阅读说明：本技术 光纤耦合器 (Optical fiber coupler ) 是由 高屋雅人 于 2018-05-28 设计创作，主要内容包括：提供一种能够抑制通过耦合部的光的偏振状态的变动的光纤耦合器。光纤耦合器包括：基板,其具有槽；耦合部,其插入所述槽,该耦合部是使多个光纤各自的中途部彼此接合在一起而成的；以及粘接剂,其将该耦合部粘接于所述基板。所述粘接剂的肖氏D硬度为10～35。通过将粘接剂的肖氏D硬度设定为10～35,能够抑制通过耦合部的光的偏振状态的变动。(Provided is an optical fiber coupler capable of suppressing variation in the polarization state of light passing through a coupling section. The optical fiber coupler includes: a base plate having a groove; a coupling portion inserted into the groove, the coupling portion being formed by joining respective intermediate portions of the plurality of optical fibers to each other; and an adhesive that bonds the coupling portion to the substrate. The Shore D hardness of the adhesive is 10-35. By setting the Shore D hardness of the adhesive to 10 to 35, the variation of the polarization state of light passing through the coupling part can be suppressed.)

1. An optical fiber coupler in which, in a fiber,

the optical fiber coupler includes:

a base plate having a groove;

a coupling portion inserted into the groove, the coupling portion being formed by joining respective intermediate portions of the plurality of optical fibers to each other; and

an adhesive that bonds the coupling portion to the substrate,

the Shore D hardness of the adhesive is 10-35.

2. The fiber optic coupler of claim 1,

the viscosity of the adhesive is 5000 mPas-15000 mPas.

3. The fiber optic coupler of claims 1 or 2,

when the azimuth angle of light passing through the coupling part is measured over time, the absolute value of the variation range of the azimuth angle with respect to the temperature change of 5 ℃ to 75 ℃ is 10 degrees or less.

Technical Field

The present invention relates to an optical fiber coupler for separating and coupling light between a plurality of optical fibers.

Background

In general, when manufacturing an optical fiber coupler, a coupling portion is formed by heating the middle portions of a plurality of optical fibers, melting the cladding of the optical fibers, and drawing and joining the middle portions. The coupling portion is inserted into, for example, a groove of the substrate, and fixed to the inside of the groove with an adhesive (see, for example, patent document 1).

According to patent document 1, when an adhesive having a tensile shear adhesive strength of 5Mpa or more is used, the amount of variation in the insertion loss of light passing through the optical fiber coupler can be suppressed.

Disclosure of Invention

Problems to be solved by the invention

However, the above-described optical fiber coupler does not consider elements other than the fluctuation amount of the insertion loss of light.

The optical fiber coupler according to the present invention is made in view of such a situation, and an object thereof is to suppress a variation in the polarization state of light passing through a coupling portion.

Means for solving the problems

The optical fiber coupler of the present invention comprises: a base plate having a groove; a coupling portion inserted into the groove, the coupling portion being formed by joining respective intermediate portions of the plurality of optical fibers to each other; and an adhesive that bonds the coupling portion to the substrate, the adhesive having a Shore D hardness of 10 to 35.

In the optical fiber coupler of the present invention, the viscosity of the adhesive is 5000 to 15000mPa · s.

In the optical fiber coupler of the present invention, when the azimuth angle of light passing through the coupling portion is measured over time, the absolute value of the variation range of the azimuth angle with respect to the temperature change of 5 to 75 ℃ is 10 degrees or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the optical fiber coupler of the present invention, the shore D hardness of the adhesive is set to 10 to 35, whereby the variation in the polarization state of light passing through the coupling portion can be suppressed.

Drawings

Fig. 1 is a sectional view schematically showing an optical fiber coupler.

Fig. 2 is a plan view schematically showing the substrate and the coupling portion.

FIG. 3 is a schematic sectional view taken along line III-III of FIG. 1.

Fig. 4 is a block diagram schematically showing a configuration for measuring the temperature dependence of the polarization state.

Fig. 5 is a diagram schematically showing a trajectory of an electric field vector projected on the XY plane when elliptically polarized light travels in the Z direction.

Fig. 6 is a graph showing the azimuth angle θ measured with the polarization measuring device over time.

Fig. 7 is a graph showing an ellipticity angle η measured with time by a polarization measuring instrument.

Fig. 8 is a graph showing a variation Δ θ of the azimuth angle θ with reference to the value at the measurement start time point.

Fig. 9 is a graph showing a variation Δ η of the ellipticity angle η with reference to a value at the measurement start time point.

Detailed Description

Hereinafter, the optical fiber coupler 1 according to the embodiment will be described with reference to the drawings. Fig. 1 is a cross-sectional view schematically showing the optical fiber coupler 1, fig. 2 is a plan view schematically showing the substrate 2 and the coupling section 13, and fig. 3 is a schematic cross-sectional view taken along line III-III shown in fig. 1.

The optical fiber coupler 1 includes a cylindrical substrate 2. The substrate 2 may be made of quartz, invar, kovar, or the like, and in the present embodiment, quartz is used. The substrate 2 is formed with a groove 2a along the longitudinal direction. The coupling portion 13 is inserted into the slot 2 a. The coupling section 13 is constituted by the 1 st optical fiber 11 and the 2 nd optical fiber 12. The 1 st optical fiber 11 has a core 11a, a cladding 11b covering the periphery of the core 11a, and a cladding 11c covering the periphery of the cladding 11 b. The 2 nd optical fiber 12 has a core 12a, a cladding 12b covering the periphery of the core 12a, and a cladding 12c covering the periphery of the cladding 12 b. After removing the coating 11c of the 1 st optical fiber 11 and the coating 12c of the 2 nd optical fiber 12, the respective claddings 11b, 12b are cleaned with ethanol or the like, and then the respective intermediate portions of the 1 st optical fiber 11 and the 2 nd optical fiber 12 are heated to melt the cladding 11b of the 1 st optical fiber 11 and the cladding 12b of the 2 nd optical fiber 12, and the respective intermediate portions are drawn and joined to form the coupling portion 13. The coupling section 13 may be formed of three or more optical fibers.

In the coupling portion 13, the ratio (branching ratio) of the amount of light passing through the 1 st optical fiber 11 to the amount of light passing through the 2 nd optical fiber 12 is a predetermined ratio. For example, when the branch ratio is set to 50: in case 50, 50% of the light quantity of the light introduced into the 1 st optical fiber 11 moves to the 2 nd optical fiber 12 through the coupling portion 13.

The adhesive 3 is provided at two positions of the groove 2 a. The adhesive 3 contains, for example, a visible light-curable resin material or an ultraviolet-curable resin material, and an epoxy-based resin material or an acrylate-based resin material. The adhesive 3 is disposed at both end portions of the groove 2 a.

The Shore D hardness of the cured adhesive 3 is, for example, 10 to 35, preferably 15 to 35. When the shore D hardness is less than 10, the adhesive 3 becomes too soft when the ambient temperature rises, and the coupling portion 13 is easily deformed. When the shore D hardness exceeds 35, strain tends to concentrate locally on the coupling portion 13, and strain tends to occur in the coupling portion 13. When the coupling portion 13 is strained, the polarization state of light passing through the coupling portion 13 is likely to change.

The viscosity of the adhesive 3 before curing is, for example, 5000 to 15000 mPas. When the viscosity is less than 5000mPa · s, the adhesive 3 excessively spreads in the groove 2a due to capillary phenomenon, and the area of the adhesive 3 adhering to the coupling portion 13 becomes excessively large. On the other hand, when the viscosity is higher than 15000mPa · s, the adhesive 3 is too hard to be applied to the coupling portion 13 in the groove 2 a.

The vicinity of both ends of the coupling portion 13, in other words, the portion of the coupling portion 13 branching into the 1 st optical fiber 11 and the 2 nd optical fiber 12, is disposed at both ends of the groove 2 a. As described above, the adhesive 3 is provided at each end of the groove 2 a. The adhesive 3 fixes the glass portions (the cladding 11b, 12b and the core 11a, 12a in which the 1 st optical fiber 11 and the 2 nd optical fiber 12 are not tapered near both ends of the coupling portion 13) of the 1 st optical fiber 11, the cladding 12c of the 2 nd optical fiber 12, and the 1 st optical fiber 11 and the 2 nd optical fiber 12 from which the cladding 11c, 12c are removed to the groove 2 a.

The coupling portion 13 and the substrate 2 are housed in a protective tube 5 made of a metal member, and are fixed to the protective tube 5 with an adhesive. The material of the protective cylinder 5 may be SUS, invar, kovar, or the like, and in the embodiment, SUS is used. Both ends of the protective tube 5 are sealed by sealing portions 6. The sealing portion 6 contains, for example, a silicone material. The 1 st optical fiber 11 and the 2 nd optical fiber 12 penetrate the sealing portion 6 and protrude outward.

By setting the shore D hardness of the cured adhesive 3 to 35 or less, it is possible to suppress the change in the polarization state of light passing through the coupling portion 13 with respect to a temperature change. Fig. 4 is a block diagram schematically showing a configuration for measuring the temperature dependence of the polarization state.

The optical fiber coupler 1 is provided to the heating/cooling device 20. The heating/cooling means 20 comprise peltier elements. A light source 21 is attached to one end of the 1 st optical fiber 11, and a power meter 22 is attached to the other end. The power meter 22 measures the amount of light passing through the coupling portion 13 of the 1 st optical fiber 11. The insertion loss of light with respect to temperature change can be measured with the power meter 22.

No member is attached to one end of the 2 nd optical fiber 12, and a polarization measuring instrument 23 is attached to the other end. The polarization measuring device 23 can use a free space type polarimeter "PAX 5710 series" manufactured by Thorlabs, and in the embodiment, "PAN 5710 IR-T" is used. The polarization measuring instrument 23 can measure the change in the polarization state of the light passing through the coupling unit 13 with respect to the temperature change.

Fig. 5 is a diagram schematically showing a trajectory of an electric field vector projected on the XY plane when elliptically polarized light travels in the Z direction. In fig. 5, the X-axis and the Y-axis are orthogonal. The Z axis is orthogonal to the X and Y axes and extends in a direction perpendicular to the plane of the paper. The light passing through the coupling portion 13 travels in an elliptically polarized manner. When light travels in the Z-axis direction, the locus of the electric field vector projected on the XY plane is an ellipse 30 as shown in fig. 5. An angle formed by the major axis 31 of the ellipse 30 and the X axis, that is, an azimuth angle is represented by θ. Let η be the ellipticity angle, which is the angle formed by the line segment 33 and the long axis 31, and the line segment 33 is a line segment connecting the intersection point of the ellipse 30 and the long axis 31 and the intersection point of the ellipse 30 and the short axis 32.

Fig. 6 is a graph showing the azimuth angle θ measured by the polarization measuring device 23 over time, and fig. 7 is a graph showing the ellipticity angle η measured by the polarization measuring device 23 over time. In fig. 6 and 7, graph 50 shows the measurement results for the optical fiber coupler 1 using the adhesive 3 having a shore D hardness of 90. Graph 51 shows the measurement results for the optical fiber coupler 1 using the adhesive 3 having a shore D hardness of 20. Graphs 52 and 53 show the measurement results for the optical fiber coupler 1 using the adhesive 3 having a shore D hardness of 32.

The temperature at the measurement start time point was 25 ℃. After the start of the measurement, the temperature of the heating/cooling device 20 was changed to 5 ℃ after 25 seconds, the temperature of the heating/cooling device 20 was changed to 75 ℃ after 300 seconds, and the temperature of the heating/cooling device 20 was changed to 25 ℃ after 500 seconds.

As shown in the graphs 50 in fig. 6 and 7, when the adhesive 3 having a shore D hardness of 90 is used, the azimuth angle θ and the ellipticity angle η greatly vary after the temperature is changed. On the other hand, as shown in graphs 51 to 53, when the adhesive 3 having a shore D hardness of 20 or 32 is used, the azimuth angle θ and the ellipticity angle η hardly change even after the temperature is changed.

The ranges of variation of the azimuth angle θ and the ellipticity angle η in the graphs 51 to 53 will be described. Fig. 8 is a graph showing a variation Δ θ of the azimuth angle θ with reference to the value at the measurement start time point. As shown in graph 51 in fig. 8, in the case of using adhesive 3 having a shore D hardness of 20, variation Δ θ was within a range of ± 1 degree. As shown in graphs 52 and 53 in fig. 8, the variation Δ θ is in the range of-2 to +3 degrees.

Fig. 9 is a graph showing a variation Δ η of the ellipticity angle η with reference to a value at the measurement start time point. As shown in a graph 51 in fig. 9, when the adhesive 3 having a shore D hardness of 20 is used, the variation Δ η is in the range of-4 to 2 degrees. As shown in graphs 52 and 53 in fig. 9, the variation Δ η is within a range of ± 4 degrees.

In this way, when the adhesive 3 having a shore D hardness of 35 or less is used, the azimuth angle θ and the ellipticity angle η hardly change. That is, the change in the polarization state of the light passing through the coupling portion 13 with respect to the temperature change can be suppressed.

By setting the viscosity of the adhesive 3 to 5000 to 15000mPa · s, the adhesive 3 can be prevented from adhering to unnecessary portions of the coupling portion 13, and the adhesive 3 can be smoothly applied to the coupling portion 13 in the groove 2 a. Therefore, the manufacturing operation of the optical fiber coupler 1 can be smoothly performed.

As a characteristic of the optical fiber coupler 1, the absolute value of the variation width of the azimuth angle θ and the ellipticity angle η is preferably 10 degrees or less, and more preferably 5 degrees or less. As described above, the absolute value of the fluctuation range of the azimuth angle θ is 3 degrees or less, and the absolute value of the fluctuation range of the ellipticity angle η is 4 degrees or less.

The optical fiber coupler 1 can be used for an optical interferometer requiring stability of polarization characteristics, for example, can be used for a device using oct (optical Coherence tomography). Typically, a polarization controller is provided in the device. In the case of using the device, the polarization controller is operated to adjust the polarization depending on the temperature of the environment in which the device is placed. In the case of manually driving the polarization controller, the user needs to perform an operation, but the user may forget the operation. Conventionally, when a user does not operate the polarization controller to adjust the polarization despite a large change in temperature, the polarization state of the optical fiber coupler 1 changes, and thus the device may be used disadvantageously.

In the case of the optical fiber coupler 1 of the embodiment, since the absolute values of the variation widths of the azimuth angle θ and the ellipticity angle η with respect to the temperature change are 10 degrees or less, it is only necessary to perform the polarization adjustment once, and it is not necessary to perform the adjustment again due to the polarization change caused by the temperature change, and the convenience of the user can be improved.

Even if the temperature is changed within the range of 5 ℃ to 75 ℃, the absolute value of the variation range of the azimuth angle theta and the ellipticity angle eta is 10 degrees or less. That is, the change in the polarization state can be suppressed at an ambient temperature assumed to be used in general.

The optical fiber used in the present invention is generally selected to transmit light in a single mode in a wavelength band of 440nm to 2200nm, and the optical fiber is selected to have a cladding diameter of 125 μm and a cladding diameter of 250 μm. In the embodiment, as an example of the optical fiber, HI780 manufactured by corning is used.

The presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The technical features described in the embodiments can be combined with each other, and the scope of the present invention includes all modifications within the claims and the scope equivalent to the claims.

Description of the reference numerals

1. A fiber coupler; 2. a substrate; 2a, a groove; 3. an adhesive; 11. 1 st optical fiber; 12. a 2 nd optical fiber; 13. coupling part