JPH07182713A - Pickup device for magneto-optical recording/reproducing - Google Patents

Abstract

PURPOSE:To provide a pickup device for a magneto-optical recording/ reproducing capable of miniaturizing the device and reducing costs by greatly reducing the number of parts, easily increasing a power for emitting lights to objects, easily adjusting positions on the optical axis of a light receiving element and easily designing an objective lens. CONSTITUTION:An objective lens 22 having a magnification rate of -6.0 to -12.0 is used and a positive spherical single lens 23 is provided between the objective lens 22 and an optical beam generating source 1 causing a combined magnificatin rate to -3.0 to -6.0. A light from the positive spherical single lens 23 is reflected by a multifunctional wallraston prism 21 having a polarizing light separating film 21c provided on light incident surface thereof, a reflective light from the objective lens 22 is transmitted by the wallraston prism 21 and made incident on an 4 optical sensor unit 26. By providing the prism 21 in the reflective light optical path, a nonparallel magnetic flux, inclined to optical axis thereof, astigmatism is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickup device for recording / reproducing information on / from a magneto-optical recording medium.

[0002]

2. Description of the Related Art In a magneto-optical recording / reproducing apparatus, conventionally, an infinite optical system, that is, a magneto-optical separation system utilizing birefringence such as a three-beam Wollaston prism in parallel light is used. The element is used to detect the magneto-optical signal.

FIG. 5 is a block diagram showing an example of the conventional magneto-optical recording / reproducing pickup device. A light beam generated by a light beam generation source 1 such as a semiconductor laser device is tracked by a diffraction grating 2. For generating a control signal, it is converted into three or more spot-shaped light beams, and these light beams are converted into parallel light beams by a collimator lens 3 which is usually composed of two pieces, and is focused through an objective lens 5 to form a magneto-optical disk. In the case of the reproducing operation, the polarization plane is rotated in the recording track in accordance with the magnetization reversal pattern corresponding to the information written in the perpendicular magnetization film.

The reflected light beam from the magneto-optical disk 6 is
The parallel light beam is returned to the beam splitter 4 by the objective lens 5, reflected by the beam splitter 4, and the reflected light beam is combined by the Wollaston prism 7 with the s-polarized component, the p-polarized component, and the s-polarized component and the p-polarized component. Separation into components, reflecting mirror 8, condenser lens 9, concave lens 1
0, incident on the photodetection unit 12 through the cylindrical lens 11 for obtaining the focusing error signal, determine the magnetization direction of the signal surface read from the intensity comparison of the p and s components, and determine the s polarization component and p A focusing error signal is obtained from the combined component with the polarization component by the astigmatism method, and a tracking error signal is obtained from the intensity comparison of the light beams of the sub beams on both sides of the three beams by the diffraction grating to obtain the focusing direction and the tracking direction. Create a control signal.

As another optical pickup device for a magneto-optical recording / reproducing apparatus having a conventional infinite optical system, parallel light from the collimator lens is disclosed in Japanese Patent Laid-Open No. 63-127436. The optical axis of the beam is converted (reflected) by the polarization beam splitter, the reflected light beam is condensed on the magneto-optical disk through the objective lens, and the reflected light beam is made into a parallel light beam again by the objective lens and passes through the polarization beam splitter. The light beam is separated into an s-polarized component, a p-polarized component, and a combined component of the s-polarized component and the p-polarized component by an analyzer to obtain a magneto-optical signal detection operation and the drive control signal in the focusing direction and the tracking direction. is there.

As described above, in all of the optical pickup devices used in the conventional magneto-optical recording / reproducing apparatus,
An infinite optical system is used to prevent changes in the separation characteristics of the polarization beam splitter 4 and the Wollaston prism 7 and to prevent deterioration of the magneto-optical signal. A certain collimator lens 3 and a condenser lens 9 for converting parallel light into a convergent light are required. Therefore, the structure is complicated, the number of constituent parts is large, and the entire optical pickup device is large.

In order to solve such a problem, as shown in FIG. 6, as an optical pickup device used in a magneto-optical recording / reproducing device, a device employing a finite optical system has been proposed (“O”). Plus E. "No. 163.
June 1993 p. 94-p. 95). In this pickup device, the divergent light from the light beam generation source 1 is passed through a convex lens 13 to enter the flat plate polarization beam splitter 14 as s-polarized light as it is, and is reflected by the polarization beam splitter 14. The diverging light beam is passed through the objective lens 15 to be focused on the recording surface of the magneto-optical disk 6, and the reflected light beam is made incident on the flat plate polarization beam splitter 14 as focused light by the flat lens polarization beam splitter 14. The film allows some of the s-polarized light and most of the p-polarized light to pass. Next, the half-wave plate 17 disposed on the back surface of the flat plate polarization beam splitter 14
Rotates the polarization direction by 45 °. After that, the flat plate analyzer 18 separates into three beams of p-polarized light, s-polarized light, and combined light of s-polarized light and p-polarized light, and the light detection unit 19 converts the light into electric signals.

In the pickup device shown in FIG. 6, in order to obtain accurate information in the photodetection unit 19, the flat plate polarization beam splitter 14 and the flat plate analyzer 18 are provided.
Since it is necessary to strictly adjust the angle with respect to the flat plate analyzer 18 and assembly is not easy, and since the flat plate analyzer 18 requires strict thickness control, it is not easy to manufacture. Also,
The half-wave plate 17 is provided in order to rotate the polarization plane by 45 ° and arrange the flat plate analyzer 18 in a planar manner. However, since the half-wave plate 17 is expensive, the price is low. There is a problem that it is difficult to achieve the purpose of reduction.

Further, as a pickup device of a finite optical system, Japanese Patent Laid-Open Nos. 5-142419 and 5-142242.
No. 0 and JP-A-5-142421. This device uses the Wollaston prism 21 shown in the perspective view of FIG. 7A and the side view of FIG. 7B, and the optical system is configured as shown in FIG. 7C to simplify the configuration. It has been transformed. The Wollaston prism 21 includes a light beam generation source 1 to the objective lens 1
5, a polarization separation film 21c for polarization-separating the light beam 24 incident on the beam 5 and the reflected light beam 25 passing through the objective lens 15 (this polarization separation film 21c is formed on the incident surface of the Wollaston prism 21 and has a refractive index of a dielectric thin film). Of the first prism 21a each of which is formed of a crystal body.
And the second prism 21b are bonded to each other,
A surface including the optical axis of the reflected light beam 25 that has passed through the objective lens 15 (the same applies to the optical axis of the incident beam 24 from the light beam generation source 1) and the optical axis 21d of the first prism 21a is the optical axis. And the optical axis 21 of the second prism 21b
e is a multifunctional Wollaston prism having a predetermined angle that is non-perpendicular to a surface including e, and is astigmatic by arranging it in the optical path of the reflected light that is a non-parallel light beam with an inclination to the optical axis. Is generated.

In this multifunctional Wollaston prism 21, as shown in FIG. 7B, a light beam a in which the P-polarized component and the S-polarized component are combined and a light beam b of the P-polarized component.
And the luminous flux c of the S-polarized component, and these are respectively received by the light receiving elements 16a, 16b and 16c shown in FIG. 7C, and the processing portion 16d compares the luminous fluxes b and c to obtain the detected information. And a focusing error signal is obtained by using a four-division photodiode for the light receiving element 16a as described later.

By using the multifunctional Wollaston prism 21 tilted with respect to the optical axis as described above, astigmatism for the focusing error signal is generated, and the polarization beam splitter and the cylindrical lens are connected to the Wollaston prism. The number of parts can be reduced, and the number of parts can be reduced. As in this example, the optical axis 21d of the first prism 21a is configured to be orthogonal to the optical axis of the light that passes through it, so that the blur of the light beam emitted from the Wollaston prism 21 can be eliminated. it can.

However, in the configuration of FIG. 7C, there is a problem that it is difficult to obtain the objective emission power only with the multifunction Wollaston prism 21. Further, it is necessary to adjust the position of the light receiving elements 16a to 16c in the optical axis direction, and this position adjustment work is troublesome.

In view of the above-mentioned problems, the present invention is capable of achieving a reduction in the number of parts, a reduction in size and cost, an increase in the objective output power, and an alignment of the light receiving element on the optical axis. It is an object of the present invention to provide a magneto-optical recording / reproducing pickup device that facilitates the design of the objective lens.

[0014]

In order to achieve the above-mentioned object, a magneto-optical recording / reproducing pickup device of the present invention has a light beam generating source and at least three light beams from the light beam generating source. And a diffraction grating for dividing the light beam from the light beam generation source into the magneto-optical recording medium so that the light beam is converged and incident on the magneto-optical recording medium, and the reflected light beam from the magneto-optical recording medium is received. As an object point
An objective lens having a magnification of 6.0 to -12.0 times, and a polarization separation film for polarization-separating a light beam incident on the objective lens from the light beam generation source and a reflected light beam passing through the objective lens And a surface including a first prism and a second prism, each of which is formed of a crystal body, bonded together, and including the optical axis of the reflected light beam passing through the objective lens and the optical axis of the first prism. Is a Wollaston prism having a predetermined angle that is non-perpendicular to the surface including the optical axis and the optical axis of the second prism, and is inclined to the optical axis in the reflected light optical path that is a non-parallel light beam. Is located between the Wollaston prism that generates astigmatism by disposing the light beam generation source, the light beam generation source, and the objective lens, and reduces the divergence of diverging light from the light beam generation source to reduce the divergence of the objective lens. And a positive spherical single lens having a composite magnification of −3.0 to −6.0 times with respect to the signal surface of the recording medium as an object point, and a plurality of light beams separated and emitted from the Wollaston prism are detected. And a photodetection unit having a built-in photodetection element.

Further, the present invention is characterized in that the diffraction grating and the positive spherical single lens are integrated to perform rotation and position adjustment.

[0016]

In the present invention, the objective lens having the above-mentioned magnification is used to form a finite optical system in which the condensing degree of the incident light in the Wollaston prism is weakened, and the divergent light emitted from the light beam generation source is formed. The positive spherical single lens reduces the divergence, shortens the optical path length, and increases the objective emission power. Further, by using the objective lens having the above-mentioned magnification, not only the finite system of the optical system can be achieved, but also the change of the separation characteristic by the Wollaston prism and the degree of the deterioration of the magneto-optical signal can be reduced. Also, the Wollaston prism causes astigmatism for producing a focusing error signal by inclining the incident surface with respect to the reflected light optical path. Further, aberration correction is facilitated by performing aberration correction not only on the objective lens but also on the positive spherical single lens. Further, by adjusting the position of the positive spherical single lens in the optical axis direction, it becomes possible to adjust the beam to be focused on the light receiving element. When the diffraction grating and the positive spherical single lens are integrated, it is possible to rotate the diffraction grating or adjust the position of the positive spherical single lens in the optical axis direction by using the same operating means.

[0017]

FIG. 1 is a block diagram showing an embodiment of a magneto-optical recording / reproducing pickup device according to the present invention. Reference numeral 1 denotes a light beam generation source formed of a semiconductor laser device, 20 denotes a diffraction grating that divides the light beam from the light beam generation source 1 into at least three or more light fluxes, 21 denotes a multifunctional Wollaston prism described with reference to FIG. Reference numeral 22 is an objective lens, 23 is a positive spherical single lens inserted between the diffraction grating 20 and the Wollaston prism 21, and 26 is a light detection unit.

The plane diffraction grating 20 has two sub-beams which are incident on the signal surface of the disc 6 when the disc 6 is incident on the disc 6 in order to generate a tracking error signal from the light beam emitted from the light beam source 1. The main beam of the beam is generated. The positive spherical single lens 23 reduces the divergence of the divergent light from the light beam generation source 1 and makes it enter the Wollaston prism 21. The polarization separation film 21c of the Wollaston prism 21 transmits or reflects the S component and the P component of the linearly polarized light incident thereon at a predetermined ratio. For example, 100% of the P component is transmitted, 30% of the S component is transmitted, and 70% of the S component is reflected. Then, the reflected divergent light is reflected toward the objective lens 22. The objective lens 22 focuses the reflected light beam on the signal surface of the magneto-optical recording medium 6. In the magneto-optical recording medium 6, the plane of polarization is rotated according to the magnetization reversal pattern corresponding to the information written in the perpendicular magnetization film. The reflected light beam from the magneto-optical recording medium 6 in which the polarization plane is rotated in this way is obliquely incident again on the Wollaston prism 21 as converged light in the objective lens 22 and is separated. The light flux that has passed through the polarization separation film 21c is divided into three light fluxes a, b, and c and emitted as shown in FIG. 7B.
Then, the information is read by comparing the intensities of the light beams b and c as described above. That is, when the intensities of the light beams b and c are Ib and Ic, respectively, Ib> Ic or Ib <Ic depending on the rotation direction on the polarization plane of the disk surface.
Becomes Accordingly, the intensities Ib and Ic of the respective light rays are used to detect the light receiving elements 16b and 16c included in the sensor unit 26.
It is possible to judge the information written on the disk surface by comparing the output of the detection with the output.

As shown in FIG. 2A, the dispersion of the light beam in the photo-detecting unit 26 is as follows. The light beams a, b and c separated by the Wollaston prism 21 of the main beam and the sub beam d. , E and f, g separated from each other in the Wollaston prism 21
And h and i, among these beams,
As shown in (B), the intensities of the sub-beams d and e are detected by the sensors 35 and 36, and the magnitude relationship between them is compared with a comparison circuit 37.
The tracking error signal is obtained by a known method for comparison with the above, and a tracking control signal is generated based on this, and the objective lens 22 is moved in the radial direction of the disk 6 so that the light beam is irradiated onto the track.

FIG. 2 shows a photodetector section for receiving the light flux a.
As shown in FIG. 2C, the optical sensor 40 is divided into four parts in the directions A to D of FIG.
43 is arranged and a known method of obtaining a focusing error signal of (A + B)-(C + D) in the arithmetic circuits 44 to 46 for these sensor outputs is used, and the objective lens 22 is moved in the optical axis direction based on this signal. The beam is always focused on the recording surface of the disc. When this method is used, the Wollaston prism 21 also functions as a cylindrical lens, and when the focal point is on the disc signal surface, the spot of the light beam a becomes circular,
(A + B)-(C + D) becomes zero, and in other cases it becomes a positive or negative value.

In the present invention, a positive spherical single lens 23 is provided between the light beam source 1 and the Wollaston prism 21.
Since the light beam generating source 1 and the Wollaston prism 21 can be shortened, the distance between the light beam generating source 1 and the Wollaston prism 21 can be further reduced, and the utilization efficiency of the light beam emitted from the light beam generating source 1 can be improved. The objective output power can be increased. Further, not only the objective lens 22 but also the positive spherical single lens 23 is responsible for the aberration correction, so that the aberration correction of the entire system can be easily performed.
Further, by moving the position of the single lens 23 in the optical axis direction, the focusing position of the light beam can be adjusted with respect to the light receiving element of the sensor unit 26, and the light receiving element 16a shown in FIG. The position adjustment becomes easier as compared with the case where the position adjustment of ~ 16c is performed.

In the case of constructing such an optical pickup device, as shown in FIG. 3A, the signal surface of the disk 6 is used as an object point (focusing point of the light beam of the objective lens 22).
Let L1 be the distance between the front principal point of the objective lens 22 and the object point, and L2 be the distance between the rear principal point of the objective lens 22 and the image point.
The ratio, that is, the magnification L2 / L1 = −6.0 to −12.
It is preferably 0, and more preferably -7.0 to -9.0. In a conventional optical pickup device for an optical disc, as a finite optical system, -4.0.
However, since the change of the separation characteristic in the Wollaston prism 21 and the deterioration of the magneto-optical signal are caused at such a magnification, only a weak read output can be obtained. In the case of being configured as the pickup device of, the magnification is preferably -6.0 or more (as an absolute value). Further, in order to achieve the object of compactification, the -1
When it exceeds 2.0, the optical detection unit 26 from the disc 6
It is not practical because the length up to Also, FIG.
As shown in (B), the composite magnification L3 / L1 when the spherical single lens 23 is included may be -3.0 to -6.0 times (more preferably -3.5 to -5 times). preferable. If this magnification L3 / L1 is less than -3.0, it becomes difficult to correct aberrations, while if it exceeds -6.0, the efficiency of capturing light from the light beam generation source 1 decreases, and the required objective emission power. Is not profitable.

FIG. 4 shows an example of a suitable mounting structure for the diffraction grating 20 and the single lens 23 in the present invention.
As shown in the perspective view of FIG. 4A and the vertical sectional view of FIG. 4B, the diffraction grating 2 is provided in a cylindrical case 50 having a hollow interior 52.
0 and the single lens 23 are accommodated to adjust the rotation direction of the diffraction grating 20 (shown by an arrow R) and the optical axis direction of the single lens 23 for focusing the light beam to the light receiving element (shown by an arrow X, 55 indicates the incident light) and the operating pin mounted in the radial direction on the tubular case 50 is used for adjusting the position R,
This is done by operating in the X direction. That is, the operation pin 51 is inserted into and fixed to the hole 50a provided in the cylindrical case 50 in the radial direction, and the pin 51 is penetrated into the fool hole 54a provided in the housing 54.
As shown in the cross-sectional views of FIGS. 4B and 4C, the case 50 is rotated about the axis of the case 50 by a leaf spring 53 fixed to the housing 54 and is slidable in the optical axis direction. It is mounted by pressing on the corner portion of the housing 54 so as to be movable.

Thus, the diffraction grating 20 and the single lens 23
By integrating and, it becomes easy to assemble and adjust, and the structure becomes simple, which can contribute to downsizing.

[0025]

According to the first aspect of the present invention, since the functions of the polarization beam splitter and the cylindrical lens are exerted by one Wollaston prism by using the multi-function Wollaston prism, the number of parts can be reduced. Needless to say, since the positive spherical single lens is provided between the light beam generation source and the objective lens, the optical path length can be shortened, so that it can be made more compact and cost can be reduced. The utilization efficiency of the light beam emitted from the light beam generation source can be increased, and the objective emission power can be increased. Further, not only the objective lens but also the positive spherical single lens is responsible for the aberration correction, so that the aberration correction can be easily performed and the objective lens can be easily designed. Also,
By moving the position of the positive spherical single lens in the optical axis direction, the focus position of the light flux is adjusted with respect to the light receiving element of the optical sensor unit. Compared with the case of adjusting, the adjusting structure becomes simpler and the adjustment can be performed easily.

According to the second aspect, since the diffraction grating and the single lens are integrated, assembly and adjustment are facilitated,
The configuration is simple and contributes to downsizing.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magneto-optical pickup device according to the present invention.

2A is a diagram showing an arrangement of light spots received by a photodetection unit, FIG. 2B is a circuit diagram showing a tracking error detection circuit, and FIG. 2C is a circuit diagram showing a focus error detection circuit. .

3A is an explanatory diagram of a magnification of an objective lens, and FIG. 3B is an explanatory diagram of a synthetic magnification obtained by combining the objective lens and a positive spherical single lens.

4A and 4B show an example of a combined structure of a diffraction grating and a positive spherical single lens according to the present invention, where FIG. 4A is an exploded perspective view of a case, and FIGS. It is a longitudinal sectional view and a transverse sectional view showing a state.

FIG. 5 is a configuration diagram showing an example of a pickup device of a conventional magneto-optical recording / reproducing apparatus.

FIG. 6 is a configuration diagram showing another example of a pickup device of a conventional magneto-optical recording / reproducing apparatus.

7A is a perspective view showing a multifunctional Wollaston prism used in a pickup device of a conventional magneto-optical recording / reproducing apparatus, FIG. 7B is a side view thereof, and FIG. 7C is a perspective view of the Wollaston prism. It is a block diagram of a pickup device of the magneto-optical recording and reproducing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light beam generation source 6 magneto-optical disk 20 plane diffraction grating 21 multifunctional Wollaston prism 21a first prism 21b second prism 21c polarization separation films 21d and 21e optical axis 22 objective lens 23 positive spherical single lens 26 light Detecting unit 50 Cylindrical case 51 Operating pin 53 Leaf spring 54 Housing 54a Dumb hole

Claims (2)

[Claims] 1. A light beam source, a diffraction grating for splitting the light beam from the light beam source into at least three or more light beams, and a light beam from the light beam source focused on a magneto-optical recording medium. And an incident lens which receives the reflected light beam from the magneto-optical recording medium and has a magnification of -6.0 to -12.0 times with the signal surface of the magneto-optical recording medium as an object point, A first prism and a second prism each having a polarization separation film for polarization-separating a light beam incident on the objective lens from a light beam generation source and a reflected light beam passing through the objective lens are formed. And a surface including the optical axis of the reflected light beam that has passed through the objective lens and the optical axis of the first prism with respect to a surface including the optical axis and the optical axis of the second prism. Non-right angle That a Wollaston prism having a predetermined angle,
A Wollaston prism that generates astigmatism by arranging the light beam in the reflected light optical path, which is a non-parallel light beam, at an angle to the optical axis; and between the light beam generation source and the objective lens, A positive spherical single lens that reduces the divergence of divergent light from the light source and makes the composite magnification with the objective lens -3.0 to -6.0 times the signal surface of the recording medium as an object point; A magneto-optical recording / reproducing pickup device, comprising: a photo-detecting unit having a plurality of photo-detecting elements for detecting a light beam separated and emitted from the Wollaston prism. 2. The pickup device for magneto-optical recording and reproduction according to claim 1, wherein the diffraction grating and the positive spherical single lens are integrated to perform rotation and position adjustment in the optical axis direction.