JP2007139841A - Variable shape mirror apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable shape mirror apparatus in which wavefront aberration is accurately corrected. <P>SOLUTION: In the variable shape mirror apparatus 1, piezoelectric members 5 and 6 are expanded and contracted by applying a driving voltage on driving electrodes 7 and 8, and a mirror base member 2 and a mirror face 3 are deformed. A common electrode 4, the piezoelectric member 6 and the driving electrode 8 have upper and lower faces of which the area is larger than the area of a radiated part 11 of a light beam on the mirror face 3 when the mirror base member 2 and the mirror face 3 are not deformed, so that the radiated part 11 stays within the region of the respective upper and lower faces of the common electrode 4, the piezoelectric member 6 and the driving electrode 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a deformable mirror device and an optical disk device using the deformable mirror device.

  Conventionally, a DVD is used as a large-capacity optical disk that replaces a CD. DVD achieves high density by setting the numerical aperture to 0.6 and the laser wavelength to 650 μm. However, since the coma caused by the disk tilt increases in proportion to the cube of the numerical aperture, the thickness of the disk base material is reduced to 0.6 mm in DVD. Further, since the spherical aberration caused by the disc base material thickness error increases in proportion to the fourth power of the numerical aperture, the dimensional tolerance of the disc base material thickness is reduced in the DVD. Thus, the wavefront aberration, which is coma and spherical aberration, can be suppressed to some extent by the structure of the disk, but correction of the wavefront aberration is also necessary.

  In addition, DVDs have a multi-layer disc having a plurality of recording layers, and further increase the capacity. Even when reproducing such a multilayer disk, it is essential to correct spherical aberration.

For correcting wavefront aberration, for example, Patent Document 1 discloses a wavefront aberration correcting mirror. This is a structure in which a common electrode is attached under the mirror substrate, a piezoelectric material is attached underneath, and a drive electrode and a sensor electrode are attached underneath it. By applying a voltage to the piezoelectric material, The mirror substrate is deformed, and the wavefront aberration of the laser beam reflected by the mirror material attached to the mirror substrate is corrected.
JP 2005-43544 A

  However, in the wavefront aberration correcting mirror disclosed in Patent Document 1, the shape of the drive electrode is such that there are many gaps between the portions where the electrodes are present, so the mirror substrate is deformed in a smooth shape. There is a problem that the wavefront aberration of the laser beam reflected by the mirror material becomes large.

  In view of the above problems, an object of the present invention is to provide a deformable mirror device capable of correcting wavefront aberration with high accuracy.

In order to achieve the above object, a deformable mirror device of the present invention includes a mirror base material on which a mirror surface is formed, a first electrode formed on the mirror base material so as to face the mirror surface, A piezoelectric material formed on the lower surface of one electrode, and a second electrode formed on the lower surface of the piezoelectric material,
The first electrode, the piezoelectric material, and the second electrode are larger in area than the area of the light beam irradiation region on the mirror surface when the mirror base material and the mirror surface are not deformed. Has upper and lower surfaces,
When viewed from above the mirror surface, the irradiation region is configured to fall within the regions of the upper and lower surfaces of the first electrode, the piezoelectric material, and the second electrode.

  According to such a configuration, the deformation shape of the irradiation region of the light beam on the mirror surface can be made smooth, and wavefront aberration can be corrected with high accuracy.

  The deformable mirror device according to the present invention is characterized in that a sensor for detecting deformation of the mirror surface is provided.

  According to such a configuration, the shape of the mirror surface can be controlled by feedback control, and wavefront aberration can be corrected with high accuracy regardless of temperature changes.

  Further, it is desirable that the sensor has a rigidity smaller than that of the mirror base material. This is because deformation of the mirror base material is not hindered. For example, when the mirror substrate is made of silicon, the sensor may be made of a piezoelectric polymer.

  If the shape change mirror device as described above is applied to an optical pickup, the wavefront aberration in the recording layer of the optical disc can be corrected with high accuracy, and reproduction and recording of the optical disc can be stabilized.

  With the variable shape mirror device of the present invention, wavefront aberration can be corrected with high accuracy.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a bottom view of a deformable mirror device 1 according to the present invention. 2 shows a cross-sectional view taken along the line AA in FIG. 1 (however, the base 9 is also shown).

  The mirror base material 2 is made of silicon, and has a hole portion having slopes in all directions by etching, and the cross-sectional shape is substantially U-shaped. For example, RIE (reactive ion etching) may be used as an etching method. A mirror surface 3 is formed on the entire upper surface of the mirror substrate 2. What is necessary is just to form the mirror surface 3 by vapor deposition of aluminum, for example.

  A common electrode 4 is formed on the entire bottom surface of the hole formed in the mirror base 2 so as to face the mirror surface 3. A cylindrical piezoelectric material 6 is formed at the center of the lower surface of the common electrode 4. A circular drive electrode 8 having the same shape as the bottom surface of the piezoelectric material 6 is formed on the bottom surface of the piezoelectric material 6. The piezoelectric material 6 may be made of PZT (lead zirconate titanate), for example. The common electrode 4 and the drive electrode 8 may be a metal film such as Pt.

  Further, on the lower surface of the common electrode 4, a piezoelectric material 5 having a shape in which one block-shaped surface is an arc-shaped surface is located, and a surface facing the arc-shaped surface is located at the center of each side of the common electrode 4. Formed to do. Each piezoelectric material 5 is disposed around the piezoelectric material 6 with a gap from the piezoelectric material 6, and the arc-shaped surfaces are opposed to each other. A drive electrode 7 having the same shape as the lower surface of the piezoelectric material 5 is formed on the lower surface of each piezoelectric material 5. The piezoelectric material 5 may be made of the same material as the piezoelectric material 6. The drive electrode 7 may be a metal film like the common electrode 4 and the drive electrode 8.

  Further, the deformation detection sensor 10 is attached from a portion corresponding to the center of the end of each drive electrode 7 on the mirror surface 3 to a further outer portion. The deformation detection sensor 10 is preferably made of, for example, a piezoelectric polymer so that the rigidity is smaller than that of the mirror base 2.

  The variable shape mirror device 1 according to the present invention is configured as described above, and is fixed to the base 9 with the lower surface of the mirror base 2 being in contact with the base 9. The common electrode 4 is at a ground potential, and when the drive potential is applied to the drive electrode 7 and the drive electrode 8, the piezoelectric material 5 and the piezoelectric material 6 expand and contract, and the mirror base material 2 and the mirror surface 3 are deformed. . Thereby, the wavefront aberration of the light beam irradiated and reflected on the mirror surface 3 is corrected.

  Here, the irradiation unit 11 in FIGS. 1 and 2 has the mirror surface 3 in a state where no potential is applied to the drive electrode 7 and the drive electrode 8 and the mirror base material 2 and the mirror surface 3 are not deformed. It is an irradiation area of the upper light beam. The common electrode 4, the piezoelectric material 6, and the drive electrode 8 have upper and lower surfaces that are larger than the area of the irradiation unit 11, and the irradiation unit 11 is viewed from above the mirror surface 3. 8 is configured to fall within the area of the upper and lower surfaces of each. Thereby, the deformation shape of the irradiation area of the light beam on the mirror surface 3 can be made smooth, and the wavefront aberration can be corrected with high accuracy.

  Further, when the mirror surface 3 is deformed, the deformation detection sensor 10 is deformed and a detection signal corresponding to the deformation is generated, so that the deformation of the mirror surface 3 can be detected. As a result, the shape of the mirror surface 3 can be controlled by feedback control, and wavefront aberration can be corrected with high accuracy regardless of temperature changes. Further, when the deformation detection sensor 10 is made of a piezoelectric polymer, the rigidity of the deformation detection sensor 10 is much smaller than that of the mirror base 2, so that the deformation of the mirror base 2 is not hindered.

  Next, an embodiment in which the deformable mirror device according to the present invention is applied to an optical disk device will be described. FIG. 3 shows an optical system of an optical pickup provided in the optical disc apparatus.

  The optical pickup includes a laser diode 12, a PBS (polarizing beam splitter) 13, a cylindrical lens 14, a photodetector 15, a collimator lens 16, a shape variable mirror device 1, a quarter wavelength plate 17, and an objective lens 18. The deformable mirror device 1 is fixed to a pickup base (not shown) included in the optical pickup corresponding to the base 9 (FIG. 2) so that the undeformed mirror surface 3 is inclined by 45 ° with respect to the optical axis. The objective lens 18 is driven in the focus direction and the tracking direction by an actuator (not shown) included in the optical pickup.

  Laser light emitted from the laser diode 12 passes through the PBS 13, is collimated by the collimator lens 16, and is incident on and reflected by the mirror surface 3 of the deformable mirror device 1. The reflected laser light passes through the quarter-wave plate 17 and is focused on the optical disk 19 by the objective lens 18. The laser beam reflected by the optical disk 19 passes through the objective lens 18 and the quarter-wave plate 17 and is incident on and reflected by the mirror surface 3 of the variable shape mirror device 1. The reflected laser light passes through the collimator lens 16, is reflected by the PBS 13, passes through the cylindrical lens 14, and is received by the photodetector 15. A focus error signal, a tracking error signal, and a reproduction signal are generated based on the laser light received by the photodetector 15, and the actuator drives the objective lens 18 based on the focus error signal and the tracking error signal to perform focus servo and tracking servo. .

  The optical disc apparatus includes a control unit and a storage unit in addition to the optical pickup. At the time of assembling the optical disk device, the jitter of the reproduction signal is measured by changing the drive potential applied to the drive electrode 7 and the drive electrode 8 of the deformable mirror device 1 while performing the focus servo and the tracking servo, and measuring the jitter. The drive potential information when the value is minimized and the information of the detection signal generated by the deformation detection sensor 10 (hereinafter, target deformation information) are stored in advance in the storage unit. When the optical disk is multi-layered, the above information for each layer is stored in advance in the storage unit. When the jitter is minimized, that is, when the spherical aberration of the laser beam in the recording layer is optimally corrected.

  When the optical disc 19 is a double-layer disc, the optical disc apparatus performs the following playback / recording operation. During the reproduction / recording operation of the first layer, the control unit generates a drive signal based on the focus error signal and tracking error signal generated based on the laser light received by the photodetector 15 and sends it to the actuator, and the objective lens 18 is driven. Focus servo and tracking servo are performed. Further, at this time, the control unit first represents the drive potential represented by the drive potential information corresponding to the first layer stored in the storage unit as the initial drive potential applied to the drive electrode 7 and the drive electrode 8 of the deformable mirror device 1. Is applied to the drive electrode 7 and the drive electrode 8. Thereafter, the control unit detects that the detection signal generated by the deformation detection sensor 10 is based on the detection signal generated by the deformation detection sensor 10 and the target deformation information corresponding to the first layer stored in the storage unit. A drive voltage is applied to the drive electrode 7 and the drive electrode 8 so as to be a signal represented by.

  By such feedback control, the mirror surface 3 is controlled to have an optimal deformed shape for the first layer reproduction recording regardless of the temperature change or the like, and the spherical aberration of the laser beam in the first layer is optimally corrected, and the reproduction recording can be performed. Stabilize. Further, during the reproduction / recording operation of the second layer, the first layer except that the drive potential information and the target deformation information corresponding to the second layer stored in the storage unit are used instead of the information corresponding to the first layer. It is the same as the case of.

  Further, the structure of the deformable mirror device 1 as described above makes it possible to make the deformed shape of the laser light irradiation area on the mirror surface 3 smooth, to correct spherical aberration with high accuracy, and to reproduce and record an optical disc. Contributes to the stabilization of

These are bottom views of the deformable mirror device according to the present invention. These are sectional drawings in the AA line of FIG. 1 (however, the base 9 is also displayed). These are figures which show the optical system of the optical pick-up based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shape variable mirror apparatus 2 Mirror base material 3 Mirror surface 4 Common electrode 5, 6 Piezoelectric material 7, 8 Drive electrode 9 Base 10 Deformation detection sensor 11 Irradiation part 12 Laser diode 13 PBS
14 Cylindrical lens 15 Photo detector 16 Collimator lens 17 1/4 wavelength plate 18 Objective lens 19 Optical disk

Claims (5)

A mirror base material formed of silicon and having a mirror surface; a first electrode formed on the mirror base material facing the mirror surface; and a piezoelectric material formed on a lower surface of the first electrode; A second electrode formed on the lower surface of the piezoelectric material,
The first electrode, the piezoelectric material, and the second electrode are larger in area than the area of the light beam irradiation region on the mirror surface when the mirror base material and the mirror surface are not deformed. Has upper and lower surfaces,
The irradiation region as viewed from above the mirror surface is configured so as to fall within the regions of the upper and lower surfaces of the first electrode, the piezoelectric material, and the second electrode,
A variable shape mirror device, wherein a sensor for detecting deformation of the mirror surface made of a piezoelectric polymer is provided on the mirror surface. A mirror base material on which a mirror surface is formed, a first electrode formed on the mirror base material so as to face the mirror surface, a piezoelectric material formed on the lower surface of the first electrode, and the piezoelectric material A second electrode formed on the lower surface of the
The first electrode, the piezoelectric material, and the second electrode are larger in area than the area of the light beam irradiation region on the mirror surface when the mirror base material and the mirror surface are not deformed. Has upper and lower surfaces,
The variable shape is characterized in that the irradiation region as viewed from above the mirror surface is configured to fall within the regions of the upper and lower surfaces of the first electrode, the piezoelectric material, and the second electrode. Mirror device.   The variable shape mirror device according to claim 2, wherein a sensor for detecting deformation of the mirror surface is provided on the mirror surface.   The variable shape mirror device according to claim 3, wherein the sensor has lower rigidity than the mirror base material.   An optical pickup comprising the variable shape mirror device according to claim 1.

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