JPH0212616A - Focus control device - Google Patents

Abstract

PURPOSE:To facilitate assembly and regulation by equipping a means to branch optical beams into mutually approximately parallel first and second optical beams and a means to regulate the position of a convergent means for a recording medium and to respond to the first and second optical beams. CONSTITUTION:First and second optical refraction bodies 18 and 19 branch the optical beams into parallel first and second optical beams L1 and L2 by the boundasy of an optical axis arranged on the light path of the incident optical beams. Next, the optical beams L1 and L2 which irradiates a photo detector 20 are converted into electric signals in respective photo detecting areas, and processed. In the processing, a focusing error signal is generated from a driving circuit 44, a current is supplied to a voice coil 8, an objective lens 16 is driven in a light axis direction, and the focus of the optical beams is controlled. Further, a tracking error signal is generated from a driving circuit 45, the current is supplied to the voice coil motor 8, an optical head 3 is moved in the surface orthogonal to the light axis of the objective lens 16, and a prescribed track is traced by the optical beams. Thus, the assembly and regulation can be facilitated.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a device for detecting the focus state of an optical device, and more particularly relates to a device for detecting a focus state of an optical device, and more specifically, for detecting a focus state of an optical device. The present invention relates to a device for focusing a light beam onto an information recording medium for reading recorded information from the information recording medium.

(Prior Art) In recent years, image information recording and reproducing devices such as optical disk devices have been developed that can record image information such as documents, retrieve the image information as necessary, and reproduce it as a hard copy or soft copy. ing.

In an optical disk device, information is recorded or reproduced by irradiating a focused 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 by being irradiated with a light beam, and as a result, information is recorded on the optical disk as, for example, pits.

Further, during reproduction, a steady light beam is irradiated onto the information recording medium, and the intensity of the light beam is modulated with bits according to the recorded information. Information is recovered by processing the modulated light beam intensity. During recording and reproduction, an optical disk is rotated at a constant linear velocity, and an optical head for directing a light beam toward the optical disk is linearly moved in a radial direction on the optical disk.

The optical head includes an objective lens that focuses a laser beam onto an optical disk, and the objective lens is supported so as to be movable in the direction of its optical axis in order to accurately irradiate a predetermined area with a focused beam. The movable mechanism of the focus control system moves the objective lens in the optical axis direction to maintain the objective lens in a focused state, and the light beam from the objective lens is focused on the optical disk. In order to keep the objective lens in focus, a defocus state on the recording medium is detected and the detection result is fed back to the objective lens moving mechanism.

A wedge prism method is known as a method for detecting this defocus.

In the wedge prism method, a light beam emitted from an information recording medium in accordance with the force focusing state passes through a condenser lens and is split into two beams by a wedge prism. In this case, the two light beams are emitted in different directions at specific angles with respect to the optical axis of the incident beam. The branched light beams are respectively irradiated onto two detectors placed at predetermined positions and converted into electrical signals. The electrical signal is processed in a predetermined manner, and a current corresponding to the forcing error is supplied to a voice coil for driving the objective lens. By supplying current to the voice coil, the objective lens is driven and the light beam is focused onto the information recording medium.

(Problems to be Solved by the Invention) In focus control using the wedge prism method, a light beam is split by a wedge prism into two beams that are emitted in different directions at a specific angle with respect to the incident optical axis. Therefore, the distance between the two detectors that detect the two beams largely depends on the distance between the wedge prism and the detectors in the optical axis direction.

To achieve accurate forcing control, the wedge prism installation requires that the detector spacing be adjusted depending on the position.

An object of the present invention is to provide a new focus control device for detecting a focus state on an information recording medium.

In addition, the present invention solves the problem of position adjustment of the detector interval caused by misalignment of optical components in the optical axis direction, thereby making it possible to easily assemble and adjust the focal point. a focusing means for focusing, and first and second light beams that are arranged at different angles with respect to the optical axis of the light beam from the recording medium, block a part of the light beam, and are substantially parallel to each other; A focus control device is provided comprising first and second parallel plates that diverge into two parallel plates, and means responsive to said first and second light beams for adjusting the position of said focusing means relative to said recording medium.

(Example) An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a plan view of an optical disk device into which a focus control device of the present invention is incorporated. In FIG. 1, an optical disc (recording medium) 1 is made of glass, plastic,
A metal film such as tellurium or bismuth is coated as an information recording film on a disc-shaped substrate such as a steel. Groups 5 defining tracking guide areas are formed concentrically on the disk-shaped substrate. An optical head 3 is provided facing the optical disc 1, and the optical disc 1 is rotated relative to the optical head 3 at a constant linear velocity during recording, reproduction, and searching. In FIG. 1, the group 5 defining the recording area extends in the Z direction.

The optical head 3 includes a semiconductor laser 11 as a light source,
A diverging laser beam L is generated from the semiconductor laser 11 . The laser beam L is generated with its light intensity modulated according to the information to be written during recording to write information on the recording film of the optical disc 1, and is generated with a constant intensity during reproduction to read information from the recording film of the optical disc 1. be done. A diverging laser beam generated from the semiconductor laser 11 is converted into a parallel beam by a collimator lens 13 and guided to a half prism 14. Half prism'1
The laser beam L guided to the optical disk 4 passes through the half prism 14 and enters the objective lens 16, and the objective lens 16 focuses the laser beam L toward the recording film of the optical disc 1.

The objective lens 16 is supported so as to be movable in its forward axis direction and in a plane perpendicular to the optical axis. When the objective lens 16 is placed at the optimal position on the optical axis, that is, at the focused position, the beam waist of the focused laser beam L emitted from the objective lens 16 is projected onto the surface of the recording film of the optical disc 1. , whereby a minimum beam spot is formed on the surface of the recording film of the optical disc 1. On the other hand, when the objective lens 16 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 disk 1 becomes the recording area. It is formed precisely on a defined track, so that the track is followed by a laser beam. By maintaining these two states (in-focus state and in-track state), writing and reading of information becomes possible. That is, during recording, a change in the state of bits, etc. is caused on the recording film by the intensity-modulated laser beam A, and during reproduction, a laser beam with a constant intensity is intensity-modulated and reflected from the recording area formed by the bits, etc. in the track. Ru.

The diverging laser beam reflected by the recording film of the optical disc 1 is converted into a parallel light beam by the objective lens 16 at the time of focusing, and is returned to the half prism 14 again. The laser beam reflected by the half prism 14 is transmitted through the converging spherical convex lens 17 and is incident on the first and second light refracting bodies 18 and 19 arranged on the optical axis thereof. 1st
The second light refractor 18.19 is arranged on the optical path of the incident light beam, and splits the forward beam into two parallel first light beam L1 and second light beam L2 with the optical axis as the boundary. do.

The branched light beams L1 and L2 are each sent to a photodetector 2.
0 is irradiated. The light beams L1 and L2 irradiated onto the photodetector 20 are converted into electrical signals in each photodetection area and processed in a predetermined manner. A forcing error signal is generated from the drive circuit 44 by a specific signal processing method, and in accordance with the generated signal, a current is supplied to the voice coil 8 to drive the objective lens 16 in the direction of its tip axis, thereby changing the direction of the light beam. Focus is controlled. Further, a tracking error signal is generated from the drive circuit 45. Current is supplied to the voice coil motor 8 in accordance with the tracking signal, and the optical head 3 is moved in a plane perpendicular to the optical axis of the objective lens 16, whereby a predetermined trough is tracked by the light beam. . Further, the signal detected in the photodetection area is processed by a signal processing circuit 43 and used as a read signal.

The functions of the first and second light refracting bodies 18, 19 will be explained in detail with reference to FIG. First and second light refracting bodies 18.
19 is made of a glass plate, for example, and is preferably formed into a substantially parallel flat plate shape having the same thickness. Each parallel plate has side surfaces parallel to the X-Z plane, and the side surfaces are arranged so as to be in contact with the optical axis of the incident beam. Furthermore, the entrance and exit surfaces of the first and second parallel plates 18.19 are arranged at a predetermined angle with respect to a plane perpendicular to the optical axis. 19 are arranged at equal angles in different directions with respect to the optical axis. This splits the incident light beam along a line in the X direction perpendicular to the direction (Y direction) in which the shadow of group 5 on the optical disk is projected, as will be described later. By tilting the incident and exit surfaces of the first and second parallel plates 18 and 19, the light beams passing through the parallel plates 18 and 19 are substantially parallel to the optical axis of the incident light beam L. and is branched into a first light beam L1 and a second light beam L2 having a predetermined interval. In this invention, the corners formed by the side surfaces of each parallel plate 18; 19 in contact with the optical axis and the output surface are removed in parallel along the long sleeve direction of the parallel plate to form cutout surfaces 28, 29.

The cutout surfaces 28 and 29 block the light beam in a band region of a specific width extending in the X direction at the center of the incident light beam L, so that the light beam in the band region does not irradiate onto the detector. It is intended as such. The area of the beam spot projected onto the detector 2"0 is therefore substantially defined by the cutout surfaces 28.29. In other words, the parallel plate 18.29.
19, a light beam L1 whose cross section is approximately semicircular;
L2 is emitted, and two substantially semicircular images are projected onto the detector accordingly. The chord of these projected approximately semicircular images, that is, the position of the straight line portion of the semicircular image is located at the notch surface 2.
8.29 and the positions of the edges 28A, 29A where they meet with the exit surface. The light beam L1 emitted from the first and second light refracting bodies 18.19 in this way,
L2 is a light beam emitted from the cutout surfaces 28 and 29 in a band region of a specific width, which is removed and irradiated onto the detector 20. 1st
The interval between the light beam L1 and the second light beam L2 is determined by the refractive index n1 of the first parallel plate 18 and the second parallel plate 19.
It depends on the thickness and the angle θ formed by the parallel plates 18,19.

This relationship is illustrated in Figures 3A and 3B.

FIG. 3A shows the optical paths of the first light beam L1 and the second light beam L2 emitted from the first and second parallel plates 18, 19 substantially parallel to the optical axis of the incident light beam L. Door. In this figure the parallel plates 18, 19 are made of the same material with the same thickness. Assuming that the thickness of the parallel plate 18.19 is t1, the refractive index of one parallel plate 18 is n, and the angle between the two parallel plates 18 and 19 is θ, then the light beam L1
The distance between the light beams L2 in the X direction is approximately expressed as (1-1/n) θt in a range where the angle θ is relatively small. Therefore, the spacing of the light beams in the X direction does not depend on the mutual distances of the condenser lens 17, the parallel plates 18, 19, and the photodetector 20.

Also, in Figure 3B, the incident ray is erroneously placed at an angle δ with respect to the optical axis.
The X of the light beams L1 and L2, which are split into two, generated when the light beams L1 and L2 are incident on the two glass plates 18 and 19 with
Indicates the deviation in directional spacing.

When the light is incident at an angle δ with respect to the optical axis, the amount of deviation due to the parallel plate 19 is increased by (1-1/n) δt, and the amount of deviation due to the parallel plate 18 is increased by (1-1/n). ) is decreased by δt. Therefore, the distance between the two light beams in the X direction does not depend on the angle δ in a range where the angle θ formed by the two glass plates is relatively small. In this way, the interval between the light beams L1 and L2 emitted from the parallel flat plates 18 and 19 of the present invention is kept substantially constant without being affected by the deviation of each optical component in the optical axis direction. Therefore, a focus control device is provided that is easy to assemble and adjust.

A photodetector 20 on which the first light beam L1 and second light beam L2 that have been transmitted through the parallel flat plates 18 and 19 as light refractors and are split is incident thereon is shown in FIG. ing.

As shown in FIG. 6, the photodetector 20 has photodetection areas 2OA, 20B, and 20H that convert the light irradiated through the first photorefractor 18 into electrical signals.

201 and photodetection regions 20C and 20D that convert the irradiated light that passes through the light refracting body 19 into electrical signals.

It is composed of eight detection areas of 20F and 20G.

The light detection area is defined by the dividing line 21 in the X direction as the first non-detection area.
．． It is divided into two in the vertical direction by 22, and divided into four in the horizontal direction by dividing lines 23 to 25 in the Y direction. Parting line 2
The distance between the light beams 3 and 24 is equal to the distance between the light beams branched substantially in parallel. Also, dividing lines 23 to 25
is set in advance to be parallel to the extending direction (Y direction) of the shadow of group 5 diffracted and projected from the optical disc. These separated detection areas 20A to 201
The output is used for focus correction, tracking correction, and information reproduction.

When the objective lens 16 is in a focused position with respect to the optical disc, an image as shown in FIG. 4B is projected onto the photodetector. The light beam that passed through the first light refractor 18 reaches the photodetection areas 2OA, 20B, and 20H.

201 as a substantially semicircular image. On the other hand, the light refractive body 1
The light beam that has passed through 9 reaches the photodetection area 20C.

It is projected onto 20D, 20F, and 20G as substantially semicircular images in opposite directions. Each of these semicircular images is formed by the light beams passed through the exit surfaces of the first and second light refractors 18, 19. In other words, the light beams emitted from each cutout surface 28.29 of each parallel plate 18.19 are not irradiated onto the detector 20. Therefore, the chord of each semicircular image irradiated onto the detector 20, that is, the straight line portion of the semicircular image is the notch surface 28.
29 is defined according to each edge 28A, 29A. For example, when the objective lens 16 is in a focused position with respect to the recording surface of the information recording medium 1, the interval between the chords of each semicircular image projected on the photodetector 20, that is, the notch of the parallel plate 18, 19 The width W of the central band area of the light beam blocked by the surfaces 28 and 29 on the detection area is determined to be a predetermined width W2.

At the same time, the light detection areas to which each approximately semicircular beam spot in focus is irradiated are separated by dividing lines 21 and 22 as first non-detection areas so that beams of equal light intensity are irradiated on the left and right sides. ing. In other words, the seventh
As shown in Figure A, if the outputs of the photodetection areas 20A to 201 are represented by ■ to ■, respectively, the positions of the dividing lines 21 and 22 are the positions where the F and E signals are equal to 0 when in focus;
That is, FE (focus error ff1) −[
It is set to satisfy the condition (■+■+■+■)-(■10■+■+■))-〇.

By setting the spot size of the light beam during focusing and the configuration of the detector as described above, a signal corresponding to the shift in focus is generated from the photodetector.

For example, when the objective lens 16 moves away from the in-focus position with respect to the optical disc, a slightly converged forward beam from the optical disc is incident on the parallel plate 18.19. Therefore, an image as shown in FIG. 4A is projected onto the detector. That is, a smaller image is formed on the detector than when focused. At the same time, the light beam is removed at the cutout surfaces 28, 29, so that a blocked beam spot of a band area of a certain width is projected onto the detector. At this time, the width W of the shielded band region
1 is formed narrower than the width W2 when in focus.

Further, the focusing error signal detected in the optical detection area satisfies F, E>0.

Conversely, when the objective lens 16 is closer to the optical disk than the in-focus position, a slightly divergent light beam from the optical disk is incident on the parallel plate 18, 19. Therefore, an image as shown in FIG. 4C is projected onto the detector.

That is, a larger image is formed on the detector than when focused. At the same time, the light beam is removed at the cutout surfaces 28, 29, so that a blocked beam spot of a band area of a certain width is projected onto the detector. The width W3 of the shielded band region is formed to be wider than the width W2 when in focus. Also, the forcing error signals detected in the light detection area are F, E<
It becomes 0.

Cutout surface 28 provided in parallel plate 18, 19 of this invention
．． 29 advantages are described below. For example, the cutout surface 28
．． When a simple parallel plate 18 , 19 without the parallel plate 29 is placed on the optical path of the light beam, all the light beams incident on the parallel plate 18 , 19 are irradiated onto the detector 20 . Therefore, the position of the string of each semicircular image projected onto the detector is always kept at a constant position regardless of whether it is in focus or not.

As described above, the position of the objective lens 16 with respect to the optical disc is the photodetection areas 2OA, 20B, and 20F.

The electric signal generated from 20G and the photodetection area 20C,
Adjustment is performed by feeding back the difference signal between the electrical signals generated from 20D, 20H, and 201. The difference signal is generally varied in proportion to the area ratio of the beam spot projected onto the detection area. Therefore, if parallel plates are simply arranged, the detection sensitivity when the objective lens 16 moves away from the in-focus position and the detection sensitivity when the objective lens 16 approaches the in-focus position are asymmetrical and substantially different, even in the same out-of-focus state. There is.

Parallel plate 18 with cutout surfaces 28 and 29 formed therein
．． At 19, the light beams excluding the light beams emitted from the cutout surfaces 28 and 29 are irradiated onto the detector 20. Therefore, a substantially semicircular beam spot is formed on the detector 20, with the band region at the center thereof being shielded by the width W. The width W of this band area is changed depending on the focus state as described above. Therefore, detection sensitivity is improved especially when the objective lens 16 is away from the in-focus position in the out-of-focus state, and symmetrical sensitivity characteristics can be obtained when the objective lens 16 is away from the in-focus position and when it approaches the in-focus position. .

On the other hand, the dark area caused by the diffraction of the guide groove 5 on the optical disk 1 used for the tracking guide appears parallel to the dividing lines 23 and 24 of the photodetection area, as shown in FIGS. 5A to 5C. .

As shown in FIG. 7B, the tracking error signal (T, E) −+(■+■+■+■)−(
■+■+■+■)), i.e., photodetection area 2OA, 201,
20C, 2'OG detection signal addition results and photodetection areas 20B, 20H.

The position of the optical head is adjusted on a plane parallel to the optical disk in accordance with the difference signal between the addition result of the detection signals 20D and 20F, that is, the track position deviation signal.

Next, a circuit for processing electrical signals detected by the photodetector will be described with reference to FIG. Photodetection area 2OA and 2
The 0G output is supplied to the amplifier circuit 31A. The outputs of photodetection regions 20D and 20H are supplied to amplifier circuit 31B. The outputs of the photodetection areas 20C and 20I are sent to the amplifier circuit 31C.
supplied to The outputs of the photodetection regions 20B and 20F are supplied to an amplifier circuit 31D. Each amplifier 31A-31
Each signal supplied to D is amplified and sent to the adder circuit 3.
6. The signal added by the adder circuit 36 is supplied to a control circuit (not shown) as an information reproduction signal. The signal from the amplifier circuit 31A is supplied to adder circuits 32 and 34. The signal from the amplifier circuit 31B is sent to the adder circuits 33 and 3.
5. The signal from the amplifier circuit 31C is supplied to adder circuits 33 and 34. The signal from amplifier circuit 31D is supplied to adder circuits 32 and 35.

The output of adder circuit 32 and the output of adder circuit 33 are used to supply focusing control signals to the voice coil. That is, the output of the adder circuit 32 is supplied to the inverting input terminal of the comparator circuit 41, and the output of the adder circuit 33 is supplied to the non-inverting input terminal of the comparator circuit 41. In the comparison circuit 41, the addition result of the detection signals of the photodetection areas 2OA, 20G, 20B, and 20F and the photodetection areas 20C, 201, and 20D.

The result of addition of the detection signal of 20H is compared, and an output corresponding to the difference signal, that is, a focus control signal, is sent to the drive circuit 44.
will be given feedback. The objective lens 1
A current is supplied to a coil (not shown) that drives 6 in its forward axial direction.

The objective lens 16 is driven in accordance with the supplied current to correct defocus.

The output of the adder circuit 34 and the output of the adder circuit 35 are used to supply a tracking control signal to the voice coil. That is, the output of the adder circuit 34 is supplied to the inverting input terminal of the comparator circuit 42, and the output of the adder circuit 35 is supplied to the non-inverting input terminal of the comparator circuit 42.

In the comparison circuit 42, the photodetection area 20A5"20
The addition result of the detection outputs of G, 20C1201 and the addition result of the detection outputs of the photodetection areas 20B, 20F, 20D, and 20H are compared, and an output corresponding to the difference, that is, a tracking deviation detection signal, is fed back to the drive circuit 45. Ru. In response to a tracking control signal fed back to the drive circuit 45, a current is supplied to a coil (not shown) that drives the objective lens 16 in a plane perpendicular to its front axis. This drives the objective lens 16 and corrects tracking deviation.

The output of the adder circuit 36 is supplied to a signal processing circuit 43.

The signal processed by the signal processing circuit 43 is used as a search signal for information reproduction.

In the focus control device described above, the diverging laser beam generated by the semiconductor laser 11 is converted into a parallel beam by the collimator lens 13 and guided to the half prism 14. The laser beam guided to the half prism 14 is incident on the objective lens 16 after passing through the half prism 14. The incident light beam is focused toward the recording film of the optical disc 1 by the objective lens 16 . In recording information, pits are formed in tracks on the optical disc 1 by irradiating the optical disc 1 with a laser beam (recording beam) modulated in intensity. In reproducing information, a steady laser beam (reproducing beam light) with a low luminous intensity is irradiated onto the optical disc 1 and its intensity is modulated by bits. The reflected light from the optical disk 1 for this reproduction beam is converted into a parallel light beam by the objective lens 16 and returned to the half prism 14 again.

Then, the beam L reflected by the half prism 14 passes through the spherical convex lens 17 and enters the first and second light refracting bodies 18 and 19.

The light beams incident on the first and second light refractors 18 and 19 are branched into a first light beam L1 and a second light beam L2 that are substantially parallel to each other, and are split into a light detection area 2OA of the photodetector 20.
, 20B, 201, 20H and photodetection areas 20C, 20
Irradiates onto D, 20G, and 20F. As a result, signals corresponding to the irradiated light are output from the photodetection regions 20A to 20, and these signals are supplied to the amplifier circuits 31A to 31D.

A focusing operation in such a state will be explained. That is, the signals from the amplifier circuits 31A and 31D are supplied to the adder circuit 32.

The signals from the amplifier circuits 31B and 31C are sent to the adder circuit 3.
3. Photo detection area 20A120G, 2'OB
, 20F are added by an adder circuit 32 and supplied to a comparator circuit 41.

The detection signals from the photodetection areas 20C, 201, 20D, and 201 (are added by the adder circuit 33 and supplied to the comparison circuit 41. Thereby, the comparison circuit 41 detects the detection signals from the photodetection areas 2
The addition results of the detection signals of OA, 20G, 20B, and 20F are compared with the addition results of the detection signals of the photodetection areas 20C1201, 20D, and 20H, and the difference signal, that is, the focus control signal is supplied to the drive circuit 44. Current is supplied to a coil (not shown) in response to a focus control signal supplied to the drive circuit 44. The objective lens 16 is driven in the optical axis direction in accordance with the supplied current to control the focus state of the forward beam.

Also, the tracking operation will be explained. That is, the signals from the amplifier circuits 31A and 31C are supplied to the adder circuit 34. The signal from the amplifier circuit 318131D is supplied to the adder circuit 35.

Signals from the photodetection areas 2OA, 20G, 20C, and 20I are added by an adder circuit 34 and supplied to a comparator circuit 42. Photodetection areas 20B and 20F.

The detection signals from 20D and 20H are added by an adder circuit 35 and supplied to a comparator circuit 42. As a result, the photodetection areas 2OA, 20G, and 20C.

The addition result of the detection signals of 201 and the detection areas 20B, 2
The addition result of the detection signals of 0F, 20D, and 20H is compared in a comparator circuit 42, and an output corresponding to the difference, that is, a tracking control signal, is fed back to the drive circuit 45.

Current is supplied from the drive circuit 45 to a coil (not shown) in accordance with the tracking control signal. The objective lens 16 is driven on a plane perpendicular to its optical axis by the supplied signals, and the tracking position of the light beam is controlled.

Next, information reproduction will be explained. When reproducing information, a laser beam L with a constant low luminous intensity is emitted from the semiconductor laser 11.
is generated, and the entire reproduction beam is intensity-modulated according to the recorded information and is incident on a photodetector. The outputs of the photodetector regions 20A to 201 of the photodetector are transmitted to amplifier circuits 31A and 31.
B, 31C.

31D. Amplifier circuit 31A, 318131C
, 31D is processed by the signal processing circuit 43, thereby reproducing the recorded data.

One embodiment of the invention described above describes an eight-divided detector that can perform focus control, track position control, and signal detection using the same detector. However, this detector need not be limited to an eight-divided detector. For example, in order to simply detect the focus state, a four-divided photodetector may be used, excluding the dividing lines 23 and 24 as non-detection areas provided in the eight-divided detector. Moreover, in this invention, 1. Although a photodetector is provided for each of the first light beam L1 and the second light beam L2 in order to improve detection sensitivity, in principle only one of the light beams may be detected.

In the embodiment described above, the light refractive body is generally formed of a glass material 18, 19 having the shape of a parallel plate, and the corner formed by the side surface and the exit surface is diagonally aligned along the long axis of the parallel plate. The notch surfaces 28 and 29 are formed. The cutout surfaces 28, 29 are intended to block a certain area approximately in the center of the incident light beam, thereby allowing a good sensitive detection at the detector. Therefore, the shape of the cutout surfaces 28, 29 of the parallel plate 18, 19 may be changed within a range that provides the same effect. Other methods may also be used to block the light beam in specific areas. Furthermore, the arrangement of the detector can also be changed in accordance with the arrangement of the light refractor. For example, in an embodiment, two light refractors are arranged symmetrically on the optical axis of the incident light beam. However, even if the two light refractors are not arranged symmetrically on the optical axis of the incident light beam, similar detection can be achieved by predetermining the arrangement of the detector and the positions of the dividing lines 21 to 25 on the detector. is possible.

(Effects of the Invention) In the present invention, the interval between the light beams emitted from the first and second light refracting bodies is kept substantially constant without being affected by the deviation of the optical axes of each optical component. Therefore, a focus control device is provided that is easy to assemble and adjust. Also the first and second
Among the light beams incident on the light refractor, the light beam in the central band region emitted from the cutout surface is blocked, resulting in symmetrical sensitivity when moving away from and approaching the focal point. A highly sensitive focus control device exhibiting characteristics is provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of an optical head equipped with a focus control device of the present invention, FIG. 2 is a perspective view showing main parts of the focus control device of the present invention, and FIGS. 3A and 3B are on the optical axis. 4A to 4C are side views showing the relationship between the two parallel Heisei arranged in the same direction and the deviation of the optical axes of the two branched light beams.
The figure is a front view of an 8-segment photodetector showing focused and out-of-focus states of the light beam, and FIGS. 5A to 5C are 8-segment photodetectors showing on-track and out-of-focus states of the light beam. Figure 6 is a front view of the 8-segment photodetector, Figure 7A is a front view of the 8-segment photodetector.
7B are electrical circuit diagrams showing a method of processing signals detected by a photodetector, and FIG. 8 is an electrical circuit diagram showing a method of processing all signals detected by a photodetector. 1... Optical disk, 3... Optical head, 1]...
Semiconductor laser, 13... Collimator lens, 14...
・Half prism, 16...Objective lens, 17...
Spherical convex lens, 18... first light refractive body (first parallel plate), 19... second light refractor (second parallel plate)
20... Photodetector, 20A-201... Photo detection area, 21-25... Parting line, 28.29... Notch surface,
28A, 29A...Edge, 31A-31D...Amplification circuit, 32-36...Addition circuit, 41.42...Comparison circuit, 43...Signal processing circuit, 44.45...Drive Circuit applicant agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] 1. A focusing means for focusing a light beam onto a recording medium; a focusing means arranged at different angles with respect to the optical axis of the light beam from the recording medium, and a focusing means for focusing a light beam on a recording medium; first and second parallel plates that block light and branch into first and second light beams that are substantially parallel to each other; and the first and second light beams that adjust the position of the focusing means with respect to the recording medium. A focus control device comprising means for responding to.