JP2602814B2 - Laser pickup device for optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser pickup device used for an optical disc such as a compact disc.

[Conventional technology]

In recent years, optical disks have been used in various fields as high-density information storage means.

FIG. 9 is a schematic diagram of such an optical disk device.
Is a disk, 2 is a head feeder, 3 is a motor, 4 is a pickup unit, 5 is a reproduction circuit, and 6 is a servo circuit.

In the figure, a disk 1 is driven to rotate by a motor 3, and a pickup unit 4 is incorporated in a head feeder 2 and moves in a radial direction of the disk 1. The control of this movement and the control of focusing and tracking are performed by a servo circuit 6, and the signal from the pickup unit 4 is converted into an image signal or an audio signal by a reproduction circuit 5 and sent to an audio device or a video device (not shown). Can be

Incidentally, a laser pickup device is used as a pickup device of such an optical disk device.

FIG. 10 is a view showing an example of such a conventional laser pickup device, wherein 7 is a semiconductor laser, 8 is a coupling lens, 9 is a beam splitter, 10 is a λ / 4 plate, 11 is a prism, and 12 is an objective lens. , 13 is a condenser lens, 14 is a four-division photodiode, and 15 is a light shielding plate.

In the figure, a laser beam from a semiconductor laser 7 is
Coupling lens 8, beam splitter 9, λ / 4 plate 1
The light is radiated on the disk 1 via the prism 11, the prism 11, and the objective lens 12, and the reflected light is focused on the four-division photodiode by the condenser lens 13 and detected. A part of this reflected light beam is shielded by a light-shielding plate 15, and an image on a surface including the light-shielding plate is collected by a condenser lens 13.
When the image is formed on the four-division photodiode by the above, the incident light amounts of the upper and lower photodiodes can be changed according to the focus state, and a focusing error can be detected by the difference output. Further, a tracking error can be detected based on a difference between the incident light amounts of the right and left photodiodes, and focusing or tracking control can be performed based on the detected output. The beam splitter 9 and the λ / 4 plate 10
Constitutes an isolator that does not return light to the light source side. Each of the above-described elements constituting the laser pickup unit 4 is integrated in an aluminum case, and is provided with a guide (head feeder) provided in the disk radial direction.
The information is accessed by this movement.

[Problems to be solved by the invention]

However, the conventional pickup device has a structure in which the semiconductor laser, beam splitter, λ / 4 plate, lens, photodetector, etc. are integrated in an aluminum case and moved so that the pickup is inevitable. The movable part becomes heavy, the inertia force becomes large, and fast control becomes impossible, so that it was difficult to achieve a fast access time. Also, it was very difficult to adjust the optical system in the pickup section.

The present invention is to solve the above problems,
It is an object of the present invention to provide a laser pickup device for an optical disk, in which a movable portion of a pickup is reduced in weight, a quick access time is obtained, the number of components is small, and optical adjustment is easy.

[Means for solving the problem]

Therefore, the laser pickup device for an optical disk of the present invention includes a semiconductor laser, an element facing the disk, connected to the semiconductor laser by an optical fiber directly or through an optical branch circuit, and having a focal length variable function and an optical deflection function. An integrated objective lens unit, an objective lens unit feed mechanism that moves in the disk radial direction and incorporates the objective lens unit, and a servo circuit that performs at least focusing and tracking control, is provided via the objective lens unit. The obtained change in reflected light from the disk is extracted as a change in oscillation output of the semiconductor laser or by a photodetector via an optical branch circuit.

[Action]

The laser pickup device for an optical disk of the present invention reduces the weight of the movable portion by moving only the objective lens portion connected directly to the semiconductor laser via an optical fiber or via an optical branch circuit in the disk radial direction, thereby reducing the weight of the movable portion and increasing the speed. In addition to enabling access, the objective lens section is composed of an electro-optic effect element and a thermo-optic effect element, and the refractive index is changed by applying voltage and heating, or the objective lens section is supported by a piezoelectric element, and the vertical position and tilt The number of optical adjustment portions is reduced as much as possible, and adjustment requiring skill is not required.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an embodiment of a laser pickup device for an optical disk according to the present invention.
The same reference numerals as those in the drawings indicate the same contents. In the figure, reference numeral 2 denotes an objective lens unit, and reference numeral 21 denotes an optical fiber.

In the figure, output light from a semiconductor laser 7 is guided to an objective lens section 20 by an optical fiber 21 and is irradiated onto the disk 1. The reflected light from the disk 1 returns to the semiconductor laser 7 through the objective lens section 20 and the optical fiber 21 again.

Now, when the amount of return light increases or decreases depending on the state of the disk surface, the amount of oscillation of the semiconductor laser increases or decreases, and the terminal voltage also changes, so-called self-coupling effect (SCOOP).
signal) is detected by the signal).

The movable portion incorporated in the head feeder 2 is reduced in weight only by the objective lens portion 20 having a configuration described later. Then, focusing or tracking control is performed by a signal from the servo circuit 6.
A micro-vibration is applied to the irradiation beam on the optical disc 1, and the wobbling method is used to detect the phase relationship between the reflected light intensity of the bright spot and the vibration at that time.

FIG. 2 is a diagram showing a schematic configuration of another embodiment of the laser pickup device for an optical disk according to the present invention, wherein the same numbers as those in FIG. 1 indicate the same contents. In the figure, 22 is an optical branch circuit, and 23 is a photodetector. The difference from FIG. 1 of this embodiment is that the photodetector 23 is used independently.

In the figure, output light from a semiconductor laser 7 passes through an optical fiber 21 via an optical branch circuit 22 and is focused on the optical disk 1 by an objective lens unit 20. The reflected light from the disk 1 is transmitted to the objective lens section 20, the optical fiber 21, the optical branching circuit 22
To the photodetector 23 through which the signal is detected.

Note that whether to use the method shown in FIG. 1 or the method shown in FIG. 2 as a method of extracting an output signal may be appropriately selected.

 Next, the configuration of the objective lens unit will be described.

FIG. 3 is a view showing one embodiment of an objective lens unit used in the pickup device of the present invention. In the drawing, 31 is a microlens element, 32 is a lens element having a focal length variable function, and 33 is a light beam. This is an element having a deflection function.

In the figure, an objective lens unit 20 includes a microlens element 31 made of glass or plastic, a lens element 32 having a variable focal length function, and an element 33 having a light beam deflecting function.
Are combined and integrated. Usually, in a pickup device such as a compact disk, a lens having a focal length f of about 5 mm is used, and focus control may be performed within a range of about 1 mm. Therefore, a microlens element 31 having a focal length f ₀ = 5 mm is used, and in combination with a lens element 32 having a focal length variable function, f = 4 mm, that is, in order to shorten the focal length f by 1 mm, the focal length is approximately f ₁ = 20mm
What is necessary is just to set the lens element 32.

FIG. 4 is a view showing an embodiment of a lens element having a variable focal length function. In the figure, reference numeral 34 denotes a cylindrical body made of PLZT;
Is a transparent electrode, E is a variable voltage power supply, and R ₁ , R ₂ and R ₃ are voltage dividing resistors.

In the lens element having the variable focal length function shown in FIG.
It uses the electro-optic effect of PLZT to change the refractive index and change the focal length. In the case of PLZT, a refractive index change Δn of about 0.01 can be achieved by applying a voltage of 200 V / mm. Therefore, as shown in the figure, for example, ITO is concentrically vapor-deposited on the cylindrical body 34 to form the transparent electrode 35, and by controlling the voltage applied to each electrode, the refractive index distribution is changed to n = n ₀ (1- 1 / 2Ar ² ) can be changed as Δn = −1 / 2Ar ² . Here, n ₀ is a refractive index at the center of the cylinder, A is a coefficient, and r is a radius. When this is done, if the thickness and l, the focal length f ₁ of the lens Given by

Now, the thickness of the lens element 32 having the focal length
Assuming 1 mm and a radius of 1 mm, to obtain f ₁ = 20 mm, Δ
n = 0.025 is required and can be achieved by applying a voltage of about 500V. In this way, the lens elements 31 and 32
Can change the focal length f in the range of 5 mm to 4 mm. FIG. 5 is a view showing another embodiment of a lens element having a variable focal length function, in which 36 is a cylindrical body made of TiO ₂ and 37 is a resistor.

In the figure, a resistor 37 is formed on the side surface of a cylindrical body 36, a current is supplied from a variable power source E to generate heat, and the cylindrical body 36 is heated, and a refractive index distribution is generated in the radial direction of the cylindrical body 36 by a thermo-optic effect. Let it. In the case of TiO ₂ , a change in the refractive index Δn = 0.01 is obtained with respect to a temperature change of 100 ° C., and therefore, the same effect as in FIG. 4 can be obtained by performing the resistance heating control.

FIG. 6 is a view showing an embodiment of an element having a light beam deflecting function according to the present invention, in which 38 is a TeO ₂ crystal, 39 is a transducer, and 40 is an RF signal generator.

In the figure, a transducer 39 made of LiNbO ₃ is adhered to a TeO ₂ crystal 38, a high frequency is applied from an RF signal generator 40 to excite, and a light beam is deflected by a grating created by an acoustic wave generated in the TeO ₂ crystal. . In this case, the RF signal
By changing the lattice gap by changing from 50 to 100 MHz,
The deflection angle can be changed by about 7 °, and the required tracking control of about 400 μm can be sufficiently achieved.

FIG. 7 is a view showing another embodiment of the microlens unit according to the present invention using a piezoelectric element, in which 41 is a piezoelectric element,
42 is a support frame.

In the figure, lens elements 31 are fixed to a support frame 42 via piezoelectric elements 41 at, for example, four locations on the circumference. Therefore, a voltage is applied to each of these piezoelectric elements 41 from the variable voltage power supply E, and by changing these voltages, the vertical position and the inclination of the lens element 31 can be controlled, so that focusing and tracking are controlled. be able to.

FIG. 8 is a view showing another embodiment of the objective lens unit according to the present invention, in which 43 is a lens element, 44 is a transparent concentric electrode, 45 is a transparent common electrode, and 46 is a plane electrode.

In the figure, a lens element 43 is made of a material having an electro-optic effect such as LiNbO ₃ or PLZT, and its optic axis is appropriately selected. Then, by changing the voltage applied to the concentric electrodes 44, the refractive index distribution changes as in the case of FIG. 4, and as a result, the focal length can be made variable. Further, by applying a voltage from the plane electrode 46 in a direction intersecting with the direction of the electric field generated by the concentric electrodes 44, it is possible to have a light deflecting effect. Therefore, concentric electrodes
44, Focusing and tracking can be controlled by controlling the voltage applied to the plane electrode 46. When a voltage is applied to the concentric electrodes, there is a possibility that light is slightly deflected. In such a case, correction may be made by applying a voltage to the flat electrode.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the movable portion of the pickup is extremely lightweight, extremely quick access is possible, and the number of optically adjustable portions is reduced, so that adjustment requiring skill is not required. A great effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of one embodiment of a laser pickup device for an optical disk according to the present invention, FIG. 2 is a schematic diagram of another embodiment of the laser pickup device for an optical disk according to the present invention,
FIG. 3 is a diagram showing an embodiment of an objective lens unit used in the pickup device of the present invention, FIG. 4 is a diagram showing an embodiment of a lens element having a variable focal length function, and FIG. FIG. 6 is a view showing another embodiment of a lens element having a function, FIG. 6 is a view showing an embodiment of an element having a light beam deflecting function according to the present invention, and FIG. 7 is an objective lens according to the present invention using a piezoelectric element. FIG. 8 is a diagram showing another embodiment of the objective lens unit according to the present invention, FIG. 9 is a schematic diagram of an optical disk device, and FIG. 10 is a configuration of a conventional laser pickup device. FIG. DESCRIPTION OF SYMBOLS 1 ... Disc 2 ... Head feeder 3 ... Motor 4 ... Pickup part 5 ... Reproduction circuit 6 ... Servo circuit 7 ... Semiconductor laser 20 ... Object lens part 21 ... Optical fiber, 22 optical branch circuit, 23 photodetector, 31 microlens element, 32 lens element having a variable focal length function, 33 element having a light beam deflecting function, 34 …… PLZT cylinder, 35 …… Transparent electrode, E ……
Variable voltage power supply, R ₁ , R ₂ , R ₃ … Dividing resistor, 36… TiO ₂ cylinder, 37… Resistor, 38… TeO ₂ crystal, 39… Transducer, 40… RF signal Generator 41, Piezoelectric element 42
…… Support frame, 43… Lens element, 44 …… Concentric electrode, 45
…… Common electrode, 46 …… Flat electrode

Continued on the front page (72) Inventor Yuji Kobayashi 1126, Ichinocho, Hamamatsu City Inside Hamamatsu Photonics Co., Ltd. Inventor Yasuji Osumi, 1126 Nomachi, Ichinohama, Hamamatsu City Inside Hamamatsu Photonics Co., Ltd. 5-1 Minatomachi, Kawasaki-ku Japan Colombia Co., Ltd. Kawasaki Office (56) References JP-A-57-18035 (JP, A) JP-A-53-47803 (JP, A) JP-A-52-32348 (JP) , A) JP-A-50-57455 (JP, A)

Claims (6)

(57) [Claims] 1. An objective lens unit in which an element having a focal length variable function and an optical deflection function is integrated with a semiconductor laser, which is opposed to a disk and is connected to the semiconductor laser by an optical fiber directly or through an optical branch circuit. And an objective lens unit feed mechanism that moves in the radial direction of the disk and has an objective lens unit incorporated therein; and a servo circuit that performs at least focusing and tracking control. The reflected light from the disk obtained through the objective lens unit A laser pickup device for an optical disk, wherein a change is picked up by a photodetector as a change in oscillation output of a semiconductor laser or through an optical branch circuit. 2. The device having a variable focal length function, wherein a focal length is changed by applying a voltage so that an electric field intensity varies spatially, thereby changing a refractive index distribution of the electro-optic effect device. 2. A laser pickup device for an optical disk according to claim 1, wherein: 3. The element according to claim 1, wherein the element having the variable focal length function changes the focal length by changing the refractive index distribution of the thermo-optic effect element by heating. Laser pickup device for optical disks. 4. The device according to claim 1, wherein the element having the light deflection function changes a deflection angle by changing a lattice gap by changing an excitation frequency of the acousto-optic effect element. A laser pickup device for an optical disk according to the above. 5. The apparatus according to claim 1, wherein the objective lens section comprises a microlens fixedly supported by a piezoelectric element, and controls a vertical position and an inclination of the microlens by changing a voltage applied to the piezoelectric element. A laser pickup device for an optical disk according to claim 1. 6. The objective lens section comprises an electro-optic effect element to which a voltage is applied in a direction crossing each other, and changes a focal length by changing a refractive index distribution by applying a voltage in one direction and changing the focal length. 2. A laser pickup device for an optical disk according to claim 1, wherein the deflection angle is changed by applying a voltage in the direction of.