JP2732633B2 - Optical information processing device - Google Patents

Description

The present invention relates to an optical information processing apparatus, and more particularly, to recording, reproducing, or erasing information using a plurality of light beams. The present invention relates to an optical information processing apparatus including a multi-beam optical head formed simultaneously.

(Prior Art) In recent years, an optical information processing device such as an optical disk device capable of recording image information of a document or the like, retrieving the image information as necessary, and reproducing as a hard copy or a soft copy has been developed. . In an optical disk device, a condensing light beam is irradiated onto a disk-shaped recording medium, that is, an optical disk to record or reproduce information. That is, at the time of recording, the irradiation of the light beam causes a change in the state of the recording medium on the recording surface, and as a result, information is recorded on the optical disk as, for example, pits. At the time of reproduction, a steady light beam is irradiated onto the information recording medium, and the light beam is intensity-modulated by pits according to the recorded information. Information is reproduced by processing the modulated light beam intensity. During recording and reproduction, the optical disk is rotated at a constant linear velocity and linearly moved in the radial direction on the optical disk to direct the light beam to the optical disk.

As these optical disk devices, recently, an optical information processing device including a multi-beam optical head for simultaneously recording and reproducing information using a plurality of light beams has been developed. FIG. 5 shows an example of a conventional multi-beam optical head.

As shown in FIG. 5, a recording light beam L1 and a reproducing light beam L2 are emitted from regions provided adjacent to each other on the semiconductor laser array 1. The recording and reproducing light beams L1 and L2 are superimposed on each other and transmitted through the beam splitter 2. The light beam transmitted through the beam splitter 2 is condensed again via the reflecting prism 3 and the objective lens 4 and condensed on the recording film surface 5A of the optical disk 5. At this time, each light beam focused on the recording surface 5A
L1 and L2 are set such that their focal points are preferably adjacent to each other and focused on the same track. Thus, adjacent recording and reproducing beam spots are formed on a predetermined track on the recording film surface. The optical disc is rotated at a constant linear velocity with the recording and reproducing beam spots formed in this way, whereby a predetermined recording area is irradiated with the recording light beam, and immediately thereafter, the reproducing light beam is irradiated. Irradiated by In this way, the reproducing operation is performed immediately after the recording operation. The light beam L1 irradiated on the recording film surface 5A,
L2 is reflected and returned to the beam splitter 2 again via the objective lens 4 and the reflecting prism 3. The recording and reproducing light beams L1 and L2 returned to the beam splitter 2 are reflected by the joint surface and enter the beam splitter 6.
Part of the incident light beams L1 and L2 are transmitted, and are respectively incident on a predetermined recording area, that is, on a tracking control photodetector for irradiating the predetermined track with the light beam. Further, the remaining light beams L1 and L2 are reflected on the joint surface and transmitted through the convex lens 12 provided on the exit surface. The light beam transmitted through the convex lens 12 is split into a recording light beam and a reproduction light beam, re-imaged, and made incident on the spatial filter 8. The light beam corresponding to one recording signal among the light beams incident on the spatial filter 8 is reflected there and condensed on the photodetector 9. The other reproduction light beam passes through a pinhole 8A that is transmitted through a pinhole 8A provided in a spatial filter according to the beam cross-section in order to control the focus of the objective lens 4 and obtain an information reproduction signal. The information reproduction signal and the focus control signal are detected by detecting the passed reproduction light beam.

As another method, an optical information processing apparatus including a multi-beam optical head that emits two light beams having different wavelengths as a reproduction light beam and a recording light beam is known. In this method, two light beams L1 and L2 having different wavelengths for reproduction and recording emitted from each light source are used.
Are approximately synthesized by a dichroic mirror or the like for synthesis, and focused by an objective lens toward a predetermined area on the optical disk. Preferably, each of the light beams L1 and L2 to be condensed is set so that the light converging points are adjacent to each other and converged on the same track. As a result, minute beam spots for recording and reproduction are formed adjacent to each other on a predetermined track on the recording film surface. After the recording operation, the reproducing operation is immediately performed by the irradiated beam spot in the same manner as in the apparatus shown in FIG. The light beam condensed on the track of the optical disk is reflected and made incident on the dichroic mirror. The light beam that has been incident on the dichroic mirror and substantially synthesized is separated for each wavelength, that is, a recording light beam and a reproduction light beam. The separated light beam is used for an information reproduction signal and a focus control signal.

(Problems to be Solved by the Invention) In a method of separating a reproduction light beam and a recording light beam by a pinhole, a light beam irradiated on a photodetector through the pinhole is used for information reproduction and focus control. It is used for Therefore, the position of the pinhole must be set accurately and with high precision when focused and out of focus. Further, since an optical system for re-imaging after passing through the pinhole is required, it is difficult to reduce the size of the entire optical head. Furthermore, since crosstalk occurs between the recording light beam and the reproducing light beam, accurate detection of the reproducing signal and the focus control signal becomes impossible.

On the other hand, in a multi-beam optical head that uses two light beams having different wavelengths as light beams for recording and reproduction, it is difficult to manufacture a laser diode as a light source on the same chip. So two L.
When installing D chips, a high degree of mounting accuracy is required adjacent to each other. Furthermore, since light beams having different wavelengths are used, it is necessary to correct for chromatic aberration of a lens caused by a difference in dispersive power of an optical system.

The present invention relates to an optical information recording and processing apparatus including a multi-beam optical head that stably detects a reproduction light beam from a recording and reproduction light beam reflected by a recording medium and performs information reproduction and focus control. The purpose is to provide.

[Constitution of the Invention] (Means for Solving the Problems) The present invention has been made based on the above-mentioned problems, and has a light source that selectively emits first and second light beams, and a light source that is arranged along an optical axis. Movable in the focused state, the first and second light beams of the light source are separated by a predetermined distance d1, and the first and second beams respectively focused on the minimum beam spot A light condensing means for condensing light on a recording medium as a spot; and a first and second reflected light beams, each of which is reflected by the first and second light beams on the recording medium, to the second light beam. Separating means for spatially separating and converging the first reflected light beam from the reflected light beam, and detecting the first reflected light beam separated by the separating means to generate a detection signal. And the light collecting means When in the focus state, the beam spot of the second reflected light beam is formed at a distance indicated by d3 with respect to the focal position where the beam spot of the first reflected light beam is formed at a magnification of m times. When detecting, the detecting means provided with an outer edge portion at a distance of d2 from the second reflected light beam, and the position of the light collecting means in the optical axis direction corresponding to the detection signal from the detecting means And a responding unit that moves along the recording medium and associates the recording medium with the recording medium, wherein the detecting unit has a light receiving surface having a size that satisfies the expressions represented by d3 <d2 and d2 <md1. An optical information processing device is provided.

(Operation) As described above, the optical information processing apparatus of the present invention has the first
And when the focusing means is in the focused state, the second reflected light beam is placed at a distance indicated by d3 with respect to the focal position where the beam spot of the first reflected light beam is formed. When the beam spot of the beam is formed at a magnification of m times, the beam can be detected by the detecting means provided with the outer edge at a distance of d2 from the second reflected light beam.
It is possible to prevent a component resulting from crosstalk due to the second light beam from being mixed into an output signal obtained by photoelectrically converting the first light beam by the detection means.

(Embodiment) FIG. 1 is a front view of a multi-beam optical head 100 provided in an optical information processing apparatus according to an embodiment of the present invention.

In FIG. 1, an optical disk (recording medium) 16 is formed by coating a disc substrate such as glass or plastic with a metal film such as tellurium or bismuth as an information recording film. Tracks 16A defining a tracking guide area are formed concentrically on the substrate of the optical disc. A multi-beam optical head 100 is provided so as to face the optical disc 1, and the optical disc 16 is driven to rotate at a constant linear velocity with respect to the multi-beam optical head 100 during recording, reproduction and erasing. In FIG. 1, a track 16A defining a recording area extends in the Z direction.

In the multi-beam optical head 100, a light source member 10 as a light source is provided. In the light source member 10, a laser diode array 10A that emits two light beams for recording and reproduction is arranged. The emission ports of the laser diode array 10A are oriented in substantially the same direction, and are set apart from each other in the Z direction on the same chip.From the emission ports, for example, a reproduction light beam Lr and a recording light beam Lw having the same wavelength are emitted. Is emitted. The light beams Lr and Lw emitted from the laser diode array 10A are superposed on each other and radiated onto the same collimator lens 12 while gradually diverging. The light beams Lr and Lw that have entered the collimator lens 12 are substantially superimposed on each other, converted into a parallel combined light beam, and converted into a beam splitter 18.
Is incident on. The combined light beam that has entered the beam splitter 18 is transmitted and radiated to the objective lens 14. When the light beam applied to the objective lens 14 passes through the objective lens 14 and is condensed, the light beam is again separated into the recording light beam Lw and the reproduction light beam Lr, and is recorded on the recording area of the optical disc 16, that is, on the track. Is collected. Preferably, the respective focal points of the recording and reproducing light beams Lw and Lr are irradiated on the same track, preferably adjacent to each other. Thus, adjacent recording and reproducing beam spots are simultaneously formed on a predetermined track. The optical disc is rotated at a constant linear velocity while the recording and reproducing beam spots are simultaneously formed. In accordance with the rotation of the optical disk, a predetermined recording area on the optical disk is first irradiated with, for example, a recording light beam Lw to record information. The area on the track where the information is recorded is moved in accordance with the rotation of the optical disk, and immediately thereafter, is irradiated with the reproducing light beam Lr. Information is reproduced by detecting reflected light of the light beam Lr applied to the recording area. When an information reproduction signal is obtained, the reproduction light beam must be maintained in a focused state and a focused track state with respect to a desired recording area. More specifically, the objective lens 14 is movably supported in its optical axis direction and in an in-plane direction orthogonal to the optical axis. When the objective lens 14 is located at the optimum position on the optical axis, that is, at the focus position, the beam waist of the converging laser beam emitted from the objective lens 14 is projected on the surface of the recording film of the optical disc 16. Thereby, the minimum beam spot is formed on the surface of the recording film of the optical disc 16. On the other hand, when the objective lens 14 is arranged at an optimum position in a plane perpendicular to the optical axis (in a plane parallel to the recording film surface), that is, at a combined track position, a beam spot formed on the optical disc 16 is defined as a recording area. Formed precisely on the track so that the track is tracked by the laser beam. These two states (focused state
The information can be reproduced by keeping the in-focus track state). That is, the intensity-modulated recording light beam Lw
A state change of pits or the like is caused in the recording film to record information, and the light beam is intensity-modulated by irradiating a laser beam Lr of a constant intensity to a recording area formed by pits or the like in the track. The information is reproduced by detecting a change in the intensity of the reflected light beam Lr.

The divergent recording and reproducing light beams Lr and Lw reflected by the recording film of the optical disk 16 are combined with each other and are incident on the objective lens. The combined light beam incident on the objective lens 14 is converted into a parallel light beam at the time of focusing, and is returned to the beam splitter 18 again. The light beam that has entered the beam splitter has its junction surface, ie, the beam split surface.
The reflected light at 18A is transmitted through a plano-convex lens 25 for condensing the combined light beam. The beam of the combined light beam transmitted through the plano-convex lens 25, that is, the light beam including the reproduction light beam Lr and the recording light beam Lw is gradually focused,
At the same time, the central axes lr, lw of the light beams Lr, Lw gradually diverge from each other. This combined light beam is applied to a plano-convex lens 25
And is incident on a beam splitter 27 integrally attached to the exit surface. The combined light beam incident on the beam splitter 27 is split into light beams LA and LB having substantially the same light intensity at the joint surface.

The light beam LA reflected from the bonding surface is used to obtain a focus control signal. The transmitted light beam is used to obtain a tracking control signal and an information reproduction signal.

The light beam reflected by the beam splitter 27 will be described in further detail.The reproducing light beam Lr and the recording light beam Lw included in the light beam LA reflected by the joint surface of the beam splitter 27 gradually include the beam. At the same time as the cross section is reduced, their central axes lr, lw expand with each other. Thus, the combined light beam LA is gradually separated into individual reproduction light beams Lr and recording light beams Lw as the constituent light beams Lr and Lw are focused. A knife edge 29 is disposed on an optical path approximately half of the center axis lr of the reproduction light beam Lr as a boundary, thereby blocking approximately half the optical path of the light beam. Therefore, only the reproducing light beam Lr that is not shielded by the knife edge 29 is gradually focused and condensed on the photodetector 20 disposed on the optical path. At this time, the photodetector 20 is set in advance so that the beam spot of the light beam irradiated on the detection area is minimized at the time of focusing, and at the same time, the size thereof is a surface including the detector surface. Are set in accordance with the distance between the central axis of the reproducing light beam Lr and the central axis of the recording light beam Lw. The light beam irradiated on the photodetector 20 is converted into an electric signal in each of the light detection areas and processed by a predetermined method. That is, a focusing error signal, that is, a signal corresponding to the amount of defocus is generated by detecting a change in the position of the beam spot irradiated on the photodetector 20, and the voice coil motor 50 is driven in accordance with the tracking error signal. An electric current is supplied to drive the objective lens 14 in the direction of its optical axis, so that the light beam is kept in focus. Note that the other recording light beam Lw is, for example, a photodetector 20 in a state where a part thereof is shielded by a knife edge 29.
Transmitted without being irradiated on the top.

On the other hand, the combined light beam transmitted through the beam splitter 27
To explain LB in detail, the transmitted synthetic light beam
As with the reflected light beam LA, the center axes lr and lw of the LB expand with each other as the beam cross sections of the reproducing light beam Lr and the recording light beam Lw gradually become smaller. Therefore, the combined light beam LA becomes individual reproduction light beam Lr and recording light beam Lw as the constituent light beams Lr and Lw are respectively focused.
Is gradually separated. A light detector 45 for detecting a tracking guide signal for maintaining the light beam on a predetermined track on the optical disk and an information reproduction signal is provided on the optical path of the separated light beam for reproduction. The photodetector 45 is set in advance so that the detection area is irradiated with a circular beam spot having a predetermined area, and at the same time, the size of the detection area is determined by the reproduction on the surface including the detector surface. The distance is set according to the distance between the central axis lr of the recording light beam Lr and the central axis lw of the recording light beam Lw. In other words, the photodetector 45 is set so that its size is within a range where only the reproduction light beam is irradiated, that is, within a range where the recording light beam is not irradiated, and at the same time, its position in the optical axis direction is It is set within a range where accurate tracking control is possible using the beam spot of the reproduction light beam irradiated on the photodetector.

The light beam converted to an electric signal by the tracking photodetector 45 is processed by a predetermined method, and a driving circuit 44 generates a tracking error signal. An electric current is supplied to the voice coil motor 50 in response to the generated tracking error signal, and the objective lens 14 is moved in a plane perpendicular to the optical axis, whereby a predetermined track is tracked by the light beam. Furthermore, the signals detected in all the detection areas on the photodetector 45 are added by the signal processing circuit 43 and used as an information reproduction signal.

The other separated recording light beam Lw passes through the focused photodetector 45 without being irradiated.

FIGS. 2 and 3 show the structures of the photodetector 20 for focus control and the photodetector 45 for tracking control provided in the multi-beam optical head of the optical information processing apparatus of the present invention.

2A to 2C show changes in the beam spot shape on the photodetector 20 during focusing and when not focused.

The focus control photodetector 20 is disposed on the optical path of the reproduction light beam Lr of the light beam LA reflected by the beam splitter 27, and serves as a vertical (X-direction) dividing line as a light non-detection area. It comprises two light detection areas 20A and 20B formed on both sides of the light detection area 22. When the objective lens 14 is in focus with respect to the optical disc 16, the minimum beam spot Sr is irradiated on the light non-detection area 22 of the photodetector.
In other words, assuming that the output of the light detection area 20A is the output of 20B, the position of the dividing line 22 as the non-detection area is the focusing error signal (FE signal) at the time of focusing.
Is equal to zero, ie, FE = ｛− ｛=
It is set to a position that satisfies the condition of 0.

On the other hand, for example, when the objective lens 14 moves away from the in-focus position with respect to the optical disc, the light beam reflected by the optical disc is focused slightly more than at the time of focusing. Therefore, the focal point of the light beam Lr that is partially irradiated by the knife edge 29 and irradiated onto the photodetector is moved forward of the detector. Therefore, a beam spot as shown in FIG. 2C is formed on the photodetector 20. That is, the light detection area 20B
On the upper side, the linear portion is in contact with the non-detection region 22, and a half-moon-shaped beam spot having a diameter larger than that at the time of focusing is formed. At this time, the focusing error signal is FE = ｛−｝ <0.

Conversely, when the objective lens 14 is closer to the optical disc than the in-focus position, the light beam reflected by the optical disc is diverged slightly more than at the time of focusing. Therefore knife edge
The condensing point of the light beam Lr, which is partially illuminated at 29 and illuminates the photodetector, is moved rearward of the detector. Therefore, a beam spot as shown in FIG. 2A is formed on the photodetector 20. That is, on the light detection area 20A, the linear portion contacts the non-detection area 22, and a half-moon-shaped beam spot having a diameter larger than that at the time of focusing is formed. At this time, the focusing error signal FE = Ｅ − ｛> 0.

The size of the photodetector thus configured is set based on the conditions described below. That is, the reproduction light beam Lr and the recording light beam formed on the same track
The interval between each beam spot of Lw is d1, the focal length of the objective lens 14 for irradiating the optical beam on the optical disk is f _O
When the focal length of the between f _D, on the detection area and the same plane of the optical detector 20, the interval d3 of the focal point of the recording light beam Lw and the converging point of the reproducing light beam Lr is, d3 = (F _D / f _O ) × d 1 = md 1. (Note that m indicates the magnification of the optical system.) Therefore, in order to irradiate only the reproduction signal onto the photodetector on the photodetector, the end extending in the vertical direction of the photodetector, that is, the recording light beam The following relationship must always be established between the distance d2 between the end of the photodetector on the side approaching the virtual focusing point and the focusing point of the reproduction light beam.

d3> d2 ... formula, from _{d2 <(f D / f O} ) × d1 = md1 ... a relationship of.

As shown in this equation, the distance between the end of the photodetector on the side approaching the virtual focal point and the virtual focal point of the recording light beam
d2 is roughly set to satisfy d2 <md1. By arranging a photodetector that satisfies these conditions, that is, d2 <md1, crosstalk between the recording light beam and the reproducing light beam is prevented, and efficient reading or reproducing of information is performed.

 The size of the photodetector will be described in more detail.

In the embodiment of the present invention, a knife edge method is used as a method for obtaining a focus control signal. The knife edge method can reduce the size of the beam spot formed on the photodetector at the time of focusing as compared with a focus control method such as the astigmatism method. It will be easier. That is, when focus control is performed by using the conventionally used astigmatism method, a beam spot having a beam diameter of 50 μm or more must be formed on the photodetector at the time of focusing. Accordingly, the central axes lr, lw of the recording and reproducing light beams are mutually shifted on a plane where the photodetector is to be arranged in order to avoid crosstalk.
must be separated by at least μm.

On the other hand, in the focus detection method such as the knife edge method used in the present invention, since the photodetector is arranged on the focal point of the lens 25, the beam of the light beam irradiated on the photodetector is used. The spot diameter is set to a minimum value determined by the numerical aperture NA and magnification m of the optical system to be used and the wavelength λ of the light source.

That is, when the numerical aperture of the lens system with respect to the recording medium side is NA ₀ , the beam spot diameter W1 on the recording medium
Is W1 ≒ λ / NA _O.

When the magnification of the lens system is m, the numerical aperture NA _D of the lens system relative to the optical detector side, the NA _D = NA _O / m.

At this time, the beam spot diameter W2 of the light beam irradiated on the photodetector is W2 = λ / NA _D = mλ / NA _O.

In practical optical systems, the numerical aperture N is generally
A: 0.4 to 0.6, λ: 600 to 900 nm, and m: 2 to 10. For example, when NA _O = 0.5, λ = 830 nm, and m = 7, the beam spot diameter W2 on the photodetector is W2 = Mλ / NA _O ≒ 10
μm.

When the photodetector is arranged at the image point of the light beam as described above, the size of the beam spot is formed very small. Therefore, the recording and reproducing light beams separated at minute intervals can be easily separated and detected.

On the other hand, FIGS. 3A to 3C show beam spots on the photodetector at the time of non-matching track and at the time of matching track. The tracking control photodetector 45 is disposed on the optical path of the reproduction light beam Lr of the light beam LB transmitted through the beam splitter, and serves as a horizontal (Y direction) dividing line 48 as a light non-detection area. And two light detection areas 45A and 45B provided on both sides of the light detection area. When the objective lens 14 is accurately formed on the track that defines the recording area of the optical disk, that is, in the combined track state, the light non-detection area 48 is formed on the photodetector 45 as shown in FIG. 3B. A substantially circular beam spot Sr having a predetermined beam diameter is formed at the center, and at the same time, a band-shaped shadow portion generated by diffraction at the track is formed around the non-detection region 48. In other words, assuming that the output of the light detection area 45A is the output of the light detection area 45B,
The position 8 is a position where the tracking error signal (T · E) becomes equal to zero at the time of tracking, that is, T · E
= ｛−｝ = 0.

On the other hand, for example, when the objective lens 14 moves away from the combined track position with respect to the optical disk, a circular beam spot is formed on the photodetector as shown in FIG. 3A or 3C. In other words, the band-shaped dark portion diffracted by the track appears asymmetrically with respect to the division line 48 as the non-detection region. At this time, the tracking error signal is T · E <
0 or T · E> 0.

The setting position of the photodetector 45 configured as described above is set based on the conditions described below. That is, to obtain the tracking control signal described above, the photodetector 45
Is set in the optical axis direction such that the beam spot diameter of the irradiated light beam is formed within a specific range. In other words, the photodetector 45 is a light beam for reproduction.
The size is set so that only Lr is irradiated.

More specifically, the position of the photodetector in the optical axis direction is set based on the conditions described below. That is, the interval between each beam spot of the reproduction light beam Lr and the recording light beam Lw formed on the same track is d1, the focal length of the objective lens for irradiating the optical beam on the optical disk is f _O , and the focal length of the lens 25 F _D , the detection surface of the photodetector 45 and the lens 25
The distance along the optical axis between the image point and Z of the distance Z is a negligibly small with respect to the focal length f _D, on the detection area and the same plane of the optical detector 20, the recording light beam
Distance d3 between Lw the focal point and the focal point of the reproducing light beam Lr _{is, d3 ≒ (f D / f} O) × d1 = md1 ... in expressed.

On the other hand, the beam diameter W which is formed on the detection area of the photodetector 45 at this time, when the diameter of the light beam incident on the lens 25 and phi, represented by _{W = Z / f D × φ} . In the formulas and formulas, d3> W must be satisfied in order to irradiate only the reproducing light beam onto the detection area of the photodetector 45. That is, when the above equation is substituted into the equation, the distance Z in the optical axis direction between the detection surface of the photodetector 45 and the image point of the lens 6 becomes Z <(f _D ) ² / f _O × ( d1 / φ)… must be installed within the range that satisfies. When substituting the relationship of φ = 2f _O · NA in the equation, the equation is generally rewritten as Z <(m ² d1) / (2 · NA). (Note that m is the magnification of the optical system with reference to the recording medium side, and NA is the numerical aperture of the objective lens.) When the photodetector 45 is set within the range described in the expression, it is used for reproduction and recording. The light beam is irradiated on the photodetector 45 in a separated state. Therefore, crosstalk between the reproducing and recording light beams Lr and Lw is prevented, and an accurate tracking control signal is detected. FIG. 4 shows a circuit for processing all signals detected by the focus control detector 20 and tracking control photodetector 45 configured as described above. As shown in FIG. 4, the signal detected by the tracking control photodetector is used as a servo signal for tracking control, while being used as a reproduction signal of information formed on an information recording medium. Is done.

In FIG. 4, the output of the light detection area 20A is an amplifier circuit 31A.
Supplied to The output of the light detection area 20B is supplied to the amplifier circuit 31B. Output signals from the amplifier circuits 31A and 31B are used to supply a focusing control signal to the voice coil. That is, the output of the amplifier circuit 31A is supplied to the inverting input terminal of the differential amplifier 41, and the output of the amplifier circuit 31B is supplied to the non-inverting input terminal of the differential amplifier 41. In the differential amplifier 41, the detection signal of the light detection area 20A and the light detection area 2
The result of addition of the 0B detection signal is compared, and an output according to the difference signal, that is, a focus control signal is supplied to the drive circuit 44. In response to the focus shift detection signal supplied to the drive circuit 44, current is fed back to a coil (not shown) that drives the objective lens 14 in the optical axis direction. The objective lens 14 is driven in the optical axis direction according to the fed back current, and the defocus is corrected.

On the other hand, the output of the light detection area 45A is supplied to the amplifier circuit 31C. The output of the light detection area 45B is supplied to the amplifier circuit 31D.
The output of the amplifier circuit 31C and the output of the amplifier circuit 31D are used to supply a tracking control signal to the voice coil. That is, the output of the amplifier circuit 31C is supplied to the inverting input terminal of the differential amplifier 42, and the output of the amplifier circuit 31D is supplied to the non-inverting input terminal of the differential amplifier 42. Differential amplifier 42
In the above, the detection output of the light detection area 45A and the light detection area 4
5B is compared with the detected output, and the output corresponding to the difference, that is,
The tracking shift detection signal is supplied to the drive circuit 44.
In response to a tracking control signal supplied to the drive circuit 44, a current (not shown) is fed back to a coil that drives the objective lens 14 in a plane perpendicular to the optical axis. Thereby, the objective lens 14 is driven in a direction perpendicular to the optical axis, and the tracking deviation is corrected.

Further, outputs of the amplifier circuits 31C to 31D, that is, all output signals of the photodetector 45 are processed by the signal processing circuit 43 and used for reproducing information.

In the above-described focus control photodetector according to one embodiment of the present invention, a detection method using a knife edge is described. However, other methods of focus detection may be used. When using other detection methods, the crosstalk between the two light beams is reduced by arranging the photodetector at the image point of the light beam and setting its size to a specific value.
A stable focus control signal can be obtained.

In the present invention, the two light beams emitted from the light source member 10 are set so that they are irradiated on the same track of the information recording medium, and the reproducing operation is performed immediately after the recording operation. However, for example, a light beam may be irradiated so as to record or reproduce information on two parallel tracks at the same time. Further, it may be used to continuously erase and record information.

Furthermore, in the present invention, the light beam Lr for reproduction is
, The photodetectors 20 and 45 are provided. However, in principle, a photodetector may be provided for another recording light beam Lw. Furthermore, the shape of the photodetector may be changed as long as a similar effect is obtained.

(Effect of the Invention) As described above, the optical information processing apparatus of the present invention
A light source that selectively emits first and second light beams;
The first and second light beams of the light source are movable at a predetermined distance d1 while being movable along the optical axis and in a focus state.
Focusing means for focusing on a recording medium as first and second beam spots which are separated only by a minimum beam spot, respectively, and first and second beam spots on the recording medium.
Separating means for spatially separating and converging the first and second reflected light beams from which the respective light beams are reflected from the second reflected light beam, and separating means for separating the first and second reflected light beams from each other. Detecting the first reflected light beam and generating a detection signal, wherein, when the focusing means is in a focus state, the focus position where the beam spot of the first reflected light beam is formed Detecting means provided with an outer edge at a distance of d2 from the second reflected light beam when a beam spot of the second reflected light beam is formed at a magnification of m times at a distance indicated by d3; Responding means for moving the position of the light condensing means along the optical axis direction in association with the detection signal from the detecting means and relating the light condensing means to the recording medium, wherein the detecting means is represented by d3 <d2, d2 <md1 Having a light-receiving surface that satisfies the formula Therefore, it is possible to prevent a component generated from crosstalk due to the second light beam from being mixed into an output signal obtained by photoelectrically converting the first light beam by the detection means.

Further, according to the optical information processing apparatus described above, it is possible to prevent a laser beam that is not necessary for focus control for a reproduction laser beam for reproducing information recorded on an optical disc from being mixed into a reproduction signal due to crosstalk. The cost is increased only by optimally setting the size of the photodetector that generates the focus error signal used for the focus control for information reproduction without adding a special device or signal processing circuit for the information. The noise component in the reproduction signal can be reduced without the need.

Further, the focus shift amount of the objective lens can be accurately detected, and the focus state of the objective lens is accurately controlled.

Therefore, by optimally setting the size of the outer edge of the photodetector, an information processing apparatus capable of performing stable information reproduction without increasing the component cost is provided.

[Brief description of the drawings]

FIG. 1 is a front view of a multi-beam optical head provided in an optical information processing apparatus according to one embodiment of the present invention, and FIGS. 2A to 2C.
FIG. 3 is a front view of a photodetector provided in the optical information processing apparatus of FIG. 1 showing a change of a beam spot in a focused state and a non-focused state of the light beam. FIGS. FIG. 4 is a front view of a photodetector provided in the optical information processing apparatus shown in FIG. 1 showing a change in a beam spot in a track state and a non-track state, and FIG. 4 is a photodetector described in FIGS. And FIG. 5 is a perspective view of a conventional optical information processing apparatus having a multi-beam optical head. 10… Light source member, 10A …… Laser diode array, 12
…… Collimator lens, 14… Objective lens, 16 …… Optical disk, 16A …… Track, 18 …… Beam splitter, 2
0: Focus control photodetector, 20A, 20B ... Light detection area, 2
2 ... Light non-detection area (dividing line), 25 ... Plano-convex lens, 27
…… Beam splitter, 29 …… Knife edge, 31A ~ 31D
…… Amplifier circuits, 41,42 …… Differential amplifiers, 43 …… Signal processing circuits, 44 …… Drive circuits, 45… Tracking photodetectors, 45A, 45B …… Light detection areas, 48… Light Non-detection area (dividing line), Lr: light beam for reproduction, Lw: beam for recording,
lr: central axis of the reproducing light beam, lw: central axis of the recording light beam.

Claims (1)

(57) [Claims] A light source for selectively emitting first and second light beams; said light source being movable along an optical axis, said first and second lights of said light source being in a focused state. The beams are separated by a predetermined distance d1 as first and second beam spots respectively focused on the minimum beam spot,
Condensing means for condensing light on a recording medium; and converting the first and second reflected light beams, each of which reflects the first and second light beams on the recording medium, into the second reflected light beam Separating means for spatially separating and converging the first reflected light beam from, and detecting the first reflected light beam separated by the separating means to generate a detection signal, When the focusing means is in a focus state, the first reflected light beam is focused on a focal position where a beam spot is formed.
When a beam spot of the second reflected light beam is formed at a magnification of m times at a distance indicated by d3, a detecting means provided with an outer edge at a distance of d2 from the second reflected light beam; Responding means for moving the position of the light condensing means along the optical axis direction in accordance with the detection signal from the detection means and relating the light condensing means to the recording medium, wherein the detection means comprises: d3 < An optical information processing device having a light receiving surface having a size that satisfies an expression represented by d2, d2 <md1.