JPH01256031A - Tracking method for optical disk - Google Patents

Abstract

PURPOSE:To improve the tracking accuracy and to make the operation stable against the use of lots of kinds of optical disks by using two light beams at both ends of a multi-beam light head so as to apply tracking. CONSTITUTION:An optical head 21 radiating plural light beams is used to apply tracking to an optical disk 26 having plural parallel tracks, then a tracking error signal by the light beam at both ends of plural light beams is detected. Then based on the tracking error signal, the angle between a straight line tying plural light beams and a track is varied so as to allow the light beam at both ends to follow a prescribed track. Thus, tracking is applied by using two light beams at both ends to collect the light beam existing inbetween onto a prescribed track and highly accurate tracking is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking method for an optical disc, and particularly to a tracking method for an optical disc having a plurality of parallel tracks.

(Prior Art) A so-called write-once type optical disc on which a user can record information usually has tracks formed with guide grooves, wobble marks, etc. for specifying the recording location of information. There are two types of tracks: spiral tracks and concentric tracks.In recent years, in order to increase the information transfer rate, methods have been proposed that use multiple light beams to perform recording and playback at the same time. Progress is being made in developing methods for forming tracks and so-called multi-beam optical heads that emit multiple light beams.

Conventionally, the following method is known as a method of tracking a plurality of parallel optical disks using such a multi-beam optical head.

A block diagram of the conventional multi-beam optical head shown in FIG. 5 is shown.

In the figure, 1 is a semiconductor laser array which outputs a plurality of light beams. 2 is a collimating lens, 3 is a polarizing beam splitter, 4 is a lunar wave plate, 5 is a converging lens, 6 is an optical disk, 7 is a beam splitter, 8 is a condensing lens,
9 is a signal detector, IO is a prism, 11 is a focus/
A track error detector is provided, and this example shows a four-beam optical head.

The light beam emitted from the semiconductor laser array 1 is directed to the optical disk 6.
The light is focused on four spots at the top. The light reflected from the optical disk 6 is again focused on the signal detector 9 as four spots, and the signals of each track channel are detected simultaneously.

On the other hand, after a part of the reflected light passes through the beam splitter 7 and enters the prism 10, due to the difference in the angle of incidence, only one of the four beams is guided to the focus/track error detector 11, which controls the focus. and track control signals are obtained.

In other words, in the conventional tracking method using a multi-beam optical head, the distance between the four beams is set by the optical disk 6.
It is set in advance to match the spacing between the parallel guide grooves shown above, and by applying tracking control to only one of the four beams, recording and reproduction onto the four grooves is performed.

(Problem to be Solved by the Invention) However, in the above-mentioned tracking method using the conventional multi-beam optical head, although one groove out of a plurality of parallel grooves is accurately tracked, the beam interval is fixed. Therefore, it was not possible to follow the fluctuations in the groove spacing, and it was not possible to accurately record and reproduce information on grooves other than the groove being tracked.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disc tracking method that solves the problems of the prior art and allows highly accurate tracking of each of a plurality of parallel tracks.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a method for tracking an optical disk having a plurality of parallel tracks using an optical head that emits a plurality of light beams.
Tracking error signals from the light beams at both ends of multiple light beams are detected, and based on the tracking error signal, the angle between the track and the straight line connecting the multiple light beams is changed so that the light beams at both ends follow a predetermined track. It is characterized by being made to do. That is, in the conventional technique, tracking control is performed using only one beam, whereas the present invention is different in that tracking control is performed using two beams at both ends.

[For production]

According to the present invention, when tracking an optical disk having a plurality of parallel tracks using an optical head that emits a plurality of light beams, a tracking error signal is detected by the light beams at both ends of the plurality of light beams. be done. Then, based on this tracking error signal, the angle between the track and the straight line connecting the plurality of light beams is changed so that the light beams at both ends follow a predetermined track.

Therefore, even if a disc with a slightly different groove spacing is used due to a difference in the original plate, or if the effective groove spacing changes due to a difference in the setting of the optical disk, tracking can be performed using the two light beams at both ends. By doing so, the light beams between them are also focused on a predetermined track, allowing highly accurate tracking.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

(Embodiment 1) FIG. 1 shows a configuration diagram of an optical system and a control system of a multi-beam optical head used when implementing a first embodiment of the optical disk tracking method according to the present invention.

In the figure, 21 is a semiconductor laser array that outputs a plurality of light beams, 22 is a collimating lens, 23 is a polarizing beam splitter, 24 is a wavelength plate, 25 is a focusing lens,
26 is a four-tree parallel helix tRG as shown in Figure 2.
27 is a beam splitter, 28 is a condensing lens, 29 is a signal detector, 3
0 and 31 are the first and second briss.

32 is a focus/track error detector, 33 is a track error detector, and 34 is a control circuit.

This embodiment shows a four-beam optical head.

The lens actuator of the multi-beam optical head according to this embodiment includes a well-known vertical movement mechanism (not shown) for focus control, and in order to apply tracking control to each of the two light beams at both ends, the lens actuator has four beams. A moving mechanism 35 for the semiconductor laser array 21 is included as a mechanism for varying the angle with respect to the linear guide groove connecting the semiconductor laser array 21.

Next, a tracking method using a multi-beam optical head according to an embodiment of the present invention will be described.

Figure 3 shows guide grooves 61 to G4 and each spot 51 of the light beam.
It is an explanatory view showing the positional relationship with ~S4. optical disk 2
The distance between each of the light spots 51 to S4 on 6 is 20 μm,
The distance between each of the guide grooves G and G4 is 1.61. There are ll11 te. Therefore, the optical head is set so that the angle it makes with the straight guide groove connecting the optical spots is about 14 degrees. In the tracking state, the four optical beams output from the semiconductor laser array 21 are made into parallel beams by the collimating lens 22, pass through the polarizing beam splitter 23, and reach the local wavelength plate 24. 2
4, it is converted into a circularly polarized light beam, which is then passed through the focusing lens 2.
5, the aforementioned spots S, ~S are placed on the optical disk 26 by
It converges to connect 4.

The light beam reflected by the optical disk 26 follows the same optical path as the outgoing path in the opposite direction, passes through the % wavelength plate 24 in the opposite direction, is reflected by the polarizing beam splitter 23 in a direction perpendicular to the outgoing path, and reaches the beam splitter 27. Then, the separated reflected light is guided to the signal detector 29 by the condensing lens 28, where a signal is detected and a part of the reflected light is guided to the first prism 30.

Among the four reflected beams guided by the first prism 30, the reflected beam by the spot S1 corresponding to the guide groove 61 is as follows:
The angle setting of the first prism 30 leads to the focus/track error detector 32, and the first prism 30
Of the reflected beams reflected by the spot S4 and guided to the second prism 31, the reflected beam by the spot S4 corresponding to the guide groove 64 is guided to the track error detector 33 by setting the angle of the second prism 31.

Signals from the focus/track error detector 32 and the track error detector 33 are sent to a control circuit 34,
As is well known, feedback control is performed by driving the moving mechanism 35 so that the error signal disappears.

This tracking control is performed by rotating the semiconductor laser array 21 and moving the center of rotation in the direction perpendicular to the guide groove G.
This is done by changing the angle between the straight line connecting the light spots 51 to 54 and the guide IG, and causing the two light spots S1 and S4 at both ends to track the grooves 61 and G4 at both ends, respectively. That is, if we now assume that the guide groove 64 has moved to 64' as shown by the broken line as shown in FIG. ), the spot S1 has a guide groove G to absorb the movement of the spot S.
, while tracking in the direction parallel to the guide groove.

Thus, since the spots S2 and S3 are also located on the straight line connecting the spots SI and S2, they will move a certain amount in the directions perpendicular and parallel to the guide groove.

Note that the example shown in FIG. 3 shows the amount of displacement enlarged to facilitate understanding of the explanation, and the actual amount is on the order of μm or less, and the tracking of the guide grooves 62 and G3 is not performed with high precision. It is something that can be done.

Next, the results of recording and reproducing experiments using the above embodiment will be described.

The optical disk 26 used was one in which a C5, Te film was formed as a recording film on a polycarbonate substrate having a diameter of 130 mm. The guide groove is based on the patent application filed by the applicant in 1982-1988.
It was formed by the method for manufacturing an optical disk master disclosed in No. 243, and had four spiral grooves arranged in parallel as shown in FIG. 2, with a groove interval of 1.6 μm. Such optical disc 26 is
When the device was installed in a recording/reproducing device including the multi-beam optical head shown in the figure and a tracking experiment was conducted, stable tracking operation was confirmed.

Next, an attempt was made to record signals of different frequencies into the four guide grooves 61 to G4. As a result, microscopic observation revealed that 4
Confirm that the prescribed recording pits are formed on each of the guide grooves 61 to G4 of the tree, and simultaneously reproduce the signals of the four track channels. The crosstalk from the groove was less than -40 dB.

Next, similar experiments were conducted on optical discs made from different originals with the same specifications, and similar good recording and reproducing characteristics were obtained. In addition, operation was stable even when changing optical discs.

[Example 2] Next, a second embodiment of the present invention will be described.

The multi-beam optical head used in this embodiment uses 5 channels, that is, 5 optical beams, and is capable of tracking with the two beams at both ends, and the other configuration is the same as that used in the first embodiment. Recording and reproducing experiments were conducted using such a multi-beam optical head. The optical disc used was manufactured by the same method as in Example 1, and had four parallel spiral grooves with a groove interval of 1.6 μm (see FIG. 4).

First, we conducted a tracking experiment and confirmed good tracking performance. In this case, the number of guide grooves is 4 (G1-64), the number of light beams is 5 (spots S1 to SS), and the light beams at both ends are used for tracking, so the track used for tracking is is only the first opening of the guide groove 61 and one tree on its extension.

Next, out of the five light beams, three light beams excluding both ends were used to record signals with different frequencies. As a result, microscopic observation revealed that the guide grooves 62 of each of the three trees
~ Confirm that the specified recording bits are formed in G4, and simultaneously reproduce the signals of 3 channels, ensuring that the C/N from all signals is 50 dB or more, and the crosstalk from adjacent guide grooves is 40 dB or less. Obtained. Furthermore, similar experiments were conducted using optical discs with the same specifications but different originals, and similar good recording and reproducing characteristics were obtained.

Furthermore, the operation was stable even when changing the optical disk.

In this way, this example shows that tracking control can be made more stable by using the guide groove Gl (including its extended portion) as a tracking-dedicated track.

As is clear from this embodiment, the present invention can be applied even when the number of beams of the multi-beam optical head and the number of parallel spiral grooves do not match.

Furthermore, in the above embodiment, an example was shown in which a movement mechanism of a semiconductor laser array was used as a mechanism for varying the angle formed by a straight line connecting a plurality of beams and a guide groove, but other mechanisms may be used as long as they perform the same function. Needless to say, it may be used.

Further, in the above-described embodiment, a guide groove was described as an example of a track, but the present invention can be similarly applied to tracking using a wobble mark used in a sample servo system.

[Effects of the Invention] As is clear from the above description, according to the optical disc tracking method of the present invention, two light beams at both ends of the multi-beam optical head are used to track the optical disc.

Since racking is performed, the tracking coverage is high, and the operation is stable even when the effective groove spacing changes due to the use of many types of optical discs or when changing optical discs. have

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of the optical system and control system of a multi-beam optical head used in carrying out the first embodiment of the present invention. FIGS. 2 and 4 are four parallel spiral grooves. FIG. 3 is an explanatory diagram showing the positional relationship between the guide groove and the light beam spot, and FIG. 5 is a configuration diagram of a conventional multi-beam optical head. 1.21... Semiconductor laser array, 2.22... Collimating lens, 3.23... Polarizing beam splitter, 4.24...
Local wavelength plate, 5.25... Focusing lens, 6.26... Disk, 7.27... Beam splitter, 8.28... Focusing lens, 9.29... Signal detector, 10.30.31... Prism, 11.32... Focus/track error detector,
33...Track error detector, 34...Control circuit, 35...Movement mechanism. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1) An optical disc having a plurality of parallel tracks,
In a tracking method using an optical head that emits a plurality of light beams, a tracking error signal from the light beams at both ends of the plurality of light beams is detected, and based on the tracking error signal, the light beams at both ends are aligned to a predetermined track. A tracking method for an optical disc, characterized in that the angle formed between the track and a straight line connecting the plurality of light beams is changed so as to follow.