JPH06349105A - Multibeam optical head - Google Patents

Abstract

PURPOSE:To eliminate the need for image rotating servo and to facilitate an adjustment operation at the time of assembly by arranging the spots on a disk in the radial direction of the disk with the multibeam optical head. CONSTITUTION:This multibeam optical head has an optical system consisting of mirrors 3, 4 having such imaging magnification as to magnify the inter-spot spacing of the laser beam from a two-beam laser beam source 10 to integer times the track pitch and an objective lens 5. The spots 12a, 12b are arranged in the radial direction of the disk.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for recording information on a recording medium which can be optically recorded / reproduced and reproducing the recorded information from this medium, and more particularly to reflection from the recording medium. The present invention relates to a multi-beam optical head for obtaining various servo signals and reproduction signals by using light.

[0002]

2. Description of the Related Art Generally, in an optical recording / reproducing apparatus,
In order to record / reproduce information at a high density, information tracks on a recording medium, such as a disk, are in a fine spiral shape with a pitch of 1 to 2 μm. Such a disc is irradiated with a spot having a diameter of about 1 μm, and information on the disc is read from the reflected light.

In such a device, when it is necessary to improve the transfer rate of information or when collation is performed in parallel during recording, a multi-beam system for guiding a plurality of light beams by one head is adopted. Often. The method of forming tracks on a disk when a multi-beam optical head is used to increase the information transfer rate is different from that of a single-beam head as shown in FIG. In FIG.
(A) is an example of a track format for two beams using two beams, and (b) is an example of a track format for three beams using three beams.

In FIG. 4A, 100 is a two-beam disc, 101 is a first information track, and 102 is a second.
This is an information track. First track 101 and second
The tracks 102 are all on a guide groove called a groove. The groove has a double spiral shape in which two helices are combined, and an interval between both tracks, that is, a track pitch is equal to an interval between grooves, that is, a groove pitch.

In FIG. 4B, reference numeral 110 is a three-beam disk, and reference numerals 111, 112 and 113 are first, second and third information tracks, respectively. First truck 111
Is on the groove, but the second and third tracks 112,
113 is located on the land. The groove is a single spiral, but the tracks 111, 112, and 113 have a shape in which three helices are combined, and the track pitch is one third of the groove pitch. The track formats (a) and (b) shown in FIG. 4 can be applied to a multi-beam optical head having an arbitrary number of beams, and an appropriate format may be selected. The disk track forming method in the case of using a multi-beam optical head for parallel verification at the time of recording is the same as that of the single-beam head.

Generally, in an optical recording / reproducing apparatus, the information track fluctuates in the disk radial direction due to the waviness of the information track or the eccentricity of the disk.
It is necessary to make the spot follow so that it always illuminates the information track. The technology for this is called tracking servo. In the case of a single-beam optical head, one spot may be made to follow a track, but in the case of a multi-beam optical head, it is necessary to make a plurality of spots follow desired tracks.
FIG. 5 shows a typical conventional example of spot arrangement on the disk surface by such a multi-beam optical head.

In FIG. 5, a laser beam emitted from a laser light source 1 for generating a plurality of beams passes through a beam splitter 2 and an image rotation prism 8 and is changed in direction by a mirror 4, and then passes through an objective lens 5 and a disc. An image is formed on the recording surface of No. 6. The light reflected by the disk 6 passes through the objective lens 5, the mirror 4, and the image rotation prism 8 and is reflected by the beam splitter 2 to reach the photodetector 7, where the recording signal and the servo signal of the disk 6 are detected. It

A spot 11 formed on the surface of the disk 6
The distance between a and 11b is determined by the distance between the light emitting points of the light source 1 and the imaging magnification of the optical system, and usually has a size of 10 to 10 μm. An appropriate angle θ is set so that 11a and 11b are projected on adjacent tracks.
This angle θ is usually 80 because of the relationship with the track pitch.
More than a degree.

With the multi-beam optical head having such a spot arrangement, as in the case of a single beam, a tracking servo is applied to a certain spot, for example, the spot 11a, so as to follow a desired track. At this time, the spot 11a is always on the track, but the other spots 11b may be deviated from the track due to the difference in curvature due to the radius of the track, the eccentricity of the disk, or the like. When the off-track amount becomes unacceptable, the image rotating prism 8 is rotated around the optical axis by the rotating means 9 and the rotation angle is adjusted to adjust the angle θ between the spot row and the disk radius. Control. This is called an image rotation servo. By combining the tracking servo and the image rotation servo, it is possible to realize control for causing all spots to follow desired tracks.

[0010]

However, in the conventional multi-beam optical head, the image rotation servo is required to make all spots follow the track when the disk is rotated, and the number of parts is smaller than that in the single-beam optical head. However, there is a problem in that the head size increases and the head size increases. Also,
In order to avoid these problems, when the image rotation servo is not performed, it is necessary to use a disk with a very small eccentricity and a small change in track radius, which makes the disk manufacturing accuracy difficult and makes the disk usable. There are new problems such as limited diameter.

Also, the angle formed by the spot row and the track must be adjusted during assembly, but the position of the spot in the disk radial direction depends on the cosine component of the angle θ, and this angle is usually 80 degrees or more. Even if the angle is changed to, the spot position changes greatly. Therefore, in order to irradiate all the spots on the desired track,
It was necessary to set the angle with sufficient accuracy, and adjustment took time.

The present invention solves the above-mentioned drawbacks, facilitates adjustment at the time of assembly, does not require an image rotation servo, and is a multi-beam optical head which can be used for a disc having a small amount of eccentricity and diameter. The purpose is to provide.

[0013]

To achieve this object, the present invention has a configuration in which spot rows on the disk surface are arranged so as to coincide with each other in the disk radial direction.

[0014]

[Function] When the array direction of the spots coincides with the disc radial direction, the spot interval becomes an integral multiple of the track pitch. Therefore, as long as any one of the spots follows the track, regardless of the size of the track radius, All spots follow their respective tracks, eliminating the need for image rotation servos.

The position of the spot in the radial direction of the disc depends on the cosine component of the angle formed by the spot row and the radial direction of the disc. Since this angle is usually small, the change in the spot position due to the variation of this angle is small. Therefore, the adjustment accuracy of the angle at the time of assembly can be loosened, and the adjustment work becomes easy or unnecessary at all.

In addition, although inaccessible tracks remain in the spots other than the spot located at the innermost position at the innermost peripheral edge of the disc and the spot located at the outermost peripheral position at the outermost peripheral edge, the amount can be seen from the entire disc. Very little,
In many cases it does not matter.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a multi-beam optical head according to an embodiment of the present invention.

In FIG. 1, a laser beam emitted from a two-beam laser light source (hereinafter referred to as a light source) 10 passes through a beam splitter 2, is changed in direction by a mirror 3 and a mirror 4 which are optical path changing means, and then an objective lens. An image is formed on the recording surface of the disk 6 via 5. The light reflected by the disk 6 passes through the objective lens 5, the mirror 4, and the mirror 3 and is reflected by the beam splitter 2 to reach the photodetector 8, where the recording signal and the servo signal of the disk 6 are detected. Light source 1
The arrangement direction of the 0 light emitting points is set to be parallel to the tangential direction of the information track on the disk 6. That is,
The light source 10 is set so that the array direction of the light emitting points and the radial direction of the disk are substantially orthogonal to each other.

A spot 12 formed on the surface of the disk 6
a and 12b are arranged in the radial direction of the disk 6, and tracking servo is applied to either one of the spots in the same manner as in the case of the single beam optical head. Since the distance between both spots is usually about 10 to 30 μm, there are 10 to 30 tracks between the spots 12a and 12b. Since both spots each access a desired track, the distance between them is equal to an integral multiple of the track pitch.
The spot spacing is determined by the spacing between the light emitting points of the light source 10 and the imaging magnification of the optical system. Therefore, select a light source 10 with an appropriate spacing between the emitting points so that it becomes an integral multiple of the track pitch, or if the imaging magnification is appropriate. Design the optical system so that the value is obtained.

In such a configuration, since the spot interval is an integral multiple of the track pitch, as long as one of the spots follows the track, both spots always follow the track regardless of the track radius. To do.

FIG. 2 is an explanatory view showing that the image rotation servo is unnecessary. In FIG. 2, 13a and 13b
Is a spot when the arrangement direction forms an angle φ with the disc radial direction due to a manufacturing error or an adjustment error. The spot 13a records or reproduces information on the A track and the spot 13b records or reproduces information on the B track. 14a, 14
Reference numeral b denotes both spot positions when the spots 13a and 13b are moved in parallel by δ in the track tangential direction due to the influence of manufacturing error / adjustment error and disk eccentricity. Spot 13a
Tracking servo is applied to the spots, the spots are always on the same track, and the spot 13b moves while maintaining the relative position to the spot 13a. Spot 14 at this time
The off-track amount ε at the position b is approximately represented by (Equation 1).

(Equation 1) ε = {W / R−δ ² / (R + P)} / 2 where W = (δ + Ssinφ) ² − (Ssinφ) ² (Equation 1), S is the distance between the spots 13a and 13b. , R is the track radius accessed by the spot 13b,
P is the track spacing of both spots.

As a typical example of the case where the track deviation is large, consider the case where the disk is eccentric at the inner peripheral portion of the disk. R = 40 mm, P = 17.6 μm, S = 1
Substituting 8 μm, φ = 12.1 deg, and δ = 100 μm into (Equation 1), the track deviation amount is 0.01.
It can be seen that the size becomes μm, which is a size with almost no problem in spot tracking accuracy. Therefore, it can be seen that an additional servo mechanism for causing the spot 13b to follow the track is unnecessary.

FIG. 3 is a diagram showing an inaccessible area of the multi-beam optical head of this embodiment. In FIG. 3, 15
Reference numerals a and 15b are spot pairs when they are located on the outermost track of the disc, and 16a and 16b are spot pairs when they are located on the innermost track. The spot 15b cannot access the track in the area 17 on the outer peripheral side of the track located when the spot 15a is on the outermost track. Similarly, spot 16
a cannot access the track in the region 18 on the inner circumference side of the track located when the spot 16b is on the innermost track.

Information cannot be recorded or reproduced in these inaccessible areas, but since the number of tracks between both spots is about 10 to 30, the disk is rotated at 1800 rpm, for example. When recording or reproducing, the amount of decrease in recording or reproducing time due to the inaccessible area is about 0.3 to 1 second, which is usually a sufficiently permissible value.

In the above description, the mirror 3 is used to match the spot array direction with the disk radial direction, but the spot array direction matches the disk 6 radial direction without using the mirror 3. With such an optical system configuration, the same effect can be obtained. Further, the arrangement and configuration of the light source 10, the beam splitter 2, the mirror 3 and the mirror 4, and the objective lens 5 are not limited to the configuration of this embodiment, and may be an optical system in which the array direction of the spots on the disk coincides with the radial direction of the disk. It ’s good. Although the two-beam head has been described, the present invention is also applicable to a multi-head having three or more beams.

As described above, according to the present embodiment, from the mirrors 3 and 4 and the objective lens 5 having the imaging magnification such that the spot interval of the laser light from the two-beam laser light source 10 becomes an integral multiple of the track pitch. Since the spots 12a and 12b are arranged in the radial direction of the disc, the arrangement direction of the spots does not completely coincide with the radial direction of the disc. It is easy to set to 10 degrees or less. At this time, since the position variation of the spot in the disc radial direction due to the variation of the crossing angle is very small, if the tracking servo is applied to any one of the spots, the tracking accuracy of the other spots can be secured.
In addition, the accuracy of the intersection angle setting at the time of assembly can be loosened.

[0028]

As described above, according to the present invention, since the arrangement of the light spots coincides with the radial direction of the disk, the plurality of spots can accurately follow desired tracks without the image rotation servo. . Further, since the position of the spot in the disc radial direction is not significantly affected by the variation in the angle formed by the spot array and the disc radial direction, the angle adjustment work of the spot array during assembly can be facilitated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a multi-beam optical head according to an embodiment of the present invention.

FIG. 2 is a diagram showing an off-track amount in the multi-beam optical head of this embodiment.

FIG. 3 is a diagram showing an inaccessible area in the multi-beam optical head according to the embodiment of the invention.

FIG. 4 is a structural diagram of a track format of a disc for a multi-beam optical head.

FIG. 5 is a block diagram of a conventional multi-beam optical head

[Explanation of symbols]

 2 Beam splitter 3 Mirror 4 Mirror 5 Objective lens 6 Disk 8 Photodetector 10 2 Beam laser light source 12a, 12b Spot

Claims (3)

[Claims] 1. A light source that emits a plurality of laser beams and a laser beam emitted from the light source are transmitted to narrow down a laser beam on a disk to determine a ratio between a light emitting point interval of the light source and a focused spot interval. A laser beam transmitting means having an image magnification set such that the spot spacing is approximately an integral multiple of the spacing between information tracks on the disc, and a multi-beam arranged so that the spots substantially coincide with each other in the radial direction of the disc. Optical head. 2. The multi-beam optical head according to claim 1, wherein the light source is set so that the arrangement direction of the light emitting points and the radial direction of the disk are substantially coincident with each other. 3. An optical path change for setting the light source so that the arrangement direction of the light emitting points and the radial direction of the disc are substantially orthogonal to each other and making the arrangement direction of the laser light substantially coincide with the radial direction of the disc in the laser light transmitting means. The multi-beam optical head according to claim 1, further comprising means.