JPH02121122A - Focus controller - Google Patents

Abstract

PURPOSE:To facilitate the assembly and the control of a focus controller by controlling the position of a condensing means in accordance with 1st and 2nd light beams. CONSTITUTION:A divergent laser beam L reflected by the recording film of an optical disk is branched into the 1st and 2nd light beams L1 and L2 which are parallel with each other when the beam L is radiated from a condensing/ branching member 10. In such a case, the branching members 18 and 19 are made of the same material in the same thickness. The thickness of both members 18 and 19 is referred to as (t) together with the refractive index of both members as (n), and the angle formed between both members as theta respectively. Thus the error distance D caused between the optical axes of the light beams L1 and L2 radiated from the members 18 and 19 is approximately equal to (1-1/n)thetat within a range where the angle theta is comparatively small. Therefore, the distance D is not dependent on the distance among a condenser lens 17, the members 18 and 19, and a photodetector 20. In such constitution, the control of a focus controller is facilitated.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a focus control device, and more specifically, to a focus control device for controlling the focal position of a light beam for recording or reproducing information. The present invention relates to a focus control device.

(Prior Art) In recent years, image information recording and reproducing devices such as disk drives 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, bits. Furthermore, during reproduction, a steady light beam is irradiated onto the recording medium, and the intensity of the light beam is modulated with bits according to the recorded information. Information is reproduced by processing the intensity modulation of the light beam. During recording and reproduction, the 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 the radial direction above 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 its front axis direction 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 according to a force beam is split into two beams by a wedge prism after passing through a condensing lens. 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 edge 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 detection device for detecting the focus state of an optical device.

Another object of the present invention is to solve the problem of position adjustment of the detector interval caused by positional deviation of optical components in the optical axis direction, thereby providing a focus control device that is easy to assemble and adjust.

[Structure of the Invention] (Means for Solving the Problems) A focus control device of the present invention includes a means for generating a light beam, a focusing means for focusing the light beam on a recording medium, and a focusing means for focusing the light beam from the recording medium. branching means for branching the beam into first and second light beams substantially parallel to each other; support means for supporting the branching member; and adjusting the position of the condensing means with respect to the recording medium. Means is provided responsive to the first and second light beams.

Furthermore, the focus control device of the present invention includes means for generating a light beam, focusing means for focusing the light beam on a recording medium, and focusing means for directing the light beam from the recording medium into first and second substantially parallel channels. and means responsive to the first and second light beams for adjusting the position of the focusing means relative to the recording medium.

(Function) The interval between the light beams L1 and L2 emitted in parallel to each other from the first and second branching members of the present invention is maintained substantially constant without being affected by the deviation of each optical component in the optical axis direction. dripping Therefore, assembly and adjustment become easy. In addition, the first and second branching members for splitting the incident light beam into two mutually parallel light beams are integrally fixed to the support member, and the spherical convex lens for condensing the first beam is also supported. It is integrally fixed to the member. Therefore further assembly and:
J8 adjustment becomes easy. Further, according to the focus control device of the present invention, the branching member is integrally molded, and the first
And the upper surface of the second branch member is molded so as to coincide with the same hand surface. Therefore, the branching member can be easily integrated and manufactured, and its installation and adjustment are also easy. Furthermore, in the photodetector used in the focus control device of the present invention, a focus control signal, a focusing control signal, and an information reproduction signal are obtained by the same detector. A more compact device is therefore provided.

(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 disk (recording medium) 1 has an information recording film made of tellurium or
It is formed by coating with a metal film such as bismuth. Groups 5 as tracking guides that define recording 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 two directions.

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 . A laser beam is generated with a modulated light intensity according to the information to be written during recording to write information on the recording film of the optical disc 1, and is generated at 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 14
The laser beam guided by the laser beam passes through the half prism 14 and enters the objective lens 16, and the laser beam is focused by the objective lens 16 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 an intensity-modulated laser beam, and during reproduction, a laser beam with a constant intensity is intensity-modulated and reflected from a recording area formed by bits, etc. in a track. Ru.

When the diverging laser beam L reflected by the recording film of the optical disc 1 is focused, it is converted into a parallel beam by the objective lens 16 and returned to the half prism 14 again. The laser beam L reflected by the half prism 14 is incident on a condensing and branching member 10 that condenses the light beam and branches it into two mutually parallel light beams. When the incident light beam is emitted from the condensing and splitting member 10, it is split into first and second light beams L1 and L2 that are parallel to each other. The split light beams L1 and L2 are gradually converged and irradiated onto the photodetector 20, respectively. 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. The signal is processed, and a signal corresponding to the amount of defocus is generated from the differential amplifier 41 for focusing. In response to the generated signal, a current is supplied to the voice coil 8 to drive the objective lens 16 in its front axis direction, thereby controlling the focus of the light beam.

Further, a tracking differential amplifier 42 generates a signal corresponding to the amount of tracking deviation. In response to the generated signal, current is supplied to the voice coil drive circuit 45 to drive the optical head 3 in a plane perpendicular to the optical axis of the objective lens 16, whereby a predetermined track 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 an information reproduction signal.

The structure and function of the light collecting and branching member 10 will be explained in detail with reference to FIG. The condensing and branching member 10 includes a spherical convex lens 17 as a condensing member for condensing the incident light beam.
, first and second branching members 18 and 19 that split the light beam incident from the spherical convex lens 17 into two light beams with the front axis as a boundary; First and second branch members 18.19 at the ends
and a support member 30 for supporting.

The support member 30 is provided to integrally support the spherical convex lens 17 and the first and second branch members 18,19. The support member 30 is made of plastic, for example, and is preferably molded into a substantially cylindrical shape having a substantially constant thickness, and has openings 30A and 30B at both ends thereof. Further, the central axis of the cylindrical support member 30 is arranged so as to coincide with the optical path of the front beam. The opening 30A of the support member 30, which is formed into a substantially cylindrical shape, is formed into a circular shape whose inner diameter is equal to the diameter of the spherical convex lens 17.
0B is arranged so that the first and second branching members 18 and 19, which are to be arranged at an angle to the optical axis, can be easily accommodated therein, so that they are aligned with each other with the X-Z plane containing the front axis as a boundary. Cut diagonally in the opposite direction. The spherical convex lens 17 is fitted into the opening 30A of the support member 30 configured as described above, and fixed so that the central axes of the spherical convex lens and the cylindrical support member coincide with each other. On the other hand, the frontage part 30B has a first
and the second branch member 18,19 is tilted at a predetermined angle and fitted therein and fixed in position. Note that the spherical convex lens 17 and the branching member 18.1 described above
In order to more easily support the spherical convex lens 17 and the first and second branch members 1 around each end in the support 30,
A pedestal may be provided to define the position of 8.19. First and second branch members 18 to be fitted into the support 30
．． 19 is made of a transparent material such as a glass plate, and is preferably formed into a parallel flat plate having a semicircular shape and a constant thickness. Each parallel plate has a side surface parallel to the x-2 plane, and is arranged such that the side surfaces are mutually in contact with the optical axis of the incident beam.

Furthermore, the entrance and exit surfaces of the first and second branch members 18,19 are arranged at a predetermined angle with respect to a plane perpendicular to the optical axis, and preferably The members 18. are arranged in mutually different directions and at equal angles to the optical axis. In more detail, the second
In the figure, for example, the entrance surface of the first branch member 18 is
It is set perpendicular to the Z plane, and at the same time, its upper part is inclined at an acute angle and its lower part is arranged at an obtuse angle with respect to the ZY plane including the optical axis of the light beam. On the other hand, for example, the entrance surface of the second branching member 19 is set perpendicular to the X-Z plane, and at the same time, its upper part is tilted at an obtuse angle with respect to the Z-Y plane that includes the optical axis of the light beam. The lower part is arranged at an acute angle.The angles of the entrance and exit surfaces of the branching member with respect to the optical axis of the incident light beam are set according to the cross-sectional shape of the light beam. The photodetector 20 for detecting the beams L1 and L2 is set according to the detection method. As a result, the branch member 18.
The light beam incident on the optical disc 19 is branched upward and downward with a line in the X direction perpendicular to the direction in which the shadow of the group on the optical disk is projected as the boundary. When converted into cash, the incident and exit surfaces of the first and second branching members 18 and 19 are tilted, so that the light beams that have passed through the first and second branching members 18 and 19 are aligned with each other. A first light beam L1 and a second light beam L2 are split into a first light beam L1 and a second light beam L2 that are substantially parallel to the optical axis of L and are spaced apart from each other by a predetermined distance.
irradiated on top. The distance between the first light beam L1 and the second light beam L2 depends on the thickness of the refractive index n1 of the first branching member 18 and the second branching member 19 and the angle θ formed by the branching members 18 and 19. . Optical path diagrams of the light beams incident on the condensing and branching member 10 shown in FIG. 2 are shown in FIGS. 3A and 3B.

FIG. 3A shows an optical path diagram when a light beam is incident along the central axis of the condensing and branching member, that is, the optical axis of the condensing lens. In this figure the branch members 18,19 are made of the same material with the same thickness. Branch member 1
8.19 Thickness t1 Refractive index of branching member 18.19 01 Assuming that the angle formed by branching member 18.19 is θ, the deviation interval of the optical axes of light beam L1 and destination beam L2 emitted from each branching member In the range where the angle θ is relatively small, (1
-1/n) θt. Therefore, the deviation D of the optical axis of the light beam is
8.19 and independent of the mutual distance of the photodetectors 20.

Further, FIG. 3B shows an optical path diagram when a light beam is incident on the central axis of the condensing/splitting member 10, that is, the optical axis of the condensing lens, while being erroneously inclined at an angle δ. When the light is incident at an angle δ with respect to the optical axis, the amount of deviation due to the branching member 19 is (
The displacement amount due to the branch member 18 is decreased by (1-1/n) δt. Therefore, the interval between the axes of the two light beams 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 first and second branch members 18 of the present invention
．． The interval between the light beams L1 and L2 emitted from 19 is
It is kept substantially constant without being affected by the deviation of each optical component in the optical axis direction. Thus, a focus control device is provided that is easy to assemble and adjust.

Furthermore, in the embodiment described, the branching member 18. which has to be arranged obliquely with respect to the optical axis of the incident light beam L.
19 is integrally attached to the support member 30. Therefore, a focus control device is provided that is easier to assemble and adjust. Further, in this embodiment, a spherical convex lens 17 as a condensing member and first and second branching members 18 and 19 are both attached to the support member 30. However, the support member 10 has first and second branch members 18.1.
9 may be attached.

Furthermore, in the embodiment described above, the first and second branch members 18, 19 are each formed in the shape of a semicircle, and the support member 10 is formed in the generally cylindrical shape. however,
The branch member and support member may be formed in other shapes.

FIG. 4 shows the main parts of a focus control device according to a second embodiment of the invention. In FIG. 4, parts exhibiting the same functions as in FIG. 2 are designated by the same reference numerals. The condensing and branching member 10 shown in FIG. 4 also includes a spherical convex lens 17 as a condensing member for condensing the incident light beam;
An integrally molded branching member 40 that splits the light beam incident from the spherical convex lens 17 into two light beams L1 and L2 with the optical axis as a boundary, and the spherical lens 17 at one end thereof.
and a support member 30 for supporting the branch member 40 at the other end.

The support member 30 is made of, for example, plastic, and is preferably molded into a substantially rectangular tube shape with a substantially constant thickness, and has rectangular openings 30A and 30B at both ends thereof. Opening 30 of support member 30 formed into a substantially rectangular tube shape
A spherical convex lens 17 is attached via a fixing member 45.

On the other hand, an integrally formed branching member 40 that is to be arranged at an angle to the optical axis of the spherical convex lens 17 is fitted into the opening 30B. The integrally molded branching member 40 is composed of a first branching member 18 and a second branching member 19 as described later, and the inner side surface to be integrally molded is as shown in FIG. Similarly, they are fixed so as to be in contact with the optical axis of the spherical convex lens 17, that is, the central axis of the front beam. Additionally, in order to more easily support the spherical convex lens 17 and the branching members 18 and 19, there are holes around each end of the supporting member 30.
A pedestal may be provided for determining the eccentricity of the spherical convex lens 17 and the branching members 18,19. The integrally molded branching member 40 to be fitted into the support body 30 is made of a light-transmitting material such as a glass plate, and preferably has a first branching member 18 and a second branching member having a constant thickness. 1
9 is manufactured in advance so as to have an integrated shape.

5 and 6 show third and fourth embodiments of the main parts of the focus control device of the present invention.

The branching member 40 shown in FIG. 5 is the same as the branching member shown in FIG. It has a structure formed by In order to simplify the explanation, the branching member 40 will be explained separately into a first branching member 18 and a second branching member 19. First and second branch members 18
．． Reference numeral 19 has the same function as the branching member shown in FIG. The first branch member 18 and the second branch member 19 are
It has side surfaces 18B and 19B parallel to the X-Z plane including the optical axis of the light beam to be incident, and a portion of each side surface is shared and integrated with each other.

Furthermore, the entrance and exit surfaces of the first and second branching members 18,19 are arranged at a predetermined angle with respect to a plane perpendicular to the optical axis of the destination beam to be incident, and preferably The first and second branch members 18, 19 are arranged in mutually different directions and at equal angles to the optical axis. In detail, for example, the entrance surface 18C of the first branching member 18
is set perpendicular to the X-2 plane, and at the same time its upper part is inclined at an acute angle and its lower part is arranged at an obtuse angle with respect to the Z-Y plane including the optical axis of the front beam. On the other hand, for example, the entrance surface 19C of one second branch member is
The upper part thereof is inclined at an obtuse angle and the lower part thereof is arranged at an acute angle with respect to the Z-Y plane which is perpendicular to the plane and includes the optical axis of the light beam. The angles of the incident surface and the exit surface of the branching member with respect to the optical axis of these incident light beams are set according to the cross-sectional shape of the light beam. It is set according to the detection method of the photodetector 20. As a result, the light beams that have passed through the first branching member 18 and the second branching member 19 are divided into the first light beam L1 which is substantially parallel to the optical axis of the incident light beam L and spaced apart from each other by a predetermined distance. The light beam is then split into a second light beam L2 and irradiated onto the photodetector 20.

In addition, in this embodiment, the upper surfaces of the first branch member 18 and the second branch member 19 are molded to be on the same plane. Therefore, the branching member 40 can be manufactured integrally with the container. When a light beam is incident on the branching member 40 configured in this manner, the light beam Ll transmitted through the first branching member 18 is slightly displaced upward in parallel and emitted, and is emitted from the other second branch. The light beam L2 transmitted through the member is slightly displaced downward in parallel and then emitted. Therefore, the light beam transmitted through the branching member 40 is divided into first and second light beams L having a constant width interval from each other.
It is branched into L2.

Further, the branching member 50 shown in FIG. 6 is different from the second branching member 19 shown in FIG. 5 except that the entrance surface and the exit surface are arranged perpendicular to the optical axis of the light beam to be incident. are the same. Therefore, when a light beam is incident on the branching member 40, the light beam L1 transmitted through the first branching member 18 is emitted as a light beam that is slightly displaced upward in parallel, similar to the branching member in FIG. , the light beam L2 transmitted through the other second branching member is transmitted straight.

Even if one side of the branching member 50 is tilted in this manner, the light beam transmitted through the branching member 50 is branched into first and second light beams L1 and L2 that are parallel to each other.

FIG. 7 shows the first light beam L branched by the branching members 18 and 19 shown in FIGS. 2, 4, 5, and 6.
A photodetector 20 is shown illuminated by the first and second light beams L2.

As shown in FIG. 7, the photodetector 20 includes a first group of photodetection areas 20A, 120B, 20H, 20 that converts the light irradiated through the first branching member 18 into an electrical signal.
A second group of photodetection regions 20C and 2 converts the light irradiated through the first and second branching members 19 into electrical signals.
0D, 20F.

It is composed of eight 20G photodetection areas.

The light detection area is divided by the dividing line 2 in the X direction as the first non-detection area.
1.22 in the vertical direction, and divided into four horizontally by dividing lines 23 to 25 in the Y direction. The distance between the dividing lines 23 and 24 is equal to the distance between the light beams that are branched substantially in parallel. The outputs of the separated detection areas 20A to 20I are used for focus correction, tracking correction, and information reproduction. Incidentally, the outputs detected in the detection areas 20A to 201 of the photodetector 20 are divided into (1) to (4). 8 and 9 show images of the light beam irradiated onto the photodetector shown in FIG. 7. FIG.

FIGS. 8A to 8C show images of the light beam irradiated onto the detection area in a focused state and in an unfocused state.

When the objective lens 16 is in a focused position with respect to the optical disc, an image as shown in FIG. 8B is projected onto the photodetector. The light beam that has passed through the first branching member 18 is projected as a semicircular image onto the first group of photodetection areas 20A, 120B, 20H, and 201. On the other hand, the light beam passing through the second branching member 19 is directed to the second group of photodetection areas 20C, 2.
0D.

It is projected onto 20F and 20G as semicircular images in opposite directions.

Parting lines 21 and 22 as first non-detection areas are predetermined so that each semicircular image is projected onto the left and right photodetection areas with equal intensity. In other words, the photodetection area 20A~
Assuming that the outputs of 201 are 1 to 2, respectively, the positions of dividing lines 21 and 22 are F at the time of focusing, as shown in FIG. 10A.

The position where the E signal is equal to 0, that is, the focus lens error - ((■+■+■+■)-(■+■+■+■))-
It is set so that the condition of 〇 is satisfied.

As a result, when the objective lens 16 moves away from the in-focus position with respect to the optical disc, the two semicircular images projected on the first group and the second group will be different from each other when in focus, as shown in FIG. 8A. is formed smaller than the image of F, and the output is F, E>0
becomes. Conversely, when the objective lens 16 approaches the in-focus position with respect to the optical disc, the two semicircular images projected onto the first group and the second group are smaller than the in-focus image, as shown in FIG. 8C. is also formed large, and the output is F, Eku0
becomes.

Further, FIGS. 9A to 9C show images of the light beam irradiated onto the detection area in the combined tracking state and the valve stand tracking state.

In FIGS. 9A to 9C, the dark area caused by diffraction of the guide groove on the optical disk 1 is located at the dividing line 2 of the photodetection area.
3 and 24. Therefore, the deviation of the track position is caused by the light detection area 2 as shown in FIG. 10A.
For output signals 0A to 201 ■ to ■, T, E () racking error) - ((■ + ■ + ■ + ■) - (■ + ■ +
It is detected by comparing ■+■)). The position of the optical head is adjusted with respect to the optical disk according to the difference signal of the compared signals, that is, the track position deviation signal.

Next, a circuit for processing electrical signals detected by a photodetector will be described with reference to FIG. The outputs of the photodetection areas 2OA and 20G are supplied to an amplifier circuit 31A. The outputs of photodetection regions 20D and 20H are supplied to amplifier circuit 31B. The outputs of the photodetection regions 20C and 201 are sent to the amplifier circuit 31.
C. The outputs of the photodetection regions 20B and 20F are supplied to an amplifier circuit 31D. Each amplifier 31A-3
Each signal supplied to 1D is amplified and supplied to an adder circuit 36. 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 amplifier circuit 31B is supplied to adder circuits 33 and 35. 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 provide a forcing control signal to voice coil driver 44 . That is, the output of the adder circuit 32 is supplied to the inverting input terminal of the differential amplifier 41, and the output of the adder circuit 33 is supplied to the inverting input terminal of the differential amplifier 41.
The output of is supplied to the non-inverting input terminal of the differential amplifier circuit 41. In the differential amplifier 41, the photodetection areas 2OA and 20G
.

Addition results of detection signals of 20B and 20F and photodetection area 20
The result of addition of the detection signals C, 201, 20D, and 20H is compared, and an output corresponding to the difference signal, that is, a focus control signal, is fed back to the drive circuit 44. A current is supplied to a coil (not shown) that drives the objective lens 16 in the forward axis direction in accordance with a defocus detection signal fed back to the drive circuit 44. 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 drive circuit 45. The output of the adder circuit 34 is supplied to the inverting input terminal of the differential amplifier 42, and the output of the adder circuit 35 is supplied to the non-inverting input terminal of the differential amplifier 42.

In the differential amplifier 42, the photodetection area 20A120G,
Addition results of detection outputs of 20C and 20I and photodetection area 2
The result of addition of the detection outputs of 0B, 20F, 20D, and 20H is compared, and an output corresponding to the difference, that is, a tracking deviation detection signal, is fed back to the drive circuit 45. 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 optical 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 this signal processing circuit 43 is used as a search signal for information reproduction.

The operation of the focus control device described above is shown below.

A diverging laser beam generated by the semiconductor laser 11 is converted into a manual beam by a collimator lens 13 and guided to a half prism 14 . The laser light guided to this half prism 14 is
After passing through the lens 4, the light enters the objective lens 16. The incident light beam is focused by the objective lens 16 toward the recording film of the previous disk 1 .

In recording information, bits are formed in tracks on the optical disc 1 by irradiating the optical disc 1 with a laser beam (recording beam) modulated with high 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. And half prism 14
The laser beam reflected by the spherical convex lens 17 is incident on the first and second branching members 18, 19 (40, 50).

The light beams incident on the first and second branching members 18 and 19 form a first light beam L1 that is substantially parallel to each other with their front axes as a boundary.
and the second light beam L2 is branched into the light detection areas 2OA, 20B, 20H, 201 and the light detection areas 20C, 20D of the photodetector 20.

Irradiates onto 20F and 20G. As a result, signals corresponding to the irradiated light are output from the photodetection regions 20A-201, and these signals are supplied to the amplifier circuits 31A-31,D.

A focusing operation in such a state will be explained. That is, the signal from the amplifier circuit 31A131D is supplied to the adder circuit 32.

Signals from amplifier circuits 31B and 31C are supplied to adder circuit 33. As a result, the photodetection areas 2OA, 20G, 2
The detection signals from 0B and 20F are added by an adder circuit 32 and supplied to a differential amplifier 41. Also, the light detection area 20C
120! , 20D, and 20H are sent to the adder circuit 3.
3 and supplied to the differential amplifier 41. As a result, in the differential amplifier 41, the photodetection area 20A120G
, 20B, 20F detection signal addition results and photodetection area 2
The addition results of the detection signals 0C, 201, 20D, and 2DH are compared, and the difference signal, that is, the focus control signal, is fed back to the drive circuit 44. Current is supplied to a coil (not shown) in response to a focus control signal fed back 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 focusing state of the light 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 31B131D is supplied to the adder circuit 35.

Thereby, the photodetection areas 2OA, 20G, and 20C.

The signals from 201 are added in an adder circuit 34 and supplied to a differential amplifier 42 . Photo detection area 20B120F, 20
The detection signals from D and 20H are added by an adder circuit 35 and supplied to a differential amplifier 42.

This results in photodetection areas 2OA, 20G, and 20C.

20! Detection signal addition result and detection area 20B120F
, 20D, and 20H are compared by a differential amplifier 42, and an output corresponding to the difference, that is, a tracking control signal, is fed back to the drive circuit 45. The coil (
(not shown) is supplied with current. The supplied signal drives the objective lens 16 on a plane perpendicular to its optical axis to control the tracking position of the light beam.

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. Therefore, the entire reproduction beam destination is intensity-modulated according to the recorded information and is incident on the photodetector.

The outputs of the photodetector regions 20A to 20I of the photodetector are supplied to amplifier circuits 31A, 131B, 31C, and 31D. The recorded data is reproduced by processing the total output of the amplifier circuits 31A, 31B, 31C, and 31D in the signal processing circuit 43.

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 is not limited to an eight-divided detector, and other four-divided photodetectors or other photodetectors may be used. For example, the focal position control signal is obtained by a four-part photodetector 20 having a simple configuration as shown in FIGS. 12A to 12C.

In the drawings of the following embodiment, the same reference numerals as those in the previously described embodiment of the invention indicate the same parts, and a description thereof will be omitted.

The photodetector 20 shown in FIGS. 12A to 12C has a first
20M and a second
It is composed of four photodetection areas, a second group of photodetection areas 2OL and 2ON, which convert the light emitted through the branching member 19 into an electrical signal.

When the objective lens 16 is in a focused position with respect to the optical disc, an image as shown in FIG. 12B is projected onto the photodetector 20. The light beam that has passed through the first branching member 18 is projected as a semicircular image at 20M onto the photodetection area 20 of the first group, and the light beam that has passed through the branching member 19 of the force cylinder 2 is projected onto the second group of photodetection areas 20 as a semicircular image. are projected onto the photodetection areas 2OL and 2ON as semicircular images in opposite directions. A dividing line 2 in the X direction as a first non-detection area is placed approximately in the middle of each semicircular image so that an image with the same light intensity as the left and right photodetection areas is projected.
1 and 22 are defined. In other words, if the outputs of ~2ON to the photodetection area 20 are represented by ■~■, respectively,
The dividing lines 21 and 22 are F, E-((■
+■)-(■10■)) - Set to satisfy the condition of 〇.

Furthermore, when the objective lens 16 moves away from the in-focus position with respect to the optical disc, the two semicircular images projected upward and downward are formed smaller than the in-focus image, as shown in FIG. 12A.
The output is E, F>0.

Conversely, when the objective lens 16 approaches the in-focus position with respect to the optical disc, as shown in FIG. 12C, two semicircular images projected upward and downward are formed larger than the in-focus image;
The output is E, F<0.

The output signal detected by the photodetector 20 shown in FIG. 12 is processed by the electric circuit of the control system shown in FIG. 13.

The output signal of ~2ON to the photodetection region 20 is sent to the amplifier circuit 31.
~31N, respectively. The signals amplified by the amplifier circuit 31K and the amplifier circuit 31N are supplied to the adder circuit 32. The signals amplified by the amplifier circuit 31L and the amplifier circuit 31M are supplied to the adder circuit 33. Addition circuit 32
The signal outputs added by one of the adder circuits 33 are supplied to the inverting input terminal of the differential amplifier 41, and the signal outputs added by one of the adding circuits 33 are supplied to the non-inverting input terminal of the differential amplifier 41.

The differential amplifier 41 compares the addition result of the detection signals of 2ON in the photodetection area 20 with the addition result of the detection signals of the photodetection areas 2OL and 20M. According to the compared difference output, that is, the defocus detection deviation signal, a current is supplied to a coil (not shown) that drives the objective lens 16 in a direction substantially perpendicular to the recording surface of the optical disc 1. is driven to correct defocus.

In all the embodiments described above, the branching element is formed by a glass plate 18, 19 having the shape of a parallel plate.

However, the branching member may also be made of other optically transparent materials. Moreover, its shape may also be changed as long as it exhibits the same effect. It is also possible to move the detector by moving the set position of the branching member. For example, in the embodiment of FIG. 2, the two branching members are arranged symmetrically with respect to the optical axis of the incident light beam. However, even if the two branching members are not arranged symmetrically on the optical axis of the incident light beam as shown in FIG. Similar detection is possible by

(Effect of the invention) The interval between the light beams L1 and L2 emitted in parallel to each other from the first and second branching members of the present invention is approximately constant without being affected by the deviation of each optical component in the optical axis direction. is maintained. Therefore, a focus control device is provided that is easy to assemble and adjust.

Further, in the focus control device of the present invention, the first and second branching members for branching an incident light beam into two mutually parallel light beams are integrally fixed to the support member. Further, a spherical convex lens for condensing the light beam is also integrally fixed to the support member. Therefore, a focus control device is provided that is further easy to assemble and adjust.

Further, in the focus control device of the present invention, the branching member molded into one body is molded so that the upper surfaces of the first and second branching members are on the same plane. Therefore, the branch member can be easily integrated and manufactured.

Furthermore, according to the photodetector used in the focus control device of the present invention, the focus control signal, forcing control signal, and information reproduction signal are obtained by the same detector. A more compact device is therefore provided.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a schematic configuration of an optical head equipped with a focus control device according to a first embodiment of the present invention, and FIG. 2 is a perspective view showing main parts of a focus control device according to a first embodiment of the present invention. Third
Figures A and 3B are optical path diagrams of the light beam incident on the condensing and branching member shown in Figure 2, and Figure 3A is an optical path diagram when the light beam is incident along the optical axis; Figure 3B is an optical path diagram when the optical axis of the first beam is shifted from the optical axis;
FIG. 5 is a perspective view showing the main parts of a focus control device according to a second embodiment of the invention, FIG. 5 is a perspective view showing main parts of a focus control device according to a third embodiment of the invention, and FIG. FIG. 7 is a front view of an eight-divided photodetector used in the focus control device of the present invention, and FIGS. 8A to 8C are perspective views showing essential parts of the focus control device of the fourth embodiment. A diagram showing a focused state and an unfocused state of the light beam irradiated to the photodetector shown in FIG. 7,
9A to 9C are diagrams showing the combined track state and non-life track state of the light beam irradiated to the photodetector shown in FIG. FIG. 11 is an electrical circuit diagram showing a method for processing all signals detected by a photodetector, and FIGS. 12A to 12C show the focused state of the irradiated light beam. FIG. 13 is an electric circuit diagram showing a method of processing signals detected by the photodetector shown in FIG. 12. FIG. DESCRIPTION OF SYMBOLS 1... Optical disk, 3... Optical head, 5... Guide groove (group), 8... Voice coil, 10...
Light condensing and branching member, 11... semiconductor laser (light source), 13
... Collimator lens, 14... Half prism,
16... Objective lens, 17... Spherical convex lens, 18
．． 19... Branching member, 20... Photodetector, 20A~
20I...Photodetection area, 20~2ON...Photodetection area, 21-25...Dividing line (non-detection area), 30.
... Supporting member, 31A to 31D... Amplifying circuit, 31 to 31N... Amplifying circuit, 32 to 36... Adding circuit,
41.42...Differential amplifier, 43...Signal processing circuit, 44.45...Voice coil drive circuit, 40, 5...Integrated branching member, L...Light beam,... First light beam, L2... second light beam.

Claims (2)

[Claims] (1) means for generating a light beam; focusing means for focusing the light beam onto a recording medium; and branching the light beam from the recording medium into first and second light beams that are substantially parallel to each other. a branching means for supporting the branching member; a supporting means for supporting the branching member; and a means responsive to the first and second light beams for adjusting the position of the focusing means with respect to the recording medium. Focus control device. (2) means for generating a light beam; focusing means for focusing the light beam onto a recording medium; and branching the light beam from the recording medium into first and second light beams that are substantially parallel to each other. A focus control device comprising: integrally molded branching means for: and means responsive to said first and second light beams for adjusting the position of said focusing means relative to said recording medium.