JPH0963103A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record and/or reproduce an optical disk even when the optical disk has a different thickness of a substrate by providing a variable aperture means for changing the transmissivity of light in accordance with the thickness of the substrate of the optical disk. SOLUTION: When an optical disk of a comparatively thin disk substrate is reproduced, a variable aperture means 15 is set with a dimmer part 15b opaque. In this state, after a light beam from a semiconductor laser element 11 is reflected by a beam splitter 12, the beam is passed through the aperture 15c of the means 15 and converged on the surface 16 of the optical disk through an objective lens 13. At this time, the numerical aperture Na is set to be NA=O.6, spherical aberration is suppressed to be low and the light beam is exactly converged on the disk surface. When the substrate is comparatively thick, the dimmer part 15b is set to be transparent, the numerical aperture is set to be NA=NAO, a lens 13 is designed whose spherical aberration is most suppressed for the optical disk of the thickness of the substrate and the light beam is exatly converged on the disk surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical disk reproducing apparatus for recording and / or reproducing information by irradiating an optical disk with light and detecting return light. It is.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for recording and / or reproducing such an optical disc is constructed as shown in FIG. In FIG. 8, an optical pickup 1 includes a semiconductor laser element 2, a beam splitter 3,
It has an objective lens 4, a photodetector 5, and the like.

The beam splitter 3 has a reflection surface 3a inclined at 45 degrees with respect to the optical axis of the objective lens 4 so that the light beam emitted from the semiconductor laser element 2 and the signal recording surface of the optical disk 6 are recorded. To separate the return light from
That is, the light beam from the semiconductor laser element 2 is reflected by the reflection surface 3a of the beam splitter 3, and the return light from the optical disk 6 passes through the beam splitter 3.

The objective lens 4 is a convex lens and converges the light beam reflected by the beam splitter 3 onto a desired track on the signal recording surface of the rotationally driven optical disk 6. Further, the objective lens 4 is moved in a biaxial direction, that is, an arrow FCS in the drawing by a biaxial actuator (not shown).
It is movably supported in the focusing direction shown by and the tracking direction shown by the arrow TRK.

[0005] The photodetector 5 is configured to have a light receiving portion for a return light beam that enters through the beam splitter 3.

According to the optical pickup 1 having such a configuration, the light beam emitted from the semiconductor laser element 2 is
The light is reflected by the reflecting surface 3a of the beam splitter 3, and further converged to a certain point on the signal recording surface of the optical disc 6 via the objective lens 4.

The return light beam reflected on the signal recording surface of the optical disk 6 again enters the beam splitter 3 via the objective lens 4. Here, the return light beam passes through the beam splitter 3 and enters the light receiving unit of the photodetector 5. Thereby, the information recorded on the signal recording surface of the optical disk 6 is reproduced based on the detection signal output from the photodetector 5.

[0008]

In recent years, the density of optical discs has been increasing as an auxiliary storage device of a computer and a package medium of audio / video information. There is a method in which the numerical aperture NA of the objective lens is made larger than the numerical aperture NA of the objective lens in the conventional optical pickup for a compact disk. However, if the numerical aperture NA is increased, the allowable range for the tilt of the optical disk is reduced. There's a problem.

The optical disk has a predetermined disk substrate thickness (generally, 1.2 mm for a compact disk or the like).
mm), the signal recording surface is provided via the transparent substrate. If the optical disk is inclined with respect to the optical axis of the objective lens of the optical pickup, a wavefront aberration occurs, and the RF
The signal reproduction will be affected. At this time, regarding the wavefront aberration, the third-order coma which occurs in proportion to the cube of the numerical aperture and the first power of the skew angle θ is dominant. Therefore, an optical disc provided with a transparent substrate made of polycarbonate or the like that is mass-produced at low cost has a skew angle θ of, for example, plus or minus 0.5 to plus or minus 1 degree, and the semiconductor of the optical pickup 1 is affected by the above wavefront aberration. The converging spot from the laser element 2 to the optical disk 6 becomes asymmetrical, and intersymbol interference significantly increases, which makes it impossible to accurately reproduce the reproduction signal (RF signal).

Therefore, paying attention to the fact that the third-order coma is proportional to the disk substrate thickness of the optical disk, the third-order coma is reduced by half by reducing the thickness of the disk substrate by half to 0.6 mm. It is possible to In this case, as an optical disc, two standards having different characteristics,
That is, the disk substrate thickness is relatively thick (for example, 1.2 mm)
And a disk substrate having a relatively small thickness (for example, 0.6
mm) are mixed.

Here, in general, the thickness t is set in the optical path of the convergent light.
When a parallel plate is inserted, a spherical aberration proportional to t × (NA) ⁴ occurs with respect to the thickness t and the numerical aperture NA, so the objective lens is designed to cancel this spherical aberration. . By the way, if the disc substrate thickness is different,
Since the spherical aberration is also different, an objective lens corresponding to one standard, for example, a disc substrate thickness of 0.6 mm is used, and the other standard, for example, a disc substrate thickness of 1.2 mm.
When reproducing an optical disc such as a compact disc, a write-once optical disc, a magneto-optical disc, etc., a fourth-order spherical aberration occurs due to the difference in the disc substrate thickness. It will greatly exceed the allowable range of. Therefore, there is a problem that a signal cannot be correctly detected from the return light from the optical disk. Thus, there is a problem that the conventional optical pickup cannot reproduce both types of optical disks.

In view of the above points, the present invention allows recording and / or recording of optical disks even if the optical disks have different substrate thicknesses.
Another object of the present invention is to provide an optical pickup for an optical disk reproducing apparatus, which is adapted to reproduce correctly.

[0013]

According to the present invention, the above object is to provide a light source for emitting a light beam, and irradiate the light beam emitted from the light source so as to be focused on a signal recording surface of an optical disk. The light source includes an objective lens, a beam splitter disposed between the light source and the objective lens, and a photodetector for receiving a return light beam from the signal recording surface of the optical disc separated by the beam splitter. And an optical disc, which is provided in the optical path between the optical disc and the optical disc, and is provided with variable aperture means for changing the light transmittance by an applied current or voltage according to the substrate thickness of the optical disc. .

According to the above arrangement, since the variable aperture means is provided between the light source and the optical disc, the current or voltage applied to the variable aperture means is changed according to the disc substrate thickness of the optical disc to be reproduced. By appropriately controlling, the numerical aperture of the variable aperture means is adjusted, and as a result, the spherical aberration is corrected according to the disc substrate thickness. As a result, the light beam from the light source is correctly focused on the signal recording surface of the optical disc through the variable aperture means, and the return light from the signal recording surface of the optical disc is incident on the photodetector, so that the light beam is always optimal. Signal reproduction will be performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. still,
The embodiments described below are preferable specific examples of the present invention, and therefore, various technically preferable limitations are given,
The scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

FIG. 1 shows an embodiment of an optical pickup according to the present invention. In FIG. 1, an optical pickup 10 is a finite optical pickup, and is arranged between the semiconductor laser element 11, the beam splitter 12, the objective lens 13 and the photodetector 14, and between the beam splitter 12 and the objective lens 13. And variable opening means 15 are provided. Here, since the semiconductor laser element 11, the beam splitter 12, the objective lens 13, and the photodetector 14 have the same configurations as those described in FIG. 8, duplicate description will be omitted and different configurations will be mainly described. To do.

The variable aperture means 15 has a frame portion 15a made of an annular light-impermeable material, a light adjustment portion 15b made of an annular light adjusting element provided in a hollow portion of the frame portion 15a, and a light control element. The aperture 15c is formed by the hollow portion of the portion 15b. These frame portion 15a and light control portion 15b
The aperture 15c is arranged concentrically with respect to the optical axis. The frame portion 15a, the light control portion 15b, and the aperture 15c are circular in the case of FIG. 2, but may be formed in an elliptical shape.

As shown in FIG. 3, for example, the light control section 15b includes two transparent substrates 21 and 22 facing each other and arranged in parallel by a spacer 20, and the transparent substrates 2 and 22.
Transparent electrodes 2 formed on the surfaces of 1, 2 facing each other
3 and the transparent electrode 24, and the electrochemical element 25 enclosed between the transparent substrates 21 and 22. As the electrochemical element 25, for example, viologen, tungsten oxide, silver or the like is used, and it is dissolved in the medium as ions.

Thus, by connecting the transparent electrode 23 to the negative side of the power source and the transparent electrode 24 to the positive side of the power source, a current or a voltage is applied between the transparent electrodes 23, 24, whereby the light control section is applied. In 15b, since an electrochemical reaction occurs, the surface of the transparent electrode 23 on the negative side,
The electrochemical element 25 is deposited by the reduction reaction. Thus, the electrochemical element 25 deposited on the negative transparent electrode 23 reduces the light transmittance of the light control section 15b and becomes substantially opaque.

When the current or voltage between the two transparent electrodes 23, 24 is reversed, the electrochemical element 25 deposited on the surface of the positive transparent electrode 23 in the light control section 15b returns to ions. Thus, since the electrochemical element 25 is not attached to the positive side transparent electrode 23, the light control section 15b has improved light transmittance and becomes substantially transparent. Thus, the variable aperture means 15 is controlled by the light control section 15b by switching the light control section 15b between transparent and opaque.
Is transparent, the light control section 15b and the aperture 1
5c substantially acts as an aperture, resulting in a relatively large opening. Further, the variable aperture means 15 includes a light control section 15b.
Is opaque, only aperture 15c substantially acts as an aperture, resulting in a relatively small aperture.

Although the variable opening means 15 is formed in a circular shape, it is not limited to this and may be formed in another shape. For example, the variable aperture means 15 may be formed in a rectangular shape as shown in FIG. 3, and in this case, the variable aperture means 15 includes two frame portions 15d, which are made of an opaque material and extend in parallel with each other. A dimming portion 15e including two dimming elements provided inside the portion 15d and extending in parallel to each other,
It is composed of an aperture 15f formed by a slit between the light control sections 15e. According to this configuration, when the light control section 15e is transparent, the variable aperture section 15 is configured such that the light control section 15e and the aperture 15f substantially function as an aperture by switching the light control section 15e between transparent and opaque. However, the opening is relatively large. Further, in the variable aperture means 15, when the dimming part 15e is opaque, only the aperture 15f substantially acts as an aperture, and the aperture is relatively small.

Here, the variable aperture means 15 has, for example, a numerical aperture NA = 0.6 when the light control section 15b or 15e is transparent, and the light control section 15b or 15e.
Is opaque, the dimmers 15b and 15e and the apertures 15c and 15c are adjusted so that the numerical aperture NA = NA0 or less.
The size of 15f is selected. NA0 is represented by 0.45 / 0.78 times the light source wavelength λ (μm).
Therefore, when the light source wavelength λ is 0.635 μm, NA0
= 0.366, NA0 = 0.37 when the light source wavelength λ is 0.650 μm, and NA0 = 0.392 when the light source wavelength λ is 0.680 μm. As a result, by making the light control sections 15b and 15e opaque for an optical disk having a relatively thin disk substrate thickness of 0.6 mm,
The numerical aperture NA of the variable aperture means 15 is set to 0.6, and the dimmer portions 15b and 15e are made transparent for an optical disc having a relatively thick disc substrate thickness of 1.2 mm. The numerical aperture NA of 15 is set to NA = NA0 or less.

Optical pickup 10 according to the present embodiment
Is constructed as described above. First, a description will be given of a case where an optical disk having a relatively thin disk substrate thickness of 0.6 mm is reproduced. In this case, in the variable aperture means 15, the light control section 15b or 15e is set to be opaque (corresponding to the structures of FIGS. 2 and 4 respectively). In this state, the light beam from the semiconductor laser device 11 emits the light beam.
After being reflected by the reflecting surface 12a of the optical disc, the light passes through the aperture 15c or 15f of the variable aperture means 15 and is further focused on the signal recording surface of the optical disc 16 via the objective lens 13. At this time, NA = 0.
Since it is set to 6, the spherical aberration can be suppressed to a low level, so that the light beam is correctly focused on the signal recording surface of the optical disc 16.

The return light from the optical disk 16 again passes through the beam splitter 12 via the objective lens 13 and the variable aperture means 15, and is converged on the photodetector 14. As a result, the recording signal of the optical disc 16 is reproduced based on the detection signal of the photodetector 14.

Next, a relatively thick disk substrate thickness of 1.2 m
When reproducing an optical disc of m, the variable aperture means 15 has the light control parts 15b and 15e set to be transparent first. Then, in this state, the light beam from the semiconductor laser element 11 is reflected by the reflecting surface 12a of the beam splitter 12, and then the apertures 15c and 15f of the variable aperture means 15 are reflected.
Further, the light passes through the light control units 15b and 15d, and is further focused on the signal recording surface of the optical disc 16 via the objective lens 13. At this time, NA = NA0 by the variable opening means 15.
Although set as below, since the objective lens 13 is designed so that the spherical aberration can be most suppressed with respect to an optical disc having a disc substrate thickness of 1.2 mm, the light beam is properly directed to the signal recording surface of the optical disc 16. It will converge.

The return light from the optical disk 16 again passes through the beam splitter 12 via the objective lens 13 and the variable aperture means 15, and is converged on the photodetector 14. As a result, the recording signal of the optical disc 16 is reproduced based on the detection signal of the photodetector 14.

FIG. 5 shows a second embodiment of the optical pickup according to the present invention. In FIG. 5, the optical pickup 30 is a finite optical pickup,
Semiconductor laser element 11, beam splitter 12, objective lens 13, photodetector 14, and variable aperture means 1 arranged between the beam splitter 12 and the semiconductor laser element 11.
It is composed of 5 and.

The semiconductor laser device 11, the beam splitter 12, the objective lens 13, the photodetector 14 and the variable aperture means 15 are the semiconductor laser device 11, the beam splitter 12, the objective lens 13 and the optical pickup 10 in the optical pickup 10 shown in FIG. The photodetector 14 and the variable aperture means 15 have the same structure. Further, the variable aperture means 15 is arranged between the beam splitter 12 and the semiconductor laser element 11, unlike the case of the optical pickup 10 shown in FIG.

According to the optical pickup 30 having such a structure, the light beam from the semiconductor laser device 11 first passes through the variable aperture means 15 and then the beam splitter 12.
After being reflected by the reflecting surface 12a of the optical disc 12, the light is converged on the signal recording surface of the optical disc 16 via the objective lens 13. The return light from the optical disc 16 passes through the objective lens 13 again,
The light passes through the beam splitter 12 and converges on the photodetector 14. As a result, the recording signal of the optical disc 16 is reproduced based on the detection signal of the photodetector 14. here,
Optical disc 16 is relatively thin Disc substrate thickness 0.6 mm
If the variable aperture means 15 is
b and 15e are opaque and the numerical aperture NA is set to 0.6. As a result, spherical aberration is reduced, and the light beam is correctly focused on the signal recording surface of the optical disc 16.

In this case, since the return light of the optical disk does not pass through the variable aperture means 15, the return light is not narrowed down by the variable aperture means 15, and therefore, the return light to the photodetector 14 is prevented. Since the amount of incident light is large, the photodetector 14 can read the signal more accurately.

FIG. 6 shows a third embodiment of the optical pickup according to the present invention. In FIG. 6, the optical pickup 40 is an infinite optical pickup,
Semiconductor laser element 41, collimator lens 42, grating 43, beam splitter 44, objective lens 4
5, a multilens 46 and a photodetector 47, and a variable aperture means 48 arranged between the beam splitter 44 and the grating 43.

The semiconductor laser device 41 is a light emitting device utilizing recombination light emission of a semiconductor and is used as a light source. The light beam emitted from the semiconductor laser element 41 is
It is guided to the beam collimator lens 42.

The collimator lens 42 is a convex lens and converts the light beam from the semiconductor laser element 41 into parallel light.

The grating 43, which is also called a diffraction grating, separates the parallel light from the collimator lens 42 into 0th-order light as a main beam and plus / minus 1st-order light as a side beam.

The beam splitter 44 has its reflecting surface 44.
a is arranged in a state of being inclined by 45 degrees with respect to the optical axis of the objective lens 45, and separates the light beam emitted from the semiconductor laser element 41 and the return light from the signal recording surface of the optical disc 49. That is, the light beam from the semiconductor laser element 41 passes through the beam splitter 12, and the return light from the optical disc 49 is reflected by the reflecting surface 44 a of the beam splitter 44.

The objective lens 45 is a convex lens and focuses the light beam transmitted through the beam splitter 44 onto a desired track on the signal recording surface of the optical disc 49 which is rotationally driven. Further, the objective lens 45 is supported by a biaxial actuator (not shown) so as to be movable in the biaxial directions, that is, the tracking direction and the focusing direction.

The multi-lens 46 is a lens formed in a cylindrical shape and has a converging property only in a direction having a curvature. As a result, the multi-lens 46 imparts astigmatism to the incident light beam to facilitate focus servo.

The photodetector 47 has a light receiving portion for each light beam incident through the multilens 46.

The variable opening means 48 is, for example, similar to the variable opening means 15 shown in FIG. 2, a frame portion made of an annular light opaque material, and an annular shape provided in the hollow portion of the frame portion. The light control unit includes a light control unit including a light control element and an aperture formed by a hollow portion of the light control unit. The variable opening means 48 is not limited to this, and may have the configuration of FIG. 4 or another configuration.

The optical pickup 4 constructed in this way
At 0, the light beam from the semiconductor laser element 41 is collimated by the collimator lens 42, then separated into three beams by the grating, transmitted through the beam splitter 44, and the aperture or aperture of the variable aperture means 48. Then, the light passes through the light control section and is further focused on the signal recording surface of the optical disc 49 via the objective lens 45.

The return light from the optical disk 49 enters the beam splitter 44 again through the objective lens 45 and the variable aperture means 48, and the reflecting surface 4 of the beam splitter 44.
After being reflected by 4a, it is focused on the photodetector 47 via the multi-lens 46. As a result, the recording signal of the optical disc 49 is reproduced based on the detection signal of the photodetector 47.

Here, when the optical disc 49 is an optical disc having a relatively thin disc substrate thickness of 0.6 mm,
In the variable aperture means 48, the light control section is set to be opaque. As a result, the variable aperture means 48 has a relatively small aperture because only the aperture transmits light, and the numerical aperture NA is set to 0.6. Therefore, since the spherical aberration is suppressed to a low level, the light beam is correctly focused on the signal recording surface of the optical disc 49 having a thin disc substrate. Further, in the case of an optical disc having a relatively thick disc substrate thickness of 1.2 mm, the variable aperture means 48 has its light control section set to be transparent. Thereby, the variable opening means 4
Reference numeral 8 has a relatively large aperture because the aperture and the light control section transmit light, and the numerical aperture NA is set to NA = NA0 or less. Here, since the objective lens 45 is designed so that the spherical aberration can be suppressed most with respect to the optical disc having the disc substrate thickness of 1.2 mm, the light beam is correctly focused on the signal recording surface of the optical disc 49. .

FIG. 7 shows a fourth embodiment of the optical pickup according to the present invention. In FIG. 7, the optical pickup 50 is an infinite optical pickup,
Semiconductor laser element 41, collimator lens 42, grating 43, beam splitter 44, objective lens 4
5, a multilens 46 and a photodetector 47, and a variable aperture means 48 arranged between the beam splitter 44 and the grating 43.

The semiconductor laser device 41, collimator lens 42, grating 43, beam splitter 4
4, objective lens 45, multi-lens 46 and photodetector 4
7 and the variable aperture means 48 correspond to the semiconductor laser element 41, the collimator lens 42, the grating 43, the beam splitter 44, and the optical pickup 40 shown in FIG.
The objective lens 45, the multi-lens 46, the photodetector 47 and the variable aperture means 48 have the same structure. Further, the variable aperture means 48 differs from the optical pickup 40 shown in FIG. 6 in that the beam splitter 44 and the grating 4 are different from each other.
It is arranged between 3 and 3.

The optical pickup 5 constructed in this way
At 0, the light beam from the semiconductor laser element 41 is collimated by the collimator lens 42, then separated into three beams by the grating, and passes through the aperture of the variable aperture means 48 or the aperture and the light control section. After passing through the beam splitter 44, it is further focused on the signal recording surface of the optical disc 49 via the objective lens 45.

The return light from the optical disk 49 again enters the beam splitter 44 via the objective lens 45,
After being reflected by the reflecting surface 44a of the beam splitter 44,
It converges on the photodetector 47 via the multi-lens 46.
As a result, the recording signal of the optical disc 49 is reproduced based on the detection signal of the photodetector 47.

If the optical disk 49 is an optical disk having a relatively thin disk substrate thickness of 0.6 mm,
In the variable aperture means 48, the light control section is set to be opaque. As a result, the variable aperture means 48 has a relatively small aperture because only the aperture transmits light, and the numerical aperture NA is set to 0.6. Therefore, since the spherical aberration is suppressed to a low level, the light beam is correctly focused on the signal recording surface of the optical disc 49 having a thin disc substrate. Further, in the case of an optical disc having a relatively thick disc substrate thickness of 1.2 mm, the variable aperture means 48 has its light control section set to be transparent. Thereby, the variable opening means 4
Reference numeral 8 has a relatively large aperture because the aperture and the light control section transmit light, and the numerical aperture NA is set to NA = NA0 or less. Here, since the objective lens 45 is designed so that the spherical aberration can be suppressed most with respect to the optical disc having the disc substrate thickness of 1.2 mm, the light beam is correctly focused on the signal recording surface of the optical disc 49. .

In this case, since the return light from the optical disk 49 enters the photodetector 47 without passing through the variable aperture means 48, the return light is the variable aperture means 4.
8 and therefore the photodetector 4
Since the incident light amount of the return light with respect to 7 is large, the photodetector 47 can read the signal more accurately.

In the above embodiment, the light control section 15 of the variable aperture means 15 is used for the optical discs having the disc substrate thicknesses of 1.2 mm and 0.6 mm, respectively.
By making b and 15e transparent or opaque, the light beam is focused on the signal recording surfaces of the optical disc having a relatively thin disc substrate thickness and the optical disc having a relatively thick disc substrate thickness. Alternatively, for example, the present invention can be applied to the case of reproducing a bonded optical disk in which two substrates are bonded and a normal optical disk.

[0050]

As described above, according to the present invention, there is provided an optical pickup in which recording and / or reproduction of an optical disc can be correctly performed even if the optical disc has a different disc substrate thickness. Will be.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a first embodiment of an optical pickup according to the present invention.

FIG. 2 is an enlarged perspective view showing a configuration of a variable aperture means in the optical pickup of FIG.

FIG. 3 is a schematic view showing the principle of the light control means using an electrochemical element that constitutes the light control section of the variable aperture means of FIG.

4 is an enlarged perspective view showing another configuration of the variable aperture means in the optical pickup of FIG.

FIG. 5 is a schematic perspective view showing a second embodiment of the optical pickup according to the present invention.

FIG. 6 is a schematic perspective view showing a third embodiment of the optical pickup according to the present invention.

FIG. 7 is a schematic perspective view showing a fourth embodiment of the optical pickup according to the present invention.

FIG. 8 is a schematic perspective view showing an example of a conventional optical pickup.

[Explanation of Codes] 10,30 Optical Pickup 11 Semiconductor Laser Element (Light Source) 12 Beam Splitter 12a Reflective Surface 13 Objective Lens 14 Photodetector 15 Variable Aperture Means 15a Frame 15b Dimmer 15c Aperture 16 Optical Disc 20 Spacers 21, 22 Transparent substrate 23, 24 Transparent electrode 25 Electrochemical element 40, 50 Optical pickup 41 Semiconductor laser element (light source) 42 Collimator lens 43 Grating 44 Beam splitter 45 Objective lens 46 Multi-lens 47 Photodetector 48 Variable aperture means 49 Optical disk

Claims (10)

[Claims] 1. A light source that emits a light beam, an objective lens that irradiates the light beam emitted from the light source so that the light beam is focused on a signal recording surface of an optical disc, and the objective lens is disposed between the light source and the objective lens. Beam splitter, and a photodetector for receiving the returning light beam from the signal recording surface of the optical disc separated by the beam splitter, and further arranged in the optical path between the light source and the optical disc. An optical pickup comprising variable aperture means for changing the transmittance of light by an applied current or voltage according to the substrate thickness of the optical disc. 2. The optical pickup according to claim 1, wherein the variable aperture means is a dimming element using an electrokeletal element. 3. The optical pickup according to claim 2, wherein the light control element is made of a solid material. 4. The optical pickup according to claim 2, wherein the light control element is made of an amorphous material. 5. The optical pickup according to claim 2, wherein the light control element is made of a liquid. 6. The optical pickup according to claim 2, wherein the light control element is made of gas. 7. The optical pickup according to claim 1, wherein the variable aperture means is arranged in an optical path between an objective lens and a light source. 8. The optical pickup according to claim 1, wherein the variable aperture means is arranged in an optical path between the objective lens and the beam splitter. 9. The optical pickup according to claim 1, wherein the variable aperture means is arranged in an optical path between the beam splitter and the light source. 10. The optical pickup according to claim 1, wherein the variable aperture means is arranged in an optical path between an objective lens and an optical disc.