JP2003084255A - Optical device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device of a small size and high reliability by realizing the joining of optical elements to each other without using adhesives. SOLUTION: The optical device which is an optical device constituted by joining at least one surface of a Faraday rotor to a polarizer across a translucent optical material without using the adhesives and functioned by transmission of light through the joint surface thereof, in which an metal oxidized film is formed on the joint surface of the translucent optical material and the method of manufacturing the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for joining optical elements to form an optical device and integrating them without using an adhesive for downsizing.

[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 in the system. In many cases, an optical device is constructed by joining an optical element to a fixing 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 joining the optical elements to each other has been studied.

For example, Japanese Patent Laid-Open No. 6-75189 discloses that
There is disclosed an optical isolator in which a polarizer, a Faraday rotator, and an analyzer are bonded and integrated by using an optical adhesive or resin. However, the optical isolator bonded with an adhesive or the like has poor moisture resistance and heat resistance and generates outgas, so that there is a problem that the optical axis of the optical isolator is deviated and other optical devices are adversely affected.

Further, a method of directly joining without using any adhesive (Japanese Patent Laid-Open Nos. 7-220923 and 200-200)
0-56265) has also been tried. In these methods, the surfaces of the optical elements are subjected to a hydrophilic treatment and then the hydrophilic surfaces are bonded to each other. In semiconductors, SOI (Silicon On
Insulator) It is put to practical use in the wafer manufacturing process.
However, when this method is applied to an optical device, it has the following problems and has not yet been put to practical use.

This direct bonding method largely depends on the shape and physical properties of the objects to be bonded. For example, in the case of warpage, it is desirable that the radius of curvature is several hundred meters or more. Further, it is said that the surface roughness of the object to be bonded is preferably Ra = 0.3 nm or less. Further, the difference in the coefficient of thermal expansion between the objects to be joined is also greatly affected.

However, there are few other optical devices that satisfy the above restrictions. For example, an iron-based garnet, which is one of the optical elements generally used in optical devices, has a stress distribution in the thickness direction, and therefore often causes a large warp. Moreover, since the polarizing glass has a structure in which silver particles are dispersed in the glass, it is difficult to control the surface roughness. Furthermore, the coefficient of thermal expansion of these optical elements often differs greatly depending on the material, and the difference in coefficient of thermal expansion between the objects to be bonded tends to increase. Therefore, it is very difficult to apply the direct bonding technique to the optical device. Thus, at present, it is extremely difficult to inexpensively and easily manufacture an optical device in which optical elements are joined without using an adhesive.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and realizes a small size and high reliability by realizing the joining of optical elements without using an adhesive. The main purpose is to provide an optical device of.

[0008]

In order to solve the above problems, in the optical device according to the present invention, at least one surface of the Faraday rotator does not use a polarizer and an adhesive via a translucent optical material. In an optical device which is formed by being bonded to an optical device and functions by transmitting light through the bonding surface, a metal oxide film is formed on the bonding surface of the translucent optical material. 1).

As described above, the transparent optical material is provided between the Faraday rotator and the polarizer, and the metal oxide film is formed on the bonding surface of the transparent optical material. Sufficient bonding strength with the polarizer can be easily achieved without the use of an adhesive, and there is no outgassing or deterioration of the bonding surface, and it functions effectively without adversely affecting the optical characteristics. A reliable optical device can be provided at low cost. In this case, the metal oxide film may or may not be present on the bonding surface on the side of the polarizer and the Faraday rotator, but more preferably, the presence of the metal oxide film provides stronger bonding.

In this case, the metal oxide film formed on the translucent optical material is one or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ and SiO _2. The film may be a single layer or a multi-layered structure (claim 2). As described above, the metal oxide film formed on the bonding surface of the translucent optical material is coated with Al ₂ O ₃ and TiO _2.
2 , one or more metal oxide films selected from SiO ₂ and if they are laminated in a single layer or multiple layers, they can be bonded to a Faraday rotator or a polarizer without using an adhesive. It is possible to provide an optical device that becomes possible and does not affect the optical characteristics.
Further, they also have an advantage of functioning as an antireflection film.

In this case, it is preferable that the Faraday rotator is made of bismuth-substituted iron garnet, and the polarizer is made of polarizing glass or rutile single crystal. Thus, for example, when a polarizer and a rutile single crystal polarizer and a Faraday rotator made of bismuth-substituted iron garnet are joined to form a joined body, a translucent optical material having metal oxide films formed on both surfaces is used. By interposing it, it is possible to construct a high-performance optical device that is strongly bonded without affecting the optical characteristics.

In this case, it is desirable that the coefficient of thermal expansion of the translucent optical material be a value between the coefficient of thermal expansion of the polarizer and the coefficient of thermal expansion of the Faraday rotator (claim 4). Thus, for example, when a polarizer and a bismuth-substituted iron garnet made Faraday rotator are joined to form a bonded body, the thermal expansion coefficient of the polarizing glass and the thermal expansion coefficient of bismuth-substituted iron garnet between them. By providing a translucent optical material that has a value between 2 and a metal oxide film on the bonding surface, it is possible to relax the distortion of the polarizing glass and the bismuth-substituted iron garnet, and obtain sufficient bonding strength. And sufficient reliability can be realized.

Further, in this case, the optical device may be an optical isolator in which the polarizer is joined to the other surface of the Faraday rotator through the translucent optical material (claim 5). By doing this, it has a strong bonding strength,
A highly reliable optical isolator having good insertion loss and extinction ratio can be provided at low cost.

Next, in the method for manufacturing an optical device according to the present invention, at least one surface of the Faraday rotator is bonded to the polarizer through a translucent optical material without using an adhesive to manufacture the optical device. The method is characterized in that metal oxide films are formed on both surfaces of the translucent optical material and then bonded together (claim 6).

In this way, if at least one surface of the Faraday rotator is bonded to one surface of the polarizer through the translucent optical material having metal oxide films formed on both surfaces, it is sufficient without using an adhesive. It is possible to inexpensively manufacture an optical device having a sufficient bonding strength and having sufficient reliability.

In this case, the Faraday rotator and the polarizer and the translucent optical material are bonded to each other by washing, hydrophilizing, and drying steps, and then directly or through water. It is preferable that the Faraday rotator, the polarizer, and the translucent optical material are integrally bonded by heat treatment thereafter (claim 7). With such bonding, the Faraday rotator, the polarizer, and the translucent optical material can be bonded easily and reliably, and a highly reliable optical device can be manufactured.

Further, in this case, the transparent optical material is formed.
The metal oxide film is₂ O₃ , TiO ₂ , SiO₂ Select from
One or two or more metal oxide films selected from
The oxide film can be laminated in a single layer or multiple layers (claim
Item 8).

In the present invention, the optical isolator can be manufactured by bonding the polarizer to both surfaces of the Faraday rotator through the translucent optical material (claim 9). in this way,
The method of the present invention is particularly useful for manufacturing a small-sized optical isolator having a strong bonding strength and a good insertion loss and extinction ratio.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. The inventors of the present invention have variously studied to provide a compact and highly reliable optical device at low cost by joining optical elements to each other without using an organic adhesive or the like. (Or an analyzer) and a Faraday rotator, a translucent optical material having a metal oxide film formed on the bonding surface to be bonded to each optical element is provided between the polarizer and the Faraday rotator, and an adhesive is used. It was found that extremely high bonding strength can be obtained by directly bonding the bonding surfaces without using
The present invention has been completed by carefully examining various conditions regarding joining.

The joining method of the present invention will be described in detail. FIG. 1 is an explanatory diagram showing an example of the configuration of an optical element and a bonded body that are bonded by the method of the present invention. First, the antireflection film 11 made of a metal oxide optimized for the refractive index of the optical element (polarizer 14, Faraday rotator 13) facing the bonding surface of the translucent optical material 12 is formed. Further, in some cases, a metal optimized for the refractive index of the optical element facing each bonding surface of the polarizer 14 (a polarizer located on the opposite side of the Faraday rotator is also called an analyzer) and the bonding surface of the Faraday rotator 13. It is also possible to cover with an antireflection film made of oxide. For example, the antireflection glass film 17 may be formed on both surfaces of the Faraday rotator 13.

In this case, the metal oxide film 11 formed on the translucent optical material 12 is one or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ and SiO ₂ , and the metal oxide film is formed. The membrane can be laminated in a single layer or multiple layers.
This makes it possible to sufficiently function as an antireflection film and increase the bonding strength. And the bonding surface of the translucent optical material, before forming the metal oxide film,
It is desirable to sufficiently polish the mirror surface until the surface roughness and the warp are predetermined. The metal oxide film can be formed by a usual electron beam evaporation method. As for the film thickness, a single layer or a multi-layer of a metal oxide film is vapor-deposited to a thickness (several tens to several hundreds nm) such that transmitted light is not reflected.

Next, at least one surface of the Faraday rotator 13 is used as a bonding surface, and the bonding surface of the polarizer 14 is not used with an adhesive agent via the translucent optical material 12 having the metal oxide film 11 formed on both surfaces. If they are bonded to each other by bonding, it is possible to manufacture the optical device 18 which has a strong bonding strength and does not affect the optical characteristics. An air antireflection film 16 is formed on the surface of the polarizer 14 opposite to the bonding surface.

In this case, the Faraday rotator and the polarizer are bonded to the translucent optical material by mirror-polishing the respective joint surfaces (in the case of the translucent optical material, before forming the metal oxide film). Performed), washing, hydrophilization treatment, and drying steps, and then directly or through water, followed by heat treatment.

The mirror-polishing is carried out by targeting surface roughness (Ra (nm)) and warp (radius of curvature (m)) set for each optical element, for example, Ra = 1n for polarizing glass and translucent optical material.
m, warpage = 60 m, and with a Faraday rotator, Ra = 0.
Normal wet mirror polishing is performed aiming at 5 nm and warp = 20 m.

Next, the joint surface of each optical element is thoroughly washed and then subjected to a hydrophilic treatment (the light-transmissive optical material is subjected to a washing and hydrophilic treatment after forming a metal oxide film on the joint surface). . Usual wet cleaning is effective for cleaning, but it is more effective to use short-wavelength ultraviolet treatment (UV treatment) or plasma treatment together. Further, for the hydrophilic treatment, an ammonia-hydrogen peroxide mixture (a mixture of ammonia water, hydrogen peroxide solution, and pure water) generally used in the semiconductor SOI wafer process, nitric acid, a diluting solution of hydrochloric acid, or a diluting solution thereof is used. An aqueous solution containing hydrogen peroxide is effective. Next, cleaning with pure water is performed to remove the hydrophilic treatment liquid. After washing with pure water, it is desirable to dry with a spin dryer or the like to prevent uneven drying. The bonding surface of each pretreated optical element thus obtained is bonded directly or through water.
Interposing water on the joint surface allows easier bonding.

When the optical element bonded by the above procedure is naturally dried or vacuum dried, it is fixed with a weak bonding force.
A necessary and sufficient bonding force can be obtained by heat-treating this at a temperature of about 80 to 200 ° C. for several hours. 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 may be atmospheric air, but it is more preferable that the atmosphere is a reduced pressure atmosphere or an atmosphere containing hydrogen. Through the above steps, the joining of the optical elements can be completed.

If the Faraday rotator constituting the optical device of the present invention is made of bismuth-substituted iron garnet and the polarizer is made of polarizing glass or rutile single crystal, for example, polarizing glass or rutile single crystal. When a polarizer and a Faraday rotator made of bismuth-substituted iron garnet are joined to form a joined body, the translucent optical material with metal oxide films formed on both sides does not affect the optical characteristics as a joining material. It works effectively.

Further, for example, when a polarizer made of polarizing glass and a Faraday rotator made of bismuth-substituted iron garnet are joined to form a joined body, the coefficient of thermal expansion of the polarizing glass and the thermal expansion of bismuth-substituted iron garnet are provided between them. By providing a translucent optical material that has a value between the coefficient and a metal oxide film on the joint surface, it is possible to relax the distortion of the polarizing glass and the bismuth-substituted iron garnet, resulting in sufficient joint strength. Can be obtained and sufficient reliability can be realized.

In the present invention, a polarizer (one of which serves as an analyzer) is bonded to both sides of a Faraday rotator through a light-transmitting optical material having metal oxide films formed on both sides,
Optical isolators can be manufactured. With this configuration, it is possible to provide an optical isolator having a strong bonding strength, a good insertion loss, and a good extinction ratio at a low cost.

As the material of the translucent optical material 12 of the present invention, a light transmissive optical material can be used as long as it can transmit a light beam emitted from a light source and the extinction ratio deterioration amount is small. Examples of such materials include various optical glasses such as soda-lime glass, aluminosilicate glass, borosilicate glass, lead glass, and barium glass.

[0031]

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. (Embodiment 1) FIG. 2 is a view showing a structure of an optical element and a bonded body which are bonded by the method of Embodiment 1. The optical element used for bonding is a 15 mm square, 0.2 mm thick polarizer 14 (polarizing glass) and a 15 mm square, 0.45 mm thick Faraday rotator 13 (bismuth-substituted iron garnet), 15 mm
It is a translucent optical material 12 (buffer glass) having a corner and a thickness of 0.1 mm, both of which are mirror-polished. Faraday rotator 13 (bismuth-substituted iron garnet with wavelength 1.
(Adjusted to θf = 45 ° at 55 μm), the anti-reflection film 17 (TiO ₂ / Al ₂ O ₃ / Si) on both surfaces was prepared.
O ₂ ). On the other hand, the polarizing glass 14 has an anti-reflection coating 16 (Al ₂ O ₃ / SiO ₂₎ on the non-bonding surface side only.
₂ ) was applied. Further, the translucent optical material 12 has a metal oxide film 11 (against a bismuth-substituted iron garnet antireflection film, TiO ₂ / Al ₂ O ₃ / SiO ₂ ) on one surface and a metal oxide film 11 (on the other surface). Polarizing glass antireflection film, TiO
₂ / Al ₂ O ₃ / SiO ₂ ). Note that these antireflection films were optimized at a wavelength of 1.55 μm.

Next, each optical element is pretreated by washing, hydrophilizing, washing with pure water and drying. Next, the bonding surface of the polarizing glass 14 and the bonding surface of the metal oxide film 11 of the translucent optical material 12 are joined to each other, and the bonding surface of the other metal oxide film 11 of the transparent optical material 12 and the Faraday rotator 13 are bonded. The bonding surfaces of the anti-reflection film for glass 17 are adhered to each other via water and then adhered, and then dried for a predetermined time, and then 110 ° C., 10
Heat treatment was performed for a time to complete the joining, and a joined body 19 was obtained.

The main manufacturing conditions of each of the above steps are shown below. Cleaning: After UV (ultraviolet) treatment with a low pressure mercury lamp, cleaning with pure water (US (UltraSonic, ultrasonic) cleaning) is performed. Hydrophilization treatment: Ammonia water: Hydrogen peroxide water: Pure water =
Immerse in 1: 1: 4 ammonia-hydrogen peroxide mixture. Wash drying: After washing with pure water (US washing), spin dryer drying is performed. Laminating: Polarization directions of two polarizing glasses are 45 each other
It is adjusted so as to be deg, and is bonded and adhered to the joint surface through pure water. Drying: vacuum drying for 24 hours after bonding. Heat treatment: 110 ° C., 10 hours, 0.2 atmosphere of hydrogen atmosphere. The heating rate was 4 ° C./h. Bonding is completed by this heat treatment.

The bonded body bonded under the above conditions was cut into 1 × 1 mm chips by a dicer, and the bonded surface was observed.
Furthermore, this chip is placed in a closed container at a temperature of 105 ° C. for 1 hour.
It was held for 00 hours (hereinafter, referred to as a pressure cooker test), and the joint interface was observed.

Next, the bonded body obtained under the above conditions (a Faraday rotator having a polarizer (one of which is an analyzer) bonded to both surfaces of the Faraday rotator through a light-transmitting optical material having metal oxide films formed on both surfaces thereof. ) Was set in a cylindrical magnet to form a junction type optical isolator. The forward insertion loss of this optical isolator was measured with a laser beam having a wavelength of 1.55 μm.

The state of the bonding interface before and after the pressure cooker test was good with no peeling observed, and the forward insertion loss of the optical isolator was 0.15 d both before and after the test.
In B, a good value was shown and there was no change before and after the test. Table 1 shows the test results of the pressure cooker test.

(Example 2) The optical element used for bonding was 1
5 mm square, 0.2 mm thick polarizer (polarizing glass) and 1
A Faraday rotator (bismuth-substituted iron garnet) having a size of 5 mm square and 0.45 mm, a translucent optical material (buffer glass) having a size of 15 mm square and 0.1 mm, and both are mirror-polished.

The Faraday rotator (bismuth-substituted iron garnet adjusted at a wavelength of 1.55 μm and θf = 45 °) has an antireflection film (TiO ₂ / Al) on both surfaces.
₂ O ₃ / SiO ₂ ). On the other hand, the polarizing glass has
Anti-reflection coating for glass (TiO ₂ / Al ₂ O ₃ /
SiO ₂ ) on the non-bonded surface side to prevent air reflection (Al ₂
O ₃ / SiO ₂ ) was applied. The translucent optical material also has a metal oxide film (anti-bismuth-substituted iron garnet anti-reflection film, TiO ₂ / Al ₂ O ₃ / SiO ₂ ) on one side and a metal oxide film (anti-polarization glass anti-reflection on the other side). Membrane, TiO ₂ /
Al ₂ O ₃ / SiO ₂ ) was applied. Note that these antireflection films were optimized at a wavelength of 1.55 μm.

Next, each optical element is subjected to cleaning, hydrophilic treatment, pure water cleaning and drying steps. Next, the bonding surface of the polarizing glass and the pair of translucent optical materials, the bonding surface of the polarizing glass metal oxide film, and the bonding surface of the transparent optical material, the pair of bismuth-substituted iron garnet metal oxide film and the Faraday rotator pair. The bonding surfaces of the glass antireflection film were brought into close contact with each other via water, and then dried and heat-treated to obtain a strong bond.

The main manufacturing conditions of each step are shown below. Cleaning: After UV (ultraviolet) treatment with a low pressure mercury lamp, cleaning with pure water (US (UltraSonic, ultrasonic) cleaning) is performed. Hydrophilization treatment: Ammonia water: Hydrogen peroxide water: Pure water =
Immerse in 1: 1: 4 ammonia-hydrogen peroxide mixture. Washing and drying: After washing with pure water (US washing), spin dryer drying is performed. Laminating: Polarization directions of two polarizing glasses are 45 each other
Adjust so that it becomes deg, and then stick and adhere via water. Drying: vacuum drying for 24 hours after bonding. Heat treatment: 110 ° C., 10 hours, 0.2 atmosphere of hydrogen atmosphere. The heating rate was 4 ° C./h. Bonding is completed by this heat treatment.

The bonded body bonded under the above conditions was cut into 1 × 1 mm chips by a dicer, and the bonded surface was observed.
Furthermore, the chips are placed in a closed container at a temperature of 105 ° C for 10
A pressure cooker test of holding for 0 hour was performed to observe the joint interface.

Next, the bonded body obtained under the above conditions was set in a cylindrical magnet to form a bonded optical isolator. The forward insertion loss of this optical isolator has a wavelength of 1.55 μm.
It was measured with a laser beam.

The state of the bonding interface before and after the pressure cooker test was good with no peeling observed, and the forward insertion loss of the optical isolator was 0.12 d both before and after the test.
In B, a good value was shown and there was no change before and after the test. The test results of the pressure cooker test are also shown in Table 1.

(Comparative Example 1) The material and dimensions of the optical element used for bonding were the same as in Example 1. The polarizing glass has an anti-reflection film (Al ₂ O ₃ / S) on the non-bonded surface side only.
iO ₂ ) was applied. This antireflection film has a wavelength of 1.55μ.
Optimized with m. On the other hand, the translucent optical material was not provided with a metal oxide film (antireflection film). In addition, a Faraday rotator (bismuth-substituted iron garnet at a wavelength of 1.55 μm
(f = 45 °) was also not coated with an antireflection film (metal oxide film) against glass on both sides.

Next, each optical element is subjected to washing, hydrophilic treatment, pure water washing and drying steps. Next, the bonding surface of the polarizing glass and the bonding surface of the translucent optical material, and the bonding surface of the translucent optical material and the bonding surface of the Faraday rotator are adhered to each other via water, and then dried. , Heat treated and joined.

The main manufacturing conditions in each of the above steps were the same as in Example 2. The bonded body bonded under the above conditions was cut into 1 × 1 mm chips by a dicer, and the bonded surface was observed.
Furthermore, the chips are placed in a closed container at a temperature of 105 ° C for 10
A pressure cooker test of holding for 0 hour was performed to observe the joint interface.

Next, the bonded body obtained under the above conditions was set in a cylindrical magnet to form a bonded optical isolator. The forward insertion loss of this optical isolator has a wavelength of 1.55 μm.
It was measured with a laser beam.

Regarding the state of the bonding interface before the pressure cooker test, the bonding itself was good although there was peeling at the ends, but after the test, peeling was observed in more than half of the contact area. The forward insertion loss of the optical isolator before and after the test was 0.50 dB and 1.47 dB, respectively, and a large loss occurred before the test and further increased after the test. The test results of the pressure cooker test are also shown in Table 1.

[0049]

[Table 1]

As is clear from the test results of Table 1, in an optical device in which at least one surface of the Faraday rotator is bonded to the polarizer through a transparent optical material without using an adhesive, If the optical optical material has a metal oxide film formed on its bonding surface, it is possible to provide a highly reliable optical isolator which has extremely strong bonding strength and has a good insertion loss and extinction ratio. it can.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, has substantially the same configuration as the technical idea described in the scope of the claims of the present invention, and has any similar effect to the present invention. It is included in the technical scope of the invention.

[0052]

As described above in detail, according to the present invention, various optical elements can be easily bonded without using an adhesive, and a strong bonding strength can be obtained. In addition, it is possible to provide a small-sized and highly reliable optical device at low cost without generation of outgas and deterioration of the joint surface.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a structure of an optical element and a bonded body that are bonded by the method of the present invention.

FIG. 2 is a diagram showing a configuration of an optical element and a bonded body that are bonded by the method of Example 1.

[Explanation of symbols]

11 ... Metal oxide film (antireflection film), 12 ... Translucent optical material, 13 ... Faraday rotator, 14 ... Polarizer (polarizing glass), 16 ... Air antireflection film, 17 ... Glass antireflection film, 18, 19 ... Optical device.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masatoshi Ishii             2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu             Gaku Kogyo Co., Ltd. Precision Materials Research Laboratory (72) Inventor Hiroki Yoshikawa             2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu             Gaku Kogyo Co., Ltd. Precision Materials Research Laboratory F-term (reference) 2H079 AA03 BA02 CA06 DA12 EA13                       KA05

Claims (9)

[Claims] 1. A Faraday rotator having at least one surface,
An optical device, which is formed by bonding a polarizer and an adhesive through a translucent optical material without using an adhesive, and functions by transmitting light through the bonding surface, wherein the bonding surface of the translucent optical material is An optical device having a metal oxide film formed thereon. 2. The metal oxide film formed on the translucent optical material is one or two or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ and SiO _2. The optical device according to claim 1, wherein the film is a single layer or a multilayer. 3. The optical device according to claim 1, wherein the Faraday rotator is made of bismuth-substituted iron garnet, and the polarizer is made of polarizing glass or rutile single crystal. 4. The coefficient of thermal expansion of the translucent optical material is a value between the coefficient of thermal expansion of the polarizer and the coefficient of thermal expansion of the Faraday rotator. Item 3. The optical device according to any one of items 3. 5. The optical device according to claim 1, wherein the optical device is an optical isolator in which a polarizer is bonded to the other surface of the Faraday rotator via a transparent optical material. The optical device according to any one of 1. 6. A method for manufacturing an optical device by bonding at least one surface of a Faraday rotator to a polarizer through a transparent optical material without using an adhesive, wherein both surfaces of the transparent optical material. A method for manufacturing an optical device, which comprises forming a metal oxide film on the substrate and then bonding the metal oxide film. 7. The Faraday rotator / polarizer and the translucent optical material are bonded to each other by directly performing a cleaning process, a hydrophilic process and a drying process, and then bonding them directly or with water. The method for manufacturing an optical device according to claim 6, wherein the Faraday rotator, the polarizer, and the translucent optical material are integrally bonded by performing heat treatment thereafter. 8. The metal oxide film formed on the translucent optical material is one or more metal oxide films selected from Al ₂ O ₃ , TiO ₂ and SiO ₂ , and the metal oxide film is The method for manufacturing an optical device according to claim 6, wherein the optical device is laminated in a single layer or a multilayer. 9. The optical isolator is manufactured by bonding a polarizer to both surfaces of the Faraday rotator through a translucent optical material to manufacture an optical isolator. A method for manufacturing the described optical device.