Abstract: The optical pickup device includes a semiconductor laser for emitting laser light of 650 nm and 780 nm in wavelengths, a semiconductor laser for emitting laser light of 400 nm in wavelength, and an optical sensor which is provided in sequence with a first light receiving surface divided into four areas in a matrix manner, a second light receiving surface divided into four areas in a matrix manner, and a third light receiving surface divided at least into two areas aligned inline. Reflected light of three beams of 400 nm in wavelength and reflected light of three beams in 780 nm in wavelength are received on the first to third light receiving surfaces respectively, and a main beam of reflected light of 650 nm in wavelength is received on the first light receiving surface on one side out of the three light receiving surfaces.

Abstract: In an optical pick-up apparatus for recording to or reproducing from an optical information recording medium, the optical pick-up apparatus includes: a light source for emitting light flux; a light converging optical system having an aperture and an objective lens and converging the light flux emitted from the light source on the optical information recording medium; a photodetector for detecting light reflected from the optical information recording medium; and a driving section for driving the objective lens and the aperture in association with the objective lens.

Abstract: An optical pickup, optical recording and/or reproducing apparatus including the same, and a method of realizing a tracking servo that is compatible between different types of optical data storage media. The optical recording and/or reproducing apparatus splits light from a light source into a main beam and four or more sub beams symmetrical with respect to the main beam, which are then emitted on an optical data storage medium, wherein the four or more sub beams include two first sub beams located close to the main beam and two second sub beams located away from the main beam, and detects a tracking error signal by a differential push-pull (DPP) method using detection signals of the main beam and the pair of first sub beams and of the main beam and the pair of second sub beams for ±R/RW and RAM type optical data storage media, respectively.

Abstract: An optical pickup includes: a first light module which records information on and/or reproduces information from a first optical recording medium having a first format, radiates a first beam having a first wavelength, and receives the first beam reflected from the first optical recording medium to detect an information signal and an error signal; a second light module which records information on and/or reproduces information from a second optical recording medium having a second format different from the first, radiates a second beam having a second wavelength different from the first, and receives the second beam reflected from the second optical recording medium to detect an information signal and an error signal; a beam splitter disposed along paths of the first and second beams and which changes the paths of the first and second beams; and an objective lens which condenses the first and second light beams to form a light spot on the first and second optical recording media, respectively.

Abstract: A tilt detection apparatus capable of detecting the tilt of the optical disk, provided with a laser for outputting a laser beam, a diffraction grating for diffracting the laser beam from said laser to generate a 0th order diffraction beam and +-first order diffraction beams which have the phase distribution equal to the phase distribution due to the wave front aberration generated on an optical disk when the optical disk is tilted, an objective lens for collecting said diffraction beams and exposing the beams to the optical disk, a photodetector for generating signals corresponding to said +-first order diffraction beams reflected at said optical disk, a signal generation circuit for generating the push-pull signals based on the generated signals, and a tilt detection circuit for detecting the tilt of the optical disk based on the push-pull signals.

Abstract: A servo device and an optical disc information recording and reproducing device using the same, which can improve the performance of a focus servo by correctly detecting a focus error when a main beam L1 and two sub-beams L2 and L3 are irradiated to an optical disc X, sizes of two sub-spots being irradiation ranges of the sub-beams L2 and L3 irradiated to the optical disc X are detected and compared after one sub-beam L2 is defocused on a positive position with respect to the optical disc X and another sub-beam L3 is defocused on a negative position with respect to the optical disc X, such that a focus of the main beam L1 on the optical disc X can be appropriately controlled.

Abstract: A method and apparatus for detecting a signal to determine on-track/off-track and/or a track cross direction, using a detection signal corresponding to a reflected main light beam and detection signals respectively corresponding to reflected first and second sub light beams, and an optical recording and/or reproducing apparatus using the same are provided. When detection signals respectively corresponding to one side portions, in a direction corresponding to a radial direction of the optical information storage medium, of the respective main light beam and first and second sub light beams are referred to as a first main signal, a first sub signal, and a second sub signal, respectively, the method and apparatus include obtaining a first operational signal, which is used to determine on-track/off-track and/or a track cross direction, by performing a subtraction on the combination of the first and second sub signals, and the first main signal.

Abstract: An optical system including an objective lens applies five light beams (31 to 35) generated by an optical pickup to a plurality of adjacent tracks on a signal plane of a CD-ROM. Light beams reflected from the signal plane are detected with photodetectors (PD1, to PD6), and in accordance with the detection outputs of the photodetectors (PD1 to PD5), a record data read system reads at the same time data recorded on respective tracks applied with the light beams (31 to 35), and outputs to read data in the record order of CD-ROM by preventing the read data from being duplicated or omitted. Prior to reading record data, a system controller performs an offset bias adjustment of a focus servo system.

Abstract: A tracking error signal generation device includes a splitting and convergence section for splitting an optical beam into a main beam and a sub beam; a two-portion main beam detection section for detecting the main beam; a main beam push-pull signal generation section for generating a main beam push-pull signal; a two-portion sub beam detection section for detecting the sub beam; a sub beam push-pull signal generation section for generating a sub beam push-pull signal; a displacement amount detection section for detecting a displacement amount of the main beam push-pull signal from a reference value based on the main beam push-pull signal and the sub beam push-pull signal; and a tracking error signal generation section for generating a tracking error signal by correcting either the main beam push-pull signal or the sub beam push-pull signal based on the displacement amount.

Abstract: Two light sources radiating two light beams having different wavelengths are simultaneously operated. Reflected beams of these two types of laser beams from an optical recording medium are simultaneously detected by two detectors. When one of the two types of light beams having different wavelengths is used while being focused on an optical recording medium, the spot diameter of the other non-focused metering beam on the optical recording medium is set larger than that of the one of the two light beams. A reflected light having a larger spot diameter is used to reduce DC offset in a tracking error signal.

Abstract: Provided are an apparatus and method for stably generating a tracking error signal in an optical recording/reading system irrespective of a disc track pitch.

Abstract: In an optical head for use in an optical data recording/reproducing apparatus of the present invention, light emitted from a semiconductor laser is split into a main beam that is zeroth order light and sub-beams that are plus and minus first-order diffracted light. A focus error signal is detected from each of the main beam and sub-beams. A diffractive optical lens causes the main beam and sub-beams to differ in light intensity distribution from each other when incident to an objective lens. As a result, when a disk or optical recording medium has a thickness error, the focus error signal derived from the main beam and focus error signals derived from the sub-beams differ in zero-crossing point from each other. The thickness error is detected on the basis of the difference between the zero-crossing points.

Abstract: A tracking servo apparatus is provided which is capable of performing correct operations even when imbalance occurs in outputs from a multi-output photodetector while an optical disk is in an unrecorded state.

Abstract: An objective lens converges a shorter wavelength laser beam on a DVD having a protective layer, which is 0.6 mm thick, and a longer wavelength laser beam on a CD having a protective layer, which is 1.2 mm thick. A common region is defined on the objective lens. The common region provides a numerical aperture appropriate for converging the longer wavelength laser beam on the CD. Coma of the objective lens in the first region is compensated better in a case where the longer wavelength laser beam is converged on the CD than a case where the shorter wavelength laser beam is converged on the DVD.

Abstract: An optical drive tracking control method allowing an optical drive to select a first tracking error detecting method or a second tracking error detecting method to generate tracking error signals when reading a CD is provided. First of all, a CD is read and the first tracking error detecting method is used to generate a first tracking error signal. Next, determine if the first tracking error signal is correct or not: if yes, continue to use the first tracking error detecting method, otherwise, change to the second tracking error detecting method. Of which, the first tracking error detecting method can be the three-beam method or the differential push pull method (DPP method), while the second tracking error detecting method can be the differential phase detection method (DPD method).

Abstract: An optical pick-up generates a 0-th order diffraction light and ±1st order diffraction lights by a diffraction grating and irradiates the same to an optical disc. The ±1st order diffraction lights have phase distributions equivalent to a wavefront aberration of the optical disc when there is a tilt in the optical disc. Distances between the center of the main optical spot and centers of sub optical spots in a disc radial direction on a recording surface are whole multiples of a track pitch. The generation circuit generates a main push-pull signal corresponding to the 0-th order diffraction light and first and second sub push-pull signals corresponding to the ±1st order diffraction lights and generates tracking error signals TE as differential push-pull signals obtained by subtracting a sum signal of the first and second sub push-pull signals from the main push-pull signal.

Abstract: A track discrimination signal can be generated without requiring the use of a large number of parts or a complex device configuration even when an optical recording medium adapted to the “land/groove recording system” such as a “DVD-RAM” is used. A main light spot is and auxiliary light spots are formed on an optical disc for signal recording and signal reproduction. The auxiliary light spots have respective distances different from that of the main light spot relative to an objective lens and formed at a position expressed by SPn/2, where S is the absolute value of the distance relative to the main spot in the normal direction of the recording tracks formed on the signal recording surface relative to the man spot, P is the track pitch and n is an integer.

Abstract: A method of selecting laser beam in an optical disk drive is disclosed. A first laser beam (such as CD laser beam) is used to read an optical disk and generate a first testing result. Whether the first testing result is normal is then determined. The first laser beam is used to read data from the optical disk if the first testing result is normal, and a second laser beam (such as DVD laser beam) is, in stead, used to read data from the optical disk if the first testing result is abnormal.

Abstract: An optical recording/reproducing apparatus having drive means for rotating a recording medium, an optical head for applying light to the recording medium being rotated by the drive means, thereby to record data signals on the recording medium or reproducing data from the recording medium, and a signal-processing circuit for processing a signal detected by the optical head. The optical head comprises a light source for emitting light, an objective lens, and signal detecting means. The objective lens has a numerical aperture NA, where 0.5<NA≦0.6. The apparatus can reliably record data on and reproduce data from high-density optical recording media that have different track pitches.

Abstract: An error signal detection apparatus for an optical recording/reproducing system including a light source emitting a light beam and an objective lens focusing the light beam to form a light spot on a recording medium, the apparatus including: a photodetecting unit dividing at least a part of the light beam passed through the objective lens after being reflected/diffracted from an information stream of the recording medium into light beam portions, and detecting the light beam portions; and a signal processor detecting phase differences between detection signals from the light beam portions to detect a tangential error signal, a defocus error signal, and/or a radial tilt error signal.

Abstract: In an optical disc drive, signals from two satellite spots are used to cancel DC offset from a tracking error signal, and for generating a quadrature signal for determining direction of radial movement. The two satellite spots generate signals that are out of phase with the main tracking error signal by about one-fourth period.

Abstract: The disclosed device is directed towards an optical data storage system. The optical data storage system comprises an optical medium including a servo plane and at least one data plane. A first laser is positioned to generate a servo laser beam and address the servo plane with a first servo focus spot. A second laser is positioned to generate a read-write laser beam and address the data plane with a second read-write focus spot. A first servo system is associated with the first laser and is configured to provide focus and tracking error correction according to servo information associated with the servo plane. A second servo system is associated with the second laser and is configured to provide focus and tracking error correction according to servo information associated with the data plane.

Abstract: When information is reproduced in an optical disk of high recording density or of low recording density, a main beam and sub-beams are emitted onto adjacent tracks. The main beam has a shape longer in a direction perpendicular to the tracks. When the optical disk of high recording density is reproduced, cross talk components from adjacent tracks included in signals reproduced from reflection light of the main beam are canceled by using signals reproduced from reflection lights of the sub-beams. When the optical disk of low recording density is reproduced, information is reproduced with a beam. Thus, two types of optical disks can be reproduced with a simple structure in a compatible way. In the cross talk canceling, discrimination marks formed along the tracks at constant distances are reproduced, and a time difference between the main beam and the sub-beams is corrected precisely by using track jump and detection of discrimination marks.

Abstract: A recording and/or reproduction apparatus, for an information medium including a substrate having concave and convex portions and a plurality of recording layers, includes a light source for emitting a light beam; an optical system for diffracting the light beam emitted by the light source so as to output a first diffracted light beam and a plurality of second diffracted light beams; and a driving section for driving the optical system. The optical system outputs the first diffracted light beam and the second diffracted light beams, such that when one of the second diffracted light beams is converged to and reflected by one of the concave and convex portions, the first diffracted light beam is converged to one of the recording layers. The driving section drives the optical system, such that the one of the second diffracted light beams is converged to the one of the concave and convex portions.

Abstract: A Cartesian scanning system for scanning a surface of a sample. The scanning system includes a light source assembly configured to produce at least one collimated beam of light, a light sensing system, a stage configured for mounting the sample thereon and a linear track having a direction of elongation. The linear track and the stage are configured to move relative to each other. The scanning system also includes a scanning head having a reflecting system which is configured to direct the collimated beam of light onto the surface and to direct a beam of light reflected from the surface to the light sensing system. The scanning head is slidably associated with the linear track so as to be moveable in a direction parallel to a direction of elongation of the linear track. Also included are a position determination system and a scan displacement correction system.

Abstract: An information reproducing method for reproducing information recorded on a medium by irradiating a laser beam and detecting a reflected light beam from the medium. The method includes detecting a plurality of reflected light beams in which the polarities of variations in reflected light beam intensity distributions are substantially inverted to each other, the distribution variation being produced when a light spot of the laser beam crosses a track on the medium, generating components of a focus error signal and components of a tracking error signal, adding the components of the focus error signal of the plurality of reflected light beams to generate a focus error signal, and taking a difference between the components of the tracking error signal of the plurality of reflected light beams to generate a tracking error signal.

Abstract: The spot diameter D3 of a side beam 21 imaged on a disc 5 is set to at least 2.5 times as large as that of a main beam. Via this configuration, an output signal from a detector detecting a reflected light via a side beam, that is, a signal representing a different in the output from photo-detection devices split by split lines in the radial contains a negligible track cross component caused by a beam spot crossing a track. The signal substantially contains a DC offset component alone caused by the shift of an objective lens in the radial direction under tracking control. Thus, by subtracting the output signal of the detector from the push-pull signal of the main beam, a tracking signal substantially containing no DC offset.

Abstract: An apparatus and method for compensating for environmental effects on media. The apparatus includes an array of servo readers that are positioned at a non-zero azimuth angle relative to a medium. The position of the array of servo readers is dynamically updateable in both a vertical direction and an azimuth angle direction based on a combination of an average position error signal of both an upper portion of the servo readers and a lower portion of the servo readers. Based on the average position error signal and a reference signal, a controller generates control signals that are output to one or more actuators. The actuators then adjust the position of the array of servo readers based on the control signals received.

Abstract: An optical disk unit for recording information on and reproducing information from a disk recording medium by projecting a light beam thereonto includes a signal level detection part detecting a level of a track error signal generated based on reflected light of the light beam from the disk recording medium, a scattered light detection part detecting scattering of the reflected light, and an off-track detection part which detects an off-track of the light beam using detection signals supplied from the signal level detection part and scattered light detection part.

Abstract: An optical detector for detecting at least three optical beams reflected by an optical information recording medium and outputting an electric signal, the optical detector having three light receiving areas each of which receives a respective one of the three optical beams and each of which has four light receiving surfaces, twelve signal lines to transmit an electric signal obtained on respective ones of the four light receiving surfaces of the three light receiving areas, selected ones of the twelve signal lines connected to the four light receiving surfaces of different ones of the three light receiving areas being joined together within the optical detector, and less than nine signal output lines formed by joining the selected ones of the twelve signal lines extend from the optical detector to a signal processing circuit.

Abstract: In order to generate a lens position signal (LCE), which describes the position of the optical axis of an objective lens (6) of an apparatus for reading from and/or writing to an optical recording medium (7) with regard to the optical axis of the remaining components (2, 3, 4, 5, 8, 9) contained in an optical scanner (21), the application of the DPP method is proposed in accordance with a first exemplary embodiment, wherein a primary-beam error signal (CPP) and a secondary-beam error signal (OPP) are obtained with the aid of the DPP method, wherein the desired lens position signal (LCE) is generated by addition of the primary-beam error signal (CPP) and the secondary-beam error signal (OPP).

Abstract: To control the gap length in the near-field area with a high accuracy, the exposure apparatus includes an exposure light source (11) to emit an exposure laser light, a gap length controlling light source (16) to emit a gap length controlling laser light different in wavelength from the exposure laser light, a condenser lens (17a), collimator lens (17b) and a dichroic mirror (12) to project the gap length controlling laser light to a condenser lens (14) and solid immersion lens (SIL) (15), and a photodetector (22) to detect the intensity of a return part of the gap length controlling laser light from an outgoing surface (15b) of the SIL (15). Thus in the exposure apparatus, the gap between the SIL (15) and object (100) is controlled based on the detected return light intensity from the photodetector (22).

Abstract: A primary spot and a secondary spot are formed on an optical disc 101. The primary spot is used for recording and reproduction. The secondary spot is positioned apart from the primary spot. The secondary spot differs from the primary spot in a distance from an objective lens. This distance (defocus amount) Def satisfies a range: 0.4×Def0≦Def≦1.7×Def0. It is assumed that a light source wavelength is &lgr;, a track pitch of the optical disc 101 is Tp, and a numerical aperture of the objective lens is NA and that Def0=[0.178&lgr;/{1−cos(sin−1 NA)}]·[{1−(&lgr;/(Tp·NA))}+2.35].

Abstract: When an optical disk is tilted in its radial direction, coma aberration may occur to cause a phase shift in a tracking signal, thereby making tracking control less accurate. There are provided an optical head that records information on an optical disk and/or reproduces information written in the optical disk, the optical head comprising an objective lens 4 that condenses light on the optical disk, light receiving means 8 of receiving a reflected beam from the optical disk to obtain a received light signal, tracking error signal detecting means 9 of detecting a tracking error signal in the received light signal, and optical means 6 of attenuating the quantity of light in a central area of a tracking error signal detecting beam of the reflected beam incident on the light receiving means 8, the tracking error signal detecting beam being used to detect the tracking error signal.

Abstract: An optical tracking system is presented which aligns a recording head with a magnetic tape. The system relies on an optically detectable servo track on the back of the tape. The servo track is formed by repeatedly engraving, at spaced intervals, three co-linear marks perpendicular to the length of the tape. Laser light reflects off the marks, and passes through a ball lens that directs the reflected light on to separate light detectors, one for each mark. By recording characteristics of the reflected light, the detectors transmit information to the system that permits the recording head to be properly aligned with the tape.

Abstract: A high density optical information recording medium comprises a substrate having rows of land and groove and a recording layer formed on the substrate. Each of the rows of land or groove includes at least two recording tracks separated by a denatured region produced by irradiating e.g. the center of each row in the recording layer with a denaturing light beam accompanied with one or two sub-beams for tracking control. Recording and reproduction of information can be performed likewise by using a recording or reproduction light beam accompanied with one or two tracking sub-beams.

Abstract: An optical pickup device has a semiconductor in which 2 light emitters laser emitting laser beams having different wavelengths for a DVD and CD are mounted on one package and disposes optical-system lenses with reference to a main beam for a DVD such that a long axis of an elliptic beam which is emitted from each light emitter for a CD and DVD and irradiated onto a disc is tilted at about 35° to the radius direction of a disc. This prevents an aberration from being generated in a converging spot at the DVD side due to image height and exhibits sufficient performance of lens to keep all CT, MTF and jitter in comparatively favorable conditions.

Abstract: In an apparatus for reading from and/or writing to an optical recording medium (7), it is desirable, in particular in the case of track jumps, to detect the direction of the track jump, i.e. the direction of movement of an objective lens (6) of the apparatus relative to the optical recording medium (7) in order to be able to carry out corresponding track regulation. For this purpose, and also for determining the number of tracks crossed by the scanning beams (14-18), it is proposed to determine the number of zero crossings and also the phase difference between at least two error signals derived from the reflected scanning beams.

Abstract: A method of arranging an optical pickup system on a deck of an optical recording and/or reproducing apparatus, which enables detection of a tracking error signal using one photodetector based on a three-beam method and by a differential phase detection method. The optical pickup system includes a light source, a diffractive optical element which diffracts a light beam incident from the light source and splits the same into at least three beams, a plate-type beam splitter which changes a propagation path of the light beam, and a photodetector including at least one main photodetector having at least four sections and a plurality of sub-photodetectors. The optical pickup system is constructed so as to have a reflecting mirror redirect the propagation path of the light beam emitted from the light source toward a recording medium.

Abstract: Substantially all of the laser light emitted from laser chip(s) 11 toward optical disk(s) 17 may be transmitted through polarizing hologram(s) 13 and may thereafter be transmitted through quarter-wave plate(s) 15, and after being reflected at optical disk(s) 17, may again be transmitted through quarter-wave plate(s) 15 and be incident on polarizing hologram(s) 13. Accordingly, where laser light is transmitted twice through quarter-wave plate(s) 15, the direction(s) of polarization thereof may be rotated by 90 degrees before it is incident on polarizing hologram(s) 13. For this reason, even if laser light is p-polarized when it is transmitted through polarizing hologram(s) 13 from laser chip(s) 11, it may be s-polarized when it is again transmitted through polarizing hologram(s) 13 after being reflected from optical disk(s) 17. Laser light, after being made s-polarized, may be diffracted by polarizing hologram(s) 13, which diffracts only s-polarized light.

Abstract: In an optical recording apparatus having an optical pickup, a rotating section is provided for rotating an optical disk which is formed thereon with a guide groove to define a spiral track having a plurality of rounds. The optical pickup has a light source for generating an optical beam and a diffractive grating for diffracting the optical beam to form a main beam and a pair of sub beams opposite with each other relative to the main beam. The optical pickup is operable for irradiating the main beam to the spiral track with accompanying the pair of the sub beams along apposite sides of the spiral track. A servo section operates the optical pickup to enable the main beam to trace the spiral track based on a tracking error signal derived from return lights of the sub beams reflected back from the optical disk. A recording section modulates the main beam for recording of information onto the spiral track while the optical dick is rotated.

Abstract: An optical pickup device for a relatively thick disc and/or a relatively thin disk including first and second laser light sources emitting first and second light beams, a first grating splitting the light beams emitted from the second light source, a beam splitter changing optical paths of the light beams emitted from the first and second laser light sources, and an objective lens focusing the light beams passing through the beam splitter onto one of the discs. A photodetector receives and detects the light beams that proceed back after being reflected by one of the discs. A second grating corrects a position of a light spot formed on the photodetector after being reflected by the relatively thin disc or the relatively thick disc, wherein the second grating includes a pattern that is rotated by a predetermined angle with respect to a pattern of the first grating.

Abstract: An optical disc drive compatible with optical discs of different types, for example, is provided. For focusing, through an optical system used in common with the different types of optical discs, a laser beam emitted from a selected one of a plurality of light sources disposed apart from each other radially of the optical disc, the optical system is moved radially of the optical disc corresponding to the selection of the light source for emitting the laser light. Namely, it is possible to prevent the optical property from being deteriorated when a single optical pickup is used in common with such optical discs of different types.

Abstract: Methods and systems for improving the storage capacity and data throughput of a digital mass storage device. The novel optimizations can be applied to a disk drive, either a hard disk drive or a disk drive having removable media, such as magnetic and optical disk drive technologies. The present invention provides at least two disk drive heads for reading and writing information from two different spinning media surfaces, e.g., platters or disks. If the disk is a read-only device, then the heads only perform the read function. A constant angular velocity drive mechanism is used meaning the rotational speed of the media is constant regardless of the head's position with respect to the media. In operation, during a media transfer, the first head accesses data by starting at the outside regions (“high track rates”) of the disk media and traversing inward towards the inner regions (“low track rates”).

Abstract: An optical appliance that is capable of processing optical media can be used to modulate a laser. In some systems, the optical appliance includes an opto-electronic transducer, a compact disk (CD) or digital versatile disk (DVD) controller and front end. A a modulated laser can be used as an optical network with a terminal node in the form of a conventional optical detector such as a compact disk (CD) or digital versatile disk (DVD) pickup. A CD or DVD controller and front end can be used to modulate the laser. Accordingly, the controller and front end can modulate the laser to emulate reading of an optical disk medium.

Abstract: A method of tracking servo for an optical pickup device comprises the steps of generating each individual push pull signal (an SPP1 signal, an SPP2 signal and an MPP signal) with a photo detector composed of a main photo detector having four photo-detecting sections crosswise and two side photo detectors having respectively two photo-detecting sections left and right, and generating a tracking error signal (a DPP signal) on the basis of operational output from the push pull signals resulting from respectively canceling the amounts of DC offset produced in each of the push pull.

Abstract: The light source package comprises a first light source for emitting a first light beam, a second light source for emitting a second light beam which is different from the first light beam, and a deflection arrangement which deflects the first and second light beam and releasing the deflected light beam as a third light beam. The deflection arrangement includes a first and second deflectors which deflects the first and second light beams such that the optical axes of the first and second deflected light beams are substantially coincide.

Abstract: An optical head according to the present invention includes: a first light source for emitting light with a first wavelength; a second light source for emitting light with a second wavelength longer than the first wavelength; and an objective lens for focusing the lights with the first and second wavelengths on information recording surfaces of information recording media corresponding to the lights with the respective wavelengths. The objective lens is designed so as to reduce aberration with respect to the light with the first wavelength. An optical-path length from the second light source to the objective lens is allowed to be shorter than that from the first light source to the objective lens so that aberration caused by the objective lens due to chromatic dispersion caused by a material of the objective lens is reduced with respect to the light with the second wavelength.

Abstract: An optical pickup apparatus which, assuming that a distance from a first light source to a first grating is a, a distance from a second light source to a second grating is b, a first predetermined grating pitch is I, a second predetermined grating pitch is J, the wavelength of a first laser beam is &lgr;1, and the wavelength of a second laser beam is &lgr;2, satisfies &lgr;1/&lgr;2>(I·b)/(J·a), and which is capable of preventing a drop in the level of a tracking error signal resulting from decentering of an optical recording medium, even in the case of using either of optical recording media of different recording densities.

Abstract: A light source for generating light beams, a diffraction grating for splitting the light beam emitted from the light source into at least three light beams, and an objective lens for receiving the reflecting light beams from the recording medium, the magnification of the objective lens being −6.0 to less than −12.0, make up a collimatorless optical system. The reflecting light beams emanating from the objective lens are split by a beam splitter, these split light beams are each split into at least three light beams by a Wollaston prism, and are incident on a photo detecting element. A tracking error signal, a focusing error signal, and a magneto-optical signal are generated using the light beams received by the photo detecting element. The beam splitter and the Wollaston prism may be substituted by a multifunctional Wollaston prism. If the nine split light beams are all received by the photo detecting element, the signals produced by the photo detecting element are large in amplitude.