JP2000249831A - Optical device and optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical device which can always read information with specified quantity of light even from an optical recording medium having double refraction, by stacking a polarizing diffraction device, wavelength plate and polarizing plate in this order. SOLUTION: This optical device 4 is produced by successively stacking a polarizing diffraction device 1 showing different diffraction efficiencies depending on the polarization direction of the incident light, a phase difference plate 2 and a polarizing plate 3 made of an org. polymer material, and the phase difference plate 2 and the polarizing plate 3 are laminated with an adhesive layer 5 to form one body. The surfaces of the polarizing diffraction device 1 and the polarizing plate 3 are laminated with adhesive layers 5 to transparent substrates 6, 7, respectively. As for the polarizing diffraction device 1, diffraction device using a birefringent org. substance such as a liquid crystal or a polymer liquid crystal prepared by aligning and polymerizing a liquid crystal material is used. The phase difference plate 2 showing birefringence and comprising an org. polymer material is a 1/4 wavelength plate or a 5/4 wavelength plate which converts linearly polarized light into circularly polarized light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element and an optical head device for writing optical information on and reading optical information from an optical recording medium such as an optical disk and a magneto-optical disk.

[0002]

2. Description of the Related Art CD (Compact Disk) and DVD
A light with a light flux controlling element such as a diffractive element for writing optical information on an optical recording medium such as an optical disc such as a (digital video disc) and a magneto-optical disc and reading optical information from the optical recording medium. A head device is used.

FIG. 6 is a side view showing a schematic configuration of the optical head device. In the optical head device, light emitted from a light source 11 such as a semiconductor laser emits light such as a hologram beam splitter which is a kind of light flux controlling element. The optical disc 1 as an optical recording medium is transmitted through the optical element 60 of FIG.
It is focused on 2. The reflected light from the optical disk 12 is
The light passes through the objective lens 14 again, is diffracted by an optical element 60 such as a hologram beam splitter, and reaches the light receiving element 5 which constitutes a photodetector. The light receiving element 5 converts the received reflected light into an electric signal, the converted electric signal is amplified by an amplifier, and the gain is multiplied by an automatic gain correction circuit to adjust the signal level to a certain range.

As a light flux controlling element such as the optical element 60, a non-polarizing hologram beam splitter has been conventionally used. FIG. 7 shows a side sectional view of the non-polarizing hologram beam splitter 61. The non-polarization hologram beam splitter 61 is, for example, a glass substrate 62
An isotropic diffraction grating 6 made of an isotropic optical material
3 is formed. In the drawing, reference numeral 64 denotes a low-reflection coat applied to both surfaces of the hologram beam splitter. In the case of a non-polarizing hologram beam splitter, the 0th-order transmission efficiency on the outward path is 50%, and the 1st-order diffraction efficiency on the return path is 20%.
%, The theoretical reciprocating efficiency is 50% × 20% = 10
%. However, actually, it is difficult to manufacture a hologram beam splitter having a reciprocating efficiency of 10%.
Since it is only necessary to obtain a reciprocating efficiency of about 7%, the non-polarizing hologram beam splitter has a problem that the reciprocating efficiency is low.

In order to increase the reciprocating efficiency of light to more than 10%, it has been proposed to use a hologram beam splitter whose diffraction efficiency changes depending on the polarization direction of light. Further, there has been proposed an optical element having a polarization diffractive element improved so that information can be read from an optical disc having birefringence. A polarizing diffractive element is an element having a different diffraction efficiency depending on the polarization direction of light incident thereon. Usually, a lattice having a concave-convex section is formed in the birefringent optical material, and the concave-convex portion is filled with an optically isotropic medium having an ordinary refractive index or an extraordinary refractive index of the birefringent optical material.
FIG. 8 is a side sectional view showing a hologram beam splitter 65 of a polarization system. Hologram beam splitter 65 of the polarization system, on a glass substrate 66, the birefringent optical material such as a polymer liquid crystal to form a polarizing diffraction grating 67, the ordinary refractive index of the birefringent optical material n _o or abnormal light isotropic medium 68 having the same refractive index n _e index of refraction n _s is,
The space between the polarizing diffraction grating 67 and the glass substrate 69 is filled.

When a hologram beam splitter 65 of a polarization system is used, a 波長 wavelength plate is inserted between the hologram beam splitter 65 and the optical disk 12 so that the light passes through the hologram beam splitter 65. Is rotated by 90 ° in the forward path and the return path.

A hologram beam splitter 65 of a polarization system
For example, the ordinary refractive index n of the birefringent optical material 68
If equal the refractive index n _S of _o and isotropic medium 8 (n _o =
n _S), when the polarization direction in the forward path of the light emitted from the light source 11 is matched to the ordinary refractive index n _o direction of the birefringent optical material 68, since the hologram beam splitter 65 does not work, to increase the zero-order transmission efficiency be able to. On the other hand, in the return path, the polarization direction of the reflected light by the / 4 wavelength plate becomes equal to the extraordinary refractive index n _e direction of the birefringent optical material 68, the hologram beam splitter 65 functions, high primary diffraction efficiency can do. As a result, a reciprocating efficiency higher than 10%, which is the theoretical reciprocating efficiency of the non-polarizing hologram beam splitter 61, can be obtained.

[0008]

However, the optical head device using the above-mentioned polarizing hologram beam splitter 65 has the following problems. In other words, the optical disk 12 as an optical recording medium is generally a resin molded product, and is required to be molded as homogeneously as possible. In some cases, the flow may be distorted due to, for example, a bias in the flow, and may have partial birefringence at one or more locations. Generally, an optical disk substrate is formed by a radial flow disk forming method having a direct gate (injection port) at the center. In the radial flow type disk forming method, a radial orientation remains in the inner circumferential direction of the substrate, and a circumferential orientation remains as approaching the outer circumference, and the flow pattern shows a partial birefringence.

Then, since the optical disk 12 is rotated at a high speed, the reflected light from the optical disk 12 having one or more partial birefringences is not constant in the polarization direction but fluctuates from time to time. The polarization direction of the return path deviates from 90 ° with respect to the polarization direction of the light. In addition, reflected light from which it is completely unknown how much the polarization direction has shifted is returned. Since the hologram beam splitter of the polarization system diffracts only a predetermined polarization component, the amount of return light fluctuates in accordance with the fluctuation of the polarization direction of the reflected light. It also happens to return. In such a case, the hologram beam splitter 65 of the polarization system can hardly diffract the reflected light, and the information from the optical disc 12 cannot be read by the light receiving element 5.

In view of the above circumstances, an object of the present invention is to provide an optical element and an optical head device that can always read information with a constant light amount even on an optical recording medium having birefringence. I do.

[0011]

According to the present invention, there is provided a polarizing diffraction element having different diffraction efficiencies depending on the polarization direction of incident light;
An optical element characterized in that a こ と or ４ wavelength plate and a polarizing plate made of an organic polymer material are stacked in this order.

In this optical element, when light polarized in a specific direction enters from the side of the polarizing diffraction element, the polarizing diffraction element transmits only a specific polarization component on the outward path. Here, the specific polarization component refers to a direction in which the light of the semiconductor laser 11 in FIG. 1 /
The four-wavelength plate or the 波長 wavelength plate converts linearly polarized light into circularly polarized light, and the polarizing plate transmits only the polarized light component of the circularly polarized light that is orthogonal to the specific polarized light component. on the other hand,
On the return path, the polarizing plate transmits only the orthogonal polarization component, and the quarter-wave plate or the 5 / 4-wave plate converts linearly polarized light into circularly polarized light. The polarizing diffractive element diffracts only the orthogonal polarization component of the circularly polarized light. When such an optical element is used in an optical head device, the influence of the birefringence of the optical recording medium is reduced, and it becomes possible to write and read optical information on the optical recording medium satisfactorily.

Further, the present invention provides an optical element characterized by using a polarizing diffraction element as the polarizing plate.

In this optical element, by using a polarizing diffraction element as the polarizing plate, the water resistance of the polarizing plate can be greatly improved. Thus, the set polarization characteristics can be stably obtained over a long period of time, and the reliability of the optical element can be improved.

Also, in an optical head device for guiding light emitted from a semiconductor laser to an optical recording medium and detecting reflected light from the optical recording medium with a photodetector, any one of the above-described optical recording devices is provided between the optical recording medium and the photodetector. Wherein the optical element is disposed with the polarizing plate facing the optical recording medium.

In this optical head device, the outgoing light of the semiconductor laser light passes through the polarizing diffraction element, the quarter-wave plate or the 5 / 4-wave plate, and the polarizing plate in order, and is irradiated on the optical recording medium. Is reflected in the reverse order, and the light diffracted by the polarizing diffraction element is detected by the photodetector. In this way, by irradiating the optical recording medium with the laser beam having a specific polarization direction, even if the optical recording medium has birefringence, the influence of the birefringence is reduced. Return light can be obtained. Thus, it becomes possible to write and read optical information on the optical recording medium having birefringence.

Further, an optical head device is characterized in that the polarization direction of the polarizing plate constituting the optical element is a radial direction or a direction perpendicular to the irradiation position of the emitted light on the optical recording medium. provide.

In this optical head device, a laser beam whose polarization direction coincides with the birefringent neutral axis which is not affected by birefringence is applied to the optical recording medium. Refractivity is canceled. As a result, a maximum and constant amount of return light is always obtained,
Optical information can be stably written to or read from an optical recording medium.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of an optical element 4 in which a polarizing diffractive element 1, a retardation plate 2, and a polarizing plate 3 of a first embodiment according to the present invention are integrated, and FIG. FIG. 6 is a diagram for explaining the operation of the optical element when used in the first embodiment. The basic configuration of the optical head device 10 is the same as that of FIG. 6, and therefore, FIG. 6 will be referred to as necessary. The optical element 4 of the present embodiment includes a polarizing diffractive element 1, a retardation plate 2, and a polarizing plate 3, which are sequentially laminated.
And the polarizing plate 3 are integrated via an adhesive layer 5. By bonding the surfaces of the polarizing diffraction element 1 and the polarizing plate 3 to the transparent substrates 6 and 7 via the adhesive layer 5, the rigidity of the optical element 4 is increased, and the optical element 4 can be easily held and used.
As the transparent substrates 6 and 7, an acrylic plastic plate or the like can be used in addition to an optical glass plate having a flat surface.

In the present invention, as described above, it is preferable to stack the transparent substrate 6, the polarizing diffraction element 1, the retardation plate 2, the polarizing plate 3, and the transparent substrate 7 in this order. As the adhesive at the time of lamination, an acrylic, epoxy, urethane, or a mixture thereof can be used. From the viewpoint of improving workability, a UV-curable or thermosetting adhesive is used. Is preferred. Further, it is necessary to apply the adhesive smoothly and thinly with a constant thickness in order to improve the wavefront aberration. For this reason, for example, a method such as spin coating or roll coating is used. These methods are preferable because they are excellent in workability and easy to control the thickness. Further, it is preferable to form a non-reflection film on the surfaces of the transparent substrates 6 and 7 to reduce light reflection loss. This anti-reflection coating is effective both when the optical element 4 is used alone and when it is used by incorporating it into the optical head device 10 described later.

Examples of the polarizing diffractive element 1 used in the optical element 4 include a diffractive element using a birefringent organic substance such as a liquid crystal or a polymer liquid crystal in which a liquid crystal material is oriented and polymerized to polymerize. And a diffraction element using a birefringent inorganic single crystal such as LiNbO ₃ or a uniaxially elongated polymer film such as polycarbonate. As a specific structure of a diffraction element using a birefringent organic substance, for example, a birefringent diffraction grating having a rectangular cross-section in a cross-sectional shape is formed on a transparent substrate such as glass by photolithography or etching. Is filled with an isotropic filler at least between the convex portions. Note that in order to use the liquid crystal in a liquid state, a structure may be employed in which a sealing material is provided between the substrate and the substrate which is opposed to the liquid crystal and the liquid crystal is sealed.

As the isotropic optical material constituting the isotropic filler, an acrylic resin or an epoxy resin can be used. In particular, a photocurable polymer and a thermosetting polymer are preferable. For example, an acrylic ultraviolet curable adhesive can be suitably used. The polarizing diffraction grating 1 may have a structure in which a grating is directly formed on a transparent substrate, or a structure in which a film on which a diffraction grating is formed is attached to the transparent substrate, in addition to the above-described configuration.

Next, a schematic method for manufacturing the polarizing diffraction element 1 will be described. First, on a transparent substrate such as a glass substrate, a birefringent film composed of uniformly oriented photocurable polymer liquid crystal is formed. The orientation direction of the polymer liquid crystal constituting the birefringent film may be either horizontal to the transparent substrate and perpendicular / parallel to the incident linearly polarized light. In either case, high transmission can be achieved. Next, a lattice having a concave-convex section is formed on the birefringent film of the polymer liquid crystal that has been formed and oriented. Means for forming a grid include:
Examples thereof include a method using photolithography and etching, and a mold pressing method having a lattice shape.

Then, an isotropic medium is filled in the uneven portions of the formed lattice. The refractive index of the isotropic medium is determined by the relationship between the direction of the incident linear polarization and the orientation direction of the polymer liquid crystal constituting the birefringent film. For example, when the incident linear polarization direction is perpendicular to the alignment direction of the polymer liquid crystal, the concave portion is filled with an isotropic medium having a refractive index substantially equal to the ordinary light refractive index of the polymer liquid crystal, and When the polarization direction and the orientation direction of the polymer liquid crystal are parallel, the concave portion is filled with an isotropic medium having a refractive index substantially equal to the extraordinary light refractive index of the polymer liquid crystal. When filling the isotropic material, in order to suppress the transmitted wavefront distortion of the entire diffraction element, a method of sandwiching and curing with a cover glass or the like coated with a low reflection coating is easy. For weight reduction, it is preferable to cure without a cover glass.

Next, the phase difference plate 2 will be described. For the retardation plate 2 made of an organic polymer material and having birefringence, for example, a material such as polycarbonate, polyvinyl alcohol, and polymer liquid crystal can be used. This phase difference plate 2
A wavelength plate having a wavelength λ of a semiconductor laser serving as a light source, for example, λ / 4 with respect to 650 nm is used. As a result, the linearly polarized light emitted from the semiconductor laser becomes circularly polarized light, and the polarization direction is rotated by 90 ° between the forward path and the return path. Further, a ／ wavelength plate may be used instead of the 波長 wavelength plate.

The polarizing plate 3 made of an organic polymer material
For example, a material such as polyvinyl alcohol and polymer liquid crystal can be used, and a linear lattice or the like is formed by photolithography and etching.

Here, the polarizing diffraction element 1 acts optically as follows. In other words, the laser beam emitted from the light source and passing through the polarizing diffraction element 1 does not undergo any change with respect to the linearly polarized light component of the polarization direction of the ordinary ray of the polarizing diffraction element 1 and is theoretically 100%. To Penetrate. On the other hand, the polarizing diffraction element 1 functions as a diffraction grating for a linearly polarized light component rotated by 90 ° with respect to this polarized light component.
Up to about 40% as primary light, up to 40% as -1st light
A degree of diffracted light is obtained. The retardation plate 2 is a 波長 wavelength plate or a ／ wavelength plate, and converts linearly polarized light into circularly polarized light. The polarizing plate 3 transmits only a polarized light component in a direction corresponding to the polarization direction.

Next, the operation of the optical element 4 will be described based on an actual example mounted on an optical head device for writing and reading optical information on an optical recording medium such as an optical disk as shown in FIG. . FIG. 2 shows an optical element 4 of the present embodiment.
Is a configuration example in which the optical head device 10 is used, and shows the polarization direction and the transmission efficiency of the polarizing diffraction element 1, the phase difference plate 2, and the polarizing plate 3 with respect to the laser light from the semiconductor laser 11. The polarization direction of the polarizing plate 3 is
2 is set in the radial direction or a direction perpendicular thereto, so that the polarization direction of the polarizing diffraction element 1 matches the polarization direction of the transmitted light of the polarizing plate 3. Also, the transmission polarization direction of the 波長 wavelength plate 2 is
The light transmission function can be achieved even if the polarization direction of the polarizing plate 3 is set between 0 ° and 90 °,
If the angle is set between 35 ° and 50 °, the diffraction function of the polarizing diffraction element 1 can be used, and it is most preferable to set the angle to 45 °. With respect to the polarization direction of the transmitted light of the polarization diffractive element 1 and the polarization direction of the quarter-wave plate 2, the same angular relationship holds for the outward path. The diffraction function of the diffractive diffractive element 1 can be used,
Particularly, it is most preferable to set the angle to 45 °. The light source 11 is arranged such that the linear polarization axis of the laser light coincides with the transmission polarization direction of the polarizing diffraction element 1. Note that the return path may be at any angle.

According to FIG. 2, on the outward path of light, linearly polarized light in the polarization direction of ordinary light with respect to the polarizing diffraction element 1 (direction in which there is no difference in refractive index between the birefringent optical material and the optically isotropic medium). The laser light from the light source 11 is polarized
When incident on, it passes through without any change,
The light enters the wavelength plate 2 and becomes circularly polarized light. Then, the polarization direction of the extraordinary light becomes parallel to the radial direction of the optical disk 12 by the polarizing plate 3, and the laser light reaches the surface of the optical disk 12. In principle, light of approximately 50% of the intensity of the emitted laser light with respect to the polarization direction of ordinary light to the polarizing diffraction element 1 arrives. As described above, the neutral axis of the birefringence of the optical disk 12 is parallel or perpendicular to the radial direction of the disk, so that linearly polarized light parallel to the radial direction of the disk that has reached the disk surface is birefringent of the optical disk 12. The light is reflected without being affected by the characteristics.

Next, on the return path of the light, the return light passes through the polarizing plate 3 as it is because the polarization direction is the polarization direction of the extraordinary light whose polarization direction coincides with the transmission polarization axis of the polarizing plate 3. And changes into circularly polarized light. Light incident on the polarizing diffractive element 1 as circularly polarized light is separated into ordinary light and extraordinary light, and the polarized component of the extraordinary light is diffracted, and about 10% (up to about 12.5%) of + 1st-order diffracted light is detected. It reaches the photodetector 13 which is a container.

With this configuration, even if the optical disc 12 has birefringence, a laser beam whose polarization direction matches the birefringent neutral axis, which is not affected by the birefringence, is applied to the optical disc 12. By irradiating, the reflected laser light has the birefringence of the optical disc 12 canceled.
As a result, a maximum and constant return light is always obtained, so that optical information can be stably written or read. Even if the polarization direction of the laser beam applied to the optical disc 12 does not completely coincide with the neutral axis of the birefringence of the optical disc, the output signal intensity of the photodetector 13 is reduced, but the writing and reading operations are sufficiently performed. It can be performed.

Further, by setting the polarization direction of the quarter-wave plate 2 at an angle of 45 ° with respect to the polarization direction of the polarizing plate 3, the output signal intensity of the photodetector 13 can be maximized. The same applies to the polarization direction of the quarter-wave plate 2 and the polarization direction of the transmitted light of the polarizing diffractive element 1, and the output signal intensity of the photodetector 13 is set by setting the angle to 45 °. Can be maximized. Note that a configuration may be adopted in which at least two lights of the 0th-order light, the + 1st-order light, and the -1st-order light diffracted by the polarizing diffraction element 1 are detected by a photodetector. In this case, a higher output signal strength is obtained. Then, by laminating and integrating the polarizing diffraction element 1, the retardation plate 2, and the polarizing plate 3, the number of components of the optical head device 10 can be reduced, and the device can be reduced in size and weight. Also,
The optical adjustment at the time of assembling the optical element 4 becomes easy, and the assembling work can be greatly simplified. Although the above-described optical element is an optical element suitable for use in an optical head device, it can be applied to other optical devices, and has the same effect.

Here, the semiconductor laser 11 has an emission wavelength of 65.
Although a wavelength of 0 nm is used, for example, an emission wavelength of 790
nm, or may be configured to emit them to the same optical axis via a half mirror 31 as shown in FIG. As described above, when a plurality of semiconductor lasers having different wavelengths are used in combination, the wavelength of one semiconductor laser is changed to the wavelength of the other semiconductor laser by using a ５ wavelength plate instead of the １ ／ wavelength plate. You can get closer. This makes it possible to write and read optical information in common regardless of the type of optical recording medium such as an optical disk such as a CD or DVD and a magneto-optical disk.

Next, a description will be given of a second embodiment according to the present invention in which a polarizing diffraction element is used as a polarizing plate. An optical element 9 was manufactured in the same manner as in the first embodiment except that the polarizing diffractive element having a rectangular cross section in the above-described first embodiment was also used as a polarizing plate. FIG. 4 shows a side sectional view of the optical element 9 of the present embodiment. The optical element 9 sequentially laminates the polarizing diffraction element 1, the retardation plate 2, and the polarizing diffraction element 8 as a polarizing plate. The retardation plate 2 is connected to the polarizing diffraction elements 1 and 8 via an adhesive layer 5. It is integrated. Transparent substrates 6 and 7 made of glass or the like are attached to the surface of the laminate of the polarizing diffraction elements 1 and 8 and the retardation plate 2.

A polarizing diffraction element 8 functioning as a polarizing plate
Is a linear grating formed on a glass substrate by photolithography and etching in the same manner as the polarizing diffractive element 1, so that the diffractive grating on the transparent substrate is on the retardation plate 2 side. 1 are stacked and integrated in a state of being turned upside down. Note that the adhesive layer 5 is not necessary when the retardation plate 2 is bonded with the filler of the polarizing diffraction elements 1 and 8.

According to the optical element 9, when a laser beam polarized in a specific direction is incident from a semiconductor laser, the refractive index of the convex portion made of the polymer liquid crystal and the refractive index of the concave portion made of the isotropic medium are different. There is no difference (both have a refractive index of about 1.5), and the laser light is transmitted without diffraction. On the other hand, when a laser beam polarized in a direction orthogonal to the specific direction is incident, the refractive index of the convex portion is about 1.6 (an extraordinary refractive index), and the refractive index of the concave portion is approximately 1.5 (the ordinary refractive index). ), The optical element 9
Functions as a diffraction grating. Thus, the polarizing diffractive element 8 functions as a good polarizing plate that diffracts light in a specific polarization direction. If the grating pitch of the polarization diffraction element is made finer, the diffraction angle becomes larger, and light leakage can be eliminated.

As described above, by using the polarizing diffractive element 8 made of a polymer liquid crystal as the polarizing plate, the water resistance of the polarizing plate can be greatly improved as compared with the case where polyvinyl alcohol is used. Thus, it is possible to stably obtain the polarization characteristic set as an inexpensive configuration over a long period of time,
The reliability of the optical element and the optical head device can be improved. In addition, since the degree of freedom in designing the grid pattern including the finer grid pitch is high, and optical components for various uses can be laminated and integrated, a polarizing plate suitable for weight reduction and thinning can be obtained. In addition to the polarizing diffractive element 8, a birefringent inorganic single crystal such as LiNbO ₃ can be used as a polarizing plate, and a similar effect can be obtained by stacking it above the retardation plate shown in FIG. An optical element that performs can be obtained.

[0038]

[Example 1] A polarizing diffraction type optical element 4 shown in Fig. 1 was manufactured by integrating a polarizing diffraction element 1, a retardation plate 2, and a polarizing plate 3. Hereinafter, a method for manufacturing the polarizing diffraction element 1 will be described with reference to FIG. First, as shown in FIG. 5A, a transparent glass substrate 6 provided with a low reflection coat
A polyimide alignment film 51 was formed on one surface of the substrate. In this example, a transparent glass substrate having a diameter of 5 inches and a thickness of 0.5 mm was used. Next, as shown in FIG. 5B, after the formed polyimide alignment film 51 is rubbed, an unpolymerized liquid of a photo-curable polymer liquid crystal is applied to the polyimide alignment film 5.
1 was dropped.

Further, polyimide is applied to the surface of another transparent glass substrate 52, and the rubbing direction of the transparent
The opposing glass substrate 52 that had been subjected to a mold release treatment after being subjected to 0 ° rubbing was overlaid as shown in FIG. 5C, so that the unpolymerized polymer liquid crystal was in a horizontal alignment state. And FIG.
As shown in FIG. 5D, polymerization is performed by irradiating 600 mJ of ultraviolet light, and then the above-mentioned opposite glass substrate 52 is release-removed, and as shown in FIG. A birefringent film 53 of 0 μm horizontally oriented polymer liquid crystal was formed.
Next, as shown in FIG. 5 (f), after irradiating 3000 mJ of ultraviolet light to perform additional polymerization, 30 ° C. at 140 ° C.
The birefringent film 53 was completely solidified by annealing (annealing) for one minute.

As shown in FIG. 5 (g), an SiO ₂ film 54 having a thickness of about 50 nm was formed as a protective film on the birefringent film 53 of the polymer liquid crystal by a sputtering method. Furthermore, S
On the iO ₂ film 55, a grid-like photoresist mask having a pitch of 4 μm was formed by photolithography in which the stripe direction of the grid was at an angle of 90 ° to the rubbing direction. Using this lattice-shaped photoresist mask, reactive ion etching was performed for 5 minutes under conditions of a pressure of 0.2 Torr and an output of 300 W using a fluorocarbon gas such as CF ₄ gas at a flow rate of 100 SCCM. Si
The lattice pattern of the photoresist mask was transferred to the O ₂ film 54. Thus, a selection mask 55 of SiO ₂ as shown in FIG. 5H was formed.

Next, using the SiO ₂ selection mask 55, ashing (ashing treatment) is performed for 20 minutes under the conditions of a pressure of 0.2 Torr and an output of 300 W using O ₂ gas at a flow rate of 100 SCCM. Was. As a result, FIG.
As shown in (1), at the same time as removing the remaining photoresist mask by reactive ion etching, a lattice body 56 having a depth of 3 μm and a pitch of 4 μm was formed on the birefringent film 53 made of a polymer liquid crystal.

Thereafter, as shown in FIG. 5 (j), the polymer liquid crystal (ordinary refractive index n _o = 1.5,
Ordinary refractive index n _o equal to the refractive index (the n = 1.5) isotropic material 57 of ultraviolet curing type having, release of which is integrally overlapped the extraordinary refractive index n _e = 1.6) Filling was performed between the treated opposite glass substrate 58. Then, the light amount 500
Curing polymerization was performed by irradiation with ultraviolet light of 0 mJ, and the opposite glass substrate 58 was released from the mold to form a diffraction element. Finally, by dicing, the outer diameter is 4mm x 4mm,
The polarizing diffraction element having a thickness of about 1 mm was finished.

When the characteristics of the polarizing diffractive element thus manufactured were examined, the wavefront aberration of the transmitted light was found to be at the center of the light incident surface of the polarizing diffractive element 1 (circular range having a diameter of 3 mm).
Was 0.020λ _rms (root mean square) or less. The retardation plate 2 was made of polycarbonate produced by uniaxial stretching, and had a retardation of 163 nm and a thickness of 45 μm. The polarizing plate 3 was formed by forming a polymer liquid crystal thin film having birefringence on a glass substrate, and forming a 4 μm pitch linear lattice by photolithography and etching.
With this linear grating, at the wavelength of 650 nm of the semiconductor laser, the 0th-order light transmittance of ordinary light is 97% and the 0th-order light transmittance of extraordinary light is 1
%, Which confirmed that the film functions well as a polarizing plate.

The optical element 4 was completed by bonding the retardation plate 2 to the polarizing diffractive element 1 with an adhesive, and further bonding the polarizing plate 3 in the same manner. Then, the obtained optical element 4 is mounted on an optical head device 10 having a semiconductor laser 11, an optical element 4, an objective lens 14, and a photodetector 13 as shown in FIG. The optical disk 12 was irradiated with laser light. As a result, a good reproduction signal of the optical disk 12 was obtained.

Example 2 An optical element 9 was manufactured in the same manner as in Example 1 except that the above-described polarizing diffractive element made of a polymer liquid crystal and having a rectangular cross section was used as a polarizing plate.
However, the difference from Example 1 is that the polarizing plate is changed to a polarizing diffraction element. The polarizing diffractive element 8 functioning as a polarizing plate was obtained by the same manufacturing method as the polarizing diffractive element 1 of Example 1, and its characteristics were examined. The transmittance was 96% for ordinary light and 2% for extraordinary light. Met. The polarizing diffraction element 8 was laminated and integrated such that the diffraction grating on the transparent substrate was on the retardation plate 2 side, that is, in a state where the diffraction grating was turned upside down with respect to the polarizing diffraction element 1. In this embodiment, the retardation plate 2 is bonded to the polarizing diffraction elements 1 and 8 with an adhesive, but the retardation plate 2 may be bonded with a filler for the polarizing diffraction elements 1 and 8.

The optical element 9 was mounted on an optical head device 10 as shown in FIG. 6, and a laser beam from a semiconductor laser 11 having a wavelength of 650 nm was irradiated on the optical disk 12. As a result, a good reproduction signal of the optical disk 12 was obtained.

[0047]

As described above, by using the optical element of the present invention in which a polarizing diffraction element, a 1/4 or 5/4 wavelength plate, and an organic polarizing plate are stacked in this order, By canceling the birefringence of the optical disc, it is possible to always obtain a maximum and constant amount of return light. further,
By using the optical element in the optical head device, a good reproduction signal of the optical recording medium can be obtained. Further, by using a polarizing diffraction element as a polarizing plate, an optical element and an optical head device having excellent durability can be provided.

[Brief description of the drawings]

FIG. 1 is a polarizing diffraction element according to a first embodiment of the present invention,
FIG. 3 is a side sectional view of an optical element in which a retardation plate and a polarizing plate are integrated.

FIG. 2 is a diagram illustrating an operation of the optical element when the optical element is used in an optical head device.

FIG. 3 is a diagram illustrating an example in which a light source is configured by combining a plurality of semiconductor lasers having different wavelengths.

FIG. 4 is a side sectional view of an optical element according to a second embodiment.

FIG. 5 is a view showing a step of producing a polarizing diffraction element.

FIG. 6 is a side view showing a schematic configuration of the optical head device.

FIG. 7 is a side sectional view of a conventional non-polarizing hologram beam splitter.

FIG. 8 is a side sectional view of a conventional hologram beam splitter of a polarization system.

[Explanation of symbols]

 1: Polarizing diffractive element 2: 1/4 wavelength plate 3, 8: Polarizing plate 4, 9: Optical element 5: Adhesive layer 6, 7: Transparent substrate 10: Optical head device 11: Semiconductor laser 12: Optical disk (optical recording 13) Photodetector (photodetector)

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2H049 AA25 AA43 AA44 AA53 AA57 BA02 BA06 BA07 BA42 BA45 BA47 BB03 BB43 BC21 5D119 AA43 BA01 DA01 DA05 EA02 EA03 EC48 FA05 JA23 JA25 JA30 JA32 JA33

Claims (4)

[Claims] 1. A polarizing diffraction element having a different diffraction efficiency depending on a polarization direction of incident light, a 1/4 or 5/4 wavelength plate,
An optical element, wherein a polarizing plate made of an organic polymer material is stacked in this order. 2. The optical element according to claim 1, wherein a polarizing diffraction element is used as the polarizing plate. 3. An optical head device for guiding light emitted from a semiconductor laser to an optical recording medium and detecting reflected light from the optical recording medium with a photodetector, between the optical recording medium and the photodetector. 3. An optical head device, wherein the optical element according to claim 2 is arranged with the polarizing plate facing the optical recording medium. 4. The optical system according to claim 3, wherein the polarization direction of the polarizing plate constituting the optical element is a radial direction at a position of irradiation of the emitted light on the optical recording medium or a direction perpendicular thereto. The optical head device as described in the above.