JP2001126294A - Optical element and optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To downsize an optical head device by constituting an optical element having plural functions, such as phase difference generation, in combination. SOLUTION: The optical element is formed by fixing a transparent substrate 11 having an opening control function and a transparent substrate 14 having a wave front aberration correction function with an adhesive 13 from both sides across an organic thin film 12 having double refractiveness such optical elements is assembled into 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 element and an optical head device used for an optical head device for recording and reproducing information by irradiating an optical recording medium with light.

[0002]

2. Description of the Related Art CD-R (write-once compact disc)
A 1.2 mm thick optical disc for recording and reproducing CD (compact disc) based optical discs including
A semiconductor laser having an oscillation wavelength of 780 nm as a light source;
An objective lens having a (numerical aperture) of 0.45 is used.
On the other hand, an optical disk having a thickness of 0.6 mm and a semiconductor laser having an oscillation wavelength of 650 nm as a light source for recording / reproducing a DVD (digital video disk) optical disk.
An objective lens with NA of 0.6 is used.

For recording / reproducing both optical disks of CD and DVD by one optical head device, one semiconductor laser of each wavelength used for optical disks of both systems and one objective lens of each NA are used. The switching system can be realized by mounting each unit. However, this switching system requires two optical systems, so the device configuration is large, the weight is heavy, the number of parts is large, the assembly is complicated, and the control voltage is high. Also had the disadvantage of becoming larger.

Recently, as shown in FIG. 6, light emitted from semiconductor lasers 1a and 1b having different wavelengths is transmitted through collimating lenses 3a and 3b, then combined and separated by a wavelength-selective beam splitter 4, and the same. It has been considered to realize a more compact optical head device by using the objective lens 5 described above. However, in the case of CD and DVD systems, the thickness of the optical disk is 1.2 mm and 0.6 m, respectively.
m, and the NA of the objective lens is 0.45
And 0.6, and the wavelength of the light source is 78
0 nm and 650 nm, etc.
And DVD using the same objective lens 5
When reproducing, it is necessary to change the NA of the objective lens 5 according to the wavelength.

Generally, a CD system and a DVD are used according to the wavelength.
As a method of changing the NA of the objective lens 5 of the system, there is a method of arranging the aperture control element 7 in an optical path from the light sources 1a and 1b to the optical disk 6 and controlling the diameter of light incident on the objective lens 5. That is, the aperture control element 7 allows the two lights having different wavelengths to pass straight through in the central region where the optical axis passes, while the wavelength 650 in the peripheral region where the optical axis does not pass.
It has a function of transmitting only light having a wavelength of 780 nm in a straight line but not transmitting light having a wavelength of 780 nm.

Further, when the same objective lens 5 is used for a CD system and a DVD system, the objective lens 5 is usually optimized for the wavefront aberration characteristic with respect to the DVD system, so that the
The system has a disadvantage that the wavefront aberration characteristics are deteriorated. Therefore, the wavefront aberration correction element 8 for correcting the wavefront aberration of the CD system should be provided in the optical path from the light sources 1a and 1b to the optical disk 6 so that the wavefront aberration characteristic of the DVD system is hardly deteriorated. Is also needed.

Generally, many optical components other than those described above are used in an optical head device. Photodetector diffraction element 1 for guiding reflected light of optical disk 6 to photodetectors 2a and 2b
Numeral 0 is also one of the important components constituting the optical head device. Further, a tracking diffraction element (not shown) for splitting light traveling from the light sources 1a and 1b to the optical disk 6, which is used in a signal detection method such as a three-beam method or a differential push-pull method, also constitutes the optical head device. It is one of the parts.

In some cases, a system utilizing polarized light is configured to increase the light use efficiency of the optical head device. In this case, a phase difference element 9 for controlling the polarization of light is provided in the optical head device. Also, in a non-polarization type optical head device, a phase difference element may be provided in the optical head device in order to prevent interference between light emitted from the light source and light returned to the light source. Conventionally, as a retardation element, a material obtained by polishing an inorganic single crystal such as quartz is widely used. However, quartz has a drawback that the number of processing steps is large and productivity cannot be improved.

As described above, the conventional optical head device for reproducing / recording both a CD and a DVD using the same objective lens 5 for the CD system and the DVD system has a large number of optical components and has a problem of further miniaturization. Remains. In particular, the objective lens 5, the aperture control element 7, the wavefront aberration correction element 8, the phase difference element 9, and the photodetector diffraction element 10 are sometimes assembled together in one actuator, and thus a reduction in size and weight is strongly desired. ing.

[0010]

As described above, in the conventional optical head device having two types of light sources, the number of components of the optical elements to be formed is increased, so that further miniaturization has been an issue.

An object of the present invention is to use a birefringent organic thin film for a phase difference element which is one of optical elements constituting an optical head device, and further provide an aperture control function, a wavefront aberration correction function, and a diffraction function. An object of the present invention is to provide an optical element which has one or more of the above functions and leads to downsizing of an optical head device incorporating the same.

[0012]

According to the present invention, a transparent organic thin film having a birefringent property is fixed on one surface of one transparent substrate, or two or more transparent substrates are superposed on each other. An organic thin film having birefringence is fixed on at least one of the substrates to form an organic thin film laminate, and at least one surface of the organic thin film laminate on which the organic thin film is not fixed has the following 3 An optical element characterized in that a structure having the function of any one of the three elements is formed. (1) The first part of the central part that transmits light of two or more wavelengths
An aperture control element comprising: a region; and a second region surrounding the first region and reflecting or diffracting light of one or more wavelengths. (2) A phase difference element having a ring-shaped groove for correcting the wavefront of transmitted light at a central portion that transmits light of two or more wavelengths. (3) A diffraction element that has a periodic uneven shape and diffracts incident light.

An organic thin film having birefringence is fixed on one surface of the transparent substrate to form an organic thin film laminate, and the organic thin film laminate on which the organic thin film is not fixed is provided on the surface of the organic thin film laminate. A structure having the function of an aperture control element including a first region in a central portion that transmits light of two or more wavelengths and a second region surrounding the first region and reflecting or diffracting light of one or more wavelengths. Wherein an annular groove for correcting the wavefront of transmitted light is formed in the first region of the optical element, or is further laminated on the organic thin film side of the optical element. The first of the transparent substrate
An optical element is provided, wherein the annular groove is formed at a position corresponding to a region.

Further, the organic thin film contains at least one of the group consisting of polycarbonate, polyimide, polyarylate, polyether sulfone, (alicyclic) polyolefin, poly (meth) acrylate, polyetherimide and high-molecular liquid crystal. An optical element as described above is provided.

Further, in an optical head device for guiding light emitted from a semiconductor laser to an optical recording medium and for guiding reflected light from the optical recording medium to a photodetector, the above-mentioned optical element comprises: An optical head device is provided in an optical path leading to the optical recording medium or in an optical path leading from the optical recording medium to the photodetector.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a configuration of the optical element according to the first embodiment.

As shown in FIG. 1, a transparent substrate 11 having an aperture control function and a transparent substrate 14 having a wavefront aberration correcting function are provided.
In between, an organic thin film 12 having birefringence is fixed with an adhesive 13. That is, the optical element shown in FIG. 1 forms an optical element having an aperture control function and a wavefront aberration correction function. Here, wavefront aberration means coma aberration, astigmatism,
Refers to spherical aberration and the like.

The transparent substrate 11 having an aperture control function is made of a glass substrate or the like, and has a first region constituting a central portion and a second region surrounding the central portion. By forming a periodic grating having an uneven cross section on the thin film formed on the surface of the transparent substrate, a desired wavelength can be selectively transmitted or diffracted. With such a configuration, a desired transmittance can be easily obtained by adjusting the phase amplitude generated by the unevenness with respect to light having a wavelength to be selectively transmitted. This is desirable as a configuration for generating the signal. Further, in order to prevent reflection loss at the interface between air and the transparent substrate 11 having the aperture control function, it is desirable to provide an antireflection film.

On the other hand, by forming a dielectric multilayer film on the second region of the transparent substrate 11, a desired wavelength can be selectively transmitted and reflected. This configuration is preferable as a configuration in which the aperture control function is generated on the transparent substrate in the optical head device because stray light due to light having a wavelength other than the wavelength that is desired to be selectively transmitted hardly occurs.

Transparent substrate 14 having wavefront aberration correction function
Is composed of a glass substrate or the like,
A region and a second region surrounding a central portion, wherein the first region is directly or in a thin film formed on the surface of the transparent substrate,
It is produced by forming an annular groove. Further, in order to prevent reflection loss at the interface between air and the transparent substrate 14 having a wavefront aberration correcting function, it is desirable to provide an antireflection film.

It is also possible to add an aperture control function by the above-mentioned periodic unevenness to the surface of the transparent substrate 14 having the wavefront aberration correcting function on which the annular groove is formed (not shown). In this case, it is preferable that an annular groove for generating the wavefront aberration correcting function and a periodic uneven diffraction grating for generating the aperture control function can be simultaneously formed on the same surface of the same transparent substrate.

As the organic thin film 12 having birefringence, birefringence is imparted to a polymer thin film such as polycarbonate, polyimide, polyarylate, polyether sulfone, (alicyclic) polyolefin, polyacrylate, etc. by uniaxial stretching or the like. Organic thin films can be used. Other resins can be used as the organic thin film having birefringence, but it is preferable to use (modified) polycarbonate, polyimide, polyethersulfone, or (alicyclic) polyolefin from the viewpoint of heat resistance. Where (denaturation)
Polycarbonate means a modified polycarbonate in which polyester carbonate is used as a part of a component of the polycarbonate composed of pisphenol A. As the organic thin film, a polymer liquid crystal thin film obtained by subjecting a fixed substrate to a normal liquid crystal alignment treatment, applying a polymer liquid crystal monomer, and curing the liquid crystal can also be used. The polymer liquid crystal may be of a side chain type or a main chain type.

In an organic thin film such as polycarbonate, the polymer chains are oriented by uniaxial stretching, so that a difference occurs between the refractive index in the stretching direction and the refractive index in the direction perpendicular thereto. Become. Also, a desired retardation can be obtained by adjusting the amount of stretching.

The organic thin film is often formed so as to cause a phase difference of λ / 4 with respect to light having a wavelength λ which is incident and transmitted vertically, such as laser light of a semiconductor laser, but 5λ / In some cases, a phase difference of 4.lambda. Therefore, it is desirable to select the magnitude of the phase difference due to the organic thin film according to the application.

As the material of the adhesive, acrylic, epoxy, urethane, polyester, polyimide,
Urea, melamine, furan, isocyanate,
Silicone-based, cellulose-based, vinyl acetate-based, vinyl chloride-based, rubber-based, and mixtures thereof can be used. The adhesive is preferably UV-curable or heat-curable because of good workability, but is not limited thereto. It is necessary for the adhesive to be applied smoothly and thinly with a constant thickness in order to improve the correction of the wavefront aberration. As a coating method, it is preferable to use a method such as spin coating or roll coating because the workability is excellent and the thickness can be easily controlled.

In order to reduce the reflection loss at the interface due to the difference between the refractive index of the adhesive and the refractive index of the organic thin film having birefringence, an adhesive having a refractive index substantially the same as that of the organic thin film is used. Is desirable.

By forming an optical element as described above, an optical element having a plurality of functions having an aperture control function and a wavefront aberration correcting function can be constructed. In the present embodiment, the number of components of the optical element can be reduced and the phase difference element can be downsized by the organic thin film laminated plate structure using the transparent substrate and the organic thin film.

FIG. 2 is a sectional view and a plan view showing the structure of the optical element according to the second embodiment.

FIG. 2A shows a transparent substrate 11 having an aperture control function as described above as an example of a configuration of an optical element.
2 shows an optical element in which an organic thin film 12 having birefringence is fixed by an adhesive 13 and an antireflection film 16 is applied to the remaining one surface of the organic thin film 12. FIG. 2 (b)
As another configuration example of the optical element, an organic thin film 12 having birefringence is bonded between a transparent substrate 11 having an aperture control function and a transparent substrate 17 provided with an antireflection film 16 as described above. Indicates an optical element fixed by. FIG. 2C is a plan view of the optical element shown in FIGS. 2A and 2B as viewed from above.

With such an organic thin film laminate structure using a transparent substrate and an organic thin film, similar to the first embodiment,
An optical element having an aperture control function can be made compact.

FIG. 3 is a sectional view and a plan view showing the structure of the optical element according to the third embodiment.

FIG. 3A shows a transparent substrate 1 having a wavefront aberration correcting function as described above as one configuration example of an optical element.
4 shows an optical element in which an organic thin film 12 having birefringence is fixed by an adhesive 13 and an antireflection film 16 is applied to the remaining one surface of the organic thin film 12. FIG.
(B) shows another configuration example of the optical element, as described above, the transparent substrate 14 having the wavefront aberration correcting function and the antireflection film 1.
6 shows an optical element in which an organic thin film 12 having a birefringent property is fixed with an adhesive 13 between transparent substrates 17 to which a 6 is applied. FIG. 3 (c) is a plan view of the optical element of FIGS. 3 (a) and 3 (b) as viewed from above in the figure.

With such an organic thin film laminate structure using a transparent substrate and an organic thin film, similar to the first embodiment,
An optical element having a wavefront aberration correction function can be made compact.

FIG. 4 is a sectional view and a plan view showing the structure of an optical element according to the fourth embodiment.

FIG. 4A shows an example of the configuration of an optical element in which an organic thin film 12 having birefringence is fixed to a transparent substrate 15 having a diffraction function by an adhesive 13, and the remaining organic thin film 12 is left. An optical element having an anti-reflection film 16 on one surface is shown. FIG. 4B shows another example of the configuration of the optical element, in which an organic thin film 12 having birefringence is bonded between a transparent substrate 11 having a diffraction function and a transparent substrate 17 provided with an antireflection film 16. The optical element fixed with the agent 13 is shown. Note that FIG. 4 (c) corresponds to FIG. 4 (a) and FIG.
It is the top view which looked at the optical element of (b) from the figure upper side.

The transparent substrate 15 having a diffraction function is directly
Alternatively, it is manufactured by forming a periodic grating or hologram having a concave-convex section on a thin film formed on the surface of a transparent substrate. Further, in order to prevent reflection loss at the interface between air and the transparent substrate 15 having the diffraction function,
It is desirable to apply an antireflection film.

With such a laminated plate structure using a transparent substrate and an organic thin film, an optical element having a diffraction function can be miniaturized similarly to the first embodiment.

Next, with reference to FIG. 5, an optical head device having two kinds of wavelength light sources used for a DVD system and a CD system will be described as an embodiment to which the optical element of the present invention is applied. .

The optical head device shown in FIG. 5 has the optical element shown in FIG. 1 incorporated in an optical system. In this optical head device, light emitted from the semiconductor lasers 1a and 1b passes through the collimating lenses 3a and 3b, respectively, and then passes through the beam splitter 4 (transmitted light of 3a) or reflects (3a).
b), the photodetector diffraction element 10, and an optical element 18 having an aperture control function and a wavefront aberration correction function.
And is focused on the optical disk 6 by the objective lens 5. The light reflected from the optical disk 6 passes through the objective lens 5 and the optical element 18 and is split by the photodetector diffraction element 10. The split light is collected on the photodetectors 2a and 2b.

As described above, by disposing the optical element having the aperture control function and the wavefront aberration correcting function in the optical path, the number of optical components of the optical head device having two types of light sources can be reduced, and the size and weight can be reduced. Cost reduction can be realized.

[0041]

EXAMPLE An optical element shown in FIG. 1 was manufactured.

As the organic thin film 12 having birefringence, a uniaxially stretched polycarbonate is used, and a transparent substrate 11 having an aperture control function is formed with a polyester adhesive 13.
The organic thin film 12 was bonded between the transparent substrate 14 having a function of correcting wavefront aberration. Further, as the organic thin film having birefringence, one that generates a phase difference of λ / 4 with respect to two average wavelengths of 650 nm and 780 nm was selected.

A quartz substrate is used as the transparent substrate 11 having an aperture control function, and a periodic grating having an uneven cross section is directly formed by photolithography in a peripheral region surrounding a central region through which the optical axis of the transparent substrate passes. It was formed by a combination of the etching method and the etching method. Further, an antireflection film was applied to the surface of the transparent substrate on which the unevenness was processed (not shown).

A quartz substrate is also used as the transparent substrate 14 having the wavefront aberration correcting function, and an annular groove is formed directly in the central region of the transparent substrate where the optical axis passes by a combination of photolithography and etching. . Further, an antireflection film was applied to the surface of the transparent substrate on which the annular groove was processed (not shown).

The optical element manufactured as described above was incorporated into an optical head device (FIG. 5). In the optical head device of FIG. 5, a semiconductor laser 1a having a wavelength of 650 nm for a DVD optical disk and a semiconductor laser 1b having a wavelength of 780 nm for a CD optical disk were used as light sources. Light emitted from these semiconductor lasers is output from a collimating lens 3a,
After passing through 3b, the optical axis is matched by the beam splitter 4 and transmitted through the photodetector diffraction element 10.

As the photodetector diffraction element 10, a birefringent polymer liquid crystal thin film is provided with lattice-like irregularities, and an optically isotropic medium having a refractive index substantially equal to the ordinary light refractive index of the polymer liquid crystal. Then, a polarization hologram in which uneven portions of the polymer liquid crystal thin film were filled was used. This polarization hologram has a different diffraction efficiency depending on the polarization direction of the incident light. The polarization direction of high transmission efficiency is used on the outward path from the semiconductor laser to the optical disk, and the polarization direction with high diffraction efficiency on the return path from the optical disk to the photodetector. To use.

The light transmitted through the photodetector diffraction element 10 is transmitted through the optical element 18 (having both an aperture control function and a wavefront aberration correction function) of the present embodiment, and is recorded on the recording surface of the optical disk 6 by the objective lens 5. Collect light. This optical disk 6
The optical path of the reflected light from the optical disk 6 having the information recorded in the optical detector 6 is slightly bent by the optical element 18 and the photodetector diffractive element 10 so that each of the photodetectors 2a, 2b
It is led to.

Further, the positions of the two semiconductor lasers are exchanged, and the semiconductor laser for DVD-type optical disks is
The semiconductor laser for the system optical disk may be 1a. In this case, the reflection characteristic of the beam splitter 4 is different from the above case, and reflects light having a wavelength of 650 nm.

In this embodiment, by incorporating an optical element having an aperture control function and a wavefront aberration correcting function as an optical element according to the present invention into the optical head device, the number of components of the optical head device can be reduced. The miniaturization was realized. In addition, this optical element performs optimal aperture control on the optical disc during reproduction of a CD optical disc and also performs wavefront aberration correction, so that noise of information light, which is reflected light from the optical disc, is reduced. A reproduction signal was obtained.

[0050]

As described above, according to the present invention, an organic thin film having birefringence is fixed to one transparent substrate or fixed so as to be sandwiched between a plurality of transparent substrates.
By generating at least one of the aperture control function, the wavefront aberration correction function, and the diffraction function on at least one of the transparent substrates, an optical element having a plurality of functions such as phase difference generation can be configured. Further, by incorporating this optical element into the optical head device, the number of components of the optical head device can be reduced, and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical element according to a first embodiment of the present invention.

FIGS. 2A and 2B show a configuration of an optical element according to a second embodiment of the present invention, in which FIG. 2A is a cross-sectional view showing one configuration example of the optical element, and FIG. A sectional view showing the
(C) is a plan view of the optical element of (a) and (b) as viewed from above in the figure.

3A and 3B show a configuration of an optical element according to a third embodiment of the present invention, in which FIG. 3A is a cross-sectional view showing one configuration example of the optical element, and FIG. 3B is another configuration example of the optical element. A sectional view showing the
(C) is a plan view of the optical element of (a) and (b) as viewed from above in the figure.

4A and 4B show a configuration of an optical element according to a fourth embodiment of the present invention, in which FIG. 4A is a cross-sectional view showing one configuration example of the optical element, and FIG. 4B is another configuration example of the optical element. A sectional view showing the
(C) is a plan view of the optical element of (a) and (b) as viewed from above in the figure.

FIG. 5 is a diagram showing an example in which the optical element of the present invention is incorporated in an optical head device.

FIG. 6 is a diagram showing an example of a conventional optical head device.

[Explanation of symbols]

1a, 1b: Semiconductor lasers 2a, 2b: Photodetectors 3a, 3b: Collimating lenses 4: Beam splitters 5: Objective lenses 6: Optical discs 7: Aperture control elements 8: Wavefront aberration correction elements 9: Phase difference elements 10: Light detection Diffusion element 11: Transparent substrate having aperture control function 12: Organic thin film having birefringence 13: Adhesive 14: Transparent substrate having wavefront aberration correction function 15: Transparent substrate having diffraction function 16: Anti-reflection film 17: Transparent substrate 18: Optical element having aperture control function and wavefront aberration correction function

Claims (4)

[Claims] An organic thin film having birefringence is fixed on one surface of one transparent substrate, or two or more transparent substrates are superposed and at least one of the transparent substrates is overlapped. An organic thin film having a refractive property is fixed to form an organic thin film laminate, and at least one surface of the organic thin film laminate to which the organic thin film is not fixed has one of the following three elements. An optical element having a structure having an element function. (1) The first part of the central part that transmits light of two or more wavelengths
An aperture control element comprising: a region; and a second region surrounding the first region and reflecting or diffracting light of one or more wavelengths. (2) A phase difference element having a ring-shaped groove for correcting the wavefront of transmitted light at a central portion that transmits light of two or more wavelengths. (3) A diffraction element that has a periodic uneven shape and diffracts incident light. 2. An organic thin film having birefringence is fixed on one surface of a transparent substrate to form an organic thin film laminate,
On the surface of the organic thin film laminate on which the organic thin film is not fixed, a first region of a central portion that transmits light of two or more types of light, and reflects light of one or more types of wavelengths surrounding the first region or An optical element having a structure having the function of an aperture control element provided with a second region that diffracts, wherein an annular groove for correcting a wavefront of transmitted light is formed in a first region of the optical element. Or the ring-shaped groove is formed at a position corresponding to the first region of a transparent substrate further laminated on the organic thin film side of the optical element. 3. The organic thin film contains at least one of the group consisting of polycarbonate, polyimide, polyarylate, polyether sulfone, (alicyclic) polyolefin, poly (meth) acrylate, polyetherimide, and liquid crystal polymer. The optical element according to claim 1. 4. An optical head device for guiding light emitted from a semiconductor laser to an optical recording medium and for guiding reflected light from the optical recording medium to a photodetector, wherein the optical element according to claim 1, 2 or 3 is used. An optical head device installed in an optical path from the semiconductor laser to the optical recording medium or in an optical path from the optical recording medium to the photodetector.