JP2731421B2 - Tracking error detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tracking error detection method used in an optical recording / reproducing apparatus.

<Summary of the Invention> The present invention provides a novel tracking error detection method applicable to any of recording, reproduction, and erasing operations, and includes two regions having different grating intervals and diffraction directions. By using a diffraction grating means having a main beam, two sub-beams composed of the first-order diffracted light in each area are generated on the same side in the track direction from the main beam, and these are irradiated on the track of the recording medium, and the reflection or A first gist is to detect a tracking error amount by detecting a difference in light amount between detection lights obtained by transmission.

Further, the ± first-order diffracted light in each area of the diffraction grating means generates first and second sub-beams from the main beam before and after the track direction, and further generates third and fourth sub-beams outside the main beam, These are irradiated onto the track of the recording medium, and the light amount difference between a pair of detection lights in front of the main beam and the light amount difference between a pair of detection lights behind the main beam out of the four detection lights obtained by reflection or transmission. The second purpose is to use the added value as the tracking error amount, and the detection signal level is made higher so that a more reliable detection signal can be obtained.

Further, in the above-mentioned second gist, the first, second,
First, second, third, derived from third and fourth sub-beams
For each light amount (e ₁ , e ₂ , f ₁ , f ₂ ) of the fourth detection light, (f ₁
The third purpose is to use the value obtained by (−e ₁ ) + (e ₂ −f ₂ ) as the tracking error amount, and the effect of the offset of the light amount due to the deviation between the center of the main beam and the division line of the diffraction grating means. Is eliminated.

Furthermore, in the second aspect, the correction constant corresponding to the detected light amount ratio between the unrecorded portion and the recorded portion, and the ratio between the reproduction output of the light source and the recording (or erasing) output. The fourth gist of the present invention is that the same device can be used for recording (or erasing) by incorporating a correction constant.

<Prior Art> Optical recording / reproducing apparatuses are known for various recording methods, such as a phase change type and a reflectivity change type, depending on a recording pit forming method. It is classified into a rewritable type and a write-once type. In general, all of these optical recording / reproducing apparatuses use a recording medium in which a guide groove (which may be a convex portion) corresponding to a recording track is formed in advance. At the time of reproducing or erasing operation, tracking control is performed so that the beam traces the guide groove.

Generally, two methods, a push-pull method using one beam and a three-beam method, are mainly used as a tracking error detection method used for this. These will be described with reference to FIGS. 3 and 4.

1.1 Push-pull method using a beam This method irradiates a track with a single beam (commonly used as a recording / reproducing beam), and splits the detection light obtained by the reflection or transmission of the beam into two areas by dividing lines that match the track direction. The tracking error amount is detected by dividing the area and detecting the light amount difference between the respective areas.

In FIG. 3A, the beam irradiated on the recording medium 33 via the beam sprinter 31 and the objective lens 32 is the recording medium 33.
, And is split by the beam sprick 31 and is incident on the two-divided photodetector. The photodetector 34 has two regions 3 divided by a dividing line 34c substantially corresponding to the track center.
4a and 34b, the respective outputs of which are connected to the positive and negative terminals of the subtractor 35. With such a configuration, when the beam spot deviates from the track center of the recording medium, a difference occurs in the light amounts of the respective regions 34a and 34b of the photodetector 34, and the level is the error amount at the output end of the subtractor 35, and the phase is A tracking error signal TES indicating the shift direction appears.

2.3 Beam method This method is applied to the reproduction of a recorded disk or the like, and is slightly shifted in the opposite direction from the track center to the target position in the track direction of the main beam 41 for reproduction as shown in FIG. The two sub-beams 42 and 43 are irradiated, the respective detection lights obtained by the reflection or transmission are detected by separate photodetectors, and the tracking error amount is detected by detecting the light amount difference between the respective areas. .

<Problems to be Solved by the Invention> The above-described conventional methods have the following problems.

1.1 Push-pull method using a beam This method is used when the perpendicular state between the recording body 33 and the beam is impaired due to gluing or bending of the recording body 33, or when the objective lens 32 has a track as shown in FIG. 3 (b). When the shift is made in the orthogonal direction, the position between the photodetector 34 and the detection light is shifted, the tracking error signal is multiplied by the offset, and normal tracking control may not be performed.

In addition, in the recording / erasing operation, there is a period when the reflection state becomes transiently unstable during the process of generating or erasing the recording pits. Also had to be considered.

2.3 Beam method This method can be used without any particular problem in the case of reproduction, but at the time of recording (or erasing), the sub beam 42 preceding the main beam 41 (the rear sub beam 43 at the time of erasing).
However, since an unrecorded portion is irradiated, a discontinuous offset occurs between the two sub beams based on the presence or absence of the recording pit 44, and a correct error signal cannot be detected.

The present invention provides a novel tracking error detection method that solves the problems of the above-described existing methods.

<Means for Solving the Problems> According to the present invention, as a first means, the first region in which the diffraction direction is inclined at a predetermined angle with respect to the track of the recording medium, and the diffraction area with respect to the track of the recording medium, A first-order diffraction in each area of the diffraction grating means is performed by using a diffraction grating means having a predetermined area inclined in a direction opposite to the one area and a second area having a different grating interval from the first area. Light generates first and second sub-beams that are deviated in opposite directions from the track center on the substantially same side in the track direction from the main beam and emitted at different angles from the main beam, and these sub-beams are recorded on a recording medium. The first obtained by irradiation or reflection or transmission,
The tracking error amount is detected based on the light amount difference of the second detection light.

Further, as a second means, a first area in which the diffraction direction is inclined at a predetermined angle with respect to the track of the recording medium, and a diffraction direction in which the recording medium is inclined by a predetermined angle with respect to the track in a direction opposite to the first area. Using a diffraction grating means having a second region that is tilted and the lattice spacing of which is different from the first region, the main beam consists of ± first-order diffracted light by the first region before and after substantially in the track direction, and the track The first and second sub-beams deviated from the center and the ± first-order diffracted light by the second region, the first and second sub-beams have different emission angles, and the Generate the third and fourth sub-beams deviated in the opposite direction to the first and second sub-beams, and irradiate the recording medium with these first, second, third and fourth sub-beams. Of the first, second, third, fourth detection light obtained by reflection or transmission, A value obtained by adding the difference between the light amounts of the first and third detection lights and the second and fourth detection lights is detected as a tracking error amount.

Further, as a third means, a first area in which the diffraction direction is inclined at a predetermined angle with respect to the track of the recording medium, and a diffraction direction in which the recording medium is inclined with respect to the track by a predetermined angle in a direction opposite to the first area. Using a diffraction grating means having a second region with a different grating interval from the first region,
Around the main beam approximately in the track direction, ±
First and second sub-beams composed of first-order diffracted light and symmetrically deviated from the track center with the main beam optical axis as the axis of symmetry, and ± first-order diffracted light by the second region, the first and second sub-beams The second and third sub-beams have different emission angles, and the first and second sub-beams having the main beam optical axis as a symmetric axis are symmetrically deviated from the track center in the opposite direction to the third and third sub-beams.
A fourth sub-beam is generated, and the first, second, third and fourth detections obtained by irradiating the recording medium with these first, second, third and fourth sub-beams to obtain a reflection or transmission. Light intensity (e ₁ ,
Based on e ₂ , f ₁ , f ₂ ), a value obtained by (f ₁ −e ₁ ) + (e ₂ −f ₂ ) is detected as a tracking error amount.

Still further, as a fourth means, a first area in which the diffraction direction is inclined at a predetermined angle with respect to the track of the recording medium, and a diffraction direction at a predetermined angle with respect to the track of the recording medium in a direction opposite to the first area. Using a diffraction grating means having a second region that is tilted and the lattice spacing of which is different from the first region, the main beam is composed of ± 1st-order diffracted light by the first region before and after approximately the track direction. The first and second sub-beams deviated from the track center, and ± first-order diffracted light by the second region, the first and second sub-beams have different emission angles, and the track Generates third and fourth sub-beams deviated from the center in the opposite direction to the first and second sub-beams, and applies these first, second, third and fourth sub-beams to a recording medium. First, second, third and fourth detections obtained by irradiation and reflection or transmission When reproducing light, a value obtained by adding the light amount difference between the first and third detection lights and the light amount difference between the second and fourth detection lights, and the first and third lights when recording (or erasing). A value obtained by multiplying the light amount difference of the detection light by a correction constant corresponding to the detection light amount ratio between the unrecorded portion and the recorded portion, and the light amount difference between the second and fourth detection lights are added. A value obtained by multiplying a correction constant corresponding to a ratio between an output during reproduction and an output during recording (or erasing) is detected as a tracking error amount.

<Operation> In each of the first means and the second, third, and fourth means described above, a sub-beam separated in advance from the main beam is used as a detection beam, and two sub-beams for performing differential detection Are arranged on the same side of the main beam in the track direction. As a result, even during the recording and erasing operations, accurate error detection is performed without unstable elements.

In the second, third and fourth means, two pairs of two sub-beams for performing differential detection are arranged before and after the main beam in the track direction, and the difference signals of each pair are added. As a result, a higher-level error signal can be obtained.

In addition, in the third and fourth means, the signals in each pair are operated so as to have opposite phases with respect to the sub-beams by the same area of the diffraction grating means. Thereby, the diffraction grating means is deviated in the direction orthogonal to the optical axis with respect to the main beam, and
Even if an imbalance occurs in the second area, this is canceled by the addition of the difference signal of each pair, and no offset occurs in the detection signal.

Further, in the fourth means, based on the second means,
At the time of recording or erasing, it corresponds to the correction constant corresponding to the offset of the detection value between each pair before and after the main beam, that is, the presence or absence of pits at the two pairs of detection positions, and the output ratio of the beam to the reproduction. The correction constant is included in the calculation formula. As a result, the same detection device can be applied to a recording or erasing operation.

Embodiment An embodiment of the present invention will be described below in detail with reference to FIGS. 1 and 2.

FIGS. 1 and 2 show an embodiment of an apparatus to which the tracking error detecting method of the present invention is applied. FIG. 1 (a) shows the arrangement of spots on a disk as a recording medium and spots on a photodetector. FIG. 1 (b) is a block diagram of a tracking error signal detection circuit, and FIGS. 2 (a) and (b) are explanatory diagrams of beam generation by an optical system and a diffraction grating of an optical head. .

First, the optical system will be described with reference to FIG. Fig. 2 (a)
1 is a semiconductor laser as a light source, 2 is an optical member having a two-divided diffraction grating 2a shown in detail in FIG. 2 (b), 3 is a half mirror for splitting a beam and generating astigmatism, 4 Is a collimating lens, 5 is an objective lens, 6 is a disk as a recording medium, 7 is a plano-concave lens, and 8 is an eight-divided photodetector shown in detail in FIG. A beam emitted from the semiconductor laser 1 is separated into a main beam and two pairs of sub-beams, which will be described in detail later, by a diffraction grating 2, an optical path is bent by a half mirror 3, and then a collimated lens 4 and an objective lens 5. The disk 6 is irradiated as five beams. Thereafter, the five return lights reflected by the disk are transmitted through the objective lens 5, the collimator lens 4, the half mirror 3, and the plano-concave lens 7 as detection light and are incident on the photodetector 8.

Next, generation of five beams by the diffraction grating 2a will be described with reference to FIG. FIG. 2 (b) shows the diffraction grating 2a.
FIG. 2 is a diagram viewed from an optical axis direction, and schematically shows respective beams generated thereby and spots projected on a disk. The diffraction grating 2a is composed of two regions, a first region E and a second region F, divided by a division line substantially coincident with the track center line T of the disk 6. First area E
Is formed such that the diffraction direction is inclined at an angle θ ₁ counterclockwise in the figure with respect to the track center line T, and has a constant first grating interval. The second region F is formed so that its grating direction is inclined at an angle θ ₂ clockwise in the drawing opposite to the first region E with respect to the track center line T with respect to the track center line T. Have different second lattice spacings. The semiconductor laser 1 is formed by the diffraction grating 2a.
Is separated into an O-order diffracted light and two types of plural high-order diffracted lights by the respective regions E and F. Of these, the O-order diffracted light is a main beam on the disk 6 as a raw beam (indicated by an optical axis). to project the S _1.

In the first region E, first and second sub-beams E ₁ and E ₂ are generated by ± first-order diffracted light of the higher-order diffracted light. This first,
The second sub-beams E ₁ and E ₂ project the first and second sub-spots S ₂ and S ₃ on the disk 6, which have the above-described inclination θ.
₁ is set to occur at a position deviated by a distance P ₁ from the track center T.

In the second region F, third and fourth sub beams F ₁ and F ₂ are generated by the ± first-order diffracted light. This third and fourth sub-beam
F ₁ and F ₂ are the third and fourth sub spots S ₄ and S ₅ on the disc 6
Projecting a but, by the slope theta ₂ these mentioned above, the distance P ₁ minute from the track center T, the first and second auxiliary spots
It is set to occur at a position deviated to the opposite side from S ₂ and S ₃ .

The third and fourth sub beams F ₁ and F ₂ are the first and second sub beams
The lattice spacing of each region is set so as to have a large diffraction angle with respect to E ₁ and E ₂ , and spots S ₄ and S ₅ are spot S ₂ and spot S ₂ , respectively.
It is arranged outside the track direction than S _3. However, according to the present invention, the detection of the differential signal, the pair of the first and third sub-beams E ₁ and F ₁ , and the second and fourth sub-beams E ₂ and F ₂ will be described in detail later. Between each of these first and third sub-beams E ₁ , F ₁ , and the second and fourth sub-beams
In each of the positions between E ₂ and F _2, the deviation distance P ₁ of each spot with respect to the track center T needs to be the same at the same time.
As in the conventional three-beam method, one using only a pair of sub-beams composed of ± first-order diffracted light of one diffraction grating disposed before and after the main beam is used to rotate the diffraction grating around the optical axis from the track center. Although the deviation distance itself of the sub-beam changes, the same condition is always always applied between the two sub-beams, and no mismatch occurs. However, in this invention,
When region division line of the diffraction grating 2a is inclined relative to the track center T, the spot comrades on the same side as described above (S ₂ and S ₄ or S ₃
S ₅₎ for deflection distance P ₁ from the track center T is not obtained the correct error signal will not match the diffraction grating 2a
Which is a necessary task to rotate about the optical axis to align the deflection distance P _1. At this time, as the diffraction angles of the sub-beams E ₁ , E ₂ , F ₁ , and F ₂ are large and the sub-spots S ₂ , S ₃ , S ₄ , and S ₅ are farther from the main spot S ₁ , the displacement due to the rotation increases. Adjustment becomes difficult. For this reason, it is desirable that each sub-spot S ₂ , S ₃ , S ₄ , S ₅ be as close as possible to the main spot S ₁ as long as the configuration of the photodetector 8 is not hindered. spot S ₂ and the interval P ₂ of S ₄ (second, fourth sub-spots
The same applies to S ₃ and S ₅ ).

The respective regions E and F of the diffraction grating 2a are designed such that the respective grating intervals and the relative angles of the gratings are based on the various conditions described above.

In FIG. 2 (b), the sub spots S ₂ , S ₃ ,
Although S ₄ and S ₅ are indicated by circles, actually the shape determined by the area dividing line of the diffraction grating 2 a and the outer shape of the beam from the semiconductor laser 1 or the aperture shape of the optical system (the dividing line is a straight line, the outer shape of the beam) Is a semi-circle if is a circle), and is slightly disturbed by various aberrations. However, since the regions E and F have a symmetric shape, this does not affect the detection of the error signal.

Next, a method of detecting various signals will be described with reference to FIG.

Photodetector in FIG. 1 (a) 8, the eight independent photodetection elements a arranged in a longitudinal way to match the track direction as shown in FIG, b, c, d, e 1, e 2 , F ₁ and f ₂ . Detecting light comprising the reflected light corresponding to the spot S ₁ to S ₅ on the disk 6 is incident on the light detector 8, respectively, to form a spot S _'1 ~S' ₅ to the position shown in FIG. In FIG. 1A, the disk 6 rotates in the direction of arrow H.

(Detection of information signal) Although the detailed circuit of the information signal is not shown, the light detection elements a, b, c,
Using d, obtained by a + b + c + d.

(Detection of Focus Error Signal) The focus error signal uses a known astigmatism method (the astigmatism is obtained by the converged light passing through the half mirror 3 which is an inclined flat plate), and the light detection elements a and b, c, d
And (a + c)-(b + d).

(Detection of tracking error signal) The tracking error signal is detected by photodetectors e ₁ , e ₂ , f ₁ , f ₂
Is generated by the detection circuit shown in FIG. 1 (b). In the figure, photodetectors e ₁ and f _{1 located} forward of the main beam
Are output by the subtractor 9 in a relationship of f ₁ −e ₁ , and the output is supplied to the movable terminal of the switch 10. switch
One fixed terminal h of 10 is connected directly to an adder 12 via a gain control circuit 11, and the other fixed terminal i is connected to an adder 12. On the other hand, the photodetector e ₂ behind the main beam
And each output of the f ₂ by a subtractor 13, is calculated in relation to e ₂ -f _1, its output is supplied to a movable terminal of the switch 14.
One fixed terminal j of the switch 14 is connected directly to the adder 12, and the other fixed terminal k is connected to the adder 12 via the gain control circuit 15. Gain control circuit 11 corrects the detected light intensity difference between the rear pits exist to pit does not exist at the main spot S ₁ forward at the time of recording, has a correction constant g ₁ for the equivalent if pits are present , And the output of the subtracter 9 is corrected so as to be represented by g ₁ · (f ₁ −e ₁ ). The gain control circuit 15 for the pit is not present in the main spot S ₁ rearward at the time of erasing, and correcting the detected light amount difference between the forward pits are present, the correction constant to the equivalent if pit exists g ₂ And a correction is given to the output of the subtractor 13 so as to be expressed by g ₂ · (e ₂ −f ₂ ). Adder 12
Are as described above, adds the calculation result of the arithmetic operation result and the main spot S ₂ behind the main spot S ₁ forward, and supplies its output to a movable terminal of the switch 16. One fixed terminal 1 of the switch 16 is connected directly to the fixed terminal m, and the other fixed terminal m is connected to an output terminal TES via a gain control circuit 17, where a tracking error signal is obtained. Gain control circuit 17
Has a correction constant G for correcting the output of the semiconductor laser 1 at the time of recording / erasing with respect to that at the time of reproduction, and obtaining a detection output equivalent to that at the time of reproduction. This is added to the output of 12 and output as a tracking error signal.

Hereinafter, the operations of detecting a tracking error signal during reproduction, recording, and erasing will be described in detail.

1. During playback During playback, switch 10 is on terminal h, and switch 14 is on terminal j.
And the switch 16 is on the terminal l side. (State shown in FIG. 1B) In this state, each of the gain control circuits 11, 1
5,17 are all paths, thus a tracking error signal is obtained by the calculation represented by _{(f 1 -e 1) + (} e 2 -f 2). During playback, the main spot
Pits exist with S ₁ before and after conditions of the respective differential detection pair (f ₁ -e ₁₎ and (e ₂ -f ₂₎ is to become the same, not give special correction. According to the above equation, when the beam and the track center are displaced, the light quantity on the same side with respect to the track (that is, f ₁ and e ₂
Or because e ₁ and f ₂ ) change in phase and by the same amount, the calculation results of each differential detection pair (f ₁ −e ₁ ) and (e ₂ −f ₂ ) change in phase and by the same amount. A doubled error signal is obtained.

In this calculation method, a device is provided which is less susceptible to the displacement between the diffraction grating 2a and the beam.
In FIG. 2 (b), when the center of the beam and the dividing line of the diffraction grating 2a are shifted in a direction orthogonal to the dividing line (left and right in the figure), they occupy the regions E and F. As a result, an offset occurs between the photodetector elements represented by e related to the region E and those represented by f related to the region F. However, according to the above equation, in each differential detection pair (f ₁ −e ₁ ) and (e ₂ −f ₂ ), the one represented by e and the one represented by f are subtracted in opposite phases. Therefore, the offset is canceled by these additions, and does not affect the error signal. Therefore, this means that the diffraction grating 2a
This means that the optical member 2 having the above can be relatively easily incorporated into the optical system.

2. During recording During recording, the switch 10 is on the i side, the switch 14 is on the j side, and the switch 16 is on the m side. In this state, the output of the subtractor 9 is interposed by the gain control circuit
g ₁ is given, and a gain control circuit 17 is interposed between the output of the adder 12 and a correction constant G. The tracking error signal is given by G · [g ₁ · (f ₁ −e ₁ ) + (E ₂ −f ₂ )]. At the time of recording, the differential detection pair (f ₁ −e ₁ ) ahead of the main spot S ₁ detects a portion where no pit exists, so that the detection equivalent to the case where a pit exists by adding the correction constant g ₁ Correct to value. Further, since the beam intensity is different from that at the time of reproduction, correction is made to a state equivalent to that at the time of reproduction by giving a correction constant G. As a result, a tracking error signal is detected in the same manner as during reproduction.

3. At the time of erasing At the time of erasing, the switch 10 is on the h side, the switch 14 is on the k side, and the switch 16 is on the m side. In this state, the output of the subtractor 13 is interposed by the gain control circuit
g _{2, and} the output of the adder 12 is provided with a correction constant G via a gain control circuit 17 as in the case of recording, and the tracking error signal is given by G · [(f ₁ −e ₁ ) + G ₂ · (e ₂ −f ₂ )]. Main spot when erasing
Since the differential detection pair (e ₂ −f ₂ ) after S ₁ detects a portion where no pit exists, correction is made to a detection value equivalent to the case where a pit exists by adding a correction constant g _2. I do. In addition, since the beam intensity is different from that at the time of reproduction similarly to that at the time of recording, correction is made to a state equivalent to that at the time of reproduction by giving a correction constant G. As a result, a tracking error signal is detected in the same manner as during reproduction.

When a different beam intensity is used at the time of erasing than at the time of recording, the value of the correction constant G may be switched accordingly.

<Effect> As described above, according to the present invention, a pair of sub-beams for tracking error signal detection are arranged on the same side in the track direction forward or backward with respect to the main beam, and error detection is performed by differential detection of these. Since the error detection is performed, accurate error detection eliminating the unstable elements of the conventional various methods can be realized not only at the time of reproduction but also at the time of recording and erasing.

Further, since two pairs of the sub-beams are provided before and after the main beam, and error detection values of the respective sub-beams are added, a higher-level error signal can be obtained.

Also, in each differential detection pair, the calculation is performed so that the sub-beams in the same area of the diffraction grating means are in opposite phases, and the results are added to cancel the influence of the shift of the diffraction grating means. In addition, high precision is not required for incorporating the diffraction grating means into the optical system.

Further, at the time of recording or erasing, a correction constant for correcting an offset generated due to the presence or absence of a pit at each differential detection position before and after the main beam, and a correction constant corresponding to a difference in beam intensity from that at the time of reproduction are used. Since the calculation is incorporated into the calculation, the same detection device can be applied to any of the operations of reproducing, recording, and erasing.

[Brief description of the drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 (a) is an explanatory view of a spot arrangement on a disk and a spot arrangement on a photodetector, and FIG. 1 (b) is a tracking error. FIGS. 2 (a) and 2 (b) are block diagrams of the signal detection circuit, and are explanatory diagrams of a beam generation state by the optical system and the diffraction grating of the optical head, respectively. 3 and 4 show a conventional method, wherein FIGS. 3 (a) and 3 (b) are illustrations of a one-beam method, and FIG. 4 is an illustration of a three-beam method. 2a: diffraction grating, E: first area, F: second area,
E ₁ , E ₂ ... First and second sub-beams, F ₁ , F ₂ ... Third and fourth sub-beams, e ₁ , e ₂ , f ₁ , f _2. … Subtractor, 12… Adder, 11, 15, 17 …… Gain control circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Taizo Yokota 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-3-8128 (JP, A) JP-A 64-64 39636 (JP, A)

Claims (4)

(57) [Claims] A first region having a diffraction direction inclined at a predetermined angle with respect to a track of the recording medium; and a diffraction direction inclined at a predetermined angle with respect to the track of the recording medium in a direction opposite to the first region. A diffraction grating means having a second area having a different grating interval from the first area is used, and a first-order diffracted light beam in each area of the diffraction grating means makes the center of the track substantially the same in the track direction from the main beam. First and second sub-beams deviated from each other in opposite directions and emitted at different angles are generated, and the first and second sub-beams obtained by reflection or transmission by irradiating each of these sub-beams to the recording medium A tracking error detection method, wherein a difference in the amount of detection light is detected as a tracking error amount. 2. A first area in which a diffraction direction is inclined at a predetermined angle with respect to a track of a recording medium, and a diffraction direction in which the recording medium is inclined at a predetermined angle with respect to the track in a direction opposite to the first area. Using a diffraction grating means having a second region having a different grating interval from the first region, the main beam is substantially ± tracked by the first region before and after the track direction.
The first, consisting of first-order diffracted light, deviated from the track center,
The second sub-beam, the second sub-beam, the ± first-order diffracted light by the second region, the first, the second sub-beam has a different exit angle, and from the track center the Generates third and fourth sub-beams deviated in the opposite directions to the first and second sub-beams, and irradiates the recording medium with these first, second, third and fourth sub-beams Of the first, second, third, and fourth detection lights obtained by reflection or transmission, the value obtained by adding the light amount difference between the first and third detection lights and the second and fourth detection lights. A tracking error detection method comprising: detecting a tracking error amount as a tracking error amount. 3. A first area in which a diffraction direction is inclined at a predetermined angle with respect to a track of a recording medium, and a diffraction direction is inclined at a predetermined angle with respect to a track of the recording medium in a direction opposite to the first area. Using a diffraction grating means having a second region having a different grating interval from the first region, the main beam is substantially ± tracked by the first region before and after the track direction.
First and second sub-beams composed of first-order diffracted light and symmetrically deviated from the track center with the main beam optical axis as the axis of symmetry, and ± first-order diffracted light by the second region, the first and second sub-beams The third and fourth beams have different exit angles from the second sub-beam and are symmetrically deviated from the track center in the direction opposite to the first and second sub-beams with the main beam optical axis as a symmetric axis. Generate sub-beams, irradiate these first, second, third, and fourth sub-beams to a recording medium to obtain first, second, third, and
Detecting a value obtained by (f ₁ −e ₁ ) + (e ₂ −f ₂ ) as a tracking error amount based on the light amount (e ₁ , e ₂ , f ₁ , f ₂ ) of the fourth detection light. Tracking error detection method characterized by the above-mentioned. 4. A first area having a diffraction direction inclined at a predetermined angle with respect to a track of a recording medium, and a diffraction direction inclined at a predetermined angle with respect to a track of the recording medium in a direction opposite to the first area. Using a diffraction grating means having a second region having a different grating interval from the first region, the main beam is substantially ± tracked by the first region before and after the track direction.
The first, consisting of first-order diffracted light, deviated from the track center,
A second sub-beam, composed of ± first-order diffracted light by the second region, having a different emission angle from the first and second sub-beams, and the first and second sub-beams from the track center Generates third and fourth sub-beams deviated in the opposite direction to the first, second, third and fourth detection light beams. The value obtained by adding the difference and the difference between the light amounts of the second and fourth detection lights, and the difference between the light amounts of the first and third detection lights during recording (or erasing) between the unrecorded portion and the recorded portion. A value multiplied by a correction constant corresponding to the detected light amount ratio is added to the difference between the second and fourth detected light amounts, and the ratio between the output of the light source during reproduction and the output during recording (or erasing) is added thereto. A tracking error detection method, wherein a value obtained by multiplying by a correction constant corresponding to (i) is detected as a tracking error amount.