JP2005293716A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup capable of recording and reproducing various DVDs by simple control without using a hologram element.
In an optical pickup including a diffraction grating for dividing a laser beam from a semiconductor laser into a main beam and a plurality of sub beams, first and second regions 122 and 123 divided by a dividing line 121 are used as the diffraction grating. In the first region 122, a lattice groove 124 is formed at an angle α in the clockwise direction with respect to the dividing line, and in the second region 123, counterclockwise with respect to the dividing line. A diffraction grating 12 in which a grating groove 125 is formed to have an angle α in the direction is used. The diffraction grating forms a total of five spots for the DVD ± R / ± RW, a central spot located in the groove and two spots located on both adjacent lands so as to sandwich the spot. The DPP method can be used for both of ± RW and DVD-RAM.
[Selection] Figure 2

Description

  The present invention relates to an optical pickup used in an optical disk drive, and more particularly to an optical pickup for DVD.

  Optical disks called DVDs include DVD-ROM, DVD-RAM, and DVD ± R / ± RW. Among these optical disks, the track pitch of DVD-ROM and DVD ± R / ± RW is 0.74 mm. On the other hand, the track pitch of DVD-RAM is 0.615 mm, which is different from other optical disks.

  The optical disc drive is a device for reading information recorded on the optical disc as described above and writing information on a writable optical disc. Therefore, the optical disc drive includes an optical pickup for irradiating the optical disc with a laser beam and detecting the reflected light.

  As described above, the track pitch of DVD-RAM is different from the track pitch of DVD ± R / ± RW. Nevertheless, it is desired that these optical discs can be read and written by a common optical disc drive. Therefore, a conventional optical pickup is configured using a hologram element and a PDIC so as to follow a track by a method called a one-beam method in order to cope with a plurality of types of optical disks having different track pitches as described above. (For example, refer to Patent Document 1).

JP-A-11-110806

  The conventional optical pickup has a problem of high cost because an expensive hologram element is used.

  The conventional optical pickup also has a problem that special control is required.

  Therefore, an object of the present invention is to provide an optical pickup capable of recording and reproducing various DVDs with simple control without using a hologram element.

  According to the present invention, in the optical pickup (10) provided with the diffraction grating (12) for dividing the incident beam from the light source (11) into the main beam and the sub beam, the diffraction grating causes the main beam to be symmetrical. As a result, an optical pickup characterized in that two or more pairs of the sub-beams are formed can be obtained.

  Specifically, the optical pickup has first and second regions (122, 123) in which lattices (124, 125) are formed along different directions.

  In the optical pickup, the light source and the diffraction grating are arranged so that the center of the incident beam is located on a boundary between the first region (122) and the second region (123), and the incident beam A beam is incident on both the first and second regions.

  In the optical pickup, the lattice formed in the first region and the lattice formed in the second region are axisymmetric with respect to a boundary line between the first region and the second region. Is formed.

  As another specific example, in the optical pickup, the diffraction grating has a concave portion (61) having a first diffraction grating angle and a convex portion (62) having a second diffraction grating angle arranged in a staggered manner. Yes.

  The numbers in the parentheses are merely used to facilitate understanding of the present invention and do not limit the present invention.

  Since the optical pickup of the present invention only needs to change the shape of the diffraction grating, it can be constructed at low cost.

  Further, since the track is traced by the DPP method using three beams, complicated control is not required.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an optical pickup 10 according to the present embodiment. This optical pickup 10 has basically the same configuration as that of a known three-beam optical pickup. That is, the semiconductor laser 11, the diffraction grating 12, the polarization beam splitter 13, the collimator lens 14, the rising mirror 15, the quarter wavelength plate 16, the objective lens 17, the sensor lens 18, and the photodetector 19 are provided.

  The semiconductor laser 11 emits a laser beam with a wavelength of 650 nm having a light intensity suitable for writing information to the optical disc (DVD) 20 or reading information from the optical disc 20 under the control of a control circuit (not shown). . The laser beam emitted from the semiconductor laser 11 enters the diffraction grating 12.

  The diffraction grating 12 divides the incident laser beam into a main beam and a plurality of sub beams as will be described later. The laser beam (main beam and sub beam) divided by the diffraction grating 12 enters the polarization beam splitter 13.

  The polarization beam splitter 13 transmits a predetermined polarization component of the laser beam incident from the diffraction grating 12 side to the collimator lens 14 side. Further, the polarization beam splitter 13 reflects a predetermined polarization component of the laser light incident from the collimator lens 14 side and causes the laser beam to enter the sense lens 18.

  The collimator lens 14 converts the laser beam incident from the side of the polarizing beam splitter 13 into parallel light and emits it to the rising mirror 15 side, and condenses the laser beam incident from the side of the rising mirror 15 to collect the polarized beam splitter. 13 is emitted.

  The raising mirror 15 causes the laser beam incident from the collimator lens 14 side to enter the quarter wavelength plate 16 and causes the laser beam incident from the quarter wavelength plate 16 side to enter the collimator lens 14.

  The quarter-wave plate 16 emits while changing the polarization state of the incident laser beam between the raising mirror 15 and the objective lens 17.

  The objective lens 17 condenses the laser beam from the quarter wavelength plate 16 side onto the track of the optical disc 20 and makes the reflected light enter the quarter wavelength plate 16.

  The sensor lens 18 is reflected by the optical disk 20 and gives astigmatism to the laser beam incident through the objective lens 17, the quarter-wave plate 16, the rising mirror 15, the collimator lens 14, and the polarization beam splitter 13, The light is incident on the detection surface of the detector 19.

  The photodetector 19 detects the laser beam from the sensor lens 18 and outputs an electrical signal corresponding to the light intensity to the control circuit as a detection signal.

  The control circuit performs focusing control, tracking control, decoding, and the like based on the detection signal from the photodetector 19.

  Next, the diffraction grating 12 used in the optical pickup according to the present embodiment will be described in detail with reference to FIGS. 2 and 3 in addition to FIG.

  As shown in FIG. 2, one surface of the diffraction grating 12 is divided into first and second regions 122 and 123 by a dividing line (which may be a virtual line) 121. In the first region 122, first lattice grooves 124 are formed in parallel at a predetermined interval so as to form an angle α in the clockwise direction with respect to the dividing line 121. Further, in the second region 123, the second grating grooves 125 are formed in parallel at a predetermined interval so as to form an angle α counterclockwise with respect to the dividing line. The first grating grooves 124 and the second grating grooves 125 are formed in line symmetry with the dividing line 121 as the axis of symmetry.

  The diffraction grating 12 is arranged so that the center thereof coincides with the center of the laser beam from the semiconductor laser 11. That is, the semiconductor laser 11 and the diffraction grating 12 are arranged so that the laser beam is incident on the hatched region in FIG.

  The diffraction grating 12 may be created by any method. For example, a substrate such as glass may be formed by etching, or a metal or the like may be deposited on the substrate surface. Or you may make it form by injection molding etc. using resin.

  In the above configuration, the laser beam transmitted through the first region 122 of the diffraction grating 12 forms three spots (corresponding to the main beam and a pair of sub beams located on both sides thereof) on the optical disc 20. Similarly, the laser beam transmitted through the second region 123 of the diffraction grating 12 also forms three spots. However, the center located among the three spots formed by the laser beam transmitted through the first region 122 and the center among the three spots formed by the laser beam transmitted through the second region 123. The spots located at the same position coincide with each other on the surface of the optical disc 20. Therefore, five spots are actually formed on the surface of the optical disc 20.

  3A and 3B show the positional relationship between the grooves (concave portions) 31 and lands (convex portions) 32 of the optical disc 20 and the laser beam spots M and S1 to S4. FIG. 3A shows a case where the optical disc 20 is a DVD-RAM, and FIG. 3B shows a case where the optical disc 20 is a DVD ± R / ± RW.

  As shown in FIGS. 3A and 3B, the width of the groove 31 and land 32 is wider in DVD-RAM than DVD ± R / ± RW. However, in the DVD ± R / ± RW, the track exists only in the groove 31, whereas in the DVD-RAM, the track exists in both the groove 31 and the land 32. Therefore, the track pitch is 0.615 mm for DVD-RAM and 0.74 mm for DVD ± R / ± RW, and the track pitch for DVD-RAM is narrower than that for DVD ± R / ± RW.

  On the other hand, with respect to the beam spot, the central spot M is a spot formed by a laser beam transmitted through both the first region 122 and the second region 123 of the diffraction grating 12. Further, the upper right spot S1 and the lower left spot S2 are spots formed only by the laser beam transmitted through the first region 122 of the diffraction grating 12. Further, the upper left spot S 3 and the lower right spot S 4 are spots formed only by the laser beam that has passed through the second region 123 of the diffraction grating 12. The reason why the spots S1 to S4 are vertically long is that they are formed by the upper or lower half of the laser beam incident on the diffraction grating 12.

  The spot diameter (M diameter, S1-S4 minor diameter) is determined so that the DPP method can be used for tracking control for DVD ± R / ± RW. Each spot is positioned so that the center of the center spot M is located on the center line of the groove 31 with respect to the DVD-RAM, and the center of the spots S1 to S4 is located on the boundary line between the land and the groove. It is determined. And the diffraction grating 12 is formed and an optical system is arrange | positioned so that these conditions may be satisfy | filled.

  Next, a method for generating a tracking error signal and a focusing error signal used for tracking control and focusing control of the optical pickup shown in FIG. 1 will be described.

  First, the case where the optical disk 20 is DVD ± R / ± RW will be described.

  FIG. 4A shows the arrangement of the photodetector integrated circuit (PDIC) included in the photodetector 19 and how light is received. The illustrated PDIC includes three quadrant photo detectors (hereinafter simply referred to as photo detectors) 41, 42, and 43 arranged in a line. The photodetector 41 located in the center corresponds to the main beam (spot M), and the remaining two photodetectors 42 and 43 correspond to the sub beams (spots S1 to S4), respectively. The detection areas E3 and E4 in the right half of the photodetector 42 and the detection areas F1 and F2 in the left half of the photodetector 43 correspond to the spots S1 and S2 formed by the first area 122 of the diffraction grating 12. Further, detection areas E1 and E2 on the left half of the photodetector 42 and detection areas F3 and F4 on the right side of the photodetector 43 correspond to spots S3 and S4 formed by the second area 123 of the diffraction grating 22.

  When the optical disk 20 is DVD ± R / ± RW, the positions of the spots formed on the surface are as shown in FIG. 4B as described above. That is, when the spots S1 and S2 are located on the land 31, the spots S3 and S4 are also located on the land 31. Further, when the spots S1 and S2 are located on the groove 42, the spots S3 and S4 are also located on the groove 32. Therefore, when the optical disk 20 is DVD ± R / ± RW, a known DPP method can be used to obtain a tracking error signal (TE signal).

  The TE signal (= DPP) by the DPP method can be obtained by the following formula 1.

[Equation 1]
MPP = (A + D)-(B + C)
SPP = (EF1 + EF4) − (EF2 + EF3)
DPP = MPP-K · SPP
Here, MPP is a push-pull signal obtained from the main beam, SPP is a push-bull signal obtained from the sub beam, and K is a constant for compensating for the light intensity difference between the main beam and the sub beam.

  FIG. 4B shows changes in MPP, SPP, and DPP when the spots S1 to S4 are moved in the tracking direction on the DVD ± R / ± RW.

  A known astigmatism method using a main beam can be used to generate a focus error signal (FE signal) when the optical disk 20 is DVD ± R / ± RW.

  Next, the case where the optical disk 20 is a DVD-RAM will be described.

  FIG. 5A shows the arrangement of the photodetector integrated circuit (PDIC) included in the photodetector 19 and the state of light reception as in FIG. 4A.

  When the optical disc 20 is a DVD-RAM, the positions of the spots formed on the surface thereof are as shown in FIG. In this case, the ratio of the lands 32 (or grooves 31) included in the spots S1 and S2 is equal to the ratio of the grooves 31 (or lands 32) included in the spots S3 and S4. Therefore, the push-pull signal based on the spots S1 and S2 and the push-pull signal based on the spots S3 and S4 have opposite polarities and the same magnitude, and the push-bull signal PSS by the sub beam is canceled (SPP = 0).

  Here, the cancellation of the push-pull signal SPP by the sub beam does not mean that the tracking error signal cannot be generated by the DPP method for the DVD-RAM. On the contrary, this means that there is no hindrance to the tracking error detection for the DVD-RAM even though the DVD ± R / ± RW configuration is adopted.

  FIG. 5B shows changes in MPP, SPP, and DPP when the spots S1 to S4 are moved in the tracking direction on the DVD-RAM. As understood from Equation 1 and FIG. 5B, when the SPP is canceled, the DPP becomes equal to the MPP. That is, in the optical pickup according to the present embodiment, the DPP method can be used to obtain the TE signal even when the optical disc 20 is a DVD-RAM. However, since the obtained TE signal is based only on the main beam, only the offset at the time of lens shift can be canceled.

  When the optical disc 20 is a DVD-RAM, a known astigmatism method using a main beam can be used to generate a focus error signal (FE signal) as in the case of DVD ± R / ± RW. A differential astigmatism method using a sub beam can also be used. The focus error signal FE by the differential astigmatism method using the sub beam is given by Equation 2. Note that when the FE signal is obtained by the differential astigmatism method using a sub beam, the crosstalk component due to tracking can be canceled.

[Equation 2]
FE = (EF1 + EF3) − (EF2 + EF4)
As described above, the optical pickup according to the present embodiment can perform tracking control and focusing control for both DVD-RAM and DVD ± R / ± RW using the same pickup. As a result, the optical pickup according to the present embodiment can read and write to both DVD-RAM and DVD ± R / ± RW.

  The basic configuration of the optical pickup according to the present embodiment is the same as that of the existing optical pickup, and only the diffraction grating needs to be changed, and an expensive hologram element is not required, so that it can be manufactured at low cost.

  Further, complicated control as in the case of using a hologram element is not required.

  Next, another embodiment of the present invention will be described with reference to FIG.

  The optical pickup according to the present embodiment has a diffraction grating as shown in FIG. The illustrated diffraction grating has a concave portion (rectangular region without hatching) 61 having a first angle (an inclination of a line connecting beam spots) and a second angle (connecting beam spots) different from the first angle. Convex portions (rectangular regions having hatching) 62 having a slope of a line are arranged in a staggered pattern.

  Here, the inclination of the line connecting the beam spots can be changed by changing the vertical width W of the concave portion 61 and the convex portion 62 in the figure. That is, if the width W is increased, the diffraction angle can be reduced and the beam spot can be brought into the state shown in FIGS. 3A and 3B. If the width W is decreased, the diffraction angle is increased, and FIG. It can be set as the state of a) and (b).

  7 (a) and 7 (b) are different from FIGS. 3 (a) and 3 (b) when the center of the center spot M is located on the center line of the groove with respect to DVD ± R / ± RW. The center of S1-S4 is located on the boundary line between the land and the groove. FIG. 8A shows the arrangement of the photodetectors and the state where the reflected light from the spot of DVD ± R / ± RW is received, and FIG. 8B shows the change of the push-pull signal at that time. FIG. 9A shows the arrangement of the photodetectors and the state where the reflected light from the spot of the DVD-RAM is received, and FIG. 9B shows the change of the push-pull signal at that time.

  As is apparent from FIGS. 8 and 9, in the present embodiment, the SPP is canceled in the case of DVD ± R / ± RW, and the SPP is obtained in the case of DVD-RAM. This is just the opposite of the case shown in FIGS. However, also in the present embodiment, tracking control and focusing control are possible for both DVD-RAM and DVD ± R / ± RW. As a result, the optical pickup according to the present embodiment can also read and write to both DVD-RAM and DVD ± R / ± RW.

  While the present invention has been described with reference to one embodiment, the present invention is not limited to the above embodiment. For example, although the case where three quadrant photodetectors are used has been described in the above embodiment, the photodetectors located on both sides may be two or more segmented photodetectors.

It is the schematic which shows the structure of the optical pick-up concerning one embodiment of this invention. It is a front view of the diffraction grating used for the optical pickup of FIG. It is a figure for demonstrating the positional relationship of the groove and land of an optical disk, and a beam spot, Comprising: (a) is a figure in DVD-RAM, (b) is a figure which shows the case of DVD ± R / ± RW. (A) is the figure which shows the arrangement | positioning of the photodetector contained in the photodetector used for the optical pick-up of FIG. 1, and the state which has received the reflected light from the spot of DVD ± R / ± RW, (b), It is a graph which shows the change of the push pull signal obtained by the output from the photodetector of (a). (A) is a figure which shows the state which has received the reflected light from the spot of DVD-RAM, and arrangement | positioning of the photodetector contained in the photodetector used for the optical pick-up of FIG. 1, (b) is (a). It is a graph which shows the change of the push pull signal obtained by the output from the photo detector. It is a figure which shows the structure of the diffraction grating used for the optical pick-up concerning other embodiment of this invention. It is a figure for demonstrating the positional relationship of the groove and land of an optical disk, and a beam spot, Comprising: (a) is a figure in DVD-RAM, (b) is a figure which shows the case of DVD ± R / ± RW. (A) is the figure which shows the arrangement | positioning of the photodetector contained in the photodetector used for the optical pick-up of FIG. 1, and the state which has received the reflected light from the spot of DVD ± R / ± RW, (b), It is a graph which shows the change of the push pull signal obtained by the output from the photodetector of (a). (A) is a figure which shows the state which has received the reflected light from the spot of DVD-RAM, and arrangement | positioning of the photodetector contained in the photodetector used for the optical pick-up of FIG. 1, (b) is (a). It is a graph which shows the change of the push pull signal obtained by the output from the photo detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical pick-up 11 Semiconductor laser 12 Diffraction grating 121 Dividing line 122 1st area | region 123 2nd area | region 124 1st grating | lattice groove 125 2nd grating | lattice groove 13 Polarization beam splitter 14 Collimator lens 15 Standing mirror 16 1/4 Wave plate 17 Objective lens 18 Sensor lens 19 Optical detector 20 Optical disk 31 Groove 32 Land 41, 42, 43 Quadrant photo detector 61 Concave part 62 Convex part

Claims (8)

In an optical pickup equipped with a diffraction grating for splitting an incident beam from a light source into a main beam and a sub beam,
2. The optical pickup according to claim 1, wherein the diffraction grating forms two or more pairs of the sub beams with the main beam as an axis of symmetry. The optical pickup according to claim 1,
The optical pickup according to claim 1, wherein the diffraction grating has first and second regions in which grating grooves are formed along different directions. The optical pickup according to claim 2,
The light source and the diffraction grating are arranged so that the center of the incident beam is located on a boundary line between the first region and the second region, and the incident beam is in the first and second regions. An optical pickup characterized by being incident on both sides. In the optical pickup according to claim 2 or 3,
The lattice formed in the first region and the lattice formed in the second region are formed symmetrically with respect to a boundary line between the first region and the second region. Features an optical pickup. The optical pickup according to claim 1,
An optical pickup, wherein the diffraction grating has a concave portion having a first diffraction grating angle and a convex portion having a second diffraction grating angle arranged in a staggered manner. The optical pickup according to claim 4 or 5, wherein
When the optical disk has one of the physical formats of the optical disk having the first physical format and the second physical format, the main beam is irradiated to the center in the width direction of the groove of the optical disk. An optical pickup characterized in that the sub-beam is irradiated on a boundary between a land and a groove of the optical disc in a state where The optical pickup according to any one of claims 1 to 6, wherein
A photo detector including a first four-divided photo detector corresponding to the main beam, and second and third two or more divided photo detectors corresponding to the sub beam and arranged to sandwich the first four-divided photo detector. An optical pickup comprising an integrated circuit. An optical disc drive comprising the optical pickup according to any one of claims 1 to 7.

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