Abstract: A signal-detecting light-receiving device formed as an integrated circuit, which receives a light beam reflected from an optical recording medium, and which outputs a signal obtained from the received reflected light beam, through a current-output-type current amplifier circuit. The light-receiving device includes the following components: at least one resistor configured as a part of the integrated circuit, the at least one resistor being an output resistor used as a termination resistor for an output terminal of the light-receiving device, the output terminal being connected to an output of the current amplifier circuit; and a selecting circuit configured as a part of the integrated circuit, which controls the at least one resistor so as to enable/disable connection of the at least one resistor to the output terminal of the light-receiving device.

Abstract: An optical disc drive includes an objective lens for focusing light on an optical disc with five or more stacked data storage layers and a tilt control mechanism for controlling a tilt angle defined between the optical axis of the light and a normal to the storage layers. The drive reads and/or writes data from/on a selected one of the storage layers by focusing the light on the selected layer. The numerical aperture NA of the objective lens is defined so as to fall within the range of 1.3009×D3?2.9315×D2+2.3133×D?0.0502 to 1.3009×D3?2.9315×D2+2.3133×D+0.2028, where D is a distance (mm) from a light incident side of the disc to the deepest one of the storage layers, which is located most distant from the light incident side.

Abstract: An optical pickup apparatus is provided with a light source device to emit selectively an ordinary polarized light ray and an extraordinary polarized light ray by controlling a polarization condition of a light flux having a wavelength of ?1; and a light converging optical system. An objective lens has a phase structure made of a doubly refracting medium in which an ordinary ray refractive index no for the ordinary polarized light ray is different from an extraordinary ray refractive index ne (ne?no) for the extraordinary polarized light ray so that the phase structure has a function for not changing a transmitted wavefront of an incident light ray being one of the ordinary polarized light ray and the extraordinary polarized light ray and for changing a transmitted wavefront of an incident light ray being the other one of the ordinary polarized light ray and the extraordinary polarized light ray.

Abstract: An information processing apparatus includes: a converging section for converging light; a shifting section for shifting the focus of the light by moving the converging section perpendicularly to an information storage layer of a storage medium responsive to a drive signal; a position control section for generating a position control signal to move the converging section at variable velocities; a focus control section for generating a focus control signal based on a light amount signal representing reflected light such that the focus is located in a focus controllable range; a switching section for selectively outputting the position control or focus control signal; and a driving section for outputting a drive signal responsive to the output signal.

Abstract: An optical pickup apparatus for recording and/or reproducing information for an optical information recording medium, comprising a light converging optical system including a coupling lens and an objective lens, wherein a first diffraction structure is installed on the objective lens, and a second diffraction structure is arranged on the coupling lens, whereby spherical aberration caused by change of ambient temperature is reduced by giving a condition to reduce the number of areas formed in a ring-shaped of the diffractive structure.

Abstract: An optical pickup device has three different light sources, a holographic element, beam splitters, and first and second photodetectors. The beam splitters each change an optical path of a light beam coming from the associated light source toward a recording medium and match an optical axis of the changed optical path with an optical axis passing through the holographic element and the first photodetector. Reflected light from the recording medium is divided into zero-order diffraction light and first-order diffraction light by the holographic element. The first photodetector receives the zero-order diffraction light and obtains an RF signal and a tracking error signal. The second photodetector receives the first-order diffraction light and obtains a focusing error signal.

Abstract: An image entering from the left side of the figure passes through a correcting lens unit, and forms an image on an image pickup device on the right side of the figure. The correcting lens unit includes a cylindrical outer frame and a lens arranged therein, and at coupling points, coupled to one end of each of electrostrictive coils and suspended thereby. Electrostrictive coils strain in response to voltages applied from a voltage applying unit, causing displacement of electrostrictive coils. The displacement is transmitted to correcting lens unit through the coupling points, and therefore, in accordance with the displacement from electrostrictive coils, position and/or direction of correcting lens unit changes.

Abstract: An optical path coupling member aligns an optical axis directed to a light condensing member of the first wavelength light having a shortest wavelength with that of the third wavelength light having a longest wavelength. A diffraction element condenses +2nd order diffracted light of the first wavelength light and +1st order diffracted light of the second wavelength light and third wavelength light into a first photodetector, the ?2nd order diffracted light of the first wavelength light and ?1st order diffracted light of the third wavelength light into a second photodetector, and ?1st order diffracted light of the remaining second wavelength light into a photodetector, using ±2nd order diffracted light of the first wavelength light and ±1st order diffracted light of the second wavelength light and third wavelength light as signal light from an optical information recording medium. Consequently, the overall size of the optical pickup apparatus is reduced.

Abstract: A system for measurement of the height, angle and their variations of the surface of an object comprises a measurement module and an astigmatic optical path mechanism. The optical path mechanism makes a laser beam pass a lens assembly and focus on an object. The reflected light passes the lens assembly and an astigmatic lens, arriving at the photo sensor assembly, forming a light spot thereon. The translational displacements of the object are measured by the variations in shape of the light spot on the photo sensors. The angular displacements of the object are measured accordingly by the movement of the light spot on the photo sensors.

Abstract: An optical sensing head, which is for reading out an optical data memory, has a substrate with a main surface. An edge-emitting laser component is configured on the main surface of the substrate and has irradiation axis oriented essentially parallel to the first main plane. A deflection device is arranged on the main surface of the substrate and deflects the laser radiation in a direction that is essentially perpendicular to the main surface. At least one signal detector is provided for sensing the laser radiation that is reflected by the optical data memory. An optical element guides the deflected laser radiation to the optical data memory and guides reflected laser radiation to the signal detector. The optical element is connected to the substrate by at least one supporting element. The invention also includes a method for fabricating such a sensing head.

Abstract: An optical bench is provided, as are a thin optical pickup that employs the optical bench, and a method of manufacturing the optical bench. The optical bench includes a light source for generating light for recording and reproducing information to and from an optical disc, a light source stand on which the light source is mounted, a mirror adjacent to the light source stand, and a bottom surface at a lower point than the light source stand and between the light source stand and the mirror surface. Sides of the light source stand besides the side facing the mirror are connected to the surface of the substrate by a flat sloped surface. Along the sloped surface, two electrodes for supplying power to the light source are connected to the light source stand. Since the metal wirings are formed along the sloped surface without trenches or windings between the light source stand and the silicon substrate, no disconnection of metal lines at a corner occurs.

Abstract: A device for storing photons between one and a plurality of reflected surfaces, and the storage of information, in particular in the form of digital data, being provided by creating at least one circulating memory using the storage device as a delay line. Each device consists of one or a plurality of photon sources, using any wavelength of light, one or a plurality of photon detectors and one or a plurality of reflective surfaces. The injected photons are delayed from reaching the output by one or a plurality of reflections from one surface of the device to the same or another surface of the device, each reflection extending the distance traveled for each photon, thereby inducing a delay.

Abstract: A system provides a signal to an actuator within an optical pickup unit of an optical disk drive. In one implementation, SUM signal data (an output from the quad sensors typically present in the optical pickup unit) is recorded within a SUM table. An error term generator processes the SUM signal data from the SUM table to produce an error term. An actuator control signal generator generates a signal to control movement of the actuator, wherein the signal is a function of a prior actuator position, the error term and an adaptation coefficient, wherein the adaptation coefficient impacts a rate at which the error term is allowed to modify the prior actuator position.

Abstract: An optical scanning device (1) for scanning an information layer (2) includes a radiation source (6) for supplying a radiation beam (14), a lens system (7) having an optical axis (OO?), and a detection system 8) including: (i) an astigmatism generating element (9) for generating a first amount of astigmatism (W1) represented by a vector (Wo,1, ?1), so as to transform the radiation beam to a first astigmatic radiation beam (29); (ii) an astigmatism correcting element (27) for generating a second amount of astigmatism (W2) represented by a vector (Wo,2, ?2), so as to transform the first astigmatic radiation beam to a second astigmatic radiation beam (30) having a third amount of astigmatism (W3) represented by a vector (Wo,3, ?3), and (iii) a detector (28) for transforming the second astigmatic radiation beam to an electrical signal. According to the invention, W3 is adapted to the detector and that Wo,2 and ?2 comply substantially with the following equation: (Wo,1, 2?1)+(Wo,2, 2?2)=(Wo,3, 2?3).

Abstract: A CD-ROM has an obscurable section wherein exists a photosensitive mask material layer or constituent operative to alter the optical properties of areas subjected to prolonged exposure to the CD-ROM read laser radiation. Digital information stored on a CD-ROM is made accessible by use of a password, which is generated from user machine unique information, and which is written on the CD-ROM via selective exposure of the CD-ROM to the radiation used to read the CD-ROM.

Abstract: An optical pickup apparatus comprises a semiconductor laser output controller for emitting laser beam, a photodetector for detecting the emitted laser beam, a sampling processor for performing a sampling process, an averaging processor for performing an averaging process, a pulse current generator for generating erase current pulses, write current pulses, and read current pulses, and a controller 200 for controlling the above components. The apparatus adds averaged values and sampled values and controls the semiconductor laser output controller based on the result of the addition and on the current pulses.

Abstract: An objective lens driving apparatus for an optical pickup includes a blade on which an objective lens can be mounted, a plurality of elastic support members supporting the blade and capable of elastically moving with respect to the blade, and a servo mechanism driving the blade up and down, left and right, and in a rotational direction. The elastic support members are grouped into pairs arranged to face each other with respect to a center of rotation of the blade, and distances between the elastic support members in the respective pairs are substantially identical. By lessening the difference in the amount of deformation between the elastic support members supporting the blade during tilt control, the elastic support members are less likely to move in undesired directions when vibration is applied.

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 imaging system (10) has a fixed lens combination (22), a spatial light modulator (SLM) (20) and a linear detector array (12). A scene image is scanned across a simple array (12) in a direction perpendicular to the array (12) by the SLM (20). This is achieved by displaying a diffraction pattern on the SLM that changes to achieve the scanning. The diffraction pattern displayed typically has a linear element (40) and a quadratic element (42). By having a programmably changed combined chirp pattern (36) displayed on the SLM, and by being able to change it thousands of times a second, an army with fast read out can take the place of a 2-D imaging array.

Abstract: It is an object of the present invention to adjust the focus position of an optical pickup. A brightness measuring apparatus having a half mirror and an objective lens focusing on the half mirror is disposed at a position facing an optical pickup PUi, in a manner such that the objective lens OB of the optical pickup PUi faces the half mirror. Then, the optical pickup PUi is operated to start a focus servo, while the position of multi-lens provided in the optical pickup PUi is changed continuously, thereby measuring a highest brightness of a spot light image incident on the half mirror through the objective lens, by virtue of the brightness measuring apparatus. Subsequently, a highest brightness change caused by changing the position of the multi-lens ML is inspected so as to fix the multi-lens ML at a position when the maximum highest brightness has been obtained, thereby effecting an optimum focus position adjustment for an optical pickup.

Abstract: The optical pickup of this invention includes a diffraction grating for dividing a light beam emitted from a semiconductor laser into a main beam, a precedent sub beam and a subsequent sub beam; a hologram element for dividing reflected light beams of the main beam, the precedent sub beam and the subsequent sub beam from an optical recording medium respectively into first through eighth main beams, first through eighth precedent sub beams and first through eighth subsequent sub beams; a main beam detector for receiving the first through eighth main beams; a precedent sub beam detector for receiving the first through eighth precedent sub beams; and a subsequent sub beam detector for receiving the first through eighth subsequent sub beams.

Abstract: An aberration detection device which can detect a spherical aberration sensitively by separating a light beam appropriately so as to enlarge a difference in the positions where the respective separated light beams have the minimum spot diameters, and thus to enlarge a deviation amount of the focus positions of the separated light beams, is provided. A hologram for separating a light beam reflected from an optical disk and passing through a dual element objective lens into a first light beam and a second light beam, and a detection device for receiving the first and the second light beams and detecting the deviation of focus positions of the first and the second light beams, are equipped.

Abstract: The object of the invention is to accurately detect the amount of tilt in the light reflector to the optical axis of an output light with a simple configuration. A tilt sensing apparatus includes a light reflector, a light source, a condensing unit for condensing an output light from the light source onto the light reflector, and a light sensing unit for sensing the reflected light from the light reflector. An optical device provided in the condensing unit for varying the light quantity of the transmitting light has first and second optical device strips that are formed at the positions of axial symmetry about the optical axis and have a predetermined shift in the direction of a straight line of connecting the axis of the light reflector to the condensed position where the light emitted from the light source is condensed onto the light reflector by the condensing unit.

Abstract: An optical pickup comprising: a diffraction grating, a beam splitter and laser beam guiding optical components that change direction of laser beams, which are placed on a light path constituted by a semiconductor laser that emits dual wavelength laser beams and an information recording surface of an optical disk, wherein a wavelength plate is provided on a light path between said diffraction grating and said semiconductor laser so that a laser beam irradiated on the recording surface of said optical disk becomes an elliptically polarized (including circularly polarized) beam or a beam having a polarizing plane that produces an angle of 30–60 degrees relative to a radius direction.

Abstract: A disk apparatus performs optical recording onto an optical disk with a record mark by using a light beam modulated in a manner of multi-pulse series, includes. A detection pulse generating part generates a detection pulse to replace the multi-pulse series; and a detection power control part controls the power of the detection pulse to be smaller than the power of the multi-pulse series.

Abstract: A system and method for using a photodiode to self-test an optical drive is disclosed. An optical drive includes a light source that emits a light for interacting with optical media. A photodiode placed adjacent the light source detects a portion of the light, such that the photodiode generates an electrical signal proportional to the light that is detected. A circuit is electrically coupled to the photodiode. The circuit receives the electrical signal and, based on the electrical signal, the circuit tests the operability of the optical drive.

Abstract: An optical recording/reproducing apparatus is intended for a recording medium having at least two information recording layers. The apparatus has at least two lenses, a first lens and a second lens, for condensing a light beam to irradiate an information recording layer. The at least two lenses are designed such that a light beam condensed by these lenses upon an information recording layer closest to these lenses has a minimum spherical aberration.

Abstract: An optical position measuring system including a periodic grating structure and a scanning unit. The scanning unit includes a light source that directs light towards the periodic grating structure and an optical lens device that receives light from the periodic grating structure and creates an image of the periodic grating structure in an image plane, the optical lens device having a periodic lens array with a grating period, AG(r) or the mutual distance between adjoining lenses of said lens array defined by the equation: A G ? ( r ) = ? ? ? ( r ) ? * [ t ? ( r ) * [ k + i + n ] + ? ] ( ? ? ? ( r ) ? + 1 ) wherein AG(r) is the grating per t(r) the period of the periodic grating structure, |?(r)| the absolute amount of the image magnification factor ? of the lens array ? a presettable defined phase shift r the radius of the grating arrangement, wherein in the case of a linear grating r=? and AG,t and |?| are constants, i, k, n ? N, i.e.

Abstract: A DVD laser emits a first light beam, and a CD laser emits a second light beam. An optical diffraction element diffracts first and second reflected lights corresponding to the first and second light beams, respectively. An optical detection element detects the first and second reflected lights reflected from a polarizing beam splitter. The optical axes of the CD and DVD lasers are set to diverge from each other. Thus, reflected light components necessary for focusing and tracking of a CD and a DVD are all detected by a detection element.

Abstract: In an optical pickup device provided with an optical system for guiding and focusing three-beam laser light along a predetermined route onto a recording surface of an optical disk and guiding a reflected light from the recording surface along the same route, a transparent plate, whereof a normal line is inclined by 45° with respect to an optical axis of the reflected light and is fixed in the direction in which the component of the normal line which is vertical to the optical axis is fixed to a direction of being rotated from a horizontal direction by 45° about the optical axis, is provided on the route of the reflected light between a beam splitter and an optical sensor.

Abstract: A focus error signal which is a differential signal indicative of a difference between a sum of amounts of reflected light detected by photodetector elements A and C of a four-split photodetector, and that of amounts of reflected light detected by photodetector elements B and D is measured. The level of the focus error signal at a timing when the amount of reflected light from the optical disc and detected by the four-split photodetector is at the maximum is set as a reference level. The gains of amplifiers 23 and 24 are individually adjusted so that the maximum and minimum values of the focus error signal are substantially symmetrical about the reference level. According to the configuration, the focus control can be performed by using the balance-adjusted focus error signal, and therefore can be stably conducted.

Abstract: A signal processing apparatus includes a lens, an image sensing device placed on an imaging plane of the lens, and a limb darkening correction section which corrects limb darkening only in the horizontal direction of the image sensing device with respect to a video signal of an object sensed by the image sensing device.

Abstract: A light beam reflected by an information medium is split by a diffraction optical system into first diffraction light and second diffraction light, which is not a complex conjugate wave of the first diffraction light, in a predetermined energy distribution ratio. The first diffraction light enters a first photodetector (195) of a photodetector and is used for reading out data information recorded on the information medium, while the second diffraction light enters second and third photodetectors (194, 195) and is used for obtaining a servo error signal. With this optical head device, the area of the first photodetector can be reduced, thus allowing a high-speed reproduction of a data signal. Further, the first photodetector becomes less susceptible to stray light. Moreover, the number of head amplifiers, which are needed for detecting the data signal, decreases, and the S/N ratio improves.

Abstract: A method of erasable/rewritable optical data storage is provided in which a laser beam from a laser (10) operated in either a pulsed or continuous wave mode is focussed by an optical system (11-18) onto a photorefractive polymeric material (32) to cause two photon excitation of the material to record data which may subsequently be erased by illuminating the material with radiation having a wavelength in the ultraviolet or visible spectrum to erase the recorded data. New photorefractive polymeric materials having a relatively narrow absorption band for use in the method are also disclosed.

Abstract: An image capture device is provided, a portion of which is insertable into an expansion slot of a handheld PC or PDA device, which is configured like a camera familiar to the user. In one embodiment, the image capture device includes a lens unit that is rotatable over about 180 ° degrees. The image capture device additionally includes an optical viewfinder rotatable with the lens unit. The image capture device advantageously includes an indicator visible from either side of the image capture device regardless of the lens position.

Abstract: A radiation detector array for radial tracking error detection and focus error detection, including a first plurality of spot detectors (100, 102, 104) for conducting multiple-spot radial tracking error detection, said first plurality of spot detectors including a first spot detector (100) arranged substantially centrally thereof. The array further includes a second spot detector (106) for conducting spot-size focus error detection in combination with said first spot detector.

Abstract: A data recording apparatus includes a laser diode applying light to a recording medium to record data, a front monitor diode detecting the intensity of light emitted from the laser diode, a switch device for switching to the lowpass filter in the operating state during the time period over which a signal of 14T mark is recorded, a lowpass filter for receiving a signal which is outputted from a front monitor diode, and a sampling/holding unit sampling the output signal which is outputted from the lowpass filter. The intensity of light emitted from the laser diode on the output signal sampled by the sampling/holding unit.

Abstract: The focal point detection method detects focal point dislocation of a coupling objective lens in accordance with a light beam passing a 60% to 80% region of a light beam effective diameter, which is centered with respect to an optical axis OZ of a light beam passing through the coupling objective lens, and which is regulated by a numerical aperture of the coupling objective lens. In this manner, focal point dislocation of a converging optical system can be performed without an offset, thereby accurately forming a focal point of the converging optical system on an information recording layer of an optical recording medium.

Abstract: Device for the reading-out and/or testing of matrices or optical storage media (2) that have been set in rotation, with an opto-electronic scanning system (1), an electronic control device (18) for the opto-electronic scanning system (1), an amplifier device (7) for the amplification of the HF signals originating in the opto-electronic scanning system (1), a decoder device (10) for the decoding of amplified HF signals, and an optionally present signal-processing device (11) for the processing of amplified HF signals for a measurement and evaluation device (19), at least the amplifier device (7) that is able to be releasably connected to the opto-electronic scanning system (1) and the decoder device (10) being configured as separate modules (6, 9) which are preferably able to be releasably connected to each other via plug connectors (17′b) and/or connection lines (25).

Abstract: A multi-layer imaging medium has a layer that absorbs radiation at a wavelength used by an optical auto-focus system. Spurious reflections are suppressed. The layer transmits radiation at a wavelength used to image the medium. The layer may function as a support layer for the medium. Thermal imaging media may be made according to the invention.

Abstract: A light intensity control apparatus for use in an information recording and reading system includes a light source driving device for driving a light source so as to generate a light having the first and higher second light intensity levels. A light intensity detection device is provided and includes a first light intensity detection member for detecting a prescribed intensity level of the light when a light modulation speed is relatively low, and a second light intensity detection member for detecting an average of the intensity of the light when it is relatively high. A detection member selection device is provided so as to select one of the first and second light intensity detection members depending upon a selection instruction so as to use one of the detection outputs. A reference level selection device is provided so as to select one of the first and the second reference levels to be compared with the one of the detection results depending upon the selection instruction.

Abstract: An optical scanning device scans a surface (23) provided with marks with a focused radiation beam (35) along a scan line. The device has a radiation-sensitive detection system (39) comprises a plurality of detectors. An electronic circuit (41) determines the time differences between corresponding parts of the detector signals relating to passage of the radiation beam over one of the marks. The time differences are used to form a signal representing a primary wavefront aberration of the radiation beam.

Abstract: A disk apparatus performs optical recording onto an optical disk with a record mark by using a light beam modulated in a manner of multi-pulse series, includes. A detection pulse generating part generates a detection pulse to replace the multi-pulse series; and a detection power control part controls the power of the detection pulse to be smaller than the power of the multi-pulse series.

Abstract: A focusing controller executes an appropriate focus jump even in a multilayer disk having layers of characteristics greatly different from each other. The focusing controller has an optical pickup including an objective lens for converging the light beam and a detector for receiving reflected light from the multilayer recording medium; an error signal generator for generating a focus error signal of the irradiated light beam from a detecting signal of the detector; an actuator for operating the objective lens; and a controller for controlling a focusing position of the light beam by operating the actuator based on the focus error signal. The controller calculates intensities of the reflected lights of two layers based on the detecting signal of the detector, and thus controls the timings of acceleration and deceleration signals of a focus jump between these two layers.

Abstract: An optical pick-up device includes a semi-conductor laser as a laser light-emitting device, a collimator lens, a directional control mirror, an objective lens, a light amount detecting device, a reflecting mirror that reflects leakage light of the laser light onto the light amount detecting device, and a light amount adjusting member that adjusts the amount of light incident on the light amount detecting device, provided between the light amount detecting device and the reflecting mirror. The light amount adjusting member may include a rotatably or slidably-supported baffle of which a rotational angle or slide position is changed so as to adjust the amount of the light.

Abstract: A focus error detecting device for an optical pickup having an aberration correcting lens group includes a diffraction optical element having an outer diameter which is smaller than a diameter of the light beam after aberration correction, and selectively diffracting light passing through an annular portion with an optical axis as a center in a plane perpendicular to the optical axis of the light beam; and a photodetector which detects the light diffracted by the diffraction optical element. The annular portion includes a portion in which residual ray aberration after aberration correction by the lens group is the smallest.

Abstract: A focusing control apparatus includes method for an optical pickup having an objective lens and an aberration correcting unit includes the steps of detecting an amount of focus error of a light beam and an amount of aberration of the reflected light beam to generate a focus error value and an aberration value; controlling a focused position of the objective lens on the basis of the focus error value while adjusting an amount of aberration correction of the aberration correcting unit on the basis of the aberration value, and performing a focus jump from one recording layer to another recording layer after adjusting the amount of aberration correction of the aberration correcting unit for the another recording layer.

Abstract: An aberration detecting method of the present invention is arranged such that a light beam, having passed through an optical convergence system provided in an optical pickup device, illuminates a flat section of an optical disk, and using the light beam which has been reflected, and the aberration occurring in the two-element objective lens is detected.

Abstract: A monolithic optical pickup has all passive optical elements aligned during fabrication, thereby requiring no alignment during the assembly of a system utilizing it. Its supporting structure is the monolithic passive device itself. A single surface incorporates all the functions of an optical pickup system including a focusing element, image creation apertures and stops, scattering/reflection reduction, and return path apertures and optics. The elements are formed from a metalized layer which is applied lithographically. Placing the apertures and stops on the principal plane of the focussing element allows for the image size to be precisely controlled by the image distance. The monolithic optical pickup is well suited for use with multiple detector elements. Alternate embodiments of the invention may omit some of the optical system elements.

Abstract: A light intensity control apparatus for use in an information recording and reading system includes a light source driving device for driving a light source so as to generate a light having the first and higher second light intensity levels. A light intensity detection device is provided and includes a first light intensity detection member for detecting a prescribed intensity level of the light when a light modulation speed is relatively low, and a second light intensity detection member for detecting an average of the intensity of the light when it is relatively high. A detection member selection device is provided so as to select one of the first and second light intensity detection members depending upon a selection instruction so as to use one of the detection outputs. A reference level selection device is provided so as to select one of the first and the second reference levels to be compared with the one of the detection results depending upon the selection instruction.