JPH0384759A - Optical pickup device - Google Patents

Abstract

PURPOSE:To realize a high C/N and to improve the recording density by detecting a luminous flux except a luminous flux at both ends in a track orthogonal direction in a reflected light as a magneto-optical signal to prevent production of a crosstalk thereby sufficiently ensuring an erasing ration. CONSTITUTION:Let split photodetector sections of a photodetector element 11 be a,b,c, and split photodetector sections of a photodetector element 12 be d,e,f, then an output difference (b-e) of middle photodetector part of both the photodetector elements 11, 12 is selected as a magneto-optical signal. That is, the luminous flux received by the photodetector sections a,c,d,f at both ends of both the photodetector elements 11, 12 includes the reflected light from the erasure leave part or the unrecorded part of a magneto-optical disk 5 and the crosstalk component of adjacent tracks. Thus, the luminous flux including the component is eliminated to improve the C/N and the recording density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device applied to a magneto-optical recording/reproducing device such as a magneto-optical disk drive or a magneto-optical card device.

[Conventional technology]

Conventionally, a magneto-optical signal recorded on a magneto-optical disk or the like is processed by using an optical pickup device as shown in FIG. The components of the amount of light received by the light receiving elements 11 and 12 are the components of the entire irradiation area of the spot light irradiated onto the magneto-optical disk. It contained. In other words, the two light-receiving elements also receive reflected light from the unerased portions and unrecorded portions at both ends of the recorded magnetic domain width of the magneto-optical disk.

Here, the basic principle of signal detection by a conventional optical pickup device will be explained in more detail with reference to FIG.

In FIG. 4, laser light emitted from a semiconductor laser 1 is converted into parallel light by a coupling lens 2,
It is reflected at right angles by the beam splitter (BS) 3.

Then, this reflected incident light passes through the objective lens 4 and is focused on the surface of the optical disc 5 as a recording medium.
A spot light with a diameter of about 1 μm is formed.

Thereafter, the reflected light from the optical disk 5 passes through the objective lens 4 and the beam splitter 3. Here, focus (
The FO) signal passes through the second beam splitter 6 and is converted into convergent light by the condensing lens 13, after which half of the light is passed through the knife 7.

The light advances toward the focus light receiving element 8 and is received.

This focusing error detection method is called the knife edge method, in which a knife edge 7 is placed in the width of the focused optical path returning from the disk 5, and the movement of a light spot image on the light receiving element 8 is detected. In the example shown in FIG. 4, the knife edge is placed at a position away from the focal position.

Further, the magneto-optical signal (M10100 and the sum signal is reflected at right angles by the second beam splitter 6, and the λ/2 plate 9
The plane of polarization can be changed by passing through the

Then, the reflected light whose polarization plane has been changed is separated into two beams by a polarizing beam splitter (PBS) 10. One of the two separated light fluxes passes through a polarizing beam splitter (PBS) 10, is made into a convergent light by a condensing lens 13, and is received by a light receiving element 11.

In addition, the other beam is transmitted through a polarizing beam splitter (PB
The light is reflected at right angles by S) 10, converged by a condensing lens 13, and received by a light receiving element 12.

Here, the sum signal is obtained by summing the outputs of the light receiving element 11 and the light receiving element 2, and signals such as a preformat signal and a tracking signal can be obtained from this sum signal. Further, the magneto-optical signal (M10100) is obtained by taking the differential signal between the light-receiving element 11 and the light-receiving element 12.

Detection of this magneto-optical signal (M/○ signal) is called a differential method, and is a detection method that uses two light-receiving elements, but M10100 detection is theoretically possible with just one light-receiving element. In this case, an analyzer is required in place of the polarizing beam splitter lO and the λ/2 plate 9. However, in reality, the differential method is generally used because it has a higher carrier-to-noise ratio (C/N ratio).

[Problem to be solved by the invention]

By the way, in the optical pickup device using the conventional differential method described above, ideally the focus of the objective lens 4 should be narrowed down to an upper point on the recording layer, but as shown in FIG.
As shown in FIG. 5(b), even at the just focus point, the light beam is not focused on one point, and as shown in the light intensity distribution diagram in FIG. 5(b),
1 μm at half width.

The width of 1/e2 is approximately 1.7 μm, which makes it easier to pick up signals from adjacent tracks n-1 and n+1 on the outside of the beam, as shown in Figure 5(b). In addition to the signal of track n, adjacent tracks n-1 and n+1
Crosstalk containing many signals occurs.

Conventionally, when detecting a reproduced signal, the recording medium is irradiated with a spot light having an area wider than the recording area.
Unerased portions and unrecorded portions at both ends of the a section width were also included in the reproduced signal, causing a deterioration of the C/N ratio.

By the way, the servo method for magneto-optical recording and reproducing devices is as follows:
There are the CC8 method and the DBF method. In the CC8 method, a continuous spiral guide groove (group portion) is formed on the recording medium, and tracking is performed based on the light reflected and diffracted by the guide groove. There is. In addition, in the DBF method, the sixth
As shown in the figure, a large number of plover marks are preformatted at regular intervals, and tracking is performed by detecting the deviation of the spot from the track center.

For this reason, the aforementioned unerased areas and unrecorded areas at both ends of the recording magnetic domain width occur in DBF type magneto-optical recording media, and although this also occurs in CC8 type magneto-optical recording media, it is not as much of a problem. .

That is, in the DBF method, the recording position and recording width shift due to tracking errors and LD power errors, resulting in unerased portions, but in the CC8 method, since there is a guide groove, the magnetic domain width can be limited to some extent. In addition, in the CCS method, the amount of light in the unerased areas and unrecorded areas at both ends is scattered and easily vignetted, making it less likely to affect the reproduced signal (see Figure 7).
On the other hand, since there is no guide groove in the DBF method, the reflected light is received as is, and the unerased portion tends to affect the reproduced signal (see FIG. 8).

This problem occurs with both optical modulation and magnetic field modulation recording methods.In the optical modulation method, the erasing power of the LD is made larger than the recording power to make the spot larger, thereby reducing the amount of unerased material. However, when rewriting a recording medium recorded by a different model of magneto-optical recording/reproducing device, the recording, erasing, and reproducing powers are different, so unerased data will still occur, and magnetic field modulation. In this method, since overriding is performed, a shift in the LD irradiation position in the magnetic domain width direction causes a problem as it causes an unerased portion.

The present invention has been made in view of the above circumstances, and
Provided is an optical pickup device that prevents the occurrence of crosstalk, secures a sufficient erasing ratio, realizes a high C/N ratio, and improves recording density in a recording/reproducing device using a magneto-optical recording medium in the F system. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention converts light from a laser light source into a discrete block format (D
In an optical pickup device that detects a magneto-optical signal by irradiating a magneto-optical recording medium of the BF) method and receiving the reflected light by a light receiving element, the light beam excluding the light beam at both ends in the direction perpendicular to the track from the reflected light is used as an optical pickup device. It is characterized by being detected as a magnetic signal.

Further, in the present invention, in the optical pickup device,
Either the light receiving element is divided into at least three parts in the direction perpendicular to the direction of movement of the recording medium relative to the pickup (tracking direction), or the width of the light receiving element in the direction perpendicular to the direction of movement of the recording medium relative to the pickup (tracking direction). is narrowed, and the light beams excluding the light beams at both ends in the direction perpendicular to the track out of the reflected light from the magneto-optical recording medium are detected as a magneto-optical signal.

Furthermore, in the present invention, light from a laser light source is irradiated onto a magneto-optical recording medium of a discrete block format (DBF) type, and the reflected light is received by a light receiving element to detect a magneto-optical signal. The pickup device is characterized in that among the light fluxes incident on the light receiving element, light fluxes at both ends in the direction perpendicular to the track are blocked, and a magneto-optical signal is obtained from the amount of light received.

[For production]

According to the present invention, out of the light flux incident on the light receiving element receiving the magneto-optical signal, the light flux excluding the light flux at both ends in the direction perpendicular to the track is detected as the magneto-optical signal. It is possible to remove reflected light from unerased areas and unrecorded areas, and I! The occurrence of crosstalk due to IiI contact tracks is also prevented.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an optical pickup device to which the present invention is applied, in which reference numeral 1 denotes a semiconductor laser;
2 is a coupling lens, 3 and 6 are beam splitters (BS), 4 is an objective lens, 5 is a magneto-optical disk, 7 is a knife, 8 is a focusing light receiving element, and 9 is a λ/ 2 plates, 10 is a polarizing beam splitter, 11.12 is a magneto-optical signal (M1
0 signal), a tracking signal, a light-receiving element for detecting a preformat signal, and the encoder 3 represents a condenser lens, respectively, and the overall configuration of this optical pickup device is similar to the conventional device shown in FIG. 4 above. It is something.

Here, the present invention is characterized in that, in the optical pickup device having the above-mentioned configuration, the light beam excluding the light beams at both ends in the direction perpendicular to the track out of the reflected light from the magneto-optical disk 5 is detected as a magneto-optical signal. As an example, as shown in FIG. 1, two light receiving elements 11 and 12 that receive a magneto-optical signal and a sum signal for tracking, etc. are each divided into three parts. This division of the light receiving element is performed in a direction perpendicular to the moving direction of the recording medium 5 relative to the pickup, that is, in a direction corresponding to the tracking direction (T direction in the figure).In other words, the irradiation light is ), the light S focused on the light receiving elements 11 and 12 moves in a direction perpendicular to the dividing line.

Here, if each divided light receiving section of the light receiving element 11 is designated as at byC, and each divided light receiving section of the light receiving element 12 is designated as d, a, and f, the magneto-optical signal is output from the central light receiving section of both the light receiving elements 11 and 12. Let the difference be b-a. That is, both light receiving elements 11 and 12
The light flux received by the light receiving sections at cy dtf at both ends of each includes reflected light from the unerased and unrecorded parts of the magneto-optical disk 5 and crosstalk components from adjacent tracks. By removing the light beam containing the component, it is possible to improve the C7N ratio and the recording density.

Note that the sum signal from both light receiving elements 11 and 12 is a + b
10 c + d + e + f is the sum of all light receiving parts, but this puts emphasis on the amount of light received, so a, C, d.

The unerased component of f does not affect this sum signal.

However, if emphasis is placed on the influence of crosstalk components included in a, a, d, and f, the sum signal will be b+e.

Now, as mentioned above, in the embodiment shown in FIG.
The light-receiving element is divided into at least three parts, and the central light-receiving part is used to detect the magneto-optical signal, so it receives light flux that excludes the unerased components and crosstalk components that were problems with magneto-optical disks using the DBF method. can do. Furthermore, when the light amount is important when detecting the sum signal, the outputs from the light receiving sections at both ends of the light receiving element can be used.

Next, FIG. 2 is a diagram showing the main part configuration of an optical pickup device showing another embodiment of the present invention. Corresponding light receiving element 11.1
This is an example in which the width of the light beam S is made narrower than the diameter of the light beam S to prevent crosstalk components and unerased components from being received, thereby achieving the same effect as the light receiving element shown in Figure 1. It is something.

In the embodiment shown in FIG. 2, unerased components and crosstalk components can be removed without dividing the light receiving element.

Next, FIG. 3 is a diagram showing the main part configuration of an optical pickup device showing still another embodiment of the present invention, and this embodiment includes two light receiving elements 11.
In this example, two light shielding plates 14 and 15 are provided between the light receiving element 12 and the condenser lens 13 and directly in front of the light receiving element 11 and 12, that is, at approximately the focal point of the light beam by the condenser lens 13. This 2
The light shielding plates 14 and 15 are arranged in a direction perpendicular to the direction of movement of the recording medium relative to the pickup, that is, in a direction corresponding to the tracking direction T. Also, these two light shielding plates 1
4. A parallel gap is created between Is.

In this manner, by providing the light shielding plates 14.15 on each of the two light receiving elements 11.12, it is possible to prevent the crosstalk component and the unerased component contained in the reflected light beam from the recording medium from being received.

Here, if the light-receiving part of one light-receiving element 11 is a, and the light-receiving part of the other light-receiving element 12 is b, the magneto-optical signal is a-
b, the sum signal becomes a+b. In addition, adjustment for removing crosstalk components and unerased components is performed using two light shielding plates 1.
This can be easily done by changing the interval of 4.15.

By the way, in order to prevent crosstalk components and unerased components from being received, there is a method of providing a dividing line on the light receiving element and receiving only the necessary part, but this is because the diameter of the received light beam changes depending on the temperature. Therefore, it is difficult to adjust the position of the light receiving element. Furthermore, it is difficult to receive an appropriate amount of light due to the dividing line of the light receiving element. On the other hand, in the method according to the present embodiment, the size of the light-receiving element only needs to be large enough to receive all the light flux, and the appropriate light flux can be received by adjusting the position and spacing of the two light-shielding plates. be able to. However, the light shielding plate must be placed immediately in front of the light receiving element, that is, approximately at the focal point of the condenser lens 13. This is because at a position where the light shielding plate is far from the light receiving element, the components of the light flux at that position do not correspond to the components of the light flux reflected from the recording medium, so even if the light shielding plate blocks the peripheral part of the light flux,
This is because the crosstalk component reflected from the recording medium and the unerased component are not cut.

As described above, in this embodiment, by simply adjusting the position and interval of the light shielding plate, it is possible to prevent the crosstalk component and the unerased component contained in the reflected light beam from the recording medium from being received. , it is possible to ensure a sufficient erasing ratio, and it is possible to improve the C/N ratio and recording density.

In the embodiment described above, the focus error signal detection and the magneto-optical signal detection are performed separately, but the focus error signal is detected using the light beam cut by the light shielding plate. It is also possible to do so.

In each of the embodiments described above, two light receiving elements are used to detect a magneto-optical signal using a method called a differential method. The present invention can be similarly applied to optical pickups that detect magnetic signals.

〔Effect of the invention〕

As described above based on each embodiment, in the optical pickup device according to the present invention, the reflected components from the unerased portions of the recording medium and adjacent tracks are removed from the light beam incident on the light-receiving element that receives the magneto-optical signal. The removed light flux can be detected as a magneto-optical signal.

Therefore, the optical pickup device according to the present invention can be used as a DBF.
When applied to a magneto-optical recording/reproducing device using a magneto-optical recording medium in this method, it is possible to prevent the effects of unerased components and the occurrence of crosstalk, and ensure a sufficient erasure ratio when detecting a magneto-optical signal. It is possible to achieve a high C/N ratio and to improve recording density.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of an optical pickup device showing one embodiment of the present invention, FIG. 2 is a diagram showing a main part configuration of an optical pickup device showing another embodiment of the invention, and FIG. A diagram showing a main part configuration of an optical pickup device showing still another embodiment of the present invention, FIG. 4 is a diagram showing a schematic configuration of a conventional optical pickup device, and FIGS. 5 to 8 are explanatory diagrams of conventional technology It is. 1... Semiconductor laser, 2... Coupling lens, 3, 6... Beam splitter, 4... Objective lens, 5... Magneto-optical recording medium, 7... Knifetsuji, 8... Light receiving element for focus signal, 9...
...λ/2 plate, 10...polarizing beam splitter,
11.12... Light receiving element for magneto-optical signal detection, 13
····Condenser lens. Figure 3 (a) (b) Figure 3

Claims (1)

[Claims] 1. An optical pickup that irradiates light from a laser light source onto a discrete block format (DBF) type magneto-optical recording medium, receives the reflected light with a light receiving element, and detects a magneto-optical signal. An optical pickup device characterized in that a light beam excluding a light beam at both ends in a direction perpendicular to the track from the reflected light is detected as a magneto-optical signal. 2. In an optical pickup device that irradiates a discrete block format (DBF) type magneto-optical recording medium with light from a laser light source and detects a magneto-optical signal by receiving the reflected light with a light-receiving element, the above-mentioned light-receiving element divided into at least three parts in the direction perpendicular to the direction of movement of the recording medium relative to the pickup (tracking direction), or narrow the width of the light-receiving element in the direction perpendicular to the direction of movement of the recording medium relative to the pickup (tracking direction). An optical pickup device characterized in that, of the reflected light from the magneto-optical recording medium, the light beam excluding the light beams at both ends in the direction perpendicular to the track is detected as a magneto-optical signal. 3. In an optical pickup device that irradiates a discrete block format (DBF) type magneto-optical recording medium with light from a laser light source and detects a magneto-optical signal by receiving the reflected light with a light-receiving element, the above-mentioned light-receiving element An optical pickup device characterized in that out of the light flux incident thereon, the light flux at both ends in the direction perpendicular to the track is blocked, and a magneto-optical signal is obtained from the amount of received light.