JP2001307339A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a highly precise tracking servo and to enable high recording density. SOLUTION: In an optical pickup device 1 wherein a beam B exited from a laser beam source 2 is divided into one main beam MB and two side beams SB by a diffraction means 3, the main beam is received by a main photodetector 8a to be used for reading or recording a signal or for detecting a servo error and two side beams are respectively received by separate side photodetectors 8b to be used for detecting a tracking error, a laser beam source position adjusting means 9 capable of moving and adjusting the laser beam source in the direction of the optical axis is provided, and the laser beam source is moved in the direction of the optical axis by the laser beam position adjusting means when intervals between a main spot and side spots which are condensed on respective photodetectors are deviated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel optical pickup device. More specifically, the present invention relates to a technology for enabling high-accuracy tracking servo even in recording, particularly in an optical pickup device used for an optical disk drive device of a recordable optical disk.

[0002]

2. Description of the Related Art An optical recording medium such as a CD (Compac
As a tracking servo system in a disk drive device such as a disc drive (D Disc), a differential push pulse (DPP) is used.
l) The method is known.

In the DPP method, a tracking error signal is generated by calculating an output signal of each light receiving element obtained from a main beam MB and two side beams SB, SB.

[0004] Specifically, in the DPP method, a diffraction means (grating) is arranged on the outward path of a beam emitted from a laser light source, and a zero-order diffracted light (main beam) and two first-order diffracted lights are placed on an optical disk. Each spot is formed by three (side beam) light beams, and these return lights are received by respective photodetectors a, b, and b, and a main spot MS by the main beam is used for writing or reading a signal. This is a system in which side spots SS by side beams are used for tracking error detection.

As shown in FIGS. 6 and 8, a main photodetector a for receiving a main spot MS is divided into four parts vertically and horizontally, and side photodetectors b and b for receiving the side spots SS and SS are divided into two sides. Is divided into two. Note that the output signals of each of the divided elements are A, B, C,
Shown as D, E, F, G, H. Then, a tracking error signal is generated from a calculation output between the output signals from the photodetectors a, b, and b.

That is, a main push-pull (MPP) signal is generated from the output signal of the main photo detector a,
Side push-pull (SPP1, SPP2) signals are generated from the output signals of the side photo detectors b, b, and the differential push-pull (DP) is calculated by the following equation.
P) signal is obtained.

MPP = (B + C)-(A + D) SPP1 = EF FP SPP2 = GH DPP = MPP-K. (SPP1 + SPP2) DPP = ((B + C)-(A + D))-K. ((E-
F) + (GH)) K: Coefficient.

FIG. 6 shows photodetectors a, b, b and each spot M when there is no variation in optical parts.
FIG. 7 schematically shows the relationship among S, SS, and SS. FIG. 7 shows the SPP1, SPP2, MPP, and DP signals in FIG.
4 shows a waveform of a P signal.

As can be seen from FIG. 7, the SPP1 signal and the SP
The P2 signal is in phase, the MPP signal is the SPP1 signal and the SP
The D signal is output in the same phase as the MPP signal, and the DPP signal is output in the opposite phase to the P signal 2.

FIG. 8 shows photodetectors a, b, and b when the intervals between the spots MS, SS, and SS are shifted due to variations in optical components and the like (in the drawing, the intervals between the spots are widened). And each spot MS, SS, S
FIG. 9 schematically shows the positional relationship with S. FIG.
3 shows waveforms of a PP1 signal, an SPP2 signal, an MPP signal, and a DPP signal. In this figure, the solid lines indicate the PP (push-pull) signals at the time of signal reading (reading), and the broken lines indicate the signal recording (writing) described later.
SPP1 signal and DPP signal. SP during signal recording
The P2 signal and the MPP signal are the same as those at the time of signal reading.

When reading a signal, the SPP1 signal, SPP
Although the two DC offsets occur in the two signals, the absolute values of the DC offsets are the same. Therefore, the DC offsets are canceled by the above equation, and the DPP signal is output without the DC offset. Therefore, the on-track state can be maintained (see the solid line in FIG. 9).

As described above, the DPP method can be canceled as described above even if a DC offset occurs in each push-pull signal. Therefore, the DPP method is a very effective tracking servo method in an optical pickup of a signal reading system. .

[0013]

However, it is possible to cancel the offset amount caused by the deviation of the intervals between the spots MS, SS, SS due to the variation of the optical parts and the like, as described above. Only when reading.

That is, an optical recording medium such as a CD-R
(Compact Disc-Recordable), CD-RW (Compact D
In a drive device of an optical disk such as isc-ReWritable), when recording a signal, as shown by a broken line in the waveform diagram of FIG.
The DC offset amount 2 of the P2 signal is different. Specifically, the offset amount 2 of the SPP2 signal has an absolute value smaller than the offset amount 1 of the SPP1 signal, and the DC offset amount 3 that cannot be canceled by the above equation occurs in the DPP signal that is the final output signal. .

By this, when the tracking servo is applied at the time of recording, a shift occurs by the DC offset of the DPP signal even though the main beam MB is in the on-track state, and the track is detracked (off-track state). This causes a problem that recording characteristics are deteriorated.

The problem is that when recording a signal on the optical disk c, one side beam (side beam preceding the main beam MB) SB1 is an unrecorded disk on which no pits d, d,... Are formed. The other side beam (side beam following the main beam MB) SB2 is reflected on the surface of the disk between the recording state track T where the pits d, d,. This is because the light is reflected (see FIG. 10).

In order to make the offset amount within the allowable range in the optical pickup device, the accuracy of the optical components themselves, their installation position accuracy, and the like must be increased, which leads to an increase in the cost of the device. In order to increase the recording density, the allowable range of the DC offset amount must be further narrowed. In the optical pickup device, it is difficult to increase the recording density. There is a problem that there is.

Therefore, an object of the present invention is to enable highly accurate tracking servo, particularly at the time of recording, and to increase the recording density.

[0019]

In order to solve the above-mentioned problems, an optical pickup device of the present invention divides a beam emitted from a laser light source into one main beam and two side beams by a diffractive means. In the optical pickup device, the beam is received by the main photodetector, for signal reading or recording and for servo error detection, and the two side beams are respectively received by different side photodetectors and used for tracking error detection. The optical component is provided with a position adjusting means capable of moving and adjusting the optical component in the optical axis direction, and when the distance between the main spot and the side spot focused on each photodetector is shifted, the optical component is moved by the position adjusting means in the optical axis direction. It is made to move to.

Therefore, according to the optical pickup device of the present invention, the optical component can be moved and adjusted in the optical axis direction.
The intervals between the main spot MS and the side spots SS can be matched, detracking that tends to occur during recording can be avoided, and highly accurate tracking servo can be achieved even during recording.

In addition, since the accuracy of the installation position of each optical component can be made rough, the manufacturing cost can be reduced and the recording density can be increased.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical pickup device of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram for explaining the configuration of optical components of an optical pickup device 1 according to the present invention.

The optical pickup device 1 comprises a laser light source 2 for generating a light beam B, a diffracting means 3 for diffracting the light beam B emitted from the laser light source 2, and a light beam B transmitted or reflected in a predetermined direction. A beam splitter 4,
A collimator lens 5 for forming a parallel light beam and an objective lens 7 for condensing the light beam B on the signal surface of the optical disk 6;
A photodetector 8 for receiving return light from the optical disk 6.

The photodetector 8 is the same as the one described in the above-mentioned prior art, and the main photodetector 8a
And two side photo detectors 8b and 8b. The main photo detector 8a is divided into four parts in the vertical and horizontal directions to receive the main spot MS, and the side photo detectors 8b and 8b are divided into two parts in the left and right sides, respectively. , SS. Also, the output signals of the respective divided elements are A, B, C, D,
Indicated by E, F, G, and H (see FIG. 2). Then, a tracking error signal is generated from a calculation output between the output signals from the photodetectors 8a, 8b, 8b.

As described in the above-mentioned “Problems to be Solved by the Invention”, if the intervals between the spots MS, SS, SS on the photodetector are shifted due to variations in optical components, etc. signal,
The DC offset amount generated in the SPP2 signal is different, and the DC offset amount cannot be canceled by the above equation, so that the DC offset amount occurs in the DPP signal and detrack occurs.

Therefore, in this embodiment, the position of the laser light source 2 is moved in the optical axis direction by the laser light source position adjusting means 9.

For example, when the laser light source 2 is moved closer to the beam splitter 4, the photodetector 8
Main spot MS and side spot SS
(See FIG. 2), and conversely, when the laser light source 2 is moved away from the beam splitter 4,
Main spot MS received by photodetector 8
The distance between the side spot SS and the side spot SS increases (see FIG. 3).

By adjusting the position of the laser light source 2 in the optical axis direction in the optical pickup device 1 according to this embodiment, the DC signal is applied to the SPP1 signal and the SPP2 signal when the main beam MB is in the on-track state.
The DPP signal is output in a state where no offset occurs and no DC offset occurs in the DPP signal, so that recording and reproduction of the signal can be performed without detracking.

FIG. 4 shows a modification 1A of the above-described optical pickup device in which the optical component movable in the optical axis direction is the diffraction means 3. The diffraction means 3 is a diffraction means position adjusting means 1.
With 0, it can be moved in the optical axis direction. Incidentally, the diffraction means 3 may be a hologram or the like in addition to the grating.

For example, when the diffraction means 3 is moved so as to approach the beam splitter 4, the distance between the main spot MS and the side spot SS received by the photodetector 8 is increased, and conversely, the diffraction means 3 When moving away from the splitter 4, the distance between the main spot MS and the side spot SS received by the photodetector 8 becomes narrow.

However, even in the optical pickup device 1A according to this modification, the position of the diffraction means 3 in the optical axis direction is adjusted so that the DC signal is not applied to the SPP1 signal and the SPP2 signal when the main beam MB is in the on-track state.
The DPP signal is output in a state where no offset occurs and no DC offset occurs in the DPP signal, so that recording and reproduction of the signal can be performed without detracking.

FIG. 5 shows a modified example 1B of the above-described optical pickup device in which the optical component movable in the optical axis direction is a collimator lens 5. The collimator lens 5 is moved in the optical axis direction by a collimator lens position adjusting means 11. Can be moved.

For example, when the collimator lens 5 is moved closer to the beam splitter 4, the distance between the main spot MS and the side spot SS received by the photodetector 8 becomes narrower, and conversely, the collimator lens 8 is moved to the beam splitter 4 When you move away from
Main spot MS received by photodetector 8
And the distance between the side spot SS is widened.

However, even in the optical pickup device 1B according to this modification, by adjusting the position of the collimator lens 8 in the optical axis direction, the DC offset is applied to the SPP1 signal and the SPP2 signal when the main beam MB is in the on-track state. Does not occur, and the DPP signal is output in a state where no DC offset occurs. Therefore, the signal can be recorded and reproduced without detracking.

In the above embodiment and each of the modifications, the optical pickup device of the present invention using the DPP system as the tracking servo system has been described.
The present invention is not limited to this, and it is needless to say that the present invention can be applied to an optical pickup device using a tracking servo system using a normal three spot system.

Further, the shapes and structures of the respective parts shown in the above-described embodiment and each modified example are merely examples for embodying the present invention. Should not be interpreted in a limited manner.

[0038]

As is apparent from the above description, the optical pickup device of the present invention divides a beam emitted from a laser light source into one main beam and two side beams by diffraction means, and separates the main beam from the main beam. An optical component in an optical pickup device in which a main photodetector is used to read or record a signal and to detect a servo error, and two side beams are respectively received by different side photodetectors to detect a tracking error. Is provided so as to be movable in the optical axis direction, and when the distance between the main spot and the side spot focused on each photodetector is shifted, the optical component is moved in the optical axis direction by the position adjusting means. It is characterized by doing so.

Therefore, according to the optical pickup device of the present invention, the optical component can be moved and adjusted in the optical axis direction.
The intervals between the main spot MS and the side spots SS can be matched, detracking that tends to occur during recording can be avoided, and highly accurate tracking servo can be achieved even during recording.

In addition, since the accuracy of the installation position of each optical component can be roughened, the manufacturing cost can be reduced and the recording density can be increased.

According to the second aspect of the present invention, since the optical component movable in the optical axis direction by the position adjusting means is used as the laser light source, the effect of the first aspect of the present invention is relatively reduced. It can be realized with a simple configuration.

According to the third aspect of the present invention, since the optical component movable in the optical axis direction by the position adjusting means is used as the diffractive means, the effect of the first aspect of the present invention can be relatively reduced. It can be realized with a simple configuration.

According to the fourth aspect of the present invention, since the optical component made movable in the optical axis direction by the position adjusting means is a collimator lens, the effect of the first aspect of the present invention is relatively small. It can be realized with a simple configuration.

[0044]

[Brief description of the drawings]

FIG. 1 shows an embodiment of the optical pickup device of the present invention together with FIG. 2 and FIG. 3, and FIG. 1 is a side view schematically showing the entire configuration.

FIG. 2 schematically shows a relationship between a photodetector and a spot together with FIG. 3, and is a diagram in a state where a laser light source is brought close to a beam splitter.

FIG. 3 is a diagram illustrating a state where a laser light source is separated from a beam splitter.

FIG. 4 is a side view schematically showing an overall configuration showing a modification of the optical pickup device of the present invention.

FIG. 5 is a side view schematically showing an overall configuration showing another modification of the optical pickup device of the present invention.

FIG. 6 is a diagram schematically showing a relationship between a photodetector and a spot in a state where there is no variation in optical components and the like.

FIG. 7 is a waveform diagram of each push-pull signal in FIG.

FIG. 8 is a diagram schematically illustrating a relationship between a photodetector and a spot in a state where optical components and the like have variations.

9 is a waveform diagram of each push-pull signal in FIG.

FIG. 10 is a diagram schematically showing an arrangement of spots on an optical disk during recording.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical pickup apparatus, B ... Beam light, MB ... Main beam, SB ... Side beam, 2 ... Laser light source, 3 ...
Diffraction means, 5: collimator lens, 6: optical disk,
8a: Main photo detector, 8b: Side photo detector, MS: Main spot, SS: Side spot, 9: Laser light source position adjusting means, 1A: Modified example of optical pickup device, 10: Diffraction means position adjusting means,
1B: Modification of optical pickup device, 11: Collimator lens position adjusting means

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Tsutomu Maruyama F-term (reference) 5D117 AA02 CC07 EE29 FF21 HH01 HH02 KK02 KK04 5D118 AA07 BA01 BB02 BF02 within 6-35 Kita Shinagawa, Shinagawa-ku, Tokyo BF03 CD03 CF05 CF17 CG04 CG14 CG24 CG33 CG44 CG47 DA33 DB04 DB12 DB22 5D119 AA39 BA01 BB03 DA01 DA05 EA02 EC40 FA05 FA37 JA02 JA70 JC07 KA04 KA19 KA24

Claims (4)

[Claims] 1. A beam emitted from a laser light source is divided into one main beam and two side beams by a diffractive means, and the main beam is received by a main photodetector to read or record a signal and to generate a servo error. In an optical pickup device used for detection and tracking light detection by receiving two side beams respectively to different side photodetectors, a position adjusting means is provided for enabling optical components to move and adjust in the optical axis direction. An optical pickup device wherein the position adjusting means moves the optical component in the optical axis direction when the distance between the main spot and the side spot focused on the photodetector is shifted. 2. The optical pickup device according to claim 1, wherein the optical component is a laser light source. 3. The optical pickup device according to claim 1, wherein said optical component is a diffraction means. 4. The optical pickup device according to claim 1, wherein the optical component is a collimator.