JP2007148133A - Faraday rotator mirror - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized Faraday rotator mirror exhibiting excellent fabrication workability, reliability and coupling efficiency. <P>SOLUTION: The Faraday rotator mirror comprises an optical fiber 2, a reflection member 4 which reflects projection light from the optical fiber 2 and makes it incident on the optical fiber 2, a Faraday rotator 3 which is arranged between the reflection member 4 and optical fiber 2 and coupled to a reflective surface of the reflection member 4 and one end of the optical fiber 2 through an optical adhesive 8, and a protection member 9 which contains a moisture absorbent and coats a surface of the optical adhesive 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a Faraday rotating mirror of an optical passive component applied to further stabilize the operation of an optical fiber sensor system, an optical amplification system, or the like.

  The optical fiber sensor has a system path mainly composed of an optical fiber and has a detection element in one of the optical paths of the optical fiber. Here, the detection element is a component that receives an optical characteristic change according to the amount detected from the detection target. In an optical fiber sensor, when an optical fiber is used as a sensing element to detect external forces such as vibration, pressure, temperature, electric field, magnetic field, and sound wave, for example, a change in the optical path length of the optical fiber due to these external forces is detected by a fiber interferometer. Is done.

  However, in such an optical fiber sensor, there arises a problem that fluctuation of the output interference fringe and disappearance of the signal occur due to an accidental change in the polarization state of light due to birefringence in the optical fiber.

  In order to solve such a problem, Patent Document 1 proposes to use a Faraday rotating mirror as a part of the fiber interferometer. This Faraday rotating mirror is an optical component that has a function of suppressing a fluctuation in polarization state caused by birefringence in an optical fiber and maintaining an arbitrary input polarization state.

  FIG. 4 is a cross-sectional view showing the configuration of a conventional Faraday rotating mirror 11. The Faraday rotation mirror 11 includes an optical fiber 12, a coupling lens 13, a Faraday rotator 15, a reflection member (hereinafter, total reflection mirror) 16, and a magnet 17.

  The optical fiber 12 is a single mode fiber. The coupling lens 13 is a member for efficiently coupling light reflected by a total reflection mirror 16 described later to the optical fiber 12, and is disposed so as to face one end of the optical fiber 12. The Faraday rotator 15 is a member having a function of rotating a polarization direction of emitted light by a predetermined angle by applying a predetermined magnetic field, and is made of, for example, a bismuth-substituted garnet crystal. The thickness of the Faraday rotator 15 is set so that, for example, the polarization direction of incident light rotates 45 °. The total reflection mirror 16 is a member for reflecting the light emitted from the optical fiber 12, and is disposed so as to face one end of the optical fiber 12 through the coupling lens 13 and the Faraday rotator 15. Yes. The magnet 17 is a member for applying a predetermined magnetic field (for example, the saturation magnetic field strength of the bismuth-substituted garnet crystal or more) to the Faraday rotator 15.

  FIG. 5 is a diagram for explaining the polarization state of light in the Faraday rotation mirror 11 as viewed from the direction of the optical fiber 12. Hereinafter, the operating principle of the Faraday rotating mirror 11 will be described with reference to FIG. The light emitted from the optical fiber 12 is referred to as outgoing light, the light reflected by the total reflection mirror 16 is referred to as reflected light, the traveling direction of the emitted light is referred to as the forward direction, and the traveling direction of the reflected light is referred to as the reverse direction. Further, although the outgoing polarization direction is a linear polarization, this description is not limited to this, and the present invention can be applied to any polarization direction.

  First, the outgoing light (FIG. 5-a) emitted from the optical fiber 12 is transmitted through the Faraday rotator 15, and its polarization direction is rotated 45 ° clockwise as seen from the forward direction (FIG. 5-b). . Thereafter, the reflected light (FIG. 5-c) reflected by the total reflection mirror 16 enters the Faraday rotator 15 from the opposite direction again. The reflected light transmitted through the Faraday rotator 15 in the reverse direction is further rotated by 45 ° in the clockwise direction when the polarization direction is viewed from the forward direction (FIG. 5D), and enters the optical fiber 12. As a result, the reflected light of the Faraday rotating mirror 11 has a polarization direction orthogonal to the outgoing light and receives birefringence opposite to that received by the outgoing light. The polarization state is stabilized in a state orthogonal thereto.

  The Faraday rotating mirror 11 as shown in FIGS. 4 and 5 is applied to an optical fiber amplification system as well as an optical fiber sensor system. In an optical fiber amplification system, a single mode fiber (length: several tens to several hundreds of meters) doped with erbium is generally used, so that the polarization state changes due to birefringence in the optical fiber. Although there is a problem of polarization mode dispersion that causes signal waveform degradation in a long-distance optical fiber communication system, since these are compensated by using the Faraday rotating mirror 11, more stable reflected light can be obtained.

  Further, in Patent Document 1, in order to reduce the size, a core expansion fiber (having the same outer diameter as the optical fiber) is used instead of the coupling lens. Furthermore, in order to reduce the number of processes and simplify the assembly, a reflecting member (total reflection mirror film) is formed on one end face of the Faraday rotator, or the core expansion fiber and the Faraday rotator are connected via an optical adhesive. Proposals for close contact have been made.

  FIG. 6A is a cross-sectional view illustrating a configuration of the Faraday rotation mirror 21 of Patent Document 1. FIG. The Faraday rotation mirror 21 includes a core expansion fiber 23, a Faraday rotator 25, a reflection member (hereinafter referred to as a total reflection mirror film) 26, a cylindrical magnet 27, and an optical adhesive 28.

  As shown in FIG. 6B, the core expansion fiber 23 includes a core 23a and a clad 23b. The Faraday rotator 25 is a member having the same configuration as the Faraday rotator 25 described above. The total reflection mirror film 26 is made of a multilayer dielectric and is directly formed on one end face of the Faraday rotator 25. The total reflection mirror film 26 has a small light loss and a high reflectance (for example, 99% or more). The cylindrical magnet 27 is a member having the same function as the magnet 17 described above.

  As the distance from the end face of the core expansion fiber 23 to the total reflection mirror film 26 becomes longer, the radiation beam diverges and the coupling efficiency decreases, so the Faraday rotator 25 is mounted in close contact with the core expansion fiber 23. In Patent Document 1, the thickness of the optical adhesive 28 is extremely small and is set to 10 μm or less.

  Further, Patent Document 2 proposes that the return light of unnecessary reflected light is suppressed by using a core expansion fiber and a trapezoidal Faraday rotator.

  FIG. 7 is a cross-sectional view showing the Faraday rotation mirror 31 of Patent Document 2. As shown in FIG. The Faraday rotation mirror 31 includes a core expansion fiber 33, a Faraday rotator 35, a reflection member (hereinafter referred to as a total reflection mirror) 36, a cylindrical magnet 37, and an optical adhesive 38.

The core expansion fiber 33 is different from the above-described core expansion fiber 23 only in that one end surface (the surface facing the Faraday rotator 35) is inclined with respect to the vertical axis of the optical axis. The Faraday rotator 35 is configured in a shape (trapezoidal shape in FIG. 7) in which the other end surface is perpendicular to the optical axis while being connected to the core expansion fiber 33 at one end surface. The total reflection mirror film 36, the cylindrical magnet 37, and the optical adhesive 38 are members having the same configuration as the total reflection mirror film 26, the cylindrical magnet 27, and the optical adhesive 28 described above.
JP-A-9-26556 Japanese Patent Laid-Open No. 9-21608

  However, the Faraday rotating mirror 11 using the coupling lens 13 shown in FIG. 4 has the following problems.

  In the detection unit of the fiber interferometer and the optical fiber amplification system, the Faraday rotating mirror 11 is connected to an optical fiber, an optical fiber coupler, or the like and mounted in a housing. The outer diameter of the optical fiber is 0.25 mm, and the optical fiber coupler Since the Faraday rotating mirror 11 is as large as 5 mm with respect to the outer diameter of 2 to 3 mm, it causes an increase in the size of the apparatus. The Faraday rotating mirror 11 has a size of about φ5 mm in addition to the coupling lens 13 having a diameter of about 2 mm, and a metal fitting for joining the coupling lens 13 to other components. Etc., it was as large as φ5 mm.

  In the Faraday rotation mirror 11, the optical fiber 12, the coupling lens 13, and the total reflection mirror 16 need to be optically adjusted with high accuracy. Therefore, in the Faraday rotating mirror 11, since the number of processes is increased and assembly is complicated, it takes a lot of manufacturing time.

  On the other hand, the Faraday rotating mirror 21 proposes a reduction in size by adopting a core expansion fiber 23 having an outer diameter of φ0.125 mm, a reduction in the number of processes, and simplification of assembly. On the other hand, in the Faraday rotating mirror 31, it has been proposed to suppress unnecessary reflected light by employing a trapezoidal Faraday rotator 35. However, in the Faraday rotating mirror 31, like the Faraday rotating mirror 21, problems such as reliability cannot be sufficiently solved. The trapezoidal Faraday rotator 35 employed in the Faraday rotator mirror 31 can suppress unnecessary reflected light, but the Faraday rotator 35 has a trapezoidal shape. It has been difficult to process the emitted light to a thickness that bears the action of rotating the emitted light by 45 °. Further, in the Faraday rotating mirror 31, the optical adhesive used for joining the core expansion fiber 33 and the Faraday rotator 35 tends to be deteriorated by moisture. Accordingly, when the Faraday rotating mirror 31 is used in an environment with a relatively high temperature and a large amount of internal water vapor, moisture penetrates into the optical adhesive, causing deterioration such as embrittlement, and the core expansion fiber 33 and the Faraday rotator. As a result, there was a change in the attachment of 35, which caused a decrease in optical transmittance and reflectance.

  The present invention has been conceived under such circumstances, and an object of the present invention is to provide a Faraday rotating mirror that is small in size and excellent in manufacturing workability, reliability, and light coupling efficiency.

  The Faraday rotating mirror according to the present invention is disposed between an optical fiber, a reflection member that reflects light emitted from the optical fiber and makes reflected light enter the optical fiber, and the reflection member and the optical fiber. A Faraday rotator joined to the reflecting surface of the reflecting member and one end of the optical fiber via an optical adhesive, a protective member comprising a hygroscopic agent and deposited on the surface of the optical adhesive; It is characterized by providing.

  In the Faraday rotating mirror of the present invention, preferably, the protective member further adheres the surface of the Faraday rotator and / or the reflecting member.

  In the Faraday rotating mirror of the present invention, preferably, the protection member is made of resin.

  In the Faraday rotating mirror of the present invention, it is preferable that the protective member contains 0.1 to 50% by mass of the hygroscopic agent.

  In the Faraday rotating mirror of the present invention, preferably, the hygroscopic agent contained in the protective member is configured to contain at least one or more of silica gel, zeolite, or polyacrylate polymer. .

  In the Faraday rotating mirror of the present invention, it is preferably held inside the cylinder.

  In the Faraday rotation mirror of the present invention, preferably, the protection member covers the Faraday rotator and the reflection member and is joined to one end of the cylindrical body.

  Since the Faraday rotator mirror according to the present invention joins the Faraday rotator joined to the reflecting surface of the reflecting member and one end of the optical fiber via the optical adhesive, for example, the thickness and angle of the optical adhesive are adjusted. As a result, it is possible to suppress deterioration of characteristics (insertion loss, etc.) of the Faraday rotating mirror due to processing variations. Furthermore, in this Faraday rotating mirror, the surface of the optical adhesive is attached to a protective member containing a hygroscopic agent, so that moisture that enters the optical adhesive can be removed even in an environment such as high temperature and high humidity. Can be suppressed. As a result, in the present Faraday rotation mirror, deterioration of the optical adhesive due to moisture can be reduced, so that deterioration of the optical insertion loss due to misalignment of the optical fiber, the Faraday rotator, and the reflection member can be suppressed, for example.

  As an embodiment, a Faraday rotating mirror according to the present invention will be described below.

  FIG. 1 schematically shows the configuration of a Faraday rotating mirror 1 according to the first embodiment of the present invention. The Faraday rotating mirror 1 includes an optical fiber 2 formed by fusing a single mode fiber 2a, a graded index fiber (GIF) 2b, coreless fibers 2c and 2a to 2c, a Faraday rotator 3, a reflecting member (hereinafter referred to as a total reflection mirror). ) 4, a magnet 5, a cylindrical body (hereinafter referred to as a ferrule) 6, a sleeve 7, optical adhesives 8 a and 8 b, and a protective member 9.

  The optical fiber 2 guides light so that light incident from one end thereof is emitted from the other end. Examples of the material constituting the optical fiber 2 include quartz glass, multicomponent glass, and plastic. Here, the single mode fiber 2a is an optical fiber that efficiently propagates only a single mode by setting a small core diameter. A graded index fiber (GIF) 2b is an optical fiber that also has a lens function, and is an optical fiber that is produced by gently varying the refractive index distribution in the radial direction of the fiber. Further, the coreless fiber is an optical fiber having a uniform refractive index made of a single material such as quartz without having a core having a different refractive index.

  The Faraday rotator 3 is a member having a function of rotating the polarization direction of light incident by, for example, applying a predetermined magnetic field by being emitted from the optical fiber 2 or reflected from the reflecting member, and is bismuth-based. It consists of substituted garnet crystals. The thickness of the Faraday rotator 3 is set so that, for example, the polarization direction of the light emitted from the optical fiber and incident on the Faraday rotator 3 is rotated by 45 °. Specifically, although it differs depending on the wavelength of incident light, in the case of 1550 nm, it is 350 to 500 μm (physical thickness). The Faraday rotator 3 is preferably provided with an antireflection film (not shown) for preventing light reflection on the surface thereof. As this antireflection film, for example, an AR coat can be cited, and as its formation position, for example, when a total reflection mirror is formed on one principal surface of the Faraday rotator 3, the other principal surface can be cited. By applying such an antireflection film to the surface of the Faraday rotator 3, unnecessary reflection (reflected return light) of the Faraday rotator mirror 1 can be reduced.

  The total reflection mirror (reflection member) 4 is a member for substantially totally reflecting light, and is bonded to the main surface of the Faraday rotator 3 via an optical adhesive. As the total reflection mirror 4, for example, a dielectric multilayer film itself, a multilayer dielectric in which a dielectric multilayer film is vapor-deposited on a substrate made of glass or the like, a metal having a high reflectivity (such as aluminum) vapor-deposited on the substrate, In addition, an aluminum plate and the like can be mentioned, but a dielectric multilayer film or a multilayer dielectric is preferable from the viewpoint of high reflectivity (for example, 99% or more) and low light loss.

  The magnet 5 is a member for applying a predetermined magnetic field (a magnetic field parallel to the optical axis) to the Faraday rotator 3 and is cylindrical in this embodiment. Note that when the Faraday rotator 3 that does not require application of a magnetic field is employed, the magnet 5 may be omitted.

  The ferrule (tubular body) 6 is a member for holding the optical fiber 2, and is configured, for example, in a cylindrical shape and has a function of holding the optical fiber 2 in the inner hole thereof. The ferrule 6 is made of, for example, ceramics such as alumina and zirconia, glass such as crystallized glass, metal such as stainless steel, or a resin mixed with metal to improve accuracy and strength. If the ferrule 6 is made of ceramics, the ferrule 6 can be obtained by firing a molded body formed in a desired shape by, for example, extrusion molding. Then, it may be formed into a desired shape.

  The sleeve 7 is a member for holding the ferrule 6 and is formed, for example, in a cylindrical shape, and has a function of holding the ferrule 6 in its inner hole. The sleeve 7 is made of a ceramic such as alumina or zirconia, or a metal such as stainless steel. If the ceramic is a ceramic, the sleeve 7 can be obtained by firing a molded body formed in a desired shape by, for example, extrusion molding, What is necessary is just to produce in a desired shape, for example by cutting, if it is a metal. In the Faraday rotating mirror according to the first embodiment of the present invention, the ferrule 6 for holding the optical fiber and the sleeve 7 for holding the ferrule 6 are used. The ferrule 6 and the sleeve 7 are used. As for, a configuration without the ferrule 6 and the sleeve 7 may be employed as long as the function of the Faraday rotating mirror is exhibited.

  The optical adhesives 8a and 8b are used to adjust the separation distance between the graded index fiber 2b and the total reflection mirror 4 and the mounting angle of the total reflection mirror 4 to set the peak of optical coupling, and to the optical fiber. 2, the Faraday rotator 3 and the reflection member 4 are members having a function of adhering and fixing each other. Hereinafter, the optical adhesives 8a and 8b are collectively referred to as an optical adhesive 8.

  Examples of the optical adhesive 8 include epoxy-based and acrylic-based translucent resins, and those having a refractive index equivalent to that of the coreless fiber 4 (for example, 1.45 to 1.5) are preferable. Further, as the optical adhesive 8, one having curability with respect to visible light, ultraviolet light, or heat is preferable from the viewpoint of workability. The adjustment of the peak of optical coupling by the optical adhesive 8 is performed by changing the thickness of the optical adhesive 8 and changing the angle of the total reflection mirror 4. Specifically, first, the optical adhesive 8 is put in a state where the optical fiber 2 (coreless fiber 2c) and the Faraday rotator 3, and the Faraday rotator 3 and the total reflection mirror 4 are in close contact with each other via the optical adhesive 8. By curing, the optical fiber 2, the Faraday rotator 3, and the total reflection mirror 4 are integrated. At this time, the thickness of the optical adhesive 8 interposed in a non-cured state (flowable state) is appropriately changed while measuring the insertion loss in order to confirm the coupling state. The insertion loss is measured by making the light emitted from the light source (Laser Source 81553SM manufactured by Agilent Technologies) incident on the Faraday rotating mirror 1 via the optical circulator, and then reflecting the reflected light again via the optical circulator. (Optical Head 81521B). Next, the optical adhesive 8 that has been changed to a desired thickness (for example, a thickness determined according to the optimum bonding distance) is cured by ultraviolet rays, heat, or the like. The above adjustment can be performed as described above. After the adjustment, the magnet 5 is disposed at a predetermined position as necessary.

  The protective member 9 is a member that is attached to the surface of the optical adhesive 8 and has a function of protecting the optical adhesive 8. Specifically, the protective member 9 mainly includes a hygroscopic agent for absorbing moisture. For example, even if moisture enters from the outside, the hygroscopic agent in the protective member 9 absorbs moisture. It is a member for suppressing deterioration of the optical adhesive 8 due to moisture.

  The protective member 9 is mainly composed of a resin, and examples of the material include an epoxy resin, a polyimide resin, a polyamide resin, and a polyamideimide resin.

  Examples of the hygroscopic agent contained in the protective member 9 include inorganic substances such as silica gel and zeolite, or organic substances such as polyacrylate polymer having high water absorption. The hygroscopic agent is preferably contained in the protective member 9 in an amount of 0.1 to 50.0% by mass. This is because if the moisture absorbent is less than 0.1% by mass, the effect of suppressing the intrusion of moisture into the optical adhesive 8 is weak, whereas if it exceeds 50.0% by mass, the protective member 9 is mainly constituted. Since the moldability of the resin accompanying the deterioration of fluidity is deteriorated, it may be difficult to mold the protective member into a predetermined shape.

  Below, the formation method of the protection member 9 is demonstrated. The optical fiber 2 (coreless fiber 2 c), the Faraday rotator 3, and the total reflection mirror 4 are arranged in a mold, for example, in a state where they are bonded and fixed with an optical adhesive 8. Next, a protective member 9 is formed on the surface of the optical adhesive 8 by pouring a resin containing a hygroscopic agent on the surface of the optical adhesive 8 in a mold and curing the resin by heating or ultraviolet irradiation. . When a magnet is mounted, for example, a resin containing a hygroscopic agent may be filled in the inner diameter portion of the magnet 5 so as to cover the surface of the optical adhesive 8 by using a dispenser and cured.

  Next, the configuration of the Faraday rotating mirror 101 according to the second embodiment of the present invention will be described with reference to FIG. In the following description, the same members as those in the first embodiment of the present invention are denoted by the same reference numerals.

In the Faraday rotating mirror 101, as shown in FIG. 2, the protective member 9 is attached to the surface of the optical adhesive 8, and the Faraday rotator 3 and the total reflection mirror 4 are also protected. In this way, if the protection member 9 is formed so as to protect the Faraday rotator 3 and the total reflection mirror 4 as well, moisture entering the Faraday rotator 3 and the total reflection mirror 4 is suppressed, and the moisture resistance of these optical components is reduced. The position shift of these members can be suppressed while improving property. In FIG. 2, both the Faraday rotator 3 and the total reflection mirror 4 are protected by the protective member 9, but either one may be protected, and as shown in FIG. 5 may be protected. The material of the protective member 9 used at this time is a relatively low coefficient of thermal expansion (6 × 10 ⁻⁶ / ° C. to 10 × 10 ^{− −} ) close to optical components (Faraday rotator 3, total reflection mirror 4), magnet 5, and the like. ⁶ / ° C.) is preferably the main component.

  The Faraday rotating mirror 101 is disposed in a mold, for example, in a state where the optical fiber 2 (coreless fiber 2c), the Faraday rotator 3, and the total reflection mirror 4 are bonded and fixed with an optical adhesive 8, respectively, and a protective member 9 It can be obtained by filling a resin containing a hygroscopic agent at a predetermined position for forming the film and transfer molding.

  Next, the configuration of the Faraday rotation mirror 201 according to the third embodiment of the present invention will be described with reference to FIG. In the following description, the same members as those in the first embodiment of the present invention are denoted by the same reference numerals.

  In the Faraday rotation mirror 201, the protective member 9 is joined to one end of the ferrule 6 that covers the Faraday rotator 3 and the total reflection mirror 4 and holds the optical fiber 2. In this Faraday rotating mirror 201, since the protective member 9 is joined to one end of the ferrule 6 in this Faraday rotating mirror 201, the optical fiber 2, the Faraday rotator, and the total reflection mirror 4 are fixed integrally with each other. Therefore, for example, even if an external force is applied to the Faraday rotation mirror 201, the positional deviation of the optical fiber 2, the Faraday rotator, and the total reflection mirror 4 can be suppressed.

  Such a Faraday rotating mirror 201 is disposed in a mold, for example, in a state where the optical fiber 2 (coreless fiber 2c), the Faraday rotator 3, and the total reflection mirror 4 are bonded and fixed with an optical adhesive 8, for example, to protect the Faraday rotating mirror 201. It can be obtained by filling a resin containing a hygroscopic agent at a predetermined position where the member 9 is formed and performing transfer molding.

  The above embodiment is an example of the present invention, and various modifications and material changes may be made to the above-described embodiment as long as the technical idea or principle of the present invention is followed.

  Next, examples and comparative examples of the present invention will be described.

[Example 1]
<Preparation of Faraday Rotating Mirror> As the Faraday rotating mirror according to Example 1 of the present invention, the Faraday rotating mirror 1 shown in FIG. 1 was prepared. A specific manufacturing method will be described below.

  First, a single mode fiber 2a for 1550 nm, a graded index fiber 2b with a relative refractive index difference of 1.5%, and a coreless fiber 2c made of pure quartz without additives are fusion-bonded while aligning the outer shape. Thus, an optical fiber 2 composed of the fibers 2a to 2c was produced. This is attached to a ferrule 6 made of ceramic or the like, and the end surface is PC-polished to obtain a ferrule with a fiber. This ferrule with a fiber is press-fitted and attached to a sleeve 7 made of stainless steel or the like. Next, when the wavelength of the emitted light is 1550 nm, the polarization direction of the emitted light is set to rotate by 45 °, and the Faraday rotation in which an AR coat is formed on one main surface as an antireflection film with a predetermined thickness The Faraday rotator 3 obtained by cutting the mother base plate into approximately 0.8 mm square is mounted on the end surface of the fiber ferrule via an optical adhesive 8b (acrylic ultraviolet curing type). Next, a total reflection mirror 4 made of a multilayer dielectric adjusted to have a reflectivity of 99% or more is placed on the surface of a transparent member made of glass or the like via an optical adhesive 8a (acrylic ultraviolet curing type). By mounting on the Faraday rotator 3, the Faraday rotator 3 with the total reflection mirror 4 was produced. Next, before this optical adhesive is cured, the optical fiber 2 is aligned so that the ratio of incident light to reflected light, that is, the insertion loss is 0.7 dB or less, and then optically bonded by irradiating ultraviolet rays. The agent was cured. Thereafter, the magnet 5 was bonded to one end of the ferrule 6 so that the Faraday rotator 3 was disposed in the inner hole. Finally, a protective agent 9 is formed by molding a resin agent made of an epoxy resin containing 25% by mass of silica gel as a hygroscopic agent using a dispenser so as to cover the surface of the optical adhesive 8 (8a, 8b), and Faraday A rotor mirror 1 was obtained.

[Example 2]
<Preparation of Faraday Rotating Mirror> The Faraday rotating mirror 101 shown in FIG. 2 was prepared as a Faraday rotating mirror according to Example 2 of the present invention. A specific manufacturing method will be described below.

  First, a single mode fiber 2a for 1550 nm, a graded index fiber 2b with a relative refractive index difference of 1.5%, and a coreless fiber 2c made of pure quartz without additives are fusion-bonded while aligning the outer shape. Thus, an optical fiber 2 composed of the fibers 2a to 2c was produced. This is attached to a ferrule 6 made of ceramic or the like, and the end surface is PC-polished to obtain a ferrule with a fiber. This ferrule with a fiber is press-fitted and attached to a sleeve 7 made of stainless steel or the like. Next, when the wavelength of the emitted light is 1550 nm, the polarization direction of the emitted light is set to rotate by 45 °, and the Faraday rotation in which an AR coat is formed on one main surface as an antireflection film with a predetermined thickness The Faraday rotator 3 obtained by cutting the mother base plate into about 0.8 mm square is mounted on the end face of the ferrule with a fiber via an optical adhesive 8b (acrylic ultraviolet curing type). A Faraday rotator is placed on the surface of a transparent member made of glass or the like via an optical adhesive 8a (acrylic ultraviolet curing type) with a total reflection mirror 4 made of a multilayer dielectric adjusted to have a reflectance of 99% or more. The Faraday rotator 101 with the total reflection mirror 4 was produced. Next, before the optical adhesive is cured, the optical adhesive is irradiated by irradiating with ultraviolet rays after adjusting the ratio of the light emitted from the optical fiber 2 to the reflected light, that is, the insertion loss is 0.7 dB or less. The agent was cured. After that, the magnet 5 was disposed and adhered to the sleeve 7 so as to cover the optical adhesives 8a and 8b joining the Faraday rotator 3 and the total reflection mirror 4 respectively. Next, a resin agent made of an epoxy resin containing 25% by mass of silica gel as a hygroscopic agent was produced. Finally, this resin agent is molded into a tablet shape, and after setting the resin agent in a mold so as to cover one end of the Faraday rotator 3, the total reflection mirror 4, the magnet 5, and the sleeve, injection molding is performed. Thus, the Faraday rotating mirror 101 on which the protective member 9 was formed was obtained.

[Comparative Example 1]
As a comparative example of the present invention, a Faraday rotating mirror in a form not including the Faraday rotating mirror protective member 9 according to Example 1 of the present invention was manufactured. In addition, the members (optical fiber, Faraday rotator, total reflection mirror, etc.) used for the Faraday rotation mirror of this comparative example were the same members as the Faraday rotation mirror according to Example 1 of the present invention.

<Environmental test>
The Faraday rotating mirrors of Example 1, Example 2, and Comparative Example 1 obtained above were subjected to the following environmental test and then measured for insertion loss and return loss as described in detail below. (Environmental test 1) Environmental test 1 is a test in which a Faraday rotating mirror is placed in, for example, a thermal shock test apparatus capable of controlling the internal temperature, and a temperature cycle of −40 ° C. to 85 ° C. is performed 100 times.

(Environmental test 2) The environmental test 2 is an environment in which the Faraday rotating mirror is placed in a high-temperature and high-humidity test apparatus capable of controlling the internal temperature and humidity, for example, and the temperature is set to about 85 ° C. and the humidity is set to about 85%. Below, the Faraday rotating mirror was exposed to 2000 hours.

  <Measurement of Insertion Loss> Using a light source with a wavelength of 1550 nm (Laser Source 81553SM manufactured by Agilent Technologies), the emitted light is incident on the first port of the optical circulator (Applied Photoelectric Laboratory, Inc.), and the second port Through the Faraday rotating mirror 1, the reflected light is again incident on the second port of the optical circulator, and the third port is connected to a light receiver (Optical Head 81521B manufactured by Agilent Technologies). went. The insertion loss is the ratio of the outgoing light and the reflected light at the second port of the optical circulator. First, the outgoing light of the second port of the optical circulator is directly connected to the photoreceiver and measured, and then the second port is connected to the Faraday. Connected to the rotating mirror 1, the amount of reflected light was measured with a light receiver. A value obtained by subtracting the insertion loss of the second port and the third port of the circulator measured in advance from the insertion loss measured by the light receiver is the true insertion loss. And before and after the environmental test shown above, the insertion loss of the Faraday rotation mirrors of Examples 1 and 2 of the present invention and Comparative Example 1 of the present invention was measured, and the difference Δ before and after the test is shown in Table 1.

<Measurement of Return Loss> The return loss was measured using a return loss measuring instrument (Precision Reflectometer 8504B manufactured by Agilent Technologies). The light source was selected to be 1550 nm, and the single mode fiber of the Faraday rotating mirror 1 was connected to the output port of the measuring instrument. This measuring instrument can measure the amount of reflected light for each position in the optical axis direction. Since the amount of other reflected light is very small compared to the amount of light reflected by the total reflection mirror 4, if the amount of light at the total reflection mirror 4 is the total amount of reflected light, the amount of reflected light at each reflection point with respect to the amount of light at the total reflection mirror 4 The ratio can be the return loss. Then, before and after the environmental test described above, the reflection attenuation amounts of the Faraday rotating mirrors of Examples 1 and 2 of the present invention and Comparative Example 1 of the present invention were measured, and the difference Δ before and after the test is shown in Table 1.

<Evaluation>
As shown in Table 1, the Faraday rotating mirror according to Examples 1 and 2 of the present invention has a protective member containing a hygroscopic agent attached to the surface of the optical adhesive, and thus the return loss before and after the temperature cycle test. It was confirmed that the characteristics could be improved by reducing the insertion loss and the insertion loss difference before and after the high temperature and high humidity test.

It is sectional drawing which represents typically the principal part structure of the Faraday rotary mirror which concerns on the 1st Embodiment of this invention. It is sectional drawing which represents typically the principal part structure of the Faraday rotary mirror which concerns on the 2nd Embodiment of this invention. It is sectional drawing which represents typically the principal part structure of the Faraday rotary mirror which concerns on the 3rd Embodiment of this invention. It is sectional drawing which represents typically the principal part structure of the conventional Faraday rotation mirror. It is a schematic diagram explaining the polarization state of the light in the Faraday rotation mirror shown in FIG. The Faraday rotation mirror of patent document 1 is represented, (a) is sectional drawing which represents the principal part structure typically, (b) is sectional drawing which represents typically only a core expansion fiber. It is sectional drawing which represents typically the principal part structure of the Faraday rotation mirror of patent document 2. FIG.

Explanation of symbols

1, 11, 21, 101, 201 ... Faraday rotating mirror 2 ... optical fibers 2a, 12, 23 ... single mode fiber 2b ... graded index fiber 2c ... coreless fibers 3, 15, 25 ... Faraday rotator 4, 16, 26 ... Total reflection mirror (reflection member)
5, 17, 27 ... magnet 6 ... ferrule (cylinder)
7 ... Sleeve 8, 28 ... Optical adhesive 9 ... Protective member 13 ... Optical coupling lens

Claims (7)

Optical fiber,
A reflecting member that reflects light emitted from the optical fiber and causes the reflected light to enter the optical fiber;
A Faraday rotator disposed between the reflecting member and the optical fiber and bonded to the reflecting surface of the reflecting member and one end of the optical fiber via an optical adhesive;
A Faraday rotation mirror comprising a protective member comprising a hygroscopic agent and deposited on the surface of the optical adhesive. The Faraday rotating mirror according to claim 1, wherein the protective member is attached to a surface of the Faraday rotator and / or the reflecting member. The Faraday rotating mirror according to claim 1, wherein the protective member is made of resin. The Faraday rotating mirror according to any one of claims 1 to 3, wherein the protective member contains 0.1 to 50 mass% of the hygroscopic agent. 5. The Faraday rotating mirror according to claim 1, wherein the hygroscopic agent includes at least one of silica gel, zeolite, or polyacrylate polymer material. 6. 6. The Faraday rotating mirror according to claim 1, wherein the optical fiber is held inside a cylindrical body. The Faraday rotating mirror according to claim 6, wherein the protective member covers the Faraday rotator and the reflecting member and is joined to one end of the cylindrical body.

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