Patent Description:
As an optical fiber, for example, an optical fiber having a long length of several tens of kilometers such as a submarine cable is manufactured in response to a request from a user. The above-described optical fiber having the long length is usually formed by fusion-splicing a plurality of optical fibers. Here, it is required that peeling and cracking do not occur at an interface between a protective resin that protects a splicing portion and an original coating resin. For example, a technology disclosed in <CIT> and <CIT> is known as a technology satisfying the above-described requirement.

<CIT> refers to an apparatus and a method for making low-loss permanent optical fiber splices. In this course, a single laser is used as a heat source to activate droplets of acid applied to two optical fibers for selective stripping of fiber coating, for forming conical sections on the coating adjacent the exposed fiber for improved boding , and for fusing the fibers together in a splice.

<CIT> refers to a method of preparing an optical fiber for fusion splicing comprising the steps of of providing an optical fiber having a fiber jacket and an end, removing a predetermined bulk of the fiber jacket from an area adjacent the end while one of substantially simultaneously moving gas over the area and exhausting gas from the area.

Further documents are <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

A method for manufacturing an optical fiber according to the present disclosure includes: the features of claim <NUM> or claim <NUM>, further embodiments are disclosed in the dependent claims <NUM>, <NUM>, <NUM>, and <NUM>.

As a factor of an increase in loss of an optical fiber, there is an influence of side pressure at the time of bobbin winding, and in order to reduce the loss, it is required to form a coating layer of the optical fiber with a two-layer structure, and to use a resin having a low Young's modulus (soft resin) in a primary layer on the center side. In a submarine cable using the optical fiber having such a coating layer of the two-layer structure, a crack may occur in a protective resin of a splicing portion.

<FIG> is a diagram illustrating a configuration of a splicing portion of a related-art optical fiber having a coating layer of a two-layer structure. The splicing portion is a portion where optical fibers <NUM>, which are provided with a glass fiber <NUM> and the coating layer of the two-layer structure including a primary layer <NUM> on the center side around the glass fiber and a secondary layer <NUM> on the outer peripheral side, are spliced to each other. The coating layer is stripped at an end portion of each optical fiber <NUM>, and the exposed glass fibers <NUM> are fusion-spliced at a fusion-splicing portion <NUM>. <FIG> illustrates a case in which the coating layer is stripped in a tapered shape whose diameter is reduced toward the side of the fusion-splicing portion <NUM>, but only the secondary layer <NUM> is stripped in the tapered shape, and the primary layer <NUM> is not stripped in the tapered shape. A protective resin <NUM> is molded and recoated so as to cover the fusion-splicing portion <NUM> and the entire stripped portion of the coating layer.

As described above, in the splicing portion of the related-art optical fiber, the coating of the end portions of the short fibers is stripped and the fusion-splicing is performed, and the splicing portion is recoated with the protective resin <NUM>. Here, when the Young's modulus of the primary layer <NUM> of the optical fiber <NUM> is low, a deformation amount of the primary layer <NUM> at a coating stripping end becomes large when screening (an intensity test) is performed. Therefore, stress becomes maximum at a contact point between a boundary of the primary layer <NUM> and the secondary layer <NUM> and the protective resin <NUM>, such that distortion may occur in the protective resin <NUM> and thus a crack X may occur.

As a countermeasure for preventing the occurrence of the crack X in the protective resin, in order to disperse the stress at the contact point between the boundary of the primary layer <NUM> and the secondary layer <NUM> and the protective resin <NUM>, for example, as illustrated in <FIG>, it is desirable that a coating layer stripping end of a splicing end of the primary layer <NUM> and the secondary layer <NUM> is formed to become a tapered shape T. That is, it is desirable that the boundary of the primary layer <NUM> and the secondary layer <NUM> after the coating layer is stripped is formed as the tapered shape T having a predetermined angle.

However, a skill is required to cut a coating layer of a thin optical fiber with a razor to form the tapered shape as illustrated in <FIG>. Particularly, when the primary layer <NUM> is a soft resin, it is difficult to cut the primary layer <NUM> well. When the coating layer is stripped with a rotary tool such as a router, the soft primary layer <NUM> adheres to a grindstone, and thus it is difficult to strip the coating layer in a desired shape. Accordingly, when the coating layer is stripped by using the related-art tool, a variation in shape occurs even due to a skill difference, thereby causing a problem that the quality of manufactured cables is not constant. Also, there is a possibility that the tool may damage the glass fiber.

The present disclosure has been made in consideration of the above-described circumstances, and an object thereof is to provide a method for manufacturing an optical fiber and the optical fiber in which occurrence of a crack in a protective resin covering a stripped portion of a coating layer and an exposed portion of a glass fiber is prevented, and quality is stable without damaging the glass fiber.

According to the present disclosure, it is possible to obtain an optical fiber capable of preventing occurrence of a crack in a protective resin covering a stripped portion of a coating layer and an exposed portion of a glass fiber, and having stable quality without damaging the glass fiber.

First, an embodiment of the present disclosure will be listed and described.

According to the embodiment, not forming part of the present disclosure, by forming the tapered shape into the regular polygonal pyramid shape, it is possible to increase the intensity against a force in a twisting direction of the optical fiber. The regular polygonal pyramid shape can be obtained by striping the coating layer of the optical fiber by laser irradiation. In a related-art razor process, since an asymmetrical polygonal pyramid is formed, distortion caused by the twisting may be concentrated on a specific portion and thus the intensity may deteriorate. In a grindstone process, a polygonal pyramid shape cannot be realized.

Hereinafter, a specific example of a method for manufacturing of an optical fiber and the optical fiber according to the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following examples but is indicated by the scope of the claims, and is intended to include all the modifications within their scope, The present disclosure includes a combination of any embodiments as long as a plurality of embodiments can be combined with each other. In the following description, configurations denoted by the same reference signs are regarded as the same configurations even in different drawings, and the description thereof may be omitted.

<FIG> is a diagram illustrating a configuration of a splicing portion of an optical fiber to be manufactured according to the present disclosure. The optical fiber to be manufactured according to the present disclosure is formed by fusion-splicing a plurality of short optical fibers <NUM>. In the fusion-splicing of the optical fibers, glass fibers <NUM> are exposed by stripping coating layers of the optical fibers <NUM> at end portions of a pair of optical fibers <NUM> spliced to each other. End surfaces of the glass fibers <NUM> which are naked by stripping the coating layer are abutted against each other, and the abutted end surfaces are spliced to each other as a fusion-splicing portion <NUM> by arc discharge.

Since the fusion-splicing portion <NUM> and the naked glass fiber <NUM> in the vicinity thereof are easily damaged and mechanically in a weak state, the fusion-splicing portion <NUM> and the naked glass fiber <NUM> are recoated with a protective resin <NUM>. As the protective resin <NUM>, an ultraviolet curable resin which is the same type as that of the coating layer is used. The coating of the protective resin <NUM> can be formed by injecting a resin by using a predetermined molding die. In the embodiment, the coating layer of the optical fiber <NUM> has a double structure including a primary layer <NUM> on the center side and a secondary layer <NUM> on the outer peripheral side. In order to cause the primary layer <NUM> on the center side to be less likely to be affected by the side pressure at the time of bobbin winding or cabling which causes a loss increase of the optical fiber <NUM>, a resin having a low Young's modulus of <NUM> MPa or less is used for the primary layer <NUM>, and a resin having a higher Young's modulus than that of the primary layer <NUM> is used for the secondary layer <NUM> on the outer peripheral side. The magnitude of the Young's modulus of the protective resin <NUM> is greater than that of the resin of the primary layer <NUM>, and is smaller than that of the resin of the secondary layer <NUM>.

In the embodiment, when coating the coating layer at the end portion of the optical fiber <NUM>, a coating diameter is formed into a tapered shape T smaller toward the end portion side. The protective resin <NUM> is molded to cover the portion of the tapered coating layer. According to the configuration, an end surface of the coating edge of the coating layer is covered and is not exposed. Since the coating edge of the coating layer has the tapered shape T, an overlapping portion <NUM> covered with the protective resin <NUM> of the coating edge can be thickened, and an adhesive area at this portion is increased, thereby making it possible to improve an adhesive force with the protective resin <NUM>. It is possible to disperse stress at a contact point between a boundary of the primary layer <NUM> and the secondary layer <NUM> and the protective resin <NUM>.

The method for manufacturing the optical fiber illustrated in <FIG> includes a stripping step of partially stripping the coating layers of the two optical fibers <NUM> so that each of their coating edges forms the tapered shape; a splicing step of fusion-splicing exposed end surfaces of the glass fibers <NUM>; and a recoating step of recoating the protective resin <NUM> that covers a stripped portion of the coating layer and an exposed portion of the glass fiber <NUM>. Hereinafter, the stripping step of the coating layer of the optical fiber will be described.

<FIG> are diagrams illustrating an example of the stripping step of the coating layer of the optical fiber. First, as illustrated in <FIG>, the coating layer at the end portion of the optical fiber <NUM> is cut at a location of C-C, and the coating layer on the end portion side is pulled out and stripped, such that the glass fiber <NUM> on the end side is exposed. The exposed glass fiber <NUM> is cut so that a distance from the coating layer becomes a predetermined length to form an end surface for fusion-splicing. The end surface for fusion-splicing may be formed after forming a tapered surface of the coating layer which will be described later.

Next, as illustrated in <FIG>, the coating layer of the optical fiber <NUM> is irradiated with a triangular laser light B, and the end portion of the coating layer is processed to become a tapered shape. Specifically, the triangular laser light B having an apex angle α of approximately <NUM>° and a height of approximately <NUM> is scanned in a radial direction from an upper surface side of the optical fiber <NUM>. Here, as the laser light, it is desirable to use a laser having an energy density of <NUM> mJ/cm<NUM> or less and a wavelength of <NUM> or less. When the energy density of the laser light exceeds <NUM> mJ/cm<NUM>, the glass may be damaged and thus an optical characteristic and intensity may be affected when the glass is irradiated with the laser light. When the glass fiber is irradiated with an ultraviolet light whose laser light wavelength is shorter than <NUM>, the ultraviolet light is absorbed by the glass and defectiveness occurs, which affects the optical characteristic and the intensity, such that it is desirable to use laser light whose wavelength is equal to or more than <NUM>. A triangular shape can be obtained by arranging a mask including a triangular opening between a light source of the laser light and the optical fiber. A diameter of the optical fiber <NUM> is approximately <NUM>.

As illustrated in <FIG>, as a laser light scanning step, a base of the triangular laser light is caused to almost coincide with the end portion of the coating layer of the optical fiber <NUM>, and in a state where an apex is positioned on the side opposite to the end surface of the optical fiber, the coating layer is sublimated by scanning the laser light from the upper surface side of the optical fiber <NUM> in a radial direction indicated by an arrow S a predetermined number of times. Since a laser light irradiation surface of the optical fiber <NUM> has a large irradiation amount of the laser light at the base portion of the triangular shape, a resin amount to be stripped by sublimation is large, and since the laser light irradiation surface thereof has a small irradiation amount of the laser light at the apex portion thereof, the resin amount to be stripped by sublimation is small. Accordingly, the coating layer on the upper surface side of the optical fiber <NUM> is stripped in an almost tapered shape.

Next, as illustrated in <FIG>, as a position changing step, the optical fiber <NUM> is rotated by a predetermined angle as indicated by an arrow R, thereby changing a position of the laser light irradiation surface of the optical fiber <NUM>. Next, the triangular laser light B is scanned again from the upper surface side of the optical fiber <NUM>, thereby stripping the coating layer on the upper surface side of the optical fiber <NUM> in a tapered shape. The laser light scanning step and the position changing step are repeatedly performed a predetermined number of times, whereby the end portion of the coating layer of the optical fiber <NUM> can be stripped so as to have a polygonal pyramid shape. Next, the rotation angle of the optical fiber <NUM>, the energy density of the laser light, and the number of scans are adjusted, whereby the end portion of the coating layer can be formed in a regular polygonal pyramid shape symmetrical with respect to an axis of the optical fiber.

As a specific laser light, it is possible to use a short wavelength excimer laser using a mixed gas of KrF having a wavelength of <NUM> or ArF having a wavelength of <NUM> with the energy density of <NUM> mJ/cm<NUM> or less. When a laser light having a long wavelength is used, the resin of the coating layer melts or burns, such that the coating layer cannot be stripped in a good shape. When a laser light greater than <NUM> mJ/cm<NUM> is used, an optical damage of the glass fiber becomes large when the glass fiber is irradiated with the laser light. A tapered surface portion is post-cured by performing a taper process with laser irradiation, such that curing of the resin proceeds as compared to before the irradiation, and the Young's modulus of the surface of the coating layer processed into the tapered shape becomes greater than the Young's modulus of a portion of the coating layer located away from the surface and at the same radial direction position as the surface.

<FIG> are diagrams illustrating another example of the stripping step of the coating layer of the optical fiber. In the embodiment, as illustrated in <FIG>, the coating layer at the end portion of the optical fiber <NUM> is cut at the location of C-C, and the coating layer on the end portion side is pulled out and stripped, such that the glass fiber <NUM> on the end portion side is exposed. This is the same as the point illustrated in <FIG>.

Next, as illustrated in <FIG>, for example, when viewed from the upper surface side, the rectangular laser light B or the triangular laser light and the optical fiber <NUM> are positioned while avoiding fiber glass so that the laser light B is obliquely applied to only the coating layer at the end portion of the optical fiber <NUM>. Next, as illustrated in <FIG>, the laser light B is emitted while rotating the optical fiber <NUM>. As a result, the resin of the coating layer of the portion irradiated with the laser light B is stripped by sublimation, and a shape of the end portion of the coating layer becomes a conical tapered shape. Here, with respect to the type and energy density of the laser light, it is possible to use the same laser light as that of the first example of the stripping step described with reference to <FIG>.

<FIG> are diagrams illustrating still another example of the stripping step of the coating layer of the optical fiber. In the embodiment, as illustrated in <FIG>, the coating layer at the end portion of the optical fiber <NUM> is cut at the location of C-C, and the coating layer on the end portion side is pulled out and stripped, such that the glass fiber <NUM> on the end portion side is exposed. This is the same as the point illustrated in <FIG>.

Next, as illustrated in <FIG>, while the optical fiber <NUM> is rotated, a base of the triangular laser light B is caused to almost coincide with the end portion of the coating layer of the optical fiber <NUM>, and the laser light B is emitted from the upper surface side in a state where an apex is positioned on the side opposite to the end surface of the optical fiber. A shape, a type, and an energy density of the laser light are the same as those of the laser light B in the first example of the stripping step illustrated in <FIG>. Since a laser light irradiation surface of the optical fiber <NUM> has a large irradiation amount of the laser light at the base portion of the triangular shape, a resin amount to be stripped by sublimation is large, and since the laser light irradiation surface thereof has a small irradiation amount of the laser light at the apex portion, the resin amount to be stripped by sublimation is small. Since the laser light B is emitted while the optical fiber <NUM> is rotated, the end portion of the coating layer of the optical fiber <NUM> is stripped in an almost conical tapered shape as illustrated in <FIG>.

The embodiment is similar to the second example of the stripping step illustrated in <FIG>, and for example, when viewed from the upper surface side, the optical fiber <NUM> is irradiated with the rectangular laser light B while avoiding fiber glass so that the laser light B is obliquely applied to only the coating layer at the end portion of the optical fiber <NUM>. That is, a mask shape of the laser light is set so that a shape of the laser light B at a portion abutting on the coating layer of the optical fiber <NUM> becomes an uneven shape B1 as illustrated in <FIG>. Accordingly, due to the rotation of the optical fiber <NUM>, as illustrated in <FIG>, the coating layer processed into a tapered shape T' at the end portion of the optical fiber <NUM> is formed with unevenness extending on the circumference thereof. Therefore, when the protective resin is recoated after the glass fiber <NUM> is fusion-spliced, an adhesion area between the coating layer and the protective resin is increased, thereby making it possible to increase the intensity of the fusion-spliced optical fiber.

<FIG> is a diagram illustrating still another example of the stripping step of the coating layer of the optical fiber. In the embodiment, it is not required to perform the step of causing the glass fiber <NUM> on the end portion side to be exposed by cutting the coating layer at the end portion of the optical fiber <NUM> at the location of C-C and by pulling out and stripping the coating layer at the end portion side as shown in the first to fourth examples of the stripping step. In the embodiment, the coating layer in the vicinity of the end portion of the optical fiber <NUM> which is entirely covered with the coating layer is partially stripped by the method according to any one of the first to fourth examples of the stripping step. Accordingly, the coating layer at the location of C-C illustrated in <FIG> is stripped, and the glass fiber <NUM> becomes in a state of being exposed at this location. The tapered shape T is formed in the coating layer at a portion A2 on the opposite end portion side from the location of C-C of the optical fiber <NUM>.

Claim 1:
A method for manufacturing an optical fiber (<NUM>), the method comprising:
a step of partially stripping a coating layer of the optical fiber (<NUM>);
a step of fusion-splicing an end surface of a glass fiber (<NUM>) exposed by stripping the coating layer of the optical fiber (<NUM>); and
a step of recoating a protective resin (<NUM>) covering a stripped portion of the coating layer and an exposed portion of the glass fiber,
wherein the step of stripping is a step of irradiating the coating layer with a laser light to strip the coating layer,
wherein the step of stripping is a step of processing an end portion of the coating layer into a tapered shape whose diameter is reduced toward the exposed portion of the glass fiber (<NUM>),
characterized in that the step of stripping is a step of repeating: a step of arranging a mask that allows the laser light to pass through only a predetermined region between the optical fiber (<NUM>) and a light source of the laser light and scanning the mask in a direction perpendicular to an axial direction of the optical fiber and in a direction perpendicular to an irradiation direction of the laser light; and a step of rotating the optical fiber (<NUM>) about an axis of the optical fiber (<NUM>) to change an irradiation position of the laser light to the optical fiber (<NUM>),
wherein the predetermined region is a triangular, and
wherein the coating layer of the optical fiber (<NUM>) has a two-layer structure including a primary layer (<NUM>) on a center side and a secondary layer (<NUM>) on an outer periphery side.