JPH02149935A - Detection of tracking error - Google Patents

Abstract

PURPOSE:To obtain a stable tracking error by converging two beams on tracks and between the tracks, guiding them to respectively corresponding optical sensors, obtaining basic signals by means of a push pull system and subtracting the signals between two basic signals. CONSTITUTION:A first beam S1 converges on the tracks of a disk, and the reflecting light is guided to the corresponding a first optical sensor, and first basic signals equivalent to the tracking error signals by the push pull system can be obtained as the outputs of a first optical sensor. On the other hand, a second beam S2 converges between the tracks of the disk, the reflecting light is guided to a second optical sensor, and the second basic signals equivalent to the tracking error signals by the push pull system can be obtained. In such a case, both basic signals output the outputs whose phases are mutually inverted. Thus, the outputs obtained by performing subtraction are effective as the tracking error signals and the influence of disk surface blurring is removed from the output obtained by subtraction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking error detection method for an optical head in an optical disk device.

[Prior Art] Conventionally, the push-pull method, which is a one-beam method, and the three-beam method are generally known as tracking error detection methods for optical heads.

[Problems to be Solved by the Invention] The push-pull method has the advantage of a simple circuit configuration, but the tracking error signal is easily affected by the inclination of the disk, which means that the disk surface runout characteristics are poor. , the disadvantage is that the tracking operation is unstable. Furthermore, although the three-beam method has a simple circuit configuration, it has disadvantages in that the angle adjustment of the three beams is complicated, the optical system is complicated, and the optical efficiency is low.

The present invention was made to eliminate the drawbacks of the one-beam method and the three-beam method, and an object of the present invention is to provide a new tracking error detection method with stable tracking operation and high optical efficiency.

[Means for Solving the Problems] The present invention for solving the above problems forms two beams, a first beam and a second beam, by separating them from a single light source or by using two light sources, and The beams are focused on and between the tracks of the disk, and each reflected beam is guided to a first optical sensor and a second optical sensor corresponding to each beam, and both optical sensors correspond to tracking error signals using a push-pull method. Obtain a first basic signal and a second basic signal, and obtain these two basic signals.
This tracking error detection method is characterized in that a tracking error signal is obtained from subtraction between two basic signals.

[Operation] In the tracking error detection method described above, the first beam converges on the track of the disk, and its reflected light is guided to the first optical sensor corresponding to the first beam, and as the output of the first optical sensor, A first basic signal corresponding to a tracking error signal based on the push-pull method is obtained. On the other hand, the second beam converges between the tracks of the disk, and its reflected light is guided to the second optical sensor, which outputs a second basic signal corresponding to a tracking error signal also based on the push-pull method. can get.

Then, an output obtained by subtracting between the first basic signal and the second basic signal is output as a tracking error signal.

The beam that provides the first basic signal converges on the track, whereas the beam that provides the second basic signal converges between the tracks (provided that when normal tracking operation is performed) ), both basic signals output outputs whose phases are inverted from each other. Therefore, the output obtained by subtracting between the two basic signals is effective as a tracking error signal. On the other hand, the influence of disk surface runout (disc inclination) appears equally on both basic signals. Therefore, the influence of disk surface runout is removed from the output (tracking error signal) obtained by subtracting both basic signals.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 7.

FIG. 1 is a diagram showing the optical system configuration of an optical head according to an embodiment of the present invention. In FIG. 1, 1 is a laser diode provided as a single light source, and 2 is a laser diode l.
This is a collimator lens that converts the scattered light emitted from the lens into parallel light. 3 is a so-called Bragg diffraction grating that strongly emits one of the ±1st-order diffracted lights of the transmitted light and weakly the other, and by using the 0th-order light and the strong 1st-order diffracted light, a laser beam (hereinafter referred to as beam) is generated from a single light source. It is arranged as a two-beam forming means for dividing the beam into two beams. 4 is a beam splitter that transmits the light incident on the disk and reflects the reflected light from the disk at right angles; 5 is an objective lens that converges the two beams onto the signal surface of the disk 6; and 7 is the beam splitter that reflects the light from the disk 6. 4 is a condensing lens for condensing the reflected light reflected at right angles, and 8 is a diagonal plate arranged for refraction of astigmatism. This diagonal plate 8 functions to sequentially change the beam shape from a vertically long ellipse to a horizontally long ellipse depending on the distance, similar to a cylindrical lens used in a general astigmatic focusing error detection method. Naturally, a cylindrical lens can be used in place of the diagonal plate 8. 9 is a photodetector that detects the reflected light transmitted through the diagonal plate 8.

FIG. 2 shows another embodiment using a birefringent wedge 3A as a two-beam forming means. This birefringent wedge 3A causes a birefringence phenomenon in which two refracted rays appear for incident light. It is a wedge-shaped piece of calcite or crystal. The other points are the same as in FIG. 1.

The two beams in the optical system having the above configuration are set to converge on the disk as shown in FIG. That is, one beam (referred to as the first beam) converges on the track 10 of the disk and the converged light spot is indicated by S+), and the other beam (referred to as the second beam) focuses on the track 10 of the disk. The light spot is adjusted to converge between the tracks (the light spot between the tracks is indicated by 82).

Further, the photodetector 9 may be, for example, as shown in FIG.
A first optical sensor 11 corresponding to the first beam (S,) and a second optical sensor 12 corresponding to the second beam (S2).
The first optical sensor 10 is a two-segment optical sensor divided into two segments E and F, and the second optical sensor 11 is composed of four segments A, B, and C used for detecting focusing errors. , D. In the embodiment, since the diagonal plate 8 that refracts astigmatism is arranged, the dividing line of the two-split optical sensor 10 and the dividing line of the two-split optical sensor in the case of the normal push-pull method are different. Note that the symbols A', B', C', D', and E shown in each light spot S, , S, in FIG.
', F' (same as in FIG. 5) means that the light reflected from those areas (A', etc.) within the optical spot on the disk corresponds to the corresponding symbol (A', etc.) on the optical sensor 11 or 12. Each segment A, B, C, D, E with the same symbol.

Indicates that each corresponds to F.

Next, to explain the tracking error detection method based on the outputs from the optical sensors 11 and 12, both optical sensors 1 and 12 will be described.
1 and 12, a first basic signal TE and a second basic signal TE, both of which correspond to tracking error signals using the push-pull method, are obtained, and the tracking error signal TE is obtained by subtracting between these two basic signals TE, , TE2. get.

That is, the tracking error signal TE is determined by the following calculation.
get. Note that each segment A of the optical sensors 11 and 12,
13. The respective outputs of C, D, E, and F are converted into A, B, C,
Represented by D, E, F.

TE=TE, -TE, but TE, = E-F TE2= (A+D)-(B+C) To explain this in detail, the optical head When the first basic signal TE is sent in the left-right direction), the first basic signal TE becomes the output shown by (a> in FIG. 5), and the second basic signal TE becomes the output shown by (b) in the same figure. outputs outputs whose phases are inverted from each other. Fig. 5 shows the case where there is no disc surface runout, but if there is disc surface runout, the outputs of each basic signal T E + and TE 2 will have the outputs shown in Fig. 6 ( a
), fluctuations occur as shown in (b). However, by subtracting between the two, the tracking error signal TE (=TE
.

By obtaining TE, ), as shown in the tracking error signal output diagram of FIG. 7, the component based on the disk surface runout is canceled out, and the influence of the disk surface runout is removed.

Note that since there is a difference in the output level of the two divided beams, the tracking error signal becomes more accurate if the gain is adjusted according to the output level and the above subtraction process is performed. That is, as shown below, one basic signal output is multiplied by a coefficient α for gain adjustment and subtracted.

TE=TE, -αTE.

On the other hand, the astigmatism method is used to detect focusing errors. That is, a focusing error signal FE is obtained from the output of the four-split optical sensor 12, which transmits and receives the light reflected by the second beam on the disc through the diagonal plate 8 which refracts the second beam with astigmatism.

FB=(A+C)-(B+D) However, it is not always necessary to use this astigmatism method, and a focusing error detection method other than the astigmatism method may be adopted.

[Effects of the Invention] Since the present invention is configured as described above, it has the following effects.

the first corresponding to the beam converging on the track of the disk;
a second beam corresponding to the fundamental signal and the beam converging between the tracks;
Since the tracking error signal is obtained by subtraction from the basic signal, the component caused by the surface runout of the disk is canceled out by the subtraction, the influence of the disk surface runout is removed, and the stability of the tracking operation is improved.

In the case of obtaining two beams from a single light source, the light efficiency is higher than the conventional three-beam method of obtaining three beams from a single light source.

The angle adjustment operation of the two beams when converging the two beams on the track and between the tracks is easier than the angle adjustment of the three beams in the conventional three beam method,
Adjustment work becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the optical system configuration of an optical head according to one embodiment to which the method of the present invention is applied, FIG. 2 is a diagram showing the optical system configuration of an optical head according to another embodiment, and FIG. FIG. 4 is an explanatory diagram of the convergence position, FIG. 4 is an explanatory diagram of the division pattern of the optical sensor, FIGS. 5 to 7 are explanatory diagrams of the principle of the tracking error detection method according to the present invention, and FIG. First basic signal output in the case where there is no ((a) in the figure)
and an explanatory diagram of the second basic signal output ((b) in the figure),
Figure 6 is a diagram of the first basic signal output ((a) in the figure) and the second basic signal ((b) in the figure) when there is disk surface runout, and Figure 7 is the diagram of the output of the second basic signal ((b) in the figure). FIG. 3 is a diagram of tracking error signal output obtained from first and second basic signal outputs. DESCRIPTION OF SYMBOLS 1... Laser diode (light source), 3... Bragg diffraction grating, 3A... Birefringence wedge, 6... Disk, 8... Diagonal plate, 9... Photodetector, 10... - Track, 11...2-split optical sensor (optical sensor). 12...Four division optical sensor (light sensor), TE...Tracking error signal, TE...First basic signal, TE,...Second basic signal. Figure 1

Claims (1)

[Claims] 1. Forming two beams, a first beam and a second beam, by separating from a single light source or by using two light sources, and converging both beams on and between tracks of a disk, respectively. , guides each reflected light to a first optical sensor and a second optical sensor corresponding to each beam, respectively, and generates a first basic signal and a second basic signal corresponding to a tracking error signal using a push-pull method in both optical sensors. A tracking error detection method characterized in that a tracking error signal is obtained from subtraction between the two basic signals and the tracking error signal is obtained from the subtraction between the two basic signals. 2. The tracking control method according to claim 1, wherein a Bragg diffraction grating is used as the two-beam forming method using the single light source. 3. The tracking error detection method according to claim 1, wherein a birefringent wedge is used as the two-beam forming method using the single light source. 4. The first optical sensor corresponding to the first beam is a two-split optical sensor, the second optical sensor corresponding to the second beam is a four-split optical sensor for detecting a focusing error, and the first and second optical sensors 2. The tracking error detection method according to claim 1, wherein the two optical sensors constitute a six-divided optical sensor. 5. When subtracting between the two basic signals, the subtraction is performed after gain adjustment according to the beam output levels of the first beam and the second beam.
Tracking error detection method according to 2, 3 or 4.