JP2003161914A - Optical device and method for manufacturing optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide at a low cost a compact optical device which has high reliability by joining optical elements without using an adhesive. <P>SOLUTION: The optical device in which at least one face of a magnetic garnet is joined with a polarizer without using an adhesive, functions by passing light through the joined plane, and is characterized by the fact that the relations among the linear thermal expansion coefficient α1(/°C) of the magnetic garnet, the linear thermal expansion coefficient α2(/°C) of the polarizer and the thickness t2 (m) of the polarizer is |(α1-α2)×t2|≤10<SP>-9</SP>and t2≥2×10<SP>-5</SP>. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device in which optical elements are bonded without using an adhesive and a method for manufacturing the optical device.

[0002]

2. Description of the Related Art In recent years, WDM (Wavelength)
With the increase in the number of wavelengths of division multiplex (wavelength division multiplexing), high integration of an optical communication system is progressing. As a result, there is an increasing demand for miniaturization of optical devices used therein. In many cases, the optical device is configured by bonding an optical element such as a Faraday rotator or a polarizer to a fixed member and combining them. However, in this method, the fixing member is an obstacle and hinders miniaturization of the optical device. Therefore, a method of removing the fixing member and adhering the optical elements to each other has been studied.

The simplest method for joining optical elements is
It is to bond using an organic adhesive. However, the organic adhesive has the drawbacks that outgas is generated, which adversely affects the laser diode, and is weak against irradiation with a high-power laser or exposure in a high temperature and high humidity atmosphere, and the device lacks reliability.

Therefore, without using an organic adhesive,
Various methods for joining optical elements have been studied. An example
For example, one of them is inorganic bonding of low melting point glass and solder.
There is a method of joining optical elements by using them as a material.
Low melting point glass is Bi_TwoO _ThreeLow melting point materials such as PbO
It is a glass for bonding that contains
Must be heated above the softening point of. Also optical
For the purpose of device miniaturization, the transparent surface of the optical element
It is effective to join them together. But such a low
When joining translucent surfaces of optical elements using melting point glass
In the case of softening the low melting point glass, it was applied to the optical element.
The antireflection film reacts with the low melting point glass, and the antireflection function is impaired.
There is a problem such as nau. Therefore, the translucent surfaces are joined together.
Practical application of optical devices using low melting point glass is difficult
It is said that.

On the other hand, when solder is used, it cannot be directly placed on the transparent surface because the solder has no translucency. Therefore, by selectively metallizing the outer frame of the translucent surface,
A joining method is adopted in which the solder is interposed only in the metallized portion. Such a joining method has a problem that a complicated metallization process is required, and it is difficult to avoid a decrease in yield and an increase in cost.

A method of directly bonding optical elements to each other without using any bonding material (see JP-A-7-220923 and JP-A-2000-56265) has also been tried. In this method, the surfaces of the optical element are hydrophilized, and then the hydrophilized surfaces are bonded to each other.
It has been put to practical use in the manufacturing process of I (Silicon On Insulator) wafers. However, when this method is applied to an optical device, there are the following problems and it is difficult to put it into practical use.

That is, the method of directly bonding the optical elements with each other by performing the hydrophilic treatment in this way largely depends on the shape and physical properties of the objects to be bonded. For example, with respect to warpage, it is desirable that the radius of curvature be several hundred meters or more. Also,
It is said that the surface roughness of the object to be bonded is preferably Ra = 0.3 nm or less. Furthermore, the difference in the coefficient of linear expansion between the objects to be joined is also greatly affected.

However, few optical elements satisfy the above requirements. For example, iron-based garnet, which is one of the optical elements generally used in optical devices, often has a large warp because it has a stress distribution in the thickness direction. Moreover, since the polarizing glass has a structure in which metal particles such as silver and copper are dispersed in glass, it is difficult to control the surface roughness. Furthermore, the linear expansion coefficient of these optical elements often differs greatly depending on the material, and the difference in the linear expansion coefficient between the objects to be bonded tends to increase. Therefore, in the bonded body in which the optical elements are directly bonded to each other as described above, peeling easily occurs on the bonded surface by heat treatment, and the adhesiveness and durability of the bonded surface are low.

Further, when such materials having different linear expansion coefficients are directly joined, thermal stress is generated between different materials,
There is a problem that optical distortion is likely to occur due to the concentration thereof on the bonding surface, and optical characteristics such as extinction ratio are deteriorated. Therefore, it is very difficult to apply the direct bonding technique to the optical device.

As described above, at present, it is extremely difficult to bond optical elements without using an organic adhesive to easily manufacture a highly reliable optical device at low cost.

[0011]

Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to:
Join optical elements together without using an organic adhesive,
It is to provide a compact and highly reliable optical device at low cost.

[0012]

In order to achieve the above object, according to the present invention, at least one surface of a magnetic garnet is bonded without using a polarizer and an adhesive, and light is bonded to the bonding surface. In the optical device that functions by transmitting light, the relationship between the linear expansion coefficient α1 (/ ° C) of the magnetic garnet, the linear expansion coefficient α2 (/ ° C) of the polarizer, and the thickness t2 (m) of the polarizer is shown. , │ (α1-α
2) × t2│ ≦ 10 ⁻⁹ and t2 ≧ 2 × 10 ⁻⁵ are provided (claim 1).

Thus, the relationship between the linear expansion coefficient α1 (/ ° C.) of the magnetic garnet, the linear expansion coefficient α2 (/ ° C.) of the polarizer, and the thickness t2 (m) of the polarizer is | (α1-α2). ) ×
If t2│ ≦ 10 ⁻⁹ and t2 ≧ 2 × 10 ⁻⁵ ,
It is possible to prevent the magnetic garnet from being separated from the polarizer during the heat treatment step at the time of bonding, and it is possible to obtain sufficient bonding strength. Further, since the thermal stress generated between the magnetic garnet and the polarizer can be reduced, it is possible to suppress the deterioration of the optical characteristics due to the optical distortion caused by the thermal stress. Furthermore, since no organic adhesive is used, there is no generation of outgas or deterioration of the joint surface due to this. Therefore, it is possible to inexpensively provide a compact and highly reliable optical device having excellent optical characteristics.

At this time, it is preferable that a metal oxide film is formed on the surface of the magnetic garnet which is joined to the polarizer (claim 2), and the metal oxide film is made of Al ₂ O ₃ or Ti.
It is preferable that the metal oxide film is one kind or two or more kinds of metal oxide films selected from O ₂ and SiO ₂ , and the metal oxide films are laminated in a single layer or multiple layers (claim 3).

As described above, since the metal oxide film is formed on the surface of the magnetic garnet to be joined to the polarizer, the metal garnet acts as an antireflection film, and the junction with the polarizer can be made stronger. The metal oxide film is Al
One or two or more metal oxide films selected from ₂ O ₃ , TiO ₂ , and SiO ₂ , which are excellent in the effect as an antireflection film because they are laminated in a single layer or multiple layers. Since the bonding strength is remarkably improved, the optical device can have high performance and high reliability.

At this time, it is preferable that the polarizer is a polarizing glass (claim 4). One of the requirements of the present invention is to appropriately set the thickness of the polarizer as described above. Therefore, it is required that the optical characteristics of the polarizer are less likely to depend on its thickness. Therefore, it is preferable that the polarizer is a polarizing glass that has little influence on the optical characteristics of the thickness, whereby the thickness of the polarizer can be appropriately set without deteriorating the optical characteristics.

Further, the magnetic garnet is preferably a bismuth-substituted iron garnet (claim 5). Thus, the magnetic garnet is a bismuth-substituted iron garnet with excellent Faraday rotation,
A Faraday rotation angle of 45 degrees can be realized with a thickness of about 0.5 mm, which is effective for downsizing an optical device.

Further, the optical device may be an optical isolator (claim 6).

The optical isolator is one of the most useful ones among optical devices and is an essential device in optical communication. As described above, since the optical device of the present invention is an optical isolator, it is possible to provide an optical device that meets the recent demand for miniaturization of an optical isolator and free organic adhesive.

Next, a method for manufacturing an optical device according to the present invention is a method for manufacturing an optical device by bonding at least one surface of a magnetic garnet without using a polarizer and an adhesive, wherein the magnetic garnet wire is used. Expansion coefficient α1
(/ ° C.), the linear expansion coefficient α2 (/ ° C.) of the polarizer, and the thickness t2 (m) of the polarizer are | (α1-α2) ×
Bonding is performed by using a magnetic garnet and a polarizer satisfying t2 | ≦ 10 ⁻⁹ and t2 ≧ 2 × 10 ⁻⁵ (claim 7).

Thus, the relationship between the linear expansion coefficient α1 (/ ° C) of the magnetic garnet, the linear expansion coefficient α2 (/ ° C) of the polarizer, and the thickness t2 (m) of the polarizer is | (α1-α2). ) ×
By manufacturing an optical device using a magnetic garnet and a polarizer satisfying t2│ ≦ 10 ⁻⁹ and t2 ≧ 2 × 10 ⁻⁵ , a sufficient bonding strength between the magnetic garnet and the polarizer can be obtained without using an adhesive. It is possible to bond by, and it is possible to suppress deterioration of optical characteristics due to optical distortion of the bonded body. Therefore, a highly reliable optical device having excellent optical characteristics can be manufactured at low cost.

At this time, the magnetic garnet and the polarizer are bonded to each other by polishing, washing, hydrophilizing and drying the bonding surfaces, and then bonding the bonding surfaces directly or via a solution. It is preferable to perform a heat treatment after that to bond them (claim 8).

As described above, after polishing, washing, hydrophilizing, and drying steps are applied to the respective bonding surfaces of the magnetic garnet and the polarizer, they are bonded directly or through a solution, and then heat treatment is performed. The interaction between the chemical species forming the magnetic garnet and the chemical species forming the polarizer effectively works, and sufficient bonding strength can be obtained. Thereby, peeling of the joint surface can be prevented.

Further, at this time, it is preferable that a liquid containing polar molecules as a main component is used alone or as a mixture as a solution used for joining the magnetic garnet and the polarizer (claim 9).

As described above, when the magnetic garnet and the polarizer are bonded together, the bonding force between the magnetic garnet and the polarizer can be further improved by using a liquid containing polar molecules as a main component alone or in combination. You can

Further, it is preferable to bond the magnetic garnet and the polarizer after forming a metal oxide film on the bonding surface of the magnetic garnet with the polarizer (claim 10).

As described above, the bonding strength can be further increased by forming the metal oxide film on the bonding surface of the magnetic garnet with the polarizer and then performing the bonding. Further, since the formed metal oxide film functions as an antireflection film in the optical device, a highly reliable and high performance optical device can be manufactured.

Further, the metal oxide film formed on the magnetic garnet is one or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ and SiO ₂ , and the metal oxide film is a single layer or It is preferable to laminate in multiple layers (claim 11).

As described above, the metal oxide film is formed of Al ₂ O ₃ and T.
By forming one or more metal oxide films selected from iO ₂ and SiO ₂ and stacking them in a single layer or multiple layers, the function of the metal oxide film as an antireflection film is further enhanced, and magnetic garnet and polarized light are used. The bonding force of the child can be significantly increased.

In the present invention, an optical isolator can be manufactured by joining a polarizer to the magnetic garnet (claim 12). Thus, by manufacturing the optical isolator, it is possible to manufacture a small-sized optical isolator having sufficient bonding strength without using an adhesive.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described below, but the present invention is not limited thereto. In order to provide a compact and highly reliable optical device, the present inventors have joined optical elements with a translucent surface with sufficient bonding strength without using an organic adhesive, and various optical elements at the time of bonding. There is no damage given to the antireflection film of the element,
Moreover, an optical device in which a magnetic garnet and a polarizer are joined as an optical device in which optical characteristics are not deteriorated even when joining between optical elements having a difference in linear expansion coefficient, and the linear expansion coefficient of the magnetic garnet and the line of the polarizer are used. It has been found that an optical device in which the expansion coefficient and the thickness of the polarizer are appropriately selected is extremely effective, and the present invention has been completed by examining various conditions regarding bonding.

That is, in the optical device that is formed by bonding at least one surface of the magnetic garnet without using a polarizer and an adhesive, and functions by transmitting light through the bonding surface, the linear expansion coefficient of the magnetic garnet. The relationship between α1 (/ ° C.), the linear expansion coefficient α2 (/ ° C.) of the polarizer and the thickness t2 (m) of the polarizer is | (α1-α
2) A small and highly reliable optical device having sufficient bonding strength and excellent optical characteristics as long as it is an optical device characterized in that xt2│ ≦ 10 ⁻⁹ and t2 ≧ 2 × 10 ^−5. Can be provided at low cost.

First, FIG. 1 shows an example of a joining method for joining the magnetic garnet and the polarizer of the present invention. First, the surfaces (bonding surfaces) where the magnetic garnet and the polarizer are bonded are sufficiently polished (process). After that, each joint surface is thoroughly washed (step), and a hydrophilic treatment (step) is performed. At that time, a normal wet cleaning is effective for cleaning the bonding surfaces, but it is more effective to use a short wavelength ultraviolet ray treatment (UV treatment) or a plasma treatment together. Further, for the hydrophilic treatment, an ammonia-hydrogen peroxide mixture (a mixed solution of ammonia water, hydrogen peroxide solution, and pure water), nitric acid, hydrochloric acid diluted solution or these diluted solutions generally used in the semiconductor SOI wafer process is used. A solution containing hydrogen peroxide solution is effective.

Next, washing with pure water is performed to remove the hydrophilic treatment liquid. After washing with pure water, it is desirable to perform drying by an IPA vapor drying method or a spin dryer to prevent uneven drying (step). Next, the pretreated magnetic garnet thus obtained and the polarizer are bonded together. At that time, although it may be directly bonded on the bonding surface, a solution is applied to the bonding surface to facilitate bonding (process),
After that, it is preferable to bond the magnetic garnet and the polarizer (step). As the solution to be applied at this time, it is desirable to use a liquid containing polar molecules such as water and ammonia as a main component, or to use a mixture thereof, and it is particularly desirable to bond them through pure water. By performing the bonding using such a solution, the bonding force between the magnetic garnet and the polarizer can be increased. In addition, it is possible to further improve the bonding strength by adding a soluble substance such as an alkali metal element or a silicate to this solution.

The bonded body bonded by the above procedure is naturally dried or vacuum dried to be fixed with a weak bonding force (step).

After drying, the obtained joined body is heated at 80 to 200 ° C.
Sufficient bonding force can be obtained by performing heat treatment at a temperature of about several hours (step). At this time, if the rate of temperature rise in the heat treatment step is too fast, peeling of the joint surface may occur during temperature rise. Therefore, it is desirable to set the heating rate to 20 ° C./h or less. The atmosphere during the heat treatment is not problematic in the air, but a reduced pressure atmosphere or an atmosphere containing hydrogen is more preferable.

However, even when the optical elements are directly bonded by the above-described bonding method, peeling may occur on the bonding surface due to the generation of thermal stress in the heat treatment of the process.

Therefore, the present inventors have paid attention to the linear expansion coefficient α1 (/ ° C.) of the magnetic garnet, the linear expansion coefficient α2 (/ ° C.), and the thickness t2 (m) of the polarizer, which are included in the optical device. Experiments were conducted while changing various conditions, and the conditions for suppressing the peeling of the joint surface were derived. That is, the relationship between α1, α2, and t2 is | (α1-α2) × t2
If an optical device bonded using a magnetic garnet and a polarizer satisfying | ≦ 10 ⁻⁹ and t2 ≧ 2 × 10 ⁻⁵ , it is possible to obtain an optical device in which peeling of the bonding surface is extremely reduced. Confirmed experimentally.

In the above bonding process, when the magnetic garnet and the polarizer are bonded together, it is desirable that an antireflection coating optimized for the refractive index of the opposing optical element is applied to the bonding surface of the optical element in advance.

For example, in the above-mentioned direct bonding method, when the magnetic garnet and the polarizer are bonded, a metal oxide film is formed on the bonding surface of the magnetic garnet with the polarizer, and then the magnetic garnet and the polarizer are bonded together. As a result, the formed metal oxide film acts as an antireflection film. Furthermore, by forming the metal oxide film in this way, the bonding strength between the magnetic garnet and the polarizer can be further strengthened.

At this time, the metal oxide film formed on the bonding surface of the magnetic garnet is chemically stable and has a communication wavelength band (0.9
Up to 1.7 μm) and is transparent, and more preferably a surface layer that is easily hydrophilized. Therefore, the metal oxide film is one or more kinds of metal oxide films selected from Al ₂ O ₃ , TiO ₂ , and SiO ₂ and is a single layer or a multi-layer laminated structure, and thus antireflection Since the effect as a film is great and the bonding force is remarkably improved, a highly reliable optical device can be obtained.

In this way, the optical device 5 functioning as an optical isolator can be obtained in which the polarizer 2 is directly bonded to both surfaces of the magnetic garnet 1 as shown in FIG. Note that FIG. 2 shows an example of an optical device in which a magnetic garnet 1 is formed with a metal oxide film 3 acting as a glass antireflection film, and a polarizer 2 is formed with an air antireflection film 4. ing. However, the present invention is not limited to this. That is, in the optical device of the present invention, the antireflection film may not necessarily be formed on the magnetic garnet or the polarizer. Further, the antireflection film 4 of the polarizer may be formed between any steps of the above-mentioned joining process.

In general, in an optical device such as an optical isolator which is easily affected by the distortion of the optical element, the extinction ratio tends to decrease when stress is applied to the joined optical element. Furthermore, in an optical device in which optical elements are joined together without using an adhesive in order to reduce the size of the optical device, the optical elements are firmly fixed to each other. A stress (thermal stress) proportional to the difference in linear expansion coefficient is applied.

Therefore, in such an optical device directly bonded without using an adhesive, the extinction ratio deteriorates with a change in temperature. The extinction ratio deterioration due to this temperature change is due to the difference in linear expansion coefficient between optical elements of 2 × 10 ⁻⁶ / ° C.
The above tends to be remarkable. Generally, the linear expansion coefficient of polarizing glass used as a polarizer is 6.5 × 10 ⁻⁶ /
C., and the linear expansion coefficient of bismuth-substituted iron garnet used as a magnetic garnet is 11 × 10 ⁻⁶ / ° C. Therefore, the difference in linear expansion coefficient between the two is 4.5 × 10.
^It becomes ⁻⁶ / ° C., and in the case of an optical device obtained by directly bonding bismuth-substituted iron garnet and polarizing glass, a large deterioration of the extinction ratio occurs.

Therefore, according to the present invention, even if the difference in the linear expansion coefficient between the magnetic garnet and the polarizer is large, the extinction can be achieved by optimizing the thickness of the polarizer according to the difference in the linear expansion coefficient between the magnetic garnet and the polarizer. We are trying to prevent ratio deterioration.

The deterioration of the extinction ratio can be suppressed as the thickness of the polarizer becomes thinner, and as the difference in linear expansion coefficient between the polarizer and the magnetic garnet becomes smaller. This is because the thermal stress acting between the polarizer and the magnetic garnet is proportional to the thickness of the polarizer when the thickness of the magnetic garnet is constant. It becomes large and the extinction ratio deteriorates. Also, when the difference in the coefficient of linear expansion is large, the thermal stress also increases, and the extinction ratio deteriorates significantly.

To describe the above relationship in detail, the difference between the linear expansion coefficient (α1) of the magnetic garnet and the thermal expansion coefficient (α2) of the polarizer is defined as | (α1-α2) | Letting t2 be t2, the deterioration of the extinction ratio can be suppressed if the product of | (α1−α2) | and t2 is less than a certain value. Therefore, the relationship between the difference in linear expansion coefficient between the polarizer and the magnetic garnet and the thickness of the polarizer | (α1−α2) × t2 | was tested and investigated, and it was found that the following conditions should be satisfied.

That is, in the above relationship of α1, α2 and t2, if the optical device satisfies | (α1-α2) × t2 | ≦ 10 ⁻⁹ , deterioration of the extinction ratio due to strain due to thermal stress is reduced. It is possible to obtain an optical device having excellent optical characteristics. Furthermore, at this time, in order for the polarizer itself to have sufficient extinction characteristics, the polarizer must be 2 ×
It must have a thickness of 10 ⁻⁵ m or more. Therefore, it is necessary to simultaneously satisfy the condition of the thickness t2 ≧ 2 × 10 ⁻⁵ of the polarizer.

In addition, as described above, the present invention is one of the requirements that the thickness of the polarizer is appropriately set, thereby preventing peeling at the joint surface and reducing thermal stress, and The joining force and optical characteristics of the device are improved. Therefore, it is required that the optical characteristics of the polarizer are less likely to depend on its thickness. Therefore, it is preferable that the polarizer is a polarizing glass that has little influence of the thickness on the optical characteristics. By doing so, the thickness of the polarizer can be appropriately set without deteriorating the optical characteristics. As the polarizing glass, a glass base material such as borosilicate glass that is generally used and in which metal particles such as silver and copper are dispersed can be used.

Further, at this time, the magnetic garnet is preferably a bismuth-substituted iron garnet excellent in Faraday rotation ability, whereby a Faraday rotation angle of 45 degrees can be realized with a thickness of about 0.5 mm. , Effective for downsizing optical devices.

[0051]

EXAMPLES The present invention will be specifically described below with reference to examples of the present invention, but the present invention is not limited thereto. (Example 1) For an optical element used for bonding, several kinds of polarizing glasses having different thicknesses were prepared as polarizers, and bismuth-substituted iron garnet (wavelength 1.31 μm) was used as magnetic garnet.
Was adjusted to θf = 45 °). Sufficient polishing is applied to these optical elements to obtain a surface roughness Ra of 0.
It was adjusted to 3 nm or less.

Then, for the Bi-substituted iron garnet
Is a glass anti-reflection film (Al_TwoO_Three, Ti
O_TwoAnd SiO_TwoSingle layer film or Al_TwoO_Three/ Ti
O_Two/ SiO_Two3 layer film) and glass reflection
Prepare one without a protective film, while
The lath has an anti-reflection film (Al_TwoO
_Three/ SiO_TwoMembrane). Incidentally, these antireflection films are
It was optimized at a wavelength of 1.31 μm. Detailed description of each optical element
The sex is shown in Table 1 below. Optical element shown in Table 1
The data are for non-bonded surface of polarizing glass and Bi-substituted iron glass.
-Measure on the net with anti-reflection coating on both sides
It was done.

[0053]

[Table 1]

FIG. 2 shows the structure of an optical device which is joined and integrated by using a magnetic garnet provided with an antireflection coating against glass. After the anti-glass anti-reflection film 3 is applied to both surfaces of the Bi-substituted iron garnet 1 and the anti-air anti-reflection film 4 is applied only to the non-bonding surface side of the polarizing glass 2, the bonding surface of the polarizing glass 2 and the Bi-substituted iron garnet 1 are applied. The optical device 5 was manufactured by bonding the glass with the bonding surface of the antireflection film 3 of glass.

The procedure for joining the Bi-substituted garnet and the polarizing glass was performed according to the flow shown in FIG. The main manufacturing conditions of each process are shown below. Polishing: Polishing is performed so that the surface roughness of each optical element becomes the value shown in Table 1. Cleaning: After UV (ultraviolet) treatment with a low pressure mercury lamp, cleaning with pure water (US (Ultra Sonic, ultrasonic) cleaning) is performed. Hydrophilization treatment: Ammonia water: Hydrogen peroxide water: Pure water =
Immerse in 1: 1: 4 ammonia-hydrogen peroxide mixture. Washing / drying: After washing with pure water (US washing), IPA vapor drying is performed. Liquid application: Pure water is applied to the bonding surface of each optical element. Laminating: Bi-substituted iron garnet and polarizing glass are laminated before the coating liquid dries. Drying: vacuum drying for 24 hours after bonding. Heat treatment: 110 ° C., 10 hours in air. The heating rate is 4 ° C./h.

After the heat treatment of the process, the obtained bonded body (optical device 5) is 1 mm × 1 mm by a dicer.
It was cut into chips. This chip, 105 ℃, 10
After processing with a pressure cooker for 0 hours, the joint surface was observed and the durability of the joint surface was evaluated. The results are shown in Table 2 below.

[0057]

[Table 2]

As shown in Table 2, Bi-substituted iron garnet
And the linear expansion coefficient of polarizing glass α1, α2 and polarizing glass
The value of (α1−α2) × t2 is 1.8.
× 10^-9In the above optical device,
Peeling was large and there was a practical problem. In contrast, (α
1-α2) × t2 is 1.8 × 10^-9If less than
(Preferably 1.0 x 10^-9Below), erosion at the joint surface
It can be seen that the bonding strength is improved. Also,
Bi-substituted iron garnet with metal oxide film is
Furthermore, the bonding strength is improved, and (α1-α2) × t2
Value is 1.8 × 10 ^-9Smaller ones have sufficient joint strength
The optical device has a high reliability.

(Example 2) Next, the thickness of the polarizer depends on the optical characteristics.
Experiments were conducted on the effects on sex. As a polarizer
As with Example 1, several types of polarizing glass with different thicknesses are used.
Also, for magnetic garnet, protect both sides with
Al as lath anti-reflection film_TwoO _Three/ TiO_Two/ SiO_Two
One type of Bi-substituted iron garnet that has only three layers of
I prepared. Under the same conditions as in Example 1 for these optical elements
Bonding was performed to produce a bonded body (optical device 5). The book
In the experiment, polarizing glass was used for various optical glasses with different linear expansion coefficients.
I replaced it with Russ.

Next, as shown in FIG. 3, the obtained optical device 5 was cut into 1 × 1 mm chips and placed in a cylindrical magnet 6 to form an optical isolator 7. After that, the extinction ratio was measured for each optical isolator having a different thickness of the produced polarizing glass.

As shown in FIG. 5, the measurement of the extinction ratio is carried out by irradiating a light beam 10 emitted from a light source (not shown) with a light isolator 7 (polarizing glass having a linear expansion coefficient Different optical glasses were used as substitutes), and the transmitted light beam 10 was again detected by the detector 8 via the polarizer 9 (analyzer).

At this time, the measurement temperature is set to the optical element temperature in the step of FIG. 1 and a temperature 40 ° C. lower than the optical element temperature, and the extinction ratio difference (extinction ratio deterioration amount) at this time is measured. The optical distortion was evaluated by. By measuring at a temperature lower than the optical element temperature by 40 ° C. as described above, the extinction ratio can be measured in a state where thermal stress is applied to the joint surface. In addition, as a result of measuring the extinction ratio of each sample at the temperature of the optical element in the process, 50
It was about dB.

In FIG. 4, the thickness t2 (m) of the polarizing glass and B
Difference in linear expansion coefficient between i-substituted iron garnet and polarizing glass | α
2 shows a two-dimensional map for 1-α2 | (/ ° C.). On this map, if the extinction ratio deterioration amount is less than 3 dB, ○,
X was plotted for those of 3 dB or more. As shown in FIG. 4, the solid line indicating the boundary of the plots of ○ and × is
It can be expressed by an expression of (α1−α2) = 10 ⁻⁹ / t2. Therefore, it was confirmed that the condition required to obtain an optical device having high optical characteristics with an extinction ratio deterioration amount of less than 3 dB was | (α1-α2) × t2 | ≦ 10 ⁻⁹ .

The present invention is not limited to the above embodiment. The above-described embodiment is merely an example, and it has substantially the same configuration as the technical idea described in the scope of claims of the present invention, and has the same operational effect.
Anything is included in the technical scope of the present invention.

For example, in the above-described embodiment, the optical isolator constituted by the minimum unit in which the polarizer is joined to both surfaces of the magnetic garnet is shown, but the present invention is not limited to this, and the polarizer and the magnetic element are not limited thereto. It can also be applied to an optical isolator having a multi-stage structure by further combining garnets. Further, in the above-described embodiment, when the magnetic garnet and the polarizer are bonded, pure water is applied to the bonding surface for bonding, but the present invention is not limited to this, and sufficient bonding is achieved. When strength is obtained, direct bonding may be performed without using a liquid.

[0066]

As described above, according to the present invention,
Magnetic garnet and polarizer can be bonded easily and with strong bonding strength without the use of adhesives, and there is no outgas generation or deterioration of the bonding surface, and it has excellent optical characteristics and is compact and highly reliable. The optical device can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of a joining method of the present invention.

FIG. 2 is a schematic diagram showing an example of a configuration of an optical device of the present invention.

FIG. 3 is a schematic diagram of a junction type optical isolator manufactured in a second example.

FIG. 4 is a graph in which an extinction ratio deterioration amount is plotted with respect to a thickness of a polarizer and a thermal expansion coefficient difference between optical elements.

FIG. 5 is a schematic diagram showing a configuration in an extinction ratio measurement of an optical isolator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic garnet (Bi substituted iron garnet), 2 ... Polarizer (polarizing glass), 3 ... Metal oxide film (anti-glass antireflection film), 4 ... Air antireflection film, 5 ... Optical device, 6 ... Cylindrical type Magnet, 7 ... Optical isolator, 8
… Detector, 9… Polarizer (temporary installation during the experiment), 1
0 ... rays.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeru Konishi             2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu             Gaku Kogyo Co., Ltd. Precision Materials Research Laboratory (72) Inventor Ryo Shirasaki             2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu             Gaku Kogyo Co., Ltd. Precision Materials Research Laboratory F-term (reference) 2H049 BA02 BA08 BB03 BB65 BC25                 2H099 AA01 BA02 CA11 DA05

Claims (12)

[Claims] 1. An optical device comprising at least one surface of a magnetic garnet bonded to a polarizer without the use of an adhesive, and the linear expansion coefficient of the magnetic garnet in an optical device that functions by transmitting light through the bonding surface. α1 (/
C), the linear expansion coefficient α2 (/ ° C) of the polarizer and the thickness t2 (m) of the polarizer are | (α1-α2) × t2.
| ≦ 10 ⁻⁹ , and t2 ≧ 2 × 10 ⁻⁵ . An optical device characterized by the following: 2. The optical device according to claim 1, wherein a metal oxide film is formed on a bonding surface of the magnetic garnet with the polarizer. 3. The metal oxide film formed on the magnetic garnet is one or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ , and SiO ₂ , and the metal oxide film is a single metal oxide film. The optical device according to claim 1 or 2, wherein the optical device is a layer or a multi-layered structure. 4. The optical device according to claim 1, wherein the polarizer is polarizing glass. 5. The magnetic garnet is a bismuth-substituted iron garnet, according to any one of claims 1 to 4.
The optical device according to claim 1. 6. The optical device according to claim 1, wherein the optical device is an optical isolator. 7. A method of manufacturing an optical device by bonding at least one surface of a magnetic garnet to a polarizer without using an adhesive, wherein a linear expansion coefficient α1 (/ ° C.) of the magnetic garnet, Linear expansion coefficient α2 (/
C) and the thickness t2 (m) of the polarizer is | (α1
−α2) × t2│ ≦ 10 ⁻⁹ , and t2 ≧ 2 × 10 ⁻⁵
A method of manufacturing an optical device, which comprises bonding using a magnetic garnet and a polarizer to be described below. 8. The magnetic garnet and the polarizer are bonded to each other by polishing, washing, hydrophilizing, and drying the bonded surfaces, and then bonding the bonded surfaces directly or together with a solution, and thereafter. The method for manufacturing an optical device according to claim 7, wherein the bonding is performed by performing heat treatment. 9. A liquid containing polar molecules as a main component is used alone or as a mixture as a solution used for bonding the magnetic garnet and the polarizer.
A method for manufacturing an optical device according to item 1. 10. The magnetic garnet and the polarizer are bonded together after a metal oxide film is formed on the bonding surface of the magnetic garnet with the polarizer.
A method for manufacturing the optical device according to any one of 1. 11. The metal oxide film formed on the magnetic garnet is one or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ , and SiO ₂ , and the metal oxide film is a single layer or The multi-layered structure is laminated in multiple layers.
0. The method for manufacturing an optical device according to 0. 12. The method for manufacturing an optical device according to claim 7, wherein a polarizer is bonded to the magnetic garnet to manufacture an optical isolator.