JP4487523B2 - Optical pickup aberration correction mirror - Google Patents

Description

  The present invention relates to an optical pickup of an optical device or an optical disk device, and more particularly to a wavefront aberration correction mirror thereof.

  As an information recording medium using an optical disk, there are a compact disk (CD) and a digital video disk (DVD). In recent years, an optical disk apparatus is generally configured to read and write a plurality of recording media with the same optical disk apparatus, and a technique for making the optical disk apparatus smaller than before is required. In particular, there is an increasing need for a compact and thin optical disk device for a notebook PC. In addition, with the development of multimedia technology, the demand for storage or recording capacity on an optical disc tends to increase year by year. (1) Use a blue laser having a shorter wavelength than conventional ones. (2) Opening of an objective lens The recording density can be improved by means such as increasing the number (NA), and (3) the recording area can be increased by using a plurality of recording layers in the medium, thereby achieving a large capacity. Yes.

  The optical disk device is provided with a laser light source, an optical pickup, a light receiving element, and the like. The laser beam emitted from the laser light source is condensed on the data surface of the optical disc through the optical pickup, reflected, and then received by the light receiving element, and the information recorded on the optical disc is read or the information is written on the optical disc. . At this time, the wavefront of the beam is subjected to aberrations by various optical components and optical disks, so that aberration correction is indispensable for reading and writing information correctly. In particular, with respect to dynamic aberrations that occur during rotation of an optical disk or when different layers are read, fixed correction means using lenses and diffractive optical elements that constitute an optical pickup are inappropriate, and dynamic correction by an actuator is not possible. It is essential.

  The conventionally proposed aberration correction means will be outlined below using prior literature.

  In the method described in Patent Document 1, spherical aberration is corrected by moving a correction lens by an actuator. However, this method has a large actuator portion, requires an extra lens, and is unsuitable for optical pickups that are required to be miniaturized, such as PC applications.

  In the method described in (Patent Document 2), a method for correcting spherical aberration by moving one of the collimator lenses by an actuator is disclosed, but similarly, the actuator portion is large and an extra lens is required. There is a problem that it is unsuitable for optical pickups that are required to be miniaturized, such as applications.

The aberration correction mirror described in (Patent Document 3) has a configuration in which a flange made of a soft material is bonded to a mirror having an initial spherical shape, and a piezoelectric element is attached to the back surface of the flange. The curvature of the mirror is changed by the deformation of. However, this method has problems that it is difficult to produce a small mirror accurately and inexpensively and that the mirror is deformed when a flange or a piezoelectric element is bonded. Moreover, even if the bonding is performed with high accuracy, it is not necessary to use a solid electrode and a piezoelectric element with a completely fixed periphery and a practical voltage range. The deformation amount of the element is extremely small, and there is a problem that the deformation amount necessary for aberration correction cannot be obtained. Furthermore, even if it is deformed, there is a problem that it is difficult to deform it into an arbitrary spherical shape. Here, the practical voltage level refers to a voltage smaller than the upper limit value of the voltage due to insulation and polarization efficiency. In addition, since a bulk piezoelectric element is used, there is a problem that a relatively high voltage of about 50 V is required for the driving voltage.

  In the method described in (Patent Document 4), in a rectangular piezoelectric element, by applying a voltage in a configuration in which a pair of opposing sides are fixed and the other pair of sides are free, the piezoelectric element is deformed, A method for reducing coma is disclosed. However, in this method, since the shape of the piezoelectric element is basically a beam shape, there is a problem that spherical aberration cannot be corrected no matter how many electrodes are combined.

  In the method described in (Patent Document 5), an example is shown in which an electrode having a shape corresponding to coma aberration is formed on a piezoelectric element, and the piezoelectric element is deformed by applying a voltage to reduce coma aberration. . However, even in this method, if the periphery of the piezoelectric element is fixed, the displacement is actually very small within the practical voltage range, and a displacement sufficient for aberration correction cannot be obtained. In particular, there is a problem that it is not suitable for an optical pickup drive using an objective lens having a high NA.

  As described above, in the prior example, the wavefront aberration of the beam is achieved by mechanically moving the position of the lens (Patent Documents 1 and 2) or mechanically deforming the mirror (Patent Documents 3, 4, and 5). It was proposed to correct. In the former example, there is a problem that the driving device for changing the position of the lens is large and does not satisfy the demand for downsizing. On the other hand, in the latter example, since the piezoelectric element is used, there is a problem that the amount of deformation is small although the requirement for miniaturization is satisfied. Here, in order to explain this problem, the basic operation of the piezoelectric element will be described with reference to FIG. A piezoelectric body is an electromechanical energy conversion element. When an electric field is applied, it generates mechanical stress and causes elastic deformation. When an elastic body is joined to the piezoelectric body, the entire body is deformed according to the material property (elasticity) of each material by the action of the piezoelectric body. FIG. 18 is a perspective view showing the state of deformation of the piezoelectric body before and after applying the voltage. The piezoelectric body 1 before applying an electric field is a rectangular parallelepiped, and is arranged as shown in FIG. 18 with respect to the orthogonal coordinate system. The piezoelectric body 1 is preliminarily polarized in the + z direction. At this time, the piezoelectric strain constant of the piezoelectric body 1 is represented by, for example, a matrix of (Expression 1) expressed in a so-called d format.

At this time, the distortion S due to the electric field E is expressed as S _i = d _ij E _{j in the} component display.
It is represented by Here, the index is i = 1, 2, 3, 4, 5, 6 and j = 1, 2, 3 is taken. As shown in FIG. 18, when the electric field is in the + z direction, since only E ₃ is non-zero, only S ₁ , S ₂ and S ₃ are non-zero from (Equation 1), and only S ₁ is present. Is negative and S ₂ and S ₃ are positive. According to the notation convention for piezoelectric elements, S ₁ = S _xx , S ₂ = S _yy , S ₃ = S _zz and only S _xx is a negative sign, so it shrinks in the x direction and y and z directions You can see that The piezoelectric body 2 in FIG. 18 schematically shows a deformed shape due to the expansion and contraction after the electric field is applied.

  FIG. 19 is a sectional view of a unimorph type piezoelectric element in which the piezoelectric body 3 and the elastic body 4 are joined together. The piezoelectric body 3 is assumed to be polarized in the + z direction as described above. An elastic body 4 is joined under the piezoelectric body 3. The displacement of the left end face of the drawing is completely restrained and the other end is made free. FIGS. 19A and 19B show states before and after application of an electric field, respectively. When an electric field is applied in the + z direction, the piezoelectric body 3 tries to shrink in the x direction as in the above discussion, but since the left end is fixed, the elastic body 4 receives a bending moment and protrudes downward. Therefore, it warps in the + z direction. The overall displacement is determined by the elastic constants of the piezoelectric body and the elastic body and the film thickness in addition to the piezoelectric strain constant. Conversely, when an electric field is applied in the -z direction, the piezoelectric body 3 tends to extend in the x direction, so that the elastic body 4 receives a bending moment with a reverse polarity and becomes convex upward and warps in the -z direction (not shown). ).

Next, a case where displacement is constrained at both ends of the piezoelectric element will be described. FIG. 20 is a sectional view of a unimorph type piezoelectric element in which the piezoelectric body 3 and the elastic body 4 are joined together. Unlike the case where only one end is fixed, when both ends are completely fixed, a bending moment hardly occurs as shown in FIG. 20, and the displacement becomes extremely small. Since there is a practical upper limit for the electric field strength applied to the piezoelectric body due to limitations such as dielectric breakdown, it can be said that almost no deformation appears within such a range of electric field strength. Even if a very small displacement is obtained, the amount of aberration to be corrected is larger than in the case of an optical system using an objective lens having a high NA number or an optical system with a short wavelength. Since the required amount of displacement of the mirror shape is several to several tens of times the wavelength of the light used, it is impossible to obtain such a large displacement in the configuration shown in FIG. In order to correct spherical aberration, first, the mirror shape is a circle, and secondly, the mirror needs to be deformed into a spherical surface. In order to transform into a spherical surface, symmetry around the mirror-shaped optical axis is very important. Therefore, in order to dynamically hold the circular mirror in an axisymmetric manner, it is necessary to completely fix the mirror circumference. However, from the above description, the displacement of the piezoelectric element mirror whose circumference is completely fixed is remarkably small. Therefore, it has been difficult to achieve aberration correction by the piezoelectric element by the conventional method.
JP-A-10-241201 Japanese Patent Laid-Open No. 10-134400 Japanese Patent Laid-Open No. 10-039122 JP 2001-34993 A JP 2002-279777 A

  The problem to be solved by the present invention is to provide an aberration correction mirror that is small in size, power saving, low voltage, inexpensive and excellent in accuracy. In particular, an object is to provide a practical mirror for correcting spherical aberration.

Therefore, the present invention comprises a substrate, a piezoelectric body, a pair of electrode films sandwiching the piezoelectric body, an elastic body, and an optical reflecting film, and the substrate has a cavity portion that is substantially symmetrical with respect to the optical axis, Each of the pair of electrode films is divided into at least two of a first electrode and a second electrode, the first electrode is substantially symmetrical with respect to the optical axis, the second electrode is disposed so as to surround the first electrode, The first electrode and the second electrode in the body are polarized so that the directions of polarization are opposite to each other, and the electric field in the piezoelectric body is in the same direction between the first electrodes and the second electrode. characterized Rukoto driven given potential. In this aberration correction mirror, since the electrodes are circular, the mirror shape when deformed becomes a spherical surface, which is optimal for correcting spherical aberration. Further, since an inflection point is generated at the electrode division position, there is an effect that a large displacement of about several microns can be obtained at a low voltage. Furthermore, by making the mirror shape elliptical, it is possible to correct spherical aberration at all incident angles, including when the angle of the light beam incident on the mirror is vertical (in this case, the mirror shape is circular). Have

  Another embodiment of the present invention is characterized in that the cavity portion is circular. This configuration has an effect of effectively correcting the spherical aberration particularly when the light beam is perpendicularly incident on the mirror.

  Another embodiment of the present invention is characterized in that the first electrode shape is circular. This configuration has an effect of effectively correcting the spherical aberration particularly when the light beam is perpendicularly incident on the mirror.

  Another embodiment of the present invention is characterized in that the cavity portion and the first electrode shape are concentric. This configuration has an effect that the accuracy of spherical aberration correction is particularly high.

  Another aspect of the present invention is characterized in that a ratio r / R between the first electrode outer diameter r and the second electrode outer diameter R is 0.7 or more and less than 1. By setting the ratio r / R to approximately 0.75, there is an effect that the maximum amount of displacement can be obtained when a certain voltage is applied regardless of the outer diameter of the element. Further, as the ratio r / R approaches 1, the size of the entire element is reduced with respect to a necessary mirror diameter, so that the number of steps is increased and the cost is reduced.

  Another embodiment of the present invention is characterized in that the initial shape of the mirror is substantially planar. Thereby, it is not necessary to form a mirror shape in the initial stage, and the manufacturing is easy.

  Another embodiment of the present invention is characterized in that the lead line from the first electrode is symmetric with respect to the axis of the first electrode. With this configuration, since the lead line does not break the symmetry of the mirror shape, effective spherical aberration correction can be performed.

  Another embodiment of the present invention is characterized in that the piezoelectric body is a thin film. This has the effect that a voltage smaller than that of the bulk is required to obtain a piezoelectric strain having an appropriate size. In particular, there is an effect that a necessary deformation amount can be obtained from several volts to ten and several volts.

  In another embodiment of the present invention, by using only the first electrode of the deformed piezoelectric element as a mirror, only a spherical portion can be selectively used, and optimal spherical aberration correction can be performed.

  With the above configuration, the reflecting surface can be accurately deformed, so that aberrations, particularly spherical aberration, can be reduced, and when used as an optical pickup, recording / reproducing characteristics can be improved.

According to the first aspect of the present invention, a substrate having a cavity portion, a piezoelectric body provided opposite to the cavity portion, a pair of electrode films sandwiching the piezoelectric body, and provided opposite to the cavity portion An elastic body and an optical reflection film provided to face the cavity, wherein the pair of electrode films are each divided into at least two of a first electrode and a second electrode, and the second electrode is the first electrode The piezoelectric body is disposed so as to surround one electrode, and the piezoelectric body is subjected to polarization treatment in different directions between the first electrode and the second electrode, and between the first electrode and the second electrode, an optical science pickup aberration correcting mirror field in the body, characterized in Rukoto driven given the potential to be the same direction, it is possible to accurately deform the optical reflective film, in particular small spherical aberration It can be.

  The invention according to claim 2 is the optical pickup aberration correcting mirror according to claim 1, wherein the cavity portion is circular, and since the incident light beam is generally circular in cross section, it is almost Aberrations can be corrected throughout.

  The invention according to claim 3 is the optical pickup aberration correcting mirror according to claim 1, wherein the first electrode is circular, and since the incident light beam is generally circular in cross section, Aberrations can be corrected almost throughout.

  The invention according to claim 4 is the optical pickup aberration correcting mirror according to claim 1, wherein the cavity portion and the first electrode are concentric with each other, and the aberration can be reliably corrected.

  According to a fifth aspect of the present invention, the ratio r / R between the first electrode outer diameter r and the second electrode outer diameter R is 0.7 or more and less than 1, and the optical according to claim 1 This is a pickup aberration correction mirror, which can efficiently deform the reflective film and increases the amount of elements that can be obtained during manufacturing, which is advantageous in terms of cost.

  The invention according to claim 6 is the optical pickup aberration correcting mirror according to claim 1, wherein the initial shape of the mirror is a substantially flat surface, and the initial state of the reflecting film can be specified, so that the operation is accurate. realizable.

  The invention according to claim 7 is the optical pickup aberration correction mirror according to claim 1, wherein the lead-out line from the first electrode is symmetric with respect to the axis of the first electrode, and the reflective film is accurately formed. Can be deformed.

  The invention according to claim 8 is the optical pickup aberration correction mirror according to claim 1, wherein the piezoelectric body is a thin film, and can be driven even at a relatively low voltage, so that power saving can be realized. .

  According to a ninth aspect of the present invention, in the reflective film, the portion corresponding to the first electrode or the inside thereof is used as a mirror. Aberration can be reduced.

  The invention according to claim 10 is the optical pickup aberration correcting mirror according to claim 1, wherein the cavity portion is substantially symmetrical with respect to the optical axis, and the aberration can be reliably reduced.

  An eleventh aspect of the present invention is the optical pickup aberration correcting mirror according to the first aspect, wherein the first electrode is substantially symmetrical with respect to the optical axis, and the aberration can be reliably reduced.

Example 1
Hereinafter, a basic configuration of an embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG. 1 is a schematic cross-sectional view of a unimorph type piezoelectric element in a beam shape in which a piezoelectric body 3 and an elastic body 4 are joined together. The piezoelectric body 3 is polarized in the + z direction. In contrast to the prior art, in the present invention, the polarization direction is not unidirectional, but is polarized in the + z direction in the left region in the figure and in the −z direction in the right region. At this time, it can be understood from the above description that the region on the left side of the drawing is convex downward and the region on the right side of the drawing is convex upward. Therefore, an inflection point is generated near the boundary between both regions. Using this fact, when a polarization distribution that is alternately inverted as shown in FIG. 2 is given, a bending moment is generated so that a convex shape is formed at the center and a convex shape is formed at both ends. Can be obtained at two locations, so that a large displacement can be obtained even when both ends are constrained. Since any number of inflection points can be created using the same method, it is possible to create a mirror having a practical amount of displacement and capable of handling various aberrations. FIG. 3 is a schematic view showing one form for realizing the same effect in a circular shape, and shows a plan view and a cross-sectional view through the center. An upper electrode is formed on the upper portion of the piezoelectric body 3 and a lower electrode is formed on the lower portion thereof. The upper electrode is divided into an upper first electrode 5 and an upper second electrode 6 by an insulating portion 7. Similarly, the lower electrode is also divided into a lower first electrode 8 and a lower second electrode 9 by the insulating portion 7. With this configuration, the first electrode and the second electrode in the upper electrode and the lower electrode can be polarized in different directions by applying electric fields having different polarities to each other, as described above. In this case, a large displacement can be obtained. Further, in the present embodiment, the insulating portion 7 is configured with a spatial gap, but the insulating portion 7 may be configured by embedding an insulating material such as silicon dioxide or alumina in the gap. In addition, when expressing as the 1st electrode and 2nd electrode demonstrated below, a 1st electrode shows at least one of the upper 1st electrode 5 and the lower 1st electrode 8, and a 2nd electrode is the upper 2nd electrode 6 And at least one of the lower second electrode 9 is shown.

Next, FIG. 16 shows a basic configuration example of the optical pickup. The light beam emitted from the light source 47 passes through the beam splitter 49, is reflected by the aberration correction mirror 48 that also serves as a rising mirror, passes through the objective lens 41, and forms an image on the optical disk 42. The reflected light is reflected by the aberration correction mirror, reflected by the beam splitter 49, and converted into an electrical signal by the light receiving element 40. In this configuration, the light beam enters the aberration correction mirror 48 at 45 degrees. The aberration correction mirror 48 is supplied with a control voltage from the driver 50. The driver 50 determines the value of the control voltage based on a signal from at least one light receiving means such as a light receiving means for monitoring (not shown) or a light receiving element 40 for detecting the amount of spherical aberration, The curvature can be changed. In particular, the above configuration is particularly useful when the light emitted from the light source 47 is light of a short wavelength from blue to violet.

  FIG. 17 shows a configuration of an optical pickup in another form. The light beam emitted from the light source 47 is transmitted through the polarization beam splitter 44, reflected from the rising mirror 45, and condensed on the optical disk 42 through the quarter wavelength plate 43 and the objective lens 41. Thereafter, the light reflected from the optical disk 42 changes its polarization state by 90 degrees, passes through the rising mirror 45, is reflected by the polarization beam splitter 44, passes through the other quarter wavelength plate 43, and is reflected by the aberration correction mirror 48. Then, after passing through the quarter-wave plate again to change the polarization state by 90 degrees, it passes through the polarizing beam splitter 44 and is converted into an electric signal by the light receiving element 40. The aberration correction mirror 48 is supplied with a control voltage from the driver 50. The driver 50 determines the value of the control voltage based on a signal from at least one light receiving means such as a light receiving means for monitoring (not shown) or a light receiving element 40 for detecting the amount of spherical aberration, The curvature can be changed. In particular, the above configuration is particularly useful when the light emitted from the light source 47 is light of a short wavelength from blue to violet.

Next, a specific configuration of the aberration correction mirror according to the embodiment of the present invention will be described with reference to FIGS. 4, 5, and 6. FIG. 4 is a cross-sectional view showing the layer structure of the aberration correction mirror. In FIG. 4, a cavity portion 33 is formed in the substrate 16. The layer structure is the reflective film 29 provided in the cavity part 33 in order from the bottom, the elastic body 4 provided so as to cover the cavity part 33 and bonded to the reflective film 29 and the substrate 16, and substantially the same plane on the elastic body 4. The lower first electrode 8 and the lower second electrode 9 provided, the piezoelectric body 3 provided on the elastic body 4 so as to cover the lower first electrode 8 and the lower second electrode 9, and substantially above the piezoelectric body 3. An elastic body 4 provided on the piezoelectric body 3 is disposed so as to cover the upper first electrode 5 and the upper second electrode 6, the upper first electrode 5 and the upper second electrode 6 provided in the same plane, and the cavity In the range within the diameter of the portion 33, the film can be freely deformed. The circumference of the cavity portion 33 serves as a fixed boundary that restrains the displacement of the film. The cavity portion 33 is made thinner than the other portions of the substrate 16 by removing a part of the substrate 16 and forming a recess. Provided. FIG. 5 shows a plan view of the lower electrode. The lower electrode is divided into two electrodes, a circular lower first electrode 8 and an annular lower second electrode 9 concentric with the lower first electrode by the insulating portion 7. The lower first electrode 8 is connected to the electrode pad 20, and the lower second electrode 9 is connected to the electrode pad 21. FIG. 6 shows a plan view of the upper electrode. The upper electrode is also divided into the same shape as the lower electrode, and is composed of the upper first electrode 5, the upper second electrode 6, and the insulating portion 7. Wirings are routed from the upper first electrode 5 and the upper second electrode 6 to the electrode pads 25 and 26, respectively. In each of the upper electrode and the lower electrode, the second electrode is provided with a portion where the electrode is not arranged in part, and a wiring drawn from the first electrode is provided through the non-arranged portion of the electrode. The second electrode has an annular shape and is substantially C-shaped.

  Next, an example of manufacturing the above configuration will be described. First, the elastic body 4, the lower first electrode 8 and the lower second electrode 9 are formed on one surface of the flat substrate 16, the piezoelectric body 3 is formed thereon, and the upper first electrode 5 is formed on the piezoelectric body 3. And the upper 2nd electrode 6 is formed and the elastic body 4 is provided on it. Thereafter, patterning is performed on the surface opposite to the surface of the substrate 16 on which the laminated film is formed using a photolithography technique or the like, and dry etching or wet etching is performed until the elastic body 4 on the substrate 16 side is exposed. To process. Thereafter, a reflective film 29 is formed from the side where the elastic body 4 is etched.

As another method, in the above process, etching is not performed until the elastic body 4 is exposed, and a part of the substrate 16 is left in the etched portion. Since a part of the substrate 16 is formed very thin, it can be easily displaced. Similar to the above, the reflective film 29 is formed on the thinned portion of the substrate 16.

  As still another method, the laminated film is formed on another substrate, and a through hole or a recess serving as the cavity portion 33 is formed in the substrate 16, and then the other substrate is pressed against the substrate 16 and the laminated film is applied to the substrate 16. Alternatively, a method of transferring so as to cover the cavity portion 33 may be used.

  In the present embodiment, the cavity portion 33 is configured such that the cross-sectional area is large on the side opposite to the side where the laminated film is provided, and the cross-sectional area is small on the laminated film side, so that light can be efficiently transmitted. Although it can be led to the reflective film 29, the cavity 33 may be configured with the same cross-sectional area depending on the specifications, or the cross-sectional area on the laminated film side may be increased and the cross-sectional area on the opposite side may be decreased. good. In the present embodiment, since the cross-sectional shape of the cavity portion 33 is circular, the cross-sectional diameter on the laminated film side is small and the cross-sectional diameter on the opposite side is large.

  Further, in the above configuration, when the upper first electrode 5 and the lower second electrode 9 are grounded and the voltage V is applied to the upper second electrode 6 and the lower first electrode 8, the contour lines (a) of the displacement of the reflective film and A displacement diagram (b) is shown in FIG. In the figure, C, C ′ and D, D ′ correspond to the positions of the insulating portion and the cavity portion circumference, respectively. The position of D and D ′ is the cavity circumference, and since the displacement is constrained here, the displacement is zero. The displacement is convex downward at the annular portion corresponding to CD and C′-D ′, and convex upward at the portion corresponding to the diameter of CC ′ with the boundary of C and C ′ as the boundary. The reason why the sign of the curvature is reversed at the electrode division position as described above is as described above. In order to correct spherical aberration, a spherical shape is generally required, but the curved surface shape at CC ′ is a spherical shape. Therefore, in the present invention, the curved surface portion in C-C ′, that is, the portion of the reflective film corresponding to the shape of the first electrode, or the inside thereof is used. Thereby, it is possible to realize aberration correction with extremely high accuracy.

  FIG. 8 shows an example of the shape of the upper electrode and the cavity portion 33 in the aberration correction mirror that is preferably applied when the light beam is obliquely incident on the aberration mirror (the extraction electrode and the routing electrode are not shown). The upper electrode (FIG. 8A) and the cavity 33 (FIG. 8B) form a concentric ellipse. With this configuration, spherical aberration can be effectively corrected even for obliquely incident light. The lower electrode has the same shape as the upper electrode (hereinafter, the electrode shape will be described using only the upper electrode). The shapes of the first electrode and the cavity need not be (elliptical) circular as long as they have symmetry with respect to the optical axis. For example, as shown in FIG. 9, it may be a regular hexagon. FIGS. 9A and 9B show the upper electrode and the cavity part, respectively (the extraction electrode and the routing electrode are not shown). FIG. 10 shows a displacement contour line and a displacement amount graph in the E-E ′ section in the configuration of FIG. 9. In each cross section passing through the central axis, the displacement has a shape represented by an even-numbered term of second order and higher order. C and C ′ are locations corresponding to the division positions that insulate the first electrode from the second electrode. D and D ′ are locations corresponding to the circumference of the cavity portion 33. The contour lines of the overall displacement reflect the shape of a regular hexagon at the periphery of the cavity, but it can be seen that it converges to a circle as it goes to the center. According to the present invention, since the inside of the first electrode is used as a mirror part, it is possible to correct spherical aberration satisfactorily even if the electrode shape is a hexagon.

  Thus, the first electrode and the cavity shape may be any regular polygon. Further, the first electrode and the cavity shape do not necessarily have the same shape as long as they have some symmetry with respect to the central axis. For example, even if the first electrode is circular and the cavity shape is a regular hexagon, the same effect can be obtained according to the present invention.

  Since the displacement is constrained by the circumference of the cavity, the shape of the second electrode essentially does not play an important role. Therefore, the effect of the present invention is not reduced even if the shape is at least the same shape as the cavity portion or the shape completely including the cavity portion.

  Any number of wiring portions from the first electrode to the electrode pad may be arranged radially from the central axis. In FIG. 11, four lines are drawn so as to be four-fold symmetric with respect to the central axis (not shown). It is also possible to draw out 8 lines with 8 times symmetry. It is preferable to arrange the lead lines so as to increase the symmetry with as few as possible. In addition, since the lead line is arranged outside the cavity portion, any geometric shape does not reduce the effect of the present invention.

A calculation example calculated using general-purpose analysis software ANSYS is shown below. The cavity was a circle with a radius of 2 mm, and a 10.7 μm thick cylinder on the cavity was used as the analysis region. From the bottom, the layer structure is SiO ₂ (elastic body): 1 μm, Ti (lower electrode): 0.2 μm, PZT (piezoelectric body): 3 μm, Cr (upper electrode): 0.5 μm, SiO ₂ (elastic body): 1 μm, Ni (elastic body): 5 μm. Both the upper electrode and the lower electrode were divided into a first electrode and a second electrode by a 20 μm annular insulating portion. The first electrode was a circle (column) having a radius of 1.49 concentric with the cavity portion, and the second electrode was a ring (column) having an inner radius of 1.51 mm and an outer radius of 2.0 mm. Piezoelectric analysis was performed by applying 0 V to the upper first electrode 5, 10 V to the lower first electrode 8, 10 V to the upper second electrode 6, and 0 V to the lower second electrode 9, and obtained a displacement as shown in FIG. FIG. 12 shows the amount of displacement in a certain cross section passing through the central axis in the entire cavity portion 33. It can be seen that a spherical shape is obtained inside the first electrode, that is, in the range of −1.49 to +1.49. FIG. 13 shows a graph in which the absolute value of the displacement is plotted with the displacement data when the potential difference of 4, 5 and 6 V is applied in the same configuration and the maximum displacement portion (center) as the origin, and only the mirror portion (reflection film 29). The displacement shape and the amount of displacement are shown. Thus, spherical shapes having different shape factors can be obtained by changing the magnitude of the potential difference.

  Further, in the same configuration, the division position in the radial direction of the cavity portion 33 of the upper electrode is set to 1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7 / with respect to the cavity radius. FIG. 14 shows a displacement diagram in the radial direction of the entire cavity portion 33 when changed to 8. The position is normalized by the cavity radius. (2) indicates the electrode division position. Thus, the displacement amount and the deformed shape can be changed also by changing the electrode dividing position. FIG. 15 shows the relationship between the maximum displacement amount in each of the cavity portion and the mirror portion with respect to the electrode division position. As a result, it was discovered that the amount of displacement of the mirror part (reflective film 29) is a maximum in the vicinity of the division ratio r / R = 0.75. Here, r and R are a mirror radius and a cavity radius, respectively. That is, it was found that a large deformation amount can be obtained particularly efficiently when the electrode split ratio r / R is in the range of 0.7 to 0.8. On the other hand, when the mirror part (reflective film 29) is created by a semiconductor process and cut out from the wafer, when the mirror diameter is determined, the number of mirrors taken increases as the division ratio r / R approaches 1, Cost is low. Therefore, in order to optimize the deformation efficiency and cost of the mirror, it is derived that the electrode division ratio r / R is preferably about 0.7 or more and less than 1. Further, the same analysis was performed with a cavity diameter of 1.5 mm and 1 mm, and the same results as in FIG. 15 were obtained. Furthermore, in the hexagonal cavity and the electrode shape as shown in FIG. 9, when the division ratio r / R is defined for the hexagonal circumscribed circle, the mirror portion displacement amount is similarly in the range of 0.7 to 0.8. The maximum value was obtained. From the above, by setting the ratio of the mirror diameter to the cavity diameter to be not less than 0.7 and less than 1, it is possible to provide an aberration correction mirror that is most efficient and inexpensive in about an arbitrary shape and an arbitrary size.

The above example is only a preferable example. As long as the present invention is used, dynamic spherical aberration can be effectively corrected by using any practical piezoelectric body 3 and elastic body 4. For example, the piezoelectric body 3 includes PZT (lead zirconate titanate), quartz, LiLiNbO ₃ , LiTaO ₃ , KNbO ₃ , ZnO, AlN, Pb (Zr, Ti) O ₃ , PVDF (polyvinylidene fluoride), and the like. Can be used. The elastic body 4 is Ni, Ti, Cu, Cr, Au, Pt, metal, and the first electrode and the cavity 33 are spherical in any shape as long as there is some degree of symmetry with respect to the central axis. It is possible to correct aberrations effectively. As long as the second electrode has the same shape as the cavity portion 33 or a shape including the cavity portion 33, the second electrode is completely arbitrary as long as wiring is possible. It is clear that the same effect can be obtained even if the upper electrode is a common electrode and the lower electrode is divided. Further, both the upper electrode and the lower electrode may be divided.

  In this embodiment, the optical pickup has been described. However, the present invention can naturally be applied to other optical devices.

  As described above, according to the present invention, it is possible to perform highly accurate spherical aberration correction that is very small, power-saving, and excellent in responsiveness. Therefore, a CD / DVD drive recorder, decoder, CD / It can be used for an optical pickup used in a DVD drive or the like, in particular, an optical pickup using a blue laser or an optical apparatus that requires correction of aberration.

The figure which shows the principle of operation of the aberration correction mirror by this invention The figure which shows the principle of operation of the aberration correction mirror by this invention The figure which shows typically the aberration correction mirror by this invention Sectional view of an aberration correction mirror according to the present invention The top view of the lower electrode in the aberration correction mirror by this invention The top view of the upper electrode in the aberration correction mirror according to the present invention The displacement contour map of the aberration correction mirror according to the present invention and a diagram showing the displacement The top view of the upper electrode and cavity part in another form of this invention The top view of the upper electrode and cavity part in another form of this invention Displacement diagram of aberration correction mirror in the present invention The top view of the upper electrode in another form of the present invention The figure which shows the displacement in the Example of this invention The figure which shows the displacement of the mirror part in the Example by this invention. Displacement diagram in an embodiment according to the present invention The figure which shows the maximum displacement amount of the aberration correction mirror by this invention The figure which shows the optical path of the optical pick-up by this invention The figure which shows the optical path of the optical pick-up in another form by this invention Perspective view showing operation of piezoelectric element Sectional view showing operation of piezoelectric element Sectional view of a piezoelectric element showing the operation of a conventional aberration correction mirror

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element before voltage application (deformation) 2 Piezoelectric element after voltage application (deformation) 3 Piezoelectric body 4 Elastic body 5 Upper first electrode 6 Upper second electrode 7 Insulating part 8 Lower first electrode 9 Lower second electrode 16 Substrate 20 Lower first electrode pad 21 Lower second electrode pad 25 Upper first electrode pad 26 Upper first electrode pad 29 Reflective film 33 Cavity part 40 Light receiving element 41 Objective lens 42 Optical disk 43 1/4 wavelength plate 44 Polarizing beam splitter 45 Raising mirror 47 Light source 48 Aberration correction mirror 49 Beam splitter 50 Driver

Claims (11)

A substrate having a cavity portion, a piezoelectric body provided facing the cavity portion, a pair of electrode films sandwiching the piezoelectric body, an elastic body provided facing the cavity portion, and the cavity portion And a pair of electrode films each divided into at least two of a first electrode and a second electrode, and the second electrode is disposed so as to surround the first electrode. The polarization treatment is performed between the first electrodes and the second electrodes so that the directions of polarization in the piezoelectric bodies are opposite to each other, and the electric field in the piezoelectric bodies is the same between the first electrodes and the second electrodes. An optical pickup aberration correcting mirror, which is driven by being given a potential so as to be in a direction. The optical pickup aberration correcting mirror according to claim 1, wherein the cavity is circular. The optical pickup aberration correcting mirror according to claim 1, wherein the first electrode is circular. The optical pickup aberration correcting mirror according to claim 1, wherein the cavity portion and the first electrode are concentric with each other. 2. The optical pickup aberration correcting mirror according to claim 1, wherein a ratio r / R of the first electrode outer diameter r and the second electrode outer diameter R is 0.7 or more and less than 1. 5. 2. The optical pickup aberration correcting mirror according to claim 1, wherein the initial shape of the mirror is a substantially flat surface. 2. The optical pickup aberration correcting mirror according to claim 1, wherein a lead line from the first electrode is symmetric with respect to an axis of the first electrode. The optical pickup aberration correcting mirror according to claim 1, wherein the piezoelectric body is a thin film. 2. The optical pickup aberration correcting mirror according to claim 1, wherein a part corresponding to the first electrode or an inside thereof is used as a mirror in the reflective film. 2. The optical pickup aberration correcting mirror according to claim 1, wherein the cavity is substantially symmetrical with respect to the optical axis. 2. The optical pickup aberration correcting mirror according to claim 1, wherein the first electrode is substantially symmetrical with respect to the optical axis.

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