JP2003322826A - Optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical isolator having good optical characteristics by improving the moisture resistance, light resistance and heat resistance of an optical isolator element and suppressing the development of a crack to the optical element. <P>SOLUTION: The optical isolator element includes one or more flat planar Faraday rotators, two or more flat planar polarizer arranged at both end faces of the optical axes of the Faraday rotators and adhesive layers for connecting the Faraday rotators and the polarizers to each other, in which a silicone resin essentially consisting of trifunctional organic siloxane is used for the adhesive layers. The use of the silicone resin essentially consisting of the trifunctional organic siloxane for connection to the optical elements, such as optical fibers, as well improves the moisture resistance, heat resistance and light resistance of bonded parts. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator used for removing return light generated when light emitted from a light source is introduced into various optical elements or optical fibers.

[0002]

2. Description of the Related 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 and optical fibers. It is reflected and scattered internally. Some of the reflected or scattered light tries to return to the light source as return light, and an optical isolator is used to prevent this return light.

Conventionally, in this type of optical isolator, a flat Faraday rotator is installed between two polarizers, and these three components are housed in a tubular magnet via a component holder. It is configured. Normally, the Faraday rotator is adjusted to have a thickness that rotates the polarization plane of light having a predetermined wavelength by 45 ° in a saturation magnetic field, and the exit plane side polarizer has a transmission polarization direction of that of the incidence plane side polarizer. It is arranged so as to be rotated by 45 ° in the transmission polarization direction and the light traveling direction.

In such an optical isolator, incident light is polarized by passing through a polarizer on the incident surface side, passing through a Faraday rotator and rotating the polarization plane by 45 °, and a polarizer on the emitting surface side. To pass through and exit. When the return light reaches the exit surface side, the return light is polarized by the exit surface side polarizer, passes through the Faraday rotator and is rotated by 45 °, and reaches the entrance surface side polarizer. Since the polarization plane of light is orthogonal to the transmission polarization direction of the polarizer on the incident surface side, the return light can be removed without being emitted from the incident surface side.

In the optical isolator having such a structure, the Faraday rotator and the two polarizers are separate parts, and a holder is required for each element. Therefore, not only the number of parts increases and the number of assembling steps increases, but also between the parts. The optical adjustment work of is complicated. Therefore, an optical isolator has been proposed in which an optical isolator element having a configuration in which a flat plate-shaped polarizer is directly bonded to both surfaces of a flat plate-shaped Faraday rotator is arranged in the central portion of a cylindrical magnet.

FIG. 7 shows a conventional optical isolator, which is composed of an optical isolator element 23 in which a Faraday rotator 19 and polarizers 20 and 21 are bonded by an optical adhesive 22, and a cylindrical magnet 24. . In the case of manufacturing the optical isolator element 23, a large number of optical isolator elements 23 are obtained by alternately stacking a large-sized polarizer substrate and a Faraday rotator substrate via an adhesive layer and cutting the laminated substrate after the completion of the adhesion. By using, the workability and the production amount are increased, and the number of parts is reduced. For the adhesive layer, an optical adhesive having a high light transmittance and a controlled refractive index is used, and for example, an organic adhesive mainly containing an epoxy resin or an acrylic resin has been used.

[0007]

Since the adhesive layer made of epoxy resin or acrylic resin has low moisture resistance and low light resistance, the optical isolator element provided with these adhesive layers may be placed under high humidity, When it is used for a long time or with a high-power laser beam, the quality of the adhesive layer may change and the characteristics of the optical isolator element may be impaired. In addition, the above-mentioned adhesive layer has poor heat resistance, and when it is fixed to a laser module or the like with solder or the like, there is a possibility that the adhesive layer may be decomposed and bubbles may be generated or parts may be peeled or dropped.

Therefore, Japanese Unexamined Patent Publication No. 8-146351 discloses an optical isolator element using a low melting point glass for the adhesive layer and having high humidity resistance and light resistance. However, a large thermal stress may be generated between the adhesive layer made of the low melting point glass and the Faraday rotator and the polarizer, which may cause cracks in the optical isolator element. Further, when thermal stress is applied to the Faraday rotator, the extinction ratio of the Faraday rotator deteriorates, which causes various characteristics of the optical isolator, particularly, the reverse loss characteristic.

Japanese Unexamined Patent Publication No. 10-48571 discloses that an adhesive for bonding a Faraday rotator and a birefringent crystal has a glass transition point of −.
Since a silicone resin having rubber elasticity at 40 ° C. or less is used, stress generated between the Faraday rotator and the birefringent crystal can be dispersed, and an optical isolator element having high thermal shock resistance is disclosed. It is a silicone resin composed of a bifunctional organic siloxane that has rubber elasticity at a glass transition point of -40 ° C or lower. Since this resin has moisture permeability, the optical isolator has poor moisture resistance, especially under high temperature and high humidity conditions. There is a problem that its use is limited.

Therefore, the present invention provides an optical isolator element and an optical isolator which are excellent in moisture resistance, light resistance, and heat resistance and which are provided with an adhesive layer having a small thermal stress generated between the Faraday rotator and the polarizer. The purpose is to do.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is one or more flat plate Faraday rotators, and two or more disposed on both end faces of the optical axis of the Faraday rotator. Is a flat polarizer, and an optical isolator element consisting of an adhesive layer connecting the Faraday rotator and the polarizer, wherein the adhesive layer is a trifunctional one having excellent moisture resistance, light resistance, and heat resistance. It is characterized by being made of a silicone resin containing an organic siloxane as a main component. Compared to the case of using low-melting glass, trifunctional organosiloxane gives less thermal stress to optical elements such as Faraday rotators and polarizers, so crack generation rate is low and deterioration of optical isolator element characteristics is reduced. Further, since the optical isolator element of the present invention and the component such as the optical fiber are bonded to form the optical isolator by using the silicone resin made of trifunctional organosiloxane as the adhesive, the moisture resistance is improved. A bonded part with excellent light resistance is formed, and there is no peeling between parts due to deterioration over time or deterioration due to high output light.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The optical isolator element of the present invention comprises:
It is configured by connecting a Faraday rotator and a polarizer disposed on both end faces of the optical axis of the Faraday rotator with an adhesive layer made of a silicone resin containing trifunctional organic siloxane as a main component. FIG. 1 is an example of an optical isolator element of the present invention, in which polarizers 3 and 4 are adhered to both sides of a Faraday rotator 2 with an adhesive layer 5 made of trifunctional organosiloxane. The optical isolator element 6 is installed inside the cylindrical magnet 7 to form the optical isolator 1. Magnet 7
Has magnetized to different poles on both end faces.

As the Faraday rotator, for example, bismuth-substituted garnet crystal yttrium, iron garnet crystal, or the like is used, and its thickness is set so that the plane of polarization of incident light having a predetermined wavelength rotates by 45 °. In order for the Faraday rotator to rotate the plane of polarization of the incident light, it is necessary to apply a sufficient magnetic field in the optical axis direction of the incident light with a magnet, etc. To place. If a self-biased Faraday rotator is used, the plane of polarization can be rotated without applying a magnetic field.

As the polarizer, an absorption type polarizer having a function of absorbing a unidirectional polarization component of incident light, or a birefringent polarizer for separating or synthesizing a unidirectional polarization component of incident light is used. . The polarizer is adhered to both end faces of the optical axis of the Faraday rotator, but the transmissive polarization direction of the polarizer on the exit face side is set to the polarization direction of the Faraday rotator with respect to the transmissive polarization direction of the polarizer on the incident face side. It is arranged with an angle of surface rotation. For example, when an absorption-type polarizer is connected to the incident light side and the emission light side of a Faraday rotator adjusted to rotate the polarization plane of incident light by 45 °, the transmission polarization of the polarizer on the emission surface side The direction is inclined by 45 ° with respect to the transmission polarization direction of the polarizer on the incident surface side, and the two are bonded.

The adhesive layer is made of a silicone resin made of trifunctional siloxane. Particularly, the adhesive layer has a good light-transmitting property with respect to the wavelength of the incident light to the optical isolator and has a refractive index which constitutes the optical isolator, that is, Faraday. It is desirable to use a silicone resin having a value close to the refractive index of the rotor or the polarizer. This is because when the silicone resin made of trifunctional siloxane and the optical element have the same refractive index, the transmitted light is not reflected at the adhesive interface between them and the deterioration of insertion loss, which is one of the various characteristics of the optical isolator, does not occur. . If there is a difference between the refractive index of the silicone resin made of trifunctional siloxane and the refractive index of the optical element, an antireflection coating may be applied to the surface of the optical element to prevent reflection of transmitted light.

A silicone resin composed of trifunctional siloxane has a higher degree of polymerization of siloxane molecules and a stronger bonding force than a silicone resin composed of difunctional siloxane. This will be described with reference to FIG. 2. Since the silicone resin made of bifunctional siloxane is a chain polymer, a silicone resin having a low glass transition point is produced from the bifunctional siloxane. On the other hand, a silicone resin composed of trifunctional siloxane becomes a spatial network polymer having molecular chains with a three-dimensional network structure, strengthening the bond between the siloxane molecular chains, and higher than that of trifunctional siloxane. A hard silicone resin is produced.

The silicone resin composed of trifunctional siloxane has water repellency due to its dense molecular structure and exhibits good water resistance. A conventional silicone resin composed of a bifunctional siloxane has moisture permeability because the molecular structure is not dense.
An adhesive layer made of a moisture-permeable adhesive is a factor that causes moisture to penetrate from the resin surface to the inside and reach the adhesive interface between the adhesive layer and the Faraday rotator or polarizer, causing peeling of the adhesive portion. It was In the present invention, since the silicone resin made of trifunctional siloxane is used for adhesion, an optical isolator element having low moisture permeability of the adhesive layer and excellent moisture resistance can be obtained.

Further, in the optical isolator 1, high output light from the laser light source passes, but the adhesive layer for bonding the optical elements to each other is deteriorated and the transmittance is lowered, so that the insertion loss characteristic of the optical isolator is deteriorated. there is a possibility. Since the silicone resin made of trifunctional siloxane has a strong bonding force between siloxane molecules and the resin is not deteriorated even by high output light, the optical isolator element of the present invention is excellent in light resistance.

As a fixing method when the optical isolator is incorporated in the laser module, for example, melting and fixing of solder, Y
There are fixing by an AG laser and bonding by a thermosetting adhesive, but the optical isolator is exposed to high temperature regardless of which bonding method is used. If the optical element is adhered with an adhesive having low heat resistance, the adhesive layer may be decomposed at the time of fixing the optical isolator to cause quality deterioration or peeling. Since the silicone resin composed of trifunctional siloxane used in the adhesive of the present invention has a strong bonding force between siloxane molecules as described above, the resin does not deteriorate even at high temperature, and a heat-resistant optical isolator element is obtained. be able to.

Here, the optical isolator element can be formed by stacking a large Faraday rotator substrate and two large polarizer substrates and then cutting them into chips.
During this manufacturing process, when laminating a large-sized optical element with an adhesive having a high glass transition point such as low-melting point glass, the low-melting point glass is generated in the laminated body after cooling and after heating and melting. Due to the influence of thermal stress, cracks or the like may occur in each optical element, or peeling may occur at the adhesive portion.

The thermal stress P generated when joining two kinds of adherends using a joining member is shown as follows. P = K × Δα × L × (t ₂ −t ₁ ) + E (1) Here, K is a coefficient based on the elastic modulus of each member, Δα is a difference in thermal expansion coefficient between adherends, and L is L. Is the size of the adherend, t ₂ is the glass transition temperature of the bonding member, t ₁ is room temperature, and E is the stress due to other factors. Thus, the thermal stress applied to the adherend is proportional to the difference in the coefficient of thermal expansion between the adherends, the glass transition temperature of the bonding member, and the size of the adherend. The stress will also increase.

The glass transition temperature of the low melting point glass is 300 ° C.
As described above, the generated thermal stress becomes so large that it cannot be ignored. In order to compensate for this, the size of the adherend, that is, the size of the large-sized optical element needs to be set to a certain value or less, so that the number of optical isolator elements that can be collectively obtained is necessarily limited. On the other hand, since the glass transition temperature of the silicone resin composed of trifunctional siloxane is sufficiently low at 200 ° C. or lower, it becomes possible to stack large optical elements with each other, and the number of optical isolator elements that can be obtained collectively is also increased. Since the number of optical isolators increases, the cost of the optical isolator can be reduced.

Further, in the optical isolator element, when thermal stress is generated in the constituent members, especially in the Faraday rotator 2, the extinction ratio of the linearly polarized light passing therethrough deteriorates, and the reverse loss characteristic of the optical isolator 1 deteriorates. . Reflected return light that enters from the opposite direction passes through the polarizer 4 and becomes linearly polarized light.
The linearly polarized light transmitted through the Faraday rotator 2 is rotated by −45 degrees, but at the same time, a polarized light component orthogonal to this is also generated.
When the extinction ratio is deteriorated, the orthogonal polarization components increase, but this is transmitted through the polarizer 3, so that the backward loss characteristic is deteriorated. FIG. 3 shows the relationship between the stress applied to the Faraday rotator and the extinction ratio. When the Faraday rotator is not stressed, the extinction ratio of transmitted light is as good as 47 dB, but the extinction ratio of transmitted light deteriorates as the stress increases, and at 3 kgf / mm ² or more, the optical isolator 1 generally has a higher extinction ratio. It can be seen that the value falls below the characteristic lower limit setting value of 25 dB. If a silicone resin made of trifunctional siloxane is used, the stress applied to the Faraday rotator will be 1.0k.
Since it is about gf / mm ² , the optical isolator element of the present invention has good reverse loss characteristics.

Thus, by bonding and fixing each optical element constituting the optical isolator element with the silicone resin made of trifunctional siloxane, an optical isolator having moisture resistance, light resistance and heat resistance can be obtained. . Furthermore, the thermal stress generated by curing the silicone resin composed of trifunctional siloxane is smaller than that of the low melting point glass,
By suppressing the occurrence of cracks etc. in the optical element and reducing the thermal stress applied to the Faraday rotator,
An optical isolator having excellent optical characteristics can be obtained.

Embodiment 1. It is possible to provide an integrated optical isolator in which the optical isolator element of the present invention and an optical fiber are bonded. When the gap between the optical isolator element and the optical fiber is filled with an optically transparent adhesive and integrally provided, the optical reflection is reduced and the optical isolator has high product reliability. Furthermore, it is preferable to use a trifunctional organosiloxane as the adhesive. For the optical fiber, in addition to ordinary single-mode fiber, use an optical fiber with an expanded core diameter at the tip of the optical fiber or an optical fiber with a lens function added at the tip to reduce the coupling loss between the optical fibers. You can

FIG. 4 shows an example of the embodiment in which an optical fiber and an optical isolator element are bonded together. The optical fiber 9 is held and fixed to the optical fiber holder 11, and the optical isolator element 6 is fixed to the end surface 13 of the optical fiber holder 11 by the silicone resin 12 made of trifunctional siloxane. The optical isolator element 6 is shown in FIG. As described above, the Faraday rotator 2 and the polarizers 3 and 4 are bonded and integrated with each other by the silicone resin 5 made of trifunctional siloxane. Further, the optical fiber holder 11 is fixed by the metal fitting 10, and the ring-shaped magnet 7 is fixed at the tip of the metal fitting 10 to apply a magnetic field to the optical isolator element 6.

The optical fiber holder 11 and the end surface 13 of the optical fiber 9 held in the small-diameter hole are processed into a flat polished surface by polishing. In order to prevent the reflected light at the end face 13 from returning to the laser side, the normal line direction of the end face 13 is processed so as to be inclined with respect to the incident optical axis.

In this embodiment, since the adhesion sites 5 and 12 exposed to the outside air are adhered by the silicone resin made of trifunctional siloxane, the moisture resistance is excellent, and the adhesion of the light transmitting portion is also trifunctional. Since the silicone resins 5 and 12 made of siloxane are used, there is no risk of deterioration or peeling of the adhesive portion even when used for a long time or under high-power transmitted light.

As another form, the optical isolator shown in FIG. 5 can be provided. The optical fiber 9 is held and fixed to the optical fiber holder 11, and a notch 15 is formed in the center of the side surface thereof. The cutout portion 15 is cut along with the optical fiber 9, and both end faces of the optical fiber 9 are polished at the same time as the processing. Further, a silicone resin 1 made of trifunctional siloxane is provided on the bottom of the cutout portion 15.
The optical isolator element 6 fixed by 2 is formed by adhering the Faraday rotator 2 and the polarizers 3 and 4 together by a silicone resin 5 made of trifunctional siloxane. A magnet can be fixed to the bottom of the notch 15 together with the optical isolator element 6 by the silicone resin 12 made of trifunctional siloxane, but the magnet is omitted in FIG.

Also in this embodiment, since the adhesion sites 5 and 12 exposed to the outside air are adhered by the silicone resin made of trifunctional siloxane, the moisture resistance is excellent, and the adhesion of the light transmitting portion is also trifunctional. Since the silicone resins 5 and 12 made of siloxane are used, there is no risk of deterioration or peeling of the adhesive portion even when used for a long time or under high-power transmitted light.

Embodiment 2. The optical isolator element of the present invention and the block magnet can be fixed on the same substrate to provide an optical isolator unit. In the optical isolator unit, the isolator element and the magnet are fixed to the flat substrate made of an inorganic material, so that the optical isolator unit can be easily and easily fixed to the laser module or the like.

FIG. 6 shows an example of an embodiment. An optical isolator element 6 is a block in which a Faraday rotator 2 and polarizers 3 and 4 are bonded and integrated with each other by a silicone resin 5 made of trifunctional siloxane. The magnet 7 and the magnet 7 are aligned and fixed on a substrate 17 made of an inorganic material by a silicone resin 12 made of trifunctional siloxane.

In this embodiment, the adhesive portions 5, 12 of the respective members are all made of a trifunctional siloxane silicone resin 5, 1
2 has excellent moisture resistance, and since the silicone resin made of trifunctional siloxane is used in the light transmitting part, it adheres even when used for a long time or under high output transmitted light. There is no risk of part deterioration or peeling.

As a fixing method when the optical isolator unit 16 is incorporated into a laser module or the like, melting and fixing of solder, and further joining using a thermosetting adhesive can be considered. In any case, the optical isolator 16 is used. Will be exposed to high temperatures. However, in the present invention,
Since each member is fixed by using a silicone resin made of trifunctional siloxane, the resin does not deteriorate even at high temperature.

[0035]

EXAMPLE As an example of the optical isolator of the present invention, the optical isolator shown in FIG. 1 was prototyped. The thickness of the polarizers 3 and 4 is 0.2 mm, and the thickness of the Faraday rotator 2 is 0.4 mm.
mm, as the adhesive used for laminating each element, an adhesive containing polyfunctional siloxane which is a trifunctional siloxane as a main component was used. In addition, the cut dimensions after completion of bonding are
The length and width were set to 1 mm. As a comparative example, an epoxy adhesive and a low melting point glass were used as the adhesive 5, and a product having the same dimensions as the product of the present invention was produced at the same time. Table 1 shows the average value of the reverse loss characteristics of the optical isolator 1 manufactured under the above conditions.

[0036]

[Table 1] (Unit: dB)

As shown here, in the case of using the polyalkylsiloxane as the adhesive 5 and the case of using the epoxy adhesive, although the reverse loss characteristics were good, the low melting point glass was used. The thing deteriorated remarkably.
Further, in the case of using the low melting point glass, cracks were generated in the polarizer portion. In addition, Table 2 shows the occurrence rate of peeling that occurred when the optical isolator manufactured under the above conditions was put into a high temperature and high humidity test (85 ° C, 85%, 2000 hours).

[0038]

[Table 2] (unit%)

As shown here, no peeling was observed in the case of using the polyalkylsiloxane as the adhesive 5 or the case of using the low melting point glass, but in the case of using the epoxy type adhesive, The peeling occurred in part. Furthermore, the optical isolator 1 manufactured under the above conditions
Light resistance test (light source output W, transmitted light beam diameter 500 μm,
Table 3 shows the values of insertion loss before and after charging for 1000 hours.
Shown in.

[0040]

[Table 3] (Unit: dB)

As shown here, the one using polyalkylsiloxane as the adhesive 5 and the one using the low melting point glass did not show an increase in insertion loss, but the one using the epoxy adhesive. Then, 0.05 dB
An increase in degree occurred.

[0042]

According to the optical isolator of the present invention, an optical isolator element is composed of a flat Faraday rotator and a flat polarizer arranged on both end faces of the optical axis of the Faraday rotator. Since it is formed by connecting with an adhesive layer made of a silicone resin containing as a main component, it has excellent moisture resistance,
There is no risk of deterioration even when used for a long time and under high output transmitted light, the occurrence of cracks etc. that occur in optical elements can be suppressed, and the thermal stress applied to the Faraday rotator is small and good reverse loss characteristics are achieved. The optical isolator element may be included.

Further, in the optical isolator of the present invention, the above optical isolator element, the optical fiber and the optical fiber holding tool are integrated by an adhesive, and the adhesive contains trifunctional organic siloxane as a main component. By using the silicone resin, an adhesive portion having excellent moisture resistance and light resistance is formed, and it is possible to obtain an optical isolator having a long life and a small optical loss due to the adhesive.

Furthermore, the optical isolator of the present invention is constructed by providing a notch portion having a depth for cutting the optical fiber in an optical fiber holder including the optical fiber, and incorporating the above optical isolator element in the notch portion. In the case of forming an optical isolator, a silicone resin containing trifunctional organosiloxane as a main component is used to fix the optical isolator element, so that an adhesive part with excellent moisture resistance and light resistance is formed, and the life is long. In addition, it is possible to obtain an optical isolator with little light loss due to the adhesive.

The optical isolator unit of the present invention is formed by bonding an optical isolator element and a magnet on a substrate,
By using a silicone resin containing trifunctional organic siloxane as a main component for the adhesive, an adhesive portion having excellent moisture resistance and heat resistance is formed, and a long-life optical isolator unit can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an optical isolator of the present invention.

FIG. 2 is a diagram showing a molecular bonding state (A) of a silicone resin composed of a bifunctional siloxane and a molecular bonding state (B) of a silicone resin composed of a trifunctional siloxane.

FIG. 3 is a graph showing extinction ratio characteristics with respect to stress in a Faraday rotator.

FIG. 4 is a perspective view showing an optical isolator according to an embodiment of the present invention.

FIG. 5 is a perspective view showing another embodiment of the present invention.

FIG. 6 is a perspective view showing another embodiment of the present invention.

FIG. 7 is a perspective view of a conventional optical isolator.

[Explanation of symbols]

1 Optical isolator 2 Faraday rotator 3, 4 Polarizer 5 Adhesive layer 6 Optical isolator element 7 magnets 9 optical fiber

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshihiro Toda             30 Toyochi, Kitami-shi, Hokkaido Kyocera Corporation             Inside Kitami Factory, Hokkaido (72) Inventor Akira Kashiwazaki             30 Toyochi, Kitami-shi, Hokkaido Kyocera Corporation             Inside Kitami Factory, Hokkaido F-term (reference) 2H049 BA02 BA08 BB03 BB51 BC14                       BC25                 2H099 AA01 BA02 CA11 DA05

Claims (4)

[Claims] 1. A Faraday rotator in the form of one or more flat plates,
The Faraday rotator includes two or more flat plate-shaped polarizers disposed on both end surfaces of the optical axis, and an optical isolator element including an adhesive layer connecting the Faraday rotator and the polarizer. An optical isolator, which is a silicone resin whose main component is trifunctional organosiloxane. 2. An optical fiber holder including an optical fiber inside, an optical isolator element arranged on the optical fiber holder on the optical axis of the optical fiber, and an optical fiber holder and an optical isolator element. An optical isolator according to claim 1, further comprising an adhesive for connecting the two, wherein the adhesive is a silicone resin containing trifunctional organic siloxane as a main component. 3. A cutout portion provided in an optical fiber holder including an optical fiber inside and cutting the optical fiber, and the optical isolator element arranged on the optical axis of the optical fiber and incorporated in the cutout portion. An adhesive that connects between the bottom surface of the cutout portion and the side surface of the optical isolator element, and connects between the side surface of the cutout portion and the incident surface and the emission surface of the optical isolator element, wherein the adhesive agent has three functional groups. The optical isolator according to claim 1, wherein the optical isolator is a silicone resin containing an organic siloxane as a main component. 4. An optical isolator holding substrate, an optical isolator element, and an adhesive connecting between the holding substrate and a side surface of the optical isolator element, wherein the adhesive is a trifunctional organosiloxane. The optical isolator according to claim 1, which is a silicone resin as a main component.