Method of configuring shape-deformable mirror, optical pickup device, and recording and reproduction unit

Abstract

A shape of a mirror face of a shape-deformable mirror that reduces aberration and has a simple configuration is calculated in a simple method. The shape of the mirror face of the shape-deformable mirror 14a is approximately calculated using fourth and fifth terms of the Zernike Polynomials. Furthermore, one of the Zernike coefficients C4 and C5, which configure the fourth and fifth terms of the Zernike Polynomials respectively, is expressed as a value with the other coefficient as a variable by using the following expression:

Description

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that the drawings are to be used for the purposes of exemplary illustration only and not as a definition of the limits of the invention. Throughout the disclosure, the word “exemplary” is used exclusively to mean “serving as an example, instance, or illustration.” Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Referring to the drawings in which like reference character(s) present corresponding parts throughout:

FIG. 1 is a block diagram of an optical pickup device 10 of an embodiment of the invention;

FIG. 2 is a Table showing expressions of j=1 to 20 of the Zernike Polynomials Z_j(ρ, θ) respectively;

FIG. 3 is a diagram of a wave front expressed by the fourth term of the Zernike Polynomials;

FIG. 4 is a diagram of a wave front expressed by the fifth term of the Zernike Polynomials;

FIG. 5 is a diagram showing values of aberration in each of cases that an injection angle is 30 degrees, 45 degrees, 60 degrees, and 75 degrees;

FIG. 6 is a block diagram of a recording and reproduction unit using the optical pickup device of an embodiment of the invention;

FIG. 7 is a block diagram showing another recording and reproduction unit using the optical pickup device of an embodiment of the invention;

FIG. 8 is a diagram showing a usual optical pickup device;

FIG. 9 is a diagram showing a shape-deformable mirror and a reflection optical path of an injected beam; and

FIGS. 10A and 10B are diagrams showing wave fronts expressed by sixth and seventh terms of the Zernike Polynomials respectively.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed and or utilized.

Hereinafter, embodiments of the invention are described according to the following order with reference to drawings. Like references are used for like or corresponding portions in the drawings, and the portions are not repeatedly described.

1. Optical pickup device

1-1. Configuration of optical pickup device

1-2. Method of calculating mirror face of shape-deformable mirror

2. Embodiments

3. Conclusion

1. OPTICAL PICKUP DEVICE

1-1. Configuration of Optical Pickup Device

Hereinafter, a configuration of an optical pickup device 10 is described with reference to FIGS. 1 to 5. FIG. 1 is a block diagram of the optical pickup device 10 of an embodiment of the invention. The optical pickup device 10 focuses an irradiated laser beam to a small-pit group formed on a read face of an optical disk 100, and converts the laser beam reflected by the optical disk 100 into a digital signal and reads the signal.

To achieve a function as above, the optical pickup device 10 is configured by a laser diode 11 for irradiating a laser beam; an objective lens 12 for focusing an injected laser beam; a lens holder 13 for holding the objective lens 12; an optical system 14 that deflects the laser beam irradiated from the laser diode 11, and irradiates the laser beam to the objective lens 12; and a detector 15 that detects the laser beam reflected by the optical disk 100. While there is one objective lens in the embodiment of the invention, the number of objective lenses is not limited to one, and can be appropriately changed depending on applications.

The optical system 14 is configured by a collimator lens 14b for deflecting the laser beam irradiated from the laser diode 11; a shape-deformable mirror 14a for reflecting the deflected beam to an optical disk side; and a half mirror 14c that is situated between the laser diode 11 and the shape-deformable mirror 14a, and transmits the laser beam from the laser diode 11, but reflects the laser beam reflected by the optical disk 100. According to the above configuration, the laser beam irradiated from the laser diode 11 is deflected by the collimator lens 14b, and then reflected in a direction approximately 45 degrees upward by the shape-deformable mirror 14a, and thereby irradiated to the objective lens 12. The objective lens 12 focuses the irradiated laser beam on the read face of the optical disk 100. A beam reflected via the half mirror 14c is injected into the detector 15 through a cylindrical lens 14d.

The shape-deformable mirror 14a is deformed in shape depending on an applied voltage, and focuses a beam to each read face of the optical disk. Specifically, the optical disk 100 is formed with read faces including a plurality of layers, and the shape-deformable mirror 14a is changed in shape so as to change an optical path of a reflected beam so that the objective lens 12 can focus the beam on each read face. Furthermore, the shape-deformable mirror 14a used in the embodiment of the invention is changed in shape of a mirror face to correspond to a face calculated by the Zernike Polynomials, so that aberration of the beam to be focused on the read face is reduced.

As the shape-deformable mirror 14a used according to an embodiment of the invention, any mirror can be used as long as it may be deformed in the tangent and radian directions depending on an applied voltage, and a shape of a mirror face for receiving a beam may be changed to be similar to a shape of a wave front calculated by the Zernike Polynomials. Therefore, the shape-deformable mirror 14a is connected to a controller 16 for changing the shape of the mirror face, and changed in shape according to control by the controller 16. Moreover, a lateral cross section of a mirror portion of the shape-deformable mirror 14a desirably has a circular shape since the wave front expressed by the Zernike Polynomials has a circular shape.

Hereinafter, a function of the optical pickup device having the above configuration is described. A laser beam irradiated from the laser diode 11 is deflected by the collimator lens 14b, and then irradiated to the shape-deformable mirror 14a. The shape-deformable mirror 14a reflects the injected beam at approximately 45 degrees and irradiates the beam to the objective lens 12. At that time, a shape of the shape-deformable mirror 14a is deformed, and the shape of the mirror face for receiving the beam is changed to correspond to the shape of the face calculated by the Zernike Polynomials as described above, resulting in reduction in aberration of the beam focused on the read face by the objective lens 12.

The laser beam irradiated to the read face of the optical disk 100 according to the above method is reflected by the read face, and injected into the half mirror 14c through the same path as an injection path. The half mirror 14c may reflect the injected laser beam so as to eject the beam to a detector 15 side. The detector 15 reads the injected laser beam and converts the beam into a digital signal, and then outputs the signal. Thus, the optical pickup device 10 reads data in the optical disk 100. The detector 15 in the embodiment of the invention uses a photodiode to convert the laser beam into the digital signal.

1-2. Method of Calculating Shape of Mirror Face of Shape-Deformable Mirror

Next, a specific method of calculating the shape of the mirror face of the shape-deformable mirror 14a is described. The shape W of the mirror face of the shape-deformable mirror 14a is calculated as follows by using the Zernike Polynomials.

$\begin{array}{cc}W\left(\xi ,\eta \right)=\sum _jc_jZ_j\left(\rho ,\theta \right)\left(\xi =\alpha \rho \cos \theta ,\eta =\alpha \rho \sin \theta \right)& \left(1\right)\end{array}$

W(ξ, η): shape of mirror face of shape-deformable mirror

c_j: Zernike coefficient

Z_j (ρ, η): Zernike Polynomials

α: radius of mirror face of shape-deformable mirror

ρ: normalized radius

θ: deviation angle

Since the expression (1) is a polynomial, it has a certain feature for approximation of a mirror face in each term j=1 or more. FIG. 2 is a table showing expressions in J=1 to 20 of the Zernike Polynomials Z_j(ρ, θ) respectively. From the figure, fourth and fifth terms of the Zernike Polynomials Z_j(ρ, θ) are as follows respectively

Z ₄=2ρ²−1Z₅=ρ² cos 2θ  (2)

The fourth and fifth terms express shapes of the shape-deformable mirror 14a as in FIGS. 3 and 4. FIG. 3 is a diagram of a wave front expressed by the fourth term of the Zernike Polynomials. FIG. 4 is a diagram of a wave front expressed by the fifth term of the Zernike Polynomials.

The shape W (ξ, η) of the mirror face of the shape-deformable mirror 14a can be expanded as follows.

W(ξ,η)=C₄(2ρ²−1)+C₅(ρ² cos 2θ)=(2C₄+C₅ cos 2θ)ρ²−C₄  (3)

At that time, θ=0° is substituted in the above expression, so that the curvature radius in the radian direction can be calculated, and the following expression is given.

2*C4+C5  (4)

Moreover, θ=90° is substituted therein, so that the curvature radius in the tangent direction can be calculated, and the following expression is given.

2*C4-C5  (5)

The ratio of the curvature radius in the radian direction to the curvature radius in the tan direction is given by the following expression.

{cos(2Φ)+1}/2  (6)

Therefore, a relationship between the expression (4) and the expression (5) is given as follows by using the expression (6).

{cos(2Φ)+1}/2(2C4+C5)=2C4−C5

This is arranged with the C4 and C5, and consequently the following expression is given.

$\begin{array}{cc}\frac{C_5}{C_4}=\frac{2\left\{1-\cos \left(2\phi \right)\right\}}{\cos \left(2\phi \right)+3}& \left(7\right)\end{array}$

C₄: fourth term of Zernike Polynomials

C₅ fifth term of Zernike Polynomials

From the above, a relational expression between the Zernike coefficients C4 and C5 is calculated.

According to the relationship between the Zernike coefficients C4 and C5, one of the C5 and C4 is calculated as a value with the other (C5 for C4, or C4 for C5) as a variable by using the expression (7). Thus, when the shape of the mirror face of the shape-deformable mirror 14a is calculated using the Zernike Polynomials (1), the shape W (ξ, η) of the mirror face can be calculated as a linear expression of C4 or C5. Thus, when the shape of the mirror face of the shape-deformable mirror 14a that reduces aberration of a beam is calculated, the shape of the mirror face can be expressed as a linear expression using C4 or C5 as a variable.

Next, values of aberration are described using FIG. 5, the values having been reduced by using the shape-deformable mirror 14a calculated according to the above method. FIG. 5 is a diagram showing values of aberration in respective cases that an injection angle φ is 30 degrees, 45 degrees, 60 degrees and 75 degrees. An injection angle φ injected into the shape-deformable mirror 14a is typically 45 degrees. As the optical disk 100 to be used, DVD having read faces including five layers is used, wherein cover layer thickness as a distance to each of the read faces is as follows: H1 is 0.125, H2 is 0.085, H3 is 0.068, H4 is 0.055, and H5 is 0.030 (mm). A distance WD from an objective lens to a surface of the DVD is set to be 1.3 (mm).

From FIG. 5, in a case that the injection angle φ is 45°, reduction in aberration in each of layers H1 to H5 is as follows. The aberration is reduced from 0.038 to 0.00 in the layer H1, 0.007 to 0.000 in H2, 0.02 to 0.001 in H3, 0.033 to 0.000 in H4, and 0.059 to 0.000 in H5 (mλ). Similarly, in cases that the injection angle φ is 30°, 60°, and 75°, aberration in each layer is reduced.

2. EMBODIMENTS

Hereinafter, description is made on an embodiment where the optical pickup device 10 according to the invention is used. FIG. 6 is a block diagram of a recording and reproduction unit using the optical pickup device of an embodiment of the invention. The recording and reproduction unit 20 performs recording of data to be recorded in the optical disk 100 such as DVD or CD and reproduction of the recorded data.

From the figure, the recording and reproduction unit 20 is configured by the optical pickup device 10 of an embodiment of the invention; a spindle motor 21 for rotating the optical disk 100; a loading motor 22 for loading a tray 20a on which the optical disk is set; a signal processing board 26 for performing reproduction or recording of data from/into the optical disk; a power supply unit 24 for power supplying; and a remote control I/F 23 for receiving an operation signal from a remote control unit 25.

Operation of the recording and reproduction unit 20 is described below. When the optical disk 100 is set on the tray 20a and the remote control unit 25 is operated, the remote control I/F 23 reads an operation signal outputted from the remote control unit 25, and outputs the signal to the signal processing board 26. The signal processing board 26 accepts an operation instruction from the remote control unit 25 via the remote control I/F 23, and thereby drives the loading motor 22 so as to accommodate the tray 20a in the recording and reproduction unit 20. Then, the signal processing board 26 drives the spindle motor 21 to rotate the optical disk 100.

Furthermore, the optical pickup device 10 is moved to follow pits on the optical disk 100 being rotated so as to read data in the optical disk 100. At that time, the optical pickup device 10 deforms the shape of the mirror face to reduce aberration of a beam focused on the read face of the optical disk 100. Then, the read data are outputted to the signal processing board 26, and subjected to signal processing therein and then outputted to external equipment via an input/output terminal 27. Here, the external equipment is an output device for outputting data to be outputted through the input/output terminal, including a monitor, projector, and personal computer. Since a configuration of the signal processing board 26 is known in the art, it is omitted to be described.

While the recording and reproduction unit 20 is separately operated to achieve a function, an embodiment where the optical pickup device 10 is used is not limited to an apparatus that is separately operated to achieve a function, and an apparatus to be incorporated in a product may be used. Therefore, as an example of a second embodiment, description is made on a recording and reproduction unit 30 that uses the optical pickup device 10 of an embodiment of the invention. The recording and reproduction unit 30 is incorporated in a product such as personal computer, and performs reproduction of data in the optical disk 100 and recording of obtained data. It is appreciated that the product, in which the recording and reproduction unit 30 is incorporated, is not limited to the personal computer, and the unit can be incorporated in any product if it uses the optical pickup device 10 of an embodiment of the invention.

FIG. 7 is a block diagram showing a recording and reproduction unit using the optical pickup device 10 of an embodiment of the invention. From the figure, the recording and reproduction unit 30 is configured by the optical pickup device 10 of an embodiment of the invention; a spindle motor 21 for rotating the optical disk 100; a loading motor 22 for loading a tray on which the optical disk is set; and a signal processing board 26 for performing control for reproducing data in the optical disk or recording obtained data into the optical disk 100.

Since each of blocks as described above has the same functions as those in the first embodiment, each of the functions is omitted to be described here. The recording and reproduction unit 30 receives an instruction from a control section such as a microcomputer disposed outside the unit 30, and accordingly performs read of data in the optical disk 100 and recording of obtained data using the optical pickup device 10.

(3) CONCLUSION

As describe hereinbefore, the shape of the mirror face for receiving a beam of the shape-deformable mirror 14a is approximately calculated by using the fourth and fifth terms of the Zernike Polynomials. Furthermore, one of the Zernike coefficients C4 and C5, which configure the fourth and fifth terms of the Zernike Polynomials respectively, has a value with the other as a variable according the expression (7). The expression (7) is substituted in the expression (1), thereby the shape of the mirror face of the shape-deformable mirror 14a is easily calculated. Moreover, the optical pickup device 10 using the shape-deformable mirror 14a is used, thereby aberration can be reduced in a simple structure.

Although the invention has been described in considerable detail in language specific to structural features and or method acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as preferred forms of implementing the claimed invention. Therefore, while exemplary illustrative embodiments of the invention have been described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention.

It should further be noted that throughout the entire disclosure, the labels such as left, right, front, back, top, bottom, forward, reverse, clockwise, counter clockwise, up, down, or other similar terms such as upper, lower, aft, fore, vertical, horizontal, proximal, distal, etc. have been used for convenience purposes only and are not intended to imply any particular fixed direction or orientation. Instead, they are used to reflect relative locations and/or directions/orientations between various portions of an object. In addition, reference to “first,” “second,” “third,” and etc. members throughout the disclosure (and in particular, claims) is not used to show a serial or numerical limitation but instead is used to distinguish or identify the various members of the group.

Claims

1. A recording and reproduction unit, having an optical pickup device that reflects a laser beam ejected from a laser diode to an objective lens using a shape-deformable mirror, and focuses the laser beam on a read face of an optical disk using the objective lens, anda control section that controls a shape of the shape-deformable mirror:the shape-deformable mirror reduces aberration through calculation of a shape of a mirror face by using fourth and fifth terms of the following Zernike Polynomials:

2. A method of configuring a shape of a shape-deformable mirror that reflects a beam ejected from a beam source to an objective lens: the shape-deformable mirror is configured by a shape of a mirror face calculated by using fourth and fifth terms of the following Zernike Polynomials in order to reduce aberration of a reflected beam;

3. The method of configuring the shape of the shape-deformable mirror according to claim 2: the Zernike coefficients C4 and C5, which configure the fourth and fifth terms of the Zernike Polynomials respectively, satisfy the following expression;

4. An optical pickup device that reflects a laser beam ejected from a laser diode to an objective lens using a shape-deformable mirror, and focuses the laser beam on a read face of an optical disk using the objective lens: the shape-deformable mirror reduces aberration through calculation of a shape of a mirror face by using fourth and fifth terms of the following Zernike Polynomials;

5. The optical pickup device according to claim 4: the Zernike coefficients C4 and C5, which configure the fourth and fifth terms of the Zernike Polynomials respectively, satisfy the following expression;