JP2003168238A - 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, the objective lens which enables a beam spot of a first laser light flux to be formed on a recording face of a first optical recording medium and which enables the beam spot of a second laser light flux having a different wavelength to be formed on the recording face of a second optical recording medium having a different substrate thickness. <P>SOLUTION: A center refracting face area 33 formed on the refracting face of the objective lens 3 in an optical head is designed to have a refracting power that is roughly suitable for a first laser light flux L1 to form a beam spot B(41) on the recording face 41a of a CD-R 41. The outer circumferential refracting face area 34 formed on the outside of the refracting face is designed to have a refracting power that is roughly suitable for a second laser light flux L2 to form a beam spot B(42) on the recording face 42a of a DVD 42. The diffraction grating 35 formed on the outer circumferential refracting face area 34 is set for the diffraction characteristic that prevents convergence at the beam spot forming position of the light flux component of the first laser light flux L1 passing through the outer circumferential refracting face area 34. <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 center-side refracting surface area And a diffraction grating is formed over the entire area of the outer peripheral side refracting surface area, and the first laser beam is directed onto the recording surface of the first optical recording medium. The refractive power is almost suitable for forming a beam spot on the And forming the outer peripheral refraction surface region 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. , The diffraction characteristics of the diffraction grating are set so that the light flux component of the first laser light flux passing through the outer peripheral side refraction surface region is not focused at the beam spot formation position on the recording surface of the first optical recording medium. It is characterized by being set.

Further, the center side refracting surface region is formed so that the second laser beam has a refracting power which is substantially suitable for forming a beam spot on the recording surface of the second optical recording medium. Is desirable.

In the present invention, the refracting surface of the objective lens is divided into two parts, and one refracting surface region is designed so that the beam spot of the first laser beam is formed on the recording surface of the first optical recording medium. The other refraction surface area is designed so that the beam spot of the second laser light flux is formed on the recording surface of the first optical recording medium. Therefore, the design of the refracting surface is easy.

Further, since the unnecessary light component in the first laser light flux is removed by the diffraction grating, the unnecessary light can be surely removed without using an aperture stop or the like.

Further, since the light flux portion, which is important for forming the beam spot in the first and second laser light fluxes, is made to pass through the objective lens without being diffracted, the utilization efficiency of each laser light flux is improved. be able to.

[0016]

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 Configuration) FIG. 1 is a schematic configuration 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 beam 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 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.
Further, FIG. 3 is an explanatory diagram showing a convergence state of the first and second laser light fluxes L1 and L2 by the objective lens 3.

The objective lens 3 of this example has an incident side having positive power on which the first and second laser light beams L1 and L2 emitted from the first laser light source 11 and the second laser light source 12 are incident. It is a convex lens having a refracting surface 31 and an emitting-side refracting surface 32 for emitting a laser beam toward the optical recording medium 4. The incident side refracting surface 31 and the exit side refracting surface 3
The lens refracting surface consisting of 2 has a circular center side refracting surface region 33 concentrically including the optical axis L around the optical axis L, and an outer peripheral side surrounding the outer periphery of the center side refracting surface region 33 in an annular shape. It is divided into two parts, that is, a refraction surface region 34. Further, the diffraction grating 35 is formed over the entire outer peripheral side refracting surface region 34 of the incident side refracting surface 31.

The central refraction surface area 33 of the objective lens 3 is
It has a refracting power to form a beam spot B (41) formed by a light beam component passing through the region of the first laser light beam L1 emitted from the first laser light source 11 on the recording surface of the CD-R 41. .

The outer peripheral refraction surface area 34 has a refracting power for forming a beam spot B (42) of a light beam portion passing through the area 34 in the second laser light beam L2 on the recording surface of the DVD 42. Further, the outer refraction surface region 3
The diffraction characteristic of the diffraction grating 35 formed in No. 4 is such that the portion of the first laser beam L1 that passes through the region is CD
It is set so that the light is not focused at the beam spot forming position on the recording surface of -R41.

In the optical head device 1 equipped with the objective lens 3 having this structure, when reproducing information from the CD-R 41,
Only the laser light source 11 is driven to emit the first laser light flux L1. Of the first laser light flux L1, as shown by the dotted line in FIG. 3, the light flux portion passing through the center side refracting surface area 33 of the objective lens 3 is recorded by the refracting power of the refracting surface area. Beam spot B on top
(41) is formed.

Here, the light flux portion of the first laser light flux L1 that passes through the outer peripheral refraction surface area 34 of the objective lens 3 is an unnecessary light component that does not contribute to recording or reproduction, and is formed in the outer peripheral refraction surface area 34. Due to the diffracting action of the diffraction grating 35 being formed, the light is not focused at the formation position of the beam spot B (41).

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, of the light flux portion of the second laser light flux L2 that passes through the outer peripheral refraction surface region 34, the 0th-order light flux component that is not diffracted by the diffraction grating 35 is refracted in that region. The light beam portion passing through the center side refracting surface area 33 forms a beam spot B (42) on the recording surface of the DVD 42 by the force and the refracting power of the refracting surface area.

As described above, in the objective lens 3 of the present example, the refracting surface is divided into two parts, so that the design and manufacture of the refracting surface are easier than in the case of a conventional objective lens having a three-part structure. Further, since the unnecessary light in the first laser light flux is removed by the diffraction grating 35, the unnecessary light can be reliably removed without using an aperture stop or the like. Furthermore, since the beam spot is formed on the recording surface of each optical recording medium by passing the first and second laser light fluxes through the objective lens without diffracting them, the utilization efficiency of each laser light flux is improved. Can

[0030]

As described above, in 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 diffraction grating is formed in the outer peripheral side refracting surface area. Has been formed. Then, the beam spot of the first laser light flux emitted when performing recording and reproducing on the first optical recording medium such as a CD-R is made by the refractive power of the central side refracting surface area of the first optical recording medium. It is formed on the recording surface, and the unnecessary light portion on the outer peripheral side of the laser light flux is diffracted by the diffraction grating so as not to be condensed at the beam spot formation position. Further, the beam spot of the second laser light flux emitted when reproducing the second optical recording medium such as a DVD is generated by the refractive power of the outer peripheral side refracting surface region of the objective lens, and by the center side of the objective lens. It is formed on the recording surface of the second optical recording medium by the refractive power of the refractive surface area.

Therefore, according to the present invention, the refracting surface of the objective lens is divided into two, and the central side refracting surface area and the outer peripheral side refracting surface area have refraction characteristics suitable for the first and second optical recording media, respectively. The diffraction grating formed in the outer refraction surface region may be diffracted so that a light beam component unnecessary for recording and reproduction on the first optical recording medium is not condensed at the beam spot formation position. It should be designed so that Therefore, as compared with the conventional case where the refracting surface of the objective lens is divided into three parts, the structure of the refracting surface is simplified and the design of each refracting surface region is facilitated.

Further, since the unnecessary light in the first laser light flux is removed by the diffraction grating, it is possible to surely remove the unnecessary light without using an aperture stop or the like.

Further, a light flux portion important for forming a beam spot in the first and second laser light fluxes,
Since the light passes through the objective lens without being diffracted, the utilization efficiency of the laser light flux can be improved.

[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 function of the objective lens in FIG.

[Explanation of symbols]

1 Optical head device 3 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 Refractive surface on incident side 32 Emission side refracting surface 33 Center side refracting surface area 34 Outer Refractive Surface Area 35 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 Ryusuke Higashi             2 Stock Association at 10801 Hara-mura, Suwa-gun, Nagano Prefecture             Inside Sanwa Seiki Seisakusho Suwa Minami Factory (72) Inventor Yuji Fujita             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 RA42                       RA46                 5D119 AA04 AA41 AA43 DA01 DA05                       EC47 FA02 FA08 JA43 JA46                       JB03                 5D789 AA04 AA41 AA43 DA01 DA05                       EC47 FA02 FA08 JA43 JA46                       JB03

Claims (3)

[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 side refracting surface area surrounding the outside of the center side refracting surface area. To form a diffraction grating so that the first side laser beam has a refracting power that is substantially suitable for forming a beam spot on the recording surface of the first optical recording medium in the central side refracting surface area. And forming the second refraction surface region on the outer peripheral side. Laser beam is formed 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 diffraction characteristics of the diffraction grating An optical head device, wherein the light flux component of the first laser light flux passing therethrough is set so as not to be focused at a beam spot forming position on the recording surface of the first optical recording medium. 2. The center side refracting surface region according to claim 1, wherein the second laser light flux 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 objective lens for an optical head device according to claim 1.