JPH1039122A - Curvature variable mirror, and optical pickup device with it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mirror capable of remarkably changing the curvature by a small deformation amount, and to provide an optical pickup device capable of miniaturizing the device constitution, reducing the driving power, and reducing the running cost. SOLUTION: This mirror is a curvature variable mirror 10 provided with a mirror main body 1 having a curved surface part 1a and a flange part 1b, a deformation member 2 consisting of dielectric material, forming electrodes 3, 3' on its upper/lower both side surfaces and connected to the flange part 1b of the mirror main body 1 and a power source circuit provided with a DC power source 4 and a switch 5 and connected to the electrodes 3, 3', and when the switch 5 is turned ON, electric charges are loaded on the electrode 3, and an electric field occurs in the deformation member 2. Then, the deformation member 2 is deformed in the radial direction by a piezoelectric effect, and compression force is imparted from the deformation member 2 to the curved surface part 1a. Thus, since the curved surface part 1a is shrunk in the radial direction, and is expanded in the curved surface direction, the curvature of the curved surface part 1a is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a curvature (radius of curvature).
More particularly, the present invention relates to a variable curvature mirror that can easily change the curvature of a mirror by an external deformation applying means such as a power supply circuit.

[0002]

2. Description of the Related Art FIG. 6 shows the structure of an optical pickup device which has been frequently used. A light beam emitted from the semiconductor laser 31 is reflected by the beam splitter 32 and converted into a parallel light by a light beam collimating lens 34. Next, the parallel light is converged by the objective lens 55 and forms an image point on the recording surface of the optical disk 36.

Here, the focusing error of the optical disk 36 is detected by the photodiode 33, and the information is sent to the objective lens actuator 35 to adjust the focus.

That is, in such an optical pickup device, the objective lens actuator 35 for moving the objective lens 55 is required when adjusting the focus of the optical disk 36. Here, the objective lens actuator 35 has a relatively large configuration and is a precise member, and therefore is relatively expensive.

[0005] For this reason, the conventional optical pickup device has a problem that the device configuration of the optical pickup device becomes large and the price becomes high. There is also a problem that driving of the objective lens actuator 35 requires a large driving power.

In order to solve such a problem, the objective lens actuator 35 may be dispensed with. For this purpose, a reflecting mirror is provided as a means for guiding a light beam to the objective lens 55, and the curvature of the reflecting mirror is reduced. What is necessary is just to make it variable. That is, according to such a variable curvature mirror, the image point position (light spot) of the light beam can be changed.
This is because the focus can be adjusted without providing a means for moving the objective lens.

Thus, the mirror is an optical pickup device,
It is widely used in the optical industry such as a camera and is an indispensable optical member, but often requires a change in the image point position of a light beam as described above.

However, most of the conventional mirrors used in this type of field have invariable curvatures, so that it is difficult to adjust the image point position by the mirror.

Recently, for example, in order to solve the above-mentioned problems, various types of variable curvature mirrors whose curvature can be changed have been proposed. Hereinafter, these variable curvature mirrors will be outlined.

(1) A variable curvature mirror proposed in JP-A-59-148014.

The variable curvature mirror has a configuration in which a piezoelectric element is attached to the entire back surface of the mirror, and the curvature of the mirror is freely changed by using a bending moment generated by expansion and contraction of the piezoelectric element.

(2) A variable curvature mirror proposed in Japanese Patent Application Laid-Open No. 62-186204.

This variable curvature mirror has a configuration in which a shape memory alloy is attached to the entire back surface of the mirror, and the curvature of the mirror is freely changed by using a bending moment generated by expansion and contraction of the shape memory alloy.

(3) A variable curvature mirror proposed in JP-A-2-210302.

This variable curvature mirror has a structure in which a part of a pressure chamber is formed by an elastic mirror, and the curvature of the mirror is freely changed by changing the amount of liquid filled in the pressure chamber. I have.

(4) A variable curvature mirror proposed in Japanese Patent Application Laid-Open No. 7-49460.

This deformable mirror has a configuration in which a voltage is applied to a metal reflection mirror and a counter electrode, and the curvature of the mirror is freely changed using electrostatic force.

[0018]

However, the conventional variable curvature mirror proposed in the above publication has the following problems.

(1) In the variable curvature mirror proposed in JP-A-59-148014, a piezoelectric element is attached to the entire back surface of the mirror, and the curvature is changed by bending the entire mirror by a bending moment. The energy required for deformation is large, and the amount of deformation of the entire mirror is small. As a result,
Since the change in the curvature of the mirror cannot be made large, the image point position cannot be largely changed.

(2) The variable curvature mirror proposed in Japanese Patent Application Laid-Open No. 62-186204 also has a small deformation amount of the entire mirror because the shape memory alloy is attached to the entire back surface of the mirror. As a result, similarly, since the change in the curvature of the mirror cannot be largely changed, the image point position cannot be changed greatly.

(3) In the variable curvature mirror proposed in JP-A-2-210302, an actuator such as a pump must be used when changing the amount of liquid filled in the pressure chamber. Cannot be achieved. In addition, there is also a problem that accuracy is deteriorated due to the influence of vibration caused by driving the pump.

(4) In the variable curvature mirror proposed in Japanese Patent Application Laid-Open No. 7-49460, the driving voltage is large due to the device configuration (for example, the applied voltage is 2300 V in the embodiment). For example, there is a problem that the running cost of the optical pickup device equipped with the deformable mirror is high.

The present invention has been made in view of the above circumstances, and has as its object to provide a variable curvature mirror that can greatly change the image point distance with a small amount of deformation and can reduce the driving voltage. .

Another object of the present invention is to provide an optical pickup device having such a deformable mirror, whereby the size of the optical system can be reduced, and the cost and running cost can be reduced.

[0025]

SUMMARY OF THE INVENTION A variable curvature mirror according to the present invention comprises a mirror body having a curved surface portion made of an elastic material and reflecting an incident light, and a flange formed on an outer periphery of the curved surface portion; A deformable member attached to the portion for expanding and contracting the mirror body in the radial direction; and a deformation applying means for deforming the deformable member, thereby achieving the above object.

Preferably, the deformation member is a disk-shaped piezoelectric member having electrodes formed on both side surfaces, and the deformation applying means is a power supply circuit for turning on / off the electrodes.

Further, an optical pickup device according to the present invention includes a variable curvature mirror according to claim 1 or 2, and is configured to guide a light beam reflected by the variable curvature mirror to an objective lens. Objective is achieved.

The operation of the present invention will be described below with reference to FIG. As shown in FIG. 2, the variable curvature mirror 10 of the present invention
Is a mirror body 1 having a curved surface portion 1a and a flange portion 1b, a deformable member 2 made of a piezoelectric material, having electrodes 3 and 3 formed on both upper and lower side surfaces, and adhered to the flange portion 1b of the mirror body 1; It has a power supply 4 and a switch 5 and includes a power supply circuit connected to the electrodes 3 and 3.

FIG. 2A shows a state where the switch 5 is OFF. In this state, the deformable member 2 does not deform, and the curved surface portion 1a
Maintains a predetermined curvature.

FIG. 2B shows a state where the switch 5 is ON. In this state, an electric charge is applied to the electrode 3 and an electric field is generated in the deformable member 2 made of a piezoelectric material. Then, the deformable member 2 tends to deform in the radial direction due to the piezoelectric effect. Therefore, a compressive force is applied from the deformable member 2 to the curved surface portion 1a. As a result, the curved surface portion 1a shrinks in the radial direction and expands in a curved surface direction orthogonal thereto, so that the curvature of the curved surface portion 1a decreases as shown in FIG. 2B.

As described above, according to the present invention, the curved surface portion 1a can be largely expanded outward with a relatively small reduction amount in the radial direction by the compressive force. That is, JP-A-59
The deformation structure of the mirror is different from that of the variable curvature mirror proposed in JP-A-148014 and JP-A-62-186204, and the energy required for the deformation is small. Therefore, the curvature of the curved surface portion 1a is largely changed with a small deformation amount. be able to. Therefore, the drive voltage may be low due to the good deformation performance. Further, according to such a variable curvature mirror, since the deformability of the curvature is large, the image point position of the light beam which is narrowed down by the objective lens and connects the image point to the far side can be largely changed. As a result, unlike the above-described conventional optical pickup device, an objective lens actuator for focus adjustment is not required. As a result, it is possible to realize an optical pickup device that has a low driving voltage, is small and inexpensive, and has a low running cost.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIGS. 1 to 3 show Embodiment 1 of the present invention. First, the configuration of the variable curvature mirror of the present invention will be described with reference to FIG.

The variable curvature mirror 10 includes a mirror main body 1 made of an elastic material and a disk-shaped deformable member 2 attached to the mirror main body 1. The DC power supply 4 shown in FIG. When a DC voltage is applied to the electrode 3 provided on the deformable member 2, the deformable member 2 contracts in the radial direction, and at that time, the mirror body 1 is deformed by a compressive force applied from the deformable member 2 to the mirror body 1, This provides a basic structure for changing the curvature.

The mirror body 1 will now be described more specifically.
Has a curved surface portion 1a and a disk-shaped flange portion 1b continuously provided on the opposite side of the curved surface portion 1a, and is made of, for example, a flexible plastic. A reflective film made of, for example, Al is formed on the surface of the curved surface portion 1a, and can reflect light rays (incident light).

The deformable member 2 is made of, for example, a piezoelectric material, and is adhered to the flange 1b of the mirror body 1 with an adhesive, for example. Electrodes 3 and 3 are formed of, for example, Ag on both side surfaces of the deformable member 2, that is, on both upper and lower surfaces in the figure.

Next, the driving principle of the variable curvature mirror, that is, the variable curvature principle will be described with reference to FIG. As shown in FIG. 2, the upper and lower electrodes 3 and 3 are connected to a power supply circuit having a DC power supply 4 and a switch 5. In brief, the upper and lower electrodes 3 and 3 are connected to the anode and cathode of the DC power supply 4, respectively. With such a configuration, loading and unloading of electric charges can be performed by turning on / off the switch 5.

FIG. 2A shows a state where the switch 5 is OFF. In this state, the deformable member 2 does not deform, and the curved surface portion 1a
Maintains a predetermined curvature.

FIG. 2B shows a state where the switch 5 is ON. In this state, an electric charge is applied to the electrode 3 and an electric field is generated in the deformable member 2 made of a piezoelectric material. Then, the deformable member 2 tends to deform in the radial direction due to the piezoelectric effect. Therefore, a compressive force is applied from the deformable member 2 to the curved surface portion 1a. As a result, the curved surface portion 1a contracts in the radial direction and expands in the curved surface direction orthogonal thereto, so that the curvature of the curved surface portion 1a decreases as shown in FIG. 2B.

As described above, according to the curvature variable mirror 10 of the first embodiment, the curved surface portion 1a can be largely expanded outward by a compressive force with a relatively small reduction amount in the radial direction. That is, the curvature of the curved surface portion 1a can be largely changed with a small amount of deformation. Therefore, the drive voltage may be low due to the good deformation performance.

As is clear from the above description, the variable curvature mirror of the present invention is configured such that the direct current is turned on / off from the power supply circuit to the electrodes 3 and 3 formed on the deformable member 2 so that the curved surface portion of the mirror main body 1 is turned on. The configuration is such that the curvature of 1a can be easily changed.

Next, the reason why the image point position can be changed by using the variable curvature mirror 10 of the present invention will be described with reference to FIG. FIG. 3 shows an optical system including the variable curvature mirror 10 of the present invention as a reflection mirror. That is, this optical system has a configuration in which a light source 7 made of, for example, a semiconductor laser is disposed on one side of the variable curvature mirror 10 and an objective lens 8 is disposed below the variable curvature mirror 10.

The light beam 6 emitted from the light source 7 travels straight in the horizontal direction, is reflected downward by the curved surface portion 1a of the mirror body 1, and
The light enters the objective lens 8. The objective lens 8 condenses the incident light and connects an image point 9 below the light.

FIG. 3A shows a state where the switch 5 is OFF. In this state, since the mirror main body 1 is not deformed, the light ray 6 follows the optical path shown in FIG.

On the other hand, when the switch 5 is turned on, the mirror main body 1 is deformed and the curvature of the curved surface portion 1a is reduced for the above-mentioned reason, so that the optical path of the light beam 6 is changed as shown in FIG. Unlike (a), the position of the image point 9 changes. Thus, by changing the curvature of the curvature variable mirror 10, the image point position of the light beam 6 can be changed.

As a specific numerical example, how much the image point position changes in the optical system shown in FIG. The constants used for the calculation are as follows.

Diameter D of mirror body: 6 mm Piezoelectric constant d _{31 of} piezoelectric material: 250 × 10 ⁻¹² m / V Thickness t of piezoelectric material: 25 μm Applied voltage V: 50 V Distance 1 between mirror body and objective lens 1: 5 mm Objective First, the amount of change in the curvature of the mirror body 1 due to contraction of the piezoelectric material is calculated. The radial contraction amount ΔL of the piezoelectric material due to the application of a voltage is given by the following equation (1).

ΔL = d ₃₁ · V · D / t = 3 μm (1) The flat curvature variable mirror 1 due to the contraction of the piezoelectric material
It is assumed that the 0 spherical portion 1a is deformed into a spherical surface. At this time, the length of the arc keeps the diameter D before deformation, and the length of the chord becomes D- 弦 L. The curvature r of the spherical surface is obtained by numerically solving the following equation (2).

Sin (D / 2r) = (D− △ L) / 2r (2) Given the above numerical values and solving equation (2), the curvature r = 54.7.
7 mm.

Next, the light beam is defined as a paraxial light beam and the mirror body 1
Is assumed to be inclined by 45 ° with respect to the optical axis, and the distance δ from the variable curvature mirror 10 to the light object point in the reflected light
Is given by the following equation (3).

Δ = r / 2√2 = 19.4 (3) Next, the distance from the object point of light to the objective lens is represented by u (= δ +
l), assuming that the distance from the objective lens 8 to the image point 9 of light is v, the following equation (4) is established.

V = uf · (uf) (4) When the spherical portion 1a is a plane, the light ray 6 is reflected while being parallel, so that if u = ∞, the image point distance v before deformation is obtained. Is found.

V = f = 3.5 mm When the spherical portion 1a is deformed into a spherical surface, u = δ + 1 = 24.
Assuming that 4, the image point distance v ′ after deformation is obtained.

V '= 4.1 mm That is, it was found that the image point position was changed by 4.1-3.5 = 0.6 mm due to the deformation of the variable curvature mirror 10.

In the variable curvature mirror 10 of the present invention, the driving voltage (applied voltage) required to cause such a change is 50 V as described above.
The driving voltage is much smaller than 2300 V described in the embodiment of the variable curvature mirror proposed in Japanese Patent No. 49460.

(Embodiment 2) FIG. 4 shows Embodiment 2 of the present invention.
Is shown. Embodiment 2 shows an example in which the variable curvature mirror of the present invention is applied to an optical pickup device. That is, FIG. 4 shows the optical pickup device of the present invention.

The same members as those of the optical pickup device shown in FIG. 6 are denoted by the same reference numerals, and redundant description will be omitted, and only different portions will be described below.

The light beam collimated by the light beam collimating lens 34 is reflected by the curvature variable mirror 10 and is reflected by the objective lens 55.
And the image point is formed on the recording surface of the optical disc 36. The focusing error of the optical disk 36 is detected by the photodiode 33, the information is sent to the power supply circuit of the curvature variable mirror 10, and the focus of the optical disk 36 is adjusted only by adjusting the power supply voltage.

That is, in the optical pickup device of the second embodiment, unlike the conventional optical pickup device shown in FIG. 6, focus adjustment is performed only by adjusting the power supply voltage of the curvature variable mirror 10 without using an objective lens actuator. It can be performed. For this reason, first, it is possible to reduce the size and cost of the optical pickup device. Further, for the above-described reason, the driving power (driving voltage) can be reduced, so that there is an advantage that the running cost of the optical pickup device can be reduced.

(Embodiment 3) FIG. 5 shows Embodiment 3 of the present invention.
Is shown. Embodiment 3 shows an example in which the curvature variable mirror of the present invention is applied to an optical pickup device. This optical pickup device shows an example in which the present invention is applied to an optical pickup device capable of accurately recording and reproducing data on two types of optical discs, namely, a DVD (digital versatile disc) and a CD (compact disc). I have.

Since the structure of this optical pickup device is common to that of the optical pickup device shown in FIG. 4, the same members are denoted by the same reference numerals, and a detailed description thereof will be omitted.

The light beam reflected by the deformable mirror 10 and focused by the objective lens 55 is a DVD 36a.
(See FIG. 5A) or CD36b (See FIG. 5B)
The image point is connected to the information recording surface of the image forming apparatus.

Here, since the plate thicknesses (disc thicknesses) of the DVD 36a and the CD 36b are 0.6 mm and 1.2 mm, respectively, the image point position is moved by 0.6 mm in order to reproduce both with one optical system. There must be.

However, the variable curvature mirror 10 of the present invention
Since the image point position can be changed by 0.6 mm with an applied voltage of 50 V as shown in the numerical example above, even if a large image point position change is required as in this application example, The image point position can be changed without using a lens actuator.

Therefore, according to the third embodiment, accurate recording / reproduction can be performed on two types of optical disks such as a DVD and a CD.
In addition, an optical pickup device with low running cost can be realized.

[0066]

According to the variable curvature mirror of the present invention described above,
Since the curvature of the mirror can be largely changed with a small amount of deformation, energy required for deformation, that is, driving power can be reduced. In addition, since the image point position can be largely changed only by changing the curvature of the mirror, when applied to an optical pickup device, the objective lens actuator which is required in the related art becomes unnecessary.

Therefore, according to the variable curvature mirror of the present invention, it is possible to realize an optical pickup device having a low driving voltage, a small size and a low price, and a low running cost.

According to the optical pickup device using such a variable curvature mirror, the driving voltage is low, the device is small and inexpensive, and the running cost is low.
It is possible to realize an optical pickup device capable of accurately recording / reproducing two types of optical disks such as a DVD and a CD.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a variable curvature mirror according to a first embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating a driving principle of a variable curvature mirror according to the first embodiment of the present invention, wherein FIG. 2A illustrates a non-deformed state, and FIG.

FIGS. 3A and 3B are views for explaining a change in an image point position by the curvature variable mirror according to the first embodiment of the present invention, wherein FIG. 3A illustrates an image point position in an undeformed state, and FIG. Indicates the image point position in the deformed state.

FIG. 4 is a configuration diagram showing an example of an optical pickup device using a variable curvature mirror of the present invention, showing Embodiment 2 of the present invention.

FIG. 5 is a configuration diagram illustrating an optical pickup device according to a second embodiment of the present invention, which is used to reproduce a DVD or a CD using the variable curvature mirror of the present invention.
(B) shows a case of applying to VD, and (b) shows a case of applying to CD.

FIG. 6 is a configuration diagram showing a conventional optical pickup device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mirror main body 1a Curved surface part 1b Flange part 2 Deformation member 3 Electrode 4 DC power supply 5 Switch 6 Light beam 7 Light source 8 Objective lens 9 Image point 10 Curvature variable mirror

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Susumu Hirata 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Co., Ltd. No. Sharp Corporation

Claims (3)

[Claims] A mirror body made of an elastic material and having a curved surface portion for reflecting incident light and a flange portion formed on an outer peripheral portion of the curved surface portion; and a mirror body attached to the flange portion and extending the mirror body in a radial direction. A variable curvature mirror comprising: a deformable member that expands and contracts; and a deformation applying unit that deforms the deformable member. 2. The variable curvature mirror according to claim 1, wherein said deformable member is a disk-shaped piezoelectric member having electrodes formed on both sides, and said deformation applying means is a power supply circuit for turning on / off said electrodes. . 3. An optical pickup device comprising the variable curvature mirror according to claim 1 or 2, and configured to guide a light beam reflected by the variable curvature mirror to an objective lens.