JP2642111B2 - Tracking method in multi-beam optical pickup - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tracking method in a multi-beam optical pickup.

(Prior Art) A multi-beam light pickup of a system in which a plurality of light beams are condensed as spots close to each other on a rotating disk-shaped record carrier to perform recording, reproduction, and erasure is intended. When such a multi-beam optical pickup is used, in the information recording mode, recording information is written with one light beam, and the newly written information is reproduced for confirmation using another light beam. DRAW (DIRECT R
EAD AFTER WRITE) and multiple track simultaneous playback.

Needless to say, focusing control and tracking control are necessary even in such a multi-beam optical pickup, but in a conventionally intended multi-beam optical pickup, a track error signal is performed by one of a plurality of light beams. In addition, there is a problem that a track shift easily occurs in a spot due to another light beam.

(Purpose) The present invention has been made in view of the above circumstances, and has as its object to provide a novel tracking method in a multi-beam optical pickup that can perform appropriate tracking control on a plurality of light beams.

(Configuration) Hereinafter, the present invention will be described.

The present invention relates to a tracking method performed in a multi-beam light pickup of a system in which a plurality of light beams are condensed as spots close to each other on a rotating disk-shaped record carrier and recording, reproduction, and erasing are performed. It has the following features.

That is, the plurality of reflected light beams from the record carrier are divided into two by the light path separating means for each reflected light beam, and two condensed light beam groups are obtained by the condensing optical system as condensed light beams for each reflected light beam. The astigmatism means arranged before the condensing position of the other condensed light beam group generates astigmatism in each of the condensed light beams of the one condensed light beam group, and the astigmatism is formed on the light receiving surface of the light receiving means By separately entering each light beam, track error signals in at least two spots in the radial and tangential directions are independently detected, and based on each detection signal, the radial and tangential signals of the two spots are detected. Perform direction tracking control.

(Example) Hereinafter, a description will be given according to a specific example.

 FIG. 1 shows an embodiment of the present invention.

In this embodiment, two light fluxes are used for writing and reproducing information, and in the information recording mode, writing is performed with one light flux and confirmation and reproduction is performed with the other light flux.

In FIG. 1 (I), two light beams emitted from a semiconductor laser having two light emitting points, that is, two light beams emitted from an LD array 10 are combined into an optical system constituting a common illumination optical path, that is, a coupling lens 12 and a beam shaping prism 13. , Beam splitter 1
4. Focus as two spots on a disk 50 as a record carrier via a deflecting mirror 15 and an objective lens 16.

As shown in FIG. 1 (II), assuming that the light beams emitted from the LD array 10 are α and β, they are condensed on the same track Tr on the disk 50 as spots SA and SB, respectively. Since the disc 50 rotates in the direction of the arrow, the spot SA precedes the SB with respect to the movement of the track. Therefore, in the following description, the light beam α is described as a preceding light beam, and the light beam β is described as a following light beam. Therefore, in the following description, the preceding light beam α performs writing, and the light beam β performs confirmation reproduction.

In order to execute the proper confirmation playback, the spot SA,
Both SBs must converge on the same track Tr.

Now, the light fluxes α and β reflected by the optical disk 50 as a record carrier are converted into an objective lens as shown in FIG.
16. The light enters the beam splitter 14 via the deflecting mirror 15, is reflected by the splitter 14, is separated from the illumination optical path, and is condensed light flux by the condenser lens 18, respectively. These two condensed light beams are split into two by a knife edge prism 20 as an optical path separating means to form two groups of condensed light beams.

That is, the knife-edge prism 20 allows the two condensed light beams from the condensing lens 18 to partially pass through and partially reflect the two light beams, thereby forming two groups of two condensed light beams. Are divided into the converged light flux group.

One condensed light beam group (knife edge prism
The condensed light beam group that has passed through the position 20 enters the half-wave plate 22. One condensed light flux group transmitted through the half-wave plate 22 is
Further, the light passes through the Wollaston prism 24 and enters the light receiving element 26.

The other condensed light flux group that is split by being reflected by the knife edge prism 20 enters the light receiving element 30 via a cylinder lens 28 that is an astigmatism unit.

Condensing lens 18, 1/2 wavelength plate 22, Wollaston prism 2
4. The light receiving element 26 constitutes first detecting means, and the cylinder lens 28 and the light receiving element 30 together with the condenser lens 18 constitute second detecting means. That is, the condenser lens 18
Is common to the first and second detection means.

Each light beam has a polarization direction of approximately 4 by passing through the half-wave plate 22.
Rotate 5 ゜. This half-wave plate 22 is a beam splitter
It may be at any position between 14 and Wollaston prism 24.

Further, when the transmitted light passes through the Wollaston prism 24, the transmitted light separates the S component and the P component in the Z direction. Also, the first
As shown in FIG. (II), the luminous flux incident on the light receiving element 26 is
The light flux α, ie, the reflected light of the preceding light flux is indicated by a solid line, and
Since the reflected light of the light beam β is separated from each other in the Y direction as shown by the broken line, the light beam incident on the light receiving element 26 is separated into four beams. The light receiving surface of the light receiving element 26 is shown in FIG.
As shown in I), the light receiving units A to F are separated, and these light receiving units output photoelectric conversion signals a to f corresponding to the amount of received light. In FIG. 1 (III), the P-polarized light component is incident on the light-receiving portions A, C, and E, the S-polarized light component is incident on the light-receiving portions B, D, and F. Is reflected light of the following light beam, and what is incident on the light receiving sections C, D, E, and F is reflected light of the preceding light beam, that is, the light beam α. As shown in the center view of FIG. 1 (III), when the spot of the light beam α is in a focused state, if this light beam is condensed on the dividing line of the light receiving sections C and E, and D and F, the defocus will be obtained. When this occurs, there is a difference in the amount of received light between the light receiving sections C and E, and between D and F, as shown in the left and right views of FIG. 1 (III). Therefore, focus control is performed using (c + d)-(e + f) as a focus servo signal. Is performed, the light flux α can always be focused on the recording surface of the disk 50. In addition, since the light flux β has a focus position close to the light flux α,
By controlling the focus of the light flux α, focusing of the light flux β can be realized. The focus servo control is of a well-known knife edge type, and the knife edge mirror 20 functions as a knife edge. When the signals obtained from the light receiving element 26 are combined to form (ab), this signal corresponds to the difference between the P-polarized light component and the S-polarized light component with respect to the succeeding light flux β. It can be a magneto-optical signal. Therefore, the magneto-optical signal written magnetically by the preceding light beam α can be confirmed and reproduced using the above signal. The use of the signal (c + e)-(d + f) makes it possible to detect a magneto-optical signal related to the light flux α. In this way, the focus servo signal and the magneto-optical signal can be detected by the first detecting means. Next, detection of a track error signal by the second detection means according to the present invention will be described.

As shown in FIG. 1 (II), the other condensed light beam group split by being reflected by the knife edge prism 20 passes through a cylinder lens 28 provided with the direction without power directed in the z direction. As a result, astigmatism can be given. Then, as shown in FIG. 1 (IV), this light beam is divided into four light receiving portions G, H, I, and J by a light receiving element 30.
Incident on. It is the luminous flux α that enters the light receiving sections G and J,
The light beam β enters the light receiving units H and I. When the spots SA and SB are on the same track Tr by using the astigmatism caused by the cylinder lens 28, as shown in FIG. Part G,
The signals g, h, i, j obtained from H, I, J are set so that g = j, h = i.

Track center and spot SA, SB due to disc eccentricity
Is shifted in the radial direction, the balance of the light receiving amounts of the light receiving units H and I, and G and J is lost as shown in the upper and lower diagrams in the center row of FIG. 2, so that the signal (g + h)-(i + j) is Tracking control is performed on the light fluxes α and β as a track error signal in the radial direction by a known push-pull method, so that tracking control in the radial direction can be performed.

Further, as shown in the left and right columns of FIG.
If A and SB are shifted in the tangential direction with respect to the track Tr, the pattern of the amount of received light on each light receiving unit changes.
Focusing on the signal (g + i)-(h + j), this signal is + if one has eccentricity, 0 if there is no eccentricity,
If it is eccentric to the other side, it becomes-, so this signal is used as an error signal in the tangential direction and servo control in the tangential direction is performed to correct the track deviation in the tangential direction for both spots SA and SB. be able to. To obtain the radial and tangential servo signals from the light receiving element 30, the third
As shown in FIG.
1,3-3,3-4 and the addition operation circuit 3-2 may be combined as shown in the figure.

In the above description, writing is performed with the leading light flux α,
Was used for confirmation reproduction, but it is also possible to perform writing with the light flux β and perform confirmation reproduction with the light flux α. Therefore, many combinations are possible, such that one of the light beams performs writing, erasing, and reading, and the other performs confirmation reproduction. When the light quantity differs between the two light beams, it can be dealt with by adjusting the gain.

Further, the spots of the two light beams do not necessarily have to be on the same track. If the spots SA and SB are on different tracks Tr1 and Tr2 as shown in FIG. 4, simultaneous writing and reading by the two light beams are possible. . Also, as shown in FIG.
When the above light beams, for example, three light beams, are used, servo control in the radial direction and tangential direction is performed on the spots SA, SB, SC out of the spots SA, SB, SC. The deviation from Tr can be made extremely small.

FIG. 6 shows the track deviation Δ of the spot of the other light beam when tracking control is performed with only one of the two light beams.
This shows how t 'is formed for the innermost track. Δd represents a deviation due to the seek system, ΔS represents a deviation due to disk eccentricity, and Δt ′ is caused by Δd and ΔS. The specific values are shown in the following table.

Table Δd + Δs Δt ′ 0 (mm) 0.042 (mm) 0.05 0.125 0.1 0.208 0.15 0.292 0.2 0.375 0.25 0.425 0.3 0.542 0.35 0.625 0.4 0.708 0.45 0.792 0.5 0.875 (Effect) As described above, according to the present invention, a novel multi-beam optical pickup is provided. it can. This multi-beam optical pickup has the above-described configuration, so that proper tracking control can be realized for a plurality of light beams in both the radial direction and the tangential direction.

When only one light beam of a plurality of light beams is used, only tracking control in the radial direction is sufficient, and there is no need to perform control in the tangential direction.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention, FIG. 2 is a diagram for explaining the above embodiment, and FIG. 3 is a circuit for generating a track servo signal of the above embodiment. , FIG. 4 is a diagram for explaining another embodiment of the present invention, FIG. 5 is a diagram for explaining another embodiment, and FIG.
FIG. 5 is a diagram for explaining a track shift occurring in a spot of the other light beam when tracking control is performed on one of the two light beams. 10 Semiconductor laser with two emission points, α, β
Luminous flux, 26, 30 light receiving element, 20 knife edge mirror, SA, SB spot

Claims (1)

(57) [Claims] 1. A multi-beam optical pickup of the type performing recording / reproducing / erasing by converging a plurality of light beams as spots close to each other on a rotating disk-shaped record carrier, wherein a plurality of reflected light beams from the record carrier are collected. The reflected light flux is divided into two by the optical path separating means, and the reflected light flux is condensed by the condensing optical system to obtain two condensed light flux groups. By astigmatism means arranged in front, astigmatism is generated in each of the condensed light beams of the one condensed light beam group, and each light beam is separately incident on the light receiving surface of the light receiving means, thereby at least. Track error signals in the radial direction and the tangential direction for the two spots are detected independently, and based on each detection signal, the radial and tangential directions of the two spots are detected. And performing tracking control, the tracking method.