JP2003168235A - Optical head device and objective lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simply structured objective lens for an optical head device, for the purpose of forming a beam spot by a first laser optical flux on the recording face of a first optical recording medium and forming a beam spot by a second laser optical flux of a different wavelength on the recording face of a second optical recording medium of a different substrate thickness. <P>SOLUTION: A refracting face 31 on the incident side of the objective lens 3 in the optical head device is bisected into a refracting face area 33 in the center around the optical axis and a refracting face area 34 on the outer circumference surrounding the outside of the area 33, with a diffraction grating 35 formed on the center side over the entire area 33. In the recording and reproduction of a CD-R41 using a first laser light source, a beam spot B(41) is formed by 1st-order diffracted light flux that can be obtained through the area 33 in the center, in the recording and reproduction of a DVD42 using a second laser light source, a beam spot B(42) is formed by the light flux passed through the area 34 on the outer circumference and the 1st-order diffracted light flux that can be obtained through the area 33 in the center. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for reproducing and recording optical recording media such as CDs and DVDs having different substrate thicknesses by using laser beams having different wavelengths. More specifically, the present invention relates to an objective lens suitable for use in such an optical head device.

[0002]

2. Description of the Related Art As optical recording media, there are known optical recording media such as CDs and DVDs which have different thicknesses and recording densities of transparent substrates for protecting recording surfaces. For example, a CD has a transparent substrate with a thickness of 1.2 mm for protecting the recording surface, and a DVD has
The thickness of the transparent substrate is 0.6 mm, which is thinner than that of the CD, and its recording density is higher than that of the CD.

In an optical head device for recording and reproducing information on and from these optical recording media, a single objective lens is used to reduce the size and size of the laser beam on the recording surface of CDs and DVDs. There has been proposed a configuration that converges.

An example of such an objective lens is disclosed in Japanese Patent Laid-Open No. 09-179020. The objective lens disclosed herein forms a fine diffraction grating on a lens surface having a single refracting power, diffracts an incident light beam by the diffraction grating, and diffracts light of different orders on different positions on the optical axis. It has multiple focus points. In addition, the light collection efficiency at two focal points of the focal points formed by the diffracted rays of each order is increased, and the diffracted ray of the higher order side of these two focal points is focused on a position having a short focal length. The diffraction characteristics of the diffraction grating are designed so as to connect.

Therefore, in the optical head device using the objective lens having this structure, for example, the laser light having a wavelength of 650 nm is diffracted into two diffracted lights, for example, first-order diffracted light and second-order diffracted light. The first on the CD recording surface
The second-order diffracted light having a high diffraction order can be converged to the second focus position on the DVD recording surface having a short focal length.

However, since this objective lens is premised on converging a laser beam of a single wavelength into two focal points, a two-wavelength light source type optical head device using laser beams of different wavelengths, for example, a CD. It is not suitable for use in an optical head device including a laser light source having a wavelength of 780 nm used for -R reproduction recording and a laser light source having a wavelength of 650 nm for DVD reproduction.

Here, in the two-wavelength light source type optical head device, for example, the objective lens disclosed in Japanese Patent Laid-Open No. 2000-028917 can be used. In the objective lens disclosed in this publication, the lens surface is divided into three parts, and a concentric circular first dividing surface, an annular second dividing surface, and an annular third surface are provided from the optical axis side toward the outer peripheral side. Divided surfaces are formed. A diffraction grating is formed on the second divided surface of the divided surfaces.

The objective lens of this structure has a wavelength of 780 nm.
Of the laser light of the first division surface and the 0th-order light having passed through the diffraction grating of the second division surface are converged to the first focus position for CD-R reproduction recording, and the wavelength is 650 nm.
The first light beam passing through the first and third split surfaces of the laser light and the first-order diffracted light diffracted by the second split surface are converged on the second focus position for DVD reproduction. Therefore, the first divided surface to the second divided surface are used as the CD-R openings, and the first divided surface to the third divided surface are DV.
It is used as a D opening.

[0009]

However, in the objective lens having this configuration, the objective lens has two types of media having different substrate thicknesses, but the objective lens has a base lens surface. Since it is divided into three, it will impose a large burden on the design of the diffraction grating,
In addition, the light utilization efficiency will be deteriorated.

Therefore, an object of the present invention is to form a beam spot of a first laser beam on the recording surface of a first optical recording medium, and to form a beam spot of a second laser beam having a different wavelength on the substrate thickness. An object of the present invention is to propose an objective lens for an optical head device having a simple structure that can be formed on a recording surface of a different second optical recording medium, and an optical head device including the objective lens.

[0011]

In order to solve the above-mentioned problems, the present invention relates to recording surfaces of a first optical recording medium and a second optical recording medium having transparent substrates of different thicknesses, respectively. First and second laser light fluxes having different wavelengths emitted from the first laser light source and the second laser light source are condensed through one condensing optical system, and information is recorded and reproduced on the recording surface. In an optical head device, a refracting surface of an objective lens that constitutes the condensing optical system is a center-side refracting surface area around the optical axis and an outer-periphery-side refracting surface that surrounds the outside of the center-side refracting surface area. When recording / reproducing of the first optical recording medium is performed by using the first laser light source, the central side diffraction grating is formed over the entire area of the central side refracting surface region. , The first-order diffracted light obtained through the center side refracting surface region When a recording / reproducing of the second optical recording medium is performed by using the second laser light source to form a beam spot, the light flux passing through the outer peripheral side refraction surface area and the center side refraction surface area. It is characterized in that a beam spot is formed by the first-order diffracted light beam obtained via the.

Here, the outer peripheral refraction surface region is formed so that the second laser beam has a refracting power that is substantially suitable for forming a beam spot on the recording surface of the second optical recording medium. do it.

Further, when recording and reproducing the second optical recording medium by using the second laser light source, the outer side diffraction grating is formed over the entire area of the outer side refraction surface area. A first-order diffracted light beam obtained through the central refraction surface region,
A beam spot can also be formed by the first-order diffracted light beam obtained through the outer peripheral side refraction surface region.

Further, the outer peripheral side refraction surface region is formed into the second refraction surface region.
Laser beam is formed so as to have a refracting power that is substantially suitable for forming a beam spot on the recording surface of the second optical recording medium, and the outer peripheral side diffraction grating is formed over the entire outer peripheral side refraction surface area. When the recording / reproducing of the second optical recording medium is performed by using the second laser light source, the first-order diffracted light flux obtained through the center side refraction surface region and the outer peripheral side are formed. A beam spot can also be formed by the 0th-order diffracted light beam obtained via the refracting surface region.

In the objective lens for the optical head device of the present invention,
Since the refracting surface has a two-division structure, the refraction surface can be designed and manufactured more easily than the conventional objective lens having a three-division structure.

Further, in the center side diffraction grating formed in the center side refracting surface region, by utilizing the difference in wavelength, the same order diffracted light beams in the first and second laser beams, that is, the first order diffracted light, Beam spots are formed on the recording surfaces of the first and second optical recording media, respectively. Therefore, by designing the diffraction grating so that the diffraction efficiency of the first-order diffracted light is maximized, the utilization efficiency of the laser light can be increased.

Further, when the outer peripheral diffraction grating is formed, unnecessary light components of the outer peripheral portion of the first laser light flux are not focused on the beam spot forming position on the recording surface of the first optical recording medium. If unnecessary, such unnecessary light can be eliminated without using an aperture stop or the like.

Next, the present invention relates to an objective lens used in an optical head device, which is characterized in that the objective lens of the present invention is provided with the refracting surface having the above construction.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an optical head device having an objective lens to which the present invention is applied will be described below with reference to the drawings.

(Overall Structure) FIG. 1 is a schematic block diagram showing mainly the optical system of the optical head device of this embodiment. The optical head device 1 of the present example reproduces and records information on a plurality of types of optical recording media 4 such as CDs, CD-Rs and DVDs having different substrate thicknesses and recording densities. Therefore, a first laser light source 11 for emitting a first laser light flux L1 having a central wavelength of 780 nm used for reproduction of a CD-R and the like, and a DV
A second laser light source 12 that emits a second laser light flux L2 having a wavelength of 650 nm used for reproduction of D and the like is provided. Each laser beam is guided to the optical recording medium 4 via the common condensing optical system Lo, and the return light of each laser beam reflected by the optical recording medium 4 is guided to the common light receiving element 25.

The focusing optical system Lo has a first laser light flux L.
1 goes straight, the second laser beam L2 is reflected, and both lights are aligned with the system optical axis L (optical axis of the objective lens), and the system optical axis L.
The second beam splitter 22 that passes the laser light beams L1 and L2 traveling along, the collimator lens 23 that makes the laser light beams L1 and L2 that have passed through the second beam splitter 22 parallel light, and the light is emitted from the collimator lens 23. The objective lens 3 for forming the beam spots of the laser beams L1 and L2 thus formed on the recording surface of the optical recording medium 4 is included. Recording surface 42 of DVD 42 which is the optical recording medium 4
a and a recording surface 41a of the CD or CD-R 41, a beam spot of the first laser beam L1 is formed on the recording surface of the CD-R 41 by the objective lens 3, and a beam of the second laser beam L2 is formed. Spots are formed on the recording surface of the DVD 42.

Further, the optical recording medium 4 is provided in the condensing optical system Lo.
It includes a grating 24 for guiding the return light of the first and second laser light fluxes reflected by the second beam splitter 22 after being reflected by the common light receiving element 25.

In the optical head device 1 having this structure, when recording / reproducing information on / from the CD-R 41 as the optical recording medium 4,
The first laser light source 11 emits a first laser light flux L1 having a wavelength of 780 nm. This first laser beam L1
Is guided to the condensing optical system Lo and, via the objective lens 3 thereof, a beam spot B on the recording surface 41a of the CD-R 41.
(41) is formed. The return light of the first laser light flux L1 reflected by the recording surface 41a of the CD-R 41 is condensed on the common light receiving element 25 via the second beam splitter 22.
The CD-R41 is detected by the signal detected by the common light receiving element 25.
Information reproduction and the like are performed.

On the other hand, a DVD is used as the optical recording medium 4.
When reproducing the information of 42, etc., the second laser light source 12
Emits a second laser beam L2 having a wavelength of 650 nm. This second laser light flux L2 is also guided to the condensing optical system Lo and forms a beam spot B (42) on the recording surface 42a of the DVD 42 via the objective lens 3 thereof. DV
Second laser light flux L2 reflected by the recording surface 42a of D42
The return light of is condensed on the common light receiving element 25 via the second beam splitter 22. Information reproduction of the DVD 42 is performed by a signal detected by the common light receiving element 25.

(Structure of Objective Lens) Next, the structure of the objective lens 3 of this example will be described in detail with reference to FIGS. 2 and 3. 2A, 2B, and 2C are a plan view, a sectional view, and a partially enlarged sectional view showing the objective lens 3, respectively, and FIG. 3 shows a converged state of light of each wavelength by the objective lens 3. FIG.

The objective lens 3 of this embodiment has an incident-side refracting surface 31 having a positive power on which the laser beams L1 and L2 emitted from the first laser light source 11 and the second laser light source 12 are incident, and the light. It is a convex lens provided with an emission side refraction surface 32 that emits a laser beam toward the recording medium 4. The incident-side refracting surface 31 has a circular center-side refracting surface area 33 concentrically including the optical axis L around the optical axis L, and an outer-side refracting surface surrounding the outer circumference of the center-side refracting surface area 33 in an annular shape. Surface area 34
It is divided into two parts. Further, the center side diffraction grating 35 is formed over the entire center side refraction surface region 33.

The central refraction surface area 33 of the objective lens 3 is
It is a refraction surface area having a refraction power different from that of the outer refraction surface area 34. The center-side diffraction grating 35 formed in the center-side refraction surface region 33 makes the beam spot of the first-order diffracted light beam of the first laser light beam L1 passing through the region CD-R4.
1 has a diffraction characteristic formed on the recording surface. In addition to this, it has a diffraction characteristic for forming a beam spot of the first-order diffracted light flux of the second laser light flux passing through the area on the recording surface of the DVD 42.

On the other hand, the outer peripheral refraction surface area 34 of the objective lens 3 has a refracting power for forming a beam spot of a light beam portion passing through the area of the second laser light beam L2 on the recording surface of the DVD 42. ing.

In the optical head device 1 provided with the objective lens 3 having this structure, when reproducing the information from the CD-R 41, the first
Of the first laser beam L1
Is emitted. Of the light flux components of the first laser light flux L1 that pass through the center-side refracting surface region 33 of the objective lens 3, a beam of the first-order diffracted light flux component generated by diffraction by the center-side diffraction grating 35 formed there. The spot B (41) is the CD as shown by the dotted line in FIG.
-It is formed on the recording surface of R41. The light flux component of the first laser light flux L1 that passes through the outer peripheral refraction surface area 34 of the objective lens 3 is not used because it is unnecessary light that is not necessary for reproduction.

Next, for reproducing information from the DVD 42, only the second laser light source 12 is driven and the second laser light flux L2 is emitted. As shown by the solid line in FIG. 3, the central refraction surface area 33 of the objective lens 3 in this laser beam L2 is shown.
Of the light flux components passing through the first-order diffracted light component generated by being diffracted by the center-side diffraction grating 35 formed there, and the second laser light flux L2 passing through the outer peripheral-side refraction surface region 34 of the objective lens 3. And the luminous flux component
A beam spot B (42) is formed on the recording surface of the DVD 42.

(Effects of the Embodiment) As described above, in the objective lens 3 of this embodiment, since the refracting surface is divided into two parts,
Refractive surface design compared to conventional objective lenses with three-part configuration,
Manufacturing is easy. Further, by utilizing the difference in wavelength, the beam spots of the first-order diffracted light flux components of the first and second laser light fluxes L1 and L2 diffracted by the center side diffraction grating 35 are respectively recorded on the recording surfaces of the CD-R 41 and the DVD 42. Formed on. Therefore, by designing the center-side diffraction grating 35 so that the diffraction efficiency of the first-order diffracted light is maximized, the utilization efficiency of the laser light can be increased.

(Another Example of Objective Lens) In the above-mentioned objective lens 3, by setting the refracting power of the outer refraction surface area 34, the beam spot due to the light flux component of the second laser light flux passing through the area is set to the DVD 42. Is formed on the recording surface. However, the outer refractive surface area 34
Alternatively, a diffraction grating may be formed so that the beam spot of the diffracted light beam component of the second laser light beam by this diffraction grating is formed on the recording surface of the DVD 42.

FIG. 4A is a plan view showing an example of an objective lens in which a diffraction grating is formed also on the outer refraction surface region.
4B is a sectional view thereof, and FIGS. 4C and 4D are partially enlarged sectional views thereof. As shown in these figures, the objective lens 3A of the present example includes the first laser light source 11
And an incident side refracting surface 31A which is a refracting surface having a positive power and on which the laser beams L1 and L2 emitted from the second laser light source 12 are incident, and an emitting side refracting face which emits the laser beam toward the optical recording medium. It is a convex lens having 32A.

The incident-side refracting surface 31A has a circular center-side refracting surface region 33A including the optical axis L, and the center-side refracting surface 33A.
An annular outer refraction surface region 34 concentrically surrounding the
It is divided into A. In addition, the central refraction surface area 33A
The center side diffraction grating 35A is formed over the entire area. Further, also in the outer peripheral side refraction surface area 34A, the outer peripheral side diffraction grating 36 is formed over the entire area.

The objective lens 3A of this example has a first laser beam L1 emitted during recording or reproduction of the CD-R 41.
A beam spot is formed on the recording surface 41a of the CD-R 41 by the light flux component passing through the central refraction surface area 33A. Specifically, of the luminous flux components, the beam spot B is formed on the recording surface of the CD-R 41 by the first-order diffracted luminous flux component generated by the diffraction effect of the central diffraction grating 35A formed in the central refractive surface area 33A. (41)
Is formed.

However, of the first laser light flux L1,
The light flux component passing through the outer peripheral refraction surface region 34A is an unnecessary light component that does not contribute to recording or reproduction, and in this example, is subjected to the diffraction effect by the outer peripheral diffraction grating 36 formed in the outer peripheral refraction surface region 34A. Then, the light is diffracted so as not to be focused on the beam spot forming position on the recording surface of the CD-R 41.

The objective lens 3A of this example is a DVD 4
A beam spot of the second laser light flux L2 emitted at the time of reproducing No. 2 is formed on the recording surface 42a of the DVD 42. That is, the second light passing through the center side refraction surface region 33A
Of the light flux components of the laser light flux of
A beam spot is formed on the recording surface of the DVD 42 by the first-order diffracted light component generated by the diffraction effect of the center side diffraction grating 35A formed on A. With this,
The outer peripheral refraction surface region 3 in the second laser light flux L2
A beam spot is formed at the same position on the recording surface of the DVD 42 even by the primary light flux component generated by the diffraction effect of the outer circumferential side diffraction grating 36 formed in the region of the light flux component passing through 4A. It

With the objective lens 3A having this structure, the same effect as that of the objective lens 3 can be obtained. In addition to this, in the objective lens 3A of the present example, the outer peripheral side diffraction grating 36 is also formed in the outer peripheral side refraction surface region 34A, and the outer peripheral side diffraction grating 36 allows the outer peripheral side portion of the first laser light flux L1 to be formed. The unnecessary light component is diffracted so as not to be condensed at the beam spot formation position on the recording surface of the CD-R 41. Therefore, unnecessary light can be reliably eliminated without using an aperture stop or the like.

[0039]

As described above, according to the present invention, the refracting surface of the objective lens for the optical head device is divided into the central side refracting surface area and the outer peripheral side refracting surface area, and the entire central side refracting surface area is provided. A center side diffraction grating is formed over the entire area. And the first
Emitted when performing recording / reproducing of the optical recording medium of
Beam spot is formed on the recording surface of the first optical recording medium by the first-order diffracted light obtained through the center side refraction surface region of the laser light flux of the second optical recording medium and recording on the second optical recording medium having a different substrate thickness. Of the second laser light flux emitted during reproduction, the second-order diffracted light flux component obtained through the center side refracting surface area and the light flux component passing through the outer peripheral side refracting surface area A beam spot is formed on the recording surface of the optical recording medium.

Therefore, as compared with the conventional objective lens in which the refracting surface is divided into three in order to converge the laser beams of different wavelengths on the recording surfaces of the first and second optical recording media having different substrate thicknesses, The structure of the refracting surface is simplified and the design of each refracting surface region is facilitated.

Since the first-order diffracted light flux component is used for both the diffracted light flux components of the first and second laser light fluxes having different wavelengths, the diffraction grating is designed to increase the diffraction efficiency of the first-order diffracted light flux. By designing, the utilization efficiency of the laser light of each wavelength can be improved.

Next, in the present invention, the outer peripheral diffraction grating is also formed in the outer refractive surface area of the objective lens, and the second laser light flux is formed in the central refractive surface area and the outer refractive surface area. A beam spot is formed on the recording surface of the second optical recording medium, which is diffracted by the diffraction grating and is formed by the diffracted light flux component obtained thereby. In this case, the first laser light flux component passing through the outer refraction surface region is diffracted so as not to be condensed at the beam spot forming position on the recording surface of the first optical recording medium,
The unnecessary light component of the first laser light flux can be removed without providing an aperture stop or the like.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram mainly showing an optical system of an optical head device to which the present invention is applied.

2 (a), (b) and (c) are respectively FIG.
FIG. 5 is a plan view, a sectional view, and a partially enlarged sectional view showing the objective lens of FIG.

FIG. 3 is an explanatory diagram showing a converged state of first and second laser beams by the objective lens of FIG.

FIG. 4 is a diagram showing another example of an objective lens, (a) is a plan view thereof, (b) is a sectional view thereof, and (c).
And (d) are partially enlarged sectional views thereof.

[Explanation of symbols]

1 Optical head device 3, 3A objective lens 4 Optical recording medium 11 First laser light source 12 Second laser light source 21 First Beam Splitter 22 Second beam splitter 23 Collimating lens 24 grating 25 Common light receiving element 31, 31A Incident side refracting surface 32, 32A Emission side refracting surface 33, 33A Center side refracting surface area 34, 34A Outer peripheral refraction surface area 35, 35A Center side diffraction grating 36 Outer Diffraction Grating 41 CD-R (first optical recording medium) 41a recording surface 42 DVD (second optical recording medium) 42a recording surface B (41) Beam spot B (42) Beam spot L Objective lens optical axis (system optical axis) Lo focusing optics L1 First laser beam L2 second laser beam

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Misaka Miyabo             2 Stock Association at 10801 Hara-mura, Suwa-gun, Nagano Prefecture             Inside Sanwa Seiki Seisakusho Suwa Minami Factory (72) Inventor Ryusuke Higashi             2 Stock Association at 10801 Hara-mura, Suwa-gun, Nagano Prefecture             Inside Sanwa Seiki Seisakusho Suwa Minami Factory (72) Inventor Tetsuro Okamura             2104 Yonezawa, Chino City, Nagano Prefecture 1 Nisshin Koki Co., Ltd.             Inside the company F term (reference) 2H087 KA13 LA01 PA01 PA17 PB01                       QA02 QA07 QA14 QA34 RA01                       RA12 RA46                 5D119 AA41 BA01 BB01 BB04 EC45                       EC47 FA08 JA44                 5D789 AA41 BA01 BB01 BB04 EC45                       EC47 FA08 JA44

Claims (5)

[Claims] 1. The wavelengths emitted from the first laser light source and the second laser light source are different with respect to the recording surfaces of the first optical recording medium and the second optical recording medium having different thicknesses of the transparent substrate. In an optical head device for converging the first and second laser beams through one condensing optical system to record and reproduce information on the recording surface, refraction of an objective lens constituting the condensing optical system. The surface is divided into a center side refracting surface area centered on the optical axis and an outer peripheral side refracting surface area surrounding the outside of the center side refracting surface area, and the whole area of the center side refracting surface area is divided. When a recording / reproducing of the first optical recording medium is performed by using the first laser light source to form a center side diffraction grating, a first-order diffracted light beam obtained through the center side refraction surface area is used. Forming a beam spot, the second laser light source At the time of recording / reproducing of the second optical recording medium performed by using, the beam spot is formed by the light flux that has passed through the outer peripheral side refracting surface region and the first-order diffracted light beam obtained through the center side refracting surface region. Forming an optical head device. 2. The outer peripheral refraction surface area according to claim 1, wherein the second refraction surface has a refracting power substantially suitable for forming a beam spot on the recording surface of the second optical recording medium. An optical head device, characterized in that 3. The recording / reproducing of the second optical recording medium according to claim 1, wherein an outer peripheral side diffraction grating is formed over the entire outer peripheral side refraction surface region and the second laser light source is used for recording / reproducing. At this time, a beam spot is formed by a first-order diffracted light beam obtained through the central refraction surface region and a first-order diffracted light beam obtained through the outer refraction surface region. apparatus. 4. The recording / reproducing of the second optical recording medium according to claim 2, wherein an outer peripheral diffraction grating is formed over the entire area of the outer peripheral refraction surface region, and recording / reproduction of the second optical recording medium is performed using the second laser light source. At this time, a beam spot is formed by a 1st-order diffracted light beam obtained through the center side refraction surface region and a 0th-order diffracted light beam obtained through the outer circumference side refraction surface region. apparatus. 5. The objective lens for an optical head device according to any one of claims 1 to 4.