Abstract: Various illustrative aspects are directed to a data storage device, comprising one or more disks; an actuator mechanism configured to position heads proximate to a recording medium of the disks; a spindle motor configured for rotating the one or more disks; and one or more processing devices comprising a servo control processor. The servo control processor is configured to receive a spindle speed error signal indicative of an error in a rotational speed of the spindle motor. The servo control processor is further configured to output an initial frequency offset signal, wherein the initial frequency offset signal is proportional to the spindle speed error signal.

Abstract: Aspects of the disclosure are related to a Lidar device, comprising: a vibrating fiber optic cantilever system on a transmit (TX) path; and a two-dimensional (2D) light sensor array on a receive (RX) path.

Abstract: A device includes a light splitter configured to receive a source light beam from a light source and split the source light beam into separate light beams, each emitted through an outlet. The device also includes resonators, each of which is optically coupled to at least one of the outlets and is configured to steer at least one of the light beams.

Abstract: A camera module is provided, including a prism base, a prism driving mechanism, a prism unit, a lens unit, and an image sensor. The lens unit is disposed on the lens driving mechanism. The prism base includes a metal member, at least one first wiring layer, and a first insulation layer disposed between the metal member and the first wiring layer. The prism driving mechanism is electrically connected to the first wiring layer. The prism unit is connected to the prism driving mechanism, and the prism driving mechanism can drive the prism unit to rotate relative to the prism base. The image sensor can catch the light reflected by the prism unit and passing through the lens unit.

Abstract: A configuration for reducing a possibility of data recording or reproduction being unperformable due to a reading error of disc management information is realized. A data processing unit records management information corresponding to a first surface as main management information on the first surface which is a data recording surface on which data recording is performed and further records mirror management information having the same content as the main management information on a second surface different from the first surface. The management information is, for example, a temporary disc management structure (TDMS) including defect region information of one surface of a disc. When one piece of management information between the main management information and the mirror management information is successfully read, data recording or reproduction can be correctly performed.

Abstract: An illumination arrangement according to the invention, in particular for an endoscope, comprises at least three light sources for generating a respective input light beam, and a beam combination device (5, 21), wherein the beam combination device (5, 21) comprises at least two beam splitters for combining the at least three input light beams to form an output light beam, at least three collimator lenses (7, 8, 9) embodied as GRIN lenses and serving for collimating and coupling a respective one of the input light beams into one of the beam splitters, and at least one further GRIN lens for coupling the output light beam into an optical waveguide. The invention also relates to a beam combination device and a method for coupling at least three input light beams into an optical waveguide, in particular into an optical waveguide of an endoscope.

Abstract: An example system may include a first vertical cavity surface emitting laser (VCSEL) that includes a first integrated polarization locking structure to produce a polarized optical data signal. The system may also comprise a second VCSEL that includes a second integrated polarization locking structure, the second integrated polarization locking structure orthogonal to the first integrated polarization locking structure, to produce an orthogonally polarized optical data signal. Lenses may be disposed on the substrate opposite the first VCSEL, to collimate the polarized optical data signal, and opposite the second VCSEL to collimate the orthogonally polarized optical data signal. A polarization division multiplexer may combine the first collimated polarized optical data signal and the second collimated orthogonally polarized optical data signal.

Abstract: According to one embodiment, an inscribed figure as circle or an oval inscribed in a rectangular pattern of designed layout data is calculated, a difference in area between a lithographic shape corresponding to the rectangular pattern and the inscribed figure is calculated, and it is determined whether the difference in area satisfies a predetermined specification.

Abstract: A cylindrical array of tightly spaced optical discs is arranged such that all optical discs in the array share the same axis of symmetry. An optical system is aligned with the optical disc array. The optical system includes a light source, such as a diffuse reflector, and a photo detector, such as a photo detector. The photo detector is aligned to receive either light transmitted through the optical disc array or light reflected off the optical disc array. Illumination directed at the optical disc array results in a pattern of alternating light and dark illuminations, or bands. The photo detector focusing on the cylinder surfaces of the optical discs detects the light/dark transitions and thus enables counting of discrete optical discs.

Abstract: An optical head device (11) provided with: an optical element (36) for transmissively diffracting a light beam emitted from a semiconductor laser (34), generating a zero-order diffracted light beam and ±1-order diffracted light beams; and a photodetector (40) for receiving the zero-order diffracted light beam and the +1-order diffracted light beam after reflection from an optical disc (2). The photodetector (40) includes a primary light receiving section (400) for receiving the zero-order diffracted light beam, and a first secondary light receiving section (401) disposed outward from the primary light receiving section (400). The first secondary light receiving section (401) is positioned to detect an outer portion of the received light spot of the +1-order diffracted light beam, performs photoelectric conversion of this portion, and outputs a secondary detected signal.

Abstract: An optical disc device and information recording/reading method for an optical disc in which a recording layer is formed through volume recording by aligning recording tracks, which hold information, in a homogenous recording region that does not internally have a layer defining a recording position. The information recording method includes a step in which a first recording layer forming a complex recording layer is formed by forming a recording track while recording information by focusing a main beam at a predetermined depth position in the recording region, and a step in which a second recording layer forming the complex recording layer is formed by forming a recording track while recording information by focusing the main beam at a depth position that is separated from the first recording layer in a depth direction by a depth offset greater than ? of a wavelength of the main beam.

Abstract: An optical-recording-medium driving apparatus includes: a light irradiating/receiving section configured to irradiate light on a medium so as to form a first side spot, a main spot, and a second side spot, and to receive reflection light from the individual spots; a first delay section configured to delay a light reception signal on the first side spot in accordance with a disposition interval between the first and the second side spots; a second delay section configured to delay a light reception signal on the main spot in accordance with a disposition interval between the main and second side spots; and a tracking-error-signal generation section configured to generate a tracking error signal on the basis of a correlation between delayed light reception signals on the first side spot and the main spot, and a correlation between the light reception signals on the second side spot and the main spot.

Abstract: There is a problem that when the relative angle between laser light and an optical disc is changed by temperature, or a chucking state of an optical disc and so forth, the formerly recorded data is overwritten. The above-mentioned problem is solved by performing focus control and tracking control independently with respect to a servo layer and a recording layer in a grooveless disc.

Abstract: A reproducing device includes a light generation and emission unit that obtains signal light as reflection light, which reflects recording signals of a land and a groove, by irradiating an optical recording medium with light and generates reference light so as to emit the signal light and the reference light in a superposed manner, a detection optical system that generates a first combination of signal light and reference light, a second combination of signal light and reference light, a third combination of signal light and reference light, and a fourth combination of signal light and reference light respectively, a light receiving unit in which the first to fourth combinations of signal light and reference light are respectively received by first to fourth light receiving elements, and a reproduction unit that reproduces the recording signals of the land and the groove on the basis of first to fourth light receiving signals.

Abstract: An optical information recording/reproduction device includes a detection unit which detects a focus-direction height of a recording medium, a focus adjustment unit which adjusts a focus-direction distance between the recording medium and a signal light optical system and a reference light system, and a control unit which controls the focus adjustment unit so that a relative distance between the object lens of the signal light optical system and the recording medium is adjusted according to the focus-direction height of the recording medium detected by the detection unit.

Abstract: An optical recording medium includes a recording and reading layer that is previously staked or formed afterword and has no concavo-convex pattern for tracking control, and a servo layer in which a concavo-convex pattern or a groove for tracking control is formed. Information can be recorded in the recording and reading layer while tracking is performed using the servo layer.

Abstract: An optical pickup apparatus includes at least: a light emitting element capable of emitting at least first wavelength light and second wavelength light; and a diffraction grating configured to split the first wavelength light into at least a first main beam and a first sub-beam and to split the second wavelength light into at least a second main beam and a second sub-beam, a following expression (1) being satisfied: 1.05 < Yp ? ? 1 Yp ? ? 2 < 2.50 ( 1 ) where: Yp1 is an interval between the first main beam and the first sub-beam when a first media corresponding to the first wavelength light is irradiated with the first main beam and the first sub-beam, and Yp2 is an interval between the second main beam and the second sub-beam when a second media corresponding to the second wavelength light is irradiated with the second main beam and the second sub-beam.

Abstract: Provided is an optical pickup device that suppresses a fluctuation of a tracking error signal caused by stray light when recording/reproducing information on/from an optical disc including a plurality of recording layers and attains size reduction. It includes a laser diode emitting laser light of about 405 nm in wavelength, an objective lens irradiating the optical disc with an optical beam emitted from the laser diode and having a numerical aperture of about 0.85, and a detector including a detection part receiving the optical beam reflected from the optical disc. An optical magnification from the optical disc to the detector is set within a range from about 10× to 15×.

Abstract: Multi-level recording is quite effective for attaining a larger capacity and a higher transfer rate in the case of an optical disk; however, with conventional technologies, a SIGNAL-TO-NOISE RATIO of a signal deteriorates along with an increase in a multi-level degree, creating a factor for limitations to the multi-level degree. In order to solve problems, when optical information is recorded by use of a standing wave occurring due to interference between two light beams, at least one of the two light beams is modulated in multi-stages. Further, at the time of regeneration, a regeneration reference beam is caused to interfere with respective polarization components of a regeneration beam, the polarization components being orthogonal to each other, thereby concurrently generating not less than three interference beams differing in interference phase from each other before being detected.

Abstract: An optical disk playback device comprises one or more lasers, an optical assembly, an optical detector, and controller circuitry coupled to the optical detector. The optical assembly is configured to direct incident light from the one or more lasers so as to form first and second scanning spots on a surface of an optical disk, and is further configured to direct corresponding reflected light from the first and second scanning spots on the surface of the optical disk to the optical detector. The optical detector is configured to process the reflected light from the first and second scanning spots to generate respective first and second data streams, and the controller circuitry is configured to generate a three-dimensional image signal from the first and second data streams.

Abstract: There is a problem that when the relative angle between laser light and an optical disc is changed by temperature, or a chucking state of an optical disc and so forth, the formerly recorded data is overwritten. The above-mentioned problem is solved by performing focus control and tracking control independently with respect to a servo layer and a recording layer in a grooveless disc.

Abstract: In one embodiment, the optical read/write apparatus includes a plurality of optical pickups arranged to cross tracks of an optical storage medium and a control section. On finding the data that has been written by any of those optical pickups inaccurate or on detecting any defect at a location where data is going to be written by any of the optical pickups, the control section instructs another one of the optical pickups to write that data on a different track from a track on which the data should have been written.

Abstract: In an optical tape drive having optical heads for writing data in tracks on an optical tape, each track having an off-track threshold, a system and method are disclosed for off-track write prevention. The system includes multiple actuators, each actuator configured to control a position of an associated optical heads. The system also includes a controller configured to determine a position of each of the optical heads relative to an associated track on the optical tape and to prevent, in response to an event causing an optical heads to have a position outside the off-track threshold of the associated track, only that optical head from writing data to the optical tape and to buffer a stream of data for that optical head for later processing.

Abstract: An optical information device used with a grooveless multilayer disc including multiple recording layers used to record and reproduce information signals and a guide layer dedicated to detect tracking error signals (TES) can always stably detect the TESs when the distance between the recording layer and guide layer varies due to selection of a target recording layer. For example, a plurality of light spots for detecting the TESs are formed by a holographic grating on the guide layer, but are defocused with respect to each other. The TESs are detected individually from the respective light spots. The TESs are subjected to an addition operation to be a signal for tracking control, thereby extraordinarily increasing the defocus dynamic range of the TESs.

Abstract: The apparatus includes a pickup for reading data from a super-resolution optical disc, the pickup comprising a laser for generating a main beam, a first and a second satellite beam, the two satellite beams each having a radial offset with regard to the main beam, a third satellite beam following the first satellite beam, having the same radial offset as the first satellite beam, and a fourth satellite beam following the second satellite beam, having the same radial offset as the second satellite beam, for providing a crosstalk correction of the HF data signal. The track pitch between adjacent tracks of the optical disc is particularly below the diffraction limit of the pickup, and the light intensity of each of the first and second satellite beams and of the main beam is sufficient to provide a super-resolution effect on the optical disc and the light intensity of each of the third and fourth satellite beams is not sufficient to provide the super-resolution effect.

Abstract: In one embodiment, an optical pickup includes an optical system which forms multiple light beams based on the light emitted from a light source and which converges a write beam and a read beam, thereby forming a main spot and a sub-spot, respectively, on an optical storage medium. This optical system converges the write and read beams onto the optical storage medium so that the main spot moves through the same region on the optical storage medium ahead of the sub-spot. The optical pickup further includes a detector for sensing the write and read beams reflected from the storage medium. The detector includes a first photodiode 10 that receives the reflected light from the main spot 50R on the storage medium and a second photodiode 11 that receives a portion of the reflected light from the sub-spot 51R.

Abstract: Provided is a lens driving unit for an optical pickup and an optical disc drive employing the lens driving unit. First and second driving coils are directly wound around a coil winding unit included in the lens frame, which is different from a conventional lens frame in which a driving coil is manufactured as a separate element and is separately attached to a lens frame.

Abstract: The present invention can properly correct spherical aberration. An optical disk device (10) displaces an objective lens (18) so that the objective lens is displaced to a reference lens position as a reference. The optical disk device (10) controls an information light condensing point changing mechanism (55) so as to adjust the focus (FM) of an information light beam (LM) to a recording depth (X) at which the information light beam (LM) is to be applied in a state of the objective lens (18) being placed at a reference lens position (SL). The optical disk device (10) controls a servo light condensing point changing mechanism (35) so as to adjust the focus (FS) of a servo light beam (LS) to a servo layer (104) in the state of the objective lens (18) being placed at the reference lens position (SL).

Abstract: In a diffractive element, its grating pattern is so configured that a diffraction angle of a diffracted light beam of a light source that is subject to the first-order diffraction in a diffraction area is matched with an angle of a light beam passing through the diffractive area emitted from a light source and a light source position is matched with a light originating point of the light source that emits a light beam to be transmitted, and the center of light intensity distribution is matched with that of the light source passing through the diffractive element by inclining an optical axis of the light source. A position of the diffractive element is adjusted based on an electric current value generated when a reflected return path light beam of the light source is diffracted by the diffractive element and enters the light source.

Abstract: Disclosed are a module to detect a tracking error signal that is easy to be assembled and robust against variation in a track angle, a diffraction grating, an optical pickup, and an optical disc apparatus that enable the module to be realized, wherein a diffraction grating divided into at least three areas, first, second, and third areas, is used; the second area is an area that do not diffract light; and focusing positions of light diffracted by the first and third areas sandwiching the second area therebetween on an optical disc are arranged with a spacing of (2n?1)×t/2 in an optical disc radial direction, respectively, where n is a nonnegative integer and t is a spacing of guide grooves of the optical disc.

Abstract: A multilayer optical recording medium includes a plurality of interfacial surfaces that reflect an incident light beam, and neighboring ones of the interfacial surfaces has a spacer therebetween. When a light incident surface side is defined as an upper surface side, a different thickness layer unit including the spacers having different thicknesses arranged sequentially is disposed on the lowermost layer side, and the spacers each having a thickness different from the thickness of any one of the spacers arranged in the different thickness layer unit are sequentially arranged above the different thickness layer unit.

Abstract: A suspension system is provided for an objective lens housing. The objective lens housing is supported by the suspension system and is moved in either a tracking direction Y or focusing direction Z by an electro-magnetic actuator. The objective lens housing is supported by upper and lower suspension springs. The suspension springs are moveable in the tracking direction by flexing the suspension springs and are moveable in a focusing direction by compressing a front portion and a back portion to fold the suspension spring at bends formed in an intermediate portion of the suspension springs.

Abstract: An optical disc device and a recording method is provided in which information can be additionally recorded on an optical disc, which has a servo layer and recording layers separately formed, by accurately correcting a relative angle between a light beam and the optical disc used in the previous recording without providing an area where recording is not performed while maintaining the stability of tracking servo. The above subject can be solved by studying with high accuracy the relative angle between the optical disc and the optical axis used in the previous recording by applying a radial tilt servo according to a signal from the recording layers with the tracking servo applied by the servo layer. Further, the additional recording can be performed stably by fixing the radial tilt at the previously studied angle when the recording is performed.

Abstract: A tilt can be detected highly accurately by minimizing the tilt detection error. An optical head includes: an objective lens for converging a light beam from a light source onto an optical disc; a photodetector section receiving the beam, reflected from the disc, at divided areas on its photodetection plane and outputting light detection signals from those areas; and a tilt detecting section for detecting a relative tilt between the lens and disc based on the detection signals.

Abstract: A compatible optical pickup including an optical unit and a focusing unit. The optical unit emits a short wavelength light for high-density recording media and a long wavelength light for low-density recording media, directs the short and long wavelength light to a recording medium, receives lights reflected by the recording medium, and detects an information reproduction signal and/or an error signal from the received lights. The focusing unit focuses light received from the optical unit to form a light spot on a recording surface of the recording medium, diffracts the short wavelength light into a zero order light and the long wavelength light into a second order light to be used as effective light for recording and/or reproduction. Thus, a high-density recording medium and a low-density recording medium having different thicknesses can be compatibly used.

Abstract: An optical pickup device including: a laser diode for emitting laser light; an objective lens which irradiates an optical beam emitted from the laser diode; an actuator which displaces the objective lens in a radius direction of the optical disc; a grating for branches an optical beam reflected by an information recording layer into plural regions; and one photodetector having plural light receiving parts for receiving the branched optical beams, wherein the photodetector has a first light receiving part which detects zero-th order grating diffracted light and plural second light receiving parts which detecting grating diffracted light having an order not less than that of ±first order grating diffracted light; a detected signal of the zero-th order grating diffracted light is defined as a reproduction signal; and a detected signal of the grating diffracted light is defined as a signal for servo controlling.

Abstract: Recording and reading method for optical information recording medium comprising: recording layer having thickness not less than 2?/n, where ? is wavelength of recording beam and n is refractive index of the recording layer, and configured to undergo a change in the refractive index by irradiation with the recording beam; and adjacent layer adjacent to the recording layer at a side opposite to an incident side, comprises the steps of: recording a recording spot by irradiating with the recording beam, while shifting focal position by offset amount d, which satisfies ?0d3?0, where ?0 is radius of the recording spot, from interface between recording layer and adjacent layer toward the incident side at a time of recording, whereby the refractive index of recording layer changes at a recording position to record recording spot; and reading out the information by irradiating with reading beam, while bringing it into focus on the interface.

Abstract: An optical head device mounted in an optical disc device. The optical head device is provided with a diffractive optical element and a photodetector. The diffractive optical element has: a primary diffraction region at a location on which the positive and negative first-order components and some of the zero-order component of a reflectively diffracted light beam are incident; and secondary diffraction regions at locations on which the rest of the zero-order component but none of the positive or negative first-order components of the reflectively diffracted light beam are incident. A main light-receiving section of the photodetector receives the zero-order component of a transmissively diffracted light beam that has passed through the primary diffraction region and the secondary diffraction regions.

Abstract: An optical drive device includes first and second light sources, an objective lens configured to receive a first light emitted from the first light source and a second light emitted from the second light source and to irradiate both the first light and the second light to an optical disc recording medium, a first focus mechanism configured to drive the objective lens in a focus direction, a second focus mechanism configured to change collimation of the second light incident to the objective lens and changing the focusing position of the second light independently of the first light, a first focus servo control unit configured to drive the first focus mechanism, an error signal subtraction unit configured to subtract the first focus error signal from a second focus error signal, and a second focus servo control unit configured to drive the second focus mechanism.

Abstract: An optical disk playback device comprises one or more lasers, an optical assembly, an optical detector, and controller circuitry coupled to the optical detector. The optical assembly is configured to direct incident light from the one or more lasers so as to form first and second scanning spots on a surface of an optical disk, and is further configured to direct corresponding reflected light from the first and second scanning spots on the surface of the optical disk to the optical detector. The optical detector is configured to process the reflected light from the first and second scanning spots to generate respective first and second data streams, and the controller circuitry is configured to generate a three-dimensional image signal from the first and second data streams.

Abstract: In the present invention, to improve CD read/write characteristics having poor image height characteristics, a third light emitting source emitting a third laser beam for CD is disposed on an optical axis of an objective lens. Thereby, the third laser beam emitted from the third light emitting source travels along the optical axis of the objective lens, thus generating no coma aberration in the third laser beam. Furthermore, in the present invention, a second light emitting source emitting a second laser beam for DVD and a first light emitting source emitting a first laser beam for BD are disposed across the third light emitting source. Thereby the phase propagation directions of coma aberrations in the first and second laser beams coincide with each other. Adjustment of the coma aberration in one of the laser beams enables the coma aberration in the other laser beam to be adjusted.

Abstract: A configurable photo detector circuit comprises a photo detector array including a plurality of photo detectors coupled to a plurality of amplifiers. A method for programming a detection pattern of the configurable photo detector circuit comprises selecting a first detection pattern for the photo detector array, generating first signals to create the first selected detection pattern, and applying the first generated signals to the photo detector circuit to implement the first selected detection pattern.

Abstract: A reproducing method includes: irradiating a laser spot for servo to which astigmatism making up a generally 45-degree angle in the tangential direction of an information recording track has been applied, and one or more laser spots for reproduction, onto a recording medium where a track group is formed with multiple information recording tracks adjacent with a narrower track pitch than a track pitch equivalent to optical cut-off, and also where a track group pitch is wider than the track pitch equivalent to optical cut-off; and subjecting one or more laser spots for reproduction to on-track control as to one of the information recording tracks by taking a tangential push pull signal obtained from reflected light information of the laser spot for servo as a tracking error signal, and performing tracking servo control using this tracking error signal, and reproducing data from the reflected light information thereof.

Abstract: A tracking signal and a focusing signal are stabilized by eliminating multi-layer crosstalk. The diffraction position, with respect to a semiconductor detector, from a center region of a multi-region diffraction grating disposed along the return path of reflection light from the layer of interest is placed further away from the optical axis than the diffraction position from a peripheral part of the diffraction grating. Stray light from other layers is thus prevented from being incident on a sensing region for a peripheral region of the diffraction grating. Further, the area of the semiconductor detector is reduced by dividing the center region.

Abstract: In one embodiment, an optical read/write apparatus includes first and second optical pickups 2a, 2b and a control section. The first optical pickup 2a includes a first lens 3a that condenses a light beam emitted from a first light source onto an optical storage medium, and a first lens actuator that can shift the first lens 3a in a track crossing section with respect to a middle position. The second optical pickup 2b includes a second lens 3b that condenses a light beam emitted from a second light source onto the optical storage medium, and a second lens actuator that can shift the second lens 3b in the track crossing section with respect to the middle position. The control section makes the lens actuators operate so that as the magnitude of shift of the first lens 3a increases, that of the second lens 3b decreases.

Abstract: The apparatus includes a pickup for reading data from a super-resolution optical disc, the pickup comprising a laser for generating a main beam, a first and a second satellite beam, the two satellite beams each having a radial offset with regard to the main beam, a third satellite beam following the first satellite beam, having the same radial offset as the first satellite beam, and a fourth satellite beam following the second satellite beam, having the same radial offset as the second satellite beam, for providing a crosstalk correction of the HF data signal. The track pitch between adjacent tracks of the optical disc is particularly below the diffraction limit of the pickup, and the light intensity of each of the first and second satellite beams and of the main beam is sufficient to provide a super-resolution effect on the optical disc and the light intensity of each of the third and fourth satellite beams is not sufficient to provide the super-resolution effect.

Abstract: An optical disk discriminating method and an optical disk device which can detect reflected rays for making discrimination among kinds of optical disks with high accuracies. By switching a plurality of lasers and moving a spherical aberration corrector while moving an objective lens to cause it to approach or keep away from an optical disk, rays reflected light from the optical disk can be detected with high accuracies. Discrimination among the kinds of a plurality of optical disks can be made on the basis of signals generated from the detected reflected rays. This ensures that the kind of an optical disk can be determined through one operation of sweeping.

Abstract: In an optical head device responding to optical disc of different track pitches, an effect of both obtaining the tracking error signal by the optimum DPP method using a single diffractive element and suppressing the lowering amount in the amplitude of the tracking error signal in a state the object lens is moved by track following is obtained. In the optical head device, the grating phase of left and right regions of a sub-beam generating diffractive element differ from each other by 180 degrees. A central region of the sub-beam generating diffractive element has a grating pattern different from the left and right regions, and is divided into a plurality of regions to form different gratings different from each other.

Abstract: The present invention relates to an optical device which includes a first laser diode, a beam splitter, a first objective lens, a photo-detector, a second laser diode, a wedged plate beam splitter, a second objective lens and a collimator. The present invention deploys two independent transmitting paths. The retrieving paths share the beam splitter and the photo-detector commonly at the returning route.

Abstract: An optical disk reader or read/write system for CD or DVD formats. First and second laser diodes operating at different wavelengths have their output beams collimated and directed at a single element objective lens, and are then reflected off the disk back through the lens to a photodetector. The single element objective lens has a central aperture zone and an outer aperture zone, the central zone being profiled to operate at a first numerical aperture at approximately 0.45 and the output beam of the first laser diode is confined to the central aperture zone. The outer aperture zone together with the central aperture zone are profiled to operate at a second numerical aperture, for example 0.60 wherein the output beam of the second laser diode has ray fans extending across the full aperture of the single element objective lens.