JP2006106795A - Coated optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber that is small in wavelength dispersion/birefringence and that facilitates mounting thereof. <P>SOLUTION: A primary coating 4 is applied on a core 2 and cladding 3. In the primary coating 4, heat/UV-curing silicone rubber with a low Young's modulus are used. The optical fiber 1, applied with the primary coating 4, is twisted at a twist rate, and a second coating 5 is applied thereon by an extrusion method. As the material of the second coating 5, heat/room temperature curing silicone rubbers, whose Young's modulus and rubber elasticity are higher than that of the primary coating 4, are used. The outside diameter of the mold for use in the extrusion method is set so as to be larger than the outside diameter of the optical fiber 1 applied with the primary coating 4, and the inside diameter becomes equal to the outside diameter of the optical fiber 1 applied with the primary coating 4, in a state where the silicone rubbers of the second coating 5 are cured and shrunk. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber used for communication and measurement, and more particularly to an optical fiber having a coating on an optical fiber.

  Optical fiber cores used for optical fiber cables are non-inductive, small diameter, light weight, superior in flexibility, low loss, wide band, etc. compared to conventional cable cores using copper. Yes. For this reason, development is progressing as a new communication transmission path and it is rapidly spreading. In addition, since optical fibers are not affected by lightning and radio noise, development of optical fiber applied sensors for measuring voltage, current, and magnetic field is also progressing.

  As an example of an optical fiber core wire used for such communication / measurement, a core wire using a single mode fiber in which the number of modes that can be transmitted at the wavelength used is one will be described with reference to FIG. That is, the optical fiber 1 is configured by forming a cladding 3 having a refractive index slightly smaller than that of the core 2 around the core 2 where light is actually propagated. Quartz is widely used as a material for the core 2 and the clad 3, but when a slight scratch occurs on the surface of the quartz, the scratch grows due to applied tension, temperature expansion and contraction, moisture penetration, and the like. It will eventually be destroyed.

  Therefore, the normal optical fiber 1 is constructed by applying a protective coating 1a around the clad 3 in the manufacturing process, thereby forming an optical fiber core wire and preventing the occurrence of scratches caused by contact with moisture or dust in the air. The improvement of the nature is aimed at. As the material of the protective coating 1a, a thermosetting or ultraviolet curable resin such as silicone rubber is used.

  By the way, in the single mode optical fiber as described above, wavelength dispersion and birefringence may occur due to thermal expansion of the protective coating 1a. In order to cope with this, twisting the optical fiber 1 is widely used. ing. This is because, when a specific twist is applied to the optical fiber 1, the chromatic dispersion becomes 0 and long-distance communication is possible. In addition, in a magnetic measuring device using the Faraday effect, birefringence can be reduced by twisting, and only the Faraday effect can be measured.

  When twisting is applied to the optical fiber 1 as described above, the twist is held by fixing both ends of the optical fiber 1 with connectors or by bonding and fixing both ends thereof.

  However, the optical fiber core configured as described above has the following problems. That is, when the optical fiber 1 is fixed to hold the twist, wavelength dispersion / birefringence occurs at the fixing portion. Further, the optical fiber 1 tends to bend locally with a small radius, which also causes birefringence. Furthermore, if the twisted optical fiber 1 is not mounted so as to always hold it by applying a pulling force, it may be tangled and broken.

  Further, the use of heat-curable or room-temperature curable silicone rubber as the material for the protective coating 1a has the following problems. That is, since the thermosetting silicone rubber needs to be cured at a high temperature, stress is applied to the optical fiber 1 due to shrinkage when the operating temperature is room temperature, and wavelength dispersion and birefringence occur. Also, room temperature curable silicone rubbers may also cause wavelength dispersion and birefringence due to shrinkage during curing.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and the object thereof can be implemented while accurately maintaining the twist of the optical fiber, and can prevent wavelength dispersion and birefringence. It is to provide an optical fiber core.

  In order to achieve the above object, the invention according to claim 1 is an optical fiber core coated with two or more layers, the inner diameter of the optical fiber coated with the first coating is cured and shrunk outside the optical fiber coated with the first coating. A second coating is provided so as to be equal to the outer diameter of the first coating.

  In the invention as described above, since the secondary coating that is equal to the outer diameter of the primary coating is applied by curing shrinkage, the stress applied to the optical fiber is reduced and the birefringence is reduced.

  According to a second aspect of the present invention, in the optical fiber core according to the first aspect, the material of the second coating has a higher Young's modulus than the material of the first coating.

  In the invention according to claim 2 as described above, since the secondary coating has a slightly higher Young's modulus than the primary coating, the twist of the optical fiber is stably maintained, and external force is absorbed by the softer primary coating, A hard secondary coating protects against damage such as delamination.

  The invention according to claim 3 is characterized in that in the optical fiber core coated with two or more layers, a gap is provided between at least one layer of the coating layer.

  In the invention according to claim 3 as described above, since the gap is provided between the coating layers, the difference in thermal expansion of the coating is absorbed in this gap, and the stress applied to the optical fiber is reduced, so that the birefringence is reduced. .

  The invention according to claim 4 is characterized in that the optical fiber is inserted into the tube.

  In the invention according to claim 4 as described above, since the optical fiber is inserted into the tube, the optical fiber is protected by the tube.

  As described above, according to the present invention, it is possible to provide an optical fiber that can be mounted in a state where the twist of the optical fiber is accurately maintained and that can prevent wavelength dispersion and birefringence.

  Embodiments of the present invention will be described below with reference to the drawings. The same members as those in the prior art shown in FIG. 1 are described with the same reference numerals.

(1) First Embodiment A first embodiment will be described below with reference to FIG.

(Constitution)
First, the configuration of the present embodiment will be described. That is, the primary coating 4 is applied on the optical fiber 1 composed of the core 2 and the clad 3. The primary coating 4 is made of a heat-curable or ultraviolet-curable silicone rubber having a low Young's modulus. Thus, the required twist rate is added to the optical fiber 1 to which the primary coating 4 is applied in advance, and the secondary coating 5 is applied by an extrusion method.

  As the material of the secondary coating 5, a thermosetting or room temperature curing type silicone rubber having a Young's modulus higher than that of the primary coating 4 and high rubber elasticity is used. In addition, the outer diameter of the mold used for the extrusion method is larger than the outer diameter of the optical fiber 1 to which the primary coating 4 is applied, and the inner diameter of the primary coating 4 is in a state where the silicone rubber of the secondary coating 5 is cured and contracted. It is set to be equal to the outer diameter of the applied optical fiber 1.

(Action / Effect)
The operations and effects of the present embodiment as described above are as follows. That is, since the secondary coating 5 has a slightly higher Young's modulus than the primary coating 4, it has a hardness that stably holds the twist, and damage such as coating peeling is effectively prevented. On the other hand, as the primary coating 4, a coating having a low Young's modulus is applied using a heat curable resin or an ultraviolet curable resin. Accordingly, the external force is absorbed by the soft primary coating 4 and the thermal expansion of the secondary coating is absorbed, so that the stress applied to the optical fiber when the temperature changes can be reduced.

  In particular, the outer diameter of the mold used for the extrusion method is such that the inner diameter of the secondary coating 5 becomes equal to the outer diameter of the optical fiber 1 with the primary coating 4 in a state where the silicone rubber of the secondary coating 5 is cured and shrunk. Therefore, it is possible to realize an optical fiber having no stress at room temperature, and it is possible to prevent the occurrence of wavelength dispersion and birefringence.

(2) Second Embodiment A second embodiment will be described below with reference to FIG.

(Constitution)
First, the configuration of the present embodiment will be described. That is, first, a twist is applied to the optical fiber 1 on which the primary coating 4 has been applied, and a secondary coating 5 is applied around the optical fiber 1 to fix the twist. A gap 7 is provided around the secondary coating 5, and a tertiary coating 6 that is harder than the secondary coating 5 is applied.

(Action / Effect)
The operations and effects of the present embodiment as described above are as follows. That is, since the gap 7 is provided between the secondary coating 5 and the tertiary coating 6, the optical fiber 1 side is not affected by the thermal expansion of the tertiary coating. For this reason, the tertiary coating 6 harder than the secondary coating 5 can be performed.

  Therefore, the Young's modulus of the primary coating can be lowered to minimize the stress applied to the optical fiber 1, and the secondary coating that affects the thermal expansion on the optical fiber 1 side is necessary to fix the twist. Further, the protection from external force is carried out by a harder tertiary coating, so that the prevention of the occurrence of wavelength dispersion and birefringence and the prevention of damage can be further ensured.

(3) Third Embodiment A third embodiment will be described below with reference to FIG.

(Constitution)
First, the configuration of the present embodiment will be described. That is, in this embodiment, the optical fiber 1 is inserted into the tube 8.

(Action / Effect)
The operations and effects of the present embodiment as described above are as follows. That is, in the present embodiment, since the optical fiber 1 is inserted into the tube 8, it is not necessary to consider the influence of thermal expansion due to the coating. Further, since the gap generated between the optical fiber 1 and the tube 8 serves as a buffer, the optical fiber 1 is protected. Therefore, it is possible to prevent the occurrence of wavelength dispersion and birefringence in the optical fiber 1 and the prevention of damage.

(4) Other Embodiments The present invention is not limited to the embodiment as described above, and the size, shape, material, quantity, and the like of each member can be changed as appropriate. For example, in the second embodiment, the torsion can be fixed by a fixing member such as a connector attached to both ends of the optical fiber 1, and the secondary coating can be omitted. It is also effective to use different materials for each coating layer or to provide an air gap 9a as shown in FIG.

(5) Reference example 1
Reference Example 1 will be described below with reference to FIG.

(Constitution)
First, the configuration of this reference example will be described. That is, in this reference example, first, the primary coating 4 is applied to the optical fiber 1 constituted by the core 2 and the clad 3. The secondary coating 5 is applied to the primary coating 4. The optical fiber 1 is provided at a position shifted from the center of the secondary coating 5 when viewed from the cross section of the secondary coating 5.

(Action / Effect)
The operations and effects of the present reference example as described above are as follows. That is, if the center of the secondary coating 5 and the optical fiber 1 coincide, a uniform compressive force is applied to the optical fiber 1 from all directions, and the resulting birefringence is minimized.

  However, in this reference example, since the center of the optical fiber 1 and the center of the secondary coating 5 are shifted, the above balance is lost and linear birefringence occurs. Therefore, it is possible to realize a simple high birefringence fiber by using this linear birefringence. For example, when using this reference example as a sensor in a coil shape, a straight line that cancels birefringence by bending Since birefringence is added, birefringence can be reduced.

  Further, if the cross-sectional shape of the optical fiber core in Reference Example 1 is not a rotating body, the same effect can be expected. For example, if the cross-sectional shape is an ellipse or a rectangular cross-section as shown in FIG. When producing a fiber coil to be used, a low birefringence optical fiber coil can be realized by controlling the amount of eccentricity so as to cancel out the occurrence of linear birefringence due to bending of the optical fiber.

(6) Reference example 2
Reference Example 2 will be described below with reference to FIG.

(Constitution)
First, the configuration of this reference example will be described. That is, in this reference example, a primary coating 4 of silicone rubber having a low Young's modulus is applied to the optical fiber 1, and a secondary coating 5 having a high Young's modulus is applied around the primary coating 4. . Further, a tertiary coating 9 made of a fluororesin is applied around the secondary coating 4.

(Action / Effect)
The operations and effects of the present reference example as described above are as follows. That is, in this reference example, since the tertiary coating 5 made of a fluororesin is applied, chemical resistance is improved and long-term use is possible. In particular, this is effective when used as the optical fiber 1 used for sensing in a high-pressure insulating device that frequently uses SF6 gas.

(7) Reference example 3
Reference Example 3 will be described below with reference to FIG.

(Constitution)
First, the configuration of this reference example will be described. That is, in this reference example, a guide 10 having a plurality of grooves and a cross-sectional cross section is used. The guide 10 is made of a rubber material by an extrusion method. The groove width formed in the guide 10 is formed within 20 times the finished outer diameter of the optical fiber 1. The optical fibers 1 are accommodated in the grooves of the guide 10, respectively, and the upper part thereof is sealed by mounting a lid 11.

(Action / Effect)
The operations and effects of the present reference example as described above are as follows. In other words, since the bending of the optical fiber 1 is constrained by the groove, kinks that occur when the optical fiber 1 is twisted can be suppressed. Accordingly, the optical fiber 1 can be mounted without causing chromatic dispersion or birefringence.

  Further, since the guide 10 is made of a rubber material by an extrusion method, the external force is absorbed and the optical fiber 1 is protected. Further, since the guide 10 made of rubber has flexibility, the degree of freedom of the arrangement shape of the optical fiber 1 is increased.

Further, the lid 11 prevents the fiber from jumping out of the groove of the guide 10.

(8) Reference example 4
Reference Example 4 will be described below with reference to FIG.

(Constitution)
First, the configuration of this reference example will be described. That is, in this reference example, a guide 14 provided with a V-shaped groove is used. The optical fiber 1 is installed and held in the groove of the guide 14.

(Action / Effect)
The operation and effect of this reference example as described above will be described below. That is, since the optical fiber 1 fits in the groove bottom of the guide 14 by its own weight and the bending is restricted, kinks generated when the optical fiber 1 is twisted are suppressed.

  In particular, if the optical fiber 1 is used where it is necessary to bend, even if tension is applied to the optical fiber 1, the tension is supported by the V-groove and separated into two orthogonal components (Fa, Fb). Birefringence is canceled out, and birefringence can be reduced.

(9) Reference Example 5
Reference Example 5 will be described below with reference to FIG. That is, the optical fiber is also used as various sensors. In particular, an optical fiber coil in which an optical fiber is wound many times is used as a sensor for detecting a magnetic field, an electric current, and a rotational motion. This reference example is an example of an optical fiber coil using the optical fiber core of Reference Example 3.

(Constitution)
First, the configuration of this reference example will be described. That is, the guide 11 is wound around the cylindrical winding frame 13, and the optical fiber 1 is wound along the groove therein. Since the guide 11 is wound obliquely so as to be shifted by one groove in one round, and further provided with a slight gap, an optical fiber when moving from the first round to the second round and from the second round to the third round. 1 steep bend is avoided. A lid 12 is attached to the guide 11 after the optical fiber 1 is wound.

(Action / Effect)
The operations and effects of the present reference example as described above are as follows. That is, the guide 11 is wound obliquely so as to be shifted by one groove per round, and further, by providing a slight gap, a sharp bend of the optical fiber 1 is avoided, so that birefringence occurs in the optical fiber coil. It becomes possible to suppress.

  Therefore, by using such an optical fiber coil for the sensor unit, errors due to birefringence can be reduced, and a highly accurate sensor can be realized.

(10) Reference example 6
Reference Example 6 will be described below with reference to FIG.

(Constitution)
First, the configuration of this reference example will be described below. That is, in this reference example, comb-shaped guides 11 are installed at several points around the winding frame 13. The optical fiber 1 is wound around the guide 11 along the groove, and a lid 12 is attached to each guide 11.

(Action / Effect)
The operations and effects of the present reference example as described above are as follows. That is, the guide 11 of the optical fiber 1 is not necessarily required for the entire circumference, and the effect can be sufficiently obtained even if the guide 11 is only partially held. In particular, when the guide 11 is partially attached as in this reference example, birefringence can be reduced when the friction between the optical fiber 1 and the guide 11 is large.

It is sectional drawing which shows 1st Embodiment of the optical fiber core wire of this invention. It is sectional drawing which shows 2nd Embodiment of the optical fiber core wire of this invention. It is a cross-sectional perspective view which shows 3rd Embodiment of the optical fiber core wire of this invention. It is sectional drawing which shows the reference example 1 of an optical fiber core wire. It is sectional drawing which shows the reference example of an optical fiber core wire. It is sectional drawing which shows other embodiment of the optical fiber core wire of this invention. It is sectional drawing which shows the reference example 2 of an optical fiber core wire. It is sectional drawing which shows the reference example 3 of an optical fiber core wire. It is sectional drawing which shows the reference example 4 of an optical fiber core wire. It is a perspective view which shows the reference example 5 of an optical fiber coil. It is a perspective view which shows the reference example 6 of an optical fiber coil. It is sectional drawing which shows an example of the conventional optical fiber core wire.

Explanation of symbols

1 ... optical fiber 1a ... protective coating 2 ... core 3 ... cladding 4 ... primary coating 5 ... secondary coating 6 ... tertiary coating 7 ... gap 8 .. Tube 9 ... Air gap 10 ... Coating 11 ... Guide 12 ... Lid 13 ... Reel

Claims (4)

In an optical fiber core coated with two or more layers,
An optical fiber core characterized in that a second coating is applied on the outer side of the optical fiber coated with the first coating so that the inner diameter thereof is equal to the outer diameter of the first coating in a cured and contracted state. line.   The optical fiber core according to claim 1, wherein the material of the second coating has a Young's modulus higher than that of the material of the first coating. In an optical fiber core coated with two or more layers,
An optical fiber core, wherein a gap is provided between at least one of the coating layers.   An optical fiber core, wherein an optical fiber is inserted into a tube.

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