JP2000348376A - Optical head and recording/reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical head capable of recording and/or reproducing to/from plural kinds of information recording media different in wavelength by providing plural light sources having different wavelengths and a common single optical system. SOLUTION: This method is provided with a 1st light source 2 for emitting the light of 1st wavelength, a 2nd light source 7 for emitting the light of 2 and wavelength longer than the 1st wavelength, and an objective lens 14 for converging the lights of 1st and 2nd wavelength on the information recording surfaces of the information recording media corresponding to the lights of respective wavelengths. The objective lens 14 is designed so that the aberration is decreased with respect to the light of 1st wavelength. For the light of 2nd wavelength, the optical path length to the objective lens from the 2nd light source 7 is arranged shorter than the optical path length to the objective lens 14 from the 1st light source 2 so that the aberration generated on the objective lens 14 by the color dispersion of the objective lens material is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head having a plurality of light sources including a short-wavelength laser light source (wavelength: 350 nm to 500 nm) and used for recording and / or reproduction of an information recording medium such as an optical disk. . Also, the present invention
The present invention relates to a recording / reproducing method for recording and / or reproducing information on / from an information recording medium using a plurality of light sources including a short wavelength laser light source.

[0002]

2. Description of the Related Art FIG. 13 is a block diagram of a conventional optical head using a short wavelength laser light source. A semiconductor laser (wavelength 850) is used as a light source for recording / reproducing the information recording medium.
nm) and SHG (Second Harmonic Genera) that converts the wavelength of the incident light into half by generating the second harmonic.
short-wavelength laser light source (425
nm). As shown in the figure, a semiconductor laser 101 and an SHG element 1 for converting the wavelength thereof to half
The laser light 103 emitted from the light source 02 is converted into parallel light by a collimating lens 104, reflected by the rising mirror 106 toward the information recording medium 109, and
After being converted into circularly polarized light by the 波長 wavelength plate 107, the information recording surface 110 of the information recording medium 109 is
Focus on The reflected light from the information recording surface 110 is converted by the quarter-wave plate 107 into linearly polarized light having a polarization direction perpendicular to the polarization direction of the outward laser light 103,
After being reflected by the polarization beam splitter 105, it is incident on the detection lens 111, is collected on the light receiving element 112, and a signal is detected.

[0003]

The wavelength is from 350 nm to 5 nm.
In a conventional optical head for recording or reproducing information on a high-density information recording medium using a short-wavelength laser light source included in a range of 00 nm, light of a red wavelength or light of an infrared wavelength is applied to the same optical system including an objective lens. When the light is made incident, aberration occurs due to chromatic dispersion of the objective lens material with respect to light of these wavelengths. Therefore, DVDs using light of these wavelengths (used wavelength: about 650 nm), DVD-Rs (used wavelength: about 65 nm)
0 nm), CD (used wavelength: about 800 nm), CD-R
(Used wavelength: about 800 nm), CD-RW (used wavelength:
(About 800 nm), there was a problem that information could not be recorded and / or reproduced using the same optical system as the optical head.

The present invention solves the above problems,
Using the same optical system, a high-density disk (used wavelength: about 350 to 500 nm), DVD, DVD-R, CD, C
It is an object of the present invention to provide an optical head capable of recording and / or reproducing information on and from an information recording medium of a plurality of specifications having different working wavelengths such as a DR and a CD-RW. In particular, a light source that emits light having a wavelength of 350 nm to 500 nm,
Light source emitting light of 00 nm to 700 nm and wavelength of 70
An object of the present invention is to provide a small-sized optical head that includes at least one of light sources that emit light of 0 nm to 900 nm and has a good light-collecting characteristic for each light using a common single optical system. And Further, the present invention uses an optical head including a plurality of light sources having different wavelengths and a common single optical system to record and / or reproduce information on and from a plurality of types of information recording media having different use wavelengths. It is an object of the present invention to provide a recording / reproducing method that can perform the recording / reproduction.

[0005]

The present invention has the following configuration to achieve the above object.

An optical head according to a first configuration of the present invention has a first light source that emits light of a first wavelength and a second light source that emits light of a second wavelength longer than the first wavelength. An optical head comprising: a light source; and an objective lens for condensing the light of the first wavelength and the light of the second wavelength on an information recording surface of an information recording medium corresponding to the light of each wavelength. The objective lens is designed such that aberration is small with respect to the light of the first wavelength, and the objective lens is designed to have a small aberration with respect to the light of the second wavelength due to chromatic dispersion of the material of the objective lens. An optical path length from the second light source to the objective lens is shorter than an optical path length from the first light source to the objective lens so as to reduce generated aberration.

By setting the two optical path lengths as described above, it is possible to reduce the aberration generated by the objective lens with respect to the light of the second wavelength, and to improve the light condensing characteristics of the light of the second wavelength. I do. Therefore, using the same optical system, recording and / or reproduction can be performed on the information recording medium corresponding to the second wavelength in addition to the information recording medium corresponding to the first wavelength. Further, by using a common optical system, the configuration of the optical head can be simplified and reduced in size.

An optical head according to a second configuration of the present invention has a first light source that emits light of a first wavelength and a second light source that emits light of a second wavelength longer than the first wavelength. An optical head comprising: a light source; and an objective lens for condensing the light of the first wavelength and the light of the second wavelength on an information recording surface of an information recording medium corresponding to the light of each wavelength. The objective lens is designed so that aberration is small with respect to the light having the second wavelength, and the objective lens is configured to have a small aberration with respect to the light having the first wavelength due to chromatic dispersion of the material of the objective lens. The optical path length from the first light source to the objective lens is set longer than the optical path length from the second light source to the objective lens so as to reduce the generated aberration.

By setting the two optical path lengths as described above, it is possible to reduce the aberration generated by the objective lens with respect to the light of the first wavelength, and to improve the light collecting characteristics of the light of the first wavelength. I do. Therefore, using the same optical system, it is possible to perform recording and / or reproduction on the information recording medium corresponding to the first wavelength in addition to the information recording medium corresponding to the second wavelength. Further, by using a common optical system, the configuration of the optical head can be simplified and reduced in size.

An optical head according to a third configuration of the present invention comprises a first light source that emits light of a first wavelength and a second light source that emits light of a second wavelength longer than the first wavelength. A light source; a third light source that emits light of a third wavelength longer than the second wavelength; and the light of each of the first, second, and third wavelengths corresponds to light of each of the wavelengths. An objective lens for focusing light on an information recording surface of an information recording medium, wherein the objective lens is designed such that aberration is reduced with respect to the light of the first wavelength. The objective lens from each of the second and third light sources so that aberrations generated in the objective lens due to chromatic dispersion of the objective lens material with respect to the light of the second and third wavelengths are reduced. Is shorter than the optical path length from the first light source to the objective lens. Characterized in that it was.

By setting the respective optical path lengths as described above, it is possible to reduce the aberration generated in the objective lens with respect to the light of the second and third wavelengths, and to reduce the light of the second and third wavelengths. Improves the light-collecting characteristics. Therefore, using the same optical system, it is possible to perform recording and / or reproduction on the information recording medium corresponding to the second and third wavelengths in addition to the information recording medium corresponding to the first wavelength. it can. Further, by using a common optical system, the configuration of the optical head can be simplified and reduced in size.

An optical head according to a fourth configuration of the present invention comprises a first light source that emits light of a first wavelength and a second light source that emits light of a second wavelength longer than the first wavelength. A light source; a third light source that emits light of a third wavelength longer than the second wavelength; and the light of each of the first, second, and third wavelengths corresponds to light of each of the wavelengths. And an objective lens for converging light on the information recording surface of the information recording medium, wherein the objective lens is designed such that aberration is small with respect to the light of the second wavelength. The second and third light sources to reduce the aberration of the objective lens due to the chromatic dispersion of the objective lens material with respect to the light of the first and third wavelengths. Is shorter than the optical path length from the first light source to the objective lens. Characterized in that it was.

By setting the respective optical path lengths as described above, it is possible to reduce the aberration generated in the objective lens with respect to the light of the first and third wavelengths, and to reduce the light of the first and third wavelengths. Improves the light-collecting characteristics. Therefore, using the same optical system, it is possible to perform recording and / or reproduction on the information recording medium corresponding to the first and third wavelengths in addition to the information recording medium corresponding to the second wavelength. it can. Further, by using a common optical system, the configuration of the optical head can be simplified and reduced in size.

In the first and second optical heads, the objective lens is provided in a common optical path from the first and second light sources to the entrance surface of the objective lens by chromatic dispersion of the objective lens material. It is preferable to provide an aberration correcting unit for further reducing the aberration generated in the above. Thereby, the aberration generated in the objective lens with respect to the light of the first or second wavelength can be reduced by inserting the aberration correcting unit. Therefore, it is possible to further improve the light collecting characteristics of the light of the first and second wavelengths.

In the third and fourth optical heads, at least in the common optical path from each of the first and second light sources to the incident surface of the objective lens, the chromatic dispersion of the objective lens material is used. It is preferable to include an aberration correcting unit for further reducing the aberration generated in the objective lens. This makes it possible to reduce the aberration generated in the objective lens with respect to at least the light of the first or second wavelength by inserting the aberration correcting unit. Therefore, the first,
The light collection characteristics of the light of the second and third wavelengths can be further improved.

In the above, the aberration correcting means may be a hologram element for correcting chromatic aberration generated by the objective lens with respect to the light of the first wavelength. This makes it possible to reduce aberrations caused by the chromatic dispersion of the material of the objective lens with respect to the light of the first wavelength, thereby improving the light-collecting characteristics of the objective lens. Further, by using a hologram element, the device can be made thin.

Alternatively, in the above, the aberration correcting means may be a hologram element for correcting chromatic aberration generated by the objective lens with respect to the light of the second wavelength. This makes it possible to reduce aberrations caused by the chromatic dispersion of the material of the objective lens with respect to the light of the second wavelength, thereby improving the light-collecting characteristics of the objective lens. Further, by using a hologram element, the device can be made thin.

In the above, it is preferable that the hologram element is integrally formed on a surface of the objective lens. Thus, the optical system including the lens and the hologram element can be reduced in weight and size, and the load on the actuator for driving the lens can be reduced.

In the first or second optical head, the aberration correcting means may be a collimating lens for converting divergent light from the first or second light source into substantially parallel light. Thereby, the allowable amount of the positioning accuracy of the objective lens in the plane perpendicular to the optical axis of the light converted into the parallel light by the collimator lens out of the divergent light from the first and second light sources is increased. Can be.

Similarly, in the third or fourth optical head, the aberration correcting means is a collimating lens for converting divergent light from the first, second or third light source into substantially parallel light. Is also good. Thereby, of the divergent light from the first, second, and third light sources, the allowable amount of the positioning accuracy of the objective lens in a plane perpendicular to the optical axis of the light converted into the parallel light by the collimator lens Can be increased.

At this time, the light emitted from the third light source may directly enter the objective lens without passing through the collimator lens. Thereby, for example, a high-density optical disk, DVD, DVD-R, CD, CD-R, CD-RW
Recording and / or reproduction of a plurality of optical discs having different specifications can be easily performed by the same optical system.

Further, the aberration correcting means may be a collimating lens having an aberration so as to reduce the aberration generated in the objective lens due to the chromatic dispersion of the material of the objective lens. That is, aberration is intentionally caused in the collimating lens so that the chromatic aberration generated in the objective lens is canceled or reduced. As a result, the aberration of the entire optical system can be further reduced.

In the third or fourth optical head, the third light source and the objective lens are arranged such that the NA (numerical aperture) of the objective lens with respect to the light having the third wavelength is 0.5 or less. It is preferable to set an optical path length between the two.
Thereby, for example, recording and / or reproduction can be easily performed on an information recording medium such as a CD, a CD-R, and a CD-RW.

In the first to fourth optical heads, the Abbe number of the objective lens material and the material of the aberration correcting means are reduced so that the aberration generated in the objective lens due to the chromatic dispersion of the objective lens material is reduced. Preferably, the Abbe number is different. Thereby, the chromatic aberration of the objective lens can be compensated for by the aberration correcting means.

In the first to fourth optical heads, it is preferable that the Abbe number of the objective lens material is 55 or more. By using a material with low chromatic dispersion as the material of the objective lens, the chromatic aberration of the objective lens can be reduced.

Further, in the first to fourth optical heads, the objective lens may be a single aspheric lens in which aberration is corrected for light having any one of the wavelengths. Thereby, only the light sources are arranged by changing the optical path length between each light source and the objective lens so that the aberration generated by the objective lens with respect to the light whose aberration has not been corrected is reduced.
Wavefront aberration can be easily improved.

Alternatively, in the first to fourth optical heads, the objective lens is a combination lens composed of a spherical or aspherical lens in which chromatic aberration and wavefront aberration are corrected for the light of each wavelength. You can also. Thereby, the wavefront aberration can be easily improved only by disposing the light sources while changing the optical path length between each light source and the objective lens.

In the first or second optical head, it is preferable that the first and second light sources selectively emit light. Thereby, recording and / or reproduction can be performed on information recording surfaces of different information recording media corresponding to two different wavelengths.

In the third or fourth optical head, it is preferable that the first, second, and third light sources selectively emit light. Thereby, recording and / or reproduction can be performed on information recording surfaces of different information recording media corresponding to three different wavelengths.

In the first or second optical head, it is preferable that the first wavelength is in a range of 350 nm to 500 nm, and the second wavelength is in a range of 600 nm to 700 nm. As a result, recording and / or reproduction can be performed with a single optical head on a plurality of optical disks having different specifications such as a high-density optical disk, a DVD, and a DVD-R.

In the third or fourth optical head, the first wavelength is in the range of 350 nm to 500 nm, the second wavelength is in the range of 600 nm to 700 nm, and the third wavelength is 700 nm to 700 nm. It is preferably within the range of 900 nm. Thus, the same optical head can be used for a high-density optical disk, DVD, DVD-R, CD, C
Recording and / or reproduction can be performed on a plurality of optical disks having different specifications such as DR and CD-RW.

Next, in the recording / reproducing method according to the present invention, light is projected from the protective layer side onto an information recording medium having an information recording surface and a protective layer on the information recording surface. A recording / reproducing method for recording information on a surface and / or reproducing information recorded on the information recording surface, comprising: a first light source that emits light of a first wavelength; and a longer light source than the first wavelength. Second
And a second light source that emits light of the wavelengths, and collects the light of the first wavelength and the light of the second wavelength on the information recording surface of the information recording medium corresponding to the light of the respective wavelengths. An objective lens, wherein the objective lens uses an optical head designed to have a small aberration with respect to the light of the second wavelength, and a color of the material of the objective lens with respect to the light of the first wavelength. The thickness of a protective layer on the information recording surface corresponding to the light of the first wavelength and the information recording corresponding to the light of the second wavelength so that aberration generated in the objective lens due to dispersion is reduced. The thickness of the protective layer on the surface is made different.

By changing the thickness of the protective layer of the information recording medium according to the wavelength of the light source used, chromatic aberration generated by the objective lens can be reduced. As a result, recording and / or reproduction can be performed on a plurality of information recording media using different wavelengths using the same optical system. Further, by using a common optical system, the configuration of the optical head can be simplified and reduced in size.

In the above-mentioned recording / reproducing method, the light having the first and second wavelengths incident on the objective lens is substantially parallel light, and the light on the information recording surface corresponding to the light having the second wavelength is provided. It is preferable that the thickness of the protective layer is 0.55 to 0.65 mm, and the thickness of the protective layer on the information recording surface corresponding to the light of the first wavelength is 0.65 to 0.75 mm. Thereby, recording and / or reproduction can be performed on the information recording surfaces of the different information recording media corresponding to the first and second wavelengths. Further, by using the parallel light, it is possible to increase the allowable amount of the positioning accuracy of the objective lens in a plane perpendicular to the optical axis.

In the above recording and reproducing method, the first
The Abbe number of the protective layer on the information recording surface corresponding to the light of the first wavelength is set such that the aberration generated in the objective lens due to the chromatic dispersion of the objective lens material is further reduced with respect to the wavelength. Preferably, the Abbe number of the protective layer on the information recording surface corresponding to the light of the second wavelength is different. By changing the Abbe number of the protective layer of the information recording medium according to the wavelength of the light source to be used, chromatic aberration generated in the objective lens can be further reduced.

In the above recording / reproducing method, as the information recording medium, a first information recording surface corresponding to the light of the first wavelength and a second information recording surface corresponding to the light of the second wavelength are used.
And a first and second protective layer formed on the first and second information recording surfaces, respectively. Recording and / or reproduction is performed by projecting light from the same side, and the first
The thickness of the first protective layer may be set so that chromatic aberration generated in the objective lens due to chromatic dispersion of the objective lens material with respect to light having a wavelength of? By changing the thickness of the protective layer of the information recording medium according to the wavelength of the light source used, chromatic aberration generated by the objective lens can be reduced. Further, by using an information recording medium having a two-layer structure, the recording capacity of the information recording medium alone can be increased.

In the above recording / reproducing method, the information recording medium may include a first information recording surface corresponding to the first wavelength light and a second information recording surface corresponding to the second wavelength light.
Has a four-layer structure in which a laminated unit composed of the information recording surface and first and second protective layers formed on the first and second information recording surfaces is bonded on the information recording surface side, Alternatively, an information recording medium capable of recording and / or reproducing by projecting light from both sides may be used. By using the double-layered information recording medium as a double-sided recording or reproduction information recording medium bonded on the information recording side, the recording capacity of the information recording medium alone can be further increased.

In the above recording / reproducing method, it is preferable that the first wavelength is in a range of 350 nm to 500 nm, and the second wavelength is in a range of 600 nm to 700 nm. Thereby, recording and / or reproduction of a plurality of optical disks having different specifications such as a high-density optical disk, a DVD, and a DVD-R can be performed with the same optical head.

[0039]

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

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 3 is a configuration diagram of an optical head according to an embodiment.

The present optical head includes a first light source 2 that emits light having a first wavelength of 400 nm, for example, included in a range of 350 nm to 500 nm, and a second light source 2 of, for example, 660 nm included in a range of 600 nm to 700 nm. And a second light source 7 that emits light having a wavelength of The first light source 2 is
Integrated with the light receiving element 3 and the first hologram element 4 to form a first LD / PD (laser diode / photo
etector) module 1. Similarly, the second light source 7 is integrated integrally with the second light receiving element 8 and the second hologram element 9 to form a second LD / PD (laser di- ode).
ode / photo detector) module 6. First
By selectively switching the light source 2 and the second light source 7, information is recorded and / or reproduced on the information recording medium corresponding to each wavelength. The information recording medium has an information recording surface 16 on which digital information is recorded, and a protective layer 15 provided on a light incident side. Actually, there are a first information recording medium corresponding to a first wavelength and a second information recording medium corresponding to a second wavelength as information recording media. In the present embodiment, both information recording media are used. Since the protective layers of the recording media have the same thickness, FIG. 1 shows both information recording media without distinction.

The first outgoing light 5 from the first light source 2 passes through the beam splitter 11. On the other hand, the second emitted light 10 from the second light source 7 is reflected at right angles by the beam splitter 11 so as to travel on the same optical axis as the first emitted light 5 in the same direction. Then, the first outgoing light 5 and the second outgoing light 10 are deflected by the rising mirror 12 in the direction perpendicular to the information recording surface 16 of the information recording medium. Next, the first outgoing light 5 and the second outgoing light 10 are １ ／
After being converted into circularly polarized light by the wave plate 13, the objective lens 1
The light is condensed on the information recording surface 16 by 4 to record or reproduce digital information. The reflected light of the light from the first and second light sources on the information recording surface 16 is a 波長 wavelength plate 13
As a result, the light is converted into linearly polarized light that is perpendicular to the polarization directions of the first and second emitted lights 5 and 10, respectively, is diffracted by the first hologram element 4 and the second hologram element 9, respectively, and is respectively received by the first light receiving element. The light is condensed on the surfaces of the element 3 and the second light receiving element 8. As described above, the reproduction signal as digital information and the focus / tracking signal as position control signal of the objective lens are detected.

In the optical system configured as described above,
The present inventors have found that, as shown in FIG. 2, generally, the refractive index of the glass material of an optical component rapidly increases (chromatic dispersion increases) when the wavelength of light is about 500 nm or less (see FIG. 2). 2 shows a case of a glass material BK-7 which is often used).

For example, consider a case where a single aspheric lens designed to converge light of the first wavelength well is used as the objective lens 14. In this case, for the above reason, the refractive index of the objective lens 14 greatly deviates from the design value with respect to the second wavelength. Therefore, if the optical path length from the second light source 7 to the objective lens 14 is substantially equal to the optical path length from the first light source 2 to the objective lens 14, the objective lens 1
There is a problem that the second outgoing light 10 is not condensed well at the image point 4, that is, chromatic aberration occurs due to chromatic dispersion of the glass material of the objective lens 14 for light of the second wavelength. Therefore, the present inventors set the optical path length from the second light source 7 to the objective lens 14 to the distance from the first light source 2 to the objective lens 14.
It has been found that by arranging the optical path so as to be shorter than the optical path length up to, the chromatic aberration generated in the objective lens 14 with respect to the light of the second wavelength can be reduced. The optical path length could be optimized so that the amount of chromatic aberration actually does not matter substantially, for example, so that the wavefront aberration is 0.04λ or less (λ is the wavelength) as an RMS value.

In the case where a single aspherical lens designed to converge light of the second wavelength satisfactorily is used as the objective lens 14, the distance from the first light source 2 to the objective lens 14 Is substantially equal to the optical path length from the second light source 7 to the objective lens 14, aberration occurs due to chromatic dispersion of the glass material of the objective lens 14 with respect to the light of the first wavelength. The characteristics deteriorate. In this case, the optical path length from the first light source 2 to the objective lens 14 is longer than the optical path length from the second light source 7 to the objective lens 14 so that the aberration in the objective lens 14 is reduced. To place.
Thereby, the amount of chromatic aberration generated for the light of the first wavelength can be made substantially not a problem.

Further, as the material of the objective lens 14, a material having small chromatic dispersion (a material having a large Abbe number indicating the degree of chromatic dispersion), for example, CaFK95 (Abbe number 95.
0), GFK70 (71.3 Abbe number), P-BK40
(Abbe number 63.5), VC79 (Abbe number 57.8)
By using a material having an Abbe number of, for example, 55 or more, chromatic aberration generated in the objective lens 14 can be further reduced. Specifically, the amount of aberration can be reduced so that a sufficiently good value including the margin characteristics, for example, the wavefront aberration of the optical system becomes 0.03λ or less.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
FIG. 3 is a configuration diagram of an optical head according to an embodiment. Elements having the same functions as in FIG. 1 are denoted by the same reference numerals, and a detailed description thereof will be omitted.

In the present embodiment, 700 nm to 900 n
A third light source 17 that emits light having a third wavelength, for example, 800 nm included in the range of m is further disposed. The third light source 17 is integrated integrally with the third light receiving element 18 and the third hologram element 19 to constitute a third LD / PD module 22.

The light of the third wavelength is applied to the information recording surface 23 of the third information recording medium corresponding to the third wavelength, and digital information is recorded and / or reproduced. The thickness of the protective layer 24 of the information recording medium corresponding to the third wavelength is different from the thickness of the protective layer 15 of the information recording medium corresponding to the first or second wavelength. By selectively switching the first to third light sources, information is recorded and / or reproduced on the information recording medium corresponding to each wavelength.

The third outgoing light 20 from the third light source 17
Is reflected by the beam splitter 21 at right angles so as to travel in the same direction on the same optical axis as the first outgoing light 5. After that, the light is converged on the information recording surface 23 along the same path as the first and second emitted lights 5 and 10. The light reflected on the information recording surface 23 is transmitted to the third
Is converted into linearly polarized light perpendicular to the polarization direction of the outgoing light 20 from the light source 17, is diffracted by the third hologram element 19, and is condensed on the surface of the third light receiving element 18.

When an objective lens 14 designed to converge satisfactorily on light of the first wavelength or the second wavelength is used as the objective lens 14, wavelength light of the third wavelength is used. And the thickness of the protective layer 24 of the third information recording medium corresponding to the third wavelength causes an aberration, thereby deteriorating the light collecting characteristics. In the present embodiment, the optical path length from the third light source 17 to the objective lens 14 is shorter than the optical path length from the first light source 2 or the second light source 7 to the objective lens 14 so as to reduce these aberrations. To be placed. As a result, it is possible to prevent the generation amount of the aberration from causing a substantial problem.

Other than the above, it is the same as the first embodiment.

(Third Embodiment) FIG. 4 shows a third embodiment of the present invention.
FIG. 3 is a configuration diagram of an optical head according to an embodiment. Elements having the same functions as in FIG. 1 are denoted by the same reference numerals, and a detailed description thereof will be omitted.

In the present embodiment, the aberration correcting means 25 is provided in a common optical path from the first light source 2 and the second light source 7 to the entrance surface of the objective lens 14, and the first wavelength or the second wavelength The aberration generated in the objective lens 14 due to the chromatic dispersion of the glass material of the objective lens 14 with respect to the light having the wavelength is further reduced. As the aberration correcting means 25, for example, a hologram element can be used.

In an optical head, a laser light source sometimes generates noise due to return light from an information recording medium or the like. For this reason, it is often the case that a high frequency is applied to oscillate at a plurality of wavelengths near the center wavelength (multimode oscillation is performed) and that the oscillation state is stabilized by giving a broader wavelength. However, there is a problem that the wavelength spread of the light source causes an aberration due to the chromatic dispersion of the glass material of the objective lens, thereby deteriorating the light-collecting characteristics. Further, when a hologram element is inserted on the incident surface side of the objective lens, the diffraction angle of the light emitted from the hologram element changes due to the fluctuation of the wavelength of the incident light. There is a problem that occurs.

In the present embodiment, the optical system is configured so that both the chromatic aberration due to the wavelength spread of the light source and the chromatic aberration due to the change in the diffraction angle are reduced (can offset each other).
As described above, it is possible to further reduce the aberration caused by the wavelength spread that occurs when the first light source 2 or the second light source 7 oscillates in multiple modes due to high frequency superposition.

In FIG. 4, aberration correcting means (hologram element)
Although 25 is installed as an independent part, an objective lens 14 'in which a hologram element is integrally formed as shown in FIG. 5 can be used. By using the objective lens 14 'having the chromatic aberration correcting function as described above, the number of parts and the number of assembly steps can be reduced.

This embodiment can be similarly applied to an optical head having the third light source as described in the second embodiment.

Other than the above, it is the same as the first and second embodiments.

(Fourth Embodiment) FIG. 6 shows a fourth embodiment of the present invention.
FIG. 3 is a configuration diagram of an optical head according to an embodiment. Elements having the same functions as in FIG. 1 are denoted by the same reference numerals, and a detailed description thereof will be omitted.

In the present embodiment, the divergent light from the first light source 2 or the second light source 7 is provided in a common optical path from the first light source 2 and the second light source 7 to the incident surface of the objective lens 14. A collimating lens 28 that converts the light into substantially parallel light is disposed. The objective lens 14 is designed such that light of the light source on the side collimated into parallel light out of the divergent light from the first light source 2 and the second light source 7 is favorably collected. At this time, for the wavelength of the light source that is not collimated, aberration occurs due to the chromatic dispersion of the glass material in the objective lens 14, and chromatic aberration and spherical aberration occur in the collimator lens 28. In the present embodiment, similarly to the first and second embodiments, the optical path length from the light source on the non-collimated side to the objective lens 14 is different from the optical path length from the light source on the collimated side to the objective lens 14. To place. Thereby, these aberrations can be reduced. Further, the tolerance of the positioning accuracy of the objective lens 14 in a plane perpendicular to the optical axis with respect to the collimated light source can be increased.

In this case, for example, the collimator lens 28
The Abbe number of the glass material of the objective lens 14 is made different from the Abbe number of the glass material of the objective lens 14, or the material and shape of the collimating lens 28 are devised to intentionally generate aberration in the collimating lens. Chromatic aberration caused by the collimating lens 28 can be reduced (canceled). Thereby, the aberration of the entire optical system can be further reduced.

A specific configuration example will be described. For example, a semiconductor laser having a wavelength of 410 nm is used as the first light source 2 and a semiconductor laser having a wavelength of 650 nm is used as the second light source 7 in FIG. The light sources are arranged such that the optical path lengths from the first light source 2 and the second light source 7 to the entrance surface of the collimator lens 28 having a focal length of 20 mm are 20 mm and 16.7 mm, respectively. The collimating lens 28 converts the light 5 emitted from the first light source 2 into parallel light, and the light 10 emitted from the second light source 7 into divergent light.
The light is made to enter the objective lens 14 using 100 (the Abbe number is 95). The optical system is configured so that the numerical aperture (NA) of the objective lens 14 for the light of the first light source 2 is 0.7 and the numerical aperture of the second light source 7 for the light is 0.6. Using the optical head thus configured, the thickness of the protective layer is 0.6
Recording and / or reproduction can be performed on a high-density disk for a wavelength of 410 nm in mm and a DVD information recording medium for a wavelength of 650 nm in which the thickness of a protective layer is 0.6 mm.

Further, as shown in FIG. 7, a third light source 17 having a wavelength of 800 nm is arranged so as not to pass through the collimator lens 28, and the numerical aperture of the objective lens 14 with respect to the light of the third light source 17 becomes 0.45. The optical system is configured as follows. Using the optical head thus configured, recording and / or reproduction can be performed on an information recording medium such as a CD, CD-R, or CD-RW in which the protective layer 24 has a thickness of 1.2 mm. it can. 7, elements having the same functions as those in FIG. 3 are denoted by the same reference numerals, and a detailed description thereof will be omitted.

As shown in FIG. 8, a combination lens 14 "composed of a plurality of aspherical or spherical lenses can be used as the objective lens. Here, the combination lens 14" is a first lens and a second lens. , And the chromatic aberration and the wavefront aberration are corrected for the wavelength of each of the third light sources. According to such a configuration, the aberration generated in the objective lens 14 can be further reduced, and the light-collecting characteristics of the optical system are improved. In FIG. 8, elements having the same functions as those in FIG. 7 are denoted by the same reference numerals, and detailed description thereof will be omitted.

Further, as shown in FIG. 9, the third embodiment is provided in a common optical path from the first light source 2, the second light source 7, and the third light source 17 to the entrance surface of the objective lens 14. Similarly to the above, an aberration correcting means (hologram element) 25 can be inserted. According to such a configuration, aberration generated in the objective lens 14 can be reduced, and the light-collecting characteristics of the optical system can be improved. In FIG. 9, FIG.
Elements having the same functions as those described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

Other than the above, it is the same as the first, second and third embodiments.

(Fifth Embodiment) FIG. 10 is an explanatory diagram of a recording / reproducing method according to a fifth embodiment of the present invention. Elements having the same functions as those in FIG. 1 are denoted by the same reference numerals,
A detailed description thereof will be omitted.

The objective lens 14 is designed so that the aberration becomes smaller with respect to the wavelength of the second light source 7. In the first embodiment, the thickness of the protective layer of the information recording medium corresponding to each of the first wavelength and the second wavelength is the same. On the other hand, in the present embodiment, the first wavelength corresponding to the first wavelength is reduced so that the aberration generated by the chromatic dispersion of the glass material of the objective lens 14 is reduced with respect to the wavelength of the first light source 2.
The thickness of the protective layer of the information recording medium is set. Specifically, on the information recording surface 27 of the first information recording medium corresponding to the wavelength of the first light source 2 so that the aberration generated in the optical system from the first light source 2 to the objective lens 14 is reduced. Is different from the thickness of the protective layer 15 on the information recording surface 16 of the second information recording medium corresponding to the wavelength of the second light source 7. As described above, by changing the thickness of the protective layer 26, it is possible to intentionally generate aberration and reduce the entire aberration.

Further, the Abbe number of the protective layer 26 was
It may be different from the Abbe number of 5. That is, by appropriately setting the Abbe number of the protective layer 26, it is possible to intentionally generate aberration and reduce the aberration generated in the objective lens 14 with respect to the first wavelength to some extent.

Other than the above, it is the same as the first, second, third and fourth embodiments.

A specific configuration example will be described. As shown in FIG. 11, a semiconductor laser having a wavelength of 410 nm is used as the first light source 2 and a semiconductor laser having a wavelength of 650 nm is used as the second light source 7. A collimating lens 28 is provided in a common optical path from the first and second light sources 2, 7 to the objective lens 14.
Is installed. The first and second light sources 2, 7 are arranged so that the optical path lengths from the first and second light sources 2, 7 to the collimating lens 28 are equal. The light 5 emitted from the first light source 2 and the light 10 emitted from the second light source 7 are
8 are converted into substantially parallel light. Objective lens 1
Reference numeral 4 is designed so that the aberration becomes smaller with respect to the wavelength of the second light source 7. The thickness of the protective layer 26 of the first information recording medium corresponding to the first light source is 0.7 mm, and the thickness of the protective layer 15 of the second information recording medium corresponding to the second light source is 0.6.
mm. The optical system is arranged such that the numerical aperture of the objective lens 14 for the light of the first light source 2 is 0.6 and the numerical aperture of the second light source 7 for the light is 0.6. From the above,
A high-density disc for a wavelength of 410 nm with a protective layer thickness of 0.7 mm and a wavelength of 650 with a protective layer thickness of 0.6 mm
Recording and / or reproduction can be performed on a DVD for nm. 11 are the same as FIG. 10 except for the above, elements having the same functions are denoted by the same reference numerals, and detailed description thereof will be omitted.

(Sixth Embodiment) FIG. 12 is an explanatory diagram of a recording / reproducing method according to a sixth embodiment of the present invention. FIG.
Elements having the same functions as those described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

This embodiment is different from the fifth embodiment in the following points. That is, in this embodiment, in order to increase the recording capacity of the information recording medium, the information recording medium in which the first information recording surface 27 and the second information recording surface 16 are formed in the same base material in a two-layer structure Is used.

Further, two such information recording media having a two-layer structure are laminated on the information recording surface side to make the information recording surface 4
The present invention can also be applied to an information recording medium having a layered structure and recording and / or reproducing from both the front and back surfaces. With such a configuration, the recording capacity of the information recording medium can be further increased.

Except for the above, it is the same as the first, second, third, fourth and fifth embodiments.

[0077]

As described above, according to the present invention, it is possible to record and / or reproduce information on a plurality of types of information recording media having different wavelengths using a single common optical system.
Further, by using a common optical system, the configuration of the optical head can be simplified and downsized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the wavelength dependence of the refractive index of a glass material (BK-7).

FIG. 3 is a configuration diagram of an optical head according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical head according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical head according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical head according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical head according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical head according to a fourth embodiment of the present invention.

FIG. 9 is a configuration diagram of an optical head according to a fourth embodiment of the present invention.

FIG. 10 is a configuration diagram showing a recording / reproducing method according to a fifth embodiment of the present invention.

FIG. 11 is a configuration diagram showing a recording / reproducing method according to a fifth embodiment of the present invention.

FIG. 12 is a configuration diagram showing a recording / reproducing method according to a sixth embodiment of the present invention.

FIG. 13 shows a conventional short-wavelength laser light source (wavelength 350 nm).
FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st LD / PD module 2 1st light source 3 1st light receiving element 4 1st hologram element 5 1st output light 6 2nd LD / PD module 7 2nd light source 8 2nd light receiving element Reference Signs List 9 second hologram element 10 second emission light 11 beam splitter 12 rising mirror 13 quarter-wave plate 14, 14 ', 14 "objective lens 15 protective layer 16 information recording surface 17 third light source 18 third Light receiving element 19 Third hologram element 20 Third emitted light 21 Beam splitter 22 Third LD / PD module 23 Information recording surface 24 Protective layer 25 Aberration correcting means (hologram element) 26 Protective layer 27 Information recording surface 28 Collimating lens Reference Signs List 101 semiconductor laser 102 SHG element 103 outgoing light 104 collimating lens 105 polarizing beam splitter 106 Raising mirror 107 Quarter-wave plate 108 Objective lens 109 Information recording medium 110 Information recording surface 111 Detection lens 112 Light receiving element

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kenichi Kasumi 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. F term (reference) 5D119 AA41 BA01 DA05 EC03 EC45 EC47 FA08 JA02 JA09 JA47 JB02 JB04 LB11

Claims (30)

[Claims] A first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength longer than the first wavelength, and light of the first wavelength. An objective lens for condensing the light of the second wavelength on an information recording surface of an information recording medium corresponding to the light of each wavelength, wherein the objective lens is The second wavelength is designed so that aberration is reduced with respect to light having the wavelength, and the aberration generated in the objective lens is reduced with respect to the light having the second wavelength due to chromatic dispersion of the material of the objective lens. An optical head, wherein an optical path length from the second light source to the objective lens is shorter than an optical path length from the first light source to the objective lens. 2. A first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength longer than the first wavelength, and light of the first wavelength. An optical lens comprising: an objective lens for condensing the light of the second wavelength on an information recording surface of an information recording medium corresponding to the light of each wavelength; wherein the objective lens is The first wavelength is designed to have a small aberration, and the first wavelength is configured such that the chromatic dispersion of the objective lens material reduces the aberration generated in the objective lens. An optical head, wherein an optical path length from one light source to the objective lens is longer than an optical path length from the second light source to the objective lens. 3. A first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength longer than the first wavelength, and a first light source that emits light of a second wavelength longer than the second wavelength. A third light source that emits light of three wavelengths, and collecting the light of each of the first, second, and third wavelengths on an information recording surface of an information recording medium corresponding to the light of each wavelength. An optical head comprising: an objective lens that emits light; wherein the objective lens is designed to have a small aberration with respect to the light of the first wavelength; The optical path length from each of the second and third light sources to the objective lens is reduced from the first light source so that the aberration generated in the objective lens by the chromatic dispersion of the objective lens material is reduced for the light of An optical head characterized in that the optical path length is shorter than the optical path length to the objective lens. 4. A first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength longer than the first wavelength, and a first light source that emits light of a second wavelength longer than the second wavelength. A third light source that emits light of three wavelengths, and collecting the light of each of the first, second, and third wavelengths on an information recording surface of an information recording medium corresponding to the light of each wavelength. An optical head comprising: an objective lens that emits light; wherein the objective lens is designed to have a small aberration with respect to the light having the second wavelength; The optical path length from each of the second and third light sources to the objective lens is reduced from the first light source so that the aberration generated in the objective lens by the chromatic dispersion of the objective lens material is reduced for the light of An optical head characterized in that the optical path length is shorter than the optical path length to the objective lens. 5. In order to further reduce aberrations generated in the objective lens due to chromatic dispersion of the objective lens material in a common optical path from each of the first and second light sources to the entrance surface of the objective lens. 2. An aberration correcting means according to claim 1.
An optical head according to claim 1. 6. In order to further reduce aberrations generated in the objective lens due to chromatic dispersion of the objective lens material in a common optical path from each of the first and second light sources to the entrance surface of the objective lens. 3. An aberration correcting means comprising:
An optical head according to claim 1. 7. A common optical path from at least the first and second light sources to the entrance surface of the objective lens,
4. The optical head according to claim 3, further comprising an aberration correcting unit configured to further reduce aberration generated in the objective lens due to chromatic dispersion of the material of the objective lens. 8. A common optical path from at least the first and second light sources to the entrance surface of the objective lens,
The optical head according to claim 4, further comprising an aberration correction unit configured to further reduce aberration generated in the objective lens due to chromatic dispersion of the objective lens material. 9. The optical head according to claim 5, wherein the aberration correction unit is a hologram element that corrects chromatic aberration generated by the objective lens with respect to the light of the first wavelength. 10. The optical head according to claim 5, wherein the aberration correction unit is a hologram element that corrects chromatic aberration generated by the objective lens with respect to the light of the second wavelength. 11. The optical head according to claim 9, wherein the hologram element is integrally formed on a surface of the objective lens. 12. The optical head according to claim 10, wherein the hologram element is integrally formed on a surface of the objective lens. 13. The optical head according to claim 5, wherein the aberration correcting unit is a collimating lens that converts divergent light from the first or second light source into substantially parallel light. 14. The method according to claim 14, wherein the aberration correction unit is configured to perform the first and second aberration correction.
9. The optical head according to claim 7, wherein the optical head is a collimating lens that converts divergent light from the third light source into substantially parallel light. 15. The collimating lens according to claim 5, wherein the aberration correcting unit is a collimating lens having an aberration such that an aberration generated in the objective lens is reduced by a chromatic dispersion of the material of the objective lens. Light head. 16. The optical path length between the third light source and the objective lens is set so that the NA of the objective lens for the light of the third wavelength is 0.5 or less. Or the optical head according to 8. 17. The Abbe number of the objective lens material and the Abbe number of the material of the aberration corrector are different so that aberration generated in the objective lens due to chromatic dispersion of the objective lens material is reduced. 9. The optical head according to any one of 8. 18. An Abbe number of the objective lens material is 55.
The optical head according to claim 1, wherein: 19. The optical head according to claim 1, wherein the objective lens is a single aspherical lens whose aberration has been corrected for light of any one of the wavelengths. 20. The objective lens according to claim 1, wherein the objective lens is a combination lens composed of a spherical or aspherical lens in which chromatic aberration and wavefront aberration have been corrected for the light of each wavelength.
5. The optical head according to any one of 4. 21. The optical head according to claim 1, wherein the first and second light sources selectively emit light. 22. The optical head according to claim 3, wherein the first, second, and third light sources selectively emit light. 23. The first wavelength is between 350 nm and 500.
nm, the second wavelength is from 600 nm to 700 n.
3. The optical head according to claim 1, wherein m is within a range of m. 24. The method according to claim 24, wherein the first wavelength is 350 nm to 500.
nm, the second wavelength is from 600 nm to 700 n.
m, the third wavelength is 700 nm to 900 nm.
The optical head according to claim 3 or 4, wherein 25. Projecting light from the protective layer side to an information recording medium having an information recording surface and a protective layer on the information recording surface to record information on the information recording surface and / or A recording / reproducing method for reproducing information recorded on an information recording surface, comprising: a first light source that emits light of a first wavelength; and a second light source that emits light of a second wavelength longer than the first wavelength. 2 light sources, and an objective lens for condensing the light of the first wavelength and the light of the second wavelength on an information recording surface of an information recording medium corresponding to the light of the respective wavelengths. The lens uses an optical head designed to reduce aberration for the light of the second wavelength, and is generated in the objective lens by the chromatic dispersion of the material of the objective lens for the light of the first wavelength. The information recording corresponding to the light of the first wavelength so that aberration is reduced; Reproducing method characterized by varying the thickness of the protective layer of the above, the thickness of the protective layer on the information recording surface corresponding to the light of the second wavelength. 26. The thickness of a protective layer on an information recording surface corresponding to the light of the second wavelength, wherein the light of the first and second wavelengths incident on the objective lens is substantially parallel light. Is 0.55 to 0.65 mm, and the thickness of the protective layer on the information recording surface corresponding to the light of the first wavelength is 0.65 to 0.75 m.
26. The recording and reproducing method according to claim 25, wherein m is m. 27. Protection on an information recording surface corresponding to light of the first wavelength so that aberrations generated in the objective lens due to chromatic dispersion of the material of the objective lens with respect to the first wavelength are further reduced. 26. The recording / reproducing method according to claim 25, wherein the Abbe number of the layer is different from the Abbe number of the protective layer on the information recording surface corresponding to the light of the second wavelength. 28. The information recording medium, comprising: a first information recording surface corresponding to the light of the first wavelength; a second information recording surface corresponding to the light of the second wavelength; And first and second protective layers formed on each of the second information recording surfaces, and perform recording and / or reproduction by projecting light from the same surface side to both the information recording surfaces. 26. The recording according to claim 25, wherein the thickness of the first protective layer is set such that chromatic aberration generated in the objective lens due to chromatic dispersion of the objective lens material with respect to the light of the first wavelength is reduced. Playback method. 29. The information recording medium, comprising: a first information recording surface corresponding to the light of the first wavelength; a second information recording surface corresponding to the light of the second wavelength; And a first and a second protective layer formed on each of the second information recording surfaces are laminated on the information recording surface side, and recording and / or reproduction is possible by projecting light from both surfaces. 26. The recording / reproducing method according to claim 25, wherein: 30. The method according to claim 30, wherein the first wavelength is 350 nm to 500 nm.
nm, the second wavelength is from 600 nm to 700 n.
The recording / reproducing method according to claim 25, wherein the value is within the range of m.