JP2007004110A - Faraday rotating mirror - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a Faraday rotating mirror that is reduced in insertion loss of light and has proper optical characteristics, with high return loss. <P>SOLUTION: The rotation mirror includes an optical fiber 1, a reflecting mirror 7 for making incident the reflected light obtained by reflecting the light emitted from the optical fiber 1, and a Faraday rotator 5 for rotating planes of polarization in the emitted and reflected light between the reflecting mirror 7 and optical fiber 1. The reflecting mirror 7 has installed a reflecting part 7b, facing the Faraday rotator and a spherical part at the rear of the reflecting part 7b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a Faraday rotating mirror of an optical passive component used for an optical fiber sensor system or an optical amplification system and used to stably operate these systems.

  In the optical fiber sensor, the path of the system is mainly composed of an optical fiber, and has a sensing element in one of the optical paths of the optical fiber. The sensing element undergoes some change in optical characteristics depending on the amount to be measured. . For example, when a single mode fiber is used as a sensing element, it can detect external forces such as vibration, pressure, temperature, electric field, magnetic field, and sound wave, and the change in optical path length of the optical fiber due to these external forces can be detected by a fiber interferometer. Detect by.

  However, in such an optical fiber sensor, there is a problem that output interference fringes fluctuate and signals disappear due to an accidental change in the polarization state of light due to birefringence in the optical fiber.

  For such problems, it has been proposed to use a Faraday rotating mirror as a part of the fiber interferometer. This Faraday rotating mirror is an optical component that removes fluctuations in the polarization state caused by birefringence in an optical fiber and preserves an arbitrary input polarization state.

  FIG. 6 shows a configuration of a conventional Faraday rotating mirror 20. The Faraday rotation mirror 20 includes an optical fiber 21, a coupling lens 22, a Faraday rotator 24, a total reflection mirror 25, and a magnet 23.

  The Faraday rotator 24 is formed of bismuth-substituted garnet or the like, and a magnetic field greater than the saturation magnetic field strength of the garnet is applied by a magnet 23 in a direction parallel to the optical axis direction. The thickness is adjusted to rotate the polarization direction of incident light by 45 °. The optical fiber 21 is a single mode fiber.

  The total reflection mirror 25 is arranged so that the light emitted from the optical fiber 21 is reflected by the total reflection mirror 25. The coupling lens 22 is disposed so that the light reflected by the total reflection mirror 25 is efficiently coupled to the optical fiber 21 again.

  FIG. 7 is a diagram illustrating the state of polarization of light in the Faraday rotation mirror 26 as viewed from the direction of the optical fiber 21. Hereinafter, the operating principle of the Faraday rotating mirror 26 will be described with reference to FIG. For convenience, the light emitted from the optical fiber 21 is referred to as incident light, the light reflected by the total reflection mirror 25 is referred to as reflected light, the incident light direction is referred to as the forward direction, and the reflected light direction is referred to as the reverse direction. Although the incident 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, incident light (FIG. 7A) emitted from the optical fiber 21 is transmitted through the Faraday rotator 24, and its polarization direction is rotated 45 ° clockwise as viewed from the forward direction (FIG. 7B). . Thereafter, the reflected light reflected by the total reflection mirror 25 enters the Faraday rotator 24 from the opposite direction again (FIG. 7C). The reflected light transmitted through the Faraday rotator 24 in the reverse direction is further rotated 45 ° clockwise when the polarization direction is viewed from the forward direction, and enters the optical fiber 21 (FIG. 7D).

  As a result, the reflected light of the Faraday rotating mirror 26 has a polarization direction orthogonal to the incident light, and receives birefringence that is just opposite to that received by the incident light. The polarization state is stabilized in a state orthogonal thereto.

  A conventional Faraday rotating mirror 20 as shown in FIG. 6 is used not only in an optical fiber sensor system but also in an optical fiber amplification system. Since the optical fiber amplification system generally uses several tens to several hundreds meters of a single mode fiber doped with erbium, there is a problem that the polarization state changes due to birefringence in the optical fiber, and further, a long-distance optical fiber communication system. However, there is a problem of polarization mode dispersion that causes signal waveform degradation. However, by using the Faraday rotating mirror 20, these can be compensated, and a stable output can be obtained.

  In Patent Document 1, instead of the coupling lens 22, a core expansion fiber having the same outer diameter as the optical fiber is used. In addition, to reduce the number of processes and simplify assembly, a proposal is made to form a total reflection mirror film on one side of the Faraday rotator, or to adhere the end face of the core expansion fiber and the Faraday rotator via an optical adhesive. Has been.

  FIG. 8A is a schematic configuration diagram showing the Faraday rotation mirror 30 of Patent Document 1. The Faraday rotation mirror 30 includes a core expansion fiber 31, a Faraday rotator 24, a total reflection mirror film 25, and a magnet 23. The magnet 23 is a ring-type magnet and gives a saturation magnetic field parallel to the optical axis to the internal Faraday rotator 24. For the Faraday rotator 24, a bismuth-substituted garnet crystal or the like is used, and its thickness is adjusted so that the polarization direction of incident light rotates by 45 °. The total reflection mirror film 25 is made of a multilayer dielectric and is directly formed on one surface of the Faraday rotator 24. The total reflection mirror film 25 made of this multilayer dielectric has a small light loss and a reflectivity of 99% or more. Here, the total reflection mirror film 25 is directly formed on the Faraday rotator 24, and the number of parts is reduced.

FIG. 8B is a cross-sectional view of the core expansion fiber 31. The core expansion fiber 31 includes a core 31a and a clad 31b, and is manufactured by locally heating a general single mode fiber and expanding the core portion by thermally diffusing Ge or the like doped in the core 31a. . In addition, the divergence angle of the radiation beam from the optical fiber 31 decreases as the core diameter increases, and approaches the parallel light. When the divergence angle is large, the reflected light becomes difficult to be coupled to the optical fiber 31. Therefore, here, the decrease in coupling efficiency is suppressed by increasing the core diameter by 3 to 4 times.
Japanese Patent Laid-Open No. 9-21608

  However, as described above, the conventional Faraday rotating mirror has the following problems.

  Patent Document 1 proposes a reduction in the number of processes and simplification of assembly along with downsizing of the Faraday rotator mirror 30, but since light rays are incident on the Faraday rotator 24 almost perpendicularly, the surface of the Faraday rotator 24 is proposed. Even when the antireflection coating is applied, unnecessary reflection cannot be sufficiently suppressed, and the reflection attenuation amount is only about 30 dB. This is because the core expansion fiber 31 is used and the NA is small, and because the Faraday rotator 24 and the total reflection mirror 25 are integrated, the Faraday rotator 24 cannot be inclined. . Further, when the Faraday rotator 24 is tilted to increase the return loss, there is a problem that the light insertion loss increases. Further, since the Faraday rotator 24 and the reflection mirror 25 are disposed in a bonded state, the angle of the reflection mirror 25 cannot be finely adjusted.

  Thus, although the Faraday rotation mirror 31 proposed in Patent Document 1 can be miniaturized, there is a problem that it is impossible to achieve both high return loss and low loss.

The present invention has been made in view of the above problems, and includes an optical fiber, a reflection mirror that reflects reflected light that is emitted from the optical fiber, and the reflection mirror and the light. A Faraday rotator mirror provided between a fiber and a Faraday rotator that rotates a polarization plane of the emitted light and the reflected light, wherein the reflection mirror includes a reflecting portion facing the Faraday rotator; In addition, the reflection mirror is supported by a mirror holder that contacts the spherical portion of the reflection mirror.

  Furthermore, the mirror holder has a through hole that supports the reflection mirror on an inner peripheral surface.

  In addition, the inner diameter of the through hole of the mirror holder is gradually increased from the Faraday rotator side toward the rear.

  Further, the reflecting mirror is characterized in that the reflecting portion includes a dielectric film or a metal film, and the spherical portion is formed of a glass base.

  Further, the reflection mirror is characterized in that the reflection portion includes a dielectric film or a metal film, and the spherical portion is formed of a metal base.

  Further, the reflecting portion is a polished surface of a metal base.

  In addition, the reflecting portion is formed of a flat plate-like member in which a dielectric film or a metal film is formed on one main surface, and the other main surface is bonded to the surface of the base constituting the spherical portion. Characterize.

  Further, at least a part of the flat plate-like member is embedded in a recess provided on the surface of the base, and is bonded to the bottom surface of the recess via an adhesive.

  The optical fiber includes a graded index fiber.

  Furthermore, the optical fiber includes a coreless fiber that is bonded to the graded index fiber at an end of the Faraday rotator side.

  As described above, according to the present invention, the optical fiber, the reflection mirror that reflects the light emitted from the optical fiber, is incident on the optical fiber, and the output mirror is interposed between the reflection mirror and the optical fiber. A Faraday rotator mirror including a Faraday rotator that rotates a plane of polarization of the reflected light and the reflected light, wherein the reflection mirror includes a reflecting portion facing the Faraday rotator, and a spherical portion behind the reflecting portion. Since it becomes possible to finely adjust the angle of the reflection mirror at the spherical portion, it is possible to suppress the scatter of light near the reflection portion and reduce the loss of light introduced into the optical fiber. At the same time, the reflection mirror can be arranged so as to have a high return loss.

  In addition, since the reflection mirror is held by the mirror holder that contacts the spherical portion of the reflection mirror, the entire spherical portion contacts the mirror holder, so that the reflection mirror can be fixed in a stable state. .

  In addition, since the inner diameter of the through hole of the mirror holder gradually increases from the Faraday rotator side toward the rear, if the tapered portion and the spherical portion of the reflecting mirror are brought into contact with each other, Since the rotation angle of the reflection mirror can be increased, the reflection mirror can be arranged with good workability.

  Further, the reflection part of the reflection mirror is formed by forming a dielectric film on the surface of the substrate made of glass, so that the reflectance of the reflection part can be increased, and as a result, a low-loss Faraday rotation mirror is configured. it can.

  In addition, the reflection mirror reflecting portion forms a dielectric film or a metal film on the surface of the base made of metal, and after adjusting the angle of the reflection mirror, fixes the base and the mirror holder by laser welding. Therefore, workability is improved and inexpensive parts can be used.

  Further, in the present invention, if the reflecting portion is formed of a flat plate-like member in which a dielectric film or a metal film is formed on one main surface, and the other main surface is bonded to the surface of the base constituting the spherical portion. Since the flatness of the main surface forming the reflective film can be easily processed with high accuracy, a reflection mirror having a high reflectance can be easily manufactured, and therefore, the light loss fluctuation can be reduced. Furthermore, since the said flat member can be produced by cutting out to the dimension suitable for use from the large-sized flat member in which the reflecting film was formed, productivity improves.

  In addition, if the flat plate member is embedded in a recess provided on the surface of the base body and bonded to the bottom surface of the recess via an adhesive, for example, resin, low-melting glass, Even if an adhesive such as a brazing material is disposed in the recess, the adhesive can be prevented from flowing out, and a strong adhesive force can be obtained even with a smaller contact area on the meniscus formed by the recess. Further, when the flat plate member is disposed on the substrate, positioning can be easily performed by using the concave shape as a guide, and the main surface position of the flat plate member on which the reflective film is formed can be adjusted by the depth of the concave portion. It becomes easy to arrange | position the said reflection part in the optimal position of a waist.

  Furthermore, the optical fiber is a grade index fiber having a condensing function at the end on the Faraday rotator side, so that it is possible to condense without using a lens outside the fiber, thus forming a small Faraday rotating mirror. it can.

  Furthermore, if the optical fiber includes a coreless fiber to be bonded to the graded index fiber at the end of the Faraday rotator side, the length of the coreless fiber can be adjusted to adjust the length of the optical fiber from the output end of the optical fiber. The distance to the beam waist can be set with high accuracy, and alignment of optical components is easy.

  Embodiments of the present invention will be described below. FIG. 1 is a sectional view showing an embodiment of a Faraday rotating mirror of the present invention.

  The Faraday rotating mirror includes a pigtail 2 having an optical fiber 1, a Faraday rotator 5 bonded to the end face of the pigtail 2, a reflecting mirror 7 having a reflecting portion 7b for reflecting light on the surface of a base 7a, a magnet 8, a metal It consists of a sleeve 6, a mirror holder 9, a cover 10, and the like.

  The optical fiber 1 may be composed of a single mode fiber 1a and a graded index fiber 1b, and preferably has a coreless fiber 1c at the end of the graded index fiber 1b. Are joined together. At this time, in the case of the optical fiber 1 to which the coreless fiber 1c is bonded, the coreless fiber 1c is disposed on the Faraday rotator 5 side, and the graded index fiber 1b is interposed between the coreless fiber 1c and the single mode fiber 1a. is doing. On the other hand, when the coreless fiber 1c is an optical fiber 1 that is not bonded, the graded index fiber 1b is disposed on the Faraday rotator 5 side.

 The graded index fiber 1b has an axially symmetrical refractive index distribution of approximately square and can be used as a refractive index distribution type lens, and thus has a light condensing function. Therefore, by cutting at an optimum length for the wavelength used, the light emitted from the single mode fiber 1a can be collimated or condensed without diverging, and the coupling of the Faraday rotation mirror is made efficient. be able to.

  Theoretically, the coreless fiber 1c is not necessary if the graded index fiber 1b can be cut at the tip of the capillary 3 so as to have an optimum length, but it is difficult to cut at the tip of the capillary 3 so as to have this optimum length. For this reason, a graded index fiber 1b that has been cut in advance to an optimum length is prepared, and the coreless fiber 1c fused to the tip is cut at the tip of the capillary 3, so that the light due to the cut length variation during assembly can be reduced. The effect on coupling efficiency is reduced.

The above-described single mode fiber 1a is mainly made of SiO ₂ and has a core whose refractive index is increased by doping GeO ₂ in the vicinity of the center thereof. Also, graded-index fiber 1b is likewise composed of SiO _2, consists of a core with an increased refractive index by doping GeO ₂ in the vicinity of its center, single-mode fiber 1a more GeO ₂ as compared with near the center Since it is doped, it has an axially symmetrical refractive index profile as described above. Further, the coreless fiber 1c is formed mainly of SiO _2.

  The pigtail 2 inserts and fixes the optical fiber 1 into the through hole of the cylindrical capillary 3 and press-fits the capillary 3 into the cylindrical metal ferrule 4. Thereafter, one end of the capillary 3 is inserted into the through hole of the cylindrical metal sleeve 6, and further, the tip surface of one end of the capillary 3 inserted into the metal sleeve 6 is polished so as to be inclined with respect to the optical axis direction. Is formed.

  Furthermore, if the end face of the pigtail 2, that is, the tip face of the capillary 3 is obliquely polished at an angle of 6 ° or more, the light reflected by this tip face does not return to the direction of the optical fiber 1, so that the return loss is 50 dB. It is also possible to do the above. Therefore, the light that has passed through the Faraday rotator is emitted with an inclination of about 3 ° from the refraction, so that the reflection portion 7b is also adjusted and tilted so as to be perpendicular to the light. As a result, a Faraday rotating mirror with high return loss and low loss is configured.

The Faraday rotator 5 is composed of a bismuth-substituted garnet crystal or the like, and the thickness thereof is adjusted so that the polarization direction of incident light rotates by 45 °. The Faraday rotator 5 is preferably provided with an antireflection film in order to prevent light reflection. With this antireflection film, the loss due to reflection at the end face of the Faraday rotating mirror 100 is reduced, and the insertion loss of the entire Faraday rotating mirror can be kept low. Reflection by other than the reflection mirror 7 causes a decrease in the S / N ratio as a sensor of the Faraday rotation mirror, but the S / N ratio is improved by this antireflection film. This antireflection film is made of, for example, a dielectric multilayer film such as SiO ₂ or TiO ₂ .

The reflection mirror 7 has a reflection part for reflecting light on a part of the surface of the base body 7a. Here, the substrate 7a is preferably made of glass or metal. This is because when the substrate 7a is made of glass, high reflection efficiency can be obtained by preventing light absorption by the substrate 7a. Furthermore, when the main component of the glass is made of SiO ₂ and the reflecting portion 7b is formed of a dielectric film containing SiO ₂ , the adhesion strength of the reflecting portion 7b to the base body 7a is improved, and a high value of 99.5% or more is achieved. This is preferable because the reflectance can be obtained. On the other hand, when the base body 7a is made of metal, after positioning the reflection mirror 7, the mirror holder 9 holding the reflection mirror 7 and the base body 7a can be fixed by laser welding, and the reflection mirror can be firmly fixed. Can do. Therefore, it is possible to prevent the displacement of the reflection mirror 7 due to the force generated from the outside with respect to the Faraday rotation mirror, so that it is possible to reduce the loss of light that occurs when the reflection mirror 7 is introduced into the optical fiber.

  Further, since the positioning of the reflecting mirror 7 can be adjusted if the base body 7a has a spherical portion on the outer peripheral surface thereof, the spherical shape as well as the semicircular shape, the elliptical shape, or the side surface is a spherical portion. It may be trapezoidal or have a cavity inside. Further, the base body 7a can be finished in a desired shape as described above, for example, by being manufactured by a casting method and subjected to polishing or the like. If the base body 7a is a sphere, the size thereof is an outer diameter φ of 0.5 to 3 mm.

Moreover, it is preferable that the reflection part 7b formed on the surface of the base body 7a is composed of a dielectric film or a metal film. In the case of a dielectric multilayer film, a combination of TiO ₂ and SiO _{2 or} a combination of Ta ₂ O ₅ and SiO ₂ can be used, and the reflectance can be 99.5% or more, respectively. On the other hand, Ag or Al can be used for the metal film, and a reflectance of 98.9% for Ag and 93.9% for Al can be obtained. The dielectric multilayer film and the metal film are formed by first vapor-depositing or sputtering the polished end surface of the substrate.

  Further, as will be described later, the dielectric multilayer film and the metal film are formed in advance on another flat glass or metal by vapor deposition or sputtering, cut to a predetermined size, and then adhered to the surface of the substrate 7a. Also good.

  The magnet 8 sandwiches the Faraday rotator and applies a saturation magnetic field parallel to the optical axis to the Faraday rotator 5 and has a ring shape, a U shape, or the like.

  The mirror holder 9 is for holding and fixing the reflection mirror 7. For example, if the mirror holder 9 has a through hole, the reflection mirror 7 can be held on the inner peripheral surface on one end side of the through hole. On the other hand, before inserting the jig for operating the reflection mirror 7 from the open end of the through hole on the other end side and bonding the reflection mirror 7 to the mirror holder 9, the reflection mirror 7 can be positioned with high accuracy. .

  When the mirror holder 9 is fixed to the sleeve 6 by laser welding, the material of the mirror holder 9 is preferably SUS304 or Ni—Fe alloy in order to avoid cracks that cause deterioration in strength of the welded portion. Moreover, when fixing with bonding agents, such as resin, SUS303 or Al can also be used. The mirror holder 9 can be processed by cutting, but can also be manufactured by metal powder injection molding.

  In the embodiment of the present invention, the reflecting mirror 7 includes a reflecting portion 7a on a surface facing the Faraday rotator 5, and has a spherical portion behind the reflecting portion 7b. The spherical portion is provided on the base body 7a of the reflection mirror 7. Since the spherical portion can freely direct the reflection portion 7b of the reflection mirror 7, the light reflected by the reflection portion 7b is reflected on the optical fiber 1. Since the base 7a can be fixed after the reflecting portion 7b is disposed at a position where the loss of light generated when the light is introduced into the light source is reduced, a reduction in light loss can be realized. Below, the operation method of a reflective mirror is explained in full detail.

  FIG. 2 is a cross-sectional view illustrating a method for adjusting the position of the reflecting mirror 7.

  In the embodiment of the present invention, as shown in FIG. 2A, first, the spherical portion of the base body 7a is disposed so as to contact the inner peripheral surface of the mirror holder 9 having a through hole, and the hollow tube 12 is used. Then, the spherical portion of the substrate 7a is sucked and held.

  Next, the hollow tube 12 is operated in the vertical direction or the like, led out from the optical fiber 1, passes through the Faraday rotator 5, and the light reflected by the reflecting portion 7 b of the reflection mirror 7 passes through the Faraday rotator 5. In the light introduced into the optical fiber 1, the reflection mirror 7 is moved so that the loss of the light is minimized. At this time, since the portion to be positioned is a spherical portion, it is possible to align at a minute angle, and the reflection mirror 7 can be arranged so as to be a position where there is little loss of light. Such alignment is necessary to efficiently return the light to the optical fiber 1, and the reflection angle of the light is set by adjusting the angle of the reflecting portion 7b of the base body 7a, that is, the angle of the reflecting mirror 7. can do.

  After adjusting the angle of the reflection mirror 7, the adhesive 11 is applied to the inner peripheral surface of the mirror holder 9 to fix the reflection mirror 7, and a cover for protecting the reflection mirror 7 is provided on the mirror holder 9. The Faraday rotating mirror 100 capable of preventing loss can be manufactured.

  Further, as shown in FIG. 2B, the base body 7a is temporarily fixed to the columnar body 13 with wax 14 or the like, and after adjusting the angle of the reflection mirror 7 as described above, it is fixed with the bonding agent 11, and then the wax 14 May be removed by heat treatment or the like.

  Note that the reflecting mirror 7 and the mirror holder 9 are fixed to the bonding agent as described above, for example, an ultraviolet curable resin or a visible light curable resin made of a monomer, epoxy acrylate, urethane acrylate, or polyester acrylate. May be used, but may be joined and fixed by laser welding.

  Furthermore, it is preferable that the inner diameter of the through hole of the mirror holder 9 is a taper shape that gradually increases toward the rear of the Faraday rotator 5, that is, toward the cover 10. As a result, if the reflecting mirror 7 is operated by bringing the spherical portion of the base 7a of the reflecting mirror 7 into contact with the tapered portion, the driving angle of the reflecting mirror 7 is increased, thereby preventing light loss. It becomes easy to position at an angle that provides a high return loss.

  The shape of the mirror holder 9 is not particularly limited as long as the position of the reflecting portion 7b of the reflecting mirror 7 can be adjusted. For example, as shown in FIG. 3 (a), if the shape is a mortar, the angle of the base body 7a can be adjusted stably, and the inner peripheral surface of the mirror holder 9 and the base body 7b of the reflection mirror 7 can be adjusted even after fixing. It is possible to fix with high reliability because it is in contact with. Further, as shown in FIG. 3B, if the cylindrical mirror holder 9 is used, the mirror holder 9 can be manufactured easily and inexpensively.

  Moreover, it is preferable that the reflecting portion 7 b of the reflecting mirror 7 is held protruding from the mirror holder 9 toward the Faraday rotator 5 side. Thereby, it is possible to prevent light from being scattered on the inner peripheral surface of the mirror holder 9, and to efficiently introduce light into the optical fiber 1.

  Further, as shown in FIG. 4, the reflecting mirror 7 has a reflecting portion 7b made of a flat plate member, and a dielectric film or a metal film is formed on one main surface of the reflecting portion 7b, and the other main surface is formed. It is preferable that the surface be bonded to the surface of the base body 7a constituting the spherical portion. Thus, if the reflection part 7b is comprised by the flat member, it becomes easy to process the flatness of the said main surface which forms a reflecting film with high precision, and can manufacture a reflective mirror with a high reflectance easily. Therefore, the fluctuation of light loss can be reduced.

  The flat plate member constituting the reflecting portion 7b can be manufactured as follows. First, glass having a thickness of 0.2 to 0.5 mm and several tens of mm square, for example, one surface of a flat plate made of BK7 is polished into a mirror surface, and a high refractive index dielectric film and a low refractive index are formed on the mirror surface portion. The dielectric film is deposited so as to be alternately stacked with a predetermined thickness. Next, this flat plate is cut into a size that is actually used. This cutting can be performed with a tolerance of ± 0.02 mm if a highly accurate dicing saw device is used. For example, glass, quartz, metal, or the like can be used as the material of the flat plate member, and aluminum or silver can be used as the material of the vapor deposition film that forms the light reflection surface.

  In addition, the flat plate-like member having the reflecting portion 7b only needs to be larger than the spot size at the beam waist position, and is desirably 0.3 mm square or more for the purpose of preventing light vignetting, and from the viewpoint of miniaturizing the Faraday rotating mirror. Can produce a small Faraday rotating mirror having an outer diameter of 3 mm or less.

  Further, the reflecting mirror 7 is flat when the rear surface of the spherical portion of the base body 7b is flat, for example, when the surface of a cover (not shown) for protecting the reflecting mirror 7 is flat. The surface and the flat surface of the cover can be easily bonded and fixed.

  Further, as shown in FIG. 5, the reflecting portion 7b made of a flat plate member is provided with an adhesive 15 in a concave portion 16 provided on the surface of the base 7a, and the reflecting portion 7b made of a flat plate member. It is preferable that at least a part is bonded to the bottom surface 16 a of the recess 16. As a result, the flow-out of the adhesive 15 is prevented by the concave portion 16, and the reflecting portion 16 can be firmly bonded to the base body 7a even with a smaller contact area to the meniscus formed by the concave portion.

  The size of the bottom surface 16a of the concave portion for adhering the flat plate member is desirably such that the adhesive can wrap around the outer peripheral portion of the flat plate member with a width of 50 to 500 μm. For example, if the flat plate member is 0.5 mm square The minimum width of the bottom surface 16a of the recess is preferably 0.8 to 1.7 mm, and if the flat plate member is 1 mm square, the minimum width of the bottom surface 16a of the recess is preferably 1.5 to 2.4 mm.

  As the adhesive 15, for example, an ultraviolet curable resin or a visible light curable resin made of monomer, epoxy acrylate, urethane acrylate, or polyester acrylate can be used. If a brazing material or the like is used, the Faraday rotating mirror having high reliability can be obtained because it can be joined more firmly.

  As an example of the present invention, the Faraday rotating mirror shown in FIG. 1 was manufactured, and optical characteristics were evaluated and a reliability test was performed. Each component and configuration will be described below.

  The pigtail 2 is formed by press-fitting a zirconia capillary 3 having an outer diameter of 1.25 mm into an SUS304 outer diameter of 2 mm ferrule, and then using the optical fiber 1 composed of a single mode fiber 1a, a graded index fiber 1b, and a coreless fiber 1c as a capillary. After insertion, it was fixed with a thermosetting bonding agent. Further, the end surface of the pigtail 2 was polished so as to be an inclined surface having an angle of 6 degrees with respect to the direction perpendicular to the optical axis direction.

  The optical fiber 1 is a single mode fiber for 1550 nm and has a mode field diameter of 8 μm.

The reflecting mirror 7 polishes a part of the surface of a base body 7a made of a glass sphere having an outer diameter of φ1.0 mm, and deposits a dielectric multilayer film SiO ₂ and TiO ₂ on the polished surface to form a reflecting portion 7b. did. The reflection part 7b had a light reflectance of 99.5% or more.

Next, the Faraday rotator 5 was bonded to the end face of the polished pigtail 2. The Faraday rotator 5 was adjusted so that the polarization direction of incident light was rotated by 45 ° at 1550 nm, and a bismuth-substituted garnet having a length of 0.5 mm, a width of 0.5 mm, and a thickness of about 0.4 mm was used. Further, the Faraday rotator 5 was provided with an antireflection film made of SiO ₂ and TiO ₂ on the surface facing the pigtail 2 and the surface facing the reflection mirror 7.

  The magnet 8 is a ring type having an outer diameter of 2.5 mmφ, and is disposed with a certain gap from the Faraday rotator 5 so as to give a saturation magnetic field parallel to the optical axis to the internal Faraday rotator 5. Glued to the end face of.

  Next, one end side of the pigtail 2 to which the Faraday rotator 5 is bonded is inserted into the open end of one end of the through hole of the sleeve 6 made of SUS304 and fixed by laser welding, and at the other open end of the through hole, A mirror holder 9 made of SUS304 having a tapered through hole was inserted and fixed by laser welding. Then, the reflection mirror 7 was disposed in the through hole of the mirror holder 9 so that the inner peripheral surface of the mirror holder 9 and the spherical portion of the base body 7a of the reflection mirror 7 contacted each other.

  Then, after the reflecting mirror 7 is aligned while the substrate 7 a is sucked and held by the hollow tube 12, the reflecting mirror 7 is joined to the through hole of the mirror holder 9 with the visible light curable bonding agent 11, and the mirror The Faraday rotating mirror 100 was produced by laser welding a SUS304 cover 10 to the holder 9. In the Faraday rotating mirror according to the embodiment of the present invention, the light source is connected to one input terminal of the input side 2 terminal and the output side 2 terminal coupler for branching light to 50%, and to the output side 1 terminal. A light output from a terminal not connected to the light source on the input side with a Faraday rotating mirror connected was measured with a detector provided at one terminal on the input side, and the light insertion loss was measured. On the other hand, the reflection attenuation amount was measured by adding the reflection amount of the reflection point other than the reflection mirror using a precision reflectometer. As a result, optical characteristics with a light insertion loss of 0.5 dB and a return loss of 55 dB were obtained.

  On the other hand, in the conventional Faraday rotating mirror shown in FIG. 8 made of the same material as that of the present invention, the Faraday rotator and the reflecting mirror are arranged in the optical system in a joined state. Therefore, the optical insertion loss was 1.0 dB, and the return loss was 28 dB. From the above results, the Faraday rotating mirror of the present invention has better optical characteristics than the conventional Faraday rotating mirror.

It is sectional drawing which shows the Faraday rotation mirror of this invention. It is sectional drawing which shows the method of adjusting the reflective mirror of the Faraday rotation mirror of this invention. It is sectional drawing which shows other embodiment of the Faraday rotation mirror of this invention. It is sectional drawing which shows other embodiment of the Faraday rotation mirror of this invention. It is sectional drawing which shows other embodiment of the Faraday rotation mirror of this invention. It is sectional drawing which shows the structure of the conventional Faraday rotation mirror. It is explanatory drawing which shows the function of a Faraday rotation mirror. It is sectional drawing which shows another structure of the conventional Faraday rotation mirror.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical fiber 1a ... Single mode fiber 1b ... Graded index fiber 1c ... Coreless fiber 2 ... Pigtail 3 ... Capillary 4 ... Ferrule 5 ... Faraday rotator 6 ... Sleeve 7 ... Reflecting mirror 7a ... Base 7b ... Reflecting part 8 ... Magnet 9 ... Mirror holder 10 ... Cover 11 ... Bonding agent 12 ... Hollow tube 13 ... Columnar body 14 ... Wax 15 ... Adhesive 16 ... Recess 16a ... Bottom surface 20, 26, 30, 100 ... Faraday rotating mirror 21 ... Optical fiber 22 ... Coupling Lens 23 ... Magnet 24 ... Faraday rotator 25 ... Total reflection mirror 27 ... Optical element block 31 ... Core expansion fiber 31a ... Core 31b ... Cladding

Claims (11)

An optical fiber, a reflection mirror that causes reflected light reflected from the light emitted from the optical fiber to enter the optical fiber, and a polarization plane of the emitted light and the reflected light between the reflection mirror and the optical fiber A Faraday rotating mirror having a Faraday rotator for rotating
The reflection mirror includes a reflection portion facing the Faraday rotator, and a spherical portion that supports the reflection portion from the rear.   The Faraday rotation mirror according to claim 1, wherein the reflection mirror is held by a mirror holder that contacts a spherical portion of the reflection mirror.   The Faraday rotation mirror according to claim 2, wherein the mirror holder has a through hole that supports the reflection mirror on an inner peripheral surface.   The Faraday rotating mirror according to claim 3, wherein an inner diameter of the through hole of the mirror holder is gradually increased from the Faraday rotator side toward the rear.   5. The Faraday according to claim 1, wherein the reflecting portion includes a dielectric film or a metal film, and the spherical portion includes a glass base. Rotating mirror.   5. The Faraday according to claim 1, wherein the reflection part includes a dielectric film or a metal film, and the spherical part includes a metal base. Rotating mirror.   The Faraday rotating mirror according to claim 1, wherein the reflecting portion is a polished surface of a metal base.   The reflecting portion is formed of a flat plate member having a dielectric film or a metal film formed on one main surface and the other main surface bonded to the surface of the base constituting the spherical portion. The Faraday rotation mirror in any one of Claims 1-4.   9. The Faraday according to claim 8, wherein at least a part of the flat plate member is embedded in a concave portion provided on a surface of the base body and is bonded to a bottom surface of the concave portion through an adhesive. Rotating mirror.   The Faraday rotating mirror according to claim 1, wherein the optical fiber includes a graded index fiber.   The Faraday rotating mirror according to claim 10, wherein the optical fiber includes a coreless fiber bonded to the graded index fiber at an end portion on the Faraday rotator side.

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