JPH06187656A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a tracking error signal having no deflection when it is recorded on a recordable optical disk. CONSTITUTION:The light beam emitted from a semiconductor laser 1 is diffracted by a 1st diffraction grating 2a and converged by a lens 10. A 2nd diffraction grating 2b arranged on a surface where a light source image is formed by the lens 10 diffracts the 0-order diffracted light of the grating 2a and transmits the + or - 1st order diffracted light as it is. A main spot is formed to record or read the information by the 0-order diffracted beams of both gratings 2a and 2b. Then, the pairs of subspots displaced by 1/4 track pitch in mutually opposite directions to each other from the center of an informtion recording tracks are formed before and after the main spot by the + or - 1st order diffracted beams of both gratings 2a and 2b. Then, a tracking error signal is obtained from the signals sent from four subspots (2 pairs) formed in such a way.

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 for recording / reproducing information on / from a recordable optical disk, and more particularly to a tracking error signal for accurately causing a light beam on the optical disk to follow a recording track even during recording. The present invention relates to an optical pickup device that eliminates the occurrence of bias.

[0002]

2. Description of the Related Art An example of an optical pickup device for obtaining a tracking error signal by a conventional three-beam method is shown in FIG. As shown in FIG. 5A, a semiconductor laser 1 which is a light source
The light emitted from passes through the diffraction grating 2, is reflected by the beam splitter 3, and is collimated by the collimator lens 4 and the objective lens 5.
Thus, it is converged on the signal recording surface of the optical disc 6.

The light reflected by the optical disc 6 is an objective lens 5, a collimator lens 4, and a beam splitter 3.
Then, the light is sequentially transmitted through the concave lens 7 and converges on the light receiver 8A.

The diffraction grating 2 is provided with a grating having a constant grating constant on the entire plane of the light flux passing through the plane-parallel plate, and the light beam passing therethrough is divided into 0th order and ± 1st order diffracted light. The 0th-order diffracted light forms a main spot S ₁ on the optical disc as shown in FIG. 5C, and the ± 1st-order diffracted lights form sub-spots S ₂ and S ₃ .

When the main spot S ₁ is on the track of the optical disk, the sub-spots S ₂ and S ₃ are arranged in front of and behind the main spot so as to sandwich the track, and the distance between the center and the track center is 1/4 track pitch. is there.

A light receiver 8A corresponding to each of these spots
As shown in FIG. 5B, the spots R ₁ , R on the light receiving surface of
₂ , R ₃ is formed. Receiving element for receiving these optical spots are divided into six light receiving unit 8 _a to 8 _f as shown, the recording and reproducing signal and focusing error signal from the light receiving unit 8 _a to 8 _d is obtained, the light receiving unit 8 _A tracking error signal is obtained by differentially amplifying the outputs of _e and 8 _f .

When recording is performed on a recordable optical disc by applying tracking servo by such a tracking error signal, as shown in FIG. 5C, the sub-spot S _{2 in} front of the main spot S ₁ is recorded. The sub-spot S ₃ behind the main spot S ₁ overlaps the guide groove where the recording pit exists.

Since the reflection state is different between the unrecorded guide groove and the guide groove having the recording pit, in the case of the three-beam method, there is a problem that the tracking error signal is biased and correct tracking cannot be performed.

A so-called push-pull method for performing recording / reproduction with one beam as shown in FIG. 6A is known as a method for preventing the deviation of the tracking error signal due to the difference in the reflection state between the guide groove and the recording pit. ing.

According to this method, the light beam from the light source passes through the beam splitter 3 and is converged on the signal recording surface of the optical disk 6 by the objective lens 5. Then, the light reflected by the optical disk 6 passes through the objective lens 5, is reflected by the beam splitter 3 and converges on the light receiver 8B.

A light spot R is formed on the light receiving surface of the light receiver 8B. The light receiving element that receives this light spot is divided into two light receiving units 8B _a and 8B _b as shown in the figure, and a recording / reproducing signal is obtained by adding the outputs of the light receiving units 8B _a and 8B _b. A tracking error signal is obtained by differentially amplifying the outputs of 8B _a and 8B _b by the differential amplifier 9.

In the case of such a push-pull method, 3
Unlike the beam method, the tracking error signal is not biased due to the difference in the reflection state between the guide groove and the recording pit,
As shown in FIG. 6B, the optical disc 6 is used for the light beam.
Tilting in the track direction also tilts the diffracted and reflected light from the optical disc, which causes a problem that the intensity distribution of the light spot on the light receiving element is biased to one of the light receiving units and the tracking error signal is biased.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to obtain a tracking error signal without bias when recording on a recordable optical disk. Another object of the present invention is to provide an optical pickup device capable of performing stable tracking control on an information track of a disc.

Another object of the present invention is to provide an optical pickup device capable of obtaining a tracking error signal without deviation even when the optical disc is tilted in the track direction with respect to the light beam.

[0015]

An optical pickup device of the present invention comprises an optical system for irradiating light emitted from a light source as a light beam spot on an information recording surface of an optical disc,
An optical pickup device having an optical system for guiding a light beam reflected on the information recording surface to a light receiver, and a diffraction grating arranged in the optical path from the light source to the information recording surface, diffracts the light beam emitted from the light source. A first diffraction grating that
A lens for converging the light that has passed through the first diffraction grating and the lens of 0
A second diffraction grating that diffracts the first-order diffracted light and allows the ± first-order diffracted light to pass therethrough is provided, and a main spot for recording or reading information is formed by the 0th-order diffracted light of both the first and second diffraction gratings. , A pair of sub-spots which are displaced by a distance of ¼ track pitch in opposite directions from the center of the information recording track by the ± 1st-order diffracted lights of the first and second diffraction gratings are formed in front of and behind the main spot. The tracking error signal is obtained from the signals from the two sets of four sub-spots thus formed.

[0016]

According to the optical pickup device of the present invention,
The 0th-order diffracted light of the light beam transmitted through the first diffraction grating is diffracted by the second diffraction grating, and the 0th-order diffracted light forms a main spot for recording or reading information.
The main spot is controlled to be at the center position of the information recording track.

The ± 1st-order diffracted light diffracted by the second diffraction grating forms a sub-spot at a position point-symmetric with respect to the main spot, and the distance of the straight line connecting the sub-spots and the angle with respect to the information recording track are the second. It can be set arbitrarily according to the lattice constant of the diffraction grating and the orientation of the grating.

Further, the ± 1st-order diffracted lights of the first diffraction grating pass through the second diffraction grating as they are, and form sub-spots at positions symmetrical with respect to the main spot. The distance of the straight line connecting the sub-spots and the angle with respect to the information recording track can be arbitrarily set by the grating constant of the first diffraction grating and the orientation of the grating.

In this way, a set of sub-spots displaced from the center of the information recording track in the opposite directions by a distance of ¼ track pitch can be formed before and after the main spot.

At the time of recording information, the sub-spots of each group are arranged in the recorded area and the unrecorded area for each group. Therefore, the pits can be formed by differentially amplifying the reflected light power of the two sub-spots. It is possible to obtain tracking error signals that are not affected by the presence or absence of formation.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an optical path diagram showing an optical pickup device according to an embodiment of the present invention.
As shown in the figure, the light emitted from the semiconductor laser 1 as the light source is diffracted by the first diffraction grating 2a, and then the convex lens 10
Is converged at.

The second diffraction grating 2b is arranged on the surface on which the light source image is formed by being converged in this way. The second diffraction grating 2b, as shown in detail in FIG.
The grating 2B is provided in a region of the a through which the 0th-order diffracted light a passes, and the ± first-order diffracted lights b and c of the first diffraction grating 2a are provided.
There is no grid in the area that passes through.

The transmitted light is diffracted by the grating 2B into 0th-order diffracted light d and ± 1st-order diffracted lights e and f. These diffracted lights pass through the collimator lens 4, are reflected by the beam splitter 3, and are further converged by the objective lens 5 on the signal recording surface of the optical disc 6 to form respective spots.

That is, the 0th-order diffracted light d forms a main spot S ₁ on the optical disk as shown in FIG. 3, and the ± 1st-order diffracted lights b, c, e, and f are sub-spots S ₂ , S ₃ and forming a S _4, S _5.

The distance of the straight line connecting the sub-spots that are point-symmetric with respect to the main spot and the angle with respect to the signal recording track can be arbitrarily set by the grating constants and orientations of the first and second diffraction gratings. It is in a state of being displaced by a quarter track pitch.

These spots are reflected by the optical disk 6, and the objective lens 5, the beam splitter 3 and the convex lens 1 are included.
1 is sequentially transmitted and converges on the light receiver 8 to form a spot on the light receiver 8. Spots R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are formed on the light receiving surface of the light receiver 8 corresponding to the respective spots converged on the signal recording surface of the optical disc 6, as shown in FIG. Receiving element for receiving these optical spots are divided into eight light receiving unit 8 _a to 8 _h as shown, the reproduced signal and a focus error signal from the light receiving unit 8 _a to 8 _d is obtained, the light receiving unit 8 _e And 8 _g and the output difference between the light receiving units 8 _f and 8 _h provide a tracking error signal that is not biased by the presence or absence of recording.

In the embodiment, the differential amplifier 9 calculates the sum of the outputs of the light receiving units 8 _e and 8 _h and the sum of the outputs of the light receiving units 8 _g and 8 _f.
The tracking error signal (T
E) is obtained.

[0028]

According to the optical pickup device of the present invention, a tracking error signal having no deviation can be obtained even for an optical disc having different reflectances in a recorded area and an unrecorded area, and stable information can be obtained for such an optical disc. Can be written or read.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a partial detailed view of FIG.

FIG. 3 is a diagram showing a light spot on an optical disc of the optical pickup device.

FIG. 4 is a diagram showing a light spot on a light receiver of the same optical pickup device.

FIG. 5 (a) is an optical path diagram showing an example of a conventional optical pickup device, FIG. 5 (b) is a diagram showing a light spot on a light receiver of the same optical pickup device, and FIG. 5 (c). FIG. 3 is a diagram showing a light spot on an optical disc of the same optical pickup device.

FIG. 6 is an optical path diagram showing another example of a conventional optical pickup device.

[Description of Reference Signs] 1 semiconductor laser 2 diffraction grating 2a first diffraction grating 2b second diffraction grating 3 beam splitter 4 collimator lens 5 objective lens 6 optical disk 7 concave lens 8 light receiver 9 differential amplifier 10 convex lens 11 convex lens

Claims (1)

[Claims] 1. An optical system for irradiating the information recording surface of an optical disc with a light emitted from a light source as a light beam spot,
An optical pickup device having an optical system for guiding a light beam reflected on the information recording surface to a light receiver, and a diffraction grating arranged in the optical path from the light source to the information recording surface, diffracts the light beam emitted from the light source. A first diffraction grating that
A lens for converging the light that has passed through the first diffraction grating and the lens of 0
A second diffraction grating that diffracts the first-order diffracted light and allows the ± first-order diffracted light to pass therethrough is provided, and a main spot for recording or reading information is formed by the 0th-order diffracted light of both the first and second diffraction gratings. , A set of sub-spots which are displaced by a distance of ¼ track pitch in opposite directions from the center of the information recording track by the ± 1st-order diffracted lights of the first and second diffraction gratings are formed before and after the main spot. An optical pickup device configured to obtain a tracking error signal by signals from two sets of four sub-spots thus formed.