JP2875650B2 - Optical information recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus such as an optical pickup suitably used for a compact disk reproducing apparatus, and more particularly to an optical information recording / reproducing apparatus characterized by detecting a servo signal. About.

[0002]

2. Description of the Related Art Various recording methods, such as a phase change type and a reflectance change type, are known for an optical information recording / reproducing apparatus depending on a method of forming a recording pit. In addition, depending on the presence or absence of reversibility of pit formation, it is classified into a rewritable type and a write-once type. In general, all of these optical information recording / reproducing devices use a recording medium in which a guide groove corresponding to a recording track is formed in advance, During recording / reproducing and erasing operations, tracking control is performed so that a light beam traces the guide groove.

As a tracking error detection method used for tracking control, two methods, a push-pull method using one beam and a three-beam method, are mainly used. Hereinafter, these methods will be described.

[Push-Pull Method Using One Beam] First,
The push-pull method using one beam will be described with reference to FIGS. This method generally involves irradiating a track on an optical disc as a recording medium with a single light beam also serving as a recording / reproducing beam, and detecting light obtained by reflection or transmission of the light into a division line corresponding to the track direction of the optical disc. The tracking error amount is detected by detecting the difference between the light amounts of the two photodetectors.

FIG. 5 shows a conventional example of an optical pickup which performs tracking error detection by a push-pull method using one beam. FIG. 6 shows a diffraction element 102 (FIG. 6A) and a photodetector 106 viewed from an optical disk 105. (FIG. 6 (b))
Indicates the positional relationship.

The schematic configuration of the optical pickup is as follows. A light beam (divergent light) emitted from the semiconductor laser 101 passes through the diffraction element 102, and subsequently, a collimator lens 103 and an objective lens 104 disposed thereabove.
Through the optical disk 105.

On the other hand, the reflected light (return light) from the optical disk 105 is converged by the objective lens 104, passes through the collimator lens 103, is diffracted by the diffraction element 102, and is condensed on the photodetector 106.

Next, a focus detection mechanism and a tracking detection mechanism of the optical pickup will be described.

(Focus detection mechanism) As shown in FIG. 6A, the diffraction element 102 has a substantially circular shape,
Two semicircular regions 102a and 102b divided into two
have. On the other hand, the photodetector 106 has a dividing line A ′,
Four photodetectors 106 divided by B ′ and C ′
a, 106b, 106c, and 106d. Of the reflected light, the light diffracted by one region 102a of the diffraction element 102 is condensed on the dividing line A ', and the light diffracted by the other region 102b is condensed on the dividing line C'. You.

In such a configuration, when the laser beam from the semiconductor laser 101 is accurately focused on the optical disk 105 by the objective lens 104, that is, when the laser beam is focused, as shown in FIG. Focus spots 108a and 108 of the diffracted light from the diffraction element 102
b is formed at one point on the dividing lines A ′ and C ′ of the photodetector 106, and the outputs of the photodetectors 106a and 106b and the outputs of the photodetectors 106c and 106d become equal.

On the other hand, when the optical disk 105 approaches the objective lens 104 for some reason, the focal point of the diffracted light is formed behind the photodetector 106. Therefore, FIG.
As shown in (c), the light condensing spot 108a is not formed at one point on the dividing line A ', and a phenomenon that the light converging spot 108a spreads in a semicircular shape on the light detection unit 106a occurs. Similarly, focus spot 108
b spreads in a semicircular shape on the light detection unit 106d.

On the contrary, the optical disk 105 is
4, the focal point of the diffracted light is in front of the photodetector 106. For this reason, as shown in FIG. 7A, the condensed spot 108a spreads in a semicircular shape on the light detection unit 106b, and the condensed spot 108b is spread on the light detection unit 106c.
Spreads in a semicircle.

Accordingly, assuming that the output signals of the photodetectors 106a, b, c, and d are S1, S2, S3, and S4, respectively, the focus error signal FES is obtained by calculating the following equation.

FES = (S 1 + S 4) − (S 2 + S 3) This operation is performed by the adders 110 a, 1 a shown in FIG.
10b and the subtractor 111.

(Tracking detection mechanism) Next, a tracking detection mechanism in the optical pickup will be described. FIG. 8 shows a focused spot 109 on the optical disk 105.
And the relative position of the information track (pit train) 120 and the intensity distribution of the return light. As shown in FIG.
When the focused spot 109 is exactly on the information track 120, the intensity distribution of the return light is symmetric with respect to the track direction.

On the other hand, for some reason, FIG.
As shown in (c), when the information track 120 is shifted to the left with respect to the condensing spot 109, the right side of the return light becomes dark (hatched portion in the figure) and the left side becomes bright. Conversely, when the information track 120 is shifted to the right with respect to the condensed spot 109, the opposite occurs. As shown in FIG. 8A, the left side is dark and the right side is bright.

Here, as shown in FIG. 6A, the return light is divided into two by the diffraction element 102, and the division line of the diffraction element 102 coincides with the track direction. Therefore, the tracking error signal TES is
It is obtained as the difference between the light amounts of a and 108b. That is, it can be obtained by performing the operation of the following equation using the output signals S1, S2, S3, and S4.

TES = (S1 + S2) − (S3 + S4) This operation is performed by adding the adders 112a, 1a shown in FIG.
12b and the subtractor 113.

As described above, the focus error signal F
When the ES and the tracking error signal TES are obtained,
An actuator (not shown) drives the objective lens 104 based on these servo signals FES and TES, so that the information track 120 on the optical disk 105 is appropriately focused on the converging spot 109.

[Three-beam method] Next, the three-beam method will be described with reference to FIGS. In this method, a light beam is divided by a diffraction grating 207 into a main beam and two sub beams, and a tracking error is detected using the sub beams.

FIG. 9 shows a conventional example of an optical pickup using the three-beam method. FIG. 10 shows a diffraction element 202 (FIG. 10A) and a photodetector 206 (FIG. 1) viewed from an optical disk 205.
0 (b)). The configuration of this optical pickup is as follows.

The light beam emitted from the semiconductor laser 201 is split by the first diffraction element 207 into a 0th-order diffracted light (main beam) and ± 1st-order diffracted light (sub-beam) for detecting a tracking shift, and The light passes through the two diffraction elements 202. Subsequently, the light is focused on the optical disk 205 by the collimator lens 203 and the objective lens 204.

On the other hand, the reflected light from the optical disk 205 is converged by the objective lens 204,
03, and then diffracted by the diffraction element 202 and collected on the photodetector 206.

(Focus Detection Mechanism) As shown in FIG. 10A, the diffraction element 202 has a substantially circular shape,
Two semicircular regions 202a and 202 divided into two by L
b. On the other hand, the photodetector 206 has five photodetectors 206a, 206b, 206c, and 20 divided by four division lines A ″, B ″, C ″, and D ″.
6d and 206e.

Diffracted by the first diffraction element 207,
After being converged on the optical disk 205, one of the areas 20 of the diffraction element 202 in the reflected light of the main beam is reflected.
The light diffracted by 2a forms a condensed spot 208a on the division line A '' as shown in FIG. 10B. Also,
The light diffracted by the other region 202b forms a converging spot 208b on the light detection unit 206d. Also,
The reflected light of one of the two sub-beams is reflected on the photodetector 206a by two converging spots 208a ',
08b ', and the reflected light of the other sub-beam forms two condensed spots 208a'', 20a on the photodetector 260e.
8b ″ is formed.

In such a configuration, when the light beam from the semiconductor laser 201 is precisely focused on the optical disk 205 by the objective lens 204, that is,
At the time of focusing, as shown in FIG. 11B, a condensed spot 208a of the diffracted light from the region 202a of the second diffraction element 202 is formed at one point on the division line A ″ of the photodetector 206, Therefore, the outputs of the light detection units 206b and 206c become equal.

On the other hand, when the optical disk 205 approaches the objective lens 204 for some reason, the focal point of the diffracted light is formed behind the photodetector 206. Therefore, in this case, as shown in FIG.
08a spreads in a semicircular shape on the light detection unit 206b. Conversely, when the optical disk 205 moves away from the objective lens 204, the focal point of the diffracted light is in front of the photodetector 206. Therefore, in this case, as shown in FIG. 11C, the condensed spot 208a spreads in a semicircular shape on the light detection unit 206c.

Accordingly, assuming that the output signals of the light detection units 206b and 206c are S2 and S3, respectively, the focus error signal FES can be obtained by performing the following equation.

FES = S2-S3... This operation is performed by the subtractor 210 shown in FIG.

(Tracking detection mechanism) Next, a tracking detection mechanism in the optical pickup will be described. FIG. 12 shows the converging spot 20 on the optical disc 205.
9 shows a positional relationship between the information track 220 and the information track 220. FIG.
As shown in FIG. 2B, the converging spots 209 ′ and 209 ″ of the two sub beams have a symmetrical positional relationship in the track direction with respect to the converging spot 209 of the main beam. They are slightly offset in opposite directions.

If for some reason the information track 220
Is shifted to the left in the figure with respect to the condensing spot 209 (FIG. 10A), the condensing spot 209 'is located almost on the information track 220, and the intensity of the reflected light decreases. On the other hand, the condensed spot 209 ″ deviates from the information track 220, and the reflected light increases. On the other hand, when the information track 220 is shifted to the right in the drawing with respect to the converging spot 209 ((c) in the figure), the opposite phenomenon occurs, and the intensity of the reflected light of the converging spot 209 ′ increases However, the intensity of the reflected light from the condensing spot 209 ″ decreases.

As described above, the converging spots 209 ', 209'
09 ″ is reflected by the photodetectors 206a and 206, respectively.
Since the light is converged on the signal e, the output signals of the photodetectors 206a and 206e are S1 and S5, respectively, and the tracking error signal TES can be obtained by performing the calculation represented by the following equation.

TES = S1-S5... This operation is performed by the subtracter 211 shown in FIG.

As described above, the focus error signal F
When the ES and the tracking error signal TES are obtained,
On the basis of these servo signals FES and TES, an actuator (not shown) drives the objective lens 104, whereby a condensed spot 209 is formed on the information track 220.

The three-beam system is hardly influenced by the inclination of the optical disk 205 and the depth of pits and guide grooves, and has a high stability. Therefore, the three-beam system is mainly used for a read-only optical pickup.

[0036]

The above two methods have excellent characteristics, respectively, but record / reproduce three types of compact discs (CD) of a rewritable type, a write-once type and a read-only type with one optical pickup. Have problems to do.

This is because the CD is a constant linear velocity (CLV) optical disk. That is, in the read-only type, the information for speed control is included in the recording information, so that the rotation speed of the optical disk can be controlled simultaneously with the reproduction of the recording information. However, in the rewritable type or the write-once type, since no information is recorded at the time of the first recording, such control is impossible.

For this reason, a guide groove is provided on a rewritable or write-once optical disk, and at the same time, as shown in FIG. 13, the guide groove 230 is meandered (wobbled) at a constant cycle to detect this. Thus, a method of keeping the linear velocity of the optical disk constant is adopted. Incidentally, since the linear velocity of the CD is 1.2 to 1.4 m / sec and the wobbling frequency is 22.1 kHz according to the standard, the meandering period L of the guide groove 230 is 54 to 63 μm.

In order to detect this signal with high sensitivity in the three-beam system, the interval between two sub-beams needs to be L × N (N is an integer). When the above numerical values are substituted, the beam intervals are about 60 μm, 120 μm,..., But are limited to 60 μm due to restrictions on optical design. Therefore, the degree of freedom in design becomes extremely small. Further, from the viewpoint of improving the tracking performance, the smaller the beam interval, the better, and it is currently about 30 to 40 μm. Further, the direction of the dividing line of the diffraction element 202 is 90 ° with respect to the track direction due to the restriction of the arrangement of the converging spot on the photodetector 206.
Most preferably, and in fact, it is designed so. This limitation is inevitable in an optical pickup using a diffraction element for splitting light.

For the reasons described above, the three-beam system has difficulty in being applied to rewritable and write-once optical pickups, and as described above, has been mainly used for read-only optical pickups.

On the other hand, since the one-beam method has one condensing spot, the design is not limited as in the three-beam method, and wobbling can generally be detected with higher sensitivity than the three-beam method. However, the push-pull method originally has a disadvantage that when the objective lens moves in the radial direction, an offset 240 occurs in the signal as shown in FIG. It also has the disadvantage that it is easily affected by the tilt of the optical disk. As described above, the push-pull method is disadvantageous in that it has the advantage of the three-beam method.

For the above reasons, an optical information recording / reproducing apparatus capable of recording / reproducing three types of CDs of a rewritable type, a write-once type and a read-only type is realized by using a single type of the two types. It is the present condition that did not reach.

The present invention solves such a drawback of the prior art. The tracking error signal can be detected by any of the three-beam system and the push-pull system.
It is an object of the present invention to provide an optical information recording / reproducing apparatus capable of recording / reproducing three types of CDs of a rewritable type, a write-once type and a read-only type on a stand.

[0044]

An optical information recording / reproducing apparatus according to the present invention comprises a light generating means for converting light from a light generating means into ± 1st-order diffracted light for detecting a tracking shift and 0th-order diffracted light for detecting a focus. A first diffraction element that splits the light into three diffracted lights, an optical system that collects the three diffracted lights on a recording medium and detects light reflected from the recording medium, and is detected by the optical system A second diffraction element that is provided on the optical axis of the reflected light, has at least two regions, and divides the reflected light by the region and diffracts the reflected light in different directions; and An optical information recording / reproducing apparatus including a photodetector for detecting the diffracted light of the recording medium, wherein the area on the second diffraction element has an angle θ (20 ° ≦ 20) with respect to the track direction of the recording medium. (θ ≦ 80 °) And the photodetector is
With deriving a first tracking error signal Ri by <br/> diffracted light receiving from the second diffraction element corresponding to the order diffracted light,
A focus error signal is received by receiving the diffracted light from the second diffraction element corresponding to the zero-order diffracted light, and a second tracking error signal is derived by a track width direction component of the diffracted light. is there.

Preferably, the grating lines of the second diffraction element
Is perpendicular to the parting line.

[0046]

As described above, the area of the diffraction element that diffracts the reflected light from the recording medium, that is, the return light, is defined by the dividing line inclined at an angle θ (20 ° ≦ θ ≦ 80 °) with respect to the track direction of the recording medium. When the light is divided into at least two or more, the diffracted light diffracted by the diffraction element has a component in the track width direction orthogonal to the track direction. Therefore, if this width direction component is used, the track error signal TES can be detected even in the push-pull method using one beam. On the other hand, according to the three-beam method, the tracking error signal TES can of course be detected. Here, as the range of the angle θ, 20 ° ≦ θ ≦ 80 °
Is set for the following reason. First, push
The amplitude (relative amplitude) of the signal depends on the angle θ.
When approaching ゜, it rapidly decreases as shown in FIG.
You. On the other hand, from the figure, if the angle θ is 80 ° or less,
When the angle θ is 0 °, an amplitude of 20% or more can be obtained.
Recognize. If this level of amplitude can be obtained, the subsequent electronic circuit
Can be easily compensated for by amplification or the like. Therefore, the corner
Degree θ may be set to 80 ° or less. Second, the angle θ is
When approaching 0 °, for example, an apparatus of the type shown in FIG.
In this case, the detection sensitivity of the focus error signal FES decreases.
However, experience has shown that if θ is set to 20 ° or more,
No detection sensitivity can be obtained. Therefore, in the present invention,
The range of the angle θ is set to 20 ° ≦ θ ≦ 80 °. What
Note that the direction of the grid line of the second diffraction element is
In the device of the type shown in FIG.
Unlike the device of the type shown, the focus error signal FES
There is no decrease in detection sensitivity. That is, according to this structure,
Focus spot (semicircular spot) 8a is divided line A
, The decrease in detection sensitivity is
Absent. By the way, in the structure of FIG.
As it crosses the secant line A, as θ approaches 0 °
As a result, the detection sensitivity is significantly reduced.

Therefore, according to the above configuration, the tracking control of the push-pull system and the three-beam system by one beam becomes possible. This means that an optical pickup suitable for both systems can be realized. That is, according to the optical pickup having the above configuration, it is possible to realize an optical pickup suitable for each of the three types of optical pickups of the rewritable type, the write-once type, and the read-only type.

[0048]

Embodiments of the present invention will be described below.

FIG. 1 shows an embodiment in which the optical information recording / reproducing apparatus of the present invention is applied to an optical pickup. A light-condensing spot is focused on the optical disk 5 below the optical disk 5 as a recording medium. The following optical system is provided.
The configuration will be described below together with the operation.

A light beam (divergent light) emitted upward from the semiconductor laser 1 is incident on a first diffraction element 7 disposed above the semiconductor laser 1, and is diffracted by the diffraction element 7 into a zero-order diffraction light. (Main beam) and ± first-order diffracted light for detecting tracking deviation. The three-divided diffracted light passes through the second diffractive element 2 disposed above the diffractive element 7 and is subsequently collimated by the collimating lens 3 disposed above it. An objective lens 4 is provided above the collimator lens 3. The objective lens 4 converges the light collimated by the collimator lens 3 onto the optical disc 5 as a converging spot.

On the other hand, the light reflected by the optical disc 5
That is, the return light is converged by the objective lens 4, transmitted through the collimator lens 3, and then diffracted by the diffraction element 2,
The light is detected by a photodetector 6 disposed at a position deviated to the side of the semiconductor laser 1.

Next, a focus detection mechanism in the optical pickup having the above-described configuration will be described. As shown in FIG. 2A, the second diffraction element 2 has a substantially circular shape and has two divided semicircular regions 2a and 2b. However, the diffraction element 2 of this embodiment is different from the diffraction element 2 of the above-described conventional example shown in FIG.
02 differs in the following points. That is, in the diffraction element 202, the two regions 202 are divided by a dividing line orthogonal to the track direction.
a and 202b are divided, but in the diffraction element 2 of the present embodiment, they are divided into two regions 2a and 2b by a division line DL inclined at an angle θ with respect to the track direction.

On the other hand, as shown in FIG. 2B, the photodetector 206 has five photodetectors 6a, 6b, 6c, 6d divided by four division lines A, B, C and D, and 6
e.

The reflected light of the main beam, which is diffracted by the first diffractive element 7 and condensed on the optical disk 5 and then reflected, is diffracted in one area 2a of the diffractive element 2 in FIG. As shown in b), a condensing spot 8a is formed on the dividing line A. The light diffracted by the other region 2b forms a converging spot 8b on the photodetecting section 6d. The reflected light of one of the two sub-beams is reflected on two light spots 8 on the photodetecting section 6a.
a ′ and 8b ′, and the reflected light of the other sub-beam is provided on the photodetecting unit 6e by two focused spots 8a ″ and 8b ″.
To form

As can be understood from the above description, the focus mechanism of the present embodiment is the same as the focus mechanism of the three-beam system except that the direction of the division line DL of the diffraction element 2 is different as described above. Therefore, also in this embodiment,
If the difference between the outputs of the light detectors 6b and 6c is detected and a calculation similar to the above equation is performed, the focus error signal FES can be obtained. Specifically, it is obtained based on the operation result of the subtractor 10.

The tracking mechanism is also described in the above 3
Since the difference is the same as that of the beam method, if the difference between the outputs of the light detectors 6a and 6b is detected and the same operation as the above expression is performed by the subtractor 11, the tracking error signal TES can be obtained.

In addition, according to the present embodiment, since the division line DL of the second diffraction element 2 is inclined by θ with respect to the track direction, it becomes possible to detect the tracking error signal TES by the push-pull method. . That is, according to the conventional three-beam system shown in FIG. 9, since the dividing line of the diffraction element 202 is in the direction orthogonal to the track direction, the diffraction element 202
, A component in the track width direction cannot be obtained, and eventually a tracking error signal TES of the push-pull system cannot be obtained.

On the other hand, in the present embodiment, since the dividing line of the second diffraction element 2 is inclined by θ with respect to the track direction, a component in the track width direction can be obtained through the diffraction element 2, so that It becomes possible to detect the pulling type tracking error signal TES.

Specifically, as shown in FIG. 2B, since the division line B of the photodetector 6 coincides with the track direction,
By subtracting the output of the light detection unit 6d from the sum of the light detection units 6b and 6c on both sides of the dividing line B by the subtractor 12, the tracking error signal TES can be obtained.

As described above, according to this embodiment, the tracking error signal TES can be detected in any of the three-beam system and the push-pull system. Therefore, according to the optical pickup of this embodiment, it is possible to realize an optical information recording / reproducing apparatus capable of recording / reproducing three types of CDs of a rewritable type, a write-once type, and a read-only type.

FIG. 3 shows another embodiment of the present invention. This embodiment is the same as the above embodiment except that the direction of diffraction of the return light is different. That is, in the above embodiment, the diffraction direction of the return light is oblique to the division line of the diffraction element 2,
In this embodiment, the direction of the diffraction is perpendicular to the dividing line. According to this embodiment, the same effect as the above embodiment can be obtained. Corresponding parts have the same reference characters allotted, and detailed description thereof will not be repeated.

The angle θ is 20 ° to 80 °
Is preferred. The reason will be described below.

First, the amplitude (relative amplitude) of the push-pull signal depends on the angle θ, and when θ approaches 90 °, decreases sharply as shown in FIG. On the other hand, FIG. 4 shows that if the angle θ is 80 ° or less, an amplitude of 20% or more when the angle θ is 0 ° can be obtained. If such an amplitude can be obtained, it can be easily compensated by amplification or the like in a subsequent electronic circuit. Therefore, it is preferable to set the angle θ to 80 ° or less.

Second, as the angle θ approaches 0 °, the sensitivity of the focus error signal FES is reduced in the method of the embodiment of FIG. On the other hand, in the method of the embodiment in FIG.
There is no decrease in the detection sensitivity of the focus error signal FES. Immediately
According to this structure, the focus spot (semicircular
(Spot) 8a will be irradiated along the division line A.
Therefore, there is no decrease in detection sensitivity. By the way, in the structure of FIG.
Shows that a semicircular spot appears to intersect with the dividing line A.
, The detection sensitivity is significantly reduced as θ approaches 0 °.
Because However, in the method of the embodiment shown in FIG. 3, the width of each of the photodetectors 6a, 6b, 6c, 6d and 6e becomes narrow, and the design becomes difficult. From this, it is empirically desirable that θ be approximately 20 ° or more.

For the first and second reasons described above, it is preferable to set the angle θ in the range of 20 ° to 80 ° in practice.

In each of the above embodiments, the diffraction element that diffracts the return light is divided into two by the division line DL. However, the number of divisions is not limited to two. A configuration in which the diffraction element is divided into four by a line may be employed.

[0067]

According to the optical information recording / reproducing apparatus of the present invention described above, the tracking error signal TE is obtained in both the one-beam push-pull system and the three-beam system.
S can be detected. Thus, according to the present invention,
An optical pickup utilizing the advantages of both types, that is, an optical pickup suitable for all three types of a rewritable type, a write-once type, and a read-only type can be realized.

Further, since only a slight design change is required for the conventional three-beam optical pickup, no cost increase is caused. Further, in particular, the optical device according to claim 2
According to the expression information recording / reproducing apparatus, the focus error signal FE
The advantage is that the detection sensitivity of S does not decrease.
You.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical pickup according to one embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between a diffraction element and a photodetector as viewed from an optical disc.

FIG. 3 is a drawing similar to FIG. 2 in another embodiment of the present invention.

FIG. 4 shows the relative amplitude of the push-pull signal on the vertical axis and the angle between the track direction and the dividing line of the diffraction element on the horizontal axis.
9 is a graph showing the angle θ dependence of the push-pull signal amplitude.

FIG. 5 is a perspective view showing a conventional example of a push-pull type optical pickup.

FIG. 6 is a view showing a positional relationship between a diffraction element and a photodetector as viewed from an optical disc in the optical pickup of FIG. 5;

FIG. 7 is a view showing a principle of detecting a focus error signal FES in the optical pickup of FIG. 5;

FIG. 8 is a view showing a principle of detecting a tracking error signal TES in the optical pickup of FIG. 5;

FIG. 9 is a perspective view showing a conventional example of a three-beam optical pickup.

FIG. 10 is a view showing a positional relationship between a diffraction element and a photodetector as viewed from an optical disc in the optical pickup of FIG. 9;

FIG. 11 is a view showing the principle of detecting a focus error signal FES in the optical pickup of FIG. 9;

FIG. 12 is a view showing a principle of detecting a tracking error signal TES in the optical pickup of FIG. 9;

FIG. 13 is a view showing a guide groove formed on the optical disc.

FIG. 14 is a diagram illustrating an offset of a signal generated in the push-pull method.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 second diffraction element 2a, 2b area 3 collimating lens 4 objective lens 5 optical disk 6 photodetector 6a, 6b, 6c, 6d, 6e photodetector 7 first diffraction element DL of first diffraction element Dividing line θ Angle between dividing line DL and track direction

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsuhiro Kubo 22-22 Nagaikecho, Abeno-ku, Osaka City Inside Sharpe Corporation (72) Inventor Hideo Sato 22-22 Nagaikecho, Abeno-ku, Osaka City Inside Sharpe Corporation ( 72) Inventor Sachio Kurata 22-22 Nagaike-cho, Abeno-ku, Osaka City Inside Sharpe Co., Ltd. (56) References JP-A-64-55746 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB G11B 7/09-7/095 G11B 7/135

Claims (2)

(57) [Claims] A first diffractive element that divides the light from the light generating means into three diffracted lights, ie, ± first-order diffracted lights for detecting a tracking shift, and zero-order diffracted lights for detecting a focus; An optical system that collects the three diffracted lights on the recording medium and detects the reflected light from the recording medium; and an optical system provided on the optical axis of the reflected light detected by the optical system; An optical system comprising: a second diffractive element having a region, dividing the reflected light by the region and diffracting the reflected light in different directions, and a photodetector for detecting diffracted light from the second diffractive element. An information recording / reproducing apparatus, wherein the area on the second diffraction element is divided by a dividing line inclined by an angle θ (20 ° ≦ θ ≦ 80 °) with respect to a track direction of the recording medium. The photodetector corresponds to the ± 1st-order diffracted light With deriving a second first tracking error signal Ri by the diffracted light receiving from the diffraction element, the second focusing error signal by the diffracted light receiving from the diffraction element corresponding to the 0-order diffracted light, and diffraction light An optical information recording / reproducing apparatus characterized in that a second tracking error signal is derived from a component in the track width direction. 2. The optical information recording / reproducing apparatus according to claim 1, wherein a direction of a grid line of the second diffraction element is perpendicular to the dividing line.