JPH05234107A - Optical pickup device and tracking error signal detecting method - Google Patents

Abstract

PURPOSE:To realize an excellent tracking operation even for any optical disk of plural kinds of optical disks having different track pitches. CONSTITUTION:Side spots 21a, 22a, 21b, 22b are obtained which respectively correspond to plural kinds of the optical disks 17a, 17b having different track titchs by using plural kinds of diffraction gratings 2a, 2b dividing a laser beam in an optical pickup device. In accordance with the track pitch of optical disk loaded, the output signals from photodetectors 10a, 11a, 10b, 11b corresponding to various kinds of side spots respectively are selected and a tracking error signal TE is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device and a tracking error signal detecting method, which are suitable for two or more types of optical discs (magneto-optical discs) having different track pitches.

[0002]

2. Description of the Related Art Among tracking servo systems adopted in optical disc recording / reproducing apparatuses, a system using a side spot for detecting a tracking error signal is widely known. For example, 3 spot system or DP
There is a P (differential push-pull) method.

FIG. 4 shows the structure of a general optical pickup device when the three-spot system is adopted. Reference numeral 1 is a semiconductor laser element (laser diode) which serves as a laser light source, 2 is a diffraction grating for splitting the laser light emitted from the laser diode 1 into 0th-order, + 1st-order, and −order beams, 3 is a deflecting beam splitter, 4 Is a collimator lens for making a laser beam a parallel beam, 5 is a quarter wavelength plate, and 6 is an objective lens. Further, 7 is a concave lens, 8 is a cylindrical lens, 9 is a 4-division photodetector, and 10 and 11 are photodetectors.

The laser light emitted from the laser diode 1 and split into 0th, + 1st, and −order beams by the diffraction grating 2 passes through the deflecting beam splitter 3 and the collimator lens 4, and then is a quarter wavelength plate. At 5 the plane of polarization is rotated 45 °,
The optical disc 17 is irradiated through the objective lens 6 as a main spot and a pair of side spots.

After passing through the objective lens 6, the light component reflected from the optical disk 17 has its polarization plane further rotated by 45 ° by the quarter-wave plate 5 and is incident on the deflection beam splitter 3 via the collimator lens 4. Then, it is deflected by 90 ° by the deflecting beam splitter 3 and is incident on the photodetection unit via the concave lens 7 and the cylindrical lens 8. Here, the reflected light component applied to the main spot is received by the four-division photodetector 9, and the reflected light component applied to the side spot is received by the photodetectors 10 and 11.

The signals (S _A , S _B , S _C , S _D ) corresponding to the detected light amount obtained by the four-division photo detector 9 are added by the adders 12 and 13 (S _A + S _C ) (S _B + S
_Then , the reproduced RF signal is obtained as the output (S _A + S _C ) + (S _B + S _D ) of the operational amplifier 14 after being _D ). Further, as the output (S _A + S _C ) − (S _B + S _D ) of the operational amplifier 15, the focus error signal FE by the astigmatism method is obtained. further,
The outputs (S _E , S _F ) of the photodetectors 10 and 11 are supplied to the operational amplifier 16, and the output of the operational amplifier 16 (S _E −S
_A tracking error signal TE is obtained as _F ).

The focus error signal FE and the tracking error signal TE are supplied to a focus servo circuit and a tracking servo circuit, respectively, to generate a drive signal for a biaxial mechanism (not shown), and the direction in which the objective lens 6 moves toward and away from the optical disk 17 and Driven in the track direction, focus and tracking control is performed.

Here, the irradiation positions of the main spot 20 and the side spots 21, 22 on the recording surface of the optical disc 17 are set as shown in FIG. The photodetectors 9, 10, 11 corresponding to each spot are also shown at the same time.

That is, the track T _n-1 , on the optical disk,
When T _n , T _{n + 1,} ... Are formed at the track pitch p, the side spots 21 and 22 are + q or −q (q) from the track center when the main spot 20 is on the track center. = P / 4), and the irradiation is shifted in the track pitch direction. That is, in order to perform such irradiation, the diffraction grating 2 is installed at an angle θg with respect to the track tangential direction. Of course, the photo detector 1
The arrangement positions of 0 and 11 are also set accordingly.

[0010]

By the way, as the wavelength of the laser light source is shortened and the recording density of the optical disc is increased, the track pitch on the optical disc is set to be narrower. Two or more different types of optical disks appear.

Correspondingly, the arrangement of the diffraction grating 2 is set so that the irradiation positions of the side spots 21 and 22 deviate from the track center by 1/4 track on the optical pickup device side, and the photodetectors 10 and 11 are further arranged. However, in this case, there arises a problem that compatibility with optical disks having different track pitches is hindered.

For example, when an optical pickup device corresponding to an optical disc having a track pitch of 0.9 μm is constructed,
A conventional CD (ROM
When trying to reproduce an optical disc having a track pitch of 1.5 μm like a disc, the side spots 21 and 22 (± 1/4 track pitch from the track center) detected by the photodetectors 10 and 11 are not located. )
The reflected light due to the signal S has a very poor S / N ratio, and a sufficient gain cannot be obtained for the outputs of the photodetectors 10 and 11, so that it is difficult to apply stable tracking servo.

Also in the DPP system, the tracking error signal is generated by utilizing the reflected light from the side spot. In this case, when the position of the side spot is displaced by 1/2 track pitch from the main spot, The maximum gain is obtained as the output of the photodetector. Therefore, if the track pitch is different,
A decrease in S / N is unavoidable as the detection output of the side spot reflected light, and the same problem occurs.

[0014]

In view of the above problems, the present invention adopts a method of generating a tracking error signal using reflected light from a side spot, and a plurality of types of optical discs having different track pitches. The present invention provides an optical pickup device and a tracking error signal detection method that can be compatible with.

That is, in the optical system for guiding the laser light from the laser output means to the optical disk recording medium, a plurality of types of diffraction gratings, which are formed integrally or separately, for dividing the laser light from the laser output means are interposed. The main spot on the optical disk recording medium and a plurality of kinds of side spots whose irradiation positions are different from each other in the track pitch direction are irradiated, and the reflected light from the main spot and the side spot is detected. In the photodetection unit, the optical pickup device is provided with a photodetection element that detects reflected light corresponding to the main spot and a photodetection element that detects reflected light corresponding to each side spot. Constitute.

Further, as a tracking error signal detecting method using such an optical pickup device, each type of tracking error signal is detected according to the track pitch of the optical disk recording medium on which the recording / reproducing operation is executed by the optical pickup device. Select the required output signal from the output signals from the photodetector corresponding to each side spot,
The tracking error signal is detected using the selected output signal.

[0017]

By preparing side spots corresponding to the optical disc recording media of various track pitches and selectively using the detection signal of the reflected light thereof, it is possible to correspond to a plurality of types of optical disc recording media having different track pitches. Therefore, a good tracking error signal can be obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical pickup device of the present invention will be described below with reference to FIGS. FIG. 1 shows the structure of the optical pickup device, and FIG. 2 shows the irradiation position of the light spot on the optical disk by the optical pickup device of FIG. 1 and the corresponding photodetector. Note that FIG.
The optical disc 17 having a track pitch of Pa
2 of the optical disc 17b having a and a track pitch of Pb
The types are shown together. In each figure, FIG.
The same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.

In this optical pickup device 2a,
Reference numeral 2b denotes a diffraction grating that divides the laser light emitted from the laser diode 1 into 0th-order, + 1st-order, and −third-order beams and outputs the beams. By providing the diffraction gratings 2a and 2b in this way, As shown in FIG. 2, the optical disc 17 is irradiated with one main spot 20 and two pairs of side spots (21a, 22a) (21b, 22b).

That is, the diffraction grating 2a is installed at an angle θg _{1 with} respect to the track tangential direction, and the + _{1st order and} −order beams obtained by the diffraction grating 2a are the side spots 2.
1a and 22a. Further, the diffraction grating 2b is installed at an angle θg _{2 in the} direction opposite to the diffraction grating 2a with respect to the track tangential direction, and therefore the + 1st-order and −order beams obtained by the diffraction grating 2b are side spots 21b and 22b. Become.

Diffraction gratings 2a, 2b arranged in this way
Thus, the side spots 21a and 22a are irradiated onto the optical disc 17a having a track pitch of Pa at positions displaced from the track center by ± 1/4 track pitch when the main spot 20 is at the track center. Also, the side spots 21b, 22b
When the main spot 20 is located at the track center, the optical disc 17b having a track pitch of Pb is irradiated at a position displaced from the track center by ± 1/4 track pitch.

Further, as can be seen from the figures, the optical disc 1
As the light detection means for detecting the reflected light from 7, a four-division photodetector 9 corresponding to the main spot 20, a photodetector 10a corresponding to the side spot 21a, and a photodetector 11a corresponding to the side spot 22a are provided. Furthermore, a photodetector 10b corresponding to the side spot 21b and a photodetector 11b corresponding to the side spot 22b are provided.

The signals ( _{SE (a)} , _{SF (a)} ) corresponding to the detected light quantity obtained from the photodetectors 10a, 11a are supplied to the operational amplifier 16a ( _{SE (a)} -SF _(a)). ), And signals (S _{E (b)} and S _{F (b)} ) corresponding to the detected light amounts obtained from the photodetectors 10b and 11b are output by the operational amplifier 1
It is supplied to 6b and output as ₍ SE _(b) -SF _(b) ). Further, the outputs of the operational amplifiers 16a and 16b are supplied to the terminals a and b of the switching circuit 18.

Reference numeral 19 denotes a disc discriminating section, which detects the types of track pitches Pa and Pb for the optical disc on which recording / reproducing operation is performed (that is, loaded) by the optical pickup device, and switches based on the detected information. Control is performed to switch the connection terminal of the circuit 18.

With the optical pickup device having such a structure, a good tracking operation can be performed for two types of optical disks 17a and 17b having different track pitches.

Reproduction RF signal and focus error signal F
E can be obtained by a common method for both the optical disks 17a and 17b. That is, the signals (S _A , S _B , S _C , S _D ) corresponding to the detected light amount obtained by the four-division photodetector 9 on which the reflected light of the main spot 20 is incident.
Is added by the adders 12 and 13 (S _A + S _C ) (S
_B + S _D ) and then supplied to the operational amplifiers 14 and 15, and output from the operational amplifier 14 (S _A + S _C ) + (S _B + S
_The reproduced RF signal is obtained as _D ). Further, as the output (S _A + S _C ) − (S _B + S _D ) of the operational amplifier 15, the focus error signal FE by the astigmatism method is obtained.

The tracking error signal TE is obtained by the following method. When the loaded optical disc is the optical disc 17a having a track pitch of Pa, the disc discriminating unit 19 which detects the disc pitch controls the switching circuit 18 to connect the a terminal. Then, the photo detector 1
The output (SE _(a) -SF _(a) ) from the operational amplifier 16a to which the outputs ( _{SE (a) and} SF _{(a) of} 0a and 11a) are supplied is
The tracking error signal TE is output via the switching circuit 18. That is, ± 1/4 from the main spot 20 corresponding to the optical disc 17a having the track pitch Pa.
The tracking error signal TE is generated from the detection signal of the reflected light by the side spots 21a and 22a which are irradiated at the positions displaced by the track pitch.

On the other hand, when the loaded optical disc is the optical disc 17b having a track pitch of Pb, the disc discriminating unit 19 which detects this has a switching circuit 18
Is controlled so that the b terminal is connected. Then, the light detector 10b, the output of 11b output from the operational amplifier 16b of _{(S E (b), S} F (b)) is supplied _{(S E (b)} -
S _{F ( b)} ) is output as the tracking error signal TE via the switching circuit 18. That is, the track pitch P
The tracking error signal TE is generated from the detection signal of the reflected light by the side spots 21b and 22b which are irradiated at a position shifted by ± 1/4 track pitch from the main spot 20 corresponding to the optical disc 17b of b.

Therefore, in this embodiment, the track pitch P
A good S / N output having a sufficient output gain as a reflected light detection output is obtained for both the optical disks 17a and 17b of a and Pb, and a stable tracking error signal is generated. That is, for each of the optical disks 17a and 17b, the response of the tracking servo system becomes stable and accurate tracking control is realized.

By the way, various discriminating methods of the track pitch of the optical disc in the disc discriminating section 19 can be considered. For example, when the track pitch information is written in a predetermined area (for example, TOC area) of the optical disc corresponding to the recording / reproducing apparatus to which this embodiment is adopted,
It is possible to determine whether the track pitch of the optical disc is Pa or Pb by the TOC information reading operation during loading.

Further, in the case where the optical disk is of a type that is housed in a cartridge housing, or the like, if the track pitch information is expressed in the cartridge housing by, for example, a detection hole or a shape, this may be detected. When this embodiment is adopted for a recording / reproducing apparatus corresponding to an optical disc having no such direct track pitch information, the optical pickup device is set to the traverse state immediately after loading the optical disc, and at that time, for example, the operational amplifier 1 is used.
The output ( _{SE (a)} -SF _(a) ) obtained from 6a and the output (SE _(b) -SF _(b) ) obtained from the operational amplifier 16b are compared,
It may be considered that the switching circuit 18 selects the one having the larger amplitude.

Although the above-mentioned embodiment adopts the three-spot method, the present invention is effective even when the tracking error signal is generated by the DPP method. The DPP method is a fixed push-pull method in which the photodetector is on the fixed side of the objective lens, and can effectively cancel the influence of the DC offset generated on the tracking error signal due to the movement of the objective lens or the radial skew of the optical disc. For example, when the main spot is irradiated to the land portion (track center) on the optical disk, the side spot is irradiated to the groove portion (position displaced by 1/2 track pitch). In this case, This is because the push-pull signals obtained from the main spot and the side spot have opposite phases, but the DC fluctuations due to the movement of the objective lens and the radial skew of the optical disk have the same phase.

Therefore, the gain is set so that the amplitudes of the push-pull signal obtained by the reflected light of the main spot and the push-pull signal obtained by the reflected light of one or both of the side spots are set, and each push-pull signal is further set. When the differential signal of is obtained, this becomes a tracking error signal from which DC fluctuation is removed.

In this case, as described above, when the position of the side spot deviates from the main spot by 1/2 track pitch, the maximum gain can be obtained as the output of the photodetector. Therefore, the track pitch is P.
When optical discs 17a and 17b different from a and Pb exist, the S / N of the detection output of the side spot reflected light is unavoidable for one of the optical discs. Therefore, even when the DPP method is adopted, two units of diffraction gratings 2a and 2b are arranged in the optical pickup device in the same manner as in FIG. 1 to obtain two pairs of side spots. Correspond.

An embodiment in this case will be described with reference to FIG. It should be noted that the laser diode and the optical system indicated by the reference numerals 1 to 8 in FIG.
However, in this case, as shown in FIG. 3, the side spots 21a,
22a is an optical disc 17 having a track pitch of Pa.
The diffraction grating 2a is installed at an angle θg _{3 with} respect to the tangential direction of the track so that it is irradiated at a position shifted by ± 1/2 track pitch with respect to the main spot 20 in correspondence with a. Spots 21b and 22b are
Corresponding to the optical disc 17b having a track pitch of Pb, the diffraction grating 2b is a diffraction grating with respect to the track tangential direction so that the main spot 20 is irradiated at a position shifted by ± 1/2 track pitch. It is installed at an angle θg _{4 in the} opposite direction to 2a.

Then, as shown in FIG.
As the light detecting means for detecting the reflected light from 7, the 4-split photodetector 9 corresponding to the main spot 20 and the 2-split photodetector 10a corresponding to the side spot 21a,
Two-split photodetector 1 corresponding to the side spot 22a
1a is further provided, and the two-divided photodetector 10b corresponding to the side spot 21b and the side spot 22 are provided.
A two-divided photodetector 11b corresponding to b is provided. The reproduction RF signal and the focus error signal FE are generated from the output of the four-division photodetector 9 as in the above embodiment, and the description thereof is omitted.

The tracking error signal TE is a push-pull signal from the main spot 20 and a side spot 21.
It is obtained as a differential output of the push-pull signal by a, 22a, or 21b, 22b. Accordingly, the push-pull signals of the main spot 20 (S _A + S _D) by first differential amplifier _{30 - (S B + S C} ) is generated.

The outputs (SE _(a1) , _{SE ( a2)} ) of the two-division photodetector 10a are supplied to the differential amplifier 31a,
A push-pull signal S _{E (ap)} (= S _{E (a1)} −S _{E (a2)} ) is obtained. Similarly, the outputs (SF _(a1) , _{SF (a2)} ) of the two-divided photodetector 11a are supplied to the differential amplifier 32a,
A push-pull signal _{SF (ap)} (= _{SF (a1)} -SF _(a2) ) is obtained. The push-pull signals S _{E (ap)} and S _{F (ap)} are supplied to the amplifier 33a and are set to have the same amplitude level as the push-pull signal (S _A + S _D ) − (S _B + S _C ) by the main spot 20. Of the push-pull signal G (S
_{E (ap)} + S _{F (ap)} ) and supplied to the a terminal of the switching circuit 18.

On the other hand, the differential amplifier 31b is supplied with the outputs (SE _(b1) , _{SE ( b2)} ) of the two-divided photodetector 10b,
A push-pull signal S _{E (bp)} (= S _{E (b1)} −S _{E (b2)} ) is obtained. Similarly, the outputs (SF _(b1) , _{SF (b2)} ) of the two-divided photodetector 11b are supplied to the differential amplifier 32b,
A push-pull signal _{SF (bp)} (= _{SF (b1)} -SF _(b2) ) is obtained. The push-pull signals S _{E (bp)} and S _{F (bp)} are supplied to the amplifier 33b and are set to have the same amplitude level as that of the push-pull signal (S _A + S _D ) − (S _B + S _C ) by the main spot 20. Of the side surface 21b and 22b, the push-pull signal G (S
_{E (bp)} + _{SF (bp)} ) and supplied to the b terminal of the switching circuit 18. Output of switching circuit 18 and main spot 20
Push-pull signal (S _A + S _D )-(S _B + S
_C ) is supplied to the differential amplifier 34.

Therefore, if the track pitch of the loaded optical disc is Pa, the a terminal of the switching circuit 18 is connected correspondingly, and the main spot 20 and a position deviated from the main spot 20 by ± 1/2 track pitch. Of the tracking error signal T due to the push-pull signals of the side spots 21a and 22a irradiated on the
E, _{i.e., TE = {(S A +} S D) - (S B + S C)} - G (S E (ap) + S F (ap)) is obtained.

If the track pitch of the loaded optical disk is Pb, the b terminal of the switching circuit 18 is connected, and the main spot 20 and the main spot 20 are connected.
More ± 1/2 track side spots 21b being irradiated on the pitch shifted position, the tracking error signal TE by each push-pull signal 22b, _{i.e., TE = {(S A +} S D) - (S B + S C)} -G (SE ( _bp) + _{SF (bp)} ) is obtained.

Therefore, even when the DPP method is adopted, the present embodiment can realize accurate tracking control for both the optical discs 17a and 17b having the track pitches Pa and Pb. In the DPP method, only one of the pair of side spots may be used. For example, the two-divided detectors 11a and 11b may be omitted so that the side spots 22a and 22b are not used.
In this case, {(S _A + S _D ) − (S _B + S _C )},
The gain G is set so that the amplitudes of G (S _{E (ap)} ) (and G (S _{E (bp)} ) are at the same level, and TE = {(S _A + S _D ) − (S _B + S _C ). _{} -G (S E (ap)} ) _{or, TE = {(S a +} S D) - (S B + S C)} - G (S E (bp)) as to obtain a tracking error signal TE selectively To do.

In each embodiment, as shown in FIGS. 2 and 3, the side spots 21a and 21b and the side spots 22a and 22b are located on opposite sides of the track center. This is because the influence of crosstalk was taken into consideration. However, the present invention does not necessarily have to be located on the opposite side.

In each embodiment, a diffraction grating 2 of 2 units is used.
Although a and 2b are used, an integrated diffraction grating formed in advance with a crossing angle of θg ₁ + θg ₂ (or θg ₃ + θg ₄ ) may be used instead of the independent diffraction grating. Further, in each of the embodiments, the optical disk having two kinds of track pitch is adapted, but it is possible to correspond to three or more kinds of track pitch by providing three or more kinds of diffraction gratings and corresponding photodetectors. Can also be considered.

[0000]

As described above, according to the present invention, a plurality of types of diffraction gratings for splitting a laser beam are used in an optical pickup device to form side spots respectively corresponding to a plurality of types of optical disk recording media having different track pitches. In addition, it is equipped with a photo-detecting element that detects reflected light corresponding to each side spot, and according to the track pitch of the loaded optical disk recording medium, Since the output signal of is selected and the tracking error signal is detected, a good tracking error signal can be obtained for a plurality of types of optical disk recording media with different track pitches, and stable tracking servo operation is realized. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a structure of an embodiment of an optical pickup device of the present invention.

FIG. 2 is an explanatory diagram of an embodiment corresponding to the three-spot method of the optical pickup device and the tracking error signal detection method of the present invention.

FIG. 3 is an explanatory diagram of an embodiment corresponding to the DPP method of the optical pickup device and the tracking error signal detection method of the present invention.

FIG. 4 is an explanatory diagram of a structure of a conventional optical pickup device.

FIG. 5 is an explanatory diagram of a conventional tracking error signal generation method using three spots.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser diode 2a, 2b Diffraction grating 9 4-division photodetector 10a, 11a, 10b, 11b Photodetector (2-division photodetector) 18 Switching circuit 19 Disk discriminating unit 20 Main spot 21a, 22a, 21b, 22b Side spot

Claims (2)

[Claims] 1. A laser output means, an optical system for guiding a laser beam from the laser output means to an optical disk recording medium and for deriving reflected light from the optical disk recording medium, and a light detection for detecting the reflected light. And a plurality of types of diffraction gratings for splitting the laser beam from the laser output means, wherein the optical system includes a main spot and an optical disc recording medium. A plurality of types of side spots whose irradiation positions are different from each other in the track pitch direction are irradiated onto the main spot, and in the photodetection unit, light for detecting reflected light corresponding to the main spot is used. A detection element and a photodetection element for detecting reflected light corresponding to each of the side spots of each type are provided. Optical pickup device. 2. A laser output means, an optical system for guiding the laser light from the laser output means to an optical disk recording medium and for deriving reflected light from the optical disk recording medium, and a photodetector for detecting the reflected light. And a plurality of types of diffraction gratings for splitting the laser beam from the laser output means are provided in the optical system, and a main spot with respect to the optical disk recording medium and a main spot with respect to the main spot. The irradiation position is different in the track pitch direction, and a plurality of types of side spots are irradiated, and in the photodetector, a photodetector element that detects reflected light corresponding to the main spot, and An optical pickup device equipped with a photodetector element for detecting reflected light corresponding to each kind of side spot is used. A desired output signal among the output signals from the photo-detecting elements corresponding to the side spots of each type is selected according to the track pitch of the optical disk recording medium on which the recording / reproducing operation is performed by the recording device. A tracking error signal detection method, characterized in that a tracking error signal is detected using the selected output signal.