JP4794298B2 - Faraday rotating mirror manufacturing method - Google Patents

Description

The present invention relates to a Faraday rotating mirror of an optical passive component applied to further stabilize the operations of a fiber laser system, a fiber sensor, and a fiber interferometer.

An optical fiber sensor is an object in which a path of an optical system is mainly composed of an optical fiber and a detection element is provided in any one of optical paths composed 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, an optical fiber is used as a detection element, and a change in the optical path length of the optical fiber due to an external force such as vibration, pressure, temperature, magnetic field, and sound wave is detected using a fiber interferometer.

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. Recently, 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 has a function of suppressing a fluctuation in polarization state caused by birefringence in an optical fiber and maintaining an arbitrary input polarization state.

  The Faraday rotating mirror is applied not only to an optical fiber sensor system but also to an optical fiber amplification system. In an optical fiber amplification system, an optical fiber doped with erbium (length: several tens to several hundreds of meters) 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 distance optical fiber communication system, since these are compensated by using a Faraday rotating mirror, a more stable output can be obtained.

  For example, as shown in FIG. 11, such a Faraday rotation mirror 200 is configured using a core expansion fiber 21, a Faraday rotator 22, a reflection mirror 23, a cylindrical magnet 24, and an optical adhesive 26 (Patent Document). 1).

The core expansion fiber 21 has the same outer diameter as that of a single mode fiber or the like, and includes a core 21a and a clad 21b. The core expansion fiber 21 locally diffuses a general optical fiber (for example, a single mode fiber), thereby thermally diffusing Ge or the like doped in the core 21a to expand the mode field diameter. In general, the divergence angle of the radiation beam from the optical fiber decreases as the mode field diameter increases, and approaches the parallel light. Therefore, it becomes easy to re-couple the reflected light to the core expansion fiber 21 by increasing the mode field diameter. In Patent Document 1, the mode field diameter is increased by 3 to 4 times to suppress a decrease in coupling efficiency, that is, an increase in insertion loss.

  The reflection mirror 23 is made of a dielectric multilayer film and is directly formed on one end surface of the Faraday rotator 2. In the Faraday rotating mirror 200, the Faraday rotator 22 is mounted such that the surface facing the surface on which the reflecting mirror 23 is formed is in close contact with the core expansion fiber 21 via the optical adhesive 26.

Further, in the Faraday rotating mirror 200, the Faraday rotator 22 is processed into a wedge shape. Further, the end surface of the core expansion fiber 21 is polished so as to be inclined with respect to the optical axis. Therefore, it is possible to suppress unnecessary reflection that occurs on the end surface of the core expansion fiber 21 and the fiber side end surface of the Faraday rotator 22 from being coupled to the core expansion fiber 21.
JP-A-9-26556

  In the Faraday rotating mirror 200 shown in FIG. 11, the optical adhesive 26 is filled between the Faraday rotator 22 and the core expanding fiber 21, and the insertion loss of the Faraday rotating mirror 200 is controlled by adjusting the thickness. ing. Specifically, since the reflection mirror 23 is directly formed on the Faraday rotator 22, the optical path of the light beam reflected by the reflection mirror 23 is adjusted by adjusting the arrangement position and angle of the Faraday rotator 22. The insertion loss into the core expansion fiber 21 is controlled. When the incident light beam is perpendicular to the reflection mirror 23, the insertion loss value is minimal.

  Here, in the Faraday rotating mirror 200, it is necessary to set the facing surfaces of the core expansion fiber 21 and the Faraday rotator 22 to the same angle with respect to the optical axis. Since the grinding process to be formed is difficult, and it is necessary to arrange the reflecting mirror 23 perpendicularly to the incident light beam as described above, the minute surfaces of the facing surfaces of the core expansion fiber 21 and the Faraday rotator 22 are minute. Thus, a difference in inclination angle will occur. Further, when the Faraday rotator 21 is displaced in the rotational direction with respect to the central axis of the core expansion fiber 21, a difference in inclination angle is caused. Accordingly, the optical adhesive 26 is formed in a wedge shape.

  Here, for example, a thermosetting resin such as Epo-Tek353ND is used for the optical adhesive 26, and when the optical adhesive 26 is cured, its curing shrinkage rate is as large as several percent. Therefore, if the optical adhesive 26 is cured during the optical adjustment operation of the Faraday rotating mirror 200, the angle of the Faraday rotator 22 that has been optically adjusted in advance, that is, the angle of the reflecting mirror 23 is reduced due to the curing shrinkage of the optical adhesive 26. It will change. As a result, in the Faraday rotating mirror 200, the optical path of the reflected light from the reflecting mirror 23 changes due to the angle change of the reflecting mirror 23, and the insertion loss into the core expansion fiber 21 tends to increase.

  Further, the Faraday rotation angle of the Faraday rotator 21 is controlled by its thickness, but since the Faraday rotator 21 is formed into a wedge shape, the Faraday rotation angle may be slightly different depending on the location where the light beam passes. In some cases, it may be difficult to sufficiently exhibit the function of making the polarization direction of the backward light perpendicular to the forward light of the Faraday rotating mirror 200.

In view of the above problems, the present invention provides a step of preparing an optical fiber whose one end surface is inclined with respect to the optical axis, and a flat plate-shaped Faraday rotation into which light derived from the optical fiber is incident Attaching a child to the inclined surface, attaching a reflective member that reflects incident light from the Faraday rotator to the Faraday rotator with a light-transmitting thermoplastic resin in between, and the thermoplastic resin Heating and softening, adjusting the distance of the reflecting member to the optical fiber and the angle with respect to the optical axis, and fixing the position of the reflecting member by cooling and hardening the thermoplastic resin it is characterized in further comprising and.

Method for producing a Faraday rotation mirror of the present invention, it is possible to suppress variations in the position of the reflection member, it is possible to prevent deterioration of the insertion loss of the Faraday rotator mirror.

  First, a first embodiment of the present invention will be described with reference to FIG. The Faraday rotating mirror 100 includes an optical fiber 1 including a single mode fiber 1a, a graded index fiber 1b, and a coreless fiber 1c, a Faraday rotator 2, a reflecting mirror 3 (corresponding to a reflecting member), a magnet 4, an optical adhesive 5, A spacer member 6 is included.

  The single mode fiber 1a is for guiding light so that light incident from one end thereof is emitted from the other end. Examples of the material constituting the single mode fiber 1a include quartz glass and multicomponent glass.

  As shown in FIG. 2 (a), the graded index fiber 1b has a refractive index distribution in the optical fiber that has been lowered stepwise or continuously from the center toward the outer periphery. The transmitted light rays periodically meander (meander cycle) and pass as shown in FIG. Therefore, by cutting the graded index fiber 1b to an appropriate length, it functions as a lens that can cope with parallel light and focused light.

  FIG. 2B shows a state where the length of the graded index fiber 1b corresponds to one cycle of the sine curve, and this length is defined as one pitch. The graded index fiber 1b is set to have a length of 0.25 pitch to 0.5 pitch, which is a range in which light emitted from the graded index fiber 1b is focused light. FIG. 2B also shows the relationship between the length (GIF length) of the graded index fiber 1b and its optimum coupling distance. Here, the optimum coupling distance is a point at which the emitted light from the optical fiber 2 forms an image with the graded index fiber 1b and the distance to the end face of the graded index fiber 1b, and is reflected at this image forming point. When the mirror 3 is provided, the reflected light forms an image at the exit end of the optical fiber 2, so that the coupling with the maximum reflectance can be obtained.

  As the characteristics of the graded index fiber 1b, as shown in FIG. 3, the optimum coupling distance becomes shorter as the length of the graded index fiber 1b becomes longer. Here, in the case of 0.25 pitch, the optimum coupling distance is theoretically infinite, while in the case of 0.5 pitch, the optimum coupling distance is theoretically zero. When the difference between the optimum coupling distance and the thickness of the Faraday rotator 2 is small (for example, 300 μm or less), the coreless fiber 1c may be omitted. The optimum coupling distance in this embodiment is substantially equal to the sum of the length of the coreless fiber 1c, the thickness of the Faraday rotator 2, and the thickness of the spacer member 6. However, the thickness of the Faraday rotator 2 referred to here is not a physical thickness but a refractive index equivalent to that of the single mode fiber 1a, graded index fiber 1b, coreless fiber 1c, optical adhesive 5, and spacer member 6. Thickness indicating optical length, matched to 1.46. For example, in the case of bismuth-substituted garnet, the refractive index is 2.34, and the optical length is a value obtained by multiplying the physical length by 1.46 / 2.34.

Here, the Faraday rotator 2 is, for example, a bismuth-substituted garnet, and is set to have a thickness that rotates the polarization plane of light having a predetermined wavelength in saturation magnetic field strength by 45 °. The general thickness of the Faraday rotator 2 is 350 to 500 μm when the wavelength of light passing through the Faraday rotator 2 is 1550 nm. Further, it is preferable to provide an antireflection film on the surface of the Faraday rotator 2. Accordingly, the insertion loss value of the Faraday rotator mirror 1 00 is reduced, also, it is possible to suppress the occurrence of unnecessary reflection. Since the Faraday rotator 2 is a parallel plate, the Faraday rotation angle takes a constant value regardless of the place where the light beam passes. Therefore, the polarization direction of the backward light can always be perpendicular to the forward light of the Faraday rotating mirror 100.

  Further, the end face of the coreless fiber 1c is polished at a predetermined angle, and the Faraday rotator 2 is bonded and fixed thereto to prevent unnecessary reflection from recombining with the fiber. FIG. 4 shows the result of calculating the coupling efficiency when unnecessary reflection recombines with the optical fiber 1 with respect to the polishing angle of the end face of the coreless fiber 1c. As shown here, if the end face of the coreless fiber is polished at an angle of 2 ° or more, the coupling efficiency is less than −100 dB, so that unnecessary reflection is sufficiently suppressed.

  The magnet 4 is a member for applying a predetermined magnetic field to the Faraday rotator 2 and is cylindrical in this embodiment. If a self-biased Faraday rotator 2 is used as the Faraday rotator 2, it is not necessary to apply a magnetic field by the magnet 4.

The reflection mirror 3 (reflection member) is a member for reflecting incident light. For example, a glass substrate in which a dielectric multilayer film or a highly reflective metal (such as aluminum) is deposited on the surface, or the surface is mirror-polished. A metal plate, a dielectric multilayer film alone, or the like can be used. Here, as a material of the dielectric multilayer film, for example, TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , Si ₃ N ₄ are used as a high refractive index material, and SiO ₂ is used as a low refractive index material. The dielectric multilayer film is formed by alternately laminating dielectric films made of the high refractive index material and dielectric films made of the low refractive index material. When using these reflecting mirrors 3, for example, an optical adhesive is used to bond and fix the tip of the spacer member 6. Further, as shown in FIG. 10, after finishing one main surface of the spacer member 6 in a mirror shape, a dielectric multilayer film or a highly reflective metal (such as aluminum) is vapor-deposited on the main surface in the mirror surface state. Thus, the reflection mirror 3 may be formed directly on the spacer member 6. In this case, by reducing the member constituting the Faraday rotator mirror 1 00, it is possible to supply reliable products at a lower cost.

  The spacer member 6 supports the reflection mirror 3 and is preferably made of a material having a relatively high translucency (translucent material), and in particular, a thermoplastic resin having translucency is used as a material. Is preferred. This light-transmitting material is a material having a low loss of light (0.05 dB or less) so that there is substantially no problem at least in the wavelength band of light used (for example, 1550 nm). Examples of the thermoplastic resin include polycarbonate, fluororesin, styrene resin, and the like. Particularly, the refractive index is preferably equivalent to the core refractive index of the single mode fiber 1a, and generally about 1.47. The spacer member 6 is interposed between the Faraday rotator 2 and the reflection mirror 3, and is bonded and fixed using a translucent optical adhesive. In addition, when the reflective mirror 3 is directly formed on the surface of the spacer member 6 described above, no optical adhesive is required.

The spacer member 6 is also a member that has a function of adjusting the separation distance between the graded index fiber 1b and the reflection mirror 3 and the inclination angle of the reflection mirror 3 with respect to the optical axis. The adjustment by the spacer member 6 is performed while measuring the insertion loss value of the Faraday rotation mirror 100. Specifically, first, as shown in FIG. 6, the light source 15, the optical circulator 16, the light receiver 17, and the Faraday rotating mirror 100 for adjustment are connected. According to this optical system, the incident light from the light source 15 is incident on the light Faraday rotator mirror 100 via the optical circulator 16, the reflected light is received by the photodetector 1 7 via the optical circulator 16 again. Note that the Faraday rotator 2, the spacer member 6, and the reflection mirror 3 are previously fixed to the end of the coreless fiber 1 c of the Faraday rotation mirror 100 using an optical adhesive 5. Next, after the spacer member 6 is heated above its softening point to have fluidity, the position of the reflection mirror 3 is appropriately changed so that the reflected light intensity is optimal. Thereafter, heating of the spacer member 6 is interrupted, and the position of the reflection mirror 3 is fixed by cooling to a softening point or less.

  As described above, after the optical adjustment, the spacer member 6 is formed in a wedge shape. Therefore, if it is formed in a wedge shape before bonding to the Faraday rotator 2 in advance, the number of steps for optical adjustment can be reduced. It becomes. Further, when the spacer member 6 is heated with hot air or the like, the coating of the optical fiber 1 is also heated at the same time, causing problems such as deformation, but the reflecting mirror 3 is heated and the spacer member 6 is heated via this. This can be avoided.

  Further, when the reflection mirror 3 is directly applied to the spacer member 6 as shown in FIG. 5, the optical adhesive 5 is used only for the Faraday rotator 2 and the spacer member 6 on the end face of the coreless fiber 1 c of the Faraday rotation mirror 110. And fix it. Next, after the spacer member 6 is heated to a temperature higher than its softening point to make it flowable, a mirror-polished metal plate or the like is pressed against the spacer member 6 and the position of the metal plate is adjusted so that the reflected light intensity is optimal. Change as appropriate. Then, the heating of the spacer member 6 is interrupted and cooled below the softening point. Since the metal plate is not bonded and fixed to the spacer member 6, it can be peeled off after the spacer member is cooled, and the surface of the spacer member 6 can obtain a mirror surface state. Then, the reflective mirror 3 is formed by vapor-depositing a dielectric multilayer film or a metal with high reflectivity on the surface of the spacer member 6 in a mirror state.

If the reflecting surface of the reflecting mirror 3 is formed in a planar shape, the reflecting mirror 3 needs to be arranged perpendicular to the optical axis of the optical fiber 1 through which light propagates. FIG. 7 shows the relationship between the angle θ formed by the reflecting surface of the reflecting mirror 3 and the optical axis and the amount of change in the insertion loss of the Faraday rotating mirror 100. At this time, the reflecting mirror 3 is arranged at the optimum coupling distance of the outgoing light from the graded index fiber 1b, and the diameter of the beam waist at this time is 40 μm. According to FIG. 7, the reflecting mirror 3, the insertion loss of the Faraday rotator mirror 1 00 in accordance with the angle θ becomes larger increases, a loss of 1dB weak alone was 0.2 ° inclination.

  Next, the volume change rate generated after the optical adjustment of the spacer member 6 in the Faraday rotating mirror 100 according to the present invention and the optical adhesive 26 in the Faraday rotating mirror 200 according to the prior art will be verified. First, in the Faraday rotating mirror 200 according to the prior art, even if an optical adhesive 26 having a low curing shrinkage (for example, epoxy resin) is selected, the linear shrinkage is about 1.5%. Due to this contraction, the reflection mirror 23 changes in the arrangement angle, and the insertion loss characteristic of the Faraday rotation mirror 200 deteriorates.

On the other hand, when polycarbonate is selected as the material of the spacer member 6, the linear expansion coefficient is 7.0 × 10 ⁻⁶ (1 / ° C.) and the softening temperature is 135 ° C. In the case of cooling to room temperature (25 ° C.) after optical adjustment of 100, the temperature change is 110 ° C., and the linear shrinkage is 0.077%. In the Faraday rotating mirror 100 of the present invention, the spacer member 6 is fixed using an optical adhesive when it is interposed between the Faraday rotator 2 and the reflecting mirror 3, and the optical adhesive here is Faraday rotating mirror 100. Since the curing is performed before the optical adjustment operation of the rotating mirror 100, the curing shrinkage of the optical adhesive does not change the arrangement angle of the reflecting mirror 3.

  Next, when the contraction occurs, the amount of change in insertion loss of the Faraday rotation mirrors 100 and 200 is verified from the amount of change in the arrangement angle of the reflection mirrors 3 and 23.

  Here, with respect to the conventional Faraday rotating mirror 200 as shown in FIG. 11, since an optical adhesive is interposed between the core expanding fiber 21 and the Faraday rotator 22, the angle tolerance of the front end surface of the core expanding fiber 21, If the wedge angle tolerance of the Faraday rotator 22 is ± 1 °, the optical adhesive 25 is formed into a wedge shape having a maximum angle of 2 °.

  On the other hand, in the Faraday rotating mirror 100 according to the present invention, as described above, if the tip of the coreless fiber 1c is polished at 2 ° in order to suppress unnecessary reflection, the spacer member 6 is also formed into a 2 ° wedge shape. It will be.

Here, it is assumed that the optical adhesive 26 in the Faraday rotating mirror 200 according to the conventional technique and the spacer member 6 in the Faraday rotating mirror 100 according to the present invention have a wedge shape as shown in FIG. I think so. At this time, as shown in FIG. 8, the volume dv of the minute region is approximately expressed by dV = dx · dy · L (Expression 1). When the above shrinkage (the linear shrinkage rate is α%) occurs, the minute volume dV is expressed by dV = dx · dy · L · (1−α / 100) ³ (Formula 2). On the other hand, since the spacer member 6 is held up and down by the Faraday rotator 2 and the reflecting mirror 3, and the optical adhesive 26 is held up and down by the capillary 27 and the Faraday rotator 22, the area dx · Since it is considered that dy does not change, the L value is approximated as an L ′ value by L ′ = L · (1−α / 100) ³ (Equation 3) by the contraction. Therefore, if the wedge angle θ is changed by Δθ due to the contraction, Δθ is expressed as Δθ = 1− (1−α / 100) ³ (Equation 4).

In view of the above-described calculation formula, when the wedge angle is 2 °, if this is the optical adhesive 26, the linear shrinkage is 1.5%, and the angle change is 8.9 × 10 ⁻² °. If the spacer member 6 is used, the linear shrinkage rate is 0.077%, and the angle change is 4.6 × 10 ⁻³ degrees.

FIG. 9 shows the relationship between the change amount Δθ of the arrangement angle of the reflection mirror 3 and the insertion loss change amount of the Faraday rotation mirror 100. The reflecting mirror 3 is arranged at the optimum coupling distance of the outgoing light from the graded index fiber 1b, and the beam waist diameter at this time is 40 μm. As shown in FIG. 9, in the Faraday rotating mirror 100, the amount of insertion loss increases as the amount of change in the arrangement angle of the reflecting mirror 3 increases. The increase in insertion loss is −0.147 dB when the linear shrinkage rate is 1.5%, and the angle change when the linear shrinkage rate is 0.077% is −4.0 × 10 ⁻⁴ dB. .

  In this way, by arranging the spacer member 6 made of thermoplastic resin between the Faraday rotator 2 and the reflecting mirror 3, the insertion loss does not increase even when the spacer member 6 contracts during optical adjustment, and stable insertion is achieved. It becomes possible to provide the Faraday rotating mirror 100 having a loss value.

  Further, as described above, polycarbonate has been proposed as an example of the thermoplastic resin constituting the spacer member 6, but this polycarbonate is also superior in that the water absorption is very small compared to a general optical adhesive. Yes. In this respect, typical optical adhesives include epoxy resins and acrylic resins, and their water absorption is about several percent, whereas polycarbonate has a water absorption of about 0.25%. That is, since the volume change due to the swelling of the spacer member is small under high temperature and high humidity conditions, the angle change amount of the reflection mirror 3 and the change amount of the insertion loss can be reduced. Therefore, the Faraday rotating mirror 1 has high reliability even under high temperature and high humidity conditions.

  Examples of the present invention will be described below.

  As the Faraday rotary mirror 100 according to Example 1 of the present invention, the Faraday rotary mirror 100 shown in FIG. 1 was produced. A specific manufacturing method will be described below. First, a single mode fiber 1a having a light wavelength of 1550 nm, a graded index fiber 1b having a relative refractive index difference of 1.5% and a thickness of about 540 μm (0.35 pitch), a fiber length of about 64 μm, and pure The coreless fiber 1c made of quartz was fused and spliced while aligning the outer shape to produce the optical fiber 1.

  Next, the optical fiber 1 produced above was inserted into the fiber holding member 18 and fixed using an optical adhesive. The fiber holding member 18 is obtained by press-fitting a zirconia capillary 10 (φ1400 μm) into a stainless steel sleeve 11 and fixed so that the tip positions of the optical fiber 1 and the capillary 10 coincide. Next, the tip of the coreless fiber 1c was mirror-polished together with the capillary 10 at a processing angle of 2 °. Since the length of the coreless fiber 1c also changes during polishing, the processing was performed while confirming the presence or absence of an unpolished portion at the tip of the capillary 10, and the polishing was terminated when the unpolished portion disappeared. By this processing, the coreless fiber 1c is polished by 24 μm, and finally the length becomes 40 μm.

  Next, the Faraday rotator 2, the spacer member 6, and the reflection mirror 3 were fixed to the tip of the capillary 10 using an optical adhesive. The Faraday rotator 2 is set to a thickness of about 380 μm (physical thickness: optical length is 240 μm) so that the polarization direction of the incident light rotates 45 ° when the wavelength of the incident light is 1550 nm. At the same time, both ends of the Faraday rotator 2 were coated with an AR coating as an antireflection film.

  The spacer member 6 is made of polycarbonate, and a spacer member 6 which has been previously processed with a wedge angle of 2 ° is used. When the spacer member 6 is attached and fixed to the Faraday rotator 2, the capillary 10 is polished so that the mounting surface (reflection surface) of the reflection mirror 3 is substantially perpendicular to the optical axis of the optical fiber 1. The direction and the inclination direction of the spacer member 6 were visually matched.

The reflecting mirror 3 is formed by depositing a dielectric multilayer film in which TiO ₂ films and SiO ₂ films are alternately laminated on a glass flat plate made of BK7, and the dielectric multilayer film is applied. The thickness of each dielectric film was set assuming that an optical adhesive having a refractive index of about 1.5 was applied to the surface.

  Next, the Faraday rotation mirror 100 was connected to the optical system shown in FIG. 6, and the angle of the reflection mirror 3 was adjusted. At this time, the reflecting mirror 3 was fixed by a collet 19 as shown in FIG. The collet 19 is provided with a through hole, and holds the reflection mirror 3 by applying a negative pressure by a vacuum pump. On the other hand, the collet 19 is provided with a heater 20 and has a function of heating and softening the spacer member 6 via the collet 19 and the reflection mirror 3. The angle of the reflection mirror 3 is adjusted by adjusting the angle and position of the reflection mirror 3 so that the light receiving intensity by the light receiver 17 shown in FIG. Cooled down. At this time, the fixing of the reflecting mirror 3 by the collet 19 was continued. Thereafter, the ring-shaped magnet 4 was fixed with an adhesive, and the Faraday rotating mirror 100 was completed.

  Furthermore, the Faraday rotating mirror 110 shown in FIG. 10 was produced as the Faraday rotating mirror according to Example 2 of the present invention. With respect to the manufacturing operation, the configuration for fixing the Faraday rotator 2 and the spacer member 6 to the tip of the capillary 10 and the optical system for optical adjustment are the same as those in the first embodiment of the present invention. Only the configuration related to angle, position adjustment and fixation was changed as follows.

  First, as shown in FIG. 10, a stainless steel plate whose end face was mirror-polished on a collet 19 was held by applying a negative pressure with a vacuum pump, and the stainless steel plate was heated with a heater 20. Next, this stainless steel plate is pressed against the spacer member 6 attached to the Faraday rotator 2, and after the spacer member 6 is heated and softened, the received light intensity by the light receiver shown in FIG. 6 is maximized. The angle and position of the stainless steel plate were adjusted. Thereafter, the heating by the heater 20 was stopped while the stainless steel plate was in contact with the spacer member 6, and the spacer member was cooled to the softening temperature or lower.

  Next, the stainless steel plate was removed from the spacer member 6, and a dielectric multilayer film in which TiO2 and SiO2 were alternately laminated was deposited on the surface of the spacer member 6 from which the stainless steel plate was removed. Finally, the ring-shaped magnet 4 was fixed with an adhesive, and the Faraday rotating mirror 110 was completed.

Five Faraday rotating mirrors 100 and 110 according to Example 1 and Example 2 of the present invention were manufactured, and their insertion loss values were compared. The insertion loss value was measured using the optical system shown in FIG. In the measurement of the insertion loss value, the light source 15 having a wavelength of 1550 nm is used, the emitted light is incident on the first port of the optical circulator 16, and the Faraday rotating mirror 100 or the Faraday rotating mirror 110 is passed through the second port. , And the reflected light is again incident on the second port of the optical circulator 16, and the evaluation is performed by connecting the third port to the light receiver 17. The insertion loss is the ratio of the light emitted from the second port of the optical circulator 16 and the light reflected from the third port. First, the light emitted from the second port of the optical circulator 16 is directly connected to the light receiver. Then, the second port was connected to the Faraday rotating mirror 1, and the amount of reflected light from the third port was measured by the light receiver 17. A value obtained by subtracting the insertion loss of the circulator 16 measured in advance from the insertion loss measured by the light receiver 17 is the true insertion loss. The results are summarized in Table 1.

  As shown in Table 1, the Faraday rotatory mirrors 100 and 110 according to the first and second embodiments of the present invention were able to obtain a good insertion loss value with an insertion loss value of 0.5 dB or less.

Next, the Faraday rotating mirrors 100 and 110 according to Example 1 and Example 2 of the present invention were put in a high temperature and high humidity for a certain period, and the amount of change in the insertion loss value before and after that was confirmed. The test contents were in accordance with Tercordia GR-121-CORE, the atmospheric conditions were a temperature of 85 ° C., a humidity of 85%, and a charging period of 2000 hours. The results are summarized in Table 2.

  As shown here, the change amount of the insertion loss value was within 0.2 dB in both the Faraday rotating mirrors according to Example 1 and Example 2 of the present invention, and good results were obtained. In particular, with respect to Example 2 of the present invention, an excellent result was obtained that the change amount was within 0.1 dB. This is because the spacer member 6 and the optical adhesive are collectively formed by the dielectric multilayer film applied after optical adjustment. It is considered that the moisture resistance is improved as a result.

  As described above, the Faraday rotating mirror of the present invention has a smaller insertion loss value than the conventional Faraday rotating mirror and is more reliable under high temperature and high humidity conditions.

It is sectional drawing of the Faraday rotation mirror of this invention. The characteristic of a graded index fiber is shown, (a) is a figure which shows the refractive index distribution of a graded index fiber. (B) is an image figure of the light ray which permeate | transmits the graded index fiber 1b. It is a graph which shows the relationship between the length of a graded index fiber, and the optimal coupling distance. It is a graph which shows the relationship between the polishing angle of a coreless fiber, and a return loss. It is sectional drawing of the Faraday rotation mirror by other Example of this invention. It is the schematic which shows the optical system for performing the optical adjustment of a Faraday rotation mirror. It is a graph which shows the relationship between the arrangement | positioning angle of a reflective mirror, and the insertion loss value of a Faraday rotation mirror. It is a schematic diagram which shows the relationship between the volume change of a spacer member, and a wedge angle change. It is a graph which shows the relationship between the arrangement | positioning angle change amount of a reflective mirror, and the insertion loss increase amount of a Faraday rotation mirror. It is sectional drawing which shows the optical adjustment method of the Faraday rotary mirror by this invention. It is sectional drawing of the conventional Faraday rotation mirror.

Explanation of symbols

100, 110, 200: Faraday rotation mirror 1: Optical fiber 1a: Single mode fiber 1b: Graded index fiber 1c: Coreless fiber 2, 22: Faraday rotator 3, 23: Reflection mirror (reflection member)
4, 24: magnet 5,25: optical adhesive 6: spacer member 10, 27: capillary 11: Stainless steel sleeves
1 3: Core expansion fiber
21 a: Core
21 b: clad
1 5: light source 16: circulator 17: photoreceiver 18: fiber holding member 19: collet 20: Heater 21: core expanded fiber

Claims (3)

Preparing an optical fiber whose one end face is inclined with respect to the optical axis;
Attaching a flat plate-shaped Faraday rotator on which light derived from the optical fiber is incident to the inclined surface;
Attaching a reflection member that reflects incident light from the Faraday rotator to the Faraday rotator via a light-transmitting thermoplastic resin;
Heating and softening the thermoplastic resin, and adjusting the distance of the reflecting member to the optical fiber and the angle to the optical axis;
And a step of fixing the position of the reflecting member by cooling and curing the thermoplastic resin. 2. The method for producing a Faraday rotating mirror according to claim 1, wherein polycarbonate is used as the thermoplastic resin. 3. The optical fiber according to claim 1, wherein a coreless fiber is disposed at one end of the Faraday rotator side and a graded index fiber is bonded to the other end of the coreless fiber. The manufacturing method of the Faraday rotation mirror of description.

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