JPH08278407A - Beam splitter and beam splitter for optical pickup - Google Patents

Abstract

PURPOSE: To enable using of a crystal material except for quartz and to obtain good optical characteristics by disposing two pieces of the crystal material having double refraction characteristics in such a manner that the joining faces are at a distant shorter than the wavelength of light and the two pieces are joined by intermolecular force. CONSTITUTION: Two pieces of a crystal material 11 comprising LiNbO3 having the crystal axis twisted by a specified angle are joined to constitute a beam splitter 16. A polarizing film is formed on the surface 12 and an reflection preventing film is formed on the surface 13 by coating. The joining faces 14 are polished to obtain <=0.02λrms wavefront aberration and are not coated but the crystal 11 itself is exposed. In this case, after the joining faces are completely cleaned with ultrapure water, the pieces are fixed parallel to each other and ultrapure water is applied on the joining faces 14 to join the two pieces 11. Then the two pieces 11 are heat treated under specified conditions to vaporize the ultrapure water on the joining faces 14 to join the faces 14 only by intermolecular force. The obtd. beam splitter 16 is used to reflect light on the surface 12 to an optical information recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam splitter suitable for use in an optical pickup used in an optical recording device for recording / reproducing information.

[0002]

2. Description of the Related Art In a beam splitter for an optical pickup used for audio equipment or information equipment for reading, reproducing or recording information on an optical information recording medium such as an optical disk, two optical elements (prisms) are bonded and joined. For this, an ultraviolet-curable or thermosetting organic adhesive is usually used.

However, characteristic deterioration due to absorption from the visible region to the near infrared region due to the reaction between the organic adhesive and the coating (multilayer film) on the adhesive bonding surface poses a problem.
Japanese Patent Laid-Open No. 1-280703 and the like have been proposed as a solution.

In this conventional example, as shown in FIGS. 11 and 12, a high-density material layer 33 is provided between a specific layer (TiO ₂ ) of a multilayer film 31 between two prisms 41 and 42 and a bonding agent 32.
Is provided in at least one layer. Thereby, even when the specific layer (TiO ₂ ) is used, the bonding agent 32 can be prevented from entering the multilayer film 31, and the generation of absorption can be suppressed.

Further, Japanese Patent Application Laid-Open No. 3-179301 discloses a polarizing prism using crystals as an optical element. Artificial quartz is used as the crystal material, the incident surface of the light flux is formed parallel to the optical axis, and two outgoing light rays having polarization characteristics different by 90 ° are obtained from the emission surface having a predetermined angle with respect to the incident surface. I am trying. This makes it possible to reduce the number of optical components and improve the polarization characteristics.

[0006]

[Patent Document 1] Japanese Patent Application Laid-Open No. 3-17930
In the case of the polarizing prism disclosed in Japanese Patent Publication No. 1, the conventional beam splitter uses the birefringence characteristics of the crystal to improve the polarization characteristics and reduce the number of parts. The difference in refractive index is about 1 × 10 ^-2 . In other words, the separation angle between ordinary light and extraordinary light is small, and unless a certain long distance is provided between the prism and the light detection member that detects light, the light is not sufficiently separated and the detection signal from the light detection member is accurate. Hard to get. Therefore, even if the prism becomes small, the optical path length must be long. Also, like the conventional example, it is also possible to arrange a triangular prism that is not joined to form a beam splitter,
Compared to the joined prism, the separation angle between the ordinary ray and the extraordinary ray cannot be made large, and the optical path length must be long as in the above.

Further, as in Japanese Patent Laid-Open No. 1-280703, it is necessary to carry out a special coating, which causes a problem of increasing the cost of the prism. Crystal materials having a large separation angle between ordinary light and extraordinary light have a relatively large refractive index. Some crystal materials have a refractive index of about 2.0 or more. That is, when the crystal materials are bonded together, the bonding agent (adhesive) also needs to have high refractive index characteristics. However, the refractive index of the organic adhesive is about 1.4 to 1.5. Therefore, in order to reduce the difference in refractive index from the crystal material, a special multilayer coating must be formed on the crystal bonding surface. No longer.

In addition, there is no inorganic adhesive that satisfies the optical characteristics, and there are cases where it cannot be used as a beam splitter while having a large separation angle between ordinary light and extraordinary light.

At present, due to the bonding problem, only crystal can be used as the crystal material having the birefringence characteristic, and there is a problem that the optical pickup cannot be downsized.

The present invention has been made in view of the above problems, and a common object of the inventions of claims 1 to 5 is to bond a crystal material without using a bonding agent (adhesive) or the like. Thus, it is possible to use a crystalline material other than quartz and to realize an inexpensive beam splitter having good optical characteristics, and contribute to the provision of a compact and inexpensive optical pickup.

[0011]

According to the first aspect of the present invention,
In a beam splitter that splits incident light into a plurality of lights and emits them, it is configured by arranging the bonding surface of two crystal materials having birefringence characteristics at a distance shorter than the wavelength of light and bonding them by intermolecular force. It is characterized by that.

According to a second aspect of the present invention, in a beam splitter for an optical pickup that separates reflected light from an optical information recording medium into a recording signal, a focus error signal, and a tracking error signal, two crystal materials having birefringence characteristics are used. It is characterized in that the bonding surface is arranged at a distance shorter than the wavelength of light and bonding is performed by intermolecular force.

The invention according to claim 3 is characterized in that the surface of the crystal material is exposed at the joint surface of the two crystal materials in the beam splitter for an optical pickup according to claim 1.

The invention according to claim 4 is characterized in that the bonding boundary line exposed on the surface of the beam splitter for optical pickup according to claim 1 is fixed by a bonding agent and / or a bonding reinforcing member. It is a thing.

According to a fifth aspect of the present invention, the refractive indices of the two crystal materials in the optical pickup beam splitter according to the first aspect are 1.6 or more.

[0016]

The function of the present invention will be described below.

FIG. 1 shows an optical system used in the present invention. The divergent light emitted from the light emitting member 4 is reflected by the surface of the beam splitter 5 and converted into parallel light by the collimator lens 6. A lens 7 is arranged in front of the collimator lens 6, and collects light on the optical information recording medium 8 and irradiates it. The light reflected and returned from the optical information recording medium 8 passes through the lens 7 and the collimator lens 6 and enters the beam splitter 5. When the light is transmitted through the beam splitter 5, the light is separated, and the separated light is detected by the light detecting member 9 and used as a recording signal, a focus error signal and a tracking error signal. A monitor light detection member 10 for detecting the light of the light emitting member 4 and controlling the light amount of the light emitting member 4 is disposed near the beam splitter 5.

Beam splitter 5 used here
As described in claims 1 and 2, for example, by using two crystal materials having birefringence characteristics in which the difference in refractive index between ordinary light and extraordinary light is large, a small light component with a small number of optical components is provided. Pickup is possible.

As described above, a crystal material having a large difference in refractive index between ordinary light and extraordinary light has a large refractive index, and an organic adhesive cannot be used. For this reason, as a method of joining crystal materials without using a bonding agent (adhesive), the bonding distance is set to a distance shorter than the wavelength of light, and bonding is performed using the intermolecular force on the surface of each bonding surface. There is a way. Microscopically, there is a space on the joint surface, but since the space is shorter than the wavelength of light, reflection at the optical interface does not occur and light can be completely transmitted.

Specifically, pure water is applied as a contact liquid to the bonding surface of the crystal material with suppressed wavefront aberration, and bonding is performed so that interference fringes are one or less. After that, a heat treatment is performed to evaporate the contact liquid. When the contact liquid evaporates, the respective bonding surfaces are attracted to each other, and the crystal material can be brought into a bonding state satisfying the optical characteristics. Thus, in the present invention, since no bonding agent (adhesive) is used, there is no absorption of light by the bonding agent,
Bonding is possible regardless of the type of crystal material, and the optical path length can be made shorter than that of quartz.

LiNbO ₃ .Li ₂ B ₄ O is a crystal material other than quartz, which has a large difference in refractive index between ordinary light and extraordinary light.
₇・ CaCO ₃ etc.

The operation of the invention according to claim 3 will be described below. The coating layer is porous when viewed microscopically. When joining the coating layers, since the joining surface is not flat, the joining is caused by weak intermolecular force, and the joining is likely to be lost. Therefore, in order to bond with the strongest intermolecular force, stronger bonding is possible if there is no non-adherent matter such as the bonding surface coating layer and the surface of the polished crystal material is exposed.

The operation of claim 4 will be described below. In the joining of intermolecular forces, a very strong joining force can be obtained in the direction perpendicular to the joining surface, but the joining force is relatively weak in the parallel direction. Therefore, by applying the bonding agent to the bonding boundary line exposed on the surface and / or fixing it with the bonding reinforcing member, there is no problem that the bonding surface is displaced. Since the joint surfaces are close to each other by a very short distance, the bonding agent does not enter the joint surface due to the capillary phenomenon.

The operation of claim 5 will be described below. In the case of crystal, it is possible to bond with an organic adhesive, but with a crystal material other than crystal having a large difference in refractive index between ordinary light and extraordinary light, the refractive index becomes large as described above, and the organic adhesive cannot be used. The present invention is particularly effective for a crystal material having a refractive index equal to or higher than that of quartz, and specifically, a crystalline material having a refractive index of 1.6 or less.
It is particularly effective for the above crystal materials. Most organic adhesives have a refractive index of 1.6 or less. When bonding a crystal material having a refractive index of less than 1.6, no special coating is required on the bonding surface and only bubbles should be used. Although they can be easily bonded, when they are used for a crystal material having a refractive index of 1.6 or more, a special coating for relaxing the refractive index is indispensable on the bonding surface.

Further, in a crystal material having a very high refractive index, the refractive index cannot be relaxed by coating, and joining with an organic adhesive is impossible. That is, according to the present invention, when a crystal material having a refractive index of 1.6 or more is bonded, a bonding agent or a coating can be omitted, and light absorption by the bonding agent can be eliminated.

[0026]

EXAMPLES Examples of the present invention will be described below.

First Embodiment (Structure) FIGS. 2, 3, 4, and 5 show a first embodiment of the present invention. FIG. 2 is a schematic diagram showing a joined state of this embodiment, FIG. 3 is a flowchart showing a joining process, FIG. 4 is a schematic diagram of interference fringes at the time of joining, and FIG. 5 is a perspective view of the joined state.

In this embodiment, the crystal material 11 is LiNb.
O ₃ is used. LiNbO ₃ has a larger refractive index than quartz (NO = 2.20 Ne = 2.28), and the difference in refractive index between ordinary and extraordinary light is Δn = 8 × 10 ^-2 . Therefore, a separation angle of about 8 times that of quartz is obtained. (The refractive index of quartz is NO = 1.54 Ne = 1.55, and the difference in refractive index between ordinary light and extraordinary light is Δn = 1 × 10 ^-2 .)

Two LiNb whose crystal axes are twisted at a predetermined angle
The crystal material 11 made of O ₃ is joined to form a beam splitter. A polarizing film is formed on the surface 12 and an antireflection film is formed on the surface 13 by coating. The bonding surface 14 has a wavefront aberration of 0.02 λrms or less by polishing, and the crystal material 11 itself is exposed without a coating.

FIG. 3 shows the joining procedure of this embodiment. First,
In order to completely remove the foreign matter on the joint surface 14, Li
Cleaning with an alkaline solution that dissolves the crystal material 11 made of NbO ₃ is performed (step S1). Next, the alkaline solution is removed by washing with ultrapure water (step S2). Ultrapure water used here is ultrapure water used in semiconductor manufacturing,
It contains almost no impurities.

After complete cleaning with ultrapure water,
The joint surfaces 14 are fixed so that they are parallel to each other, and the above-mentioned ultrapure water is applied to the joint surfaces 14 (step S3), and the two crystal materials 11 are put together. At this time, as shown in FIG. 4, from the state in which a large number of interference fringes 15 on the joint surface 14 are seen, by repeatedly pressing the joint surface 14, the interference fringes 15 are reduced to one or less. (Step S
4). In this state, the two crystal materials 11 are heat-treated under constant conditions (50 ° C. to 500 ° C.) to evaporate the ultrapure water on the joint surface 14, and the joint surface 14 is subjected to only intermolecular force as shown in FIG. To join.

The beam splitter 16 formed in this way reflects the light emitted from the light emitting member 4 to the optical information recording medium 8 on the surface 12 on which the polarizing film is formed. And
The beam splitter 1 receives the return light from the optical information recording medium 8.
When transmitted through 6, repeats the separation into ordinary and extraordinary light,
The light separated into four is emitted from the surface 13 on which the antireflection film is formed. These four separated lights are used as a recording signal, a focus error signal and a tracking error signal.

(Operation) According to the present embodiment described above, pure water is applied as the contact liquid to the bonding surface 14 of the crystal material 11 in which the wavefront aberration is suppressed, and the interference fringes 15 are bonded so as to be one or less. To do. By the heat treatment, when the contact liquid evaporates, the bonding surfaces 14 are attracted to each other, and the crystal material 11 can be brought into a bonding state satisfying the optical characteristics.

Crystal material 1 having a large difference in refractive index between ordinary light and extraordinary light
No. 1 has a large refractive index and cannot use an organic adhesive,
By using the bonding by intermolecular force as in this embodiment,
The restrictions due to adhesives can be eliminated. That is, in the bonding by intermolecular force, the bonding distance can be set to a distance shorter than the wavelength of light, light is completely transmitted without reflection at the optical interface.

In the case of quartz, since it has a refractive index of 1.6 or less, it can be bonded by an organic adhesive, but a crystal material such as lithium niobate (LiNbO ₃ ) having a large difference in refractive index between ordinary light and extraordinary light. In this case, the refractive index becomes 1.6 or more, and it is not possible to bond even if a special multilayer coating and an organic adhesive (refractive index 1.6 or less) are used.

In this embodiment, since no bonding agent (adhesive) is used, there is no absorption of light by the bonding agent, and a crystal material having a large difference in refractive index can be bonded regardless of the type of the crystal material 11 and the optical path length can be bonded. Can be shorter than quartz. In addition, the crystal material 11
The coating process for relaxing the refractive index between the adhesive and the adhesive can be dispensed with. Then, the surface of the crystal material 11 having a small wavefront aberration is exposed at the bonding surface 14, and a strong intermolecular force is obtained, so that strong bonding can be achieved.

(Effect) By bonding the crystal material 11 having a large refractive index difference between ordinary light and extraordinary light and having a high refractive index, the optical path length can be greatly shortened and the optical pickup can be made compact. Further, there is no absorption of light at the bonding surface 14, and a beam splitter with good optical characteristics can be manufactured.
Furthermore, the coating process on the joint surface 14 is not required, and the manufacturing cost can be reduced. The crystal material 11 is LiNbO ₃
But not limited to Li ₂ B ₄ O ₇ · CaCO ₃
The same joining can be performed by using such as. In this case, non-adherent matter can be completely removed by washing with an acid or an organic solvent instead of washing with an alkaline solution.

Second Embodiment (Structure) FIG. 6 shows a joined state of the beam splitter 16 of the second embodiment of the present invention. Note that, in the second embodiment, only parts different from the first embodiment will be described.

In the second embodiment, two crystal materials 11 are used.
Is bonded by an intermolecular force, and then the bonding agent 18 is applied to a portion where the bonding boundary line 17 is exposed. In this embodiment, the ultraviolet curable adhesive 18 is applied and cured at two locations on the boundary line exposed on the square chamfered portion 19.

(Action) In the joining of intermolecular forces, a very strong joining force can be obtained in the direction perpendicular to the joining surface (tensile force), but a relatively strong joining force in the parallel direction (shearing force). Is weak. Therefore, by applying and fixing the bonding agent 18 on the surface where the bonding boundary line 17 is exposed, there is no problem such as a displacement of the bonding surface. Since the joining surfaces are close to each other by a very short distance, the bonding agent 1 is attached to the joining surface due to the capillary phenomenon.
8 never intrudes.

Further, as shown in FIG. 7, even if the crystal material 11 is not formed with the square chamfered portion 19, by applying the adhesive 18 so as to cover the joining boundary line 17, the same effect is exhibited. The same effect can be obtained by fixing another boundary line with the adhesive 18.

In the case of further firm fixing, as shown in FIG. 8, a plate member 20 having a shape substantially the same as the side shape of the beam splitter 16 is adhesively fixed to the surface where the joining boundary line 17 is exposed. Can be realized by In this case, a thermosetting or anaerobic adhesive is suitable instead of the ultraviolet curable adhesive 18. Other functions are the same as in the first embodiment.

(Effects) According to this embodiment, the bonding force due to the intermolecular force can be supplemented, and the beam splitter 16 that is strong against external force can be manufactured. Therefore, it is not necessary to perform special handling at the time of work, workability can be greatly improved, and mass productivity can be improved.

Third Embodiment (Structure) FIGS. 9 and 10 show a third embodiment of the present invention. FIG. 9 is a conceptual diagram of this embodiment, and FIG. 10 is a beam splitter 1.
6 shows a schematic diagram of 6. Only the parts different from the first embodiment will be described below.

The beam splitter 16 is packaged in a case 21 as shown in FIG. 9 after joining by intermolecular force. The case 21 is a joining reinforcing member, and joins the boundary line 1 of the beam splitter 16.
It is formed of a square-shaped (square tubular) resin so that 7 is exposed and covers all the side surfaces. Light absorbing paint or the like is applied to the inner surface of the case 21. The beam splitter 16 is inserted inside the case 21, and the case 21 and the beam splitter 16 are adhesively fixed.

(Operation) In this embodiment, in order to fix all the junction boundaries 17, the strong beam splitter 16 is used.
Moreover, since all the side surfaces are covered, stray light generated by impurities existing inside the crystal material 11 can be prevented from leaking from the beam splitter 16 to the outside. Then, by applying a light absorbing paint or the like for the countermeasure against stray light to the inner wall of the case 21, the action can be further improved.

(Effect) According to the present embodiment, a beam splitter that can be more firmly fixed and that is extremely workable can be manufactured. Since stray light can be removed, signal noise of the photodetection member can be reduced, and a highly reliable optical pickup can be realized.

[0048]

According to the invention described in claim 1, it is possible to provide a beam splitter which can use a crystal material other than quartz and has good optical characteristics.

According to the second aspect of the invention, it is possible to provide a beam splitter for an optical pickup, which can use a crystal material other than quartz, has good optical characteristics, and can contribute to downsizing of the optical pickup. .

According to the third aspect of the present invention, it is possible to provide a beam splitter for an optical pickup, which has a high reliability and can be bonded by a strong intermolecular force.

According to the fourth aspect of the present invention, it is possible to provide a beam splitter for an optical pickup, which has good workability and high mass productivity.

According to the fifth aspect of the present invention, it is possible to provide a beam splitter for an optical pickup, which can obtain good bonding characteristics even for a crystal material having a high refractive index and which can be manufactured in various types.

[Brief description of drawings]

FIG. 1 is an engineering layout diagram of an optical system used in the present invention.

FIG. 2 is an exploded perspective view showing a manufacturing process of the beam splitter in the first embodiment of the present invention.

FIG. 3 is a flowchart showing manufacturing steps of the beam splitter in the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of interference fringes generated in the manufacturing process of the beam splitter in the first embodiment of the present invention.

FIG. 5 is a perspective view showing a joined state of the beam splitter in the first embodiment of the present invention.

FIG. 6 is a perspective view showing a joined state of the beam splitter in the second embodiment of the present invention.

FIG. 7 is a perspective view showing a joined state of the beam splitter in the second embodiment of the present invention.

FIG. 8 is a perspective view showing a modified example of the beam splitter in the second embodiment of the present invention.

FIG. 9 is an exploded perspective view showing the manufacturing process of the beam splitter in the third embodiment of the present invention.

FIG. 10 is a perspective view showing a beam splitter in a third embodiment of the present invention.

FIG. 11 is a cross-sectional view showing a bonding layer in a conventional beam splitter.

FIG. 12 is a side view showing a conventional beam splitter.

[Explanation of symbols]

 5 Beam splitter 6 Collimator lens 7 Lens 8 Optical information recording medium 9 Photodetection member 10 Photodetection member for monitor 11 Crystal material 14 Bonding surface 15 Interference fringe 16 Beam splitter 17 Bonding boundary line

Claims (5)

[Claims] 1. A beam splitter for separating incident light into a plurality of lights and emitting the separated lights, wherein a bonding surface of two crystal materials having birefringence characteristics is arranged at a distance shorter than the wavelength of light, and bonding is performed by intermolecular force. A beam splitter characterized by being configured by. 2. In a beam splitter for an optical pickup, which separates reflected light from an optical information recording medium into a recording signal, a focus error signal and a tracking error signal, a junction surface of two crystal materials having a birefringence characteristic is used as a wavelength of light. A beam splitter for an optical pickup, which is characterized in that it is arranged at a shorter distance than that and is bonded by intermolecular force. 3. The joint surface of the beam splitter comprises:
The beam splitter for an optical pickup according to claim 1, wherein the surface of the crystal material is exposed. 4. The beam splitter for an optical pickup according to claim 1, wherein the bonding boundary line exposed on the surface of the beam splitter is fixed by a bonding agent and / or a bonding reinforcing member. 5. The beam splitter for an optical pickup according to claim 1, wherein the beam splitter is made of a crystalline material having a refractive index of 1.6 or more.