JP2005317106A - Optical head apparatus and optical information recording/reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head apparatus having: high sensitivity of a substrate thickness deviation signal and a radial tilt signal; satisfied quality of a focus error signal, a track error signal, the substrate thickness deviation signal and the radial tilt signal; and the simple constitution of an arithmetic circuit for obtaining each signal, and also to provide an optical information recording/reproducing apparatus. <P>SOLUTION: An outgoing light from a light source is divided by a diffraction optical element 3a into a main beam which is a zero-order light, a 1st sub-beam which is a +1st order diffracted light, and a 2nd sub-beam which is a -1st order diffracted light. A focus error signal is detected according to a differential astigmatic method and a track error signal is detected according to a differential push-pull method, by using the diffracted light from areas 11b, 11d among the main beam and 1st sub-beam and using the diffracted light from areas 11a, 11c among the 2nd sub-beam. Also, the substrate thickness deviation of the optical recording medium and the radial tilt are detected by using the diffracted light from the area 11a among the 1st sub-beam and the diffracted light from the area 11b among the 2nd sub-beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical head device and an optical information recording / reproducing device for performing recording and / or reproduction on an optical recording medium, and in particular, an offset is not generated in a focus error signal and a track error signal, and the optical recording medium The present invention relates to an optical head device and an optical information recording / reproducing device capable of detecting a substrate thickness deviation and a radial tilt.

  Grooves for tracking are usually formed in write-once and rewritable optical recording media in which no RF signal is recorded in advance. Generally, when viewed from the side of incident light on the optical recording medium, the concave portion of the groove is called a land, and the convex portion is called a groove. When a focus error signal is detected for such write-once and rewritable optical recording media, the focus error signal at the position where the defocus amount is 0 is not strictly 0, and there is a groove in the optical recording medium. In principle, lands and grooves have offsets of opposite signs. This offset is called an offset due to groove crossing noise.

  In addition, when detecting a track error signal for a write once type and rewritable type optical recording medium, detection is usually performed by a push-pull method, but the track error signal by the push-pull method is detected by an objective lens of the optical head device. An offset occurs when the optical recording medium is shifted in the radial direction. This offset is called an offset by lens shift. In order to prevent the deterioration of the recording / reproducing characteristics due to these offsets, the optical head device and the optical information recording / reproducing device are required to have a device that does not cause an offset in the focus error signal and the track error signal.

  By the way, the recording density in the optical information recording / reproducing apparatus is inversely proportional to the square of the diameter of the focused spot formed on the optical recording medium by the optical head apparatus. That is, the smaller the diameter of the focused spot, the higher the recording density. The diameter of the focused spot is inversely proportional to the numerical aperture of the objective lens in the optical head device. That is, the higher the numerical aperture of the objective lens, the smaller the diameter of the focused spot.

  On the other hand, when the thickness of the substrate of the optical recording medium deviates from the design value, the shape of the focused spot is disturbed due to spherical aberration due to the substrate thickness deviation, and the recording / reproducing characteristics deteriorate. Since the spherical aberration is proportional to the fourth power of the numerical aperture of the objective lens, the higher the numerical aperture of the objective lens, the narrower the margin of the substrate thickness deviation of the optical recording medium with respect to the recording / reproducing characteristics.

  Further, when the optical recording medium is tilted in the radial direction with respect to the objective lens, the shape of the focused spot is disturbed by coma aberration caused by the radial tilt (radial tilt), and the recording / reproducing characteristics are deteriorated. Since coma is proportional to the third power of the numerical aperture of the objective lens, the higher the numerical aperture of the objective lens, the narrower the margin of radial tilt of the optical recording medium with respect to the recording / reproducing characteristics.

  Therefore, in an optical head device and an optical information recording / reproducing apparatus in which the numerical aperture of the objective lens is increased in order to increase the recording density, the substrate thickness deviation and the radial tilt of the optical recording medium are detected in order not to deteriorate the recording / reproducing characteristics. It is necessary to correct.

  As an optical head device and an optical information recording / reproducing device capable of detecting a substrate thickness shift and a radial tilt of an optical recording medium without causing an offset in a focus error signal and a track error signal, Patent Document 1 discloses. There are an optical head device and an optical information recording / reproducing device.

  FIG. 19 shows the configuration of the first optical head device described in Patent Document 1.

  The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and is transmitted by the diffractive optical element 3g as one transmitted light as the main beam, two diffracted lights as the first sub-beam, and 2 as the second sub-beam. The light is divided into a total of five lights of one diffracted light. These lights are incident on the polarization beam splitter 4 as P-polarized light and almost 100% are transmitted. The light passes through the quarter-wave plate 5 and is converted from linearly polarized light to circularly polarized light. Focused.

  The five reflected lights from the disk 7 are transmitted in the opposite direction through the objective lens 6, are transmitted through the quarter wavelength plate 5, and are converted from circularly polarized light to linearly polarized light whose outgoing path and polarization direction are orthogonal to each other. Is incident as S-polarized light, and almost 100% is reflected, passes through the cylindrical lens 8 and the lens 9, and is received by the photodetector 10b. The photodetector 10b is installed in the middle of the two focal lines of the cylindrical lens 8 and the lens 9.

  FIG. 20 is a plan view of the diffractive optical element 3g.

  The diffractive optical element 3g has a configuration in which diffraction gratings are formed in an inner region 13a and an outer region 13b of a circle having a diameter smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. The directions of the gratings in the diffraction grating are almost parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice spacing in the region 13a is equal to the lattice spacing in the region 13b.

  About 80.0% of the light incident on the region 13a is transmitted as 0th order light, about 3.2% is diffracted as ± 1st order diffracted light, and about 3.0% is diffracted as ± 2nd order diffracted light. The On the other hand, about 91.0% of the light incident on the region 13b is transmitted as 0th-order light, about 3.6% is diffracted as ± first-order diffracted light, and is not diffracted as ± second-order diffracted light.

  If the 0th order light from the diffractive optical element 3g is the main beam, the ± 1st order diffracted light is the first subbeam, and the ± 2nd order diffracted light is the second subbeam, the main beam and the first subbeam are transmitted from the region 13a. Both the light or diffracted light and the transmitted light or diffracted light from the region 13b are included in the same ratio, and the second sub-beam includes only the diffracted light from the region 13a.

  As a result, the main beam and the first sub beam have the same intensity distribution, and the main beam and the second sub beam have different intensity distributions. The second sub-beam has a lower intensity at the periphery than the main beam.

  FIG. 21 shows the arrangement of the focused spots on the disk 7.

  The condensed spots 17a, 17j, 17k, 17l, and 17m correspond to the 0th order light, the + 1st order diffracted light, the −1st order diffracted light, the + 2nd order diffracted light, and the −2nd order diffracted light from the diffractive optical element 3g, respectively. The focused spot 17a is on the track 16 (land or groove), the focused spot 17j is on the track (groove or land) adjacent to the right side of the track 16, and the focused spot 17k is adjacent to the left side of the track 16. On the track (groove or land), the focused spot 17l is on the track (land or groove) adjacent to the two right sides of the track 16, and the focused spot 17m is the track (land or groove) adjacent to the two left sides of the track 16. Each is arranged above.

  Since the first sub-beam has the same intensity distribution as the main beam, the condensing spots 17j and 17k as the first sub-beam have the same diameter as the condensing spot 17a as the main beam. On the other hand, since the second sub-beam has a lower intensity at the peripheral portion than the main beam, the condensing spots 17l and 17m as the second sub-beam have a larger diameter than the condensing spot 17a as the main beam.

  FIG. 22 shows the pattern of the light receiving part of the photodetector 10b and the arrangement of the light spots on the photodetector 10b.

  The light spot 18a corresponds to zero-order light from the diffractive optical element 3g, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at ~ 20d.

  The light spot 18f corresponds to + 1st order diffracted light from the diffractive optical element 3g, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received in ~ 20h.

  The light spot 18g corresponds to -1st order diffracted light from the diffractive optical element 3g, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at 20i to 20l.

  The light spot 18h corresponds to + second order diffracted light from the diffractive optical element 3g, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at ~ 20p.

  The light spot 18i corresponds to -second order diffracted light from the diffractive optical element 3g, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at 20q to 20t.

  The rows of focused spots 17a, 17j, 17k, 17l, 17m on the disk 7 are substantially tangential, but due to the action of the cylindrical lens 8 and the lens 9, the light spots 18a, 18f, 18g on the photodetector 10b. , 18h, 18i are substantially in the radial direction.

  When the outputs from the light receiving portions 20a to 20t are respectively expressed as V20a to V20t, the condensed spot 17a as the main beam, the condensed spots 17j and 17k as the first sub-beam, and the condensed spot 17l as the second sub-beam, The focus error signal by 17m is obtained from (V20a + V20d)-(V20b + V20c), (V20e + V20h + V20i + V20l)-(V20f + V20g + V20j + V20k), and (V20m + V20p + V20q + V20t)-(V20V + V20) + V20V + V20V + V20V + V20 + 20.

  The focus error signal by the differential astigmatism method is obtained from the calculation of (V20a + V20d) − (V20b + V20c) + K {(V20e + V20h + V20i + V20l) − (V20f + V20g + V20j + V20k)} (K is a constant).

  On the other hand, the track error signals from the focused spot 17a as the main beam, the focused spots 17j and 17k as the first sub-beam, and the focused spots 17l and 17m as the second sub-beam are respectively (V20a + V20b) by the push-pull method. )-(V20c + V20d), (V20e + V20f + V20i + V20j)-(V20g + V20h + V20k + V20l), (V20m + V20n + V20q + V20r)-(V20o + V20p + V20s + V20t).

  The track error signal by the differential push-pull method is obtained from the calculation of (V20a + V20b) − (V20c + V20d) −K {(V20e + V20f + V20i + V20j) − (V20g + V20h + V20k + V20l)}.

  Further, the RF signal from the focused spot 17a, which is the main beam, is obtained from the calculation of V20a + V20b + V20c + V20d.

  23A to 23C show various focus error signals.

  23A to 23C, the horizontal axis represents the defocus amount of the disk 7, and the vertical axis represents the focus error signal.

  A focus error signal 25a shown in FIG. 23A is a focus error signal generated by the focused spot 17a when the focused spot 17a is arranged on the land, and the focused error signal 25b is a groove generated by the focused spot 17a. It is a focus error signal by the condensing spot 17a when arrange | positioning on the top.

  Further, a focus error signal 25c shown in FIG. 23B is a focus error signal due to the focused spots 17j and 17k when the focused spot 17a is arranged on the land, and the focused error signal 25d is the focused error signal 25d. This is a focus error signal due to the condensed spots 17j and 17k when the spot 17a is arranged on the groove.

  Strictly speaking, the focus error signal at the position where the defocus amount is 0 is not 0, and in FIG. 23A, the land is positive, the groove is negative, and in FIG. 23B, the land is negative, the groove. Then it has a positive offset.

  On the other hand, the focus error signal 25e shown in FIG. 23 (c) is based on the focus error signal by the focused spot 17a and the focused spots 17j and 17k when the focused spot 17a is arranged on the land and the groove. It is a focus error signal by the differential astigmatism method, which is the sum of focus error signals. In FIG. 23C, the offset of the focus error signal in FIGS. 23A and 23B is canceled, and no offset occurs in the focus error signal.

  24A to 24C show various track error signals.

  24A to 24C, the horizontal axis represents the off-track amount of the disk 7, and the vertical axis represents the track error signal.

  A track error signal 26a shown in FIG. 24A is a track error signal caused by the focused spot 17a when the objective lens 6 is shifted outward in the radial direction of the disk 7, and the track error signal 26b is obtained by the objective lens 6. This is a track error signal due to the focused spots 17j and 17k when shifted outward in the radial direction of the disk 7.

  A track error signal 26c shown in FIG. 24B is a track error signal generated by the focused spot 17a when the objective lens 6 is shifted inward in the radial direction of the disk 7, and the track error signal 26d is an objective lens. 6 is a track error signal by the focused spots 17j and 17k when shifted inward in the radial direction of the disk 7.

  The track error signal by the focused spot 17a and the track error signal by the focused spots 17j and 17k have opposite polarities, but the sign of the offset when the objective lens 6 is shifted in the radial direction of the disk 7 is the same. 24 (a) has a positive offset and FIG. 24 (b) has a negative offset.

  On the other hand, the track error signal 26e shown in FIG. 24C is a track error signal generated by the focused spot 17a and the focused spots 17j and 17k when the objective lens 6 is shifted to the outer side and the inner side in the radial direction of the disk 7. This is a track error signal by the differential push-pull method, which is a difference in track error signal due to. In FIG. 24C, the offset of the track error signal in FIGS. 24A and 24B is canceled, and no offset occurs in the track error signal.

  25A to 25C show various focus error signals related to detection of substrate thickness deviation.

  In FIGS. 25A to 25C, the horizontal axis represents the defocus amount of the disk 7 and the vertical axis represents the focus error signal.

  A focus error signal 27a shown in FIG. 25A is a focus error signal due to the condensing spot 17a and focus error signals due to the condensing spots 17l and 17m when the disc 7 has no substrate thickness deviation.

  On the other hand, the focus error signal 27b shown in FIG. 25B is a focus error signal due to the focused spot 17a when the disc 7 has a positive substrate thickness shift, and the focus error signal 27c is a positive substrate on the disc 7. This is a focus error signal due to the condensed spots 17l and 17m when there is a thickness deviation.

  Further, the focus error signal 27d shown in FIG. 25C is a focus error signal due to the focused spot 17a when the disc 7 has a negative substrate thickness shift, and the focus error signal 27e is a negative substrate thickness shift to the disc 7. This is a focus error signal due to the condensing spots 17l and 17m when there is a light beam. The position where the focus error signal by the focused spot 17a crosses the zero point corresponds to the just focus.

  When there is no substrate thickness deviation on the disk 7, the focus error signal from the condensing spots 17l and 17m coincides with the focus error signal from the condensing spot 17a and the zero cross point, and becomes zero in just focus.

  On the other hand, when the disc 7 has a positive substrate thickness shift, the focus error signal due to the focused spots 17l and 17m shifts to the left in the figure with respect to the focus error signal due to the focused spot 17a. Becomes positive.

  Further, when the disc 7 has a negative substrate thickness shift, the focus error signal due to the focused spots 17l and 17m is shifted to the right in the figure with respect to the focus error signal due to the focused spot 17a, and the focus error is negative due to the just focus. It becomes.

  Therefore, the focus error signal from the focused spots 17l and 17m, which are the second sub-beams when the focus servo is applied using the focus error signal from the focused spot 17a as the main beam, can be used as the substrate thickness deviation signal. .

  26A to 26C show various track error signals related to detection of radial tilt.

  In FIGS. 26A to 26C, the horizontal axis represents the off-track amount of the disk 7, and the vertical axis represents the track error signal.

  A track error signal 28a shown in FIG. 26A is a track error signal due to the focused spot 17a and a track error signal due to the focused spots 17l and 17m when the disk 7 has no radial tilt.

  On the other hand, the track error signal 28b shown in FIG. 26B is a track error signal due to the focused spot 17a when the disc 7 has a positive radial tilt, and the track error signal 28c has a positive radial tilt on the disc 7. This is a track error signal due to the focused spots 17l and 17m in a certain case.

  Further, the track error signal 28d shown in FIG. 26C is a track error signal due to the focused spot 17a when the disc 7 has a negative radial tilt, and the track error signal 28e is a case where the disc 7 has a negative radial tilt. This is a track error signal by the condensing spots 17l and 17m. The position where the track error signal by the condensed spot 17a crosses the 0 point from the − side to the + side corresponds to the land, and the position where the track error signal crosses the 0 point from the + side to the − side corresponds to the groove.

  When there is no radial tilt on the disk 7, the track error signal from the focused spots 17l and 17m coincides with the track error signal from the focused spot 17a and the zero cross point is zero in both the land and the groove.

  On the other hand, when the disc 7 has a positive radial tilt, the zero error point of the track error signal due to the condensing spots 17l and 17m is shifted to the left side of the figure with respect to the track error signal due to the condensing spot 17a. In the groove, it is negative.

  In addition, when the disk 7 has a negative radial tilt, the track error signal due to the focused spots 17l and 17m is shifted to the right in the figure with respect to the track error signal due to the focused spot 17a. Then it becomes positive.

  Accordingly, the track error signals generated by the focused spots 17l and 17m when the track servo is applied using the track error signal generated by the focused spot 17a can be used as the radial tilt signal.

  Patent Document 1 also describes the configuration of the second optical head device. In the second optical head device described in Patent Document 1, the diffractive optical element 3g and the photodetector 10b in the first optical head device described in Patent Document 1 are replaced with the diffractive optical element 3h and the photodetector 10a, respectively. The configuration is the same as that shown in FIG.

  FIG. 27 is a plan view of the diffractive optical element 3h.

  The diffractive optical element 3h has regions 13c and 13d which are straight lines passing through the optical axis of incident light and parallel to the radial direction of the disk 7 inside a circle having a diameter smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. The diffraction grating divided into two regions 13e and 13f is formed on the outer side by a straight line passing through the optical axis of the incident light and parallel to the radial direction of the disk 7. It is the formed structure. The directions of the gratings in the diffraction grating are almost parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at equal intervals. The lattice intervals in the regions 13c, 13d, 13e, and 13f are all equal.

  About 40.5% of light incident on the regions 13c and 13f is transmitted as 0th order light, about 40.5% is diffracted as + 1st order diffracted light, and only about 4.5% is diffracted as -1st order diffracted light. Not. On the other hand, about 40.5% of the light incident on the regions 13d and 13e is transmitted as 0th order light, about 40.5% is diffracted as −1st order diffracted light, and only about 4.5% as + 1st order diffracted light. Not diffracted.

  When the 0th-order light from the diffractive optical element 3h is the main beam, the + 1st-order diffracted light is the sub-beam 1, and the -1st-order diffracted light is the sub-beam 2, the transmitted light from the regions 13c, 13d, 13e, and 13f is the same ratio in the main beam. The sub-beam 1 mainly includes only diffracted light from the regions 13c and 13f, and the sub-beam 2 mainly includes only diffracted light from the regions 13d and 13e.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. The sub beam 1 has lower peripheral strength in the upper half than the main beam, and the peripheral strength is higher in the lower half, and the sub beam 2 has higher peripheral strength in the upper half and lower half. Then the strength of the periphery is low. The sum of the intensity distribution of the sub beam 1 and the intensity distribution of the sub beam 2 is the same as the intensity distribution of the main beam.

  FIG. 28 shows the arrangement of focused spots on the disk 7.

  The condensed spots 17a, 17n, and 17o correspond to the 0th order light, the + 1st order diffracted light, and the −1st order diffracted light from the diffractive optical element 3h, respectively. The focused spot 17a is on the track 16 (land or groove), the focused spot 17n is on the track (groove or land) adjacent to the right side of the track 16, and the focused spot 17o is a track adjacent to the left side of the track 16. (Groove or land) are arranged on each.

  FIG. 29 shows the pattern of the light receiving portion of the photodetector 10a and the arrangement of the light spots on the photodetector 10a.

  The light spot 18a corresponds to 0th-order light from the diffractive optical element 3h, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. The light is received at ~ 19d.

  The light spot 18j corresponds to + 1st order diffracted light from the diffractive optical element 3h, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at ~ 19h.

  The light spot 18k corresponds to −1st order diffracted light from the diffractive optical element 3h, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at 19i to 19l.

  The row of the condensed spots 17a, 17n and 17o on the disk 7 is substantially tangential, but due to the action of the cylindrical lens 8 and the lens 9, the row of the light spots 18a, 18j and 18k on the photodetector 10a is Nearly radial direction.

  When the outputs from the light receiving portions 19a to 19l are respectively represented by V19a to V19l, the focus error signals generated by the condensed spot 17a as the main beam and the condensed spots 17n and 17o as the sub beams are respectively (V19a + V19d) by the astigmatism method. )-(V19b + V19c), (V19e + V19h + V19i + V19l)-(V19f + V19g + V19j + V19k).

  The focus error signal by the differential astigmatism method is obtained from the calculation of (V19a + V19d) − (V19b + V19c) + K {(V19e + V19h + V19i + V19l) − (V19f + V19g + V19j + V19k)} (K is a constant).

  On the other hand, the track error signals generated by the focused spot 17a as the main beam and the focused spots 17n and 17o as the sub beams are calculated by the push-pull method. can get.

  The track error signal by the differential push-pull method is obtained from the calculation of (V19a + V19b) − (V19c + V19d) −K {(V19e + V19f + V19i + V19j) − (V19g + V19h + V19k + V19l)}. The RF signal from the focused spot 17a, which is the main beam, is obtained from the calculation of V19a + V19b + V19c + V19d.

  The focus error signal from the focused spot 17a, which is the main beam, is the same as the focus error signal 25a in FIG. 23 (a) and the focus error signal 25c in FIG. 23 (b). Further, the sum of the intensity distribution of the sub-beam 1 and the intensity distribution of the sub-beam 2 is the same as the intensity distribution of the main beam. Therefore, the focus error signal due to the condensed spots 17n and 17o, which are sub-beams, is shown in FIG. This is the same as the focus error signal 25b of FIG. 23 and the focus error signal 25d of FIG.

  Therefore, the focus error signal by the differential astigmatism method, which is the sum of the focus error signal by the focused spot 17a and the focus error signal by the focused spots 17n and 17o, is the same as the focus error signal 25e in FIG. is there. That is, in this optical head device, no offset occurs in the focus error signal.

  The track error signal by the focused spot 17a which is the main beam is the same as the track error signal 26a in FIG. 24A and the track error signal 26c in FIG. Further, the sum of the intensity distribution of the sub-beam 1 and the intensity distribution of the sub-beam 2 is the same as the intensity distribution of the main beam. Therefore, the track error signal by the condensed spots 17n and 17o, which are sub-beams, is shown in FIG. The track error signal 26b is the same as the track error signal 26d in FIG.

  Therefore, the track error signal by the differential push-pull method, which is the difference between the track error signal by the focused spot 17a and the track error signal by the focused spots 17n and 17o, is the same as the track error signal 26e in FIG. . That is, in this optical head device, no offset is generated in the track error signal.

  The focus error signal from the focused spot 17a, which is the main beam, shows the focus error signal 27a in FIG. 25A when the disc 7 has no substrate thickness deviation, and the case where the disc 7 has a positive substrate thickness deviation. When the focus error signal 27b of 25 (b) and the disc 7 has a negative substrate thickness deviation, the same as the focus error signal 27d of FIG. 25 (c).

  19e-19g which is a focus error signal (focus error signal in the upper half) due to diffracted light from the region 13c of the diffractive optical element 3h in the condensed spot 17n which is the sub beam 1, and diffraction in the condensed spot 17o which is the sub beam 2. 19l-19j which is a focus error signal (lower half focus error signal) by the diffracted light from the region 13d of the optical element 3h is the focus error signal 27a shown in FIG. When the disc 7 has a positive substrate thickness deviation, the focus error signal 27c in FIG. 25B is the same, and when the disc 7 has a negative substrate thickness deviation, the same as the focus error signal 27e in FIG. 25C. It is.

  19h-19f which is a focus error signal (lower half focus error signal) due to diffracted light from the region 13f of the diffractive optical element 3h in the condensed spot 17n which is the sub beam 1, and diffraction in the condensed spot 17o which is the sub beam 2. The focus error signal 19i-19k, which is a focus error signal (upper half focus error signal) by the diffracted light from the region 13e of the optical element 3h, is the focus error signal 27a of FIG. When the disc 7 has a positive substrate thickness deviation, the focus error signal 27e in FIG. 25C is the same, and when the disc 7 has a negative substrate thickness deviation, the same as the focus error signal 27c in FIG. 25B. It is.

  Therefore, the difference (19e + 19f + 19k + 19l) − (19g + 19h + 19i + 19j) between the focus error signal of the upper half of the sub beam 1 and the lower half of the sub beam 2 and the focus error signal of the lower half of the sub beam 1 and the upper half of the sub beam 2 is When there is no thickness shift, the focus is 0. When the disc 7 has a positive substrate thickness shift, the focus is positive. When the disc 7 has a negative substrate thickness shift, the focus is negative. That is, when focus servo is applied using the focus error signal of the main beam, the focus error signal of the upper half of sub beam 1 and the lower half of sub beam 2 and the focus error signal of the lower half of sub beam 1 and the upper half of sub beam 2 This difference can be used as a substrate thickness deviation signal.

  The track error signal by the focused spot 17a which is the main beam is shown in FIG. 26 (a) when the disc 7 has no radial tilt, and when the disc 7 has a positive radial tilt. When the track error signal 28b of b) and the disk 7 have a negative radial tilt, the same as the track error signal 28d of FIG.

  19e-19g which is a track error signal (upper half track error signal) by the diffracted light from the region 13c of the diffractive optical element 3h in the condensed spot 17n which is the sub beam 1, and diffracted in the condensed spot 17o which is the sub beam 2. 19j-19l which is a track error signal (lower half track error signal) due to the diffracted light from the region 13d of the optical element 3h is the track error signal 28a in FIG. When the disc 7 has a positive radial tilt, the track error signal 28c shown in FIG. 26B is the same. When the disc 7 has a negative radial tilt, the track error signal 28e shown in FIG.

  19f-19h which is a track error signal (lower half track error signal) by the diffracted light from the region 13f of the diffractive optical element 3h in the condensed spot 17n which is the sub beam 1, and diffracted in the condensed spot 17o which is the sub beam 2. 19i-19k, which is a track error signal (upper half track error signal) due to the diffracted light from the region 13e of the optical element 3h, is the track error signal 28a in FIG. When the disc 7 has a positive radial tilt, the track error signal 28e shown in FIG. 26C is the same. When the disc 7 has a negative radial tilt, the track error signal 28c shown in FIG.

  Therefore, the difference (19e + 19h + 19j + 19k) − (19f + 19g + 19i + 19l) between the track error signal of the upper half of the sub beam 1 and the lower half of the sub beam 2 and the track error signal of the lower half of the sub beam 1 and the upper half of the sub beam 2 is When there is no tilt, both land and groove are 0, when the disc 7 has a positive radial tilt, the land is positive, the groove is negative, and when the disc 7 has a negative radial tilt, the land is negative, the groove Then it becomes positive.

That is, when the track servo is applied using the track error signal of the main beam, the track error signal of the upper half of the sub beam 1 and the lower half of the sub beam 2, and the track error signal of the lower half of the sub beam 1 and the upper half of the sub beam 2 Can be used as a radial tilt signal.
JP 2003-051130 A Japanese Patent Laid-Open No. 9-81942 Japanese Patent Laid-Open No. 11-296875

  In the first optical head device described in Patent Document 1 and the optical information recording / reproducing device using the same, five focused spots 17a, 17j, 17k, 17l, and 17m are formed on the disk 7. When the recording surface of the disk 7 and the straight line connecting the condensing point positions of the five condensing spots are not parallel due to surface deflection of the disk 7, the condensing points of the condensing spots 17j, 17k, 17l, and 17m that are sub-beams. The position deviates from the recording surface of the disk 7 in a direction perpendicular to the recording surface of the disk 7, and defocusing occurs.

  With respect to the focused spots 17j and 17k as the first sub-beam, the distance from the focused spot 17a as the main beam is short, so that the amount of defocus due to surface deflection of the disk 7 is small. However, the focused spots 17l and 17m, which are the second sub-beams, have a large distance from the focused spot 17a, which is the main beam, and therefore the amount of defocus due to surface deflection of the disk 7 is large. Further, if the angle between the track 16 of the disk 7 and the straight line connecting the centers of the five focused spots is deviated from the original angle due to the eccentricity of the disk 7, the sub-beam focused spots 17j, 17k, 17l, 17m The center shifts from the center of the corresponding track of the disk 7 in the radial direction of the disk 7, resulting in off-track.

  Regarding the focused spots 17j and 17k as the first sub beam, the distance from the focused spot 17a as the main beam is short, and therefore the amount of off-track due to eccentricity of the disk 7 is small. However, the focused spots 17l and 17m, which are the second sub-beams, have a large distance from the focused spot 17a, which is the main beam, and therefore the amount of off-track due to the eccentricity of the disk 7 is large.

  The condensing spots 17l and 17m, which are the second sub-beams, are used for detecting the substrate thickness deviation and the radial tilt of the disk 7, but when the defocusing spots 17l and 17m are largely defocused due to surface deflection of the disk 7 or the like. Then, the sensitivity of the substrate thickness deviation signal is lowered, and the substrate thickness deviation of the disk 7 cannot be detected correctly. In addition, if a large off-track occurs in the condensed spots 17l and 17m due to the eccentricity of the disk 7, the sensitivity of the radial tilt signal is lowered, and the radial tilt of the disk 7 cannot be detected correctly.

  In the second optical head device described in Patent Document 1 and the optical information recording / reproducing device using the same, in order to obtain a focus error signal by the differential astigmatism method and a track error signal by the differential push-pull method, Calculations are performed based on outputs from the twelve light receiving portions 19a to 19l of the photodetector 10a. Further, in order to obtain a substrate thickness deviation signal and a radial tilt signal, calculation is performed based on outputs from the eight light receiving portions 19e to 19l of the photodetector 10a. The current output from the light receiving units 19a to 19l is converted into a voltage by the corresponding current-voltage conversion circuit and then sent to the arithmetic circuit, but the number of light receiving units related to the calculation for obtaining each signal is large. The number of current-voltage conversion circuits related to the operation for obtaining each signal is also increased, and the quality of the focus error signal, the track error signal, the substrate thickness deviation signal, and the radial tilt signal due to the noise of the current-voltage conversion circuit. Deteriorates. In addition, since the number of light receiving units related to the calculation for obtaining each signal is large, the configuration of the calculation circuit for obtaining each signal is complicated.

  An object of the present invention is to provide a conventional optical head device and an optical information recording / reproducing device capable of detecting a substrate thickness shift and a radial tilt of an optical recording medium without causing an offset in a focus error signal and a track error signal. The above-mentioned problems are solved, the sensitivity of the substrate thickness deviation signal and radial tilt signal is high, and the quality of the focus error signal and track error signal, as well as the substrate thickness deviation signal and radial tilt signal is good, An object of the present invention is to provide an optical head device and an optical information recording / reproducing device having a simple configuration of an arithmetic circuit for obtaining the same.

  An optical head device according to the present invention receives a light source, an objective lens that condenses the light emitted from the light source on a disk-shaped optical recording medium having a groove forming a track, and the reflected light from the optical recording medium. And a main beam, a first sub-beam, and a second sub-beam as light condensed on the optical recording medium by the objective lens from the light emitted from the light source. Beam generating means for generating, wherein the first sub-beam is composed of first and second parts having a plane including the optical axis as a boundary, and the second sub-beam is bounded by a plane including the optical axis The first portion of the first sub-beam and the fourth portion of the second sub-beam have a corresponding portion of the main beam and an optical axis. In The intensity distribution normalized by the intensity on the optical axis in a straight section is different, and the second portion of the first sub-beam and the third portion of the second sub-beam correspond to the main beam. And a beam generating means configured so that the intensity distribution normalized by the intensity on the optical axis in a cross section perpendicular to the optical axis is substantially the same, and the photodetector includes the optical recording medium The reflected light from the main beam reflected by the optical recording medium, the first and second portions of the first sub-beam reflected by the optical recording medium, and the reflected by the optical recording medium The third and fourth portions of the second sub-beam are individually received in order to detect a focus error signal and / or a track error signal from each.

  The optical information recording / reproducing apparatus of the present invention includes the optical head apparatus of the present invention, the main beam reflected by the optical recording medium, individually received by the photodetector, and reflected by the optical recording medium. The focus error signal and / or from each of the first and second portions of the first sub-beam, and the third and fourth portions of the second sub-beam reflected from the optical recording medium. And detecting means for detecting the track error signal and detecting a focus error signal used for focus servo and / or a track error signal used for track servo based on the focus error signal and / or the track error signal. To do.

  In the optical head device and the optical information recording / reproducing apparatus of the present invention, three condensing spots are formed on the optical recording medium. If the recording surface of the optical recording medium and the straight line connecting the condensing point positions of the three condensing spots are not parallel due to surface deflection of the optical recording medium, the two condensing spots that are the first and second sub-beams The focal point position is shifted from the recording surface of the optical recording medium in a direction perpendicular to the recording surface of the optical recording medium, and defocusing occurs. However, the two focused spots that are the first and second sub-beams have a short distance from the focused spot that is the main beam, and therefore the amount of defocus due to the surface shake of the optical recording medium is small. Further, when the angle between the track of the optical recording medium and the straight line connecting the centers of the three condensing spots is deviated from the original angle due to the eccentricity of the optical recording medium, the two condensing light beams that are the first and second sub beams are collected. The center of the spot is shifted from the center of the corresponding track of the optical recording medium in the radial direction of the optical recording medium, resulting in off-track. However, regarding the two focused spots that are the first and second sub beams, the distance from the focused spot that is the main beam is short, so the amount of off-track due to eccentricity of the optical recording medium is small.

  For this reason, the two focused spots, which are the first and second sub-beams, are used to detect the substrate thickness deviation and the radial tilt of the optical recording medium. Even if defocusing occurs, the sensitivity of the substrate thickness deviation signal does not decrease, and the substrate thickness deviation of the optical recording medium can be detected correctly. In addition, even when off-track occurs in the two focused spots due to the eccentricity of the optical recording medium, the radial tilt signal sensitivity is not lowered, and the radial tilt of the optical recording medium can be detected correctly.

  In the optical head device and the optical information recording / reproducing apparatus of the present invention, in order to obtain a focus error signal by the differential astigmatism method and a track error signal by the differential push-pull method, the eight light receiving sections ( Output from four light receiving parts for receiving the main beam, two light receiving parts for receiving the second part of the first sub beam, and two light receiving parts for receiving the third part of the second sub beam) Calculate based on In addition, in order to obtain a substrate thickness deviation signal and a radial tilt signal, the four light receiving portions of the photodetector (two light receiving portions that receive the first portion of the first sub beam, and the fourth light receiving portion of the second sub beam). The calculation is performed based on the outputs from the two light receiving sections that receive the portion.

  The current output from each light receiving unit is converted to a voltage by the corresponding current-voltage conversion circuit and then sent to the arithmetic circuit, but since the number of light receiving units related to the calculation for obtaining each signal is small, The number of current-voltage conversion circuits related to the calculation for obtaining each signal is reduced, and the noise of the current-voltage conversion circuit reduces the quality of the focus error signal, the track error signal, the substrate thickness deviation signal, and the radial tilt signal. Does not deteriorate. In addition, since the number of light receiving portions related to the calculation for obtaining each signal is small, the configuration of the calculation circuit for obtaining each signal is simplified.

  As described above, the effects of the optical head device and the optical information recording / reproducing device of the present invention are that the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high, the focus error signal, the track error signal, and the substrate thickness deviation. The quality of the signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.

  The reason why the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high is that the two focused spots that are the first and second sub beams have a short distance from the focused spot that is the main beam. The amount of off-track due to defocus due to surface shake or the like and eccentricity is small, and the sensitivity of the substrate thickness deviation signal and radial tilt signal does not decrease.

  The reason why the quality of the focus error signal, the track error signal, the substrate thickness deviation signal, and the radial tilt signal is good and the configuration of the arithmetic circuit for obtaining each signal is simple is the reason for the computation for obtaining each signal. Since the number of light receiving units involved is small, the number of current-voltage conversion circuits related to the calculation for obtaining each signal is also reduced, and the quality of each signal is not deteriorated by noise of the current-voltage conversion circuit. .

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
In the optical head device according to the first embodiment of the present invention, the diffractive optical element 3g and the photodetector 10b in the first optical head device described in Patent Document 1 are replaced with a diffractive optical element 3a and a photodetector 10a, respectively. The configuration is the same as that shown in FIG. The diffractive optical element 3a corresponds to the beam generating means of the present invention.

  FIG. 1 is a plan view of the diffractive optical element 3a.

  The diffractive optical element 3a has regions 11a and 11b which are straight lines passing through the optical axis of incident light and parallel to the radial direction of the disk 7 inside a circle having a diameter smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. The diffraction grating is divided into two regions 11c and 11d along a straight line that passes through the optical axis of the incident light and is parallel to the radial direction of the disk 7. It is the formed structure. The directions of the gratings in the diffraction grating are almost parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice intervals in the regions 11a, 11b, 11c, and 11d are all equal.

  2A to 2D are cross-sectional views of the diffractive optical element 3a.

  In the region 11a, the diffractive optical element 3a has a rectangular cross section 15a formed on the substrate 14 as shown in FIG. 2A, and the region 11b in FIG. 2B. As shown, a grid 15b having a rectangular cross-sectional shape is formed on the substrate 14, and the region 11c has an eight-level step-like cross-sectional shape on the substrate 14 as shown in FIG. A lattice 15c is formed, and the region 11d has a structure in which a lattice 15d having an eight-level step-like cross-sectional shape is formed on the substrate 14 as shown in FIG.

  The intervals between the lattices 15a, 15b, 15c, and 15d are all P.

  The cross-sectional shape of the lattice 15a is a repetition of a portion where the width is P / 2 and the height is H2, and a portion where the width is P / 2 and the height is H1 + H2. The cross-sectional shape of the grating 15b is a repetition of a portion having a width of P / 2 and a height of H1 + H2, and a portion having a width of P / 2 and a height of H2.

  On the other hand, the cross-sectional shape of the lattice 15c is that the width is P / 8 and the height is 0, the width is P / 8 and the height is H5, the width is P / 8 and the height is H4, and the width is P / 8 and height H4 + H5, width P / 8 and height H3, width P / 8 and height H3 + H5, width P / 8 and height H3 + H4, This is a repetition of a portion where the width is P / 8 and the height is H3 + H4 + H5. The cross-sectional shape of the grating 15d is as follows. The width is P / 8 and the height is H3 + H4 + H5. The width is P / 8 and the height is H3 + H4. The width is P / 8 and the height is H3 + H5. P / 8, height H3, width P / 8, height H4 + H5, width P / 8, height H4, width P / 8, height H5, It is a repetition of a portion where the width is P / 8 and the height is 0.

  Here, λ is the wavelength of the semiconductor laser 1, and n is the refractive index of the gratings 15a, 15b, 15c, 15d, and H1 = 0.115λ / (n−1), H2 = 0.0773 / (n−1), It is assumed that H3 = 0.078λ / (n−1), H4 = 0.122λ / (n−1), and H5 = 0.061λ / (n−1). Further, the + 1st order diffracted light in the diffractive optical element 3a is deflected to the upper side of FIG. 1 and the left side of FIGS. 2 (a) to (d), and the −1st order diffracted light is lower to FIG. It shall be deflected to the right of (d).

  At this time, the transmittance, + 1st order diffraction efficiency, and −1st order diffraction efficiency of the gratings 15a and 15b are about 87.5%, about 5.1%, and about 5.1%, respectively. On the other hand, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15c are about 78.0%, about 0.6%, and about 4.5%, respectively. Further, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15d are about 78.0%, about 4.5%, and about 0.6%, respectively.

  That is, about 87.5% of the light incident on the regions 11a and 11b is transmitted as 0th-order light, and about 5.1% is diffracted as ± first-order diffracted light. On the other hand, about 78.0% of the light incident on the region 11c is transmitted as 0th order light, about 4.5% is diffracted as −1st order diffracted light, and only about 0.6% is diffracted as + 1st order diffracted light. . In addition, about 78.0% of the light incident on the region 11d is transmitted as 0th order light, about 4.5% is diffracted as + 1st order diffracted light, and only about 0.6% is diffracted as −1st order diffracted light. .

  When the 0th-order light from the diffractive optical element 3a is the main beam, the + 1st-order diffracted light is the sub-beam 1, and the -1st-order diffracted light is the sub-beam 2, the main beam includes the transmitted light from the regions 11a and 11b and the light from the regions 11c and 11d. Transmitted light is included at a ratio of about 1.1: 1.

  On the other hand, only the diffracted light from the region 11a is mainly included in the upper half of the sub beam 1, and the diffracted light from the region 11b and the diffracted light from the region 11d are about 1.1: 1 in the lower half of the sub beam 1. It is included in the ratio. The upper half of the sub beam 2 includes the diffracted light from the region 11a and the diffracted light from the region 11c at a ratio of about 1.1: 1. The lower half of the sub beam 2 mainly includes the diffracted light from the region 11b. Only light is included.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. In the upper half, the sub beam 1 has a lower intensity at the periphery than the main beam, and the lower half has substantially the same intensity distribution as the main beam. Further, the intensity distribution of the sub beam 2 is substantially the same as that of the main beam in the upper half, and the intensity of the peripheral portion is lower in the lower half than that of the main beam.

  FIG. 3 shows the arrangement of the focused spots on the disk 7.

  The condensed spots 17a, 17b, and 17c correspond to the 0th order light, the + 1st order diffracted light, and the −1st order diffracted light from the diffractive optical element 3a, respectively. The focused spot 17 a is on the track 16 (land or groove), the focused spot 17 b is on the track (groove or land) adjacent to the right side of the track 16, and the focused spot 17 c is on the track adjacent to the left side of the track 16. (Groove or land) are arranged on each.

  Since the sub beam 1 is the upper half and the intensity of the peripheral portion is lower than that of the main beam, the focused spot 17b, which is the sub beam 1, has a larger diameter than the focused spot 17a, which is the main beam. Further, since the sub beam 2 has a lower half and lower peripheral strength than the main beam, the focused spot 17c, which is the sub beam 2, has a larger diameter than the focused spot 17a, which is the main beam.

  FIG. 4 shows the pattern of the light receiving part of the photodetector 10a and the arrangement of the light spots on the photodetector 10a.

  The light spot 18a corresponds to zero-order light from the diffractive optical element 3a, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. The light is received at ~ 19d.

  The light spot 18b corresponds to + 1st order diffracted light from the diffractive optical element 3a, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at ~ 19h.

  The light spot 18c corresponds to −1st order diffracted light from the diffractive optical element 3a, and is divided into four parts by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at 19i to 19l.

  Although the rows of the condensed spots 17a, 17b, and 17c on the disk 7 are substantially tangential, the rows of the light spots 18a, 18b, and 18c on the photodetector 10a are almost due to the action of the cylindrical lens 8 and the lens 9. Radial direction.

  When the outputs from the light receiving portions 19a to 19l are represented by V19a to V19l, respectively, the focus error signal due to the focused spot 17a which is the main beam is obtained from the calculation of (V19a + V19d) − (V19b + V19c) by the astigmatism method.

  The focus error signal (lower half focus error signal) due to the diffracted light from the regions 11b and 11d of the diffractive optical element 3a in the condensed spot 17b as the sub beam 1 is obtained from the calculation of V19h-V19f by the astigmatism method. It is done.

  The focus error signal (upper half focus error signal) by the diffracted light from the regions 11a and 11c of the diffractive optical element 3a in the condensed spot 17c which is the sub beam 2 is obtained from the calculation of V19i-V19k by the astigmatism method. It is done.

  The focus error signal by the differential astigmatism method is obtained from the calculation of (V19a + V19d) − (V19b + V19c) + K {(V19h + V19i) − (V19f + V19k)} (K is a constant).

  On the other hand, the track error signal from the focused spot 17a as the main beam is obtained from the calculation of (V19a + V19b) − (V19c + V19d) by the push-pull method.

  The track error signal (lower half track error signal) by the diffracted light from the regions 11b and 11d of the diffractive optical element 3a in the condensed spot 17b which is the sub beam 1 is obtained from the calculation of V19f-V19h by the push-pull method. .

  The track error signal (upper half track error signal) by the diffracted light from the regions 11a and 11c of the diffractive optical element 3a in the condensed spot 17c as the sub beam 2 is obtained from the calculation of V19i-V19k by the push-pull method. .

  The track error signal by the differential push-pull method is obtained from the calculation of (V19a + V19b) − (V19c + V19d) −K {(V19f + V19i) − (V19h + V19k)}. The RF signal from the focused spot 17a, which is the main beam, is obtained from the calculation of V19a + V19b + V19c + V19d.

  The focus error signal from the focused spot 17a, which is the main beam, is the same as the focus error signal 25a in FIG. 23 (a) and the focus error signal 25c in FIG. 23 (b). Further, since the intensity distribution of the lower half of the sub beam 1 and the intensity distribution of the upper half of the sub beam 2 are substantially the same as the intensity distribution of the main beam, the focus error signal and the sub beam of the lower half due to the condensed spot 17b which is the sub beam 1 are used. 2 is the same as the focus error signal 25b in FIG. 23 (a) and the focus error signal 25d in FIG. 23 (b).

  Therefore, the focus error signal by the differential astigmatism method, which is the sum of the focus error signal from the focused spot 17a, the lower half focus error signal from the focused spot 17b, and the upper half focus error signal from the focused spot 17c, is This is the same as the focus error signal 25e in FIG. That is, in this optical head device, no offset occurs in the focus error signal.

  The track error signal by the focused spot 17a which is the main beam is the same as the track error signal 26a in FIG. 24A and the track error signal 26c in FIG. Further, since the intensity distribution of the lower half of the sub beam 1 and the intensity distribution of the upper half of the sub beam 2 are substantially the same as the intensity distribution of the main beam, the track error signal and the sub beam of the lower half by the condensed spot 17b which is the sub beam 1 are used. 2 is the same as the track error signal 26b in FIG. 24 (a) and the track error signal 26d in FIG. 24 (b).

  Therefore, the track error signal by the differential push-pull method, which is the difference between the track error signal by the focused spot 17a and the lower half track error signal by the focused spot 17b and the upper half track error signal by the focused spot 17c, is shown in FIG. This is the same as the track error signal 26e of 24 (c). That is, in this optical head device, no offset is generated in the track error signal.

  The focus error signal from the focused spot 17a, which is the main beam, is the focus error signal 27a shown in FIG. 25A when the disk 7 has no substrate thickness shift, and the focus error signal 27a shown in FIG. The focus error signal 27b of b) and the case where the disc 7 has a negative substrate thickness deviation are the same as the focus error signal 27d of FIG.

  19e-19g which is a focus error signal (upper half focus error signal) due to the diffracted light from the region 11a of the diffractive optical element 3a in the condensed spot 17b which is the sub beam 1, and diffracted in the condensed spot 17c which is the sub beam 2. 19l-19j which is a focus error signal (lower half focus error signal) by the diffracted light from the region 11b of the optical element 3a is the focus error signal 27a shown in FIG. When the disc 7 has a positive substrate thickness deviation, the focus error signal 27c in FIG. 25B is the same, and when the disc 7 has a negative substrate thickness deviation, the same as the focus error signal 27e in FIG. 25C. It is.

  Therefore, the focus error signals (19e + 19l) − (19g + 19j) of the upper half of the sub beam 1 and the lower half of the sub beam 2 are 0 in the just focus and the positive substrate in the disk 7 when there is no substrate thickness deviation. When there is a thickness shift, it is positive with just focus, and when the disk 7 has a negative substrate thickness shift, it is negative with just focus. That is, the focus error signals of the upper half of the sub beam 1 and the lower half of the sub beam 2 when the focus servo is applied using the focus error signal of the main beam can be used as the substrate thickness deviation signal.

  The track error signal by the focused spot 17a which is the main beam is shown in FIG. 26 (a) when the disc 7 has no radial tilt, and when the disc 7 has a positive radial tilt. When the track error signal 28b of b) and the disk 7 have a negative radial tilt, the same as the track error signal 28d of FIG.

  19e-19g which is a track error signal (upper half track error signal) due to diffracted light from the region 11a of the diffractive optical element 3a in the condensed spot 17b which is the sub beam 1, and diffraction in the condensed spot 17c which is the sub beam 2. 19j-19l, which is a track error signal (lower half track error signal) due to the diffracted light from the region 11b of the optical element 3a, is the track error signal 28a, FIG. When the disc 7 has a positive radial tilt, the track error signal 28c shown in FIG. 26B is the same. When the disc 7 has a negative radial tilt, the track error signal 28e shown in FIG.

  Accordingly, the track error signals (19e + 19j) − (19g + 19l) of the upper half of the sub beam 1 and the lower half of the sub beam 2 are 0 in both the land and the groove and positive in the disc 7 when the disc 7 has no radial tilt. When there is a radial tilt, the land is positive, the groove is negative, and when the disk 7 has a negative radial tilt, the land is negative, and the groove is positive. That is, the track error signals of the upper half of the sub beam 1 and the lower half of the sub beam 2 when the track servo is applied using the track error signal of the main beam can be used as the radial tilt signal.

  In the present embodiment, three focused spots 17a, 17b and 17c are formed on the disk 7.

  If the recording surface of the disk 7 and the straight line connecting the condensing point positions of the three condensing spots are not parallel due to surface deflection of the disk 7, the condensing point positions of the condensing spots 17 b and 17 c that are sub-beams are the disc 7. Defocusing occurs in the direction perpendicular to the recording surface of the disk 7. However, the focused spots 17b and 17c that are sub-beams have a short distance from the focused spot 17a that is the main beam, and therefore the amount of defocus due to the surface shake of the disk 7 is small.

  Further, if the angle between the track 16 of the disk 7 and the straight line connecting the centers of the three focused spots is deviated from the original angle due to the eccentricity of the disk 7, the centers of the focused spots 17b and 17c, which are sub-beams, are changed. Deviation from the center of the corresponding track in the radial direction of the disk 7 results in off-track. However, the focused spots 17b and 17c that are sub-beams have a small distance from the focused spot 17a that is the main beam, and therefore the amount of off-track due to eccentricity of the disk 7 is small.

  For this reason, the condensing spots 17b and 17c, which are sub-beams, are used for detecting the substrate thickness deviation and the radial tilt of the disk 7, but even if defocusing occurs in the condensing spots 17b and 17c due to surface deflection of the disk 7, etc. The sensitivity of the substrate thickness deviation signal does not decrease, and the substrate thickness deviation of the disk 7 can be detected correctly.

  Further, even if the off-track occurs in the focused spots 17b and 17c due to the eccentricity of the disc 7, the sensitivity of the radial tilt signal does not decrease, and the radial tilt of the disc 7 can be detected correctly.

  In the present embodiment, in order to obtain a focus error signal by the differential astigmatism method and a track error signal by the differential push-pull method, the eight light receiving portions 19a to 19d, 19f, 19h, and 19i of the photodetector 10a. , 19k is calculated based on the output from 19k. Further, in order to obtain a substrate thickness deviation signal and a radial tilt signal, calculation is performed based on outputs from the four light receiving portions 19e, 19g, 19j, and 19l of the photodetector 10a.

The current output from the light receiving portions 19a to 19l is converted into a voltage by the corresponding current-voltage conversion circuit and then sent to the arithmetic circuit, but the number of light receiving portions related to the calculation for obtaining each signal is small. The number of current-voltage conversion circuits related to the calculation for obtaining each signal is reduced, and the quality of the focus error signal, the track error signal, the substrate thickness deviation signal, and the radial tilt signal due to the noise of the current-voltage conversion circuit. Does not deteriorate. In addition, since the number of light receiving portions related to the calculation for obtaining each signal is small, the configuration of the calculation circuit for obtaining each signal is simplified.
(Second embodiment)
The optical head device in the second embodiment of the present invention is obtained by replacing the diffractive optical element 3a in the first embodiment with a diffractive optical element 3b, and the configuration is the same as that shown in FIG. .

  FIG. 5 is a plan view of the diffractive optical element 3b.

  The diffractive optical element 3b has regions 11e and 11f which are straight lines passing through the optical axis of incident light and parallel to the radial direction of the disk 7 inside a circle having a diameter smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. A diffraction grating divided into two is formed. On the outside, a diffraction grating divided into two regions 11g and 11h is formed by a straight line passing through the optical axis of incident light and parallel to the radial direction of the disk 7. It is a configuration. The directions of the gratings in the diffraction grating are almost parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice intervals in the regions 11e, 11f, 11g, and 11h are all equal.

  The cross-sectional view of the diffractive optical element 3b in the present embodiment is the same as that shown in FIGS. 2A to 2D, and the regions 11g, 11h, 11e, and 11f are shown in FIGS. 2A and 2B, respectively. , (C), (d). Here, H1 = 0.115λ / (n−1), H2 = 0.073λ / (n−1), H3 = 0.078λ / (n−1), H4 = 0.122λ / (n−1) , H5 = 0.061λ / (n−1).

  At this time, the transmittance, + 1st order diffraction efficiency, and −1st order diffraction efficiency of the gratings 15a and 15b are about 87.5%, about 5.1%, and about 5.1%, respectively. On the other hand, the transmittance, + 1st order diffraction efficiency, and -1st order diffraction efficiency of the grating 15c are about 78.0%, about 0.6%, and about 4.5%, respectively. Further, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15d are about 78.0%, about 4.5%, and about 0.6%, respectively.

  That is, about 87.5% of light incident on the regions 11g and 11h is transmitted as 0th order light, and about 5.1% is diffracted as ± first order diffracted light. On the other hand, about 78.0% of the light incident on the region 11e is transmitted as 0th order light, about 4.5% is diffracted as −1st order diffracted light, and only about 0.6% is diffracted as + 1st order diffracted light.

  Further, about 78.0% of the light incident on the region 11f is transmitted as 0th order light, about 4.5% is diffracted as + 1st order diffracted light, and only about 0.6% is diffracted as −1st order diffracted light. .

  When the 0th-order light from the diffractive optical element 3b is the main beam, the + 1st-order diffracted light is the subbeam 1, and the -1st-order diffracted light is the subbeam 2, the main beam is transmitted through the regions 11g and 11h and transmitted through the regions 11e and 11f. Light is included in a ratio of about 1.1: 1.

  On the other hand, only the diffracted light from the region 11g is mainly included in the upper half of the sub beam 1, and the diffracted light from the region 11h and the diffracted light from the region 11f are approximately 1.1: 1 in the lower half of the sub beam 1. It is included in the ratio. Further, the upper half of the sub beam 2 includes the diffracted light from the region 11g and the diffracted light from the region 11e at a ratio of about 1.1: 1, and the lower half of the sub beam 2 mainly includes the diffracted light from the region 11h. Only light is included.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. In the upper half, the sub beam 1 has a higher intensity at the periphery than the main beam, and the lower half has substantially the same intensity distribution as the main beam. Further, the intensity distribution of the sub beam 2 is substantially the same as that of the main beam in the upper half, and the intensity of the peripheral portion is higher in the lower half than the main beam.

  FIG. 6 shows the arrangement of the focused spots on the disk 7.

  The condensed spots 17a, 17d, and 17e correspond to the 0th-order light, the + 1st-order diffracted light, and the -1st-order diffracted light from the diffractive optical element 3b, respectively.

  The focused spot 17a is on the track 16 (land or groove), the focused spot 17d is on a track (groove or land) adjacent to the right side of the track 16, and the focused spot 17e is a track adjacent to the left side of the track 16. (Groove or land) are arranged on each.

  Since the sub beam 1 is an upper half of the sub beam 1 and has a higher intensity at the periphery, the condensing spot 17d, which is the sub beam 1, has a smaller diameter and a larger side lobe than the condensing spot 17a, which is the main beam.

  Further, since the sub beam 2 has a lower half and a higher intensity at the peripheral portion than the main beam, the focused spot 17e as the sub beam 2 has a smaller diameter and a larger side lobe than the focused spot 17a as the main beam. .

  FIG. 7 shows the pattern of the light receiving portion of the photodetector 10a and the arrangement of the light spots on the photodetector 10a.

  The light spot 18a corresponds to zero-order light from the diffractive optical element 3b, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. The light is received at ~ 19d.

  The light spot 18d corresponds to the + 1st order diffracted light from the diffractive optical element 3b, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at ~ 19h.

  The light spot 18e corresponds to −1st order diffracted light from the diffractive optical element 3b, and is divided into four by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at 19i to 19l.

  The row of the condensed spots 17a, 17d, and 17e on the disk 7 is substantially tangential, but due to the action of the cylindrical lens 8 and the lens 9, the row of the light spots 18a, 18d, and 18e on the photodetector 10a is Nearly radial direction. In the present embodiment, a focus error signal, a track error signal, and an RF signal are obtained by a method similar to the method described in the first embodiment.

  In the present embodiment, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  Further, in the present embodiment, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by the same method as that described in the first embodiment.

Furthermore, in the present embodiment, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness deviation are high. The quality of the signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.
(Third embodiment)
The optical head device in the third embodiment of the present invention is obtained by replacing the diffractive optical element 3a in the first embodiment with a diffractive optical element 3c, and the configuration is the same as that shown in FIG. .

  FIG. 8 is a plan view of the diffractive optical element 3c.

  The diffractive optical element 3c has regions 11i and 11j which are straight lines passing through the optical axis of incident light and parallel to the radial direction of the disk 7 inside the band having a width smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. The diffraction grating is divided into two regions 11k and 11l along a straight line passing through the optical axis of the incident light and parallel to the radial direction of the disk 7. It is the formed structure. The directions of the gratings in the diffraction grating are almost parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice intervals in the regions 11i, 11j, 11k, and 11l are all equal.

  The sectional view of the diffractive optical element 3c in the present embodiment is the same as that shown in FIGS. 2A to 2D, and the regions 11i, 11j, 11k, and 11l are shown in FIGS. 2A and 2B, respectively. , (C), (d). Here, H1 = 0.115λ / (n−1), H2 = 0.073λ / (n−1), H3 = 0.078λ / (n−1), H4 = 0.122λ / (n−1) , H5 = 0.061λ / (n−1).

  At this time, the transmittance, + 1st order diffraction efficiency, and −1st order diffraction efficiency of the gratings 15a and 15b are about 87.5%, about 5.1%, and about 5.1%, respectively.

  On the other hand, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15c are about 78.0%, about 0.6%, and about 4.5%, respectively.

  Further, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15d are about 78.0%, about 4.5%, and about 0.6%, respectively.

  That is, about 87.5% of the light incident on the regions 11i and 11j is transmitted as 0th order light, and about 5.1% is diffracted as ± first order diffracted light.

  On the other hand, about 78.0% of light incident on the region 11k is transmitted as 0th order light, about 4.5% is diffracted as −1st order diffracted light, and only about 0.6% is diffracted as + 1st order diffracted light. .

  Further, about 78.0% of the light incident on the region 11l is transmitted as 0th order light, about 4.5% is diffracted as + 1st order diffracted light, and only about 0.6% is diffracted as −1st order diffracted light. .

  If the 0th order light from the diffractive optical element 3c is the main beam, the + 1st order diffracted light is the subbeam 1, and the −1st order diffracted light is the subbeam 2, the main beam includes the transmitted light from the regions 11i and 11j and the light from the regions 11k and 11l. Transmitted light is included at a ratio of about 1.1: 1.

  On the other hand, only the diffracted light from the region 11i is mainly included in the upper half of the sub beam 1, and the diffracted light from the region 11j and the diffracted light from the region 11l are approximately 1.1: 1 in the lower half of the sub beam 1. Included as a ratio. The upper half of the sub beam 2 includes the diffracted light from the region 11i and the diffracted light from the region 11k at a ratio of about 1.1: 1, and the lower half of the sub beam 2 mainly includes the diffracted light from the region 11j. Only light is included.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. In the upper half, the intensity of the peripheral portion in the radial direction of the disk 7 is lower in the upper half, and the intensity distribution in the lower half is substantially the same as that in the main beam. Further, the intensity distribution of the sub beam 2 in the upper half is substantially the same as that of the main beam, and the intensity of the peripheral portion in the radial direction of the disk 7 is lower in the lower half than in the main beam.

  The arrangement of the condensed spots on the disk 7 in the present embodiment is almost the same as that shown in FIG. 3, but the sub beam 1 is the upper half of the main beam and the intensity of the peripheral portion in the radial direction of the disk 7. Therefore, the condensing spot 17d that is the sub beam 1 has a larger diameter in the radial direction of the disc 7 than the condensing spot 17a that is the main beam. Further, the sub beam 2 has a lower half compared to the main beam and the intensity of the peripheral portion in the radial direction of the disk 7 is low. Therefore, the condensing spot 17e as the sub beam 2 has a lower intensity than the condensing spot 17a as the main beam. 7 has a large diameter in the radial direction.

  The pattern of the light receiving portion of the photodetector 10a and the arrangement of the light spots on the photodetector 10a in the present embodiment are substantially the same as those shown in FIG. In the present embodiment, a focus error signal, a track error signal, and an RF signal are obtained by a method similar to the method described in the first embodiment.

  In the present embodiment, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  Further, in the present embodiment, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by the same method as that described in the first embodiment.

Furthermore, in the present embodiment, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness deviation are high. The quality of the signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.
(Fourth embodiment)
The optical head device in the fourth embodiment of the present invention is obtained by replacing the diffractive optical element 3a in the first embodiment with a diffractive optical element 3d, and the configuration thereof is the same as that shown in FIG. .

  FIG. 9 is a plan view of the diffractive optical element 3d.

  The diffractive optical element 3d has regions 11m and 11n in a straight line passing through the optical axis of incident light and parallel to the radial direction of the disk 7 inside the band having a width smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. The diffraction grating divided into two regions 11o and 11p is formed on the outer side by a straight line passing through the optical axis of the incident light and parallel to the radial direction of the disk 7. It is the formed structure. The directions of the gratings in the diffraction grating are almost parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice intervals in the regions 11m, 11n, 11o, and 11p are all equal.

  The cross-sectional view of the diffractive optical element 3d in the present embodiment is the same as that shown in FIGS. 2A to 2D, and the regions 11o, 11p, 11m, and 11n are respectively shown in FIGS. This corresponds to (c) and (d). Here, H1 = 0.115λ / (n−1), H2 = 0.073λ / (n−1), H3 = 0.078λ / (n−1), H4 = 0.122λ / (n−1) , H5 = 0.061λ / (n−1).

  At this time, the transmittance, + 1st order diffraction efficiency, and −1st order diffraction efficiency of the gratings 15a and 15b are about 87.5%, about 5.1%, and about 5.1%, respectively.

  On the other hand, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15c are about 78.0%, about 0.6%, and about 4.5%, respectively.

  Further, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15d are about 78.0%, about 4.5%, and about 0.6%, respectively.

  That is, about 87.5% of light incident on the regions 11o and 11p is transmitted as 0th order light, and about 5.1% is diffracted as ± first order diffracted light.

  On the other hand, about 78.0% of the light incident on the region 11m is transmitted as 0th order light, about 4.5% is diffracted as −1st order diffracted light, and only about 0.6% is diffracted as + 1st order diffracted light. .

  Further, about 78.0% of the light incident on the region 11n is transmitted as 0th order light, about 4.5% is diffracted as + 1st order diffracted light, and only about 0.6% is diffracted as −1st order diffracted light. .

  Assuming that the 0th order light from the diffractive optical element 3d is the main beam, the + 1st order diffracted light is the subbeam 1, and the −1st order diffracted light is the subbeam 2, the main beam includes the transmitted light from the regions 11o and 11p and the light from the regions 11m and 11n. Transmitted light is included at a ratio of about 1.1: 1.

  On the other hand, only the diffracted light from the region 11o is mainly included in the upper half of the sub beam 1, and the diffracted light from the region 11p and the diffracted light from the region 11n are about 1.1: 1 in the lower half of the sub beam 1. It is included in the ratio. The upper half of the sub beam 2 includes the diffracted light from the region 11o and the diffracted light from the region 11m at a ratio of about 1.1: 1, and the lower half of the sub beam 2 mainly includes the diffraction from the region 11p. Only light is included.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. In the upper half, the intensity of the peripheral portion in the radial direction of the disk 7 is higher in the upper half, and the intensity distribution in the lower half is almost the same as that in the main beam. Further, the intensity distribution of the sub beam 2 in the upper half is substantially the same as that of the main beam, and the intensity of the peripheral portion in the radial direction of the disk 7 is higher in the lower half than in the main beam.

  The arrangement of the converging spots on the disk 7 in the present embodiment is almost the same as that shown in FIG. 6, but the sub beam 1 is the upper half of the main beam and the intensity of the peripheral part in the radial direction of the disk 7. Therefore, the condensing spot 17d that is the sub beam 1 has a smaller diameter in the radial direction of the disk 7 and a larger sidelobe than the condensing spot 17a that is the main beam. Further, since the sub beam 2 has a lower half in the radial direction of the disk 7 compared with the main beam and the intensity of the peripheral portion in the radial direction of the disk 7, the focused spot 17e as the sub beam 2 is larger than the focused spot 17a as the main beam. 7 has a small diameter in the radial direction and a large side lobe.

  The pattern of the light receiving portion of the photodetector 10a and the arrangement of the light spots on the photodetector 10a in the present embodiment are substantially the same as those shown in FIG. In the present embodiment, a focus error signal, a track error signal, and an RF signal are obtained by a method similar to the method described in the first embodiment.

  In the present embodiment, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  Further, in the present embodiment, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by the same method as that described in the first embodiment.

Furthermore, in this embodiment, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness deviation are high. The quality of the signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.
(Fifth embodiment)
The optical head device in the fifth embodiment of the present invention is obtained by replacing the diffractive optical element 3a in the first embodiment with a diffractive optical element 3e, and the configuration is the same as that shown in FIG. .

  FIG. 10 is a plan view of the diffractive optical element 3e.

  The diffractive optical element 3e has a straight line parallel to the radial direction of the disk 7 passing through the optical axis of the incident light and parallel to the tangential direction inside the circle having a diameter smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. The diffraction grating is divided into four regions 12a, 12b, 12c, and 12d with a straight line. On the outside, the diffraction grating passes through the optical axis of the incident light and is parallel to the radial direction of the disk 7 and in the tangential direction. This is a configuration in which a diffraction grating divided into four regions 12e, 12f, 12g, and 12h by parallel straight lines is formed. The directions of the gratings in the diffraction grating are all parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice spacings in the regions 12a, 12b, 12c, 12d, 12e, 12f, 12g, and 12h are all equal. The phase of the grating in the regions 12a, 12c, 12e, and 12g and the phase of the grating in the regions 12b, 12d, 12f, and 12h are shifted from each other by π.

  The cross-sectional view of the diffractive optical element 3e in the present embodiment is the same as that shown in FIGS. 2A to 2D, the regions 12a and 12b are FIG. 2A, and the regions 12c and 12d are FIG. b), regions 12e and 12f correspond to FIG. 2C, and regions 12g and 12h correspond to FIG.

  Here, H1 = 0.115λ / (n−1), H2 = 0.073λ / (n−1), H3 = 0.078λ / (n−1), H4 = 0.122λ / (n−1) , H5 = 0.061λ / (n−1).

  At this time, the transmittance, + 1st order diffraction efficiency, and −1st order diffraction efficiency of the gratings 15a and 15b are about 87.5%, about 5.1%, and about 5.1%, respectively.

  On the other hand, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15c are about 78.0%, about 0.6%, and about 4.5%, respectively.

  Further, the transmittance, the + 1st order diffraction efficiency, and the −1st order diffraction efficiency of the grating 15d are about 78.0%, about 4.5%, and about 0.6%, respectively.

  That is, about 87.5% of the light incident on the regions 12a, 12b, 12c, and 12d is transmitted as 0th order light and about 5.1% is diffracted as ± first order diffracted light.

  On the other hand, about 78.0% of the light incident on the regions 12e and 12f is transmitted as 0th order light, about 4.5% is diffracted as −1st order diffracted light, and only about 0.6% as + 1st order diffracted light. Not diffracted.

  Further, about 78.0% of light incident on the regions 12g and 12h is transmitted as 0th order light, about 4.5% is diffracted as + 1st order diffracted light, and only about 0.6% is obtained as -1st order diffracted light. Not diffracted.

  If the 0th order light from the diffractive optical element 3e is the main beam, the + 1st order diffracted light is the subbeam 1, and the −1st order diffracted light is the subbeam 2, the main beam includes the transmitted light from the regions 12a, 12b, 12c, and 12d and the region 12e. , 12f, 12g, and 12h are included at a ratio of about 1.1: 1.

  On the other hand, the upper half of the sub beam 1 mainly includes only diffracted light from the regions 12a and 12b, and the lower half of the sub beam 1 includes diffracted light from the regions 12c and 12d and diffracted light from the regions 12g and 12h. It is included at a ratio of about 1.1: 1.

  The upper half of the sub beam 2 includes the diffracted light from the regions 12a and 12b and the diffracted light from the regions 12e and 12f at a ratio of about 1.1: 1. Only the diffracted light from 12c and 12d is included.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. In the upper half, the sub beam 1 has a lower intensity at the periphery than the main beam, and the lower half has substantially the same intensity distribution as the main beam. Further, the intensity distribution of the sub beam 2 is substantially the same as that of the main beam in the upper half, and the intensity of the peripheral portion is lower in the lower half than that of the main beam. The phase of the + 1st order diffracted light from the regions 12a, 12c, and 12g and the phase of the + 1st order diffracted light from the regions 12b, 12d, and 12h are shifted from each other by π, and similarly the phase of the −1st order diffracted light from the regions 12a, 12c, and 12e. The phases of the −1st order diffracted lights from the regions 12b, 12d, and 12f are shifted from each other by π.

  FIG. 11 shows the arrangement of the focused spots on the disk 7.

  The condensed spots 17a, 17f, and 17g correspond to the 0th order light, the + 1st order diffracted light, and the −1st order diffracted light from the diffractive optical element 3e, respectively. The three focused spots 17a, 17f, and 17g are arranged on the same track 16 (land or groove). The sub-beams are shifted in phase from each other by π on the left and right sides of a straight line that passes through the optical axis and is parallel to the tangential direction of the disk 7, so that the condensed spots 17 f and 17 g that are sub-beams It has two peaks with equal intensity on the right side.

  The pattern of the light receiving portion of the photodetector 10a and the arrangement of the light spots on the photodetector 10a in the present embodiment are substantially the same as those shown in FIG. In the present embodiment, a focus error signal, a track error signal, and an RF signal are obtained by a method similar to the method described in the first embodiment.

  By shifting the phase of the grating in the regions 12a, 12c, 12e, and 12g of the diffractive optical element 3e and the phase of the grating in the regions 12b, 12d, 12f, and 12h by π, the phase of the sub beam passes through the optical axis and is tangent to the disk 7 By shifting the left and right sides of the straight line parallel to the direction by π, the sub-beam condensing spot on the disc 7 is shifted from the main beam condensing spot by a half period of the groove of the disc 7 with respect to the main beam condensing spot. Displacement in the radial direction is equivalent to an error signal. The reason is described in Patent Document 2, for example.

  Therefore, in the present embodiment, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  Further, in the present embodiment, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by the same method as that described in the first embodiment.

  Furthermore, in the present embodiment, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness deviation are high. The quality of the signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.

Furthermore, in the present embodiment, three focused spots are arranged on the same track of the disk 7. For this reason, the arrangement of the three converging spots is not changed even for discs having different track pitches, and the above-described effect can be obtained for a disc having an arbitrary track pitch.
(Sixth embodiment)
The optical head device according to the sixth embodiment of the present invention is obtained by replacing the diffractive optical element 3a in the first embodiment with a diffractive optical element 3f, and the configuration is the same as that shown in FIG. .

  FIG. 12 is a plan view of the diffractive optical element 3f. The diffractive optical element 3f has a straight line that passes through the optical axis of the incident light and is parallel to the radial direction of the disk 7 and the light of the incident light inside a circle having a diameter smaller than the effective diameter of the objective lens 6 indicated by a dotted line in the drawing. A diffraction grating divided into four regions 12i, 12j, 12k, and 12l is formed by two straight lines that are symmetrical with respect to the axis and parallel to the tangential direction of the disk 7, and on the outer side, the optical axis of the incident light passes through. A diffraction grating divided into four regions 12m, 12n, 12o, and 12p is formed by a straight line parallel to the radial direction of the disk 7 and two straight lines symmetrical to the optical axis of the incident light and parallel to the tangential direction of the disk 7. It is a configuration.

  The directions of the gratings in the diffraction grating are all parallel to the radial direction of the disk 7, and the patterns of the gratings are all linear at regular intervals. The lattice intervals in the regions 12i, 12j, 12k, 12l, 12m, 12n, 12o, and 12p are all equal. The phase of the lattice in the regions 12i, 12j, 12m, and 12n and the phase of the lattice in the regions 12k, 12l, 12o, and 12p are shifted from each other by π.

  The sectional view of the diffractive optical element 3f in the present embodiment is the same as that shown in FIGS. 2A to 2D, the regions 12i and 12k are FIG. 2A, and the regions 12j and 12l are FIG. b), the regions 12m and 12o correspond to FIG. 2C, and the regions 12n and 12p correspond to FIG. Here, H1 = 0.115λ / (n−1), H2 = 0.073λ / (n−1), H3 = 0.078λ / (n−1), H4 = 0.122λ / (n−1) , H5 = 0.061λ / (n−1).

  At this time, the transmittance, + 1st order diffraction efficiency, and −1st order diffraction efficiency of the gratings 15a and 15b are about 87.5%, about 5.1%, and about 5.1%, respectively.

  On the other hand, the transmittance, + 1st order diffraction efficiency, and -1st order diffraction efficiency of the grating 15c are about 78.0%, about 0.6%, and about 4.5%, respectively.

  Further, the transmittance, + 1st order diffraction efficiency, and -1st order diffraction efficiency of the grating 15d are about 78.0%, about 4.5%, and about 0.6%, respectively.

  That is, about 87.5% of the light incident on the regions 12i, 12j, 12k, and 12l is transmitted as 0th-order light and is diffracted by about 5.1% as ± first-order diffracted light.

  On the other hand, about 78.0% of the light incident on the regions 12m and 12o is transmitted as 0th order light, about 4.5% is diffracted as −1st order diffracted light, and only about 0.6% as + 1st order diffracted light. Not diffracted.

  Further, about 78.0% of the light incident on the regions 12n and 12p is transmitted as 0th order light, about 4.5% is diffracted as + 1st order diffracted light, and only about 0.6% as -1st order diffracted light. Not diffracted.

  Assuming that the 0th order light from the diffractive optical element 3f is the main beam, the + 1st order diffracted light is the subbeam 1, and the −1st order diffracted light is the subbeam 2, the main beam includes the transmitted light from the regions 12i, 12j, 12k, and 12l, the region 12m, Transmitted light from 12n, 12o, 12p is included at a ratio of about 1.1: 1.

  On the other hand, only the diffracted light from the regions 12i and 12k is mainly included in the upper half of the sub beam 1, and the diffracted light from the regions 12j and 12l and the diffracted light from the regions 12n and 12p are approximately contained in the lower half of the sub beam 1. 1.1: 1 ratio is included.

  The upper half of the sub beam 2 includes the diffracted light from the regions 12i and 12k and the diffracted light from the regions 12m and 12o at a ratio of about 1.1: 1. The lower half of the sub beam 2 mainly includes the region 12j. , Only the diffracted light from 12l is included.

  As a result, the main beam, the sub beam 1 and the sub beam 2 have different intensity distributions when entering the objective lens 6. In the upper half, the sub beam 1 has a lower intensity at the periphery than the main beam, and the lower half has substantially the same intensity distribution as the main beam. Further, the intensity distribution of the sub beam 2 is substantially the same as that of the main beam in the upper half, and the intensity of the peripheral portion is lower in the lower half than that of the main beam. The phase of the + 1st order diffracted light from the regions 12i, 12j and 12n and the phase of the + 1st order diffracted light from the regions 12k, 12l and 12p are shifted from each other by π, and similarly the phase of the −1st order diffracted light from the regions 12i, 12j and 12m. The phases of the −1st order diffracted lights from the regions 12k, 12l, and 12o are shifted from each other by π.

  FIG. 13 shows the arrangement of the focused spots on the disk 7.

  The condensed spots 17a, 17h, and 17i correspond to the 0th-order light, the + 1st-order diffracted light, and the -1st-order diffracted light from the diffractive optical element 3f, respectively. The three focused spots 17a, 17h, and 17i are arranged on the same track 16 (land or groove). The sub beams are symmetrical with respect to the optical axis and are out of phase with each other by π between the two straight lines parallel to the tangential direction of the disk 7, so that the condensed spots 17 h and 17 i that are sub beams are in the radial direction of the disk 7. Have two peaks of equal intensity on the left and right sides.

  The pattern of the light receiving portion of the photodetector 10a and the arrangement of the light spots on the photodetector 10a in the present embodiment are substantially the same as those shown in FIG. In the present embodiment, a focus error signal, a track error signal, and an RF signal are obtained by a method similar to the method described in the first embodiment.

  By shifting the phase of the grating in the regions 12i, 12j, 12m and 12n of the diffractive optical element 3f and the phase of the grating in the regions 12k, 12l, 12o and 12p by π, the sub-beam phase is symmetrical with respect to the optical axis and the disk 7 Shifting the outer and inner sides of two straight lines parallel to the tangential direction by π means that the sub-beam focusing spot on the disk 7 is ½ period of the groove of the disk 7 with respect to the focusing spot of the main beam. Displacement in the radial direction of the disk 7 is equivalent to the error signal. The reason is described in Patent Document 3, for example.

  Therefore, in the present embodiment, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  Further, in the present embodiment, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by the same method as that described in the first embodiment.

  Furthermore, in the present embodiment, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness deviation are high. The quality of the signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.

  Furthermore, in the present embodiment, three focused spots are arranged on the same track of the disk 7. For this reason, the arrangement of the three converging spots is not changed even for discs having different track pitches, and the above-described effect can be obtained for a disc having an arbitrary track pitch.

  As an embodiment of the optical head device of the present invention, the diffractive optical element 3b in the second embodiment, the diffractive optical element 3c in the third embodiment, and the diffractive optical element 3d in the fourth embodiment, Similar to the diffractive optical element 3e in the fifth embodiment, a straight line passing through the optical axis of the incident light and parallel to the tangential direction of the disk 7 is further divided into a left region and a right region, and the grating in the left region is divided. A configuration is also possible in which the phase and the phase of the grating in the right region are replaced with a diffractive optical element shifted by π from each other.

  In these embodiments, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  In these embodiments, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by a method similar to the method described in the first embodiment.

  Further, in these embodiments, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness are increased. The quality of the deviation signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.

  Furthermore, in these embodiments, three focused spots are arranged on the same track of the disk 7. For this reason, the arrangement of the three converging spots is not changed even for discs having different track pitches, and the above-described effect can be obtained for a disc having an arbitrary track pitch.

  As an embodiment of the optical head device of the present invention, the diffractive optical element 3b in the second embodiment, the diffractive optical element 3c in the third embodiment, and the diffractive optical element 3d in the fourth embodiment, Similarly to the diffractive optical element 3f in the sixth embodiment, the outer region is further divided into an outer region and an inner region by two straight lines that are symmetric with respect to the optical axis of the incident light and parallel to the tangential direction of the disk 7. A configuration is also possible in which the phase of the grating in and the phase of the grating in the inner region are replaced with diffractive optical elements that are shifted from each other by π.

  In these embodiments, no offset occurs in the focus error signal and the track error signal for the same reason as described in the first embodiment.

  In these embodiments, the substrate thickness deviation and the radial tilt of the disk 7 can be detected by a method similar to the method described in the first embodiment.

  Further, in these embodiments, the sensitivity of the substrate thickness deviation signal and the radial tilt signal is high for the same reason as described in the first embodiment, and the focus error signal, the track error signal, and the substrate thickness are increased. The quality of the deviation signal and the radial tilt signal is good, and the configuration of the arithmetic circuit for obtaining each signal is simple.

  Furthermore, in these embodiments, three focused spots are arranged on the same track of the disk 7. For this reason, the arrangement of the three converging spots is not changed even for discs having different track pitches, and the above-described effect can be obtained for a disc having an arbitrary track pitch.

  In the first to sixth embodiments, the focus error signals of the upper half of the sub beam 1 and the lower half of the sub beam 2 when the focus servo is applied using the focus error signal of the main beam are used as the substrate thickness deviation signal. Used. On the other hand, when the focus servo is applied using the focus error signal by the differential astigmatism method which is the sum of the focus error signal of the main beam and the focus error signals of the lower half of the sub beam 1 and the upper half of the sub beam 2. A form in which the focus error signals of the upper half of the sub beam 1 and the lower half of the sub beam 2 are used as the substrate thickness deviation signal is also conceivable.

  In this embodiment, the substrate thickness deviation can be detected without causing an offset due to the groove crossing noise in the focus error signal.

  Incidentally, an offset due to groove crossing noise also occurs in the substrate thickness deviation signal. At this time, if the difference between the focus error signal of the main beam and the focus error signal of the lower half of the sub beam 1 and the upper half of the sub beam 2 is called a focus offset signal, the component representing the focus error in the focus offset signal is canceled and the groove crossing is performed. Only the offset component due to noise remains.

  Therefore, if a signal obtained by subtracting the focus offset signal from the focus error signal of the upper half of the sub beam 1 and the lower half of the sub beam 2 is used as the substrate thickness deviation signal, the substrate thickness does not occur in the substrate thickness deviation signal without causing an offset due to cross-groove noise. Deviation can be detected.

  In the first to sixth embodiments, the track error signals of the upper half of the sub beam 1 and the lower half of the sub beam 2 when the track servo is applied using the track error signal of the main beam are used as the radial tilt signals. ing. On the other hand, when the track servo is applied using the track error signal by the differential push-pull method which is the difference between the track error signal of the main beam and the track error signal of the lower half of the sub beam 1 and the upper half of the sub beam 2. A configuration in which the track error signals of the upper half of the sub beam 1 and the lower half of the sub beam 2 are used as the radial tilt signal is also conceivable.

  In this embodiment, the radial tilt can be detected without causing an offset due to lens shift in the track error signal. Incidentally, an offset due to lens shift also occurs in the radial tilt signal. At this time, if the sum of the track error signal of the main beam and the track error signal of the lower half of the sub beam 1 and the upper half of the sub beam 2 is called a track offset signal, the component representing the track error in the track offset signal is canceled and the lens shift is performed. Only the offset component due to remains.

Therefore, if a signal obtained by subtracting the track offset signal from the track error signal of the upper half of the sub beam 1 and the lower half of the sub beam 2 is used as the radial tilt signal, the radial tilt is detected without causing an offset due to lens shift in the radial tilt signal. be able to.
(Seventh embodiment)
FIG. 14 shows a seventh embodiment of the present invention.

  The present embodiment is an optical information recording / reproducing apparatus in which an arithmetic circuit 21a, a drive circuit 22a, and relay lenses 23a and 23b are added to the optical head device in the first embodiment of the present invention. The arithmetic circuit 21a corresponds to the detection unit of the present invention, and the drive circuit 22a and the relay lenses 23a and 23b correspond to the correction unit of the present invention.

The arithmetic circuit 21a calculates a substrate thickness deviation signal based on the output from each light receiving unit of the photodetector 10a. The drive circuit 22a moves one of the relay lenses 23a and 23b surrounded by a dotted line in the drawing in the optical axis direction by an actuator (not shown) so that the substrate thickness deviation signal becomes zero. When either one of the relay lenses 23a and 23b is moved in the optical axis direction, the magnification of the objective lens 6 changes and the spherical aberration changes. Accordingly, the objective lens 6 generates spherical aberration that cancels out the spherical aberration caused by the substrate thickness deviation of the disk 7 by adjusting the position of one of the relay lenses 23a and 23b in the optical axis direction. Thereby, the substrate thickness deviation of the disk 7 is corrected, and the adverse effect on the recording / reproducing characteristics is eliminated.
(Eighth embodiment)
FIG. 15 shows an eighth embodiment of the present invention.

  The present embodiment is an optical information recording / reproducing apparatus in which an arithmetic circuit 21a and a drive circuit 22b are added to the optical head apparatus according to the first embodiment of the present invention. The arithmetic circuit 21a corresponds to the detection means of the present invention, and the drive circuit 22b corresponds to the correction means of the present invention.

The arithmetic circuit 21a calculates a substrate thickness deviation signal based on the output from each light receiving unit of the photodetector 10a. The drive circuit 22b moves the collimator lens 2 surrounded by a dotted line in the drawing in the optical axis direction by an actuator (not shown) so that the substrate thickness deviation signal becomes zero. When the collimator lens 2 is moved in the optical axis direction, the magnification of the objective lens 6 changes and the spherical aberration changes. Therefore, the objective lens 6 generates spherical aberration that adjusts the position of the collimator lens 2 in the optical axis direction to cancel the spherical aberration caused by the substrate thickness deviation of the disk 7. Thereby, the substrate thickness deviation of the disk 7 is corrected, and the adverse effect on the recording / reproducing characteristics is eliminated.
(Ninth embodiment)
FIG. 16 shows a ninth embodiment of the present invention.

  The present embodiment is an optical information recording / reproducing apparatus in which an arithmetic circuit 21b and a drive circuit 22c are added to the optical head apparatus in the first embodiment of the present invention. The arithmetic circuit 21b corresponds to the detection means of the present invention, and the drive circuit 22c corresponds to the correction means of the present invention.

The arithmetic circuit 21b calculates a radial tilt signal based on the output from each light receiving unit of the photodetector 10a. The drive circuit 22c tilts the objective lens 6 surrounded by the dotted line in the figure in the radial direction of the disk 7 by an actuator (not shown) so that the radial tilt signal becomes zero. As a result, the radial tilt of the disk 7 is corrected and the adverse effect on the recording / reproducing characteristics is eliminated.
(Tenth embodiment)
FIG. 17 shows a tenth embodiment of the present invention.

  The present embodiment is an optical information recording / reproducing apparatus in which an arithmetic circuit 21b and a drive circuit 22d are added to the optical head apparatus in the first embodiment of the present invention. The arithmetic circuit 21b corresponds to the detection means of the present invention, and the drive circuit 22d corresponds to the correction means of the present invention.

  The arithmetic circuit 21b calculates a radial tilt signal based on the output from each light receiving unit of the photodetector 10a. The drive circuit 22d tilts the entire optical head device surrounded by the dotted line in the figure in the radial direction of the disk 7 by a motor (not shown) so that the radial tilt signal becomes zero. As a result, the radial tilt of the disk 7 is corrected and the adverse effect on the recording / reproducing characteristics is eliminated.

As an embodiment of the optical information recording / reproducing apparatus of the present invention, a combination of the seventh or eighth embodiment and the ninth or tenth embodiment is also conceivable. In these embodiments, both the substrate thickness deviation and the radial tilt of the disk 7 can be corrected.
(Eleventh embodiment)
FIG. 18 shows an eleventh embodiment of the present invention.

  The present embodiment is an optical information recording / reproducing apparatus in which an arithmetic circuit 21c, a drive circuit 22e, and a liquid crystal optical element 24 are added to the optical head device according to the first embodiment of the present invention. The arithmetic circuit 21c corresponds to the detection means of the present invention, and the drive circuit 22e and the liquid crystal optical element 24 correspond to the correction means of the present invention.

  The arithmetic circuit 21c calculates a substrate thickness deviation signal and a radial tilt signal based on outputs from the respective light receiving portions of the photodetector 10a. The drive circuit 22e applies a voltage to the liquid crystal optical element 24 surrounded by a dotted line in the drawing so that the substrate thickness deviation signal and the radial tilt signal become zero. The liquid crystal optical element 24 is divided into a plurality of regions. When the voltage applied to each region is changed, the spherical aberration and the coma aberration with respect to the transmitted light change. Therefore, the liquid crystal optical element 24 adjusts the voltage applied to the liquid crystal optical element 24 to cause the spherical aberration to cancel the spherical aberration due to the substrate thickness deviation of the disk 7 and the coma aberration to cancel the coma aberration due to the radial tilt. generate. Thereby, the substrate thickness deviation and the radial tilt of the disk 7 are corrected, and the adverse effect on the recording / reproducing characteristics is eliminated.

  In the ninth to eleventh embodiments, the sign of the radial tilt signal is reversed when the track servo is applied to the land and the track servo is applied to the groove. Therefore, in the land and the groove, the polarity of the circuit constituted by the arithmetic circuits 21b and 21c and the drive circuits 22c, 22d, and 22e for correcting the radial tilt is switched.

  As an embodiment of the optical information recording / reproducing apparatus of the present invention, a configuration in which an arithmetic circuit, a drive circuit, etc. are added to the optical head device in the second to sixth embodiments of the present invention is also conceivable.

It is a top view of the diffractive optical element of the optical head apparatus in 1st embodiment of this invention. It is sectional drawing of the diffractive optical element of the optical head apparatus in 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the condensing spot on the disk of the optical head apparatus in 1st embodiment of this invention. It is a figure which shows arrangement | positioning of the pattern of the light-receiving part of the photodetector of the optical head apparatus in 1st embodiment of this invention, and the light spot on a photodetector. It is a top view of the diffractive optical element of the optical head apparatus in 2nd embodiment of this invention. It is a figure which shows arrangement | positioning of the condensing spot on the disk of the optical head apparatus in 2nd embodiment of this invention. It is a figure which shows arrangement | positioning of the pattern of the light-receiving part of the photodetector of the optical head apparatus in 2nd embodiment of this invention, and the light spot on a photodetector. It is a top view of the diffractive optical element of the optical head apparatus in 3rd embodiment of this invention. It is a top view of the diffractive optical element of the optical head apparatus in the 4th embodiment of this invention. It is a top view of the diffractive optical element of the optical head apparatus in the 5th embodiment of this invention. It is a figure which shows arrangement | positioning of the condensing spot on the disk of the optical head apparatus in the 5th Embodiment of this invention. It is a top view of the diffractive optical element of the optical head apparatus in the 6th Embodiment of this invention. It is a figure which shows arrangement | positioning of the condensing spot on the disk of the optical head apparatus in the 6th Embodiment of this invention. It is a figure which shows the optical information recording / reproducing apparatus in the 7th Embodiment of this invention. It is a figure which shows the optical information recording / reproducing apparatus in the 8th Embodiment of this invention. It is a figure which shows the optical information recording / reproducing apparatus in the 9th Embodiment of this invention. It is a figure which shows the optical information recording / reproducing apparatus in the 10th Embodiment of this invention. It is a figure which shows the optical information recording / reproducing apparatus in the 11th Embodiment of this invention. It is a figure which shows the structure of the conventional 1st optical head apparatus. It is a top view of the diffractive optical element in the conventional 1st optical head apparatus. It is a figure which shows arrangement | positioning of the condensing spot on the disk in the conventional 1st optical head apparatus. It is a figure which shows arrangement | positioning of the pattern of the light-receiving part of the photodetector in the conventional 1st optical head apparatus, and the light spot on a photodetector. It is a figure which shows various focus error signals. It is a figure which shows various track error signals. It is a figure which shows the various focus error signals in connection with the detection of a substrate thickness shift. It is a figure which shows the various track error signals in connection with the detection of radial tilt. It is a top view of the diffractive optical element in the conventional 2nd optical head apparatus. It is a figure which shows arrangement | positioning of the condensing spot on the disk in the conventional 2nd optical head apparatus. It is a figure which shows arrangement | positioning of the pattern of the light-receiving part of the photodetector in the conventional 2nd optical head apparatus, and the light spot on a photodetector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3a-3h Diffractive optical element 4 Polarizing beam splitter 5 1/4 wavelength plate 6 Objective lens 7 Disc 8 Cylindrical lens 9 Lens 10a, 10b Photodetectors 11a-11p area 12a-12p area 13a-13f area 14 Substrate 15a to 15d Grating 16 Tracks 17a to 17o Condensing spots 18a to 18k Light spots 19a to 19l Light receiving units 20a to 20t Light receiving units 21a to 21c Arithmetic circuits 22a to 22e Driving circuits 23a to 23b 25e Focus error signals 26a to 26e Track error signals 27a to 27e Focus error signals 28a to 28e Track error signals

Claims (33)

A light source;
An objective lens for condensing the light emitted from the light source on a disk-shaped optical recording medium having a groove forming a track;
In an optical head device having a photodetector for receiving reflected light from the optical recording medium,
Beam generating means for generating a main beam, a first sub beam, and a second sub beam as light condensed on the optical recording medium by the objective lens from the light emitted from the light source, The sub-beam is composed of first and second parts bounded by a plane including the optical axis, and the second sub-beam is composed of third and fourth parts bounded by the plane including the optical axis. The first portion of the first sub-beam and the fourth portion of the second sub-beam are intensities on the optical axis in a section perpendicular to the corresponding portion of the main beam and the optical axis. While the normalized intensity distribution is different, the second portion of the first sub-beam and the third portion of the second sub-beam are within a cross section perpendicular to the corresponding portion of the main beam and the optical axis. Further comprising a configured beam generating means as normalized intensity distribution is approximately the same in intensity on definitive optical axis,
The photodetector includes the main beam reflected by the optical recording medium and the first and second portions of the first sub-beam reflected by the optical recording medium as reflected light from the optical recording medium. The third and fourth portions of the second sub beam reflected by the optical recording medium are individually received in order to detect a focus error signal and / or a track error signal from each of them. Optical head device.   The beam generation unit includes a diffractive optical element that divides light emitted from the light source into the main beam, the first sub beam, and the second sub beam between the light source and the objective lens. The optical head device according to claim 1.   In the diffractive optical element, a diffraction grating divided into first and second regions by a straight line passing through the optical axis of incident light and parallel to the radial direction of the optical recording medium is formed on one of predetermined boundaries. And a diffraction grating divided into third and fourth regions by a straight line passing through the optical axis of incident light and parallel to the radial direction of the optical recording medium. 2. The optical head device according to 2. The first, second, third, and fourth regions are straight lines that pass through the optical axis of incident light and are parallel to the tangential direction of the optical recording medium. Divided into regions and first, second, third and fourth right regions,
The phase of the grating in the first, second, third, and fourth left regions and the phase of the grating in the first, second, third, and fourth right regions are shifted from each other by approximately π. The optical head device according to claim 3. The first, second, third, and fourth regions are two straight lines that are symmetrical with respect to the optical axis of incident light and parallel to the tangential direction of the optical recording medium. Are divided into an outer area and a first, second, third and fourth inner area,
The phase of the grating in the first, second, third, and fourth outer regions and the phase of the grating in the first, second, third, and fourth inner regions are shifted from each other by approximately π. The optical head device according to claim 3.   The focused spot of the first sub beam and the second sub beam formed on the optical recording medium by the objective lens is the focused spot of the main beam formed on the optical recording medium by the objective lens. 4. The optical head device according to claim 3, wherein the optical head device is arranged so as to be shifted in the radial direction of the optical recording medium by approximately ½ period of the groove of the optical recording medium.   The focused spot of the first sub beam and the second sub beam formed on the optical recording medium by the objective lens is the focused spot of the main beam formed on the optical recording medium by the objective lens. The optical head device according to claim 4, wherein the optical head device is disposed on the same track of the optical recording medium. Zero-order light from the first, second, third and fourth regions is the main beam,
+ 1st order diffracted light from the first region is the first portion of the first sub-beam,
+ 1st order diffracted light from the second and fourth regions is the second portion of the first sub-beam,
−1st order diffracted light from the first and third regions is the third portion of the second sub-beam,
8. The optical head device according to claim 3, wherein −1st-order diffracted light from the second region is used as the fourth portion of the second sub-beam. 9. The cross-sectional shape of the grating in the first and second regions is a rectangular shape such that the + 1st order diffraction efficiency and the -1st order diffraction efficiency are substantially equal,
The cross-sectional shape of the grating in the third region is stepped such that the −1st order diffraction efficiency is higher than the + 1st order diffraction efficiency,
9. The light according to claim 3, wherein the cross-sectional shape of the grating in the fourth region is a step shape such that the + 1st order diffraction efficiency is higher than the −1st order diffraction efficiency. Head device. One of the predetermined boundaries is inside a circle having a diameter smaller than the effective diameter of the objective lens;
10. The optical head device according to claim 3, wherein the other of the predetermined boundaries is outside a circle having a diameter smaller than the effective diameter of the objective lens. One of the predetermined boundaries is outside a circle having a diameter smaller than the effective diameter of the objective lens;
10. The optical head device according to claim 3, wherein the other of the predetermined boundaries is an inside of a circle having a diameter smaller than an effective diameter of the objective lens. One of the predetermined boundaries is the inside of a band having a width smaller than the effective diameter of the objective lens;
10. The optical head device according to claim 3, wherein the other of the predetermined boundaries is outside a band having a width smaller than an effective diameter of the objective lens. One of the predetermined boundaries is outside a band having a width smaller than the effective diameter of the objective lens;
10. The optical head device according to claim 3, wherein the other of the predetermined boundaries is an inner side of a band having a width smaller than the effective diameter of the objective lens. An optical head device according to any one of claims 1 to 13,
The main beam reflected by the optical recording medium individually received by the photodetector, the first and second portions of the first sub-beam reflected by the optical recording medium, and the optical recording medium And detecting the focus error signal and / or the track error signal from each of the third and fourth portions of the second sub-beam reflected at, and based on the focus error signal and / or the track error signal An optical information recording / reproducing apparatus comprising detection means for detecting a focus error signal used for focus servo and / or a track error signal used for track servo.   The detection means is a sum of a focus error signal detected from the main beam and a focus error signal detected from the second portion of the first sub-beam and the third portion of the second sub-beam. 15. The optical information recording / reproducing apparatus according to claim 14, wherein a focus error signal used for focus servo is used.   The detection means includes a difference between a track error signal detected from the main beam and a track error signal detected from the second portion of the first sub-beam and the third portion of the second sub-beam. 15. The optical information recording / reproducing apparatus according to claim 14, wherein a track error signal used for track servo is used.   The detection means includes a zero cross point of a focus error signal detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam with respect to a focus error signal detected from the main beam. The optical information recording / reproducing apparatus according to claim 14, further detecting a substrate thickness deviation of the optical recording medium based on a deviation of the optical recording medium.   The detection means includes a zero cross point of a track error signal detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam with respect to the track error signal detected from the main beam. The optical information recording / reproducing apparatus according to claim 14, further detecting a radial tilt of the optical recording medium based on a deviation of the optical recording medium.   The detection means is configured to detect from the first portion of the first sub beam and the fourth portion of the second sub beam when focus servo is applied using a focus error signal detected from the main beam. 18. The optical information recording / reproducing apparatus according to claim 17, wherein a substrate thickness deviation of the optical recording medium is detected based on the detected focus error signal.   The detection means is a sum of a focus error signal detected from the main beam and a focus error signal detected from the second portion of the first sub-beam and the third portion of the second sub-beam. A substrate of the optical recording medium based on focus error signals detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam when focus servo is applied using The optical information recording / reproducing apparatus according to claim 17, wherein thickness deviation is detected.   The detection means uses a focus error signal detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam as a substrate thickness deviation signal of the optical recording medium. 21. The optical information recording / reproducing apparatus according to claim 19 or 20.   The detection means includes a focus error signal detected from the main beam from a focus error signal detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam; Substrate thickness deviation of the optical recording medium is obtained by subtracting a focus offset signal, which is the difference between the focus error signal detected from the second portion of the first sub-beam and the third portion of the second sub-beam. 21. The optical information recording / reproducing apparatus according to claim 19, wherein the optical information recording / reproducing apparatus is a signal.   The detection means includes the first portion of the first sub-beam and the fourth portion of the second sub-beam when track servo is applied using the track error signal detected from the main beam. 19. The optical information recording / reproducing apparatus according to claim 18, wherein a radial tilt of the optical recording medium is detected based on the detected track error signal.   The detection means includes a difference between a track error signal detected from the main beam and a track error signal detected from the second portion of the first sub-beam and the third portion of the second sub-beam. Of the optical recording medium based on track error signals detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam when track servo is applied using 19. The optical information recording / reproducing apparatus according to claim 18, wherein a tilt is detected.   The detection means uses a track error signal detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam as a radial tilt signal of the optical recording medium. The optical information recording / reproducing apparatus according to claim 23 or 24.   The detection means includes a track error signal detected from the main beam from a track error signal detected from the first portion of the first sub-beam and the fourth portion of the second sub-beam; A signal obtained by subtracting a track offset signal that is the sum of the track error signal detected from the second portion of the first sub-beam and the third portion of the second sub-beam is a radial tilt signal of the optical recording medium. 25. The optical information recording / reproducing apparatus according to claim 23 or 24.   27. The optical information recording / reproducing apparatus according to claim 14, further comprising a correcting unit that corrects a substrate thickness shift and / or a radial tilt of the optical recording medium.   The correction means has two relay lenses between the light source and the objective lens, and corrects the substrate thickness deviation of the optical recording medium by moving one of the two relay lenses in the optical axis direction. 28. The optical information recording / reproducing apparatus according to claim 27.   The correction means includes a collimator lens between the light source and the objective lens, and corrects a substrate thickness deviation of the optical recording medium by moving the collimator lens in an optical axis direction. 27. An optical information recording / reproducing apparatus according to 27.   28. The optical information recording / reproducing apparatus according to claim 27, wherein the correcting unit corrects a radial tilt of the optical recording medium by tilting the objective lens in a radial direction of the optical recording medium.   28. The optical information recording / reproducing apparatus according to claim 27, wherein the correcting unit corrects a radial tilt of the optical recording medium by tilting the entire optical head device in a radial direction of the optical recording medium.   The correction means includes a liquid crystal optical element between the light source and the objective lens, and corrects a substrate thickness shift and / or a radial tilt of the optical recording medium by applying a voltage to the liquid crystal optical element. 28. The optical information recording / reproducing apparatus according to claim 27.   31. The correction means switches a polarity of a circuit for correcting a radial tilt of the optical recording medium between a land which is a concave portion of the groove of the optical recording medium and a groove which is a convex portion of the groove. 33. The optical information recording / reproducing apparatus according to any one of items 1 to 32.

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