JP2002040257A - Aperture limiting element and optical head device - Google Patents

Abstract

(57) [Summary] An apparatus that obtains an aperture limiting element with high productivity, mounts it on an optical head device, and realizes a high light-collecting ability with a single optical system even for optical discs with different thicknesses. And A two wavelengths lambda _1, with respect to lambda ₂ light fluxes, the retardation value is m ₁ · λ ₁ and (m ₂ -1/2) · _{λ 2} of birefringent organic thin film region A _1, etc. A retarder layer 11 composed of an anisotropic medium region A ₂ , a central opening region through which both light beams are transmitted without being diffracted, and an aperture limit in a peripheral portion through which one light beam is diffracted and the other diffracted light is transmitted. An aperture limiting element 101 is obtained by sandwiching the polarization diffraction grating layer 12 comprising the region between the transparent substrates 13 and 15, and is disposed between the collimating lens and the objective lens of the optical head device.

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 recording and reproducing information on an optical recording medium.

[0002]

2. Description of the Related Art In an optical head device for recording / reproducing information on an optical disk (optical recording medium) such as a CD or a DVD, light emitted from a semiconductor laser as a light source is focused on the optical recording medium by a lens. The light is reflected by the optical recording medium and becomes return light. This return light is guided to a light receiving element, which is a photodetector, using a beam splitter, and information on the optical recording medium is converted into an electric signal.

[0003] CD / DVD compatible optical head devices have been commercialized for recording and reproducing information on CD optical disks and DVD optical disks, which are optical recording media of different standards, using the same optical head device. As a recording layer of an optical recording medium, a medium having a high wavelength dependence with respect to reflection and absorption of light is used,
In an optical head device on the premise of reproducing a CD-R or the like, a semiconductor laser used for a CD has a wavelength band of 790 nm. At this time, a DVD uses a semiconductor laser having a wavelength band of 660 nm.

[0004] CDs and DVDs have different standards, that is, used wavelength bands for recording and reproduction, substrate (optical disk) thicknesses, recording densities, and the like. Therefore, optical systems for CD recording and reproduction and DVD recording and reproduction are different from each other. It is necessary to change the numerical aperture in the range of 0.45-0.5 and 0.6-0.65.

[0005] For this reason, a 660 nm wavelength band light is transmitted using a dielectric multilayer film as an aperture limiting element, and 790 nm is used.
An aperture limiting element in which a wavelength-selective donut-shaped region that reflects light in the m-wavelength band is formed, and a dielectric multilayer film that adjusts the phase difference with the donut-shaped region in the center is formed, has been proposed and put into practical use. I have.

[0006]

However, the above-mentioned two types of dielectric multilayer films are usually as thick as 3 to 4 μm, and about 20 thin films are formed with an optical thickness accuracy of 1% or less. It is necessary to form a film, and there is a problem that productivity is low and yield is remarkably reduced.

[0007]

Means for Solving the Problems The present invention has been made to solve the above problems, are both linearly polarized, the light beam L ₁ and the wavelength lambda ₂ wavelength lambda ₁ light beam L ₂ (lambda ₁
≠ λ ₂ ), which is a wavelength-selective aperture limiting element that limits the size of the diameter of the light beam L ₂ that can be transmitted, wherein the aperture limiting element is formed by stacking a retarder layer and a polarizing diffraction grating layer. becomes, the phase shifter layer is isotropic medium portion a ₂ is formed in a central portion, a birefringent organic thin film region a ₁ is formed in the peripheral portion surrounding the central portion, and a birefringent organic thin film region a ₁ retardation values, the m ₁ and m ₂ is a natural number, m ₁ · lambda ₁ to the light flux L _1, a relative luminous flux _{L 2 (m 2 -1/2) ·} λ 2, polarization grating layer an opening area B ₁ to transmit without both diffract the light beam L ₁ and the light beam L ₂ in the central portion is formed, and transmits without diffracting the light beam L ₁ diffracts light beam L ₂ in the peripheral portion surrounding the central portion aperture limiting region B ₂ is formed, and wherein the isotropic medium regions a ₂ and the size of the opening area B ₁ is being in substantially the same Providing that the aperture limiting element.

A wavelength λ, which is linearly polarized light,₁of
Luminous flux L₁And wavelength λ_TwoLuminous flux L_Two(Λ ₁≠ λ_Two)
Light flux L that can be transmitted_TwoSelectivity that limits the size of the diameter
Wherein the aperture limiting element comprises a retarder layer and
The polarizing diffraction grating layer is superimposed, and the retarder layer is
Birefringent organic thin film region A₁Is formed and the central part
Surround and surround isotropic medium region A_TwoIs formed and
Refractive organic thin film area A₁Is the retardation value of m₁When
m_TwoIs a natural number, the luminous flux L₁For m₁・ Λ₁, Luminous flux L
_TwoFor (m_Two−1/2) · λ_TwoAnd a polarization grating
The layer has a light flux L in the center.₁And luminous flux L_TwoTransmitted without diffraction
Opening area B₁Formed around the center
Luminous flux L_TwoDiffracts the light beam L₁Aperture that transmits light without diffracting it
Restricted area B _TwoIs formed, and the birefringent organic thin film region A₁When
Opening area B₁That the size of the
An aperture limiting element is provided.

Further, a light source for emitting the wavelength lambda ₁ of the light beam L ₁ and wavelength lambda ₂ of the light beam _{L 2 (λ 1 ≠ λ 2} ), an objective lens for converging the light beam L ₁ and the light beam L ₂ to the optical recording medium An optical head device comprising a polarization hologram element in an optical path between a light source and an objective lens, wherein the aperture limiting element is disposed between the light source and the polarization hologram element. An optical head device is provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment The first embodiment of the present invention
Aperture limit element of embodiment 101, the wavelength lambda ₁ light beam L ₁
And a light beam L ₂ (λ ₁ ≠ λ ₂ ) having a wavelength λ ₂ is an aperture limiting element when the respective polarization planes are incident as parallel linearly polarized light, as shown in the cross-sectional view of FIG. Basically, the retarder layer 11 and the polarization diffraction grating layer 12 are overlapped.

On the transparent substrate 14, a birefringent organic thin film
Area A₁And isotropic medium region A_TwoLayer 11 composed of
1 (b)) is formed. In addition, on the transparent substrate 15,
A polarization diffraction grating layer 12 having substantially the same planar shape as the retarder layer 11
It is formed. That is, the central portion is opened on the transparent substrate 15.
Mouth area B₁(Not shown) and opening area B₁Opening the surrounding area
Mouth restriction area B_Two(Not shown), polarization grating layer
12 are formed. Here, the opening area B₁Is an isotropic medium
Area A_TwoAnd is substantially isotropic in size.
Area A_TwoAnd the aperture limiting region B_TwoIs birefringent
Organic thin film area A ₁It corresponds to. Opening restriction area B
_TwoIs composed of a birefringent organic thin film and an isotropic medium 13.
Opening area B₁And isotropic medium region A_TwoSo that
The retarder layer 11 and the polarization diffraction grating layer 12 are overlaid.

[0012] The numerical aperture NA ₁₂ numerical aperture NA ₁₁ retarder layer 11 with respect to the light beam L ₂ and polarization grating layer 12 from each isotropic size of the medium regions A ₂ and the size of the opening area B ₁ Decided. Numerical aperture NA ₁₁ determines the magnitude of such isotropic medium portion A ₂ and the opening area B ₁ becomes equal to or higher numerical aperture NA _12. That is, the aperture limiting element 101 outputs the light beam L incident from below in FIG.
To _2, so that the numerical aperture limiting the diameter of the light beam L ₂ to be equal to NA _11.

As the transparent substrates 14 and 15, an optically isotropic medium such as glass or quartz can be used.
The birefringent organic thin film of the retarder layer 11 is formed by applying an alignment treatment to the transparent substrate 14, and then applying a solution of a liquid crystal monomer to align the optical axes of the liquid crystal molecules in the alignment direction. For example, a polymer liquid crystal film that has been polymerized by, for example, can be used. Alternatively, a thin film formed by obliquely depositing poly (1,3-butadiyne) or the like on the transparent substrate 14 can be used, but a polymer liquid crystal film is used in consideration of adjustment of birefringence and ease of film formation. Is preferred.

Furthermore, the thickness d ₁₁ of the birefringent thin organic film, the product [Delta] n ₁₁ · d of the difference [Delta] n ₁₁ of thickness d ₁₁ and extraordinary refractive index of the birefringent thin organic film material and ordinary refractive index ₁₁ (Retardation value) is determined to be the following value. That is, if m ₁ and m ₂ are natural numbers, the light flux L ₁ is determined to be m ₁ · λ ₁ , and the light flux L ₂ is determined to be (m ₂ -1/2) · λ ₂ . It is preferable that m ₁ and m ₂ have a value of 3 or less because the influence of the wavelength fluctuation on the retardation value is small.

For processing the birefringent organic thin film formed on the transparent substrate 14, it is preferable to use a photolithography technique with good patterning accuracy and an etching technique with easy shape processing in order to enhance productivity.

The isotropic medium 13 used for the retarder layer 11 and the polarization diffraction grating layer 14 is preferably an adhesive. The retardation layer 11 on the transparent substrate 14 and the polarization diffraction grating layer 14 on the transparent substrate 15 are opposed to each other, and the isotropic medium 13 is filled and cured between them to form the aperture limiting element 101. In addition, as the material of the adhesive, acrylic, epoxy, or polyester UV-curable or heat-curable adhesive is preferred because of good workability, but is not limited thereto.

The refractive index of the isotropic medium 13 is controlled by the retarder layer 11.
And the ordinary light refractive index of the birefringent organic thin film of the present invention and the ordinary light refractive index of the birefringent organic thin film of the polarization diffraction grating layer 12 are selected. With this selection, the phase shifter layer 11 and the polarization diffraction grating layer 12 function as an isotropic medium layer for linearly polarized light that is incident on the phase shifter layer 11 and the polarization diffraction grating layer 12 with ordinary light.

The retardation value Δn ₁₁ · d ₁₁ of the birefringent organic thin film of the retarder layer ₁₁ is a natural number multiple of the wavelength with respect to the light beam L ₁ that is not restricted by the aperture by the aperture limiting element 101. and since the ordinary refractive index and the refractive index of the filling adhesive of the birefringent thin organic film is equal and does not disturb the wavefront phase shifter layer birefringent organic thin film region a ₁ in 11 and isotropic medium portion a ₂ .

Aperture limiting area B of polarization diffraction grating layer 12
₂ , the birefringent organic thin film formed on the transparent substrate 15 in the same manner as the retarder layer 11 is processed using photolithography and etching techniques. In addition, the polarization diffraction grating layer 1
It is preferable to use the same material as the material of the birefringent organic thin film 2 and the material of the birefringent organic thin film of the retarder layer 11 in order to improve productivity. It is not limited to the same material.

The thickness d of the polarization diffraction grating layer 12₁₂as,
Thickness d₁₂And the birefringent organic of the polarization grating layer 12
Between the extraordinary light refractive index of the object thin film and the refractive index of the isotropic medium 13
Δn ₁₂Product Δn₁₂・ D₁₂Is the wavelength λ₁Natural number times
(The reason will be described later). Also, polarization diffraction
The grating pattern of the sub-layer 12 is
Beam L subject to aperture restriction_TwoDiffracted light on the photodetector
Decide not to focus.

The aperture limiting element 10 manufactured as described above
In the case of No. 1, since the precision required for photolithography and etching in the manufacturing process is lower than the precision required for forming the dielectric multilayer film, it can be produced without lowering the yield. Further, it is possible to easily realize the structure does not disturb the wavefront birefringent organic thin film region of the retarder layer 11 A ₁ and isotropic medium region A _2. Further, it is easy to increase the size of the substrate in order to further improve the productivity.

The "second embodiment" the present embodiment, except the point that the location of the birefringent organic thin film region A ₁ and the isotropic medium portion A ₂ of the retarder layer 11 is replaced, the It is the same as the first embodiment. Here, the light beam L ₁ and the light beam L ₂ are:
Each polarization plane is incident as orthogonal linearly polarized light.
In this case, as shown in FIGS.
One birefringent organic thin film region A ₁ and an isotropic medium region A ₂ can be coped with, and similarly to the first embodiment, a light beam L ₂ incident on this element from below in FIG. Can be effectively limited by the retarder layer 11 and the polarization diffraction grating layer 12.

Third Embodiment The optical head device shown in FIG. 3 of this embodiment is an optical head device for recording / reproducing information on a DVD-based optical disk 6 and a CD-based optical disk 7, and uses a DVD as a light source. It includes two kinds of light sources of the semiconductor laser 1B for emitting a light beam L ₂ having a wavelength lambda ₂ of the semiconductor laser 1A and CD for emitting a light beam L ₁ having a wavelength lambda ₁ of the use, the first embodiment of the present invention The aperture limiting element 101 and the polarization hologram element 201 according to the embodiment are mounted.

The light beam L ₁ emitted from the semiconductor laser 1A is
After reflecting off the beam splitter 2 and passing through the collimating lens 4, the aperture limiting element 101 and the polarization hologram element 20
1 and is focused on the DVD 6 by the objective lens 5. Further, the light beam L ₂ in which the semiconductor laser 1A, and 1B emitted is plane beam splitter 9, the beam splitter 2 proceeds in the same manner as transparent halo flux L _1, and collected on the CD7. The light beam L ₁ reflected by DVD6 eventually converged on the photodetector 8A, whereas the light beam L ₂ reflected by the CD7 is
The light is split by the flat plate beam splitter 9 and collected on the photodetector 8B.

[0025] Figure 4 is the forward pass of the optical head apparatus, the light beam L ₂ is limited to a range of effectively the numerical aperture 0.45 to 0.5 by the aperture limiting element 101, an objective lens after the polarization hologram element 201 transmission 5 shows how light is condensed on the optical disk 7. Figure 5 is the forward pass of the optical head apparatus, after the light beam L ₁ is the aperture limiting element 101 transmission also, without changing the numerical aperture in the range of 0.6 to 0.65, the objective lens 5 after the polarization hologram element 201 transmitting the optical disk FIG.

As the polarization hologram element 201, 1)
An element in which a holographic pattern is formed on a birefringent organic thin film formed on a transparent substrate such as glass using photolithography and etching techniques, and lattice recesses are filled with an isotropic medium. 2) Lithium niobate Proton exchange on birefringent crystals such as holographic
An element on which a pattern is formed can be used.
Further, the polarization hologram element is often used in combination with a wave plate that converts linearly polarized light into circularly polarized light, and it is preferable to integrate the polarization hologram element and the wave plate in order to reduce the size of the element.

In FIG. 4, reference numeral 201 denotes a polarization hologram element in which a polarization hologram layer 22 having a holographic pattern formed on a birefringent organic thin film made of a polymer liquid crystal on a transparent substrate 21 and a wave plate 24 are integrated. In FIG. 4, 23 is a filling adhesive made of an isotropic medium, 25 is an adhesive, and 26 is a transparent substrate.

[0028] wave plate 24, the circularly polarized light linearly polarized light with respect to the light beam L ₁ uses a wave plate that does not change its polarization state to the light beam L _2. This wave plate, the polarization hologram element 201, the forward of an optical head device light beam L ₁ is incident as ordinary light passes through, the return path of the incident as extraordinary light can generate diffracted light, whereas the light flux L ₂ is, Both the forward path and the return path function as an isotropic medium.

[0029] In the optical head device of the present embodiment, the light beam L ₁ whereas the aperture limiting element 101 and the polarization hologram element 201, is incident as ordinary light in the forward path, incident as extraordinary light in the return path. For this reason, the diffracted light of the light beam L ₁ by the polarization hologram element 201 is
1 so as not to be further diffracted by
The thickness d ₁₂ of the polarization diffraction grating layer ₁₂ is determined. That is, the product Δn ₁₂ · d ₁₂ of the thickness d ₁₂ and the difference Δn ₁₂ between the extraordinary refractive index of the birefringent organic thin film of the polarization diffraction grating layer 12 and the refractive index of the isotropic medium 13 is the wavelength λ ₁ The aperture limiting element 101 is manufactured so as to be a natural number times.

Therefore, the aperture limiting element 1 as described above
In the optical head device of the present invention equipped with the optical hologram element 201 and the polarization hologram element 201, by limiting the aperture according to the length of the wavelength of the incident linearly polarized light, the numerical aperture of the objective lens is effectively limited and the linearly polarized light is reduced. Focus on an optical disc. Therefore, even with optical disks having different thicknesses, such as CDs and DVDs, a single optical system can exhibit high light-collecting ability, and good recording / reproduction of information on the optical disk can be realized.

In this embodiment, the aperture limiting element 101 and the polarization hologram element 201 have been described as separate elements.
The aperture limiting element 101 and the transparent substrate of the polarization hologram element 201 may be bonded and integrated. Further, as shown in FIG. 6, as a polarization hologram element mounted on the optical head device, a light beam L is applied to a wave plate constituting the polarization hologram element.
It is also possible to use _one and the light beam polarization hologram element 202 employing the wave plate of the broadband quarter serves as a quarter-wave plate for both L _2. In this case, due to the polarization hologram element 202 can be realized a system which detects the diffracted light of the light beam L ₁ and the light beam L ₂ in one photodetector.

The numerical aperture NA ₁₁ of the retarder layer 11 of the aperture limiting element 101 is set to be larger than the numerical aperture NA ₁₂ of the polarization diffraction grating layer 12, so that the light flux L ₂ is larger than the numerical aperture on the outward path of the optical head device. Also, the numerical aperture on the return path can be reduced.
In other words, the smaller the numerical aperture, the smaller the deterioration of the light-collecting ability caused by the inclination and uneven thickness of the optical disk.
It is effective in signal reproduction on optical detector 8 of the light beam L _2.
Reference numeral 3 denotes a beam splitter, and reference numerals in FIG.
The components having the same reference numerals as those in FIG. 3 are the same as the components in FIG.

[Fourth Embodiment] FIG. 7 is a cross-sectional view of an aperture limiting element 103 according to a fourth embodiment of the present invention. The aperture limiting element and the polarization hologram element are made of three transparent substrates. It is integrated so as to have a single-piece configuration and is downsized. The aperture limiting element 103 fixes the retarder layer laminated on the transparent substrate 14 described in the first embodiment to the polarization hologram element 201 described in the third embodiment with the isotropic medium 13 made of an adhesive. Can be produced. 1 and FIG. 3 are the same as those in FIG. 1 and FIG.

In the aperture limiting element 103, the polarization diffraction grating layer used to limit the diameter of the light beam L _{2 having} the wavelength λ ₂ is:
Since the peripheral region of the polarization hologram layer 22, the diffracted light generated in the peripheral area of the polarization hologram layer 22 of the light beam L ₂ whose diameter is limited, if not focused on the optical detector of the optical head apparatus, the opening limit The element 103 can be used for an optical head device.

The aperture limiting element 103 shown in FIG. 7 has a configuration in which, when the optical head device is mounted, the planes of polarization of the light beam L ₁ and the light beam L ₂ incident on the element are parallel linearly polarized light. Aperture limiting element shown in FIG. 8 shows the configuration when the plane of polarization of the light beam L ₁ and the light beam L ₂ is incident on the device is a linearly polarized light orthogonal. 7 with reference numerals in FIG.
Components having the same reference numerals as those in FIG. 7 are the same as those in FIG.

[0036]

EXAMPLE 1 This example is a specific example of the aperture limiting element 101 (FIG. 1) of the first embodiment. Aperture limiting element 101
Hereinafter, the members, materials, and the manufacturing method of the above will be described. Glass substrates having a thickness of 0.3 mm were used as the transparent substrates 14 and 15. The birefringent organic thin film region A ₁ retarder layer 11 was formed as follows. A rubbing treatment was performed on the polyimide for an alignment film applied on the surface of the transparent substrate 14 to obtain an alignment film. A solution of a birefringent liquid crystal monomer is applied onto the alignment film, and the photopolymerization curing agent previously contained in the liquid crystal monomer solution is applied to the photopolymerization curing agent with the optical axes of the liquid crystal molecules aligned in the direction of the alignment treatment. The liquid crystal monomer was polymerized by irradiating a light source for polymerization to form a polymer liquid crystal layer. Further, in photolithography and etching techniques to remove the center portion of the liquid crystal polymer as the numerical aperture NA ₁₁ becomes 0.45, to form a birefringent organic thin film region A _1.

The birefringent organic thin film region A of the retarder layer 11
_{As the} polymer liquid crystal which is the material of _{No. 1} , the difference Δn ₁₁ between the ordinary light refractive index and the extraordinary light refractive index for light having a wavelength of 660 nm is 0.15, and the ordinary light refractive index, extraordinary light refractive index and using a polymer liquid crystal difference [Delta] n ₁₁ is 0.14, 8.8 .mu.m thickness d ₁₁ of the retarder layer 11 (=
2 × 0.66 / 0.15 ≒ (2-1 / 2) × 0.79 /
0.14).

The polarization diffraction grating layer 12 is formed by the same process as the birefringent organic thin film region A ₁ of the retarder layer 11.
The size of the opening area B ₁ NA NA ₁₂ decided to be 0.45. Examples of the polymer liquid crystal as the polarization diffraction grating layer 12 material, using the same as the polymer liquid crystal which is a material of the birefringent organic thin film region A ₁ of the retarder layer 11. The diffraction grating pattern formed on the polarization diffraction grating layer 12 was determined by the arrangement of the optical system of the optical head device and the photodetector. The thickness d ₁₂ of the polarization diffraction grating layer ₁₂ is
To light of 0 nm, the product [Delta] n ₁₂ · d ₁₂ of the difference [Delta] n ₁₂ and the thickness d ₁₂ of the refractive index of the extraordinary light refractive index of the birefringent thin organic film of the polarization diffraction grating layer 12 and the isotropic medium 13, the wavelength It was determined to be 8.8 μm so as to be twice as large as that of the above, and when mounted on an optical head device, light having a wavelength of 660 nm was not diffracted on the return path.

Finally, the retarder formed on the transparent substrate 14
Birefringent organic thin film region A of layer 11 ₁And the transparent substrate 15
The polarization diffraction grating layer 12 formed thereon is opposed to
An aperture limiting element is fixed by using an isotropic medium 13 as an adhesive.
The child 101 was produced. As the isotropic medium 13, polyether is used.
Using a stell type UV curable adhesive, the refractive index is phase
Of the polymer liquid crystal used for the sub-layer 11 and the polarization diffraction grating layer 12
Those which were almost equal to the light refractive index were selected.

Example 2 Aperture limiting element 10 manufactured in Example 1
1 was mounted on an optical head device as shown in FIG. As described in the third embodiment, the optical head device of FIG.
This is an optical head device for recording and reproducing information on the D-type optical disk 6 and the CD-type optical disk 7. DV as a light source
The semiconductor laser 1A includes a semiconductor laser 1A that emits light having a wavelength of 660 nm as linearly polarized light for D and a semiconductor laser 1B that emits light having a wavelength of 790 nm for CD as linearly polarized light. The limiting element 101 and the polarization hologram element 201 are mounted.

As shown in FIG. 4, the polarization hologram element 201 includes a polarization hologram layer 22 formed between transparent substrates 21 and 26 and a wave plate 25, and is manufactured by the same process as the aperture limiting element 101 of Example 1. Produced. 0.3mm thick
Using the glass substrate described above as the transparent substrate 21, the polymer liquid crystal used in Example 1 was formed in the same manner as in Example 1, and the polarization hologram layer 22 was formed using photolithography and etching techniques. Next, a glass substrate having a thickness of 0.3 mm is
6, a wave plate 24 was fixed using an acrylic UV-curable adhesive 25.

As the wave plate 24, a plate in which polycarbonate was stretched to induce birefringence was used. The retardation value of the wave plate 24 is 82 for light having a wavelength of 660 nm.
5 nm (= 5/4 × 660 nm), and a wavelength of 790 n
It is adjusted to be 800 nm (≒ 1 × 790 nm) for m light. By setting the optical axis of the wave plate in the 45 ° direction with respect to the polarization direction of the linearly polarized light having a wavelength of 660 nm, the wave plate 24 converts the linearly polarized light having a wavelength of 660 nm into circularly polarized light. And functions as an isotropic medium. Finally, the polarization hologram layer formed on the transparent substrate 21 and the wave plate 24 fixed to the transparent substrate 26 were fixed using an isotropic medium 23 as an adhesive. As the isotropic medium 23, the isotropic medium 1 used in Example 1 was used.
The same as 3 was used.

On the outward path of the optical head device of this embodiment (FIG. 3),
The light having a wavelength of 790 nm was effectively restricted to a numerical aperture of 0.45 by the aperture limiting element 101, and was condensed on the CD optical disk 7 by the objective lens 5 (FIG. 4). on the other hand,
The light having a wavelength of 660 nm is not changed in diameter even after passing through the aperture limiting element 101, and is not changed by the objective lens 5, but the DVD optical disk 6 is used.
Focused on top (FIG. 5). That is, one optical system showed high light-collecting ability for optical disks having different thicknesses.

Further, the light having a wavelength of 660 nm reflected from the DVD-type optical disk 6 is diffracted by the polarization hologram element 201 and condensed on the photodetector 8A. Light having a wavelength of 790 nm reflected by a CD optical disk was not diffracted by the polarization hologram element 201, was deflected by the flat plate beam splitter 9, and was condensed on the photodetector 8B. As a result, DVD-based optical discs or CDs with different standards
Recording and reproduction of information on the optical disk of the system were realized.

[0045]

The aperture limiting element of the present invention can be easily manufactured by using a process with higher productivity as compared with the conventional aperture limiting element using a dielectric multilayer film. Further, in the optical head device of the present invention, the above-described aperture limiting element is disposed between the collimator lens and the objective lens, so that the productivity of the optical head device can be improved. Further, in the optical head device according to the present invention, the numerical aperture of the objective lens is effectively limited according to the magnitude of the wavelength of the light emitted from the light source, and one optical system is used for optical discs having different thicknesses. And high light-collecting ability can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an aperture limiting element according to a first embodiment of the present invention, (a) a sectional view, and (b) a plan view of a retarder layer.

FIG. 2 is a diagram showing an example of an aperture limiting element according to a second embodiment of the present invention, (a) a cross-sectional view, and (b) a plan view of a retarder layer.

FIG. 3 is a conceptual diagram showing an example of an optical head device according to a third embodiment of the present invention.

FIG. 4 is a conceptual diagram illustrating a state in which linearly polarized light having a wavelength of λ ₂ is condensed on an optical disk with a limited diameter in the optical head device.

FIG. 5 is a conceptual diagram showing a state in which linearly polarized light of wavelength λ ₁ is condensed on an optical disk without changing its diameter in the optical head device of FIG.

FIG. 6 is a conceptual diagram showing another example of the optical head device according to the third embodiment of the present invention.

FIG. 7 is a sectional view showing an example of an aperture limiting element according to a fourth embodiment of the present invention.

FIG. 8 is a sectional view showing another example of the aperture limiting element according to the fourth embodiment of the present invention.

[Explanation of symbols]

 101, 102, 103, 104: aperture limiting element 201, 202: polarization hologram element 11: retarder layer 12: polarization diffraction grating layer 13, 23: isotropic medium 14, 15, 21, 26: transparent substrate 22: polarization Hologram layer 24: Wave plate 25: Adhesive 1A, 1B: Semiconductor laser 2: Beam splitter 4: Collimating lens 5: Objective lens 6, 7: Optical disk 8, 8A, 8B: Photodetector 9: Plate beam splitter

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H049 AA03 AA13 AA33 AA37 AA45 AA50 AA57 AA64 AA68 BA06 BA42 BB01 BB03 BC02 BC05 BC14 BC21 CA05 CA07 CA09 CA11 CA15 5D119 AA38 AA41 BA01 DA01 DA05 EC45 EC47 FA05 JA08 JA12 JA12

Claims (3)

[Claims] _1. A light beam L _{1 having} a wavelength λ ₁ , both of which are linearly polarized light.
And a wavelength-selective aperture limiting element that limits the size of the diameter of the light flux L ₂ that can be transmitted, of the light flux L ₂ (λ ₁ ≠ λ ₂ ) of the wavelength λ ₂ , wherein the aperture limiting element is a phase shifter it is superimposed a layer and polarization grating layer, the phase shifter layer is isotropic medium portion a ₂ is formed in a central portion,
Birefringent organic thin film region A ₁ is formed in the peripheral portion surrounding the central portion, and the retardation value of the birefringent organic thin film region A ₁ is a m ₁ and m ₂ is a natural number, m with respect to the light beam L _{1 1} · lambda _1, a light (m ₂ -1/2) against beam L ₂ · lambda _2, the polarization diffraction grating layer, the opening transmits not both diffract the light beam L ₁ and the light beam L ₂ in the central region B ₁ is formed, the opening restriction region B ₂ to transmit without diffracting the light beam L ₁ diffracts light beam L ₂ in the peripheral portion surrounding the central portion is formed, isotropic medium regions a ₂ and the opening area B ₁ Wherein the sizes of the aperture limiting elements are substantially the same. 2. A light beam L _{1 having} a wavelength λ ₁ , both of which are linearly polarized light.
And a wavelength-selective aperture limiting element that limits the size of the diameter of the light flux L ₂ that can be transmitted, of the light flux L ₂ (λ ₁ ≠ λ ₂ ) of the wavelength λ ₂ , wherein the aperture limiting element is a phase shifter it is superimposed a layer and polarization grating layer, retarder layer, birefringent organic thin film region a ₁ is formed in the center portion, isotropic medium portion a ₂ in the peripheral portion surrounding the central portion is formed is, and the retardation value of the birefringent organic thin film region a ₁ is as m ₁ and m ₂ the natural number, m ₁ · lambda ₁ to the light flux L _1, the light flux L ₂ (m ₂ -1/2 ) and · lambda _2, the polarization diffraction grating layer, the opening area B ₁ to transmit without both diffract the light beam L ₁ and the light beam L ₂ is formed in the center portion, the light beam L ₂ in the peripheral portion surrounding the central portion opening restriction region B ₂ to transmit without diffracting the light beam L ₁ is diffracted are formed, the size of the birefringent organic thin film region a ₁ and the opening area B ₁ Are substantially the same. 3. A light flux of the light flux of the wavelength lambda ₁ L ₁ and wavelength lambda ₂ L ₂
(Λ ₁ ≠ λ ₂ ), a light beam L ₁ and a light beam L ₂
An optical head device comprising an objective lens for converging light onto an optical recording medium, and a polarization hologram element in an optical path between the light source and the objective lens, wherein between the light source and the polarization hologram element, Item 3. An optical head device provided with the aperture limiting element according to Item 1 or 2.