JP2004102218A - Optical isolator element, its manufacturing method, and optical isolator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical isolator in which resistance for moisture, light, and heat is made superior, occurrence of cracks in the optical element is suppressed, and good optical characteristic is obtained. <P>SOLUTION: One or more flat plate shaped Faraday rotator and two or more flat plate shaped polarizers are directly joined to produce a laminated and an integrated body. <P>COPYRIGHT: (C)2004,JPO

Description

【００７４】
ここで示されたように、低融点ガラスを用いた光アイソレータ用素子では大きな熱応力が生じたためにアイソレーション特性が著しく劣化し。また、偏光子部にクラックが発生した。これに対し本発明の方法に従ったものでは良好なアイソレーション特性が得られ、クラックも発生もしなかった。
【００７５】
また、チップ化された光アイソレータ用素子のせん断試験を行ったところ、全ての素子は接合面では破断が発生せず、素子内部からの破壊となり、接合強度は十分であることを確認した。
【００７６】
以上の試作により、接着剤を用いた光アイソレータ素子と同等の工数、小型化が実現し、かつ、接合面の長期安定性、樹脂フリー構成が実現した。
【００７７】
【発明の効果】
上述のように本発明による光アイソレータは１以上の平板状のファラデー回転子と２以上の平板状の偏光子を、直接接合して積層、一体化させたことにより、熱応力によるクラックの発生を抑制し、耐光性、耐熱性、アイソレーション特性に優れた光アイソレータ用素子を一括して作製することができる。また非常に小型で均一な品質の光アイソレータが作製できる。
【図面の簡単な説明】
【図１】本発明の光アイソレータの実施形態を示す斜視図である。
【図２】（ａ）〜（ｃ）は本発明の光アイソレータ用素子の作製方法を示す図である。
【図３】本発明の光アイソレータ用素子の接合界面を示す模式図である。
【図４】本発明の第２の実施形態を示す斜視図である。
【図５】ファラデー回転子に加わる応力と消光比の関係を示す図である。
【図６】従来の光アイソレータの構成を示す斜視図である。
【図７】従来の光アイソレータの構成を示す斜視図である。
【符号の説明】
１、１５、３１：光アイソレータ
２、１６：ファラデー回転子
３、４、１７、１８：偏光子
５、２０、３０：光アイソレータ用素子
６、２１：磁石
７：光学素子
８：ポリッシングパッド
９：コロイダルシリカ
１０：真空槽
１１：真空ポンプ
１２：ビーム源
１３：不活性ガス導入装置
１４：大型の光学素子
１９：接着剤
３２、３３：原子
３５：汚染物質
３６：中性原子
３７：研磨砥粒
３８：金属膜[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an element for an optical isolator used for removing return light generated when light emitted from a light source is introduced into various optical elements and optical fibers, and a method for manufacturing the same.
[0002]
[Prior art]
In an optical communication module or the like, light emitted from a light source such as a laser light source is incident on various optical elements or optical fibers, but a part of the incident light is reflected on various optical elements or the end face or inside of the optical fiber. Or scattered. A part of the reflected or scattered light tends to return to the light source as return light, and an optical isolator is used to prevent the return light.
[0003]
Conventionally, this type of optical isolator is configured by installing a flat Faraday rotator between two polarizers and storing these three components in a cylindrical magnet via a component holder. Was. Normally, the Faraday rotator is adjusted to a thickness that rotates the plane of polarization of light having a predetermined wavelength by 45 ° in a saturation magnetic field, and the two polarizers are rotated so that their transmission polarization directions are shifted by 45 °. Adjusted and configured.
[0004]
In the optical isolator having such a configuration, the Faraday rotator and the two polarizers are separate parts, and each element requires a holder. Therefore, not only the number of parts and the number of assembling steps are increased, but also the optical performance between the parts is increased. Adjustment work is complicated, resulting in high costs. Also, miniaturization was difficult.
[0005]
For this reason, there has been proposed an optical isolator in which an optical isolator element having a configuration in which a flat polarizer is bonded and integrated on both surfaces of a flat Faraday rotator is arranged in the center of a cylindrical magnet.
[0006]
FIG. 6 is a diagram showing a configuration of a conventional miniaturized optical isolator 15.
[0007]
Patent Document 1 discloses a conventional optical isolator shown in FIG. 6, and its configuration will be described below.
[0008]
The optical isolator 15 includes an optical isolator element 20 in which a Faraday rotator 16 and polarizers 17 and 18 are adhered with an optical adhesive 19 having a good light transmittance and a controlled refractive index, and a cylindrical magnet 21. Here, the polarizers 17 and 18 have a function of absorbing a polarized component in one direction of transmitted light and transmitting a polarized component orthogonal to the polarized component, and the Faraday rotator 16 has a function of a saturated magnetic field strength. Has a function of rotating the plane of polarization of light of a predetermined wavelength by about 45 degrees. Further, the two polarizers 17 and 18 are arranged such that their transmission polarization directions are shifted by about 45 degrees.
[0009]
FIG. 7 is a view showing a method of manufacturing the conventional optical isolator element 20.
[0010]
First, as shown in FIGS. 7A and 7B, a polarizer substrate 22, a Faraday rotator substrate 23, and a polarizer substrate 24 of about 10 mm square are bonded and integrated. Here, the transmission polarization direction of the polarizer 22 is set to a direction parallel to a certain side, and the transmission polarization direction of the polarizer 24 is set to a direction of 45 degrees to one side. To fix the optical substrates, the polarizer 22, the Faraday rotator 23, and the polarizer 24 are bonded so that one side of each optical substrate is parallel. As described above, an optically transparent resin is used as an adhesive for bonding and integrating the optical elements, and an epoxy-based or acrylic-based organic adhesive is generally used.
[0011]
Here, when high isolation is required for the optical isolator, it is necessary to precisely adjust the rotation shift between the polarizers 22 and 24 to 45-α degrees with respect to the polarization rotation angle of the Faraday rotator of 45 + α degrees. There is. Specifically, light is incident from the opposite direction (from the polarizer substrate 24 side), and the polarizers 22 and 24 are rotationally adjusted so that the transmitted light is minimized.
[0012]
Next, as shown in FIGS. 6C and 6D, the optical isolator element substrate 25 is processed into a large number of small chip-like optical isolator elements 20 by dicing or the like.
Furthermore, the authors have proposed a miniaturized optical isolator that does not use a resin for joining each optical element.
[0013]
In the case of manufacturing the optical isolator element 20, a large polarizer substrate and a Faraday rotator substrate are alternately laminated, and after the bonding is completed, this is cut to obtain a large number of optical isolator elements 20. By using, the workability and the production amount can be increased, and the number of parts can be further reduced. As the optical adhesive 19, an epoxy-based or acrylic-based organic adhesive is generally used.
Furthermore, the authors have proposed a miniaturized optical isolator that does not use a resin for joining each optical element.
[0014]
Patent Literature 2 discloses a miniaturized optical isolator that does not use a resin. In this optical isolator, light-transmitting low-melting glass is used without using resin for bonding the optical isolator element 20 shown in FIG. Things. The manufacturing method is almost the same as that shown in FIG. 7, but when integrating the polarizer substrate 22, the Faraday rotator substrate 23 and the polarizer substrate 24, a light-transmitting low-melting glass is interposed between the elements. The elements are joined at a temperature at which the low-melting glass is sandwiched and melted.
[0015]
[Patent Document 1]
JP-A-4-338916
[Patent Document 2]
JP-A-8-146351
[0016]
[Problems to be solved by the invention]
However, when the adhesive 19 is an organic adhesive in the optical isolator element 20 in which the plate-shaped polarizers 17 and 18 are integrated on both surfaces of the Faraday rotator 16 with the adhesive 19 as described above, the moisture resistance is low. In particular, there is a problem that the use under high temperature and high humidity conditions is restricted. Further, there is a risk of deterioration of the adhesive 19 when used for a long time or in a high-power laser beam, and there is a problem in reliability.
[0017]
When the optical isolator element 20 is incorporated in the laser module, the optical isolator 15 is exposed to a high temperature. However, when an organic adhesive is used as the adhesive 19, it is decomposed, and bubbles are generated, and the members fall off. Etc. occur. Furthermore, outgas from the organic adhesive 19 adheres to the surface of an optical component such as a laser chip or a lens, and there is a risk of deteriorating optical characteristics.
[0018]
Further, in the optical isolator element 20 in which the plate-like polarizers 17 and 18 are bonded and integrated on both surfaces of the Faraday rotator 16 with the low melting point glass 19, the glass transition temperature of the low melting point glass 19 is as high as several hundred degrees. After melting and fixing the members to each other, when cooling to room temperature, there is a risk that thermal stress increases and cracks and the like occur. Further, when a thermal stress is applied to the Faraday rotator 16, the extinction ratio of light passing through the Faraday rotator 16 deteriorates, and various characteristics of the optical isolator 15, particularly, the reverse loss characteristics deteriorate.
[0019]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and is characterized in that one or more flat Faraday rotators and two or more flat polarizers are laminated and integrated by directly bonding. It is assumed that.
[0020]
Further, one or more flat Faraday rotators and two or more flat polarizers are laminated and integrated by directly bonding via a multilayer film made of an inorganic material. .
[0021]
Further, in an optical isolator element obtained by laminating and integrating one or more flat Faraday rotators and two or more flat polarizers, a cover made of the flat Faraday rotator and the flat polarizer is provided. A method for manufacturing an element for an optical isolator, comprising a step of cleaning the surface of a bonding material and a step of bringing the materials to be bonded into contact with each other in a vacuum and bonding them by van der Waals force.
[0022]
A step of cleaning a surface of a material to be joined comprising the flat Faraday rotator and the flat polarizer; and adsorbing a hydroxyl group to at least one surface of the joining surfaces of the material to be joined. And a step of bringing the materials to be joined into contact with each other in a vacuum and joining them by a hydrogen bonding force generated between a hydroxyl group on one surface of the material to be joined and an oxygen atom on the surface of the other material to be joined. A method for manufacturing an element for an optical isolator including:
[0023]
Furthermore, the present invention is characterized by a method for manufacturing an element for an optical isolator, including a step of forming a multilayer film made of an inorganic material on the surface of the material to be joined.
[0024]
Further, the bonding of the materials to be bonded is performed at room temperature.
[0025]
Furthermore, a magnet is provided around the optical isolator element to constitute an optical isolator.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0027]
FIG. 1 is a perspective view showing an embodiment of the optical isolator of the present invention.
[0028]
As shown in FIG. 1, the optical isolator 1 is composed of an optical isolator element 5 and a cylindrical magnet 6 which are laminated by integrating the Faraday rotator 2 and the polarizers 3 and 4 directly, and are integrated. Note that the optical isolator element 5 is manufactured by directly bonding two large polarizer substrates, like the large Faraday rotator substrate, and then subdividing it into an appropriate size.
[0029]
The Faraday rotator 2 is, for example, a bismuth-substituted garnet crystal or the like, and its thickness is set so that the plane of polarization of an incident light beam having a predetermined wavelength is rotated by 45 degrees. Generally, in order to rotate the plane of polarization, it is necessary to apply a sufficient magnetic field in the direction of the optical axis L of the incident light. Also, if a self-biased Faraday rotator is used, the optical isolator 1 operates without a magnet, and the magnet 6 becomes unnecessary.
[0030]
The two polarizers 3 and 4 are absorption polarizers having a function of absorbing one-way polarized light components of incident light, or birefringent polarizers that separate or combine one-way polarized light components of incident light. It consists of. For example, when the Faraday rotator 2 rotates the polarization plane of the incident light around the optical axis at 45 °, and when the absorption polarizers are used as the polarizers 3 and 4, the transmission polarization direction of the polarizer 3 is changed to the polarizer. The configuration may be such that it is shifted about the optical axis by 45 ° with respect to the transmitted polarization direction of No. 4.
[0031]
In the present embodiment, the bonding surfaces of the polarizer 3 and the Faraday rotator 2 and the bonding surface of the Faraday rotator 2 and the polarizer 4 are such that the atoms on each surface are directly bonded at normal temperature, and Does not exist. At the bonding interface between the polarizers 3 and 4 and the Faraday rotator 2, only a very thin intermediate layer of several nm is present.
[0032]
FIG. 2 is a view showing a method for manufacturing an element for an optical isolator of the present invention.
[0033]
First, as shown in FIG. 2A, the surface of the optical element 7 (the large polarizer substrate and the Faraday rotator substrate) is smoothed by polishing to directly join the large polarizer substrate and the Faraday rotator substrate. Next, as shown in FIG. 2B, cleaning and surface activation are performed by sputtering.
[0034]
The polishing step uses a method called CMP (Chemical Mechanical Polishing) for polishing by mixing abrasive grains of ceramics or diamond with a liquid having a chemical corrosive action, and has a flatness of 10 μm or less and a surface roughness of 10 nm or less. A super smooth surface is desirable. For joining, polishing is performed so as to remove the work-affected layer on the surface. The above polishing method can be polished in a unit of several nm and hardly damages a lower portion of the polishing layer. Further, in the case of simple mechanical polishing, even if the desired flatness and surface roughness are achieved, a damaged layer that has been chemically changed by processing remains, and subsequent surface bonding cannot be performed.
[0035]
In addition, CMP consists of polishing and washing. As shown in FIG. 2A, the optical element 7 is polished in ultrapure water using a polishing pad 8, and then the SiO 2 having an average particle diameter of 30 nm is polished.₂The particles are polished in colloidal silica 9 suspended in a NaOH solution. The washing is performed by (a) an ultrasonic bath using alcohol, (b) an ultrasonic bath using ultrapure water, and (c) drying using a spin dryer. Rinse with ultrapure water between each step.
[0036]
After the above-mentioned polishing step, as shown in FIG. 2B, a large-sized optical element 7 (a polarizer substrate and a Faraday rotator substrate) is opposed to the inside of the vacuum chamber 10, and an ion beam or neutral atoms are removed. By irradiating each optical element, cleaning and surface activation are performed. This is for removing a layer of gas molecules, a contaminant, and an oxide film attached to the bonding surface in the air, thereby providing a clean surface. The surface activation is usually performed by irradiating an inert gas (Fast Atom Beam) such as an argon fast atom beam and sputtering the material surface to remove these surface layers. The surface becomes active with a strong bond to other atoms.
[0037]
Here, the vacuum chamber 10 is evacuated and evacuated by the vacuum pump 11, and the degree of vacuum affects the degree of cleaning of the bonding surface.^{― 2}Pa or more is required. In FIG. 2B, reference numeral 12 denotes a beam source, and 13 denotes an inert gas introducing device. Here, the irradiation intensity and irradiation time of the ion beam or neutral atom are appropriately set, and about 10 nm of the surface layer of the optical element 7 is removed. The optical element 7 is placed in a vacuum chamber 10 and the vacuum pump 11^-4Exhaust to about Pa. Next, each optical element is irradiated with an ion beam or a neutral atom by an inert gas such as argon.
[0038]
After the above steps, if the surfaces of the respective optical elements 7 are brought into close contact with each other in a vacuum at room temperature at room temperature, the optical elements 7 are naturally adsorbed by van der Waals force. In addition, on the surface of the cleaned optical element 7, many orbits in a non-bonded state, that is, many dangling bonds are generated. Since these dangling bonds are extremely active, even if the vacuum chamber 10 is maintained at a high vacuum, impurities such as nitrogen, carbon, and hydrocarbons remaining in the vacuum chamber 10 may chemically react on the surface even if the vacuum chamber 10 is maintained at a high vacuum. Adsorbs and inactivates the surface. Therefore, it is necessary to complete the optical element 7 in a short time after the cleaning step until the respective elements are brought into close contact with each other.
[0039]
In addition, in order to strengthen the bonding of the optical elements 7, it is desirable to apply pressure during surface contact. Here, the pressing force is largely related to the surface roughness of the bonding surface. For example, when the bonding surface has a surface roughness of about 10 nmRa, the close contact between the surfaces can be achieved even with a pressure as small as 1 kgf.
[0040]
Here, when a high isolation is required for the optical isolator 1 shown in FIG. 1, the rotation shift of the transmission polarization direction of the polarizer 3 and the polarizer 4 with respect to the polarization rotation angle 45 + α degrees of the Faraday rotator 2. Needs to be precisely adjusted to 45-α degrees. Specifically, when joining a large Faraday rotator substrate and two large polarizer substrates, light is incident from the opposite direction, and the large polarizer substrates are rotated so that transmitted light is minimized. adjust. If the polarization characteristics of each optical element 7 such as the transmission polarization direction with respect to the outer shape of the large polarizer substrate and the polarization rotation angle of the large Faraday rotator substrate are measured in advance, each After adjusting the relative angle of the outer shape of the optical element 7 and joining them together, the element 5 for an optical isolator having excellent optical characteristics can be obtained.
[0041]
When the Faraday rotator 2 and the two polarizers 3 and 4 are directly joined, a part of the incident light is reflected because the respective refractive indices are different at the boundary portion, but the optical element facing the boundary portion This can be prevented by applying an antireflection film made of a multilayer film of an inorganic material on the surface of 7 in advance. In that case, the boundary portion is, for example, SiO 2₂Or TiO₂Or Ta₂O₅Is formed, but the bonding principle does not change. If a material having a refractive index similar to that of an adjacent optical element is formed on the surface of the formed antireflection film in a thickness of several hundred nm to several μm, several tens of Even if the nm is removed, the antireflection film operates normally.
[0042]
Finally, the large optical element 14 directly joined as shown in FIG. 2C is cut into an appropriate size using a method such as dicing or wire cutting to obtain a number of optical isolator elements 5.
[0043]
FIG. 3 is a schematic view showing a bonding interface of the optical isolator element 5 of the present invention.
[0044]
First, the bonding surface is smoothed in advance by polishing abrasive grains 37. An oxide film and a contaminant 35 are attached and bonded to the smoothed atoms 32 on the polarizer substrate surface and the atoms 33 on the Faraday rotator substrate surface. This is etched and cleaned by ions or neutral atoms 36, and the surface is activated so that bonds of the atoms 32 and 33 appear. When the activated surfaces where the bonding hands remain remain in contact with each other, the atoms bond with each other and the substance is joined. At this time, even if the surface is slightly uneven at the atomic level, the bonding can be performed by the interatomic force acting between the surfaces, but pressure is applied to further bring the atoms into close contact with each other and bond them.
[0045]
The polarizer substrate and the Faraday rotator substrate thus bonded have extremely high bonding strength, and have almost the same strength as the bulk. It is also understood from the principle of the present invention that the surface atomic state of each element is a very important factor for the bonding strength of the element.
[0046]
FIG. 4 is a perspective view showing a second embodiment of the present invention.
[0047]
The optical isolator element 30 includes a polarizer 3, a Faraday rotator 2, and a polarizer 4, and these are joined by a soft material 38 formed on a joint surface of each element. The soft material is a metal or metalloid thin film, and the film is formed by vapor deposition or plating. Further, it is necessary that the thickness of the soft material is not greater than λ / 4, where λ is the wavelength of light, and the thickness of the soft material is preferably λ / 4 or less.
[0048]
By depositing a soft material on the bonding surface, the surface becomes SiO 2₂And TiO₂Because it is softer than the dielectric hard material described above, it deforms when pressurized and is more easily joined. As the soft material, for the metal, for example, Au, Al, Ag, Cu, Sn, Zn, Ga and the like are used, and for the semimetal, Si or an alloy mainly containing these metals is used.
[0049]
The manufacturing method of this embodiment is the same as the method shown in FIG. However, the degree of smoothing, the degree of vacuum, and the pressure₂And TiO₂As compared with the first embodiment in which the bonding is performed, the bonding conditions are relaxed, and the bonding at room temperature is facilitated.
[0050]
In addition, in order to obtain stable bonding, it is desirable that atoms at the bonding interface be the same metal or metalloid. For example, a thin film of aluminum (Al) or silicon (Si) is vapor-deposited and bonded to the bonding surface of the polarizer substrate and the Faraday rotator substrate in a thickness of several tens nm in advance.
[0051]
As described above, when manufacturing the large-sized optical element 14 in the above manufacturing process, the bonding surface of the Faraday rotator substrate and the polarizer substrate is smoothed and cleaned, and the surface of the optical element 7 is activated. Pressing and direct bonding by Van der Waals force, but furthermore, a hydroxyl group is adsorbed on the surface of each optical element 7 to activate the surface of the optical element, and then both are brought into close contact with each other, so that direct bonding is performed by hydrogen bonding force. There is also.
[0052]
In this case, in order to adsorb the hydroxyl group, in a vacuum atmosphere, water molecules are sprayed on the cleaned optical element 7 to adsorb the water molecules and the hydroxyl groups, and then the energy for removing the water molecules is increased by plasma. It may be applied to the surface of the optical element 7 by a beam or a microwave to remove water molecules on the adsorbed surface and leave only hydroxyl groups.
[0053]
Alternatively, a high-frequency or direct-current voltage is applied to water molecules, and the purified optical element is decomposed into hydroxyl groups by the electromagnetic field generated by the generated electromagnetic field or by the plasma energy generated by the electromagnetic field, and in the form of hydroxyl groups. It can also be realized by spraying on the surface 7 to adsorb hydroxyl groups.
[0054]
As described above, in the present invention, the optical elements 7 are directly joined to each other, and no organic matter such as an adhesive is used, so that the optical isolator element 5 having excellent moisture resistance can be obtained.
[0055]
Also, high output light from an LD light source passes through the optical isolator element 5, but when the optical elements 7 are bonded to each other with an adhesive, the adhesive portion is deteriorated and the transmittance is increased. There is a concern that the insertion loss characteristics of the device for use may deteriorate. However, in the present invention, since no organic substance such as an adhesive is used, the light isolator element 5 having light resistance can be obtained.
[0056]
Further, as a fixing method when the optical isolator element 5 is incorporated in the laser module, fusion and fixing of solder, fixing with a YAG laser, and bonding using a thermosetting adhesive are conceivable. Also in this case, the optical isolator element 5 is exposed to a high temperature. However, in the present invention, since no organic matter such as an adhesive is used at all, the resin does not deteriorate even at a high temperature, and the optical isolator element 5 having heat resistance can be obtained.
[0057]
Here, the optical isolator element 5 is obtained by laminating a large-sized Faraday rotator substrate and two large-sized polarizer substrates and then subdivided into an appropriate size. When a large-sized optical element is laminated using glass, cracks and the like occur in each optical element and peeling occurs in the bonded portion due to the influence of the generated thermal stress. The thermal stress P generated when two types of adherends are joined using a joining member is shown as follows.
[0058]
P = K × Δα × L × (t2-t1) + E (Equation 1)
K is a coefficient based on the elastic modulus of each member, etc., Δα is a difference in thermal expansion coefficient between the adherends, L is the size of the adherend, and t2 is a heating temperature at the time of bonding (for bonding using low melting glass, In this case, glass transition temperature), t1 is room temperature, and E is stress due to other factors. In this way, the thermal stress applied to the adherend is proportional to the difference in thermal expansion coefficient between the adherends, the heating temperature at the time of bonding, and the size of the adherend. Will increase.
[0059]
Generally, the glass transition temperature of low-melting glass is 300 ° C. or higher, and the (t2−t1) term increases, thereby increasing the thermal stress. To compensate for this, the size L of the adherend, that is, the size of the large optical element, must be kept at a certain value or less, so that the number of optical isolator elements 5 obtained in a lump is necessarily limited.
[0060]
On the other hand, if the method according to the present invention is used, the optical elements are joined at room temperature, so that the term (t2−t1) becomes small, and the generation of thermal stress can be sufficiently suppressed. Therefore, large-sized optical elements can be joined together to collectively obtain optical isolator elements. Therefore, the cost of the optical isolator can be reduced.
[0061]
In the optical isolator 1, when a thermal stress is generated in the constituent members, in particular, the Faraday rotator 2, the extinction ratio of the linearly polarized light passing therethrough is degraded, and the reverse loss characteristic of the optical isolator 1 is degraded. This will be described with reference to FIG. The reflected return light incident from the opposite direction passes through the polarizer 4 and becomes linearly polarized light. The linearly polarized light transmitted through the Faraday rotator 2 rotates by -45 degrees, but at the same time, a polarization component orthogonal thereto is also generated. When the extinction ratio deteriorates, the orthogonal polarization component increases. However, since the orthogonal polarization component passes through the polarizer 3, the reverse loss characteristic deteriorates.
[0062]
FIG. 5 is a diagram showing the relationship between the stress applied to the Faraday rotator and the extinction ratio.
[0063]
In FIG. 5, the horizontal axis indicates stress, and the vertical axis indicates the extinction ratio of light transmitted through the Faraday rotator 2. As can be seen, in the state where no stress is applied, even if the extinction ratio of the transmitted light is as good as 47 dB, the extinction ratio of the transmitted light is degraded as the stress increases, and 3 kgf / mm²From the above, it can be seen that the value is lower than 25 dB which is a general characteristic lower limit set value of the optical isolator 1.
[0064]
Now, if a low-melting glass is used as the bonding member in the optical isolator 1, the thermal stress applied to the Faraday rotator increases. However, according to the method of the present invention, all the optical elements constituting the optical isolator element are replaced. Since the bonding is performed at room temperature, generation of this thermal stress can be sufficiently suppressed. That is, the optical isolator element 5 having excellent optical characteristics can be obtained.
[0065]
In addition, in this invention, below room temperature means the temperature range of -20-70 degreeC.
[0066]
【Example】
As an example of the optical isolator of the present invention, the optical isolator element shown in FIG. 1 was prototyped.
[0067]
The size of the large polarizer substrate is 10 mm × 10 mm × t0.2 mm, the refractive index is 1.47, the thickness of the large Faraday rotator base is 10 mm × 10 mm × t0.4 mm, and the refractive index is 2.35. The polarization characteristics such as the transmission polarization direction with respect to the outer shape of the two large polarizer substrates and the polarization rotation angle of the large Faraday rotator substrate are measured in advance. Are calculated.
[0068]
Further, a polar core substrate (product name) manufactured by Corning Incorporated was used for a large polarizer substrate, and bismuth-substituted garnet was used for a large Faraday rotator substrate. On the surface of a larger Faraday rotator substrate, TiO₂And SiO₂Are appropriately formed into layers and an antireflection film is applied to a medium having a refractive index of 1.45.₂Is formed to a thickness of only 100 nm. Note that SiO₂Has a refractive index of 1.45.
[0069]
Next, the surface of the large polarizer substrate and the SiO 2 on the outermost surface of the large Faraday rotator substrate were₂Chemical polishing is applied to the film surface. As the polishing liquid, a mixed solution of sulfuric acid and hydrogen peroxide having a chemical corrosive action was used. As a result, the surface roughness of each substrate became about 10 nmRa.
[0070]
Next, the surface activation and bonding of the polarizer substrate and the Faraday rotator substrate were performed in a vacuum chamber. The substrate is held in a predetermined jig in a vacuum chamber.^-7Evacuated to Torr. Thereafter, the substrate surface was irradiated with an Ar beam for 60 seconds to clean and activate the surface. The energy of the Ar beam was about 1 keV, and the irradiation angle was 45 degrees with respect to the surface. Etching by Ar beam irradiation is sufficiently small at about 5 nm, and does not affect optical characteristics. Thereafter, the polarizer substrate and the Faraday rotator substrate were adjusted in relative angle based on the outer shape in a vacuum chamber, and then directly contacted with each other, pressed and joined. Pressure was applied at 1 kgf for 3 minutes for bonding. With this bonding, a large polarizer substrate with a refractive index of 1.47 and a SiO film with a refractive index of 1.45 formed on the surface of a large Faraday rotator substrate.₂However, since the refractive index difference between the two is sufficiently small, the reflectance at this interface is also sufficiently small at 0.01%. Were pressed and joined. Pressure was applied at 1 kgf for 3 minutes for bonding.
[0071]
The joined large-sized optical element was cut by dicing to produce 49 1.2 mm × 1.3 mm block-shaped optical isolator elements 5.
[0072]
These 49 optical isolator elements had no cracks, chips, peeling, etc., and a saturated magnetic field was applied to the manufactured optical isolator elements.As a result of measuring the characteristics, all the optical isolators had insertion loss. It was confirmed that it had good and uniform characteristics of 0.2 dB or less and isolation of 40 dB or more. As a comparative example, a product in which each optical element was bonded with a low-melting glass and other dimensions and the like were equal to those of the product of the present invention was simultaneously manufactured. Table 1 shows the average value of the isolation characteristics of the optical isolator element manufactured under the above conditions and the rate of occurrence of cracks generated in the optical element.
[0073]
[Table 1]

[0074]
As shown here, in the optical isolator element using the low melting point glass, a large thermal stress is generated, so that the isolation characteristic is significantly deteriorated. In addition, cracks occurred in the polarizer. On the other hand, according to the method of the present invention, good isolation characteristics were obtained, and no crack was generated.
[0075]
Further, when a shear test was performed on the chip-formed optical isolator elements, it was confirmed that all the elements did not break at the bonding surface, but were broken from inside the element, and that the bonding strength was sufficient.
[0076]
With the above prototype, man-hours and size reduction equivalent to those of the optical isolator element using an adhesive were realized, and the long-term stability of the bonding surface and a resin-free configuration were realized.
[0077]
【The invention's effect】
As described above, the optical isolator according to the present invention reduces the occurrence of cracks due to thermal stress by directly bonding, laminating, and integrating one or more flat Faraday rotators and two or more flat polarizers. It is possible to collectively manufacture optical isolator elements which are suppressed and have excellent light resistance, heat resistance and isolation characteristics. Also, an optical isolator of very small size and uniform quality can be manufactured.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of an optical isolator of the present invention.
FIGS. 2A to 2C are diagrams illustrating a method for manufacturing an element for an optical isolator according to the present invention.
FIG. 3 is a schematic view showing a bonding interface of the optical isolator element of the present invention.
FIG. 4 is a perspective view showing a second embodiment of the present invention.
FIG. 5 is a diagram showing a relationship between a stress applied to a Faraday rotator and an extinction ratio.
FIG. 6 is a perspective view showing a configuration of a conventional optical isolator.
FIG. 7 is a perspective view showing a configuration of a conventional optical isolator.
[Explanation of symbols]
1, 15, 31: Optical isolator
2, 16: Faraday rotator
3, 4, 17, 18: polarizer
5, 20, 30: Optical isolator element
6, 21: magnet
7: Optical element
8: Polishing pad
9: Colloidal silica
10: vacuum chamber
11: vacuum pump
12: Beam source
13: Inert gas introduction device
14: Large optical element
19: Adhesive
32, 33: atom
35: Pollutant
36: Neutral atom
37: Abrasive abrasive
38: Metal film

Claims (10)

An element for an optical isolator, wherein one or more flat Faraday rotators and two or more flat polarizers are directly joined to be laminated and integrated. An element for an optical isolator, wherein one or more flat Faraday rotators and two or more flat polarizers are laminated and integrated by directly bonding via a multilayer film made of an inorganic material. . An element for an optical isolator, wherein one or more flat Faraday rotators and two or more flat polarizers are laminated and integrated by directly bonding via a film made of a soft material. In a device for an optical isolator in which one or more flat Faraday rotators and two or more flat polarizers are laminated and integrated, a bonded object including the flat Faraday rotator and the flat polarizer is provided. A method for manufacturing an element for an optical isolator, comprising: a step of cleaning and activating a surface of a material; and a step of bringing the materials to be joined into contact with each other in a vacuum and joining them by van der Waals force. In a device for an optical isolator in which one or more flat Faraday rotators and two or more flat polarizers are laminated and integrated, a bonded object including the flat Faraday rotator and the flat polarizer is provided. A step of cleaning the surface of the material, a step of activating the surface by adsorbing a hydroxyl group on at least one surface of the bonding surfaces of the material to be bonded, and bringing the materials to be bonded into contact with each other in a vacuum; A method for manufacturing an element for an optical isolator, comprising a step of bonding by a hydrogen bonding force generated between a hydroxyl group on one surface of a material to be bonded and an oxygen atom on the surface of another material to be bonded. 6. The method for manufacturing an optical isolator element according to claim 4, further comprising a step of smoothing a surface of the material to be joined, and wherein a surface roughness Ra of the surface is 10 nm or less. The method for manufacturing an optical isolator element according to claim 4, further comprising a step of forming a multilayer film made of an inorganic material on a surface of the material to be joined. The method for manufacturing an optical isolator element according to claim 4, further comprising a step of forming a thin film made of a metal or a metalloid on the surface of the material to be joined. 9. The method for manufacturing an optical isolator element according to claim 4, wherein the bonding of the materials to be bonded is performed at room temperature. An optical isolator comprising a magnet around the optical isolator element according to claim 1.

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