to record on or reproduce from an extra-high density optical disc; a red semiconductor laser which emits a second laser light having a wavelength longer than that of the first laser light to record on or reproduce from a DVD having a low recording density; an objective lens; and an aberration correction element. The objective lens is designed for the extra-high density optical disc, and has a numerical aperture (NA) of 0.75 or more. The aberration correction element passes the first laser light as such and thereafter allows the light to be incident upon the objective lens, whereas the element limits an aperture with respect to the second laser light and diffracts the second laser light so as to correct an aberration with respect to the DVD and thereafter allows the light to be incident upon the objective lens.

Abstract: In a data decoding apparatus that performs decoding of recorded data played back from a recording medium by Viterbi decoding according to a decoding trellis based on a recording signal characteristic, a pathmetric calculation circuit has run length counters (20) and (25) for detecting the run length of recorded data, a target value control circuit (1) for varying the target value used for metric calculation of Viterbi decoding based on run length information, and a monitoring means, provided in the target value control circuit (1), for protecting against faulty operation caused by using a count value that should not be used as an information source.

Abstract: An objective for an optical disk is made of a single double-sided aspherical lens having a numerical aperture (NA) equal to or greater than 0.75 and capable of minimizing axial aberration, off-axis aberration, surface-to-surface eccentricity aberration, and chromatic aberration. The objective (11) has a first aspherical surface (1). The vertex of the first surface has a radius of curvature R1 defined as follows: 0.95·A<R1<1.05·A A=B/C B=0.85f(n−1) C=n (0.60866−0.11·t/f−0.1272·d/f)(0.83+0.2·NA) where n is a refractive index of the lens, f is a focal length of the lens, t is a thickness along optical axis through the center of the lens and d is the thickness of a transmission layer of the optical disk.

Abstract: An optical pick-up emits three laser beams onto an optical disk. The three laser beams are reflected on the optical disk and incident to a condenser lens. The three laser beams are further incident to a holographic device via the condenser lens. The surface of the holographic device is divided into a first and a second hologram region by a bisecting line oriented almost parallel to the track formed on the optical disk. The holographic device generates ±1th-order diffracted light beams on the hologram regions. The ±1th-order diffracted light beams are incident to a photodetector having a plurality of photo-detecting segments corresponding to the ±1th-order diffracted light beams. The photodetector detects signals recorded on the optical disk based on the ±1th-order diffracted light beams.

Abstract: An objective for an optical disk is made of a single double-sided aspherical lens having a numerical aperture (NA) equal to or greater than 0.75 and capable of minimizing axial aberration, off-axis aberration, surface-to-surface eccentricity aberration, and chromatic aberration.

Abstract: Disclosed is such an optical pickup controlling an aberration even if optical axes of an objective lens and another optical system are shifted from each other.

Abstract: An optical pickup suppresses aberration including one caused when the optical axis of an objective lens deviates from that of a chromatic aberration corrector.

Abstract: There is disclosed an objective lens for an optical disk, comprising a bi-aspherical single lens having a numerical aperture of 0.7 or more, wherein a center thickness of the lens is larger than a focal distance.

Abstract: An optical information recording medium (1) is composed of a pit recording area (2), wherein various control information is recorded by a prepit, and an user recording area (3) having a guide groove formed in a groove format, and a phase depth for the prepit and the groove are approximately the same that the phase depth is less than or equal to &lgr;/10, wherein &lgr; is a wavelength for reproducing light source. A recording/reproducing apparatus (4) for the optical information recording medium (1) is composed of decoding means (12) for decoding information by detecting a tangential push-pull reproduced signal from the prepit recording area (2) and detecting an aggregated signal from the user recording area (3).

Abstract: An optical pick-up emits three laser beams onto an optical disk. The three laser beams are reflected on the optical disk and incident to a condenser lens. The three laser beams are further incident to a holographic device via the condenser lens. The surface of the holographic device is divided into a first and a second hologram region by a bisecting line oriented almost parallel to the track formed on the optical disk. The holographic device generates ±1th-order diffracted light beams on the hologram regions. The ±1th-order diffracted light beams are incident to a photodetector having a plurality of photo-detecting segments corresponding to the ±1th-order diffracted light beams. The photodetector detects signals recorded on the optical disk based on the ±1th-order diffracted light beams.

Abstract: An information recording medium provides a first signal recording area (A) on which a first data is recorded, and a second signal recording area (B) which is a signal recording area outer from the first area in the radius direction, records a second data at a density higher than that of the first data, and wherein the second data includes the same contents of information as the first data. The recording density of the second data may be 2 to 10 times that of the first data. The sampling rate, the number of quantized bits, and the number of pixels of the second data may be more than the sampling rate, the number of quantized bits, and the number of pixels of the first data, respectively. The first data may be recorded at a fixed transfer rate, and the second data may be recorded at a variable transfer rate. A music signal of an audible band may be recorded for the first data, and a music signal up to an ultrasound band other than an audible band may be recorded for the second data.