JPH0758554B2 - Optical head device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information processing apparatus for recording, reproducing and erasing information by using light, and more particularly to an optical axis of a light beam for information storage and reproduction and information. The present invention relates to an optical head device that corrects an angle with a recording surface of a storage medium.

[Prior Art] A conventional optical head device will be described with reference to FIGS. 11 to 15. In the figure, 1 is a semiconductor laser (hereinafter referred to as LD) which is a light source for emitting a diffused light flux, 2 is a light flux emitted from the LD 1, and 3 is a diffraction which separates the light flux 2 emitted into three light fluxes having different converging positions. The grating, 7 is a collimating lens that makes the emitted light beam 2 into a parallel light beam 2a, and 5 is a light collecting lens that is a light collecting means for collecting the parallel light beam 2a on an optical disk 6 which is an information storage medium. Has a track 8 on which information is stored concentrically. Reference numeral 4 reflects the outgoing light beam 2, makes it enter the collimating lens 7, and reflects the reflected light beam 2b from the optical disk 6 into the outgoing light beam 2
The beam splitter 4 is a flat plate-shaped beam splitter which separates the reflected light beam 2b and the reflected light beam 2b, which is first-order diffracted light, into astigmatism and has a fringe shape with a grating period that gradually changes within the aperture. Let 2b be a light beam given astigmatism. Reference numeral 10 is a first photodetector that receives the reflected light beam 2b. As shown in FIG. 12, the first photodetector 10 is divided into four optical elements 11a to 11d inside, and a main detector 11t for detecting a main reflected light beam 2t and a main detector 1t.
Comprising optical elements 11e, 11f arranged on both sides of 1t, arithmetic elements 12, 13, 16 for performing each arithmetic operation based on the output signal of each optical element 11a ~ 11f, and phase compensation circuits 18, 19. Have. 2
Reference numerals 0 and 21 denote a focusing actuator and a tracking actuator, which are the first driving means. The focusing actuator 20 drives the condenser lens 5 in the optical axis direction (± Z axis direction), and the tracking actuator 21 operates as described above. The condenser lens 5 is driven in the direction perpendicular to the track 8 (± X axis direction). 26 is a motor for rotating the optical disk 6. As shown in FIG. 15, the condensing lens 5 has a condensing part 5a for condensing the emitted light flux 2a, a flange part 5b for holding the condensing part 5a, and a condensing lens 5 for the flange part. It is composed of a mounting portion 5c which is mounted on each of the actuators 20 and 21 via 5b, and is integrally molded or processed.

In the above configuration, the outgoing light flux 2 emitted from LD1 is
The diffraction grating 3 separates the light into two outgoing light beams 2. Next, the emitted light beam 2 is reflected by the beam splitter 4, and is collimated by the collimator lens 7 and the condenser lens 5 through the transparent substrate 25 of the optical disc 6 as three aberration-free condensed spots 9a, 9e, 9f of the optical disc 6. The track 8 on the recording surface 27 is irradiated. Then, the reflected light beam 2b diffused and reflected from the optical disk 6 again enters and passes through the beam splitter 4 via the condenser lens 5 and the collimator lens 7, is separated from the outgoing light beam 2, and is transmitted through this beam splitter 4 The reflected light beam 2b with point aberration is incident on the first photodetector 10. The first photodetector 10 is placed at the position in the optical axis direction (Z direction) where the reflected light beam 2b becomes the minimum circle when the focused spot 9a on the optical disc 6 is in focus. At this time, the reflected light beam 2b is three reflected light beams.
2t, 2e, 2f, the reflected light beam 2t is the main light detector 11t
The reflected light beam 2e is reflected by the optical element 11e, and the reflected light beam 2f is reflected by the optical element 11f.
Is received by. Each optical element 11a of the main light detection unit 11t ~
The reflected light beam 2t is detected by 11d and a signal is output, and the arithmetic element 16 calculates [11a + 11b + 11c + 11d] based on the above output to obtain the sum output V _HF which is a reproduction signal. Can be read.

However, in the optical disc 6, the center of rotation of the motor 26 and the center of the optical disc 6 do not normally coincide with each other due to a mounting error or the like. Therefore, the track shift occurs due to the rotation. The twin spot method is known as a method for detecting the track deviation. Since the reading of information must be performed correctly on the track 8 in order to perform reading at the focused spot 9a, the line connecting the focused spots 9a, 9e, 9f is arranged so as to be slightly inclined with respect to the track 8. The focused spots 9e and 9f are diffused and reflected to become reflected light beams 2e and 2f, respectively.
The light is received by the optical elements 11e and 11f via the collimator lens 7, the condenser lens 5 and the beam splitter 4. This optical element 1
The outputs of 1e and 11f (the difference in reflection intensity between the focused spots 9e and 9f) are obtained by the arithmetic element 13, and the phase compensation circuit 18 obtains an output proportional to the track deviation, that is, the tracking error signal V _AT . This tracking error signal V
_AT is applied to the tracking actuator 21 to operate it, and the focused spot 9a is constantly focused on the center of the track 8.

Further, the surface of the optical disk 6 is usually not flat, and surface wobbling occurs due to rotation, and defocus occurs.

As this defocus detection method, an astigmatism method is known in which astigmatism is applied to the reflected light beam 2b from the optical disk 6 and the defocus is detected from the change in the shape of the light beam. Hereinafter, a method of detecting a focus shift will be described. The beam splitter 4 gives astigmatism to the reflected light beam 2b. At this time, the first photodetector
In the detection area of the main photodetector 11t of 10, the reflected light flux 2t changes such that the elliptical direction differs by 90 ° from the circle to the perspective due to the shift of the focal position of the condenser lens 5 on the optical disk 6.
That is, from the reflected light beam 2t in the reference state of Figure 12, the reflected light beam 2t ₁ when the optical disc 6 approaches the focal position, when away changes as reflected light beam 2t _2. The change in the reflected light flux 2t is detected by the optical elements 11a to 11d. Each of the optical elements 11a to 11d outputs an output corresponding to the amount of received light, and the computing element 12 outputs [(11a + 11c)-(11b + 11
d)] is calculated to obtain a comparison output, and the phase compensation circuit 19
Thus, an output proportional to the focus shift, that is, a focusing error signal V _AF is obtained. This focusing error signal V _AF is applied to the focusing actuator 20 to operate it, and the focus shift of the focused spot 9 on the optical disk 6 is corrected. As described above, the conventional optical head device has the beam splitter 4, and the beam splitter function and the astigmatism generating function for detecting the focus shift can be realized by one component, so that the configuration is simple. Further, since the diffraction grating 3 is provided and the twin spot method is used, stable tracking deviation can be corrected.

It has been well known that the direction of astigmatism generated by the flat beam splitter 4 is preferably 45 ° with respect to the extending direction of the track 8 (Y direction). The luminous flux 2 is arranged so as to form an angle of 45 ° with respect to the Y direction.

Further, in the conventional optical head device, when recording and reproducing of information is performed through the transparent substrate 25, the recording surface 27 is not recorded due to the warp of the transparent substrate 25, the inclination of the optical disc 6 when mounted on the motor 26, and the like. It may not be perpendicular to the optical axis of the condenser lens 5. That is, for example, the transparent substrate 25 having a thickness of about 1.25 mm is incorporated in the lens design as one element of the objective lens together with the condenser lens 5. However, when the transparent substrate 25 is tilted, coma aberration occurs, and the original recording, There is a problem that the black stroke from the adjacent tracks 8a and 8b of the track 8 to be reproduced increases. This phenomenon has been a serious problem in that the image quality is deteriorated especially in an optical video disc in which analog signals are recorded. In the conventional optical head device, in order to solve the above problem, the perpendicularity between the optical axis of the condenser lens 5 and the transparent substrate 25 is secured by the tilt servo. This tilt servo will be described with reference to FIG. In the figure, reference numeral 33 denotes a head holding portion having a housing and having the optical head device therein, and the head holding portion 33 is rotatably supported by a support body 35 by a rotary shaft 34. 36 is a motor which is a second driving means for driving the head holding part 33, 37 is a screw provided on the shaft of the motor 36 and screwed to the end of the head holding part 33, and 30 is the head holding part The emitting diodes (hereinafter referred to as LEDs) 31, 32 arranged on the upper surface of the portion 33 are second photodetectors for detecting the reflected light beam 30b reflected by the optical disk 6. The LED 30 and the second photodetectors 31, 32 are arranged in a line in the X direction. Reference numeral 38 is a subtractor that calculates the outputs of the photodetectors 31 and 32, and 39 is a phase compensation circuit.

The operation of the tilt servo will be described. The light ray 30a emitted from the LED 30 is reflected by the recording surface 27 of the optical disc 6 to become a reflected light ray 30b, and this reflected light ray 30b is incident on the second photodetectors 31, 32 arranged on both sides of the LED 30. . Second
The outputs of the photodetectors 31 and 32 of [31-3] are input to the subtractor 38 and [31-3
2] is calculated. The amount of light incident on the second photodetectors 31 and 32 is set to be equal when the optical axis of the condenser lens 5 and the transparent substrate 25 are vertical as shown in FIG. Therefore, when the transparent substrate 25 is tilted about the Y direction as shown in FIG. 14, the amount of light incident on the second photodetectors 31 and 32 becomes unbalanced. Therefore, the output of the subtractor 38 changes between positive and negative depending on the inclination of the transparent substrate 25. Subtractor 38
Is applied to the motor 36 via the phase compensation circuit 39,
The head holding unit 33 rotates according to the rotation speed of the screw 37.
It is rotated around 34. In this way, the optical axis of the condenser lens 5 and the transparent substrate 25 are always kept perpendicular, the occurrence of coma aberration is minimized, and the increase of black stroke from the adjacent tracks 8a, 8b is prevented.

[Problems to be Solved by the Invention] Since the conventional optical head device is configured as described above, a light source (LED30) for tilt detection must be newly provided in order to prevent occurrence of coma aberration. Additional optical components are required, which increases the cost. Further, there is not so much space between the upper surface of the head holding portion 33 and the transparent substrate 25 of the optical disk 6, and the LED 30 and the second photodetector 31,
There is a problem that the arrangement of 32 is a big constraint on the design of the optical head device.

The present invention has been made to solve the above problems, and an optical system that can prevent coma from occurring without newly providing a light source for tilt detection and can simplify the configuration of the device and reduce the size thereof The purpose is to obtain a head device.

[Means for Solving the Problem] An optical head device according to the present invention is provided on the outer periphery of a light converging means, changes a traveling direction of a part of a light flux emitted from a light source, and separates the light flux onto an information storage medium. And a second photodetector for receiving the reflected light flux separated by the refraction means and reflected by the information recording medium.
The correction control of the second driving means for correcting the angle between the optical axis of the light collecting means and the recording surface of the information storage medium is performed by the output of the photodetector.

[Operation] In the optical head device according to the present invention, the refracting means provided on the outer periphery of the light collecting means and the second detecting means for detecting the separated reflected light flux
And a second photodetector detects the separated reflected light flux from the information storage medium by changing the direction of travel and separating a part of the light flux emitted from the light source. Then, correction control of the second driving means is performed based on the output of the second photodetector so that the angle between the optical axis of the light collecting means and the recording surface of the information storage medium is always kept vertical. .

[Embodiment] An optical head device according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 5. Note that FIG. 11 to FIG.
15 that are the same as those in FIG.
In the figure, 55 is a condenser lens.
As shown in FIG. 2 and FIG. 3, is a condensing part 55a for condensing the light beam 2 emitted from the LD1 at the center and the light beam 2 for emission.
Is deflected so as to spread in the X direction to change the traveling direction to separate the outgoing light beam 2 and a prism portion 55b which is a refraction means for generating a tilt outgoing light beam 50a. The prism portion 55b of the condenser lens 55 is obtained by processing the flange portion 5b of the conventional condenser lens 5 shown in FIG. 15 into a prism shape. Reference numeral 52 denotes a second photodetector, which is composed of optical elements 53a to 53d, has subtraction elements 61, 61 and an addition element 62, as shown in FIG. 4, and is provided on both sides of the condenser lens 55. , X-direction are arranged in a line.

In the above configuration, the outgoing light flux 2 that has passed through the condenser lens 55
Is condensed only the light flux incident on the condensing part 55a to become three condensing spots 9a, 9e, 9f on the optical disk 6. The condensed spots 9a, 9e, 9f are diffused and reflected by the optical disc 6 to form a reflected light beam 2b, which is incident on the first photodetector 10. Further, the outgoing light flux 2 that has entered the prism portion 55b is changed in the traveling direction in the X direction by the prism portion 55b to become a tilt outgoing light flux 50a, and becomes tilt spots 51a and 51b on the recording surface 27 of the optical disk 6. The tilt spots 51a and 51b are reflected by the optical disc 6 to become a tilt reflected light flux 50b.
The tilt reflected light flux 50b is incident on the second photodetector 52. The outputs of the optical elements 53a to 53d are input to the subtractor 61 and the adder 62, respectively, and are given as [(53a-53b) + (53c
-53d)] is performed to obtain the tilt detection signal 63. The amount of light incident on the optical elements 53a, 53b and the optical elements 53c, 53d is set to be equal when the optical axis of the condenser lens 55 and the transparent substrate 25 are in the vertical state as shown in FIG. 5 (b). Has been done. Therefore, when the transparent substrate 25 is tilted about the Y direction, the amount of light incident on the optical elements 53a and 53b and the optical elements 53c and 53d becomes unbalanced. That is, as shown in FIG. 5 (c), when the outer circumference of the optical disk 6 is tilted to be low, the output of the optical elements 53a and 53c becomes larger than the output of the optical elements 53b and 53d, and FIG. ), The optical element 53a,
The output of 53c is smaller than the outputs of the optical elements 53b and 53d. Therefore, the tilt detection signal 63 changes between positive and negative depending on the inclination of the transparent substrate 25. By applying the tilt detection signal 63 to the motor 36, the angle between the optical axis of the condenser lens 55 and the recording surface 27 of the optical disk 6 can be always kept in the vertical state.

Further, in the method of using ambient light which is originally weak in intensity, the emitted light beam is refracted by the prism portion 55b, and the reflected light from the optical disk 6 is received by the photodetector 52 shown in FIG. The strength of can be taken large. further,
Light is obliquely incident on the optical disk 6 by the prism portion 55b, so that the reflected light does not return to the condenser lens 55 again, and therefore does not return to the first photodetector 10. The detection light received by the first photodetector 10 does not unnecessarily affect information reading or servo signal detection.

In the present embodiment, the second photodetector 52 is composed of the optical elements 53a to 53d and arranged on both sides of the condenser lens 55, but as shown in FIGS. 6 (a) to 6 (c). In addition, the second photodetector 52 may be arranged on only one side. At this time, the prism portion 55b of the condenser lens 55 only needs to be on the side where the second photodetector 52 is located. Further, each of the second photodetectors 52 is composed of one optical element 53a, 53b as shown in FIGS. 7 (a) to 7 (c), and the tilt detection signal is obtained by the circuit shown in FIG. Even if you get 63, you get the same effect.

Further, in this embodiment, the condenser lens 55 is
55a and a prism portion 55b for refracting the outgoing light beam 2 in the X direction
However, the prism portion 56b of the condenser lens 56
May have a lens function of refracting the outgoing luminous flux 2 in the X direction and condensing the refracted tilt outgoing luminous flux 50a, as shown in FIG.
Since the tilt-reflected light flux 50b entering the photodetector 52 is condensed, it has an effect of further increasing the sensitivity of tilt detection.

Further, in the present embodiment, the outgoing light flux 2 is collimated by the collimator lens 7 into the parallel light flux 2a, and then is condensed by the condenser lens 5. However, as shown in FIG.
The same effect can be obtained even with a finite system condensing lens capable of condensing without using the collimator lens 7. At this time, since the outgoing light flux 2 that is incident on the prism portion 57 of the condenser lens 57 is a diffused light flux, it is preferable to use a structure in which the prism portion 57b has a lens function like the condenser lens 56 of FIG. desirable.

As described above, according to the present invention, the optical head device is
A refraction unit which is provided on the outer periphery of the light converging unit, separates a part of the light flux emitted from the light source by changing the traveling direction and irradiates the information storage medium, and the refraction unit separates and reflects the information recording medium. Second drive means for correcting the angle between the optical axis of the condensing means and the recording surface of the information storage medium by the output of the second photodetector. Since the correction control is performed, it is not necessary to newly provide a light source for tilt detection, and the size is reduced by the simple configuration.

Further, as in the present application, in the method of using the ambient light, which is originally weak in intensity, the outgoing light beam is refracted by the refracting means and the reflected light from the optical disc is received. High detection light intensity can be obtained.
Further, it is possible to obtain a highly reliable device in which the detection light received by the first photodetector does not unnecessarily affect information reading or servo signal detection.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical head device according to an embodiment of the present invention, FIGS. 2 and 3 are sectional views and a plan view of a condenser lens, and FIG. 4 is a configuration of a second photodetector. Figure, Figure 5 (a)
6A to 6C and FIGS. 6A to 7C are tilt detection operation diagrams of other embodiments, and FIG. 8 is another embodiment. A block diagram of an example second photodetector,
9 and 10 are configuration diagrams of an optical head device of another embodiment, FIG. 11 is a configuration diagram of a conventional optical head device, and FIG.
FIG. 13 is a configuration diagram of a photodetector, FIGS. 13 and 14 are configuration diagrams of tilt detection, and FIG. 15 is a sectional view of a condenser lens. 1 ... LD, 2 ... outgoing light flux, 2b ... reflected light flux, 3 ... diffraction grating, 4 ... beam splitter, 6 ... optical disk,
7 ... Collimating lens, 9a ... Focus spot, 10 ...
First photodetector, 50a ... Tilt output light flux, 50b ... Tilt reflection light flux, 51a, 51b ... Tilt spot, 52 ... Second
Photodetectors, 53a-53d …… Optical element, 55 …… Condenser lens,
55a: light condensing part, 55b: prism part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Yoshihara, No. 1 Baba Institute, Nagaokakyo, Kyoto Prefecture Mitsubishi Electric Corporation, Electronic Products Development Laboratory (72) Inventor, Takashi Saito, No. 1 Baba Institute, Nagaokakyo, Kyoto Mitsubishi Electric (56) Reference JP 63-66735 (JP, A) JP 59-33637 (JP, A) JP 60-32143 (JP, A)

Claims (5)

[Claims] 1. A light collecting means for collecting and irradiating a light beam emitted from a light source onto an information storage medium, a light beam separating means for separating a light beam reflected from the information storage medium from the light beam emitted, and a light beam receiving the reflected light beam. A first photodetector, and first drive means for performing attitude control of focus error and tracking error of the light condensing means by the output of the first photodetector,
An optical head device comprising a second drive means for correcting the angle between the optical axis of the light converging means and the recording surface of the information storage medium, the optical head device being provided on the outer periphery of the light converging means, And a second photodetector for receiving the reflected light flux separated by the refraction means and reflected by the information recording medium. And an optical head device comprising: a second photodetector for correcting and controlling the second drive means by the output of the second photodetector. 2. The second photodetector comprises two sets of two-divided photodetectors, each photodetector being arranged in the radial direction of the information storage medium with the condensing means interposed therebetween. The optical head device according to claim 1, wherein: 3. The second photodetector comprises a set of two-divided photodetectors, and is arranged in the radial direction of the information storage medium with respect to the light converging means. The optical head device according to item 1. 4. The second photodetector is composed of two sets of one-divided photodetectors, and each photodetector is arranged in the radial direction of the information storage medium with the condensing means interposed therebetween. The optical head device according to claim 1, wherein: 5. The refracting means has a lens function of condensing a refracted light beam.
An optical head device according to the item.