JP2005122878A - Information apparatus and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform wavefront correction in which an effect of lens shift is reduced with high accuracy without necessitating a special exclusive member for aligning the optical axis of a light beam with that of an objective lens. <P>SOLUTION: An information apparatus for reading and/or writing data from/on an optical disk 7 with a light beam is provided. The information apparatus includes: a light source 1 for generating the light beam; an objective lens 6 for focusing the beam onto the optical disk 7; a wavefront sensor for detecting the wavefront of the beam; a lens shift sensor for sensing how much the optical axis of the objective lens has shifted from that of the beam; a wavefront corrector (variable mirror 5), in which correcting elements 5b are arranged as a two-dimensional array so as to locally correct the wavefront of the beam and to be driven independently of each other; a wavefront arithmetic means for making correspondence of each coordinate on a cross section of the beam to the wavefront phase of the beam according to the output of the wavefront sensor; a lens shift correction arithmetic means for changing the correspondence of the coordinate position to the wavefront phase according to the output of the lens shift sensor; and a controller for controlling the wavefront corrector (variable mirror 5) in accordance with the output of the lens shift correction arithmetic means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an information apparatus for optically recording or detecting information (data) on a medium, and more particularly to an information apparatus and an optical pickup provided with wavefront correction means for controlling the wavefront of a light beam.

  In an optical recording / reproducing apparatus such as an optical disk apparatus, a liquid crystal is provided in the optical path in order to compensate for aberrations caused by changes in the inclination of the optical disk, which is a recording medium, and the substrate thickness (information surface depth). Wavefront correction means such as elements and deformable mirrors are arranged. At this time, it is important to prevent a decrease in aberration correction performance due to an optical axis shift (hereinafter referred to as “lens shift”) between the light beam and the objective lens.

  In general, the objective lens of an optical disc apparatus is mounted in an optical pickup, and is used to converge a laser beam emitted from a light source in the optical pickup on the information surface of the optical disc to form a beam spot.

  In the optical disc apparatus, tracking control is performed so that the beam spot of the laser beam accurately follows the target track of the optical disc. This tracking control is executed so that the objective lens in the optical pickup is driven by an actuator to minimize the positional deviation of the beam spot with respect to the target track on the optical disk.

  When the objective lens moves in the direction parallel to the information surface of the optical disk and perpendicular to the track by the tracking control described above, a lens shift occurs, so that wavefront correction for compensating for aberration cannot be properly achieved.

  One way to reduce the effects of lens shift is to construct the wavefront correction means integrally with the objective lens. By doing so, the center of the optical axis of the objective lens and the wavefront correction pattern always coincide with each other, so that a reduction in aberration correction performance is prevented. However, on the other hand, there arise problems such as a decrease in response characteristics accompanying an increase in the weight of the movable part, a complicated actuator structure for wiring to the wavefront correction element, and an obstacle to making the optical pickup thinner. As the wavefront correction means requires high-precision correction, and it becomes necessary to divide the wavefront correction pattern into multiple divisions and support a plurality of types of aberration modes, it becomes difficult to achieve both of these problems.

  For these reasons, various configurations have been proposed in which the wavefront correcting means is arranged not on the objective lens but on the base side of the optical pickup to reduce the influence of lens shift. As an example of this, there is a method in which a parallel plate is inserted between the wavefront correcting means and the objective lens, and this is inclined according to the lens shift (see, for example, Patent Document 1). In addition to this, Patent Document 1 discloses a configuration in which a light source and a photodetector are moved according to lens shift.

In addition to the first electrode group used when the wavefront correction means has no lens shift, the second electrode group corresponding to the outward lens shift and the third electrode group corresponding to the inward lens shift are provided. Some have a configuration in which these electrodes are selectively used for a lens shift of a predetermined amount or more (see, for example, Patent Document 2). Patent Document 2 discloses an example in which the second and third electrode groups are combined with the first electrode group of the liquid crystal element for correcting the tilt of the optical disk substrate. As another embodiment, an embodiment in which the second and third electrode groups are combined with the first electrode group of the liquid crystal element for correcting spherical aberration is also disclosed.
Japanese Patent Laid-Open No. 11-96577 JP 2001-167470 A

  However, the above prior art has the following problems.

  First, in the lens shift correction configuration described in Patent Document 1, there is a problem that the apparatus is increased in size and cost. In order to correct the lens shift, members such as a parallel plate and a drive unit for tilting it are added, and in order to correct the lens shift accurately, the operation of these mechanisms is sufficiently accurate for the movement of the objective lens. A control mechanism is required to make it follow well. Thus, the complexity of the apparatus accompanying the addition of the lens shift correction configuration is inevitable.

  Secondly, in the configuration using the second and third electrode groups as described in Patent Document 2, there are problems in the wavefront correction accuracy obtained and the flexibility of the types of wavefronts that can be corrected. Since the first electrode group cannot be arranged in the portion where the second and third electrode groups are arranged, the electrode group arrangement for improving the wavefront correction accuracy and the electrode group for reducing the influence of the lens shift The arrangement is in a trade-off relationship with each other. Therefore, there is a problem that it is difficult to cope with a wide range of lens shift while maintaining sufficient wavefront correction accuracy. In addition, electrode patterns that reduce the effect of lens shift are individually designed for tilt correction and spherical aberration correction, but depending on the device, tilt aberration and spherical aberration are combined. In some cases, it is necessary to deal with aberrations or a wider range of arbitrary aberrations. There is also a problem in flexibility for accurately reducing the influence of lens shift with respect to such an arbitrary aberration.

  Thirdly, in the configuration described in Patent Document 2, there is a problem in that fine wavefront correction cannot be performed for a minute lens shift. In Patent Document 2, correction is not performed for a lens shift of 200 μm or less, and correction is performed only in one step for a lens shift of 200 μm or more. As described above, the correction is selected only in two steps, that is, whether correction is performed or not, and it is difficult to meticulously cope with a minute lens shift.

  The present invention has been made in view of the above circumstances, and an object thereof is to reduce the influence of lens shift with high accuracy without requiring a special member for optical axis alignment with a special objective lens. It is an object of the present invention to provide an information apparatus and an optical pickup that perform wavefront correction.

  An information device according to the present invention is an information device that writes data to a medium with a light beam and / or reads data from the medium, the light source generating the light beam, and the light beam into the medium An objective lens for focusing the light beam, lens shift detection means for detecting the amount of positional deviation of the optical axis of the objective lens with respect to the optical axis of the light beam, and a correction element for locally correcting the wavefront of the light beam. Wavefront correction means arranged in a three-dimensional array, and each correction element is driven independently of each other; wavefront calculation means for associating each coordinate position in the cross section of the light beam with the wavefront phase of the light beam; Lens shift correction calculation means for changing the correspondence between the coordinate position and the wavefront phase based on the output of the lens shift detection means, and the output of the lens shift correction calculation means And a control means for controlling the wavefront correction means based.

  In a preferred embodiment, the apparatus further comprises a wavefront sensor that detects a wavefront of the light beam, and the wavefront calculation means includes each coordinate position in the cross section of the light beam and the wavefront phase of the light beam based on the output of the wavefront sensor. Is associated.

  In a preferred embodiment, the optical system further comprises means for detecting an inclination of the medium with respect to the light beam, and the wavefront calculating means has each coordinate position in the cross section of the light beam and the light according to the inclination of the medium with respect to the light beam. Correlation with the wavefront phase of the beam is performed.

  In a preferred embodiment, it further comprises means for detecting spherical aberration in the medium, and the wavefront computing means associates each coordinate position in the cross section of the light beam with the wavefront phase of the light beam according to the spherical aberration. I do.

  In a preferred embodiment, the lens shift correction calculating means shifts the coordinate position of the light beam in the direction of the positional deviation of the optical axis of the objective lens with respect to the optical axis of the light beam, thereby moving the coordinate position and the wavefront. Change the correspondence with the phase.

  In a preferred embodiment, when the adjacent pitch interval of the correction element regarding the direction of the positional deviation of the optical axis of the objective lens with respect to the optical axis of the light beam is p, the lens shift correction calculation means is smaller than the p. The coordinate position of the light beam is shifted with respect to the shift amount of the optical axis.

  In a preferred embodiment, the wavefront calculating means calculates a total aberration by combining a first aberration mode associated with a change in substrate thickness of the medium and a second aberration mode associated with the tilt of the medium. .

  In a preferred embodiment, the first aberration mode includes a sixth-order term or more with respect to a distance r from the optical axis center in a single mode.

  In a preferred embodiment, the second aberration mode includes a fifth-order term or more with respect to a distance r from the optical axis center in a single mode.

  In a preferred embodiment, each correction element of the wavefront correction unit includes a minute reflection mirror that reflects the light beam, and the wavefront correction unit functions as a deformable mirror.

  In a preferred embodiment, the wavefront correction means includes a liquid crystal element, and each correction element of the wavefront correction means has a liquid crystal region that optically modulates the light beam.

  An optical pickup according to the present invention includes a base, a light source provided on the base, and an objective that is movably supported on the base, collects a light beam emitted from the light source, and irradiates the medium. A lens, an objective lens actuator capable of moving the objective lens in a direction perpendicular to the optical axis of the light beam, and a base of the optical pickup for locally correcting the wavefront of the light beam; Wavefront correction means for arranging correction elements to be arranged in a two-dimensional array and independently controlling these correction elements to form a spatial wavefront correction pattern. The wavefront correction pattern formed by the wavefront correction means is And shifting in the direction of deviation of the optical axis of the objective lens with respect to the optical axis of the light beam.

  According to the present invention, the wavefront computing means associates the coordinate position of the light beam with the wavefront phase, and the lens shift correction computing means changes the association between the coordinate position and the wavefront phase according to the lens shift amount. Since the wavefront correction control unit controls the wavefront correction unit based on this output, a dedicated member for lens shift correction is not required, and a wavefront correction operation with high correction accuracy can be performed.

(Embodiment 1)
Hereinafter, a first embodiment of an information device according to the present invention will be described with reference to FIGS. The information device in this embodiment is an optical disk device.

  First, refer to FIG. FIG. 1 is a schematic configuration diagram of an optical disc apparatus according to the present embodiment. This optical disk device is an information device that writes data to a medium (optical disk) with a light beam and / or reads data from the optical disk.

  A light beam emitted from a light source 1 such as a GaN laser is converted into an infinite system light beam by a collimator lens 2 and enters a polarization beam splitter 3. Of this light beam, only the P-polarized light component is transmitted through the polarizing beam splitter 3, and the remaining S-polarized light component is reflected and enters a front light monitor (not shown). The transmitted P-polarized light component is converted into circularly polarized light by the quarter-wave plate 4.

  The deformable mirror 5 in the present embodiment is a mirror in which a large number of displaceable micro mirrors 5b are provided on a substrate 5a. Such a deformable mirror 5 is, for example, an international publication WO 03/061488 pamphlet (international application date: January 29, 2002) or an international publication WO 03/0665103 pamphlet (international application date: November 2002). 26th). The application relating to the pamphlet of the international publication WO 03/061488 entered the US national phase on July 29, 2003 (application number 10 / 470,685), and the application relating to the pamphlet of the international publication WO 03/0665103 was issued on July 7, 2004. On March 23, it has entered the US domestic phase.

  The micromirrors 5b are arranged in a two-dimensional array, and a reflection surface is formed by a large number of micromirrors 5b. Each micromirror 5b is driven by a drive unit 5c connected to the back surface thereof. The vertical displacement of the individual micromirrors 5b from the substrate 5a and / or the tilt with respect to the substrate 5a is independently controlled. An important function required for the deformable mirror 5 of the present embodiment is that each micromirror 5b is not only inclined with respect to the substrate 5a, but is also inclined or parallel to the substrate 5a from the substrate 5a. It is that it can be displaced as a whole. Since such a displacement is possible in addition to the inclination, the phase of the wavefront can be corrected with high accuracy.

  Since the wavefront of the light beam can be locally changed by the displacement of the micromirror 5b, each micromirror 5b and the drive unit 5c function as a correction element that is a minimum unit for performing wavefront correction. The incident angle and the outgoing angle of light with respect to the deformable mirror 5 can be set to 45 degrees, for example. Details of the structure of the deformable mirror 5 will be described later.

  The light beam whose phase is modulated by the deformable mirror 5 is condensed on the recording layer of the optical disk 7 by the objective lens 6. The objective lens 6 is configured to be movable in parallel in two directions, that is, an optical axis direction A of the light beam and a direction B perpendicular to the optical axis by the objective lens actuator 8. It is possible to follow the recording track. A direction B orthogonal to the optical axis is a radial direction of the optical disc 7 and is a direction orthogonal to the drawing.

  The optical disc 7 is an optical recording medium comprising a plurality of recording layers arranged at predetermined intervals and a light-transmissive base material portion that covers and protects the recording layers. The tracking method is a sample servo method, and staggered prepits are formed in the servo areas of each layer. The light beam reflected by the recording layer of the optical disc 7 passes through the deformable mirror 5 and the quarter wavelength plate 4 again. Since most of the light beam is an S-polarized component, the light beam is reflected by the polarization beam splitter 3, and the wavefront is detected by a wavefront sensor including the hologram 9, the lens 10, and the photodetector 11. This wavefront sensor is a modal type, which can be constructed using a known technique as disclosed in the following document, for example.

M. A. A. Neil, M. J. Booth, and T. Wilson, "New modal wave-front sensor: a theoretical analysis," J. Opt. Soc. Am. A / Vol. 17, no. 6, pp. 1098-1107 (2000)
The hologram 9 generates ± first-order light in different directions for n (n is an integer of 2 or more) orthogonal aberration modes Mi (i = 1 to n). These ± first-order lights corresponding to the respective modes Mi are given a bias aberration of + BiMi for the + 1st order light and −BiMi for the −1st order light, where Bi is a predetermined bias coefficient. The hologram 9 is a multistage binary hologram having a cross section close to a sine wave or a blazed hologram having a cross section of an isosceles triangle, and is provided so as to increase the diffraction efficiency by reducing the ratio of higher order light other than ± first order light. Further, the depth of the diffraction groove is set to an appropriate value, and the 0th-order light is provided so as to transmit at a predetermined rate.

  The lens 10 condenses the n pairs of light beams deflected by the hologram 9 on the photodetector 11. If the focal length of the lens 10 is f, the hologram 9 and the photodetector 11 are arranged at a distance f from the main plane of the lens 10, and the lens 10 functions as a Fourier transform lens.

  The photodetector 11 generates a differential output Si of the intensity signal of ± primary light for each n pair. The differential output Si corresponding to the aberration mode Mi is a signal corresponding to the magnitude Ai of the aberration mode Mi. The sensitivity Si / Ai for the aberration mode Mi is determined in advance by design parameters such as the bias coefficient Bi.

  As a basis function of orthogonal aberration modes, a basis function Zi by a Zernike polynomial may be used, but as a basis function that more directly represents an aberration due to a change in the substrate thickness of the optical disc 7 and a tilt, (Equation 1) to (Equation 3) M1 to M3 shown in FIG. As the aberration M4 due to defocusing of the objective lens 6, a basic function Z2 relating to defocusing of a normal Zernike polynomial is applied as shown in (Expression 4).

(Equation 1)
M1 = 1.78-8.75r ² + 4.50r ⁴ + 2.49r ⁶ + 1.27r ⁸ + 0.67r ¹⁰ + 0.37r ¹²
(Equation 2)
M2 = (4.47r−4.60r ³ −1.78r ⁵ −0.75r ⁷ −0.34r ⁹ ) cos θ
(Equation 3)
M3 = (4.47r−4.60r ³ −1.78r ⁵ −0.75r ⁷ −0.34r ⁹ ) sin θ
(Equation 4)
M4 = Z2 = √3 (2r ² −1)

  M1 is a spherical aberration mode associated with a change in the substrate thickness of the optical disc 7, M2 is an aberration mode associated with the tilt of the optical disc 7 in the radial direction, and M3 is an aberration mode associated with the tilt of the optical disc 7 in the tangential direction. They are orthogonal and the norm is approximately 1. Note that (r, θ) is a polar coordinate position on the surface of the hologram 9, and r is a radius normalized to 0 ≦ r ≦ 1.

  The basis function Z11 of the Zernike polynomial for the first-order spherical aberration is up to the fourth-order term of the radius r as shown in (Equation 5), and the basis functions Z7 and Z8 of the Zernike polynomial for the first-order coma aberration are (Equation 6), As shown in (Expression 7), it includes up to the third order term of the radius r. On the other hand, the aberration mode M1 includes a sixth or higher order term of the radius r in one mode, and the aberration modes M2 and M3 include a fifth or higher order term of the radius r.

(Equation 5)
Z11 = √5 (6r ⁴ -6r ² +1)
(Equation 6)
Z7 = 2√2 (3r ³ −2r) cos θ
(Equation 7)
Z8 = 2√2 (3r ³ -2r) sinθ

  It is obvious that the Zernike polynomial can be arbitrarily considered as a higher-order basis function, and the aberration mode Mi can be approximated by a combination Mi = ΣkjZj of the basis function Zj of the Zernike polynomial including up to a higher-order term. Such basis transformation has a practical effect. That is, when the main cause of the occurrence of aberration can be specified in advance, such as the change in the substrate thickness and the inclination of the optical disk 7, the number of aberration modes to be detected can be greatly reduced by utilizing the property, and higher order aberrations can be achieved. The mode can be corrected. As can be seen from (Equation 1) to (Equation 3), the aberration associated with the change in the substrate thickness and the inclination of the optical disk 7 has a relatively low convergence of the higher-order term with respect to the radius r. For this reason, when the basis function Zi of the Zernike polynomial is selected as the aberration mode, a considerable number of pairs of photodetectors are required from the low-order mode to the high-order mode, or only the low-order mode is targeted for correction. In this case, the residual error in the higher order mode becomes large. On the other hand, when the aberration modes M1 to M3 based on the change in the substrate thickness and the inclination of the optical disk 7 are selected, aberration detection up to higher order terms can be performed with one mode number each, and one detector. The amount of light per unit is large and the S / N ratio is good.

  The light detector 11 outputs signals S1 to S4 indicating the magnitudes of the aberration modes M1 to M4. In addition, a signal S5 modulated by the prepits and recording marks of the optical disc 7 is output from the focused spot of the zero-order light of the hologram 9. Details of the photodetector 11 will be described later. The coefficients of (Equation 1) to (Equation 3) are obtained under conditions such as the standard substrate thickness of the optical disc 7 of 85 μm, NA 0.85, the refractive index of the disc substrate 1.62, and the like. The numbers themselves depend on these conditions.

  The light source 1, the collimator lens 2, the polarization beam splitter 3, the quarter wavelength plate 4, the deformable mirror 5, the objective lens actuator 8, the hologram 9, the lens 10, and the photodetector 11 are fixed on an optical pickup base (not shown). The objective lens 6 is movably supported on the optical pickup base by a supporting structure such as a four-wire structure.

  The control circuit 12 includes a wavefront calculation unit 13, a lens shift correction calculation unit 14, an overall control unit 15, and a wavefront correction control unit 16.

  The wavefront calculator 13 uses the output signals S1 to S3 of the photodetector 11 to calculate a phase function ψ (x, y) for correcting the wavefront aberration associated with the change in the substrate thickness and the tilt of the optical disc 7. Here, x and y are coordinates corresponding to the mirror position of the deformable mirror 5. As this procedure, coefficients A1 to A3 of the basis functions M1 to M3 are first obtained from the signals S1 to S3, and the phase of polar coordinate display on the hologram 9 surface is obtained by (Equation 1) to (Equation 3) and (Equation 8). A function ψ (r, θ) is obtained.

(Equation 8)
ψ (r, θ) = ΣAiMi

  Next, the wavefront calculation unit 13 converts the phase function ψ (r, θ) given by the polar coordinates on the hologram 9 surface into an orthogonal coordinate display ψ (x, y) on the surface of the variable mirror 5. This result is output to the lens shift correction calculation unit 14.

  The lens shift correction calculation unit 14 receives the lens shift amount x0 of the objective lens 6 from the overall control unit 15, and based on this, the phase function ψ (x, y) input from the wavefront calculation unit 13 is ψ (x−x0, y). This ψ (x−x0, y) becomes a target wavefront when the wavefront correction control unit 16 controls the deformable mirror 5.

  The overall control unit 15 creates a focus control signal Fo and a tracking control signal Tr for the objective lens actuator 8 based on S4 and S5 input from the photodetector 11. Further, by passing the tracking control signal Tr through a low-pass filter, the lens shift amount x0 of the objective lens 6 is calculated. The method for obtaining the lens shift amount x0 is not limited to this. For example, the displacement of the objective lens 6 relative to the base of the optical pickup may be detected by a displacement sensor.

  The wavefront correction control unit 16 controls the displacement and inclination of each micromirror 5 b of the deformable mirror 5 based on the output ψ (x−x0, y) from the lens shift correction calculation unit 14. Although the operation of the wavefront correction control unit 16 will be described later, when the control converges, the entire reflecting surface shape of the deformable mirror 5 approximates the target wavefront with sufficient accuracy. Since this phase function ψ (x−x0, y) is a position shifted by x0 while maintaining its wavefront shape according to the lens shift amount x0 of the objective lens 6, it always follows the position of the objective lens 6. Thus, the wavefront correction pattern on the deformable mirror 5 moves.

  FIG. 9 schematically shows how the wavefront correction pattern shifts in accordance with the shift of the objective lens 6. A portion indicated by a broken line represents a state before the lens shift, and a portion indicated by a solid line represents a state after the lens shift. In FIG. 9, the right direction is the x direction. As can be seen from FIG. 9, when the objective lens 6 is displaced by x0 in the x direction, the displacement and inclination of each smiling mirror 5b change, and the reflection surface as a whole is shifted by x0 in the x direction. The diameter of the light beam that irradiates the deformable mirror 5 is about several millimeters, for example, but the size of the lens shift amount x0 is, for example, about 0 to 200 μm. The lens shift amount x0 is sufficiently small compared to the overall size of the wavefront correction pattern.

  Even when the lens shift amount x0 is smaller than the arrangement pitch of the micromirrors 5b, it is necessary to appropriately shift the wavefront correction pattern. As will be described in detail later with reference to FIG. 7, the deformable mirror 5 used in this embodiment can appropriately cope with a minute lens shift amount x0.

  Reference is now made to FIG. FIG. 2 is an exploded perspective view of the deformable mirror 5 of the present embodiment. In FIG. 2, one correction element is shown in an enlarged manner, but in reality, a large number of correction elements are arranged on the substrate 5a to form a two-dimensional array.

  An insulating layer 21 provided on the substrate 5a, a base 22 provided on the insulating layer 21, and three pairs of fixed electrodes 23 to 25 are provided on the fixed portion side of the drive unit 5c. The base 22 and the fixed electrodes 23 to 25 are formed by patterning a conductive film such as aluminum (Al) or polycrystalline silicon. The fixed electrodes 23 to 25 are each divided into two fixed electrode pieces 23a, 23b to 25a, and 25b. The fixed electrode pieces 23 a, 23 b to 25 a, 25 b are connected to a drive circuit formed on the substrate 5 a by vias (not shown) formed in the insulating layer 21. The drive circuit can apply independent voltages to the fixed electrode pieces 23a, 23b to 25a, 25b within a range of 0 to 5V. The voltages applied to the six fixed electrode pieces 23a, 23b to 25a, 25b can be set as multi-stage values of about 16 bits, for example. On the other hand, the base 22 is set to the ground potential.

  On the movable portion side of the drive unit 5c, three yokes 27 to 29 are attached by a pair of hinges 26, respectively, and an intermediate connecting member 30 for connecting these yokes 27 to 29 to the micromirror 5b is provided. ing. In the present embodiment, the hinge 26 is integrally joined to the base 22.

  The yokes 27 to 29 face the corresponding fixed electrodes 23 to 25, and each function as a movable electrode. The yokes 27 to 29 are formed by patterning a conductive member such as aluminum (Al) or polycrystalline silicon, and are connected to the base 22 and set to the ground potential. The yokes 27 to 29 have first portions 27a to 29a and second portions 27b to 29b at positions facing the fixed electrode pieces 23a, 23b to 25a, and 25b, respectively. The yokes 27 to 29 have the same shape as each other, and unless otherwise specified, the description of one yoke is applicable to other yokes.

  The yoke 28 is supported so as to be rotatable about a rotation axis A1, and the yokes 27 and 29 are supported so as to be rotatable about a rotation axis A2. Assuming that the direction orthogonal to the rotation axis A1 (or A2) is x and the pitch interval between the drive units adjacent in the x direction is p, the rotation axis A1 and the rotation axis A2 are each half a pitch in the x direction ( = P / 2). In this way, the yokes adjacent to each other in the y direction are arranged in a checkered pattern with rotational axes shifted from each other by a half pitch in the x direction. The hinge 26 that supports the yoke 27 is disposed along the gap between the yoke 28 and the adjacent drive unit 28 ′. With this configuration, the length of the hinge 26 in the y direction can be extended without colliding with an adjacent yoke. For this reason, the spring constant of the hinge 26 related to the rotation of the yoke can be lowered, and the area reduction of the yoke directly related to the rotational force can be minimized. Even when the hinge 26 and the yokes 27 to 29 are formed in the same process as in the present embodiment, and the material and thickness are the same, this configuration ensures both the rigidity of the yokes 27 to 29 and the flexibility of the hinge 26. can do.

  When a driving voltage is applied to the fixed electrode piece 23a, the first portion 27a of the yoke 27 is attracted to the fixed electrode piece 23a side. On the other hand, when a driving voltage is applied to the fixed electrode piece 23b, the second portion 27b is attracted to the fixed electrode piece 23b side. In this way, the rotational force can be selectively applied to both the CW (clockwise) direction and the CCW (counterclockwise) direction around the rotation axis A.

  The yoke 27 is coupled to the protrusion 30a of the intermediate connecting member 30 at a driving point 27c (indicated by hatching) near the free end of the first portion 27a. Further, a slot 27d penetrating the yoke 27 is provided in the vicinity of the drive point 27c. The slot 27d has the following two effects at the same time. The first effect is that the torsional stress generated when the yokes 27 to 29 are individually displaced is alleviated and crosstalk of the displacement amount between the yokes is prevented. The second effect is to balance the amount of displacement in the upward direction (positive in the z direction) and the downward direction (negative in the z direction) of the drive point 27c. Since the slot 27d is provided, the area of the first portion 27a is smaller than the area of the second portion 27b, and the rotational torque generated around the rotational axis A2 is smaller in the CCW direction than in the CW direction. Therefore, when considering the displacement of the drive point 27c accompanying the rotation around the rotation axis A2, the upward displacement is larger than the downward displacement. On the other hand, the electrostatic attractive force acting between the yoke 27 and the fixed electrode 23 gives the hinge 26 not only a simple rotational deformation but also a downward bending deformation. This gives a downward displacement to the drive point 27c when any of the fixed electrode pieces 23a and 23b is driven. Since the displacement of the drive point 27c is the sum of the displacement accompanying the rotation and the displacement accompanying the bending, the difference in displacement between the upward direction and the downward direction cancels each other, improving the balance of the displacement amount in both directions. . In addition, since the rotational displacement and the deflection displacement are linearly proportional to the electrostatic attraction force, if the area of the slot 27d is appropriately set according to the torsional rigidity and the flexural rigidity of the hinge 26, the displacement amount can be increased over a wide displacement range. Balance improvement effect is demonstrated. In the present embodiment, the second effect is realized by providing the slot 27d. However, the same effect can be achieved by an arbitrary configuration if the rotational torque in the direction of sucking the drive point 27c is reduced. This includes, for example, a configuration in which the area of the first portion 27a is made smaller than that of the second portion 27b, or the area of the fixed electrode piece 23a is made smaller than that of the fixed electrode piece 23b. With such a configuration, the displacement amount of the driving point 27c can be controlled with good symmetry in both the upward and downward directions according to the voltage applied to the fixed electrode pieces 23a and 23b.

  The intermediate connecting member 30 includes three protrusions 30 a to 30 c, the protrusion 30 a is connected to the drive point 27 c of the yoke 27, the protrusion 30 b is connected to the drive point 28 c of the yoke 28, and the protrusion 30 c is the drive point of the yoke 29. 29c. For this reason, when the yokes 27 to 29 are individually driven to rotate, the displacements of the protrusions 30a to 30c can be controlled independently, whereby the posture of the intermediate connecting member 30 is determined. Slots 32a to 32c penetrating the intermediate connecting member 30 are provided in the vicinity of the protrusions 30a to 30c. These slot holes 32a to 32c, like the slot holes 27d to 29d of the yokes 27 to 29, relieve the torsional stress generated when the yokes 27 to 29 are individually displaced, and cause crosstalk of the displacement amount between the yokes. To prevent.

  The micromirror 5 b is formed from an SOI substrate different from the substrate 5 a and is Au-bonded to the hatched portion 31 of the intermediate connecting member 30 by the protrusion 33. Since the micro mirror 5 b and the intermediate coupling member 30 are integrally coupled, the attitude of the micro mirror 5 b is determined by the attitude of the intermediate coupling member 30. The pitch interval between the micromirrors 5b adjacent in the x direction is p, and the mirror length in the x direction is L.

  With such a configuration, if the fixed electrode pieces 23a, 23b to 25a, 25b are appropriately selected and the drive voltage is set independently, the micromirror 5b is displaced in the z direction, tilted around the x axis, tilted around the y axis. It can be driven in both positive and negative directions.

  Next, the coordinate positions of the drive points 27c to 29c for improving the accuracy of the polygonal line approximation of the wavefront of the deformable mirror 5 will be described with reference to FIGS. FIG. 3 is an explanatory diagram showing the relationship between the drive point of the deformable mirror 5 and the wavefront approximation accuracy. Here, in order to simplify the description, first, a one-dimensional graph will be described.

  First, a general method of approximating a broken line of wavefront will be described with reference to FIG.

  In FIG. 3A, the horizontal axis represents the coordinate position in the x direction of the deformable mirror 5, and the vertical axis represents the wavefront phase. A phase function ψ which is a correction target in the deformable mirror 5 is indicated by a two-dot chain line. The phase function ψ is given in the function form of the coordinate position x as already described. Since each micro mirror 5b of the deformable mirror 5 can control the displacement and the inclination with respect to the substrate 5a, the phase function ψ is reproduced by a polygonal line approximation. Since the adjacent pitch interval of the micro mirror 5b is p, the coordinate point xj (j is an integer) is taken for each interval p, and the value ψ (xj) of the phase function ψ with respect to two adjacent coordinate points xj and xj + 1, The displacement and inclination of the micromirror 5b can be obtained so as to connect ψ (xj + 1). This approximate broken line ψ 'is indicated by a solid line. This method requires a small amount of calculation and can perform high-speed calculation processing, but has a large wavefront error.

  As another broken line approximation method, for each section [xj, xj + 1], it is possible to obtain the displacement and the slope that minimize the error from the phase function ψ by the least square method. According to this method, the wavefront error can be reduced, but the calculation amount increases.

  Therefore, a wavefront broken line approximation method with improved accuracy with a small amount of calculation will be described with reference to FIG. Here, two coordinate points xj, a, xj, b are taken in the section [xj, xj + 1]. The coordinate points xj, a, xj, b are in symmetrical positions with respect to the mirror center and are separated from each other by d. The distance d is set to an appropriate value, and the mirror surface is a line segment passing through two points of coordinates (xj, a, ψ (xj, a)) and (xj, b, ψ (xj, b)). Think about prescribing as

FIG. 3C plots the relationship between the radius of curvature R of the phase function ψ and the value of the distance d that minimizes the wavefront error in the interval [xj, xj + 1]. The dimension of the mirror is L, the dimensionless radius of curvature R / L is taken on the horizontal axis, and the dimensionless distance d / L that minimizes the wavefront error is taken on the vertical axis. The wavefront error is defined as the square root of the definite integral value ∫ (ψ−ψ ′) ² dx of the square of the error in the length L mirror. The curvature radius R of the phase function ψ can take an arbitrary value, but from FIG. 3C, the dimensionless distance d / L that minimizes the wavefront error hardly depends on the dimensionless curvature radius R / L. It can be seen that it takes a constant value of about 0.58. Accordingly, the coordinate points xj, a, xj, b set as the distance d = 0.58L are made to coincide with the coordinate position of the drive point of the deformable mirror 5, and the displacement target value of each drive point is set to ψ (xj, a), If ψ (xj, b), the wavefront error can be minimized to the same extent as the method using the least square method, and the displacement target value of the driving point can be directly calculated from the phase function ψ. The amount of calculation can be reduced.

  The case where the above items are extended to a two-dimensional model will be described with reference to FIG. FIG. 4 is an explanatory diagram two-dimensionally showing the relationship between the drive point of the deformable mirror 5 and the wavefront approximation accuracy.

  FIG. 4A is a plan view of the deformable mirror 5, in which a minute mirror 5b and driving points 27c to 29c are described. The drive points 27c to 29c are substantially located on the circumference of the diameter d with the center point O of the micromirror 5b as the center.

FIG. 4B plots the relationship between the radius of curvature R of the phase function ψ in the micromirror 5b and the value of the distance d that minimizes the wavefront error. The micromirror 5b has a square shape with a side length of L, the dimensionless curvature radius R / L is taken on the horizontal axis, and the dimensionless diameter d / L that minimizes the wavefront error is taken on the vertical axis. . The wavefront error is defined as the square root of the definite integral value ∫∫ (ψ−ψ ′) ² dxdy of the square of the error in the L × L mirror plane.

  The result when the phase function ψ is spherical is shown by a solid line. It can be seen that the dimensionless distance d / L that minimizes the wavefront error is almost independent of the dimensionless radius of curvature R / L and takes a constant value of about 0.82. In addition, the result of the previous one-dimensional model is shown with a dotted line. This corresponds to the case where the phase function ψ is a cylindrical surface having a curvature only in the x direction and no curvature in the y direction, but as described above, the dimensionless diameter d / L is about 0.58. If the flatness is 0 when the phase function ψ is spherical and the flatness is 1 when the phase function ψ is cylindrical, the general wavefront has an intermediate flatness. Therefore, as indicated by the hatched portion in the figure, it can be understood that the range of the dimensionless diameter d / L may be 0.58 or more and 0.82 or less.

  In this way, the drive points 27c to 29c are located between the first circle having the diameter d = 0.58L and the second circle having the diameter d = 0.82L centered on the center point O of the micromirror 5b. By disposing in, the approximation accuracy of the wavefront error can be increased. Since the displacement target values of the drive points 27c to 29c are directly calculated by inputting the coordinate position (x, y) of each drive point to the function of the phase function ψ, the amount of calculation is extremely small. Further, as described in FIG. 4A, in this embodiment, the coordinate position of the drive point is changed to a simple lattice shape of translation vectors (p / 2, p / 4) and (p / 2, −p / 4). Provided. For this reason, the setting of the coordinate points for all the micromirrors 5b can also be performed by simple increment calculation.

  Next, details of the photodetector 11 will be described with reference to FIGS. 5 and 6. FIG. 5 is a plan view of a light receiving unit in the photodetector 11 of the present embodiment. The photodetector 11 is a PIN photodiode array.

  As shown in FIG. 5A, the photodetector 11 receives the light receiving areas 41a, 41b to 44a and 44b corresponding to the differential signals S1 to S4 for detecting the aberration, and the light receiving corresponding to the signal S5 for detecting the disc information. Region 45.

  The light receiving areas 41a and 41b receive the + 1st order light and the −1st order light for detecting the spherical aberration mode M1 accompanying the change in disk base material thickness. The light receiving areas 42a and 42b receive the + 1st order light and the −1st order light for detecting the spherical aberration mode M2 accompanying the radial tilt of the disc. The regions 43a and 43b receive the + 1st order light and the −1st order light, respectively, for detecting the spherical aberration mode M3 accompanying the inclination of the disk in the tangential direction. The light receiving regions 44a and 44b receive + 1st order light and −1st order light for detecting the spherical aberration mode M4 accompanying defocusing of the objective lens 6, respectively.

  An enlarged view of the light receiving region 41a is shown in FIG. The structure of other light receiving regions is basically the same. The light receiving area 41a includes 6 × 6 independent light receiving elements 41a (1,1) to 41a (6,6). Wiring to each of the light receiving elements 41a (1, 1) to 41a (6, 6) is performed by a transparent electrode such as ITO or via wiring with a lower wiring layer, and the wiring does not run in the gap between the light receiving elements. It is provided as follows. This increases the effective light receiving area of the light receiving element.

  The shaded area represents the size of the light spot A0 when there is no aberration, and the radius of the air disk of the light spot A0 is r0. The size Le of the light receiving element is set to a value smaller than the air disk radius r0. In detecting the amount of light in the light receiving region 41a, only the light receiving element 41a (1,1) to 41a (6,6) located at the center of the light spot A0 is used. In the state shown in the figure, output signals from the four light receiving elements 41a (3, 3), 41a (3,4), 41a (4, 3), 41a (4, 4) are detected effectively. . For example, when the center position of the light spot A0 is shifted due to a temperature change or the like, four light receiving elements near the shifted center position are newly used. In this way, a light receiving element to be effectively operated is selected from a plurality of minute light receiving elements so that only the light intensity near the center position of the light spot A0 can be detected. This detection configuration will be described with reference to FIG.

  FIG. 6 is a schematic configuration diagram of a detection circuit in the photodetector 11 of the present embodiment. Here, the areas 41a and 41b will be described as an example, but the same applies to other light receiving areas. The switching unit 45a includes 36 switches 45a1 to 45a36 connected to the light receiving elements 41a (1,1) to 41a (6,6) terminals in the light receiving region 41a, and a switch 45a37 connected to the ground terminal 46a. An arbitrary terminal is selected and connected to the + side input of the differential amplifier 47. The switching unit 45b includes 36 switches 45b1 to 45b36 connected to the light receiving elements 41b (1,1) to 41b (6,6) terminals in the light receiving region 41b, and a switch 45b37 connected to the ground terminal 46b. An arbitrary terminal is selected and connected to the negative side input of the differential amplifier 47.

  The output amplified by the differential amplifier 47 is converted into digital data by the AD converter 48 and output to the control circuit 12.

  When the apparatus is started up or when a temperature change not less than a predetermined value of the apparatus is detected by a temperature sensor (not shown), the control circuit 12 performs a light receiving element selection operation to correct the positional deviation of the light spot. At this time, the light source 1 is turned on and the photodetector 11 is in a state of receiving the reflected light from the optical disc 7.

  First, selection of the light receiving element on the light receiving region 41a side will be described. First, the switching unit 45b turns on only the switch 45b37, and connects the negative input of the differential amplifier 47 to the ground terminal 46b. In this state, the switching unit 45a is turned on while sequentially switching the switches 45a1 to 45a36 one by one. Then, the outputs of the light receiving elements 41 a (1, 1) to 41 a (6, 6) are amplified by the differential amplifier 47 and digitized by the AD converter 48. The output data of each light receiving element is held in the memory of the control circuit 12. These output data represent the light amount distribution in the light receiving area 41a. The control circuit 12 compares the output data, determines that the portion where the largest amount of light is obtained is the center of the light spot, and determines four light receiving elements around the center of the light spot as selection targets.

  The selection of the light receiving element on the light receiving region 41b side is performed in exactly the same manner. That is, the switching unit 45a turns on only the switch 45a37 and connects the + side input of the differential amplifier 47 to the ground terminal 46b. In this state, the switching unit 45b is turned on while sequentially switching the switches 45b1 to 45b36 one by one. Then, the outputs of the light receiving elements 41 b (1, 1) to 41 b (6, 6) are amplified by the differential amplifier 47 and digitized by the AD converter 48. The output data of each light receiving element is held in the memory of the control circuit 12. These output data represent the light amount distribution in the light receiving area 41b. The control circuit 12 compares the output data, determines that the portion where the largest amount of light is obtained is the center of the light spot, and determines four light receiving elements around the center of the light spot as selection targets.

  When the selection of the light receiving element is completed in this way, the control circuit 12 instructs the switching units 45a and 45b to connect to create the aberration detection signal S1. The switching unit 45 a turns on the switch connected to the terminals of the selected four light receiving elements, and connects to the + side input of the differential amplifier 47. Similarly, the switching unit 45b turns on the switch connected to the terminals of the four selected light receiving elements, and connects to the negative side input of the differential amplifier 47.

  Then, the differential amplifier 47 obtains a differential amplification output of the light receiving element selected from each of the light receiving regions 41a and 41b. The aberration detection signal S1 is obtained as data digitized by the AD converter 48.

  Unless the re-correction of the light spot position is requested from the control circuit 12, the switching units 45a and 45b always maintain this connection, and the aberration detection signal S1 that is always valid is output during the recording and reproducing operations of the information apparatus. Therefore, aberration detection with high responsiveness is possible.

  Further, since it is possible to cope with the positional deviation of the light spot, the assembly adjustment accuracy of the photodetector 11 is greatly eased, and it is also strong against the positional deviation of the light spot accompanying the change in the state of the information device such as temperature characteristics. The reliability of the apparatus can be improved.

  Further, since the switching unit 45 is provided between the light receiving elements and the differential amplifier 47, the differential amplifier 47 and the AD converter 48 can be greatly reduced with respect to the number of light receiving elements. For this reason, the circuit configuration becomes extremely simple, and it is possible to realize a reduction in circuit cost and power saving.

  The signals S2 to S4 are also generated with the same configuration as described above. The signal S5 is also created with the same configuration except that it is not a differential signal. Since the signal S5 also has such a confocal optical configuration using only such a small effective light receiving region, the influence of stray light from other layers in the multilayer disk can be reduced.

  Here, the case where the number of light receiving elements to be operated effectively is four and fixed in a square arrangement has been described, but this may be changed in number and arrangement shape for each aberration mode, or in time series It may be changed. In particular, the number of light-receiving elements to be operated effectively is increased at first, so that the coarse adjustment of the aberration can be performed even if the light spot position is slightly shifted, and the rough adjustment of the aberration and the detection of the light spot position are completed. It is also possible to reduce the number of light receiving elements to be operated effectively later so that precise adjustment can be performed. This is effective in increasing the operational reliability by rapidly converging both the aberration and the light spot position to the target accuracy when a large aberration that occurs transiently reduces the detection accuracy of the light spot position. .

  Regarding the deviation of the center position of the light spot due to the assembly error of the apparatus, the center position of the light spot after assembly is measured in advance and stored in the ROM memory in the control circuit 12, and this value is read when the apparatus is started. It is issued and used.

  The operation of the information apparatus according to the present embodiment will be described with reference to FIG. 1 again.

  When the apparatus is activated, the light source 1 is turned on, the deformable mirror 5 is made flat, and the focus of the objective lens 6 is drawn into a predetermined recording layer of the optical disc 7. This predetermined recording layer is at an intermediate position between the uppermost layer and the lowermost layer, and is a position designed so that the spherical aberration of the objective lens 6 is minimized when the deformable mirror 5 is flat. Here, the light spot position of the photodetector 11 is detected, and the light receiving element to be effectively operated is determined.

  Thereafter, the objective lens 6 is moved to the target track of the recording layer where data is actually recorded / reproduced. The overall control unit 15 outputs the lens shift amount x0 of the objective lens 6 based on the tracking control signal Tr at this time. On the other hand, the aberration signals S1 to S3 are output from the photodetector 11, and the wavefront calculation unit 13 outputs the phase function ψ (x, y) converted on the surface of the variable mirror 5 by using the aberration signals S1 to S3.

  Further, the phase function ψ (x, y) is added with a shift transformation ψ (x−x0, y) corresponding to the lens shift amount x0 in the lens shift correction calculation unit 14, and this is a target for controlling the deformable mirror 5. It becomes the wave front. The wavefront correction control unit 16 determines the target displacement by substituting the coordinate position of the driving point of each micromirror 5b into the phase function ψ (x−x0, y) of the target wavefront, and multiplies it by a predetermined gain constant to perform closed loop control. I do. As a result, the wavefront aberration modes M1 to M3 associated with the change in the substrate thickness and the tilt of the optical disc 7 are corrected.

  As described above, for the aberration modes M1 to M3 associated with the change in the substrate thickness and the inclination of the optical disc 7 and the aberration mode M4 due to defocusing, the photodetector 11 configured so that the respective aberration modes to be detected are orthogonal to each other is used. Then, the wavefront detection is performed, and the lens shift factor x0 of the objective lens 6 is detected without directly measuring the aberration of the lens shift factor that is not orthogonal to the aberration modes M1 to M4, and the phase function ψ is correspondingly detected. The coordinate of (x, y) is shifted by x0 and applied to the deformable mirror 5. For this reason, interference between modes at the time of aberration detection can be prevented with a simple configuration, and approximation accuracy can be improved.

  The aberration modes M1 to M4 are invariant with respect to the rotation of the coordinate axes, like the basis function Zi of the Zernike polynomial. That is, M1 and M4 are rotationally symmetric, and M2 and M3 can represent modes obtained by rotation by a combination of M2 and M3. In order to correct the lens shift in a system that is invariant with respect to the rotation of the coordinate axes, many aberration modes up to higher orders are required. However, according to the above configuration, accurate aberrations can be achieved with only a few aberration modes. Correction is possible.

  Next, with reference to FIG. 7, it will be described that appropriate wavefront correction can be achieved even when the lens shift amount x0 takes an arbitrarily small value. FIG. 7 is an explanatory diagram showing the corrected wavefront shape of the deformable mirror 5 when there is a lens shift amount x0. Here, for simplification, a one-dimensional graph will be used.

  FIG. 7A shows a case where the lens shift amount x0 is just equal to the pitch interval p of the minute mirror 5b.

  In the graph on the left side in the figure, the phase function ψ (x, y) when there is no lens shift is indicated by a one-dot chain line, and the corrected wavefront shape of the deformable mirror 5 is indicated by a broken line. The target displacement amounts of the drive points xj, a, xj, b are ψ (xj, a) and ψ (xj, b), respectively. In the graph on the right side of the drawing, the phase function ψ (x−p, y) when the lens shift amount is p is indicated by a two-dot chain line, and the corrected wavefront shape of the deformable mirror 5 is indicated by a solid line. The target displacement amounts of the drive points xj + 1, a and xj + 1, b are ψ (xj + 1-p, a) and ψ (xj + 1-p, b), respectively.

  As is obvious from the figure, when the lens shift amount x0 is just equal to the pitch interval p of the minute mirror 5b, the target displacement amount ψ (xj, a) of the drive points xj, a, xj, b when there is no lens shift. , Ψ (xj, b) may be shifted to the driving points xj + 1, a and xj + 1, b of the adjacent micromirrors. It is also clear that there is no deterioration in the correction wavefront accuracy of the deformable mirror 5 accompanying the lens shift correction at this time.

  FIG. 7B shows a case where the lens shift amount x0 is α · p (α <1) which is smaller than the pitch interval p of the minute mirror 5b.

  In the graph on the left side in the figure, the phase function ψ (x, y) when there is no lens shift is indicated by a one-dot chain line, and the corrected wavefront shape of the deformable mirror 5 is indicated by a broken line. The target displacement amounts of the drive points xj, a, xj, b are ψ (xj, a) and ψ (xj, b), respectively. In the graph on the right side of the figure, the phase function ψ (x−α · p, y) when the lens shift amount is α · p is indicated by a two-dot chain line, and the corrected wavefront shape of the deformable mirror 5 is indicated by a solid line. Yes. The target displacement amounts of the drive points xj + 1, a and xj + 1, b are ψ (xj + 1-α · p, a) and ψ (xj + 1-α · p, b), respectively.

  Here, the target displacement amounts ψ (xj + 1−α · p, a) and ψ (xj + 1−α · p) at the drive points xj + 1, a and xj + 1, b when the lens shift correction is performed. , b) is different from the target displacement amounts ψ (xj, a), ψ (xj, b) of the drive points xj, a, xj, b when there is no lens shift, so that the wavefront approximation accuracy is improved. .

  Thus, even when the lens shift amount x0 is smaller than the pitch interval p between the micromirrors 5b, the target displacement value is shifted by controlling the target displacement amount of each micromirror 5b in multiple stages, so that the wavefront approximation accuracy is changed. The lens shift can be corrected without lowering the lens. Accordingly, wavefront lens shift correction can be performed for an arbitrary minute lens shift amount x0.

  As described above, the information device according to the present embodiment generates the phase function ψ (x, y) for the wavefront calculation unit 13 to associate the coordinate position of the light beam with the wavefront phase based on the output of the photodetector 11. Then, the lens shift correction calculation unit 14 creates a phase function ψ (x−x0, y) in which the correspondence between the coordinate position and the wavefront phase is changed according to the lens shift amount x0, and this phase function ψ (x−x0). , Y), the wavefront correction control unit 16 controls the deformable mirror 5. With this configuration, it is possible to perform a correction operation only by calculation processing without requiring a dedicated member for lens shift correction. Further, only the minute mirror 5b is actually displaced in accordance with the lens shift correction operation, which has a small mass and a small displacement amount on the order of nm, so that an extremely high-speed follow-up response is possible. Further, there is no deterioration of the wavefront correction accuracy when the lens shift correction is performed, and the same processing can be applied to an arbitrary wavefront. Furthermore, lens shift correction can be performed even for an arbitrary minute lens shift amount.

  In the present embodiment, (Equation 1) to (Equation 3) for the aberration mode when the light detection unit 11 detects and the aberration mode when the wavefront calculation unit 13 reproduces the phase function ψ (r, θ). ) Are commonly used, but other configurations are also conceivable. For example, the light detection unit 11 detects aberration using the aberration mode Zi of the Zernike polynomial expressed by (Expression 5) to (Expression 7), and the wavefront calculation unit 13 is expressed by (Expression 1) to (Expression 3). It is also possible to reproduce the phase function ψ (r, θ) using the aberration mode Mi. If the correlation between the aberration mode Zi and the aberration mode Mi is obtained in advance, a certain effect can be obtained even with such a configuration.

(Embodiment 2)
Next, a second embodiment of the information device according to the present invention will be described with reference to FIG. FIG. 8 is a schematic configuration diagram of the information device in the present embodiment.

  In the present embodiment, the light source 1, the collimator lens 2, the deformable mirror 5, the objective lens 6, the optical disk 7, the objective lens actuator 8, the photodetector 11, the control circuit 12, the wavefront calculation unit 13, the lens shift correction calculation unit 14, The overall control unit 15 and the wavefront correction control unit 16 are the same as those described in the first embodiment.

  The light beam emitted from the light source 1 is converted into an infinite light beam by the collimator lens 2 and enters the half mirror 50. The component of the light beam that has passed through the half mirror 50 is incident on the polarization beam splitter 51, and the P-polarized component is transmitted through the polarization beam splitter 51 and converted into circularly polarized light by the quarter wavelength plate 52. This light beam is reflected by the deformable mirror 5 and its phase is modulated, and is transmitted again through the quarter-wave plate 52 and converted into an S-polarized component.

  The light beam of this S-polarized component is reflected by the polarization beam splitter 51, enters the objective lens 6, and is condensed on the recording layer of the optical disc 7. The light beam reflected by the recording layer of the optical disk 7 passes through the objective lens 6, the polarization beam splitter 51, and the quarter wavelength plate 52 again and enters the deformable mirror 5. The phase of the light beam reflected by the deformable mirror 5 is modulated, transmitted again through the quarter-wave plate 52, converted into a P-polarized component, and incident on the half mirror 50.

  A component of the light beam reflected by the half mirror 50 is detected by a wavefront sensor constituted by the hologram 53 and the photodetector 11. The hologram 53 is provided by being integrally bonded to the photodetector 11.

  The hologram 53 forms a condensing spot pair similar to the combination of the hologram 9 and the lens 10 described in the first embodiment. That is, with respect to the aberration mode Mi as shown in (Equation 1) to (Equation 4) and the bias coefficient Bi, a light spot to which a bias aberration of + BiMi is given, and a light spot to which a bias aberration of -BiMi is given. And create. Further, a light spot for detecting the signal S5 modulated by the pre-pits and recording marks of the optical disc 7 is also formed at the same time.

  According to the present embodiment, since the light beam is perpendicularly incident on the deformable mirror 5, the coordinate calculation corresponding to the mirror position in the wavefront calculation unit 13 can be simplified. In addition, since the hologram 53 is configured integrally with the photodetector 11, the configuration is simplified, the assembly adjustment process is simplified, and the misalignment of the focused spot due to a temperature change or the like can be effectively prevented.

(Embodiment 3)
Next, a third embodiment of the information device according to the present invention will be described with reference to FIG. FIG. 10 is a schematic configuration diagram of the information device in the present embodiment.

  In the present embodiment, the light source 1, the collimator lens 2, the polarizing beam splitter 3, the quarter wavelength plate 4, the deformable mirror 5, the objective lens 6, the optical disk 7, the objective lens actuator 8, the lens 10, and the lens shift correction calculation unit 14 The configuration and operation of the wavefront correction control unit 16 are the same as the configuration and operation of the corresponding parts included in the information device of the first embodiment.

  The light beam returned from the optical disk 7 to the polarization beam splitter 3 is reflected, passes through the lens 10, is given astigmatism by the cylindrical lens 20, and enters the photodetector 11b. The photodetector 11b includes four light receiving units (not shown), generates a focus error signal by an astigmatism method, and generates a tracking error signal by a push-pull method. The focus error signal and the tracking error signal are input to the overall control unit 15b.

  The overall control unit 15b calculates the change amount of the base material thickness of the recording layer of the optical disc 7 and the tilt amount of the recording layer, and determines the coefficients A1 to A3 of the basis functions M1 to M3 based on these amounts.

  The wavefront calculation unit 13b receives signals indicating the coefficients A1 to A3 of the basis functions M1 to M3 from the overall control unit 15b, and calculates the phase function ψ (x, y) based on the coefficients A1 to A3. A signal indicating the phase function ψ (x, y) is sent to the lens shift correction calculation unit 14.

  FIG. 11 is a flowchart illustrating a procedure in which the overall control unit 15b determines the coefficients A1 to A3.

  In step ST01 shown in FIG. 11, the type of the optical disc 7 is determined. This step ST01 is executed promptly when the optical disc 7 is inserted into the apparatus. In step ST02, based on the determination result in step ST01, the corresponding disc information is read out from various disc information stored in advance in a memory (not shown). The disc information includes, for example, the number of recording layers of the optical disc 7 and the value of the base material thickness (recording layer depth) in each recording layer.

  In step ST03, the base material thickness change amount of the layer to be recorded / reproduced is calculated. The objective lens 6 is designed so that the spherical aberration is minimized at a predetermined base material thickness. The magnitude of the spherical aberration is determined by the base material thickness and the base material thickness of the recording layer on which recording / reproduction is performed. It occurs in proportion to the amount of change in substrate thickness that is the difference.

  In step ST04, the coefficient A1 of the basis function M1 is calculated. The coefficient A1 is calculated by multiplying the base material thickness variation by a preset proportionality constant.

  In step ST05, the objective lens 6 is moved to the inner peripheral side of the optical disc 7. In step ST06, the objective lens actuator 8 is driven on the inner peripheral side to focus on the recording layer to be recorded and reproduced. The driving amount C1 in the focus direction of the objective lens actuator 8 at that time is recorded in a memory (not shown).

  In step ST07, the objective lens 6 is moved to the outer peripheral side by a predetermined distance D. In step ST08, as in step ST06, the recording layer to be recorded and reproduced is focused, and the driving amount C2 of the objective lens actuator 8 at that time is recorded in a memory (not shown).

  In step ST09, the tilt amount of the recording layer is calculated based on the actuator drive amounts C1 and C2 and the distance D. The amount of inclination of the recording layer is obtained by dividing the difference between the actuator driving amount C1 and the actuator driving amount C2 by the distance D.

  In step ST10, coefficients A2 and A3 of the basis functions M2 and M3 are calculated. The coefficients A2 and A3 are calculated by multiplying the tilt amount of the recording layer by a preset proportionality constant.

  According to the present embodiment, since the wavefront function is generated without using the wavefront sensor, the light detection unit can be realized with a simple configuration. The method for determining the substrate thickness (recording layer depth) of each recording layer included in the optical disc 7 is not limited to the above method. For example, the base material thickness of each recording layer may be calculated based on the respective driving amounts when the objective lens actuator 8 focuses each recording layer. Further, the method for calculating the tilt amount of the recording layer is not limited to the above method. For example, a tilt sensor that detects the tilt amount of the optical disc 7 may be provided separately, and calculation may be performed based on the output.

  As described above, in this embodiment, the wavefront sensor is not used, but after determining the state of each correction element (micromirror) in the deformable mirror functioning as the wavefront correction unit, the objective lens relative to the optical axis of the light beam is determined. When the amount of positional deviation of the optical axis is detected, the state of each micromirror can be appropriately corrected so as to compensate for this positional deviation.

  The important point in the present invention is that the state of the element functioning as the wavefront correction means is reconfigured according to the lens shift. The initial state of the element functioning as the wavefront correction means can be determined by detecting the wavefront of the light beam, but the tilt of the optical disc, the depth from the surface of the recording layer of the optical disc (base material thickness), etc. Can also be determined based on The tilt of the optical disc is information necessary for compensating coma aberration, and the substrate thickness of the optical disc is information necessary for compensating spherical aberration.

  Thus, according to a preferred embodiment of the present invention, the shape of the reflecting surface of the deformable mirror (the state of the micromirror) is optimized as appropriate in order to minimize the above aberration, and then the lens shift is performed. When this occurs, correction according to the range shift is performed.

  In each of the above-described embodiments, a deformable mirror provided with a large number of displaceable micromirrors on the substrate is used as the wavefront correction means. However, instead of such an element, it is desired within the cross section of the light beam. Alternatively, a liquid crystal element capable of forming a refractive index distribution may be used.

  The present invention is widely applied to an information apparatus such as an optical disk apparatus that requires aberration correction in a situation where a lens shift occurs.

It is a schematic block diagram of the information apparatus in Embodiment 1 of this invention. It is a disassembled perspective view of the deformable mirror in Embodiment 1 of the present invention. It is a one-dimensional explanatory diagram showing the relationship between the drive point of the deformable mirror and the wavefront approximation accuracy. It is a two-dimensional explanatory diagram showing the relationship between the drive point of the deformable mirror and the wavefront approximation accuracy. It is a top view of the light-receiving part of the photodetector in Embodiment 1 of this invention. It is a schematic block diagram of the detection circuit of the photodetector in Embodiment 1 of this invention. It is explanatory drawing which shows the correction | amendment wavefront shape of a deformable mirror when there exists a lens shift. It is a schematic block diagram of the information apparatus in Embodiment 2 of this invention. It is a schematic diagram which shows a mode that a wavefront correction pattern moves according to the shift of the optical axis of the objective lens. It is a schematic block diagram of the information apparatus in Embodiment 3 of this invention. It is a flowchart which shows the operation | movement in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 Deformable mirror 6 Objective lens 11 Photo detector 11b Photo detector 12 Control circuit 12b Control circuit 13 Wavefront calculating part 13b Wavefront calculating part 14 Lens shift correction calculating part 15 Overall control part 15b Overall control part 16 Wavefront correction control part

Claims (12)

An information device for writing data to a medium with a light beam and / or reading data from the medium,
A light source for generating the light beam;
An objective lens for condensing the light beam on the medium;
Lens shift detecting means for detecting the amount of positional deviation of the optical axis of the objective lens with respect to the optical axis of the light beam;
Correction elements for locally correcting the wavefront of the light beam are arranged in a two-dimensional array, and each correction element is driven independently of each other;
Wavefront computing means for associating each coordinate position in the cross section of the light beam with the wavefront phase of the light beam;
Lens shift correction calculation means for changing the correspondence between the coordinate position and the wavefront phase based on the output of the lens shift detection means;
Control means for controlling the wavefront correction means based on the output of the lens shift correction calculation means;
An information device. A wavefront sensor for detecting a wavefront of the light beam;
The information device according to claim 1, wherein the wavefront calculation unit associates each coordinate position in a cross section of the light beam with a wavefront phase of the light beam based on an output of the wavefront sensor. Means for detecting a tilt of the medium relative to the light beam;
The information device according to claim 1, wherein the wavefront calculation unit associates each coordinate position in a cross section of the light beam with a wavefront phase of the light beam according to an inclination of the medium with respect to the light beam. Further comprising means for detecting spherical aberration in the medium;
The information apparatus according to claim 1, wherein the wavefront calculation unit associates each coordinate position in the cross section of the light beam with a wavefront phase of the light beam according to the spherical aberration.   The lens shift correction calculation means associates the coordinate position and the wavefront phase by shifting the coordinate position of the light beam in the direction of the positional deviation of the optical axis of the objective lens with respect to the optical axis of the light beam. The information device according to claim 1, wherein the information device is changed. When the adjacent pitch interval of the correction element regarding the direction of the positional deviation of the optical axis of the objective lens with respect to the optical axis of the light beam is p,
The information device according to claim 5, wherein the lens shift correction calculation unit shifts the coordinate position of the light beam with respect to the optical axis shift amount smaller than the p.   The total wave aberration is calculated by combining the first aberration mode associated with a change in the substrate thickness of the medium and the second aberration mode associated with the inclination of the medium. Information devices.   The information device according to claim 7, wherein the first aberration mode includes a sixth-order term or more with respect to a distance r from the optical axis center in a single mode.   The information apparatus according to claim 7, wherein the second aberration mode includes a fifth-order term or more with respect to a distance r from the optical axis center in a single mode.   The information device according to claim 1, wherein each correction element of the wavefront correction unit includes a minute reflection mirror that reflects the light beam, and the wavefront correction unit functions as a deformable mirror.   The information apparatus according to claim 1, wherein the wavefront correction unit includes a liquid crystal element, and each correction element of the wavefront correction unit includes a liquid crystal region that optically modulates the light beam. The base,
A light source provided on the base;
An objective lens that is movably supported on the base and collects the light beam emitted from the light source and irradiates the medium;
An objective lens actuator capable of moving the objective lens in a direction perpendicular to the optical axis of the light beam;
Spatial wavefront correction is performed by arranging correction elements that are provided on the base of the optical pickup and locally correct the wavefront of the light beam in a two-dimensional array and control these correction elements independently. Wavefront correction means for forming a pattern;
With
An optical pickup that shifts a wavefront correction pattern formed by the wavefront correction means in a direction of deviation of an optical axis of the objective lens with respect to an optical axis of the light beam.

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