Abstract: In an optical disk drive mounting a drive unit 20 having a control use circuit 21, and a pickup 1 having an aberration correction liquid crystal element 13 and a drive use circuit 2 which drives the aberration correction liquid crystal element, wherein the drive use circuit 2 stores astigmatic data for correcting a static astigmatism peculiarly provided in an optical system in the pickup 1 in an astigmatic data storage 6, and drives the aberration correction liquid crystal element 13 based on the astigmatic data. By storing the static astigmatic data peculiar to the pickup, inside the pickup, it is possible to transfer the stored astigmatic data to the optical disk drive side easily, and to correct the astigmatism by driving the aberration correction liquid crystal element based on the astigmatic data.

Abstract: An optical disc includes an information recording layer having a record of information as a pit train with a predetermined track pitch and a light-transmissive layer formed on the information recording layer so that the information can be reproduced by a beam of light illuminated through the light-transmissive layer to the information recording layer by an objective lens. The optical disc includes a feature in that a relationship of 0.194(?/NA)2?TP ×Tmin?0.264(?/NA)2 is satisfied, provided that the track pitch is TP, a pit shortest length is Tmin, a wavelength of the light beam is ? and a numerical aperture of the objective lens is NA. The optical disc also includes a feature in that a pit width is 120 nm or smaller in a range of a track pitch of 0.280 to 0.325 ?m.

Abstract: In an optical disk drive mounting a drive unit 20 having a control use circuit 21, and a pickup 1 having an aberration correction liquid crystal element 13 and a drive use circuit 2 which drives the aberration correction liquid crystal element, wherein the drive use circuit 2 stores astigmatic data for correcting a static astigmatism peculiarly provided in an optical system in the pickup 1 in an astigmatic data storage 6, and drives the aberration correction liquid crystal element 13 based on the astigmatic data. By storing the static astigmatic data peculiar to the pickup, inside the pickup, it is possible to transfer the stored astigmatic data to the optical disk drive side easily, and to correct the astigmatism by driving the aberration correction liquid crystal element based on the astigmatic data.

Abstract: A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index “n” and a thickness “t” disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface.

Abstract: An optical disc comprises an information recording layer having a record of information as a pit train with a predetermined track pitch and a light-transmissive layer formed on the information recording layer so that the information can be reproduced by a beam of light illuminated through the light-transmissive layer to the information recording layer by an objective lens. The optical disc is characterized in that a relationship of 0.194 (/NA)2 TP×Tmin 0.264 (/NA)2 is satisfied, provided that the track pitch is >TP, a pit shortest length is Tmin, a wavelength of the light beam is and a numerical aperture of the objective lens is NA. The optical disc is characterized in that a pit width is 120 nm or smaller in a range of a track pitch of 0.280 to 0.325 m.

Abstract: So as to prevent from illegally copying and illegally reproducing data with reliability, a ROM disk comprises: a data area where data to be reproduced is recorded; and a PEP area where the information necessary to reproduce the data recorded in the data area is recorded in the form of the zonal pit rows, and a recordable optical disk records a signal which prevents from recording the zonal pit rows into the area which is equivalent to the PEP area of the ROM disk, of the recordable optical disk.

Abstract: A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index “n” and a thickness “t” disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface.

Abstract: A tilt detector is adapted to be used for a storage medium provided with a recording track on which information is recorded and a first and a second header portions, each arranged in a manner shifted in opposite directions to each other from a center line of the recording track. The detector includes a light irradiation unit for irradiating a light beam onto the first header portion, the second header portion and the recording track; a light receiving unit having a first light receiving surface and a second light receiving surface arranged adjacently and for receiving the light beam reflected by the storage medium, the first light receiving surface outputting a first output and the second light receiving surface outputting a second output; an operation unit for executing an arithmetic operation of the first output and the second output to generate an operation result signal; and an error signal generation unit for generating a tilt error signal based on the operation result signal.

Abstract: The invention relates to an optical disc of the next generation which is capable of recording data at a high density by using an optical system having a larger numerical aperture and a reproduce beam of light with a shorter wavelength than those used with a conventional DVD. The optical disc includes an information recording layer where information is recorded as an array of pits at a predetermined track pitch, and a light transmitting layer formed on the information recording layer and having a film thickness of 0.13 mm or less. The information recorded therein is reproduced upon irradiation of a beam of light having a wavelength ranging from 400 nm to 415 nm onto the information recording layer through the light transmitting layer from an objective lens having a numerical aperture ranging from 0.75 to 0.86. In this disc, a taper angle of the pits is 55 degrees or higher.

Abstract: Disclosed is an optical disk having rows of pits, corresponding to information signals, formed on a transparent substrate, and a reflective film formed on this substrate. The reflective film is formed of amorphous silicon (a-Si) or indium antimonide (InSb), which exhibits a third-order non-linear optical effect. Thus, the reflectance of the reflective film formed of this material increases nearly in proportion to the intensity of the irradiated beam spot. The beam spot irradiated on the optical disk has the highest intensity at the center portion and this intensity becomes weaker as a point in the spot approaches the edge. Therefore, the effective spot size of the beam spot can be reduced, making it possible to reproduce from the reflection type optical disk information signals with a spatial frequency above the cutoff spatial frequency defined by the reproducing optical system. In other words, a row of pits recorded at a high density can be reproduced.

Abstract: A multi-layered disk which can improve a data recording density and also can record signals and allow reading and reproduction of the recorded signals in good conditions and a recording system as well as a reproducing system using the same and a multi-layered recording disk in which a plurality of data recording surfaces are laminated. In a band wherein, against an MTF level obtained when a read light is on-focus to one of the data recording surfaces, an MTF level obtained when the read light is defocusing to other data recording surfaces is 1/N (N is a real number larger than 1), data signals are recorded in each of the data recording surfaces. A distance t between each data recording surface, numerical aperture NA of an objective lens guiding a read light to any of the data recording surfaces, a wavelength.lambda. of the read light, an equivalent refractive index n between each data recording surface, and a number i of laminated data recording surfaces satisfy the following relation:1.4 n.lambda./(NA).sup.

Abstract: An information detection light intensity control apparatus in an apparatus reproducing information recorded in an optical disc in which a reflectance has a dependency on an incident light intensity, comprising a light source for emitting an information detection light which enters the optical disc and a control system for controlling an intensity of the information detection light which enters the optical disc so that a ratio of an intensity of the information detection light which enters the optical disc and an intensity of the information detection light reflected from the optical disc is set to a predetermined value.

Abstract: A reflective film is formed over a recording surface of an optical disk on which pits are formed. The reflective film is made of a non-linear optical material which, when light is incident thereon, generates second harmonics of the incident light. In a reproduction optical system for reproducing this optical disk, when a reading beam reflected by the reflective film of the optical disk impinges on a filter for filtering out the basic wave of the reading beam, the filter only transmits the second harmonics which are then incident on a light receiver. Since information signals recorded on an optical disk is reproduced by reading only second harmonics of the reflected beam, the cut-off spatial frequency of the OTF can be made twice higher as compared with a conventional reproducing apparatus. In other words, the recording density of the recording medium can be made higher.

Abstract: An optical disk having two transparent and a refelection film. The reflection film is made of a non-linear optical material in which reflectance increases according to intensity of incident light thereto. The reflection film has a multiple reflectance.

Abstract: A reflected beam from a reflective film of an optical disk exhibiting light intensity dependency is efficiently received. In the optical system, a collimator lens, a polarization beam splitter, a quarter wave plate and an objective lens are disposed in turn in an optical path between a laser and an optical disk from the laser side. A light receiver is disposed on another optical path extending from the polarization beam splitter. A light receiving aperture diameter of the objective lens for passing the reflected beam from the optical disk therethrough is made larger than an incident aperture diameter of the objective lens for impinging the reading beam on the recording medium. This structure enables information signals to be recorded at higher density on the recording medium to be reproduced.

Abstract: A tracking error signal generating device using a four-segment detector in which signals from diagonally opposed elements are combined and the two so combined signals are phase compared. According to the invention, either before or during the combining, the output signals of the segments have high level components removed so as to reduce offsetting due to a non-uniform beam illuminating the detector.

Abstract: A fibre-type light conversion device for converting the wavelength of an incident light. According to the first feature of the invention the device has a structure in which a holographic element whose complex transparency varies periodically with respect to the distance from an optical axis is used as a means for transforming the light, to which the conversion of wavelength has been performed by a fibre-type SHG, into a parallel light. According to the second feature of the invention, the device is constructed so that the temperature of the light source or the holographic element can be controlled, thereby a parallel light having planer wave fronts is surely generated irrespectively of differences in the shape of the fibre-type SHG or variations in the refractive index.

Abstract: A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index “n” and a thickness “t” disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface. The deepest recording layer is formed at an optical distance d1 from the light incident side surface satisfying an equation d1=nt.

Abstract: A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index “n” and a thickness “t” disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface. The deepest recording layer is formed in an optical distance d1 from the light incident side surface satisfying an equation d1?nt.

Abstract: A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index “n” and a thickness “t” disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface. The deepest recording layer is formed at an optical distance d1 from the light incident side surface satisfying an equation d1=nt.