JP6139070B2 - Method for manufacturing double-clad optical fiber, and method for manufacturing double-clad optical fiber - Google Patents

Description

The present invention relates to a method for producing a double-clad fiber-optic, and a method of manufacturing a double-clad optical fiber.

  Double clad optical fibers are used in the field of fiber lasers or fiber amplifiers.

  Patent Document 1 discloses a double-clad optical fiber in which a core to which a rare earth element is added is coated with a first cladding, and the first cladding is further coated with a second cladding. The core and the first cladding are formed of quartz. In addition, the one in which the second cladding is formed of an ultraviolet curable resin is disclosed.

  In Patent Documents 2 and 3, a double-clad optical fiber in which a core is coated with a first cladding, a first cladding is further coated with a second cladding, the core and the first cladding are formed of quartz, It is disclosed that the coating layer to be coated is composed of a plurality of layers, and among the coating layers, the second cladding layer is preferably formed of an ultraviolet curable resin.

JP 2011-60854 A JP 2010-250167 A JP 2010-250168 A

  In a double clad optical fiber used for a fiber laser or fiber amplifier, since a rare earth element is added to the core, it reacts with ultraviolet light irradiated at the time of drawing or the like, and the ultraviolet wavelength region and a wavelength close to 1 μm This is a core in which the transmission loss of the core increases in the wavelength region of excitation light such as 1.5 μm or the signal light and the transmission characteristics deteriorate, that is, the core is susceptible to ultraviolet deterioration.

  An object of the present invention is to obtain a double-clad optical fiber having excellent transmission characteristics by making it difficult for the core to undergo UV degradation.

The method for producing a double-clad optical fiber according to the present invention includes a core made by drawing a glass preform to coat a core to which a rare earth element is added and a quartz first clad having a refractive index lower than that of the core. And applying a liquid second clad material to the surface of the first clad formed in the first clad forming step and the core and the first clad forming step by using a pressurizing die to press and adhere to the surface. And a second cladding forming step of forming a second cladding having a refractive index lower than that of the first cladding, wherein the second cladding material is cured by crosslinking by hydrosilylation reaction. characterized in that it is a fluoroether polymer.

  The method of manufacturing the double-clad optical fiber of the present invention is thermally cured by attaching a liquid overcoat material to the surface of the double-clad optical fiber manufactured by the method of manufacturing a double-clad optical fiber of the present invention and heating it. An overcoat forming step is provided.

  According to the present invention, since the second clad is not made of an ultraviolet curable resin but is made of a thermosetting resin, it is difficult to cause ultraviolet deterioration during drawing, and as a result, a double clad optical fiber having excellent transmission characteristics can be obtained. Can be obtained.

It is a perspective view which shows the double clad optical fiber core wire which concerns on embodiment. (A)-(c) is explanatory drawing of the measuring method of the glass transition temperature of a 2nd clad material, and hardening start temperature. It is a figure which shows the fiber laser using the double clad optical fiber core wire which concerns on embodiment. It is explanatory drawing which shows the manufacturing method of the double clad optical fiber core wire which concerns on embodiment. (A) is explanatory drawing which shows the manufacturing method of the double clad optical fiber core wire using a pressurizing die, (b) is explanatory drawing which shows the manufacturing method of the double clad optical fiber core wire using an open die. . It is explanatory drawing which shows the modification of the 2nd heating furnace for forming overcoat. (A) And (b) is a graph which shows the relationship between each wavelength before and behind warm water immersion, and transmission loss. It is a graph which shows the relationship between the retention time to a high temperature atmosphere, and NA of a 1st clad. It is a graph which shows the relationship between the retention time to 85 degreeC and 85% high temperature, high humidity atmosphere, and NA of a 1st clad. It is a graph which shows the relationship between fiber length and NA of the 1st clad.

  FIG. 1 shows a double-clad optical fiber core wire 10 according to an embodiment. The double clad optical fiber core wire 10 according to this embodiment is used in applications such as a fiber laser or a fiber amplifier, for example.

  A double-clad optical fiber core wire 10 according to the embodiment is composed of a double-clad optical fiber 11 having a circular cross section and an overcoat 12 covering the same. The core wire diameter is, for example, 100 μm to 1000 μm.

  The double clad optical fiber 11 is coated with a core 11a to which a rare earth element having a circular cross section at the center of the fiber is added and a first clad 11b having a lower refractive index than the core 11a provided to cover the core 11a. The second clad 11c is lower in refractive index than the first clad 11b provided. The first clad 11b may have a circular cross-sectional shape. However, as will be described later, when excitation light is input to the first clad 11b, the excitation light becomes skew light that does not cross the core 11a. From the viewpoint of prevention, the cross-sectional shape is preferably a polygon or a non-geometric shape. The outer diameter of the second clad 11c of the double clad optical fiber 11 is, for example, 50 μm to 700 μm.

  The core 11a and the first cladding 11b are integrally formed of glass.

If the glass that forms the core 11a is a glass to which rare earth elements (Er, Yb, Nd, etc.) are added, for example, quartz glass (SiO ₂ ), a dopant that increases the refractive index, such as Ge, and a refraction, such as F, etc. Quartz to which a dopant for lowering the rate or other functionalizing dopant is added may be used. Note that the higher the concentration of the rare earth element added to the core 11a, the more easily the core 11a reacts with ultraviolet light, and the transmission loss of the core 11a increases in the ultraviolet wavelength region, resulting in a deterioration in transmission characteristics. The transmission loss of the core 11a increases in the wavelength region of excitation light or signal light having a wavelength close to 1 μm or 1.5 μm, or the transmission characteristics tend to deteriorate. Accordingly, examples of the concentration of the rare earth element added to the core 11a include 1 to 10% by mass.

  The core diameter is, for example, 5 μm to 100 μm. The refractive index of the core 11a is higher than the refractive index of the first cladding 11b, and the relative refractive index difference (Δ) between the core 11a and the first cladding 11b is, for example, 0.1 to 1%.

The glass forming the first cladding 11b may be pure quartz glass (SiO ₂ ), and is added with a dopant that lowers the refractive index such as F or a dopant that increases the refractive index such as Ge. It may be. The thickness of the first cladding 11b is, for example, 25 μm to 350 μm, and the diameter of the inscribed circle of the cross-sectional shape is, for example, 50 μm to 700 μm.

  The second cladding 11c is made of a thermosetting resin. In particular, the second clad 11c is greatly reduced in refractive index, and as a result, the first clad 11b having a high output NA (hereinafter also simply referred to as “NA”) can be obtained, and thus cured by cross-linking by a hydrosilylation reaction. It is preferable that the second cladding material containing the perfluoroether polymer is formed. The thickness of the second cladding 11c is, for example, 10 μm to 100 μm.

  The refractive index of the second cladding 11c is lower than the refractive index of the first cladding 11b, for example, 1.32 to 1.45. In this case, if the first cladding 11b is quartz, the NA of the first cladding 11b. Becomes 0.13 to 0.60 when measured at a fiber length of 2 m. In particular, in the double clad optical fiber 11 formed of the second clad material containing a perfluoroether polymer cured by cross-linking by hydrosilylation reaction, the second clad 11c has a low refractive index of 1.32 to 1.40. In this case, if the first clad 11b is quartz, the NA of the first clad 11b is 0.40 to 0.60 regardless of whether the fiber length is 2 m or the fiber length is 500 m. NA is measured by the FFP method described in JIS C6822.

  Hereinafter, the case where the second cladding material is used will be described in detail.

  The density of the second cladding material is, for example, 1.7 to 1.8. The density of the second cladding material is measured according to JIS K0061.

  The Young's modulus of the second cladding material is, for example, 0.5 to 50 MPa, and is preferably 1 to 10 MPa from the viewpoint of excellent buffering action against external force. The tensile strength of the second cladding material is, for example, 1 to 100 MPa, preferably 10 MPa or more from the viewpoint of excellent resistance to external force, and 70 MPa from the viewpoint of excellent followability to bending when the optical fiber 11 is bent. The following is preferred. The elongation at the time of cutting of the second cladding material is, for example, 5 to 100%, and is preferably 20% or more from the viewpoint of excellent followability to bending when the optical fiber 11 is bent, and is excellent in buffering action against external force. From the point, 70% or less is preferable. The Young's modulus of the second clad material is based on JIS K 6251, and the tensile strength at 2.5% when the second clad material formed into a film is pulled at a tensile speed of 1 mm / min is divided by the cross-sectional area. Is required. The tensile strength and elongation at break of the second clad material are measured according to JIS K 6251.

  The Shore A hardness of the second cladding material is, for example, 10 to 80, and is preferably 25 to 80 from the viewpoint of excellent resistance to external force. The Shore A hardness of the second cladding material is measured by a type A durometer described in JIS K 6253.

  The glass transition temperature (Tg) of the second cladding material is, for example, −150 to 0 ° C., and is preferably −150 to −50 ° C. from the stability of characteristics in the operating temperature range. The glass transition temperature (Tg) of the second cladding material is as follows using a rigid pendulum type physical property tester 20 (for example, model number: RPT-3000W, manufactured by A & D) as shown in FIG. It is measured by the procedure. The rigid pendulum type physical property tester 20 includes a sample boat 21 (for example, made of aluminum), in which a pipe edge 22 (for example, model number: RPN160 manufactured by A & D Co., Ltd.) is provided, from which a weight 23 is provided. (For example, model number: FRB100 manufactured by A & D Corporation) is hung and a pendulum is configured. Under a room temperature air atmosphere, a film of the second cladding material M1 having a thickness of about 100 μm is placed on the sample stage 21, and the sample boat 21 is heated from −100 ° C. to 150 ° C. at a rate of 10 ° C./min for a certain time Each time, the pendulum is vibrated and the vibration period is measured. When the viscoelasticity of the second cladding material M1 changes, the logarithmic attenuation rate changes. Therefore, as shown in FIG. 2B, the temperature at which the absolute value of the change rate of the logarithmic attenuation rate is maximized is obtained, The glass transition temperature is assumed. When Tg is present at −100 ° C. or lower, it can be obtained from a tan δ peak measured by a device capable of measuring −100 ° C. or lower or a dynamic viscoelasticity measuring device according to the same principle.

  The gel fraction of the second cladding material is, for example, 90 to 100%, and prevents changes in characteristics of the second cladding 11c caused by volatilization of low molecular weight components in a high temperature use environment or elution of low molecular weight components in a high humidity use environment. From this point, it is preferably 96 to 100%. The gel fraction of the second cladding material is measured by mass change during solvent extraction. Specifically, Soxhlet extraction is performed on the second cladding material at a circulation rate of about 10 times per hour for 5 hours using methyl ethyl ketone (boiling point) as a solvent, and the dry mass of the second cladding material after extraction is initially set. The value expressed as a percentage is taken as the gel fraction.

  The 90 ° peel force of the second clad material to the glass, which is an index of the adhesion of the second clad 11c to the first clad 11b, is preferably 10 N / m or more, and the second clad optical fiber 11 is bent when the second clad optical fiber 11 is bent. In view of maintaining the adhesion between the clad 11c and the first clad 11b, it is more preferably 20 N / m or more. The 90 ° peel force of the second clad material to the glass is such that the second clad material is applied on the glass substrate with a thickness of 100 to 200 μm and cured, and only the second clad material is strip-like at intervals of 2.5 cm in width. This can be obtained by making a cut, measuring the tension when one end of the strip is pulled up perpendicularly from the glass substrate at a pulling speed of 100 mm / min, and dividing the value by the width of the strip.

  The overcoat 12 is made of resin or rubber. Examples of the resin or rubber forming the overcoat 12 include a photocurable resin such as an ultraviolet curable resin, a thermoplastic resin such as a polyimide resin, a curable rubber such as a thermosetting resin, and silicone rubber. In addition, although rare earth element is added to the core 11a and it becomes the core 11a which is easy to produce ultraviolet deterioration, since the 2nd clad 11c formed as mentioned above exists, the overcoat 12 is ultraviolet curable resin. However, even when ultraviolet rays are irradiated when the overcoat 12 is formed, the ultraviolet rays are hardly deteriorated. Therefore, the resin forming the overcoat 12 may be an ultraviolet curable resin. However, in order to make it difficult for ultraviolet degradation to occur, it is preferable not to irradiate ultraviolet rays when the overcoat 12 is formed. In this respect, thermoplastic resins such as polyimide resins, thermosetting resins, curable rubbers such as silicone rubber, etc. Is preferred. In particular, in order to improve the heat dissipation from the double clad optical fiber 11, a silicone rubber excellent in thermal conductivity is preferable. Further, from the viewpoint of improving the wettability to the second cladding 11c, it is preferable that a small amount of fluorine is added to the resin forming the overcoat 12.

  The thickness of the overcoat 12 is, for example, 10 to 100 μm. The refractive index of the overcoat 12 is, for example, 1.4 to 1.57, and is preferably higher than the refractive index of the second cladding 11c from the viewpoint of suppressing the dissipation of the cladding mode light. The Young's modulus of the resin forming the overcoat 12 is, for example, 100 to 400 MPa, and is preferably higher than the Young's modulus of the second cladding material from the viewpoint of reducing the stress and transmission loss that occur during bending. The gel fraction of the resin forming the overcoat 12 is, for example, 80 to 100%, and is preferably lower than the gel fraction of the second cladding material. Further, by reducing the difference in shrinkage due to the dissipative low molecular weight component that occurs when dried after water absorption, the occurrence of floating between the overcoat 12 and the second cladding 11c is restricted, thereby reducing transmission loss. From the viewpoint of suppressing this, it is preferable that the difference in gel fraction between the resin forming the overcoat 12 and the second cladding material is smaller than 5%.

  According to the double clad optical fiber core wire 10 according to the above embodiment, the second clad 11c is formed of a thermosetting resin, preferably a thermosetting resin containing a perfluoroether polymer cured by cross-linking by a hydrosilylation reaction. Therefore, the second cladding 11c is greatly reduced in refractive index, and as a result, the first cladding 11b having a high NA can be obtained. Here, if the second clad 11c is a thermosetting resin containing a perfluoroether polymer cured by crosslinking by a hydrosilylation reaction, the bonding portion between the carbon atom and the silicon atom in the resin is hydrophobic, Excellent moisture resistance can be obtained. More preferably, the second clad 11c is a thermosetting resin containing a perfluoroether polymer cured by cross-linking by a hydrosilylation reaction, and when the resin contains an alkoxy group bonded to a silicon atom, The affinity between the clad 11c and the glass forming the first clad 11b is increased, resulting in high adhesion between them. As a result, more excellent moisture resistance can be obtained. Further, when the excitation light emitted from the light source is collected and incident on the first cladding 11b, the higher the NA, the larger the incident angle, so that the amount of excitation light that can be incident can be increased. Therefore, more excitation light can be confined in the first cladding 11b, and high oscillation efficiency can be obtained. Conventionally, as a double clad optical fiber capable of obtaining a high NA, there is a structure in which an air hole is formed in a clad. However, this has a difficult manufacturing technique and also screens non-defective products. Therefore, the yield is poor, and further, a support layer for reinforcement is required on the outer periphery of the optical fiber in order to form an air hole. Therefore, since the optical fiber diameter is increased, the allowable bending diameter is also large. However, there is no such demerit in the double clad optical fiber core wire 10 according to the present embodiment.

  Furthermore, the second clad 11c formed of a perfluoroether polymer cured by cross-linking by a hydrosilylation reaction is expected to have low temperature dependency of optical properties and excellent heat resistance, and therefore is used in a severe environment. Possibility and long life can be expected.

  FIG. 3 shows a fiber laser 30 as an example of a device using the double clad optical fiber core wire 10 according to the embodiment.

  The fiber laser 30 includes a fiber laser main body 31, an input side FBG 32 (Fiber Bragg Grating) is connected to an input end thereof, an output side FBG 33 is connected to an output end thereof, and an input end of the input side FBG 32 is also connected. The optical combiner 34 is connected to the optical head 35, and the output end of the output side FBG 33 is connected to the optical head 35 constituting the laser emission unit.

  The fiber length of the fiber laser main body 31 is, for example, 3 to 100 m.

  The input side FBG 32 is composed of a double clad optical fiber core wire in which a rare earth element is not added to the core and a diffraction grating 32a is formed. The input side FBG 32 is configured to reflect 98 to 100% of light (for example, light having a wavelength of 1085 nm) from the fiber laser main body 31 side by the core diffraction grating 32a. The fiber length of the input side FBG 32 is, for example, 0.3 to 10 m.

  The output side FBG 33 is also composed of a double clad optical fiber core wire in which a rare earth element is not added to the core and a diffraction grating 33a is formed. The output side FBG 33 is configured to reflect 5 to 15% of light (for example, light having a wavelength of 1085 nm) from the fiber laser main body 31 side by the core diffraction grating 33a. The fiber length of the output side FBG 33 is, for example, 0.3 to 10 m.

  In the optical combiner 34, a plurality of pigtail optical fibers 34a are bundled on the exit end side and fused and integrated. The number of pigtail optical fibers 34a is, for example, 2 to several tens of cores, and typical examples include 7 cores, 19 cores, and 37 cores. An excitation light source 36 is connected to each input end of the plurality of pigtail optical fibers 34a. The excitation light source 36 is configured by, for example, a semiconductor laser. The output of each excitation light source 36 is 5 to 500 W, for example.

  The fiber laser 30 is configured to transmit the laser light from each of the plurality of excitation light sources 36 via the pigtail optical fiber 34a and to input them together to the input side FBG 32. Further, the input side FBG 32 constituted by a double clad optical fiber core, the fiber laser main body 31 constituted by the double clad optical fiber core 10 according to the embodiment, and the output side FBG 33 constituted by a double clad optical fiber core. Then, laser light from each of the plurality of excitation light sources 36 is transmitted as multimode excitation light in the first cladding 11b, and the rare earth elements in the core 11a are excited when the multimode excitation light crosses the core 11a. Thus, an inversion distribution between the energy orders is formed, so that the single mode laser beam generated by the stimulated emission is transmitted through the core 11a. Then, the single mode laser beam transmitted through the core 11a is oscillated by being reflected by the diffraction gratings 32a and 33a of the input side FBG 32 and the output side FBG 33, and a part of the laser beam having a specific wavelength which is made high power by the oscillation. Is output from the optical head 35 through the output end of the output side FBG 33. The output of the fiber laser 30 is 10 to 200 W, for example.

  Here, for example, when the optical fiber diameter of the pigtail optical fiber 34a is 125 μm and the output NA is 0.15, when the number of the pigtail optical fibers 34a is 7 cores, the outer diameter of the optical fiber bundle is 375 μm, and when the optical fiber bundle is 19 cores When the optical fiber bundle has an outer diameter of 625 μm and 37 cores, the optical fiber bundle has an outer diameter of 875 μm. In order to connect this to the input end having an outer diameter of the input side FBG 32 of 250 μm, it is necessary to form the output end portion of the optical combiner 34 in a tapered shape such as a tapered shape. Is 0.225, 19 cores have an output NA of 0.375, and 37 cores have an output NA of 0.525. Therefore, the output NA increases as the number of pigtail optical fibers 34a increases. On the other hand, since the double clad optical fiber core 10 has a high NA, the laser light from the multi-core pigtail optical fiber 34a is input to the input side FBG 32 without leaking, and the double clad optical fiber core 10 Can be transmitted. Therefore, the fiber laser 30 can be coupled with many excitation light sources 36, and as a result, high-power laser light can be output.

  In the fiber laser 30, the pump light is input by the optical combiner 34. However, the present invention is not particularly limited to this, and the first cladding exposed by forming a V-groove or the like on the side surface of the input side FBG 32. The pumping light may be input to the first cladding, and the second cladding of the input side FBG 32 may be partially removed to fuse the pumping light input multimode optical fiber to the exposed first cladding. It is good also as a structure which inputs.

  Next, the manufacturing method of the double clad optical fiber core wire 10 concerning embodiment is demonstrated based on FIG. In the following, a case where the overcoat 12 is formed of a thermosetting rubber is taken as an example, but the present invention is not particularly limited thereto.

  First, a glass preform P for forming the core 11a and the first cladding 11b is produced. Examples of the method for producing the preform P include known methods such as a CVD method and a VAD method. The preform P is, for example, a cylindrical body having a length of 10 to 1000 mm and an outer diameter of 10 to 50 mm.

  Next, the preform P is set on the drawing machine 40.

  Here, the drawing machine 40 includes a spinning furnace 41 that heats the preform P, a second clad forming part 42 at the subsequent stage, and an overcoat forming part 43 at the subsequent stage. The second clad forming part 42 includes a first coating die 42a and a first heating furnace 42b. The overcoat forming part 43 is composed of a second coating die 43a and a second heating furnace 43b.

  Then, the wire drawing machine 40 is operated, and the core 11a and the first clad 11b are formed from the preform P in the spinning furnace 41. Subsequently, the core 11a and the first clad 11b are passed through the second clad forming part 42 to form the second clad 11c. Then, the double-clad optical fiber 11 is manufactured, and the double-clad optical fiber 11 according to the first embodiment is manufactured by passing the double-clad optical fiber 11 through the overcoat forming portion 43 to form the overcoat 12.

  At this time, in the spinning furnace 41, the preform P is heated and drawn to form the core 11a and the first cladding 11b (core and first cladding forming step). Here, the set temperature (drawing temperature) of the spinning furnace 41 is, for example, 2000 to 2300 ° C. The drawing speed is, for example, 1 to 100 m / min.

  In the second clad forming part 42, the drawn core 11a and the first clad 11b are passed through the first coating die 42a, and the liquid second clad material is adhered to the surface thereof with a uniform thickness, and then the first heating is performed. The second clad 11c is formed by thermosetting by passing through the furnace 42b and heating (second clad forming step).

  Here, as the first coating die 42a, as shown in FIG. 5A, a pressing die that pressurizes the second cladding material M1 and adheres to the surface of the first cladding 11b may be used. As shown in FIG. 5B, an open die for attaching the second cladding material M1 to the surface of the first cladding 11b without applying pressure may be used, but from the viewpoint of uniformly attaching the second cladding material M1. It is preferable to use the former pressure die.

  The second cladding material is a thermosetting resin and includes a C = C double bond and a perfluoroether polymer that is cured by cross-linking by SiH hydrosilylation reaction, and the C = C double bond and SiH are 1: It is preferable to include it in the ratio of 1.

  The second cladding material may be composed of a single component. The single-component second cladding material is composed of a perfluoroether polymer having at least one C═C double bond and at least one SiH in the molecule, and when heated, the C═C double between the molecules. The bond and SiH crosslink by hydrosilylation reaction.

  The second cladding material may be composed of a plurality of components. The multi-component second cladding material is composed of, for example, a perfluoroether polymer component having at least two C═C double bonds in the molecule and a fluorine-containing organosiloxane component having at least two SiH, and is heated. And a C = C double bond and SiH bridge | crosslink by hydrosilylation reaction between both components.

  The C═C double bond may be contained in the main chain, may be contained in the side chain, and may be further contained at the end of the main chain or the side chain. The C═C double bond is preferably introduced as an alkenyl group in the molecule. Examples of the alkenyl group include a vinyl group, a propenyl group, a styryl group, an isopropenyl group, a cyclopropenyl group, a butenyl group, a cyclobutenyl group, a cyclopentenyl group, a hexenyl group, and a cyclohexenyl group.

The SiH may be contained in the main chain, may be contained in the side chain, and may be further contained at the end of the main chain or the side chain. SiH is preferably introduced into the molecule as a repeating structure of siloxane bonds ((—SiH ₂ —O—) _n ). The number of repeating siloxane bonds (n) is, for example, 2-5.

  The second cladding material may contain only a single kind of perfluoroether polymer, or may contain a plurality of kinds of perfluoroether polymers.

  The second clad material may contain other polymer components as long as the high NA and excellent moisture resistance of the double clad optical fiber 11 are not impaired. Further, the second cladding material may contain a platinum-based catalyst or the like.

  The viscosity of the second cladding material is, for example, 0.5 to 50 Pa · s, and is preferably 1 to 10 Pa · s in that a coating film having a preferable thickness as the second cladding 11c can be obtained. The viscosity of the second cladding material is measured with a cone-plate rotational viscometer described in JIS Z 8803.

  The curing start temperature of the second cladding material is, for example, 70 to 150 ° C., and preferably 90 to 130 ° C. from the viewpoint of obtaining a pot life and processing speed that are preferable as the second cladding material. The curing start temperature of the second cladding material is the same as the glass transition temperature, using a rigid pendulum type physical property tester 20 (for example, model number: RPT-3000W manufactured by A & D) as shown in FIG. Measured by the following procedure. In an air atmosphere at room temperature, the second cladding material M1 is injected into the sample boat 21 to a depth of 0.5 mm, and the sample boat 21 is heated from room temperature to 200 ° C. at a rate of 10 ° C./min. Also, the vibration period is measured by applying vibration to the pendulum at regular intervals. When the second cladding material M1 is cross-linked and cured, the elasticity of the liquid is increased and the vibration period is shortened. Therefore, as shown in FIG. And the intersection of the linear part where the vibration period decreases is determined as the curing start temperature.

  In addition, the perfluoroether polymer contained in the second cladding material includes a SIFEL series manufactured by Shin-Etsu Chemical Co., Ltd. as a commercially available material.

  The in-furnace set temperature of the first heating furnace 42b is, for example, 100 to 500 ° C. The heat treatment time in the first heating furnace 42b is, for example, 0.05 to 0.5 seconds.

  In the overcoat forming portion 43, the double clad optical fiber 11 in which the first clad 11b is coated with the second clad 11c is passed through the second coating die 43a, and a liquid overcoat material is adhered to the surface thereof with a uniform thickness. Subsequently, it is cured by passing through the second heating furnace 43b to form the overcoat 12 (overcoat forming step).

  Here, as the second coating die 43a, as shown in FIG. 5A, a pressure die that adheres to the surface of the double clad optical fiber 11 while pressing the overcoat material M2 may be used. As shown in FIG. 5B, an open die that adheres to the surface of the double-clad optical fiber 11 without applying pressure to the overcoat material M2 may be used, but from the viewpoint of uniformly attaching the overcoat material M2, It is preferable to use the former pressure die.

  The second heating furnace 43b may be a single furnace. In this case, the set temperature in the furnace of the second heating furnace 43b is, for example, 100 to 500 ° C. The heat treatment time in the second heating furnace 43b is, for example, 0.05 to 0.5 seconds.

  Further, as shown in FIG. 6, the second heating furnace 43b may be composed of a pair of upstream heating furnace 431b and downstream heating furnace 432b, and double clad light when forming the overcoat 12 From the viewpoint of reducing the influence of heat on the fiber 11, the double-clad optical fiber 11 to which the liquid overcoat material is adhered is set to the upstream side heating furnace 431b and the furnace set temperature, which are set relatively high in the furnace. The overcoat material is preferably thermally cured by passing through a relatively low downstream heating furnace 432b in order. In this case, the upstream side heating furnace 431b and the downstream side heating furnace 432b may be provided continuously without any interval, and may be provided with an interval of, for example, 0 to 1000 mm. The time required for the double clad optical fiber 11 with the overcoat material attached to exit from the upstream heating furnace 431b and enter the downstream heating furnace 432b is, for example, 0 to 0.5 seconds. The in-furnace set temperature of the upstream heating furnace 431b is, for example, 100 to 500 ° C. The set temperature in the furnace of the downstream heating furnace 432b is, for example, 100 to 450 ° C. The in-furnace set temperature difference between the upstream heating furnace 431b and the downstream heating furnace 432b is preferably 50 to 200 ° C, more preferably 50 to 100 ° C.

  Examples of the overcoat material include uncured thermosetting silicone rubber. The viscosity of the overcoat material is, for example, 0.5 to 5 Pa · s. The curing start temperature of the overcoat material is, for example, 70 to 150 ° C.

[Test Evaluation 1]
(Double clad optical fiber)
<Invention Example>
A double-clad optical fiber core having the same configuration as that of the above-described embodiment was produced and used as an invention example.

  The core diameter of the double clad optical fiber core wire of the inventive example was 350 mm. The outer diameter of the second clad of the double clad optical fiber was 300 mm. The core diameter was 10 μm. The outer diameter of the first cladding was 200 μm.

  The core was formed of quartz to which ytterbium (Yb) and aluminum (Al) were added. The first cladding was made of quartz. The second cladding was formed of a perfluoroether polymer (curing start temperature 128 ° C.) cured by cross-linking by hydrosilylation reaction. The overcoat was formed of thermosetting silicone rubber (curing start temperature: 86 ° C.).

<Comparative Examples 1 and 2>
Two types of double-clad optical fiber cores having the same configuration except for the above-described invention example and the second clad were produced, and these were designated as comparative examples 1 and 2.

  In Comparative Examples 1 and 2, both of the second claddings are made of an ultraviolet curable fluorinated acrylate resin, but different ultraviolet curable fluorinated acrylate resins are used.

(Test evaluation method)
<Transmission loss>
About each of the invention example and the comparative example 1, 200 m was bundled, and based on JIS C 6823, the transmission loss when the wavelength was modulated and the signal light was transmitted was measured. Moreover, it was immersed in the warm water adjusted to 85 degreeC in a water bath for 2 days, and the transmission loss was measured similarly.

<NA>
For each of the inventive examples and comparative examples 1 and 2, the NA of the first cladding was measured by the FFP method described in JIS C 6822. Specifically, light enters from the red LED into the first clad of the double clad optical fiber through the lens, and the far field pattern (FFP) of the emitted light is measured, and the FFP profile is 5% of the maximum value. The value which becomes is NA. The NA measurement device used was the FFP measurement system LEPAS11 manufactured by Hamamatsu Photonics. A lens having a NA slightly larger than the NA of the first cladding of the double-clad optical fiber to be measured was used as the lens. The measurement of NA was performed for each of fiber lengths of 2 m and 500 m.

<Heat resistance>
Each of the fiber lengths 60 m of the inventive example and the comparative example 1 was held in a temperature atmosphere of 160 ° C. and 80 ° C., and the relationship between the elapsed days and the NA of the first cladding was determined. The NA measurement method is the same as described above.

  Note that the light intensity increases in the vicinity of the interface between the first clad made of glass and the second clad made of resin as the light with a higher NA component increases. However, if the second clad made of resin deteriorates, the light absorption increases and the second is increased. Due to the increase in scattering due to the peeling of the clad, the NA of the first clad becomes smaller due to the greater influence of the higher NA component light. Therefore, the degradation of the second cladding can be evaluated by measuring the NA of the first cladding.

<Heat and heat resistance>
The respective fiber lengths of 60 m of the inventive example and the comparative example 1 were held in a high-temperature and high-humidity atmosphere at 85 ° C. and 85%, and the relationship between the elapsed days and the first cladding NA was determined. The method for measuring the NA of the first cladding is the same as described above.

(Test evaluation results)
7A and 7B show the relationship between the wavelength and transmission loss before and after immersion in hot water.

  According to these, before immersion in warm water, although there is a local peak difference (for example, absorption peak due to OH in the wavelength 1400 nm band), the invention example and the comparative example 1 generally show the same level of transmission loss, It can be seen that after immersion in warm water, the change in transmission loss is extremely small in the inventive example, whereas the transmission loss is significantly increased in Comparative Example 1.

  Table 1 shows the NA of the first cladding.

  In the inventive example, the NA at a fiber length of 2 m was 0.59, and the NA at a fiber length of 500 m was 0.54. Comparative Example 1 has an NA of 0.46 at a fiber length of 2 m and NA of 0.45 at a fiber length of 500 m. Comparative Example 2 has an NA of 0.60 at a fiber length of 2 m and a fiber length of 500 m. NA was 0.24.

  From these results, in the inventive example, the first cladding 11b having a higher NA than Comparative Examples 1 and 2 can be obtained regardless of whether the fiber length is short (2 m) or long (500 m). It can be seen that this is preferable.

  FIG. 8 and Table 2 show the relationship between the retention days in a high temperature atmosphere and NA.

  In the invention example, the NA of the first cladding when held in a high temperature atmosphere of 160 ° C. is 0.57 at the initial stage (0 days elapsed), 0.55 after 7 days, 0.54 after 16 days, and after 23 days. 0.54, 0.51 after 37 days, and 0.50 after 101 days. In Comparative Example 1, the initial (elapsed days of 0 days) is 0.47, 7 days later is 0.43, and 14 days later is 0. The results were 0.33 after 38 and 28 days, and 0.13 after 92 days.

  In the invention example, the NA of the first cladding when kept in a high temperature atmosphere of 80 ° C. is 0.57 at the initial stage (0 days elapsed), 0.57 after 7 days, 0.57 after 14 days, and after 28 days. After 0.57 and 91 days, it was 0.57, and in Comparative Example 1, the initial value (0 days elapsed) was 0.47, after 8 days was 0.46, and after 71 days was 0.43.

  From these results, it can be seen that in the invention example in which the second clad is formed of a thermosetting resin, the decrease in NA of the first clad is small even when the holding time in the high temperature atmosphere is long. On the other hand, in Comparative Example 1 in which the second clad is formed of an ultraviolet curable resin, it can be seen that the NA of the first clad greatly decreases as the holding time in the high temperature atmosphere becomes longer. In Comparative Example 1, it is considered that the NA of the first cladding is reduced due to the increase in light absorption due to the deterioration of the second cladding due to heat and the increase in scattering due to the peeling of the second cladding.

  FIG. 9 and Table 3 show the relationship between the retention days in the high temperature and high humidity atmosphere and the NA of the first cladding.

  In the invention example, the NA of the first cladding when held in a high-temperature and high-humidity atmosphere at 85 ° C. and 85% is 0.57 at the initial stage (0 days elapsed), 0.57 after 7 days, and 0.1 after 14 days. 57, after 28 days is 0.57, after 35 days is 0.57, and after 99 days is 0.52, and in Comparative Example 1, the initial (0 days elapsed) is 0.47, and after 8 days is 0.45, It was 0.36 after 15 days and 0.36 after 70 days.

  From these results, it can be seen that in the invention example in which the second clad is formed of a thermosetting resin, the decrease in NA of the first clad is small even when the holding time in a high-temperature and high-humidity atmosphere becomes long. On the other hand, in Comparative Example 1 in which the second clad is formed of an ultraviolet curable resin, it can be seen that the NA of the first clad greatly decreases as the holding time in the high temperature and high humidity atmosphere becomes longer. In Comparative Example 1, it is considered that the NA of the first cladding is reduced by peeling the second cladding due to high temperature and high humidity.

[Test evaluation 2]
(Manufacture of double clad optical fiber core wire)
A double-clad optical fiber core having the same configuration as that of the inventive example of Test Evaluation 1 was produced by changing the overcoat heating conditions.

  Specifically, in condition 1, a pressure die is used as the first and second coating dies, the furnace set temperature of the first heating furnace is 300 ° C., the furnace set temperature of the second heating furnace is 400 ° C., and The drawing speed was 20 m / min.

  Condition 2 was the same as Condition 1 except that the set temperature in the second heating furnace was 450 ° C.

  Condition 3 was the same as Condition 1 except that the set temperature in the second heating furnace was 500 ° C.

  In condition 4, the second heating furnace is composed of an upstream heating furnace and a downstream heating furnace connected in series without any interval, and the former furnace set temperature is 400 ° C. and the latter furnace set temperature is 300. The condition was the same as condition 1 except that the temperature was changed to ° C.

(Test evaluation method)
The appearance of the double-clad optical fiber core wire produced under conditions 1 to 4 was visually observed, A: no appearance abnormality, B: appearance abnormality portion at a frequency of one in several meters, and C: appearance abnormality portion It was evaluated in a number of three stages.

  Further, the tackiness of the surface was evaluated in two stages, A: None and B: Existence, from the tactile sensation when grasped by hand.

  Further, the NA of the first cladding with a fiber length of 60 m was measured by the same method as in Test Evaluation 1.

(Test evaluation results)
Table 4 shows the test evaluation results.

  The appearance was B in condition 1 and A in conditions 2-4.

  The tackiness was B in condition 1 and A in conditions 2-4.

  Regarding the NA of the first cladding, it was 0.56 under condition 1, 0.20 under condition 2, 0.18 under condition 3, and 0.57 under condition 4.

  From these results, it can be seen that under conditions 2 and 3, the NA of the first cladding is reduced. In the conditions 2 and 3 where the in-furnace set temperature of the second heating furnace is set as high as 450 ° C. and 500 ° C., it is considered that the second clad has been altered by heat. On the other hand, it can be seen that, under condition 1, the NA of the first cladding is not reduced, but the appearance and tackiness are poor. It is considered that the overcoat was not completely cured under the condition 1 where the in-furnace set temperature of the second heating furnace was set as low as 400 ° C.

  On the other hand, in the condition 4 in which the second heating furnace is composed of an upstream heating furnace and a downstream heating furnace, the former furnace set temperature is 400 ° C. and the latter furnace set temperature is 300 ° C., A double-clad optical fiber core wire with no decrease in NA and excellent appearance and tackiness could be obtained.

[Test Evaluation 3]
(Manufacture of double clad optical fiber core wire)
A double-clad optical fiber core having the same configuration as that of the inventive example of Test Evaluation 1 is produced using a pressure die as the first coating die for forming the second cladding, and an open die as the first coating die. It was also produced using

(Test evaluation method)
For the double-clad optical fiber core wire obtained when a pressure die is used as the first coating die and when an open die is used, the length of the first clad is changed by the same method as in Test Evaluation 1 by varying the fiber length. NA was measured.

(Test evaluation results)
FIG. 10 and Table 5 show the relationship between the fiber length of the double-clad optical fiber and the NA of the first cladding obtained when a pressure die is used as the first coating die and when an open die is used. .

  The NA of the first cladding is 0.57 when the fiber length is 1 m, 0.56 when the fiber length is 8 m, 0.56 when 13 m, 0.56 when 23 m, and 0 when 33 m. 0.55 for .55 and 43 m, and 0.54 for 53 m, and when using an open die, the fiber length is 0.57 for 1 m, 0.56 for 2 m, and 0.52 for 7 m. , 0.46 at 17 m, 0.40 at 27 m, 0.38 at 37 m, 0.30 at 47 m, and 0.26 at 57 m.

  From this result, when the pressure die is used, the fiber length dependency of the NA of the first cladding is small, whereas when the open die is used, the fiber length dependency of the NA of the first cladding is large. It can be seen that the length decreases as the fiber length increases.

  In addition, when the He-Ne laser was incident on both the double-clad optical fiber cores, many bright spots were observed with the open die, and the part was magnified with a microscope. Then, it was found that light leaked from the portion where the outer diameter of the second clad fluctuated and became thin. On the other hand, such a bright point was not observed in the case of using a pressure die. Therefore, by using a pressure die, the outer diameter of the second cladding is stabilized, thereby suppressing light leakage, and as a result, the NA of the first cladding is less dependent on the fiber length, and in the length direction. It is thought to be stable.

The present invention is useful for a manufacturing method of the double-clad fiber-optic method of manufacturing the same, and a double-clad optical fiber.

DESCRIPTION OF SYMBOLS 10 Double clad optical fiber core 11 Double clad optical fiber 11a Core 11b 1st clad 11c 2nd clad 12 Overcoat 20 Rigid pendulum type physical property tester 21 Sample boat 22 Knife edge 23 Weight 30 Fiber laser 31 Fiber laser main body 32 Input side FBG
32a Diffraction grating 33 Output side FBG
33a Diffraction grating 34 Optical combiner 34a Pigtail optical fiber 35 Optical head 36 Excitation light source 40 Drawing machine 41 Spinning furnace 42 Second clad forming part 42a First coating die 42b First heating furnace 43 Overcoat forming part 43a Second coating die 43b Second heating furnace 431b Upstream heating furnace 432b Downstream heating furnace M1 Second clad forming material M2 Overcoat material P Preform

Claims (5)

Forming a core made of a rare earth element by drawing a preform made of glass, and forming a first clad made of quartz having a refractive index lower than that of the core, and a first clad forming step;
A liquid second clad material is pressurized and attached to the surface of the first clad formed in the core and the first clad formation step by using a pressure die, and the first clad is thermally cured by heating. A second cladding forming step of forming a second cladding having a lower refractive index;
A method of manufacturing a double clad optical fiber comprising:
The method for producing a double-clad optical fiber, wherein the second clad material is a perfluoroether polymer that is cured by crosslinking by a hydrosilylation reaction. In the manufacturing method of the double clad optical fiber according to claim 1 ,
In the second clad forming step, a method for producing a double clad optical fiber in which a furnace setting temperature of the heating furnace when heating the second clad material is 100 to 500 ° C. According to claim 1 or 2 double clad optical fiber having an overcoat formation step of thermally cured by heating to adhere the liquid overcoat material to the surface of the double-clad optical fiber prepared by the method described in Production method. In the manufacturing method of the double clad optical fiber core wire according to claim 3 ,
In the overcoat formation step, the double clad optical fiber to which the liquid overcoat material is adhered is heated in the upstream heating furnace in which the furnace set temperature is relatively high and in the downstream heating in which the furnace set temperature is relatively low. A method of manufacturing a double-clad optical fiber in which an overcoat material is thermally cured by sequentially passing through a furnace. In the manufacturing method of the double clad optical fiber core wire according to claim 3 or 4 ,
In the overcoat forming step, a double-clad optical fiber manufacturing method in which a liquid overcoat material is attached to the surface of the double-clad optical fiber using a pressure die that pressurizes the liquid overcoat material.

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