JPH0721890B2 - Magneto-optical head device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical head device for a magneto-optical disk player applied to a magneto-optical disk capable of recording / reproducing / erasing information.

2. Description of the Related Art Conventionally, a magneto-optical head device for a magneto-optical disc player has
Since the beam utilization efficiency of the laser light source is good, a one-beam system that detects signals is often used. In this one-beam type magneto-optical head device, for example, focus error detection is performed by the astigmatism method, and tracking error detection is performed by the push-pull method. Focus error detection and tracking error detection are performed by separating the return light reflected from the disc into two directions via a half-wave plate and a polarization beam splitter in the return path optical system that constitutes the signal detection system. This is performed by arranging photodetectors in each of the specified directions and detecting the light received by each photodetector. The Kerr rotation angle of the reflected return light is detected by the differential output of the signals detected by the two photodetectors, and the information is read.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the conventional one-beam type magneto-optical head device, disk eccentricity / surface deviation (± 70 μm / ± 0.
If it is large (about 5 mm), there is a problem that the tracking characteristic becomes unstable, and there is a problem in reliability in practical use.

To improve this tracking characteristic, eccentricity of the disc
It is known that a 3-beam type signal detection method that is strong against surface wobbling may be adopted. However, in the three-beam method, the laser light is split into three beams to irradiate the disc,
Since the reflected light is guided to the photodetector by three beams, the optical system becomes complicated, expensive, and not suitable for mass production. Further, the return path optical system that constitutes the error signal detection and Kerr rotation angle detection system needs an expansion optical system for separating the return light from the disk into three beams, and the light detector is completely separated into three beams. A long optical path length was needed to guide. Therefore, there is a problem that the main body of the magneto-optical head device becomes large.

The present invention has been made in view of the above points, and an object of the present invention is to provide a head structure that is small in size, inexpensive, and suitable for mass production, while making full use of the characteristics of the three-beam method having good tracking characteristics and high reliability. I am trying.

Means for Solving the Problems In order to achieve the following object, the present invention provides a magneto-optical head device applied to a magneto-optical disk player for performing magneto-optical recording / reproducing / erasing on a magneto-optical disk. A diffraction grating that separates the laser beam into 0th order light and ± 1st order light is arranged on the outward path that guides the laser beam from the laser light source to the disk surface through the objective lens. A half mirror that separates the return light into two directions is provided in the return path that guides the return light to the photodetector through the objective lens, and the ± first order light is removed in one direction of the return light separated by this half mirror, and only the zero order light is emitted. It is characterized in that a shielding plate having a slit for taking out light is arranged, and the Kerr rotation angle of the 0th-order light is detected by receiving and detecting the 0th-order light passing through this slit with a photodetector. That.

Effect According to the present invention, only the 0th-order light of the three beams of the return light is extracted through the shielding plate having the slit, and the Kerr rotation angle is detected using only the 0th-order light. I am trying to read it. Therefore, the optical path length of the Kerr rotation angle detection system in the 3-beam system is shortened, and the optical system is simplified. Therefore, the head structure becomes small and compact. Since the error signal is detected by the 3-beam method, the tracking characteristic is good and the reliability of the head device is kept high.

EXAMPLES Examples of the present invention will be described below with reference to the drawings.

1 and 2 show a magneto-optical head device according to the present invention, in which 10 is an opt base, 11 is a laser diode, 12 is an objective lens, and 13 is an objective lens actuator.

High-power laser diode at one end of Optbase 10
11 are provided. An objective lens 12 is provided at the other end of the opt base 10 while being supported by an objective lens actuator 13. The objective lens actuator 13 is a biaxial actuator that servos the objective lens 12 in biaxial directions orthogonal to the focus direction and the tracking direction, and is composed of an electromagnetic drive system, but its detailed structure is not shown.

A collimator lens 15 having a large numerical aperture, a pair of triangular prisms (anamorphic biprisms) 16, 16 for beam shaping, a diffraction grating 17, and a half mirror 18 are arranged in the irradiation direction of the laser light emitted from the laser diode 11. , A 45-degree mirror 19 is provided.

The laser light emitted horizontally from the laser diode 11 is 45
The light is reflected by a mirror 19 by 90 degrees, is converged via an objective lens 12 above the mirror 19, and is formed into a beam spot on the disk surface.

The return light reflected from the disk is reflected by the 45-degree mirror 19 and returned to the half mirror 18, and is polarized by 90 degrees via the half mirror 18. In this polarization direction, the convex lens 20,
A half mirror 21 is arranged. This half mirror 21
In the straight direction, which is separated into two directions via the
2, shield plate 23 with slit 231 formed in the center, half-wave plate 2
4. A polarization beam splitter 25 is provided. Photodetectors 26 and 27 are respectively arranged in the two directions separated by the polarization beam splitter 25.

On the other hand, a concave lens 28, a cylindrical lens 29, and a 6-division photodetector 30 are arranged in a direction polarized by 90 degrees via the half mirror 21.

The laser light that is emitted from the laser diode 11 and spreads anisotropically is converted into elliptical parallel light through the collimator lens 15 having a large numerical aperture. The elliptical parallel light is beam-formed into a circular parallel light via a pair of triangular prisms 16, 16. Circular parallel light passes through the diffraction grating 17 and is the 0th order light, ± 1
It is separated into three beams of the next light and reaches the objective laser 12 via a 45 degree mirror 19. The three beams of 0th order light and ± 1st order light are converged through the objective lens 12 to form three beam spots, which are irradiated onto the disc. This beam spot is 0
The beam spot of the next light irradiates the track groove of the disc, and the beam spots of the ± 1st order light irradiates the track groove. Therefore, the diffraction grating 17 is arranged at a predetermined angle so that the beam spot is separated and the disk is irradiated as described above. The diffraction grating 17 may be attached at a position between the collimator lens 15 and the triangular prism 16 instead of the front of the half mirror 18.

The return light from the disc is returned to the one in which the three beams are overlapped through the objective lens 12, and is guided to the signal detection optical system via the half mirror 18. 0 led to the detection optical system
The three beams of the next light and the ± 1st light are respectively converged via the convex lens 20 and separated into two directions via the half mirror 21.
The three beams that go straight through the half mirror 21 are the concave lens 22.
The optical paths of the ± first-order light beams are converted to a direction that spreads outward through. The ± 1st order light of these three beams is blocked by passing through the shield plate 23, and only the central 0th order light is transmitted through the slit 231 formed in the center of the shield plate 23 to the half-wave plate.
24, reaching the polarization beam splitter 25. This 0th order light is 1 /
The plane of polarization is rotated by 45 degrees via the two-wave plate 24, and is polarized in two directions via the optical beam splitter 25.
It reaches 27, and the received light is detected. The Kerr rotation angle is detected by the differential output of the electric signals photoelectrically converted by the photodetectors 26 and 27, and the reproduction signal (HF signal) is read by this detection signal.

On the other hand, the three beams polarized by 90 degrees through the half mirror 21 are subjected to optical path conversion through the concave lens 28 to the direction in which the ± first-order light spreads outward, and through the cylindrical lens 29, 6
It is guided to the split photodetector 30. The 6-division photodetector 30 has a 4-division photodetector 30a at the center, and photodetectors 30b on both sides thereof,
It is configured by arranging 30c. 0 in 3 beams
The secondary light component is imaged on the four-division photodetector 30a, and the focus error is detected by the astigmatism method only by the zero-order light. Then, the ± first-order light is imaged on the photodetectors 30b and 30c, respectively, and the tracking error signal is detected by the differential output of the detection outputs.

The focus / tracking error signal thus detected drives the objective lens actuator 13 to servo the objective lens 12 in the focus or tracking direction. As a result, the beam spot is accurately controlled to follow the track groove of the disk.

As described above, since the magneto-optical head apparatus according to the present embodiment employs the error detection method based on the three-beam method, stable and reliable tracking servo can be performed without being affected by the disk eccentricity and surface wobbling. it can.

In addition, since the ± 1st order light in the three beams is blocked and only the 0th order light is extracted to detect the reproduction signal,
A magnifying optical system for splitting into 3 beams is not required, and the optical path length can be made finer. Therefore, the head structure can be made smaller even though it is a 3-beam type magneto-optical head device.
Can be made compact. FIG. 3 shows another embodiment of the reproduction signal detecting system, in which the same parts as those in the above embodiment are designated by the same reference numerals, and only the essential parts will be described.

As shown in FIG. 3, 0 taken out through the shielding plate 23
After passing through the half-wave plate 24, the next light is polarized by the polarization beam splitter 31 by 90 degrees. This polarization beam splitter 31
Is formed integrally by combining a triangular prism 31a and a parallelogram prism 31b. In the polarization beam splitter 31, the 0th-order light is split into two by the triangular prism 31a and the parallelogram prism 31b, is polarized by 90 degrees, and is guided in the same direction. A two-part photosensor 32 is arranged in this polarization direction. Then, the two divided 0th-order lights are received and detected by the two light receiving portions of the two-divided photosensor 32, respectively, and the reproduction signal is detected by the differential output of the detection output.

According to this, only one photodetector for detecting the reproduction signal is required, the number of parts can be reduced, and the signal detection system can be further simplified.

FIG. 4 shows still another embodiment of the reproduction signal detecting system.

As shown in FIG. 4, 0 taken out through the shielding plate 23
A polarization beam splitter 33 and a high-sensitivity high-detector 34 are arranged in the direction in which the next light goes straight. Polarizing beam splitter 33
Are arranged so as to rotate about 6 degrees with respect to the plane of polarization of the 0th-order light, and are arranged so that the amount of the 0th-order light traveling straight is small and the amount of polarized light is large. As the photodetector 34, an APD (avalanche photodiode) having a high electron multiplication factor of M40 is used. Since the multiplication factor is extremely high and the sensitivity is high as described above, the photodetector 34 is arranged at the position where the returning light is extinguished.

As a result, the car is rotated in different directions and returned 0
The next light is extracted by the photodetector 34 as a strong and weak signal with high sensitivity, and the reproduction signal is detected.

Although the polarization beam splitter 33 is arranged as an analyzer by rotating it by a certain angle with respect to the plane of polarization of the returning 0th order light, it is used as an analyzer, but a polarizer may be used instead.

FIG. 5 shows an example of the configuration of the magneto-optical head device of the present invention in a bent shape.

In FIG. 5, the backward optical system after the half mirror 18 'arranged to guide the return light from the disc to the photodetection system is on the disc center side with respect to the forward optical system, and its optical axis is the forward route. It is tilted at an angle toward the center of the disc with respect to the optical axis of the optical system. The optical axis is substantially along the linear feed direction of the head device with respect to the disk radial direction. The longitudinal center line of the objective lens actuator 13 is inclined in the disc center direction with respect to the optical axis of the outward optical system. This constitutes a vent type head device. In this configuration, the half mirror 18 'that guides the return light to the photo detection system and the half mirror 21' that separates the return light guided to the photo detection system into the error signal detection system and the reproduction signal detection system are flat plates. Things are used. The half mirrors 18 'and 21' are arranged so as to be inclined more than 45 degrees.

With this bent shape, the size of the head device itself is reduced, and at the same time, when incorporated into the player body, the amount of protrusion from the outer peripheral portion of the disc is reduced, and the player can be minimized in size.

EFFECTS OF THE INVENTION As described above, according to the magneto-optical head apparatus of the present invention, since the 3-beam method is adopted, tracking error detection can be performed without being affected by eccentricity and surface wobbling of the disk. , Stable and reliable tracking servo can be performed. Therefore, the tracking characteristic can be improved. Further, since only the 0th-order light is extracted and the reproduction signal is detected through the shielding plate formed with the slit, the magnifying optical system is not required, and the optical path length of the reproduction signal detection system can be shortened. Therefore, the head device can have a small, simple and inexpensive structure suitable for mass production while fully utilizing the characteristics of the three-beam system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical system of a magneto-optical head device according to the present invention, FIG. 2 is a block diagram showing its signal detection system, and FIG. 3 is a block diagram showing another example of a reproduction signal detection system. FIG. 4 is a block diagram showing another example of the same, and FIG. 5 is a plan view showing an example of a vent type magneto-optical head device according to the present invention. 10 …… Optobase, 11 …… Laser diode, 12 …… Objective lens, 13 …… Objective lens actuator, 17 …… Diffraction grating, 23 …… Shield plate, 231 …… Slit, 26,27,30,32 , 34 …… Photodetector.

Claims (4)

[Claims] 1. A magneto-optical head device applied to a magneto-optical disk player for performing magneto-optical recording / reproducing / erasing on a magneto-optical disk, wherein a laser beam from a laser light source is guided onto a disk surface through an objective lens. The laser beam on the outward path is ± 1 with the 0th order light
A diffraction grating that separates into the next light is provided, and a half mirror that separates the return light into two directions is provided on the forward path that guides the return light of the laser beam reflected on the disk surface through the objective lens to the photodetection system. Then, a magnifying optical system consisting of a convex / concave lens and a cylindrical lens is arranged in one direction of the return light separated by this half mirror, the focus error signal is detected by the 0th order light, and the tracking error signal is detected by the ± 1st order light. Detecting, removing ± 1st order light in the other direction, and disposing a shielding plate with a slit that extracts only 0th order light,
A magneto-optical head device characterized in that the Kerr rotation angle of the 0th-order light is detected by detecting the received light of the next-order light. 2. A patent in which zero-order light passing through the slit is guided to two photodetectors via a half-wave plate and a polarization beam splitter, and the Kerr rotation angle is detected by the differential output thereof. The magneto-optical head device according to claim (1). 3. The polarization beam splitter is formed of a triangular prism and a parallelogram prism, and 0-order light passing through the slit is guided in the same direction and detected. The magneto-optical head device according to the item (1). 4. A polarization angle analyzer such as a polarization beam splitter is arranged at the 0th-order light extinction position behind the shielding plate, and the 0th-order light is transmitted through the analyzer with high sensitivity such as an avalanche photodiode. The magneto-optical head device according to claim 1, wherein the magneto-optical head device is configured to guide light to a photodetector to detect light reception.