JPH02227839A - Optical information processor - Google Patents

Abstract

PURPOSE:To reduce crosstalk between reproducing light beams and recording light beams by providing a detecting means, which is set so as to satisfy specific conditions. CONSTITUTION:The means, which detects third and fourth light beams separated by a pair of light refracting substances is set so as to satisfy an unequality d2<mdl when an interval on a recording medium of first and second light beams condensed on the recording medium is set at d1, the multiplying factor of an optical system provided between the recording medium and the means is set at (m), and the interval between the irradiated position of the respective light beams to irradiate the means and an edge part on a side where the second light beams of the means is approached is set at d2. That is, the range of a photo detector 45 is set so that is irradiated with only the reproducing light beams, namely, so that is not irradiated with the recording light beams, and simultaneously set in a range in which a position in the optical axis direction may be correctly tracking-controllable with the use of the beam spot of the reproduced light beams which irradiates the photo detector. Thus the crosstalk is prevented, and the information can be efficiently read and reproduced.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention relates to an optical information processing device, and more specifically, to an optical information processing device that records, reproduces, or erases information using a plurality of light beams. The present invention relates to an optical information processing device equipped with a multi-beam optical head that can be used simultaneously.

(Prior Art) In recent years, optical information processing devices such as optical disk devices have been developed that can record image information such as documents, retrieve the image information as needed, and reproduce it as a hard copy or soft copy. has been done. In an optical disk device, information is recorded or reproduced by irradiating a condensing light beam toward a disk-shaped recording medium, that is, an optical disk. That is, during recording, a state change is caused on the recording surface of the recording medium by being irradiated with a light beam, and as a result, information is recorded on the optical disk as, for example, bits. Further, during reproduction, a steady light beam is irradiated onto the information recording medium, and the intensity of the light beam is modulated by the pits according to the recorded information. Information is recovered by processing the modulated light beam intensity. During recording and reproduction, the optical disk is rotated at a constant linear velocity, and the light beam is linearly moved in the radial direction on the optical disk.

As these optical disk devices, information processing devices equipped with multi-beam optical heads that simultaneously record and reproduce information using a plurality of light beams have recently been developed. In a conventional multi-beam optical head, a recording light beam L1 and a reproduction light beam L2 are emitted from two semiconductor lasers provided adjacent to each other. The recording and reproducing light beams L1 and L2 are superimposed on each other and enter the collimator lens. The light beams L1 and L2 incident on the collimator lens are converted into parallel light beams in a superimposed state, and then incident on the beam splitter. The light beam incident on the beam splitter is transmitted and incident on the objective lens. The combined light beams L1 and L2 incident on the objective lens are condensed and at the same time are re-divided into individual light beams L1,
Branched to L2. At this time, the light beams L1 and L2 irradiated onto the recording area are preferably set so that their focal points are adjacent to each other and are focused on the same track. As a result, recording and reproducing beam spots are formed adjacent to each other on predetermined tracks on the recording film surface. With the recording and reproducing beam spots formed in this manner, the optical disk is rotated at a constant linear velocity, so that the predetermined recording area is irradiated with the recording light beam L1 and then immediately exposed to the reproducing light beam L1. It is irradiated by a light beam L2.

a light beam L1 irradiated onto a predetermined recording area on the recording surface;
L2 is reflected after predetermined recording and reproducing operations, passes through the objective lens again, and returns to the beam splitter. recording and reproducing light beam L1 returned to the beam splitter;
The combined light beam of L2 is reflected by the joint surface of the beam distributor and transmitted through the convex lens. The light beams transmitted through the convex lens are converged and separated into a recording light beam and a reproduction light beam. On the optical path of one of the two separated light beams for reproduction, the position of the objective lens relative to the recording medium is determined by W! A means for adjusting the J angle is provided, namely a knife or cylindrical lens. The reproduction light beam transmitted through the knife lens or cylindrical lens is detected by a photodetector whose size, position, and detection area position are set in advance, and is used to obtain a focus control signal and an information reproduction signal. be done. In the so-called knife method, in which a knife is installed on the optical path of the reproduction light beam and the light beam is transmitted through the knife and detected on a photodetector, the focus state of the light beam on the recording medium is determined. Information reproduction and focus control are performed using changes in the position of the beam spot image irradiated onto the photodetector, which changes accordingly.

Furthermore, in the so-called astigmatism method, a cylindrical lens is installed on the optical path of the reproduction light beam and the light beam transmitted through the lens is detected on a photodetector.
Information reproduction and focus control are performed using changes in the shape of a beam spot image irradiated onto a photodetector, which changes depending on the focus state of the light beam on the recording medium.

(Problem to be Solved by the Invention) In the Naifetsu method, the position of the light beam irradiated at the time of focusing is set in advance as a reference position, and the light beam is irradiated onto two divided light detection regions provided on both sides of the reference position. The focus state is detected by comparing the light intensities of the beam spots. Therefore, if the irradiation position of the light beam incident on the photodetector shifts to an asymmetrical position from the reference position due to changes in the external environment such as vibrations or temperature changes, the light intensity detected in each photodetection area will change. The difference signal corresponding to the difference varies greatly with respect to the amount of shift. Therefore, in order to further improve detection accuracy, the mounting positions of the photodetector and other optical components must be set accurately in advance.

On the other hand, in the astigmatism method, the shape of the beam spot that is irradiated during focusing is determined as a beam spot with a substantially cross-sectional shape having a predetermined area as a reference value, and changes in the beam spot shape with respect to the reference value are detected. The focus state is detected by In this method, the size of the light beam spot to be formed during focusing must be set to a larger value than a specific value. Depending on the size of the beam spot formed, the recording light beam and the reproduction light beam are brought close to each other, which tends to cause crosstalk between the respective light beams, which causes problems with the reproduction signal and focus control signal. Accurate detection becomes impossible.

The present invention provides an optical information processing device equipped with a multi-beam optical head that stably detects a reproduction light beam from recording and reproduction light beams reflected by a recording medium to reproduce information and control focus. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) The present invention includes means for emitting first and second light beams, and means for directing the first and second light beams onto a recording medium. a condensing means for condensing the light beams, a condensing and separating means for converging and separating the first and second light beams emitted from the recording medium, and a first beam separated by the condensing and separating means. a pair of light refractors that split one light beam into third and fourth light beams substantially parallel to each other; and a pair of light refractors for detecting the third and fourth light beams separated by the pair of light refractors. means, wherein dl is the distance between the first and second light beams focused on the recording medium, and ml is the magnification of an optical system provided between the recording medium and the means.
The distance between the irradiation position of each light beam to be irradiated on the means and the end of the means on the side approaching the second light beam is d2.
, a detection means whose size is set to satisfy d2 < mdi, and a detection means that focuses the light onto the recording medium in response to the third and fourth light beams detected by the detection means. and a response means for adjusting the position of the means in the optical axis direction.

(Function) In this invention, there is no need for a special optical system to separate and detect the reproduction light beam and the recording light beam, and there is no need for a special optical system to separate and detect the reproduction light beam and the recording light beam. Talk is reduced. Therefore, an optical information processing device equipped with a multi-beam optical head with lower cost and higher precision is provided.

Furthermore, by providing a new focus control device,
An optical information processing device is provided that includes a multi-beam optical head that is less affected by positional deviation of optical components.

(Embodiment) FIG. 1 shows 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 disk substrate made of glass or plastic with a metal film such as tellurium or bismuth as an information recording film.

Tracks 16A defining tracking guide areas are formed concentrically on the substrate of the optical disk. A multi-beam optical head 100 is provided facing the optical disc 16, and during recording, reproduction, and erasing, the optical disc 16 is rotated relative to the multi-beam optical head 100 at a constant linear velocity.

In FIG. 1, a track 16A defining a recording area extends in the Z direction.

A light source member 10 as a light source is provided inside the multi-beam optical head 100. A laser diode array 1OA that emits two light beams for recording and reproduction is arranged within the light source member 10. The emission apertures of the laser diode array 1OA are oriented in substantially the same direction and are set apart from each other in the Z direction on the same chip, and from the emission apertures, for example, a reproduction light beam L and a recording light beam of the same wavelength are emitted. The laser diode array 10A emits the laser diode array 10A.
The light beams Lr and Lw emitted from the collimator lens 12 are gradually diverged, overlapped, and irradiated onto the same collimator lens 12. The light beams Lr and Lw incident on the collimator lens 12 are substantially overlapped with each other and converted into a parallel combined light beam, which is then incident on the beam splitter 18 . The combined light beam incident on the beam splitter 18 is transmitted and irradiated onto the objective lens 14. When the light beam irradiated to the objective lens 14 passes through the objective lens 14 and is condensed, the light beam Lw for recording and the light beam L for reproduction are reused.
The light beam is separated into two parts and focused on the recording area, that is, the track, of the optical disc 16. Note that the recording and reproducing light beam L
Each focal point of the wSLr is preferably adjacent to each other and illuminated on the same track. As a result, adjacent recording and reproducing beam spots are simultaneously formed on a predetermined track. In this manner, the optical disk is rotated at a constant linear velocity while recording and reproducing beam spots are simultaneously formed.

As the optical disc rotates, a predetermined recording area on the optical disc is first irradiated with, for example, a recording light beam LW to record information. The area on the track where information is recorded is moved in accordance with the rotation of the optical disc, and is then immediately irradiated with the reproduction light beam L. The reflected light of the light beam L that has been irradiated onto the recording area is detected. The information is reproduced by.When obtaining the information reproduction signal,
The reproducing light beam must be maintained in focus and on track with respect to the desired recording area.

More specifically, the objective lens 14 is supported so as to be movable in its front axis direction and in a plane perpendicular to the optical axis.

When the objective lens 14 is placed at the optimal position on the optical axis, that is, at the focused position, the beam waist of the focused laser beam emitted from the objective lens 14 is projected onto the surface of the recording film of the optical disc 16. , whereby a 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 placed at the optimum position in a plane perpendicular to the optical axis (in a plane parallel to the recording film surface), that is, at the alignment track position, the beam spot formed on the optical disc 16 is determined as a recording area. The laser beam is then tracked by the laser beam.

Information can be reproduced by maintaining these two states (in-focus state and in-focus track state). That is, the intensity-modulated recording light beam Lw causes state changes such as pits in the recording film and information is recorded, and the laser beam L' with a constant intensity is applied to the recording area formed by the bits in the track. Upon irradiation, the light beam is intensity-modulated and reflected, and information is reproduced by detecting changes in the intensity of the reflected light beam Lr.

The diverging recording and reproducing light beams Lr and Lw reflected by the recording film of the optical disc 16 are combined with each other and enter the objective lens 14 . The combined light beam incident on the objective lens 14 is converted into a parallel light beam upon focusing, and is returned to the beam spot 18 again. The light beam incident on the beam splitter is reflected by its cemented surface 18 and transmitted through a plano-convex lens 25 for condensing a combined light beam. 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, and at the same time, the central axis 1 of each light beam L', Lw is focused. , 1w are gradually diverged from each other. The combined light beam is split into light beams LA and LB with approximately equal light intensity at the joint surface.The light beam LA reflected at the joint surface is used to obtain a focus control signal.In addition, the transmitted light beam is used to obtain a tracking control signal and an information reproduction signal.

To describe the light beam reflected by the beam splitter 27 in more detail, the reproduction light beam L' included in the light beam LA reflected by the joint surface of the beam splitter 27.
The beam cross section of the recording light beam Lw is gradually made smaller, and at the same time, the central axes 1r and 1w thereof become wider. Therefore, as the constituent light beams Lr and Lw are respectively focused, the combined light beam LA is gradually separated into individual reproduction light beams L and recording light beams Lw. A first light refractive body 2 disposed on both sides of the central axis 1r of the light beam Lr.
9A and the second light refracting body 29B are mutually parallel light beams LrA and LrB.
separated into Light beam L rA separated by a photorefractor
The SL rB is gradually focused onto a photodetection area of a photodetector 20 placed on the optical path. In addition, at this time, the photodetector 20 is installed in advance so that each beam spot of the light beam L'^, LrB irradiated onto the detection area becomes the minimum at the time of focusing, and at the same time, its size is Each reproduction light beam LrA on the plane including the detector plane
It is set according to the interval between the central axis of SLrB and the central axis of each recording light beam LwA, LvB. Photodetector 20
The light beam LrAsLrB irradiated onto the top is converted into an electrical signal in each photodetection area and processed in a predetermined manner.

More specifically, by detecting changes in the position of the beam spot on the photodetector, which changes depending on the relative position of the objective lens with respect to the information recording medium, the force focusing error signal, that is, the amount of defocus is detected. A corresponding signal is generated, and in response to the focusing error signal, current is supplied to the voice coil motor 50 to drive the objective lens 14 in its front axis direction and maintain the light beam in focus. Note that the other recording light beam LwASLvB
As shown in FIG. 2, after being transmitted through the light refractor, the light is transmitted without being irradiated onto the light detector 20.

On the other hand, to explain in detail the combined light beam LB transmitted through the beam splitter 27, the transmitted combined light beam LB is similar to the reflected light beam LA, as well as the reproduction light beam L and the recording light beam included therein. As the beam cross section of the optical beam Lw gradually becomes smaller, its central axes l' and 1w spread out from each other. Therefore, in the combined light beam LA, the constituent light beams Lr and Lw are respectively focused. Accordingly, each reproducing light beam Lr
and a recording light beam Lw. On the optical path of the separated reproduction light beam, there is a photodetector 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. The photodetector 45 is set in advance so that its detection area is irradiated with a circular beam spot having a predetermined area. It is set according to the distance between the central axis 1r of the recording light beam Lr and the central axis IW of the recording light beam Lw. In other words, the size of the photodetector 45 is set within the range where only the reproduction light beam is irradiated, that is, within the range where the recording light beam is not irradiated, and at the same time, its position in the front axis direction is It is set within a range that allows accurate tracking control using the beam spot of the reproduction light beam irradiated onto the photodetector.

The light beam converted into an electrical signal by the tracking photodetector 45 is processed by a predetermined method, and a tracking error signal is generated from the drive circuit 44. In response to the generated tracking error signal, current is supplied to the voice coil motor 50 to move the objective lens 14 in a plane perpendicular to its optical axis, so that 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.

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

FIGS. 2 and 3 are schematic perspective views showing an embodiment of a light refractor and a photodetector, which are the main parts of the present invention.

In one embodiment shown in FIG. 2, the first and second light refracting bodies 29A and 29B are arranged on both sides of the central axis of one of the incident reproduction light beams L' in different directions. First and second parallel plates arranged at an angle are used.The first and second parallel plates are arranged at an angle of
first and second parallel flat plates having side surfaces substantially parallel to the plane, the side surfaces being arranged so as to be in contact with the central axis of the reproducing light beam L'; 29A and 29B are installed such that their entrance and exit surfaces are tilted in mutually different directions with respect to the axis of the input reproduction light beam L'', and more preferably, the angle of inclination is such that the angle of inclination is such that the angle of inclination is such that They are installed at equal angles in different directions from a plane perpendicular to the axis.In this way, by tilting the first and second parallel plates 29A and 29B in different directions at equal angles, the light passes through the parallel plates 29A and 29B. One reproduction light beam Lr is branched into first and second light beams L'^ and LrB, which are substantially parallel to the incident light beam L' and spaced apart from each other by a predetermined distance, and each of the branched light beams LrAsLrB is irradiated onto a photodetector 20 placed on its optical path.

The other recording light beam Lw is parallel to the first and second light beams LV^, LvB that are spaced apart from each other by a predetermined distance.
The light is branched into the light beam and is transmitted without being irradiated onto the photodetector 20.

Further, FIG. 3 shows another embodiment of the light refracting body provided in the optical information processing apparatus of the present invention.

In FIG. 3, two first and second light refracting bodies A, 2
As 9B, first and second prism plates 29A and 29B are used, which are arranged on both sides of the central axis of the incident reproduction light beam Lr. This first and second
The prism plates have side surfaces substantially parallel to the X-Y plane, and the side surfaces are mutually arranged so as to be in contact with the axis of the reproduction light beam L. The second parallel flat plates 29A and 29B are, for example, arranged so that their entrance surfaces are perpendicular to the axis of the reproduction light beam L', and their exit surfaces are arranged at predetermined angles from the plane perpendicular to the axis of the reproduction light beam Lr. To be more specific, the output surfaces of each prism plate 29A, 29B are arranged to be tilted in different directions from a plane perpendicular to the axis of the reproduction light beam Lr, and more preferably in different directions. In this way, the first and second prism plates 3
By tilting the entrance surfaces or exit surfaces of 0A and 30B in different directions at equal angles, one of the reproducing light beams Lr that passes through the first and second prism plates 30A and 30B is mutually incident light beam. The first and second light beams Lr are substantially parallel to L' and are spaced apart from each other by a predetermined distance.
^, branched into LrB, each branched light beam LrA,
LrB is irradiated onto a photodetector 20 placed on the optical path.

The other recording light beam Lw is parallel to the first and second light beams L1/A and Lw, which are parallel to each other and spaced apart from each other by a predetermined distance.
The light is branched to ll13 and is transmitted without being irradiated onto the photodetector 20.

FIGS. 4A to 4C show changes in the shape of the beam spot on the photodetector 20 when the beam is in focus and when it is out of focus.

The photodetector 20 for focus control is arranged on the optical path of the reproduction light beam Lr of the light beam LA reflected by the beam splitter 27, and is located on the vertical (X direction) dividing line as the first non-detection area. 22B and the horizontal (Y direction) dividing line 22A
2O
It is composed of L, 20M and 2ON, and an electric signal corresponding to the received amount of the irradiated reproduction light beam L is outputted to each photodetection area 20 for each of 2OL, 20M and 2ON.

As shown in FIG. 7, each photodetection area 20K.

The output signals from 2OL, 20M, and 2ON are supplied to the amplifier circuit 31, 31L, 31M, and 31N, respectively, and the output signals amplified by the amplifier circuit 31 and 31N are supplied to the adder circuit 32, and the amplifier circuit 31L. , 31M are supplied to an adder circuit 33. Addition circuit 3
The signal output added by the adder circuit 33 is supplied to the inverting input terminal of the differential amplifier 41, and the signal output added by the adding circuit 33 is supplied to the non-inverting input terminal of the differential amplifier 41. Differential amplifier 4
1, a forcing error signal (FE signal) is output.

When the objective lens 14 is in focus on the optical disc 16, the smallest beam spot Sr is irradiated onto the front non-detection area 22B of the photodetector.

In other words, the position of the dividing line 22B as a non-detection area is the position where the forcing error signal (F-E signal) is equal to zero during focusing, that is, the position of the photodetection area 20, as shown in FIG. 4B. ni, 2OL, 20M, 2
Let the ON outputs be SK, SL, SM, and SN, respectively, and F
-E- (Set at a position that satisfies the conditions of SK/SNSN-3L-3-0. Also, dividing line 2 as a non-detection area
The position of 2A is set between two beam spots where the light beams LrA and LrB split by the light refractors 29A and 29B are formed on the photodetector 20, and preferably the interval between these two beam spots is set. It is set at the position where it divides into two.

When the objective lens 14 moves away from the focused position with respect to the optical disc, the forward beam reflected by the optical disc is slightly more focused than when it is focused. Therefore, the convergence point of the light beam L'' irradiated onto the photodetector 20 is moved to the front of the photodetector 20.Therefore, there is a A beam spot is formed.That is, the non-detection area 22 is located on the photodetection area 20M.
The [[ portion thereof touches B, and a half-moon-shaped beam spot having a larger diameter than when focused is formed. At this time, the forcing error signal is FE-(S
K4SN-SL-8M)<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 becomes slightly more divergent than when it is in focus.

Therefore, the focal point of the light beam Lr irradiated onto the photodetector 20 is moved to the rear of the photodetector 20. Therefore, a beam spot as shown in FIG. 4A, for example, is formed on the photodetector 20. That is, photodetection area 2
0, a half-moon-shaped beam spot is formed whose linear portion touches the non-detection region 22B and whose diameter is larger than when focused. At this time, the forcing error signal is F-E-+SK-3N-5L-3Ml
>Q.

The drive circuit 44 operates the voice coil motor 5 according to the forcing error signal output from the differential amplifier 41.
0 drives the objective lens 14 and keeps the light beam in focus. That is, when a focus lens error signal; be approached. Conversely, when a focusing error signal; F −E>O is input to the drive circuit, a current that moves the objective lens 14 away from the optical disk 16 is supplied to the voice coil motor 50, and the lens 14 is moved away from the optical disk 16. .

In this way, objective lens 14 is maintained in a position to focus the light beam.

5A to 5C show changes in the shape of the beam spot on the photodetector 20 when the light beam is in focus and out of focus when the light beam is irradiated onto a regular irradiation position. Further, FIGS. 6A to 6C show changes in the shape of the beam spot on the photodetector 20 when the light beam is in focus and out of focus when the irradiation position of the light beam is shifted. On the other hand, FIGS. 10A to 10C show changes in the shape of the beam spot on the photodetector when the light beam is in focus and out of focus when the light beam is irradiated to the correct irradiation position in the Naifetsu method. Figures 11A to 11C show changes in the shape of the beam spot on the photodetector when the light beam is in focus and out of focus when the irradiation position of the light beam is shifted in the Knifezi method. There is.

In an embodiment of the invention, the forcing error signal is output at FE-1sK-SN-5L-3M). On the other hand, in the knife method, a single light beam whose part is blocked by a knife is irradiated onto the two divided photodetection areas 2OA and 20B, and the difference signal between these two photodetection areas 2OA and 20B is output as a four-light beam. A flashing error signal is output. That is, the photodetection areas 2OA, 2
Letting the outputs of 0B be SA and SB, respectively, FE-(SA-5B) is output as a focus lens error signal.

To explain in more detail quantitatively, in the embodiment of the present invention, when a positional shift occurs in the irradiation beam, the light intensity detected in the entire photodetection area (20, 2OL, 20M, and 2ON) is 100. , 2OL in each photodetection area 20 in FIG. 6A.

The light intensity of 20M and 2ON is 25.5° and 25.5°, respectively.
45, forcing error signal; F-E-4
0 is output. In each photodetection area 20 in FIG. 6B, the light intensity of 2OL, 20M, and 2ON is 0 and 5, respectively.
0.0.50, force error signal, F
-E-0 is output. In each photodetection area 20 in FIG. 6C, the light intensity of 2OL, 20M, and 2ON is 5°25.45.25, respectively, and a forcing error signal, FE-40, is output. On the other hand, when a positional shift occurs in the irradiation beam in the Naifetsu method, assuming that the light intensity detected in the entire photodetection area (2OA, 20B) is 100, each photodetection area 2 in the 11th person figure
The light intensity of OA and 20B is 50.50, respectively.
A forcing error signal 2F.E-0 is output. The light intensity of each of the photodetection areas 2OA and 20B in FIG. 11B is 0.100, and a forcing error signal of FE--100 is output.

The light intensity of each of the photodetection areas 2OA and 20B in FIG. 11C is 10.90, and a forcing error signal of FE--80 is output. in this way,
In the Naifetsu method, when the irradiation position of the light beam shifts, the forcing error signal fluctuates greatly and an erroneous forcing error signal is output, but in the embodiment of the present invention, when the irradiation position of the light beam shifts, The forcing error signal is output correctly even when the force is out of alignment.

The size of the photodetector configured in this way is set based on the conditions described below. That is, the interval between the beam spots of the reproduction light beam Lr and the recording light beam Lw formed on the same track is dl, and the focal length of the objective lens 14 that irradiates the light beam onto the optical disk is fO.
s When the focal length of the lens 25 is fD, the distance d between the focal point of the recording light beam Lw and the focal point of the reproduction light beam L' on the same plane as the detection area of the photodetector 20
3 is d3 = (fo/fc))Xdl -mdl -■
Let it rain. Note that m indicates the magnification of the optical system. Therefore, in order to irradiate only the reproduced signal onto the photodetector, it is necessary to irradiate only the reproduced signal onto the photodetector at the end of the photodetector that extends in the lateral direction, that is, the side that approaches the virtual focal point of the recording light beam. The following relationship must always hold between the distance d2 between the end of the detector and the focal point of the reproduction light beam.

d3 > d2...
・・■Formula■,■ from d2<(fo/fo)Xdl-mdi ---・-・・
■There is a relationship.

As shown in this equation, the distance d between the end of the photodetector on the side approaching the virtual focal point and the virtual focal point of the recording light beam
2 is roughly set to satisfy d2<mdl. By arranging a photodetector that satisfies these conditions, d2 < mdi, crosstalk between the recording light beam and the reproduction light beam is prevented, and information is efficiently read or reproduced.

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

In the embodiment of the present invention, the size of the beam spot formed on the photodetector at the time of focusing can be made smaller compared to a focus control method such as the astigmatism method. manufacturing becomes easier. That is, when controlling the focus using the conventional astigmatism method, a beam spot with a beam diameter of 50 μm or more must be formed on the photodetector during focusing. Accordingly, the central axes l', 1w of the recording and reproducing light beams must be separated from each other by 100 μm or more on the plane on which the photodetector is to be arranged in order to avoid crosstalk.

On the other hand, in the focus detection method of the present invention, since the photodetector is placed on the focal point of the lens 25, the beam spot diameter of the light beam irradiated onto the photodetector is determined by the numerical aperture of the optical system used. The minimum value is determined by the NA, the magnification m1, and the wavelength λ of the light source.

That is, if the numerical aperture of the lens system with reference to the recording medium side is NAo, the beam spot diameter W on the recording medium is
l becomes Wl-λ/NA.

If the magnification of the lens system is m, the numerical aperture NAD of the lens system with respect to the photodetector side is NAD-mNAo/m.

At this time, the beam spot diameter W2 of the light beam irradiated onto the photodetector is W2-s/NAO-mλ/NA
It becomes o.

For practical optical diameters, the numerical aperture NA is generally
:0.4~0.6, λ:600~900nm%m:2~
For example, when NAo=0.5, λ-830nm, m-7, the beam spot diameter W2 on the photodetector is W2s=
mλ/N A □ '= 10 p m.

When the photodetector is placed at the image point of the light beam in this manner, the size of the beam spot is formed to be extremely small.

Therefore, it is possible to easily separate and detect the recording and reproducing light beams that are separated by a minute interval.

FIGS. 8A to 8C show beam spots on the photodetector during non-aligned tracks and aligned tracks. A 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 is located on the horizontal (Y direction) dividing line 48 as a non-detection area. It is composed of two forward light detection areas 45A and 45B provided on both sides of the front light detection area 45A and 45B.

When the objective lens 14 is accurately formed on the track that defines the recording area on the optical disk, that is, in the aligned track state, there is a non-detection area 48 on the photodetector 45 as shown in FIG. 8B. A substantially circular beam spot Sr having a predetermined beam diameter is formed with the center at
At the same time, a band-shaped portion generated by diffraction by the track is formed around the non-detection region 48. In other words, if the output of the photodetection area 45A is S^ and the output of the photodetection area 45B is SB, the position of the first non-detection area 48 is such that the tracking error signal (T - E) is equal to zero at the time of matching. position, that is, T・E−+S^−5BI−
It is set to satisfy the condition of 0.

On the other hand, for example, when the objective lens 14 moves away from the on-track position with respect to the optical disk, a circular beam spot as shown in FIG. 3A or 3C is formed on the photodetector. In other words, the band-shaped dark area generated by diffraction by the track is asymmetrical with respect to the dividing line 48 serving as a non-detection area.

At this time, the tracking error signal is T-E<0 or T
-E>O.

The set position of the photodetector 45 configured in this way is set based on the conditions described below.

In other words, in order to obtain the tracking control function mentioned above,
The position of the photodetector 45 in the optical axis direction is set so that the beam spot diameter of the irradiated light beam is formed within a specific range. In other words, the photodetector 45 is
Its size is set so that only the reproduction light beam Lr is irradiated.

More specifically, the position of the photodetector in the optical axis direction is set based on the conditions described below.

In other words, the reproducing light beam L formed on the same track
``and the interval between each beam spot of the recording light beam Lw is dl, and the objective lens 1 that irradiates the light beam onto the optical disk.
The focal length of lens 4 is f Os The focal length of lens 25 is fD
, the distance in the optical axis direction between the detection surface of the photodetector 45 and the image point of the lens 25 is Z, and the distance Z is the focal length f. , the distance d3 between the focal point of the recording light beam Lw and the focal point of the reproduction light beam L'' on the same plane as the detection area of the photodetector 20 is d3.
”= (fo /1o)Xdl −mdl +++・
＋■ will make you feel sad.

On the other hand, the beam diameter W formed on the detection area of the photodetector 45 at this time is W-Z/fD×φ, where φ is the diameter of the light beam incident on the lens 25.
■It will be hailed.

In equations (2) and (2), in order to irradiate only the reproduction light beam onto the detection area of the photodetector 45, d3 > W...
・It must be ■. In other words, the above equations ■, ■
Substituting into equation (■), the detection surface of the photodetector 45 and the lens 6
The distance Z in the optical axis direction between the image point and the image point is z< (fo)
2/fo X (di/φ)... Must be installed within a range that satisfies ■.

When substituting the relationship φ-2fo-NA into equation (2), equation (2) is generally rewritten as Z< (m2dl)/(2-NA) - (2). Note that m indicates the magnification of the optical system based on the recording medium side, and NA indicates the numerical aperture of the objective lens.

By installing the photodetector 45 within the range described in equation (2), the reproduction length and recording light beams are irradiated onto the photodetector 45 in a separated state.

Therefore, crosstalk between the reproducing and recording light beams LrsLw is prevented and accurate tracking control signals are detected.

FIG. 9 shows a processing circuit for all signals detected by the tracking control photodetector configured as described above. The output of the photodetection region 45A is supplied to the amplifier circuit 31C. The output of the photodetection region 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. In the differential amplifier 42, the photodetection region 45
The detection output of A and the detection output of the photodetection area 45B are compared, and an output corresponding to the difference, that is, a tracking deviation detection signal, is supplied to the drive circuit 44. In response to a tracking control signal supplied to the drive circuit 44, a current is fed back to a coil (not shown) that drives the objective lens 16 in a plane perpendicular to its optical axis. As a result, the objective lens 16 is driven in a direction perpendicular to the optical axis, and tracking deviation is corrected.

Furthermore, the outputs of the amplifier circuits 31C to 31D, that is, the entire output signal of the photodetector 45, are processed by a signal processing circuit 43 and used for information reproduction.

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

It may also be used to continuously erase and record information.

Furthermore, in this invention, the reproduction light beam L'
Although a photodetector 20.45 is provided for the recording light beam Lw, in principle a photodetector may be provided for other recording light beams Lw. Furthermore, the shape of the photodetector may also be varied within a range that produces similar effects.

(Effects of the Invention) According to the present invention, the beam spot irradiated onto the photodetection area is small and the forcing error signal is output correctly even if the irradiation position of the beam spot changes, so that the An optical information processing apparatus is provided that includes a multi-beam optical head that stably detects a reproduction light beam from among the use and reproduction light beams to perform information reproduction and focus control.

[Brief explanation of the drawing]

FIG. 1 is a front view of a multi-beam optical head provided in an optical information processing device according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing an embodiment of a light refractor and a photodetector, which are the main parts of the present invention. A perspective view, FIG. 3 is a schematic perspective view showing another embodiment of a light refractor and a photodetector, which are the main parts of the present invention, and FIGS. 4A to 4C.
The figure is a front view of a photodetector included in the optical information processing device of FIG. 1, showing changes in the beam spot in a focused state and an out-of-focus state of the light beam, and FIGS. 5A to 5C are Figures 6A to 6C show changes in the beam spot in the focused state and in the out-of-focus state, and FIGS. 6A to 6C show changes in the beam spot in the focused state and out-of-focus state of the light beam when the irradiation position of the light beam is shifted. Figure 7 shows the 4th
An electrical circuit diagram showing a method of processing a forcing error signal detected by the photodetector shown in the figure. Figures 8A to 8C show changes in the beam spot in the alignment track state and the valve platform track state of the light beam. FIG. 1 is a front view of a photodetector provided in the optical information processing device; FIG. 9 is a method for processing a tracking error signal detected by the photodetector shown in FIG. 8; 10A to 10C are electrical circuit diagrams showing the changes in the shape of the beam spot on the photodetector when the light beam is in focus and out of focus when the light beam is irradiated to the correct irradiation position in the Naifetsu method. Figures 11A to 11C are diagrams showing changes in the shape of the beam spot on the photodetector when the light beam is in focus and out of focus when the irradiation position of the light beam is shifted in the Knifezi method. be. 10... Light source member, IOA... Laser diode array 12... Collimator lens, 14... Objective lens, 16... Destination disk, 16A...Truck, 18...
・Beam splitter, 20... Focus control photodetector, 20, 2OL, 20M, 2ON... Light detection area, 22A, B... Light non-detection area ( dividing line), 25...Plano-convex lens, 27...
Beam splitter, 29A, 29B... light refractor, 31, 31L, 31M, 31N... amplifier circuit,
32.33...Addition circuit, 41.42...Differential amplifier, 43...Signal processing circuit, 44...Drive circuit,
45...Tracking photodetector, 45A, 4
5B... Light detection area, 48... Light non-detection area (dividing line), Lr... Light beam for reproduction, Lw.
...Recording beam, 1" ... Central axis of reproduction optical beam, 1w ... Central axis of recording target beam. Applicant's agent, patent attorney Takehiko Suzue g4A Figure @4C Figure! 4B Figure 11A Figure 118 Figure 11C

Claims (1)

[Scope of Claims] Means for emitting first and second light beams, condensing means for condensing the first and second light beams onto a recording medium, and the recording medium. a condensing and separating means for converging and separating the first and second light beams emitted from the medium; a pair of light refractors that branch into four light beams; and a means for detecting third and fourth light beams separated by the pair of light refractors, the means for detecting third and fourth light beams that are focused on the recording medium. The distance between the first and second light beams on the recording medium is d1, the magnification of the optical system provided between the recording medium and the means is m, and each light beam to be irradiated onto the means is irradiated. When the distance between the position and the end of the means on the side approaching the second light beam is d2, the size is d2<
detecting means set to satisfy md1, and adjusting the position of the focusing means in the optical axis direction with respect to the recording medium in response to third and fourth light beams detected by the detecting means. An optical information processing device comprising a response means for.