JPH1064099A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a recording and a reproducing with respect to a high-density recording medium by lighting only a light source whose wavelength is longer or both light sources at the time of a recording and lighting only the light source of one side at the time of a reproduction to execute an aberration correction with a simple constitution. SOLUTION: When a semiconductor laser 1 is lighted, a light beam whose oscillation wavelength is 650nm propagates in a straight line through a dichroic mirror 3 and when a semiconductor laser 2 is lighted, a light beam whose oscillation wavelength is 780nm is reflectingly refracted in the mirror 3 and both light beams are made incident on a diffraction grating 4. After the light beams are separated into a main beam (for focusing error signal) and a subbeam (for tracking error signal), the beams are made to be parallel beams by a collimating lens 5 to be made incident on a beam splitter 6 to be converged on an optical recording medium 9 by being passed through an optical element 7 and an objective lens 8 to form spots. Reflected beams of the medium 9 are made to be parallel light beams in the lens 8 to pass through the splitter 6 to be converged on an anamorphic lens 11. Then, at the time of the recording, only the light source having the wavelength of 780nm is made to be lighted or the light source having the wavelength of 680nm is also made to be lighted and at the time of the reproduction, only the light source of one side of either of two light sources is made to be lighted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup device, and more particularly to an optical pickup device having two or more light sources.

[0002]

2. Description of the Related Art In recent years, as the application range of optical recording media has been widened, various types of light having different recording densities, substrate (protective layer) thicknesses, substrate (protective layer) materials, recording / reproducing methods, disk sizes and the like have been changed. A recording medium is provided. Therefore, the optical pickup device is required to have high versatility capable of handling different types of media in addition to basic functions such as recording and reproduction.

For example, as a recording medium having a different recording / reproducing method, a read-only type in which pits (fine irregularities) are provided on a recording surface, an organic dye is applied to a recording surface, and a high-power light beam is used during recording to apply the organic dye A write-once type in which the signal is recorded by changing the reflectivity of the signal, a magneto-optical type in which the signal is recorded by magnetization and this signal (magnetization direction) is detected by using the Kerr effect, and the signal is formed by a crystalline state such as a crystalline state and an amorphous state. And there is a phase change type in which this signal is detected by a reflected light amount difference due to a difference in optical constant N (= n−ik). In these recording media, the light intensity of the light beam is larger at the time of recording than at the time of reproduction. Need to be larger.

Next, the relationship between the recording density and the light beam spot will be described.

The recording density of a recording medium is defined by the size of a recording unit (recording mark). In the case of a low-density recording medium, the diameter of the recording mark is about 0.5 μm. The diameter of the recording mark is about 0.3 μm. On the other hand, the spot diameter also needs to be adjusted according to the diameter of the recording mark.
In this case, the spot diameter needs to be about 1.4 μm, and when the recording mark diameter is about 0.3 μm, the spot diameter needs to be about 0.9 μm.

In order to adjust the spot diameter according to the recording density of the recording medium as described above, it is necessary to change the numerical aperture of the objective lens and the wavelength of the light beam. Next, the relationship between the spot diameter, the numerical aperture of the objective lens, and the wavelength of the light beam will be described.

The spot diameter R is given by the following equation.

R = 0.61λ / NA In this equation, λ is the wavelength of the light beam, and NA is the numerical aperture of the lens, which is given by the following equation.

NA = n × sin θ In this equation, n is a refractive index, and θ is a value shown in FIG.
Is an angle to the exit pupil diameter as shown in FIG.

As can be seen from these equations, in order to reduce the spot diameter R, it is necessary to shorten the wavelength λ of the light beam or increase the numerical aperture NA of the lens, ie, θ.

However, when the numerical aperture NA of the lens increases, the spherical aberration generated on the substrate (protective layer) increases.
Here, the spherical aberration is a wavefront aberration generated when converged light passes through a parallel flat plate having a refractive index not equal to 1 (a parallel flat plate having a refractive index different from that of air), and narrows the light beam to the diffraction limit. In such an optical system, it is necessary to sufficiently reduce the wavefront aberration of the light beam. Generally, a standard called Marechal's criterion is known, and according to this criterion, the wavefront aberration amount needs to be smaller than 0.07λRMS.

Here, the fact that the wavefront aberration of the light beam contributing to the image formation is small means that the wavefront, that is, the equal phase surface of the light beam is a spherical surface centering on the spot 42 as shown in FIG. That's what it means.

However, the equal phase plane of the light beam is
In the case of a spherical surface centered on the spot 42 in FIG. 0 (a spherical surface indicated by a curve connecting the points a and a ′), a spherical surface centered on the spot 42 (point b, point b) outside the protective layer 40 ',
(A curved surface connecting the points b ″).

As described above, the reason why the equal phase plane of the light beam does not become a spherical surface centered on the spot 42 outside the protective layer 40 is that the refractive index of the protective layer 40 (for example, 1.55 in polycarbonate) and the air (vacuum) ) And the refractive index
Speed of light beam traveling in protective layer 40 and air (vacuum)
This is because the velocities of the light beams traveling inside are different.

That is, the speed of the light beam traveling in the protective layer 40 having a refractive index of 1.55 (the speed between dc) is higher than the speed of the light beam traveling in air (vacuum) (the speed between cb "). Is also slow, the line segment bd (or the line segment b ′) having the same optical path length
The length of d) is not equal to the length of the line segment b "d. The difference between the line segment bd (or the line segment b'd) and the line segment b" d becomes larger when the numerical aperture NA is large. .

Further, when the numerical aperture NA increases, FIG.
As shown in (1), the coma aberration generated when the optical axis of the light beam is inclined with respect to the optical recording medium 36 also increases. Specifically, the coma aberration is expressed by the following equation, the coma aberration amount W _c as can be seen from this equation increases in proportion to the cube of the numerical aperture.

[0017]

(Equation 1)

The inclination of the optical recording medium with respect to the optical axis of the light beam is mainly due to the warpage of the optical recording medium, and it is not uncommon that an inclination of, for example, about 0.7 degrees occurs.

Accordingly, when the wavelength λ of the light beam is shortened and the numerical aperture NA of the lens is increased in accordance with the increase in the density of the optical recording medium, the substrate ( The thickness of the protective layer is often reduced.

An optical recording medium having different thicknesses of the substrate (protective layer), for example, a low-density recording medium having a substrate (protective layer) thickness of 1.2 mm, and an optical recording medium having a substrate (protective layer) thickness of 0.6 mm
Since the amount of spherical aberration generated on the substrate (protective layer) differs from that of the high-density recording medium, the amount of spherical aberration previously given to the convergent light beam of the optical pickup device must be changed.

For this reason, in an optical pickup device which handles optical recording media having different thicknesses of the substrate (protective layer), usually,
The objective lens cannot be shared, and a means for exchanging a plurality of objective lenses according to the thickness of the substrate (protective layer) is provided. There is also known an optical pickup device that uses a liquid crystal element or a correction element without replacing an objective lens, and handles an optical recording medium having a different thickness of a substrate (protective layer) with a simple configuration.

Next, an optical pickup device using a liquid crystal element and an optical pickup device using a correction element will be described.

FIG. 14 shows an optical pickup device using a liquid crystal element described in Japanese Patent Application Laid-Open No. H8-102079.

In this optical pickup device,
The light beam emitted from the semiconductor laser 31 is
After being separated into a main beam (for a focus error signal and a recording / reproducing signal) and a sub-beam (for a tracking error signal) in 2, it is incident on a collimator lens 33. The light beam that has entered the collimator lens 33 is converted from divergent light into parallel light, and then enters the beam splitter 34. The light beam that has entered the beam splitter 34 is reflected in the direction of the objective lens 35 and enters the objective lens 35 via the liquid crystal element 51. The light beam incident on the objective lens 35 is changed from parallel light to convergent light, and forms a spot on the recording surface of the optical recording medium 36.

This light beam is reflected by the recording surface and is modulated according to the information recorded on the recording surface. The light beam reflected by the recording surface is converted into parallel light again by the objective lens 35, and enters the beam splitter 24. The light beam that has entered the beam splitter 24 travels straight through the beam splitter 24 and enters the condenser lens 37. The light beam that has entered the condenser lens 37 is converted from parallel light into convergent light, and enters the anamorphic lens 38. The light beam that has entered the anamorphic lens 38 generates astigmatism for detecting a focus error signal, and enters the light receiving element 39. The light beam incident on the light receiving element 39 is converted into an electric signal such as a tracking error signal, a focus error signal, and a recording / reproducing signal.

In order to obtain an accurate electric signal in the optical pickup device, it is necessary to form an appropriate spot on the recording surface. In this optical pickup device, the influence of aberration of the light beam using the liquid crystal element 51 is used. Has been reduced.

FIGS. 15 and 16 show a case where recording and reproduction are performed on a high-density recording medium having a thin substrate (protective layer) and a low-density recording medium having a thick substrate (protective layer) by using the liquid crystal element 51.

FIG. 15A is a plan view of the liquid crystal element, and FIG.
(Explanational diagram showing a light beam transmitted through a liquid crystal element) shows a case of reproducing a high-density recording medium. A light beam incident on the liquid crystal element 51 is transmitted uniformly through the liquid crystal element 51,
The light is converged by the objective lens 52. Also, the objective lens 52
When the light beam passes through, the light beam is provided with a spherical aberration in the opposite direction to cancel the spherical aberration generated on the substrate (protective layer) 53a of the high-density recording medium (hereinafter, referred to as aberration correction). The light beam of the convergent light having the aberration corrected as described above transmits through the substrate (protective layer) 53a, and forms a small spot 55a on the recording surface 54a.

FIG. 16A is a plan view of the liquid crystal element, and FIG.
An explanatory diagram showing a light beam transmitted through a liquid crystal element) shows a case of reproducing a low-density recording medium. The liquid crystal element 51 blocks a peripheral portion of the light beam, and only the central light beam is transmitted to the objective lens 52. The light enters and is converged by the objective lens 52.
Here, when the light beam is transmitted through the objective lens 52, the light beam is subjected to the same aberration correction as in the case of the high-density recording medium. The convergent light beam thus corrected for aberration passes through the substrate (protective layer) 53b and forms a spot 55b on the recording surface 54b. However, since θ1> θ2, an effective aperture The number becomes smaller, and the spot diameter becomes larger than when reproducing a high-density recording medium.

A low-density recording medium substrate (protective layer) 53
Since b is thicker than the substrate (protective layer) 53a of the high-density recording medium, aberration correction is insufficient with the same aberration correction as in the case of the high-density recording medium.
2, that is, since the numerical aperture is small, the spherical aberration that cannot be completely corrected is small and can be ignored. Therefore, it can be considered that spherical aberration is approximately corrected.

That is, the amount of spherical aberration generated is large in the peripheral portion of the light beam (light beam) and extremely small in the central portion of the light beam (light beam). Even if sufficient, spherical aberration hardly matters.

As described above, in the optical pickup device using the liquid crystal element 51, by controlling the diameter (effective numerical aperture) of the light beam incident on the objective lens, the low-density recording medium and the low-density recording medium can be controlled. In this case, the spot diameter was changed, and the spherical aberration was approximately corrected.

Next, an optical pickup device using a correction element described in Japanese Patent Application Laid-Open No. 5-120720 will be described.

FIG. 17 shows an optical pickup device for performing recording and reproduction on a high-density recording medium with a thin substrate (protective layer) and a low-density recording medium with a thick substrate (protective layer) using the correction element 60. In this optical pickup device, the light beam emitted from the long wavelength semiconductor laser 31a is
a, collimator lens 33a, beam splitter 34
a, a light beam emitted from the short-wavelength semiconductor laser 31b through the objective lens 35 and spotted on the recording surface of the optical recording medium 36 through the diffraction grating 32b, the collimator lens 33b, the beam splitter 34b, and the objective lens 35. To form

In the above optical pickup device, when the light beam passes through the objective lens 36, the light beam is given a spherical aberration in the opposite direction to cancel the spherical aberration generated on the substrate (protective layer) of the high-density recording medium. Therefore, the short wavelength semiconductor laser 3
When recording / reproducing is performed on the high-density recording medium by using the light beam emitted from 1b, recording / reproducing is performed without inserting the correction element 60 in the optical path. On the other hand, when performing recording and reproduction on a low-density recording medium having a substrate (protective layer) thicker than a high-density recording medium, the correction amount is insufficient only by the aberration correction given by the objective lens 36. To compensate for the missing correction amount.

As described above, by attaching and detaching the correction element by a mechanical mechanism, recording and reproduction can be performed on a high-density recording medium having a thin substrate (protective layer) and a low-density recording medium having a thick substrate (protective layer).

In the optical pickup device, the objective lens moves in a focus direction (a direction perpendicular to the recording surface of the recording medium) or a tracking direction (a direction parallel to the recording surface of the recording medium) during recording and reproduction. The amount of wavefront aberration generated when the correction element 60 is inserted into the optical path by the tracking operation changes.

First, when the focusing operation is performed as shown in FIG.
It changes as shown in FIG. Here, the amount of wavefront aberration is lowest when the objective lens 36 is in a neutral position, and is within a range of -0.5 to +0.5 mm, which is a general movable range in the focusing operation, and is based on Marechal's standard. (0.07λRMS) can be sufficiently satisfied.

On the other hand, when the tracking operation is performed as shown in FIG.
It changes as shown by the curve 61 in (b). This curve 6
The change in the amount of wavefront aberration shown in FIG. 1 corresponds to the change in the amount of wavefront aberration in the optical pickup device using the liquid crystal element (curve 6).
Recording and reproduction cannot be performed unless the optical recording medium (disc) is much larger than 2) and has a very small eccentricity.

In the optical pickup device in which the correction element 60 is inserted in the optical path, the tolerance for the inclination of the recording medium is small, and it is difficult to perform recording and reproduction on an optical recording medium with a large warp.

[0041]

Problems to be solved by the invention are described below in JP-A-8-1.
Problems with an optical pickup device using a liquid crystal element described in Japanese Patent Application Laid-Open No.
Problems in the optical pickup device using the correction element described in Japanese Patent Publication No. 720 are listed.

[Problems in Optical Pickup Apparatus Using Liquid Crystal Element] (1) Since the liquid crystal element has a complicated structure and is expensive, an optical pickup apparatus using the liquid crystal element becomes expensive.

(2) Since the liquid crystal element requires an operation power supply, the structure of the optical pickup device becomes complicated, and the power consumption increases.

(3) Since the liquid crystal element is composed of a combination of a liquid crystal, a conductive transparent film, and a polarizing filter, the loss of the light beam is large, and the utilization efficiency of the light beam is reduced. Therefore, a high-output semiconductor laser is required, and the power consumption of the optical pickup device increases.

(4) It is necessary to use a short-wavelength semiconductor laser in order to perform recording / reproducing on a high-density recording medium. However, a high-output type short-wavelength semiconductor that outputs a light beam having a high light intensity required for recording. Lasers are very expensive and unreliable.

(5) When the optical pickup device is constituted only by the short-wavelength semiconductor laser, the write-once recording medium (using an organic dye) corresponding to the long-wavelength light beam is used as the light beam output from the short-wavelength semiconductor laser. Write-once recording medium)
Cannot be reproduced, and if it is attempted to reproduce, there is a possibility that the recording medium will be irreparably damaged.

[Problems in Optical Pickup Apparatus Using Correction Element] (1) It is difficult to perform recording / reproducing on an optical recording medium having a small allowance for the tracking operation and a large eccentricity.

(2) It is difficult to perform recording and reproduction on an optical recording medium having a small allowance for the inclination of the optical recording medium and a large warpage.

(3) Depending on the thickness of the substrate (protective layer) of the optical recording medium, a high precision is required for a mechanical mechanism for attaching and detaching the correction element, and it is difficult to manufacture an optical pickup device.

Accordingly, the present invention solves the above-mentioned problems, and comprises means capable of correcting aberrations with a simple configuration, and performs recording and reproduction on a high-density recording medium without using a high-output short-wavelength semiconductor laser. An object of the present invention is to provide an optical pickup device that can perform the operation.

[0051]

According to a first aspect of the present invention, there is provided an optical pickup device having two light sources for generating light beams having different wavelengths, and for guiding the light beams emitted from the light sources to an optical recording medium. In the optical pickup device having the means, there is a portion where the transmittance of the light beam having the longer wavelength mainly decreases in the optical path through which the two light beams having different wavelengths pass together. Or both light sources are turned on, and at the time of reproduction, only one of the light sources is turned on.

The optical pickup device according to claim 2 is
In the optical pickup device according to claim 1, a portion where the transmittance of the light beam having a longer wavelength mainly decreases is:
The transparent base material is coated with a dye having a transmittance different depending on the wavelength.

The optical pickup device according to claim 3 is
The optical pickup device according to claim 2, wherein the transparent substrate coated with the dye is an objective lens.

The optical pickup device according to claim 4 is
The optical pickup device according to claim 2 or 3,
The dye is naphthalocyanine.

The optical pickup device according to claim 5 is
In the optical pickup device according to any one of claims 1 to 4, the transmittance at the outer peripheral portion of the cross section of the light beam is mainly reduced at a portion where the transmittance of the light beam having a longer wavelength mainly decreases. It is characterized by being reduced.

The optical pickup device according to claim 6 is:
In the optical pickup device according to any one of claims 1 to 4, the outer peripheral portion and the central portion of the cross section of the light beam mainly correspond to the portion where the transmittance of the light beam having the longer wavelength mainly decreases. It is characterized in that there is a portion that decreases and the transmittance hardly decreases between the outer peripheral portion and the central portion of the cross section.

[0057]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup device according to the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are explanatory diagrams showing the configuration of an optical pickup device according to the present invention including a semiconductor laser 1 having an oscillation wavelength of 650 nm and a semiconductor laser 2 having an oscillation wavelength of 780 nm. FIG. FIG. 2 shows the case where the semiconductor laser 2 is turned on. Here, the light beam output from the semiconductor laser 1 travels straight through the dichroic mirror 3, the light beam output from the semiconductor laser 2 is reflected by the dichroic mirror 3, and any light beam is diffracted by the diffraction grating 4.
Incident on. The light beam incident on the diffraction grating 4 is split into a main beam (for a focus error signal and a recording / reproducing signal) and a sub beam (for a tracking error signal), and then enters the collimator lens 5. The light beam that has entered the collimator lens 5 is converted from divergent light into parallel light, and enters the beam splitter 6. The light beam incident on the beam splitter 6 is
The light is reflected in the direction of the objective lens 8 and enters the objective lens 8 via the optical element 7. The light beam incident on the objective lens 8 is changed from parallel light to convergent light, and forms a spot on the recording surface of the optical recording medium 9.

The light beam having a spot formed on the recording surface of the optical recording medium 9 in this manner is reflected by the recording surface,
The light enters the objective lens 8. The light beam that has entered the objective lens 8 is converted into parallel light again, passes through the optical element 7, travels straight through the beam splitter 7, and enters the condenser lens 10.
The light beam that has entered the condenser lens 10 is converted from parallel light into convergent light, and enters the anamorphic lens 11. The light beam incident on the anamorphic lens 11 generates astigmatism for detecting a focus error signal, and reaches the light receiving element 12. The light beam reaching the light receiving element 12 is a tracking error signal,
It is converted into a focus error signal and a recording / reproducing signal.

In the optical pickup device, the effective numerical aperture of the objective lens 8 (the substantial numerical aperture for the light beam incident on the objective lens 8) depends on whether the wavelength of the light beam is 650 nm or 780 nm. Number) changes. The effective numerical aperture is such that the wavelength of the light beam is 78.
The light beam output from the semiconductor laser 1 having the oscillation wavelength of 780 nm forms an image with a smaller numerical aperture as shown in FIG.

The change in the effective numerical aperture is caused by the fact that the optical element 7 coated with a dye whose transmittance changes according to the wavelength of the light beam.
This causes the diameter of the light beam incident on the objective lens 8 to change.

FIG. 3 is a perspective view showing an example of the optical element 7 installed in the optical path of the optical pickup device according to the present invention. The optical element shown in FIG.
The colorant 7b is applied to the outer periphery of the entrance surface or the exit surface of the parallel plate transparent substrate 7a made of K7, and there is a circular area at the center portion where the pigment 7b is not applied. On the other hand, the optical element shown in (b) is obtained by applying the dye 2 to the entirety of the incident surface or the outgoing surface of the same transparent base material 7a. (A portion where the dye 7b is thinly applied).

In the above optical element, a naphthalocyanine dye was used as the dye 7b. As shown in FIG. 4, the transmittance of the dye sharply decreases around the wavelength of 780 nm.

The transparent substrate 7a may be made of a material other than optical glass that transmits light, such as plastic.

FIG. 5 is a sectional view of the optical element shown in FIG.
FIG. 3A is a cross-sectional view and FIG. 4B shows a transmittance distribution along the AA ′ cross-section ((a) cross-sectional view, (b) transmittance distribution for a light beam having a wavelength of 650 nm, (b) wavelength 780 nm).
Distribution of transmittance for the light beam).

As shown in the sectional view of FIG. 5A, a dye is applied to the outer periphery of this optical element, and the transmittance of the dye to a light beam having a wavelength of 650 nm is substantially one.
In the case of a light beam having a wavelength of 650 nm, FIG.
As shown in (b), almost 100% of the light beam incident on the optical element is transmitted over the entire surface irrespective of the central portion or the outer peripheral portion.
On the other hand, the transmittance of the dye to a light beam having a wavelength of 780 nm is almost 0%. Therefore, in the case of a light beam having a wavelength of 780 nm, as shown in FIG. No (transmittance is almost 0
%), And the light beam incident on the central portion is transmitted by almost 100%.

FIG. 6 shows the optical element B shown in FIG.
It shows a cross-sectional view taken along the line B 'and a distribution of transmittance along the cross-section BB' ((a) cross-sectional view, (b) distribution of transmittance for a light beam having a wavelength of 650 nm, (b) wavelength 780 nm).
Distribution of transmittance for the light beam).

As shown in the cross-sectional view of FIG. 6A, this optical element is coated with a dye that is thicker at the outer periphery and thinner at the center, and has a transmittance for a light beam having a wavelength of 650 nm of the dye. Therefore, in the case of a light beam with a wavelength of 650 nm, almost 100% of the light beam incident on the optical element is transmitted over the entire surface irrespective of the central portion or the outer peripheral portion, as shown in FIG. On the other hand, the transmittance of the dye to a light beam having a wavelength of 780 nm is almost 0%. Therefore, the transmittance of the light beam approaches 0% in the outer periphery where the dye is applied thickly, and in the center where the dye is thinly applied. The light beam transmittance approaches 100%.

Therefore, when the optical element as shown in FIG. 3 is installed in the optical path of the optical pickup device, the wavelength 65
For a light beam of 0 nm, a small spot is formed because the effective numerical aperture is large. On the other hand, for a light beam having a wavelength of 780 nm, the spot diameter increases as the wavelength is longer and the effective numerical aperture is smaller.

Next, a case where a signal recorded on a recording medium is reproduced by using the optical pickup device shown in FIGS. 1 and 2 will be described.

First, when reproducing a high-density recording medium, only the semiconductor laser 1 having an oscillation wavelength of 650 nm is turned on, a small spot is formed on the recording surface, and a signal recorded on the recording medium is read. On the other hand, when reproducing a low-density recording medium, only the semiconductor laser 2 having an oscillation wavelength of 780 nm is turned on, a relatively large spot is formed on the recording surface, and a signal recorded on the recording medium is read.

Here, the high-density recording medium and the low-density recording medium usually have different thicknesses of the substrate (protective layer) (usually,
Since the low-density recording medium has a thicker substrate (protective layer), the amount of spherical aberration generated on the substrate (protective layer) is also different, but the aberration correction performed by the objective lens or other optical elements is performed by high-density recording. Be suitable for the medium. Therefore, in the case of a low-density recording medium, although sufficient aberration correction is not performed, only the light beam at the center of the objective lens, which generates a small spherical aberration, contributes to image formation. be able to.

In this optical pickup device, the thickness of the substrate (protective layer) of the high-density recording medium was 0.6 mm, and the thickness of the substrate (protective layer) of the low-density recording medium was 1.2 mm.
When reproducing the high-density recording medium, the numerical aperture of the objective lens is 0.6,
The substantial numerical aperture of the objective lens during reproduction of the low-density recording medium was 0.35. The thickness of the dye applied to the optical element was 800A.

Next, a case where a signal is recorded on a recording medium will be described.

Normally, when a signal is recorded on a recording medium, a small spot is not required as in the case of reproduction, but the light intensity of the light beam needs to be stronger than in the case of reproduction. Therefore, even with a high-density recording medium, signals can be recorded using only the semiconductor laser 2 having an oscillation wavelength of 780 nm. However, at this time, the semiconductor laser needs to be turned on with a higher output than in the case of reproduction. In order to further increase the light intensity at the center of the spot, both the semiconductor laser 2 having an oscillation wavelength of 780 nm and the semiconductor laser having an oscillation wavelength of 650 nm may be turned on.

Also in the case of a low-density recording medium, a signal can be recorded using only the semiconductor laser 2 having an oscillation wavelength of 780 nm by adjusting the lighting output.

If a high-power semiconductor laser 1 having an oscillation wavelength of 650 nm is used, a signal can be recorded on a recording medium using only the semiconductor laser 1 having an oscillation wavelength of 650 nm. Since the output type is very expensive, it is possible to provide an optical pickup device at a lower price by using only a semiconductor laser having an oscillation wavelength of 780 nm, that is, a semiconductor laser having a long oscillation wavelength, as a high output type.

FIG. 7 shows a light intensity distribution along a radial direction of a spot formed by a light beam. Here, 20 is the light intensity distribution when only the semiconductor laser 2 having the oscillation wavelength of 780 nm is turned on, 21 is the light intensity distribution when only the semiconductor laser 1 having the oscillation wavelength of 650 nm is turned on, and 22 is the oscillation intensity. This is a light intensity distribution when both the semiconductor laser 2 having a wavelength of 780 nm and the semiconductor laser 1 having an oscillation wavelength of 650 nm are turned on. As is clear from the figure, when both the semiconductor laser 2 having the oscillation wavelength of 780 nm and the semiconductor laser 1 having the oscillation wavelength of 650 nm are turned on, the light intensity at the center of the spot can be further increased.

In the optical element 7, a dye is applied only to the outer peripheral portion of the transparent base material to block the light beam on the outer peripheral portion of the objective lens where the generated spherical aberration is large. In the case where the spot becomes too large due to the decrease in the effective numerical aperture, FIG. 8 (a) is a perspective view, and FIG.
As shown in (C 'cross-sectional view), the size of the spot may be adjusted by applying the dye 7b also to the center of the transparent substrate 7a. This is an application of the super-resolution effect. By blocking the light at the central portion of the light beam, a spot smaller than the theoretical diffraction limit can be formed.

FIG. 9 shows a light intensity distribution along a radial direction of a spot formed by a light beam when the optical element shown in FIG. 8 is used. Here, 23 indicates the light intensity distribution when the light at the center of the light beam is not blocked, and 24 indicates the light intensity distribution when the light at the center is blocked, that is, when the super-resolution effect is used. . As shown in the figure, when the super-resolution effect is used, the spot (diameter of the spot) can be reduced, but the side lobe 24a becomes larger than when the super-resolution effect is not used.

Therefore, when utilizing the super-resolution effect,
In consideration of the influence of the side lobe 24a, it is necessary to adjust the diameter of the dye 7b applied to the center of the transparent substrate 7a.
Here, the area of the portion where light was shielded in order to use the super-resolution effect was about 10% of the transmission portion when the super-resolution effect was not used.

In the optical pickup device shown in FIGS. 1 and 2, an optical element coated with a dye is separately installed, and a spot of a light beam output from a semiconductor laser having a longer oscillation wavelength is provided. The diameter (effective numerical aperture, super-resolution effect) of the lens was adjusted, and the effect of spherical aberration was reduced.
Dye may be applied to the surface of the beam splitter, diffraction grating, collimator lens, or other optical element.
In this case, there is no need to provide a separate transparent substrate,
The number of parts can be reduced. Further, a dye may be applied to the surface of a plurality of optical elements.

As shown in FIG. 10 (cross-sectional view of the objective lens), when the pigment 26 is applied to the surface of the objective lens 25, the following effects can be obtained. Usually, the objective lens always moves using a servo mechanism in order to follow a track of the optical recording medium (hereinafter, referred to as a tracking operation). Apply dye to optical elements other than the objective lens,
When the diameter of the light beam is controlled, the intensity distribution in the cross section of the light beam does not move together with the tracking operation of the objective lens, but when the pigment is applied to the objective lens, the tracking operation is performed. However, since the intensity distribution is always concentric about the optical axis of the objective lens, a more preferable spot can be formed.

The same effect can be expected even if an optical element coated with a dye is provided on the objective lens driving means. However, it is desirable that the mass of the movable part for performing the tracking operation and the focusing operation be smaller, It is preferable to apply the dye directly to the surface of the objective lens, rather than providing the optical element described above.

As described above, in the optical pickup device of the present invention, two light sources (semiconductor lasers) having different oscillation wavelengths share an optical system and output from the semiconductor laser having the longer oscillation wavelength. Light beam
By adjusting the luminous flux that contributes to the formation of the spot,
Adjustment of spot diameter (effective numerical aperture, super-resolution effect),
The effect of spherical aberration is reduced.

When reproducing a signal recorded on a recording medium, a light beam output from a semiconductor laser having a shorter oscillation wavelength or a semiconductor having a longer oscillation wavelength is used in accordance with the recording density of the recording medium. The light beam output from the laser is used.

On the other hand, when recording a signal on a recording medium,
Depending on the recording density of the recording medium, a light beam output from a semiconductor laser with a longer oscillation wavelength or a light beam output from a semiconductor laser with a longer oscillation wavelength and a light beam output from a semiconductor laser with a shorter oscillation wavelength Both light beams are used.

In recording a signal on a recording medium in this way, regardless of the recording density of the recording medium, only the semiconductor laser having a longer oscillation wavelength is used, and light intensity sufficient to record a signal is secured. doing.

Incidentally, the optical pickup device of the present invention
The present invention can be widely applied to an optical pickup device having more than two beam sources, a finite system optical pickup device, and the like.

In the optical pickup device of the present invention, as a means for adjusting a light beam contributing to the formation of a spot, an optical element having a different transmittance depending on the wavelength, such as a dichroic mirror using a dielectric multilayer film, is used. You may.

The dye material for adjusting the luminous flux contributing to the formation of spots by the dye film is a dye other than the naphthalocyanine dye as long as its transmittance changes according to the wavelength of the light beam. There may be.

Regarding the method of forming the dye film, a method other than coating (coating and drying a dispersion of a dye in an organic solvent), for example, a vapor deposition method (physical vapor deposition method, chemical vapor deposition method) and a sputtering method Or the like.

The dye material may be a dye other than the naphthalocyanine dye, as long as the transmittance changes according to the wavelength of the light beam.

Further, regarding the film shape and film thickness distribution of the dye,
Although not particularly limited, it is necessary to appropriately set these in consideration of the recording density of the optical recording medium, the thickness of the substrate (protective layer), and the like.

Here, the relative relationship between the numerical apertures when handling a high-density recording medium and when dealing with a low-density recording medium is as follows.
The effective numerical aperture of the objective lens when handling low-density recording media is preferably in the range of 40% to 85% when handling high-density recording media, and more preferably in the range of 50% to 80%.

When a low-density recording medium is handled, the ratio of the light intensity between the central portion and the outer peripheral portion (transmitting portion and blocking portion) is 2: 1 to 1
It is preferably in the range of 100: 1, more preferably in the range of 4: 1 to 50: 1. Of course, ideally, there is no light intensity at the outer periphery, that is, it is desirable that the light be completely blocked. If the film thickness is too large, the light intensity at the outer peripheral portion is reduced even at a wavelength of 650 nm (when dealing with a high-density recording medium). It is desirable to set the film thickness in consideration of the following. Further, if the thickness of the dye is in the range of 50A to 2000A, the amount of wavefront aberration generated in the film portion of the dye can be almost ignored, so that the thickness of the dye is desirably in this range.

When the light at the center of the light beam is shielded in order to utilize the super-resolution effect, the shape of the light shielding portion does not necessarily have to be concentric, but may be elliptical, square, or the like. It may be.

The area of the portion that blocks light when the super-resolution effect is used is preferably 30% or less, more preferably 5% or more of the transmission portion when the super-resolution effect is not used. 15% or less.

The recording medium may be an optical recording medium such as an optical card or an optical tape other than the disc.

[0100]

According to the present invention, the following effects can be obtained by the above configuration.

(1) Compared to the case where a liquid crystal element is used, the configuration of the optical pickup device is simplified, and the product cost is reduced.

(2) Regarding the control of the diameter of the light beam incident on the objective lens, it is not necessary to perform a switching operation or the like, so that the diameter of the light beam is controlled without increasing the power consumption of the optical pickup device. Can be.

(3) In the present invention, since the means for adjusting the light beam contributing to the formation of the spot has a small amount of aberration and a small loss of light amount, the light beam can be used efficiently.

(4) In a writable recording medium using an organic dye (for example, according to the CD-WO standard), if the dye applied to the recording surface has wavelength dependency, a plurality of In some cases, it is necessary to use a light source that outputs light beams of different wavelengths. In such a case, the optical pickup device can be configured without significantly increasing product cost and power consumption.

(5) Only a long-wavelength semiconductor laser is required as a high-output semiconductor laser required for recording a signal on a recording medium, so that an inexpensive optical pickup device can be provided.

(6) Since the allowable width for the tracking operation is wide (the fluctuation of the wavefront aberration due to the tracking operation is small), it is possible to correspond to a recording medium having a large eccentricity. That is, the recording medium has a high resistance to eccentricity.

(7) Since the tolerance for the inclination of the recording medium is large, it is possible to cope with a recording medium having a large warpage. That is, the recording medium has a high resistance to warpage.

(8) Since there is no need for a mechanical mechanism for attaching and detaching an optical element for correction according to the thickness of the substrate (protective layer) of the recording medium, the configuration of the optical pickup device can be simplified.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an optical pickup device of the present invention (when a semiconductor laser 1 is turned on).

FIG. 2 is an explanatory diagram showing the configuration of the optical pickup device of the present invention (when the semiconductor laser 2 is turned on).

FIG. 3 is a perspective view showing a dye applied to an entrance surface or an exit surface of a transparent substrate.

FIG. 4 is a graph showing the relationship between the transmittance of a dye and the wavelength of a light beam.

FIG. 5 is a cross-sectional view of an optical element coated with a dye (the optical element shown in FIG. 3A) (AA ′ cross section shown in FIG. 3A) and the transmittance distribution along the cross section. is there.

6 is a cross-sectional view (BB ′ cross section shown in FIG. 3B) of an optical element coated with a dye (the optical element shown in FIG. 3B) and a transmittance distribution along the cross section. is there.

FIG. 7 is a light intensity distribution along a radial direction of a spot.

FIG. 8 is a perspective view and a cross-sectional view (CC ′ cross-section) showing a dye applied to an incident surface or an outgoing surface of a transparent base material (when the super-resolution effect is used).

FIG. 9 is a light intensity distribution along the radial direction of a spot (when the super-resolution effect is used).

FIG. 10 is a cross-sectional view showing a case where a pigment is applied to the surface of the objective lens.

FIG. 11 is an explanatory diagram for explaining a numerical aperture.

FIG. 12 is an explanatory diagram for describing spherical aberration generated on a substrate (protective layer).

FIG. 13 is an explanatory diagram showing an inclination of an optical recording medium (optical disc).

FIG. 14 is an explanatory diagram showing a configuration of a conventional optical pickup device (when a liquid crystal element is used).

FIG. 15 is an explanatory view showing a plan view of a liquid crystal element and a light beam transmitted through the liquid crystal element (when reproducing a high-density recording medium).

FIG. 16 is an explanatory view showing a plan view of a liquid crystal element and a light beam transmitted through the liquid crystal element (when reproducing a low-density recording medium).

FIG. 17 is an explanatory diagram showing a configuration of a conventional optical pickup device (when a correction element is used).

FIG. 18 is an explanatory diagram showing a focusing operation and a change in the amount of wavefront aberration during the operation.

FIG. 19 is an explanatory diagram illustrating a tracking operation and a change in a wavefront aberration amount during the operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Semiconductor laser 3 Dichroic mirror 4 Diffraction grating 5 Collimator lens 6 Beam splitter 7 Optical element (optical element coated with pigment) 7a Transparent substrate 7b Pigment 8 Objective lens 9 Optical recording medium 10 Condensing lens 11 Anamorphic lens 12 Light receiving element

Claims (6)

[Claims] 1. An optical pickup device comprising two light sources for generating light beams having different wavelengths and optical means for guiding a light beam emitted from the light sources to an optical recording medium. There is a portion where the transmittance of the longer wavelength light beam mainly decreases in the optical path through which the two different light beams pass together. During recording, only the longer wavelength light source or both light sources are turned on. An optical pickup device characterized in that only one of the light sources is turned on during reproduction. 2. The optical pickup device according to claim 1, wherein a portion where the transmittance of the light beam having the longer wavelength mainly decreases is coated with a dye having a transmittance different depending on the wavelength. An optical pickup device, characterized in that: 3. The optical pickup device according to claim 2, wherein the transparent substrate coated with the dye is an objective lens. 4. The optical pickup device according to claim 2, wherein the dye is naphthalocyanine. 5. The optical pickup device according to claim 1, wherein the transmittance of the light beam having a longer wavelength mainly decreases in the portion of the outer periphery of the cross section of the light beam. An optical pickup device characterized in that transmittance is mainly reduced. 6. The optical pickup device according to claim 1, wherein the transmittance of a light beam having a longer wavelength is mainly reduced at an outer peripheral portion of a cross section of the light beam. An optical pickup device characterized in that a central portion is mainly reduced, and a portion where transmittance is hardly reduced between the outer peripheral portion of the cross section and the central portion.