JP4555760B2 - Filler composition and method for producing hole assist fiber using the same - Google Patents

Description

  The present invention relates to a filler composition for filling holes in a hole assist fiber, which is a kind of optical fiber having holes therein, and more specifically, after the holes present in the cladding of the hole assist fiber are cured. The present invention relates to a filler composition that can be filled so that the refractive index is close to the refractive index of the clad without exceeding the refractive index of the clad, and a method for producing a hole assist fiber using the filler composition and the hole assist fiber.

  In order to construct an optical communication network using optical fibers, it has been pointed out that conventional optical fibers in which a waveguide called a core is formed by adding an additive to silica glass have limitations on optical characteristics. On the other hand, in recent years, an optical fiber having a new structure having pores inside has attracted attention.

  The optical fiber having the above-described new structure has a plurality of tubular holes extending in the axial direction of the optical fiber in the core part and / or the cladding part, and when the optical fiber is cut, a number of holes appear in the cross section. However, it can be divided into several types according to the size, number, spacing, arrangement, etc. of the holes. A hole assist fiber, which is a kind of such an optical fiber, has a refractive index difference between the core and the clad, and is provided with several holes near the core of the clad. It is known that it can exhibit characteristics that cannot be obtained with optical fibers. Typically, it has a relatively small number of, for example, four or more, holes, which are line-symmetric with respect to the central axis of the core and equally spaced. Such hole assist fibers are particularly popular because they can reduce bending loss. In addition, since the optical fiber of the above-mentioned structure does not necessarily have a uniform name, several names are used. To point out some examples of such names, there are, for example, hole-assisted optical fibers, hole-added optical fibers, hole-added holey fibers, and the like.

  When connecting the hole assist fiber, it is necessary to consider the mode shape of the light propagation mode in order to reduce loss. In the hole assist fiber, it is known that the mode shape takes a hexagonal shape by avoiding the holes when six holes are arranged due to the influence of the refractive index due to the presence of the holes in the cladding. Yes. When connecting an optical fiber, it is desirable to match the hexagonal mode shape on the connection surface in order to reduce loss. For this purpose, the mode shape of the optical fiber is detected, and the deviation of the mode shape is eliminated. Thus, an extremely time-consuming process of connecting optical fibers is required, and when such a time cannot be taken, it is impossible to reduce the loss without omitting the construction. As described above, the hole assist fiber has a problem of peculiar end face processing.

  In addition, it is necessary to optically polish the end face for connection, but if abrasive grains or polishing debris used at the time of polishing enter the pores, not only the optical characteristics of the optical fiber are deteriorated, but also in use In some cases, polishing dust or the like may be ejected from the holes, thereby degrading the transmission characteristics. Also, when a fiber is cut, since there are holes, unlike a normal optical fiber, cracks may be generated from the holes at the time of cutting.

  Therefore, as a filler composition, it is necessary for an optical fiber, such as good filling ability to pores, heat resistance in consideration of heat generation during polishing, and good end surface polishing workability. It is also required to be an optical resin that ensures properties.

  Examples of the optical resin include an adhesive composition for an optical fiber connector (for example, refer to Patent Document 1), an epoxy-based fluorine compound and a specific alicyclic epoxy group-containing compound, a specific linear aliphatic epoxy resin, and the like. An ultraviolet curable epoxy resin composition containing a linear fluorinated epoxy resin (for example, see Patent Document 2), an optical waveguide resin containing an epoxy resin and a compound having an oxetane ring (for example, Patent Document 3) See). However, these compositions generally have a refractive index of 1.45 or more, which is not lower than the refractive index of the silica-based glass that is the cladding material.

JP 2003-96424 A JP 2004-339246 A JP 2000-356720 A

  As a filler for the holes in the end face of the hole assist fiber, it is desirable to fill the holes in the clad so that the mode shape is circular on the end face. This is because, in this case, a mode shape deviation does not occur on the connection surface, and it is needless to say that it is advantageous in connection with a single mode optical fiber (mode shape is circular). . For that purpose, it is desirable to match the refractive index of the filler with that of the cladding, and even if it does not match, it is desirable to be as close to the refractive index of the cladding as possible, and to prevent light leakage, the cladding The refractive index of the filler should not be greater than the refractive index.

  Therefore, the present invention provides a filler characteristic necessary to solve the connection problem peculiar to the hole assist fiber, which is close to the refractive index of the cladding material and does not exceed the refractive index of the cladding material. It is an object to provide a filler that satisfies all of viscosity, heat resistance, fillability, polishing processability, and adhesive strength above a required level.

The present invention is a composition for filling the holes of the hole assist fiber, which is an optical fiber having holes in the cladding, and (A) a compound represented by the following general formula (I),
(B) a compound represented by the following general formula (II),
(C) Monofunctional or bifunctional aliphatic chain acrylate compound, alicyclic acrylate compound, aliphatic chain glycidyl compound, alicyclic glycidyl compound, aliphatic chain oxetane compound and alicyclic oxetane compound At least one compound selected from the group, and
(D) A filler composition containing a photopolymerization initiator and having a refractive index after curing of 0.94 to 1.0 times the refractive index of the cladding.
_{Tf1- (O) a - (CH} 2) b - (CF 2) m - (CH 2) b - (O) a -Tf1 (I)
_{Tf2- (O) a - (CH} 2) b - (CF 2) m - (CH 2) b - (O) a -Tf2 (II)
In formula (I) and formula (II), a plurality of a are the same and represent 0 or 1, a plurality of b are the same and represent 0 or 1, and m is an integer of 4 to 12, respectively. Tf1 represents a glycidyl group, and Tf2 represents CH ₂ ═CH—C (O) —.

  The present invention also includes a step of filling the filler composition into the holes in the end face of a hole assist fiber having holes in the cladding, and a step of irradiating the filled filler composition with ultraviolet rays. This is a method of sealing fiber holes.

  The present invention further includes the step of filling the filler composition into the holes in the end face of the hole assist fiber having holes in the cladding, the step of irradiating the filled filler composition with ultraviolet rays, and the ultraviolet rays. It is a manufacturing method of the hole assist fiber by which the end surface including the process of grind | polishing the said end surface after passing through an irradiation process was grind | polished.

  In the said sealing method and manufacturing method, Preferably, after the ultraviolet irradiation process, you may have the process of thermosetting further.

The present invention further provides a portion in the longitudinal direction of the end face of the hole-assisted fiber with voids in the cladding is filled with filler composition described above to the air hole above the holes coincides with the axial direction of the optical fiber Is also a hole assist fiber that is blocked.

As described below, the present invention is close to the refractive index of the clad material and does not exceed the refractive index of the clad material, and the low viscosity, heat resistance, filling property, polishing workability, and adhesive strength are all higher than necessary. The holes of the hole assist fiber can be filled.
(1) The filler composition of the present invention can achieve a refractive index close to that of quartz glass without exceeding the refractive index of quartz glass by the above-described configuration.
(2) The filler composition of the present invention has a viscosity of 3 to 500 mPa · s at 25 ° C. and excellent filling properties due to the above-described configuration.
(3) The filler composition of the present invention achieves a Tg of the cured product of 70 to 150 ° C. and an adhesive strength of 4.0 N / mm ² or more with the above-described configuration, and has a filling processability, polishing processability, and heat resistance. Excellent in properties.
(4) The hole sealing method of the present invention ensures heat resistance and polishing processability with a refractive index lower than the refractive index of the clad material and with a refractive index close to that of quartz glass. However, the holes of the hole assist fiber can be blocked.
(5) The manufacturing method of the present invention is a hole assist fiber having a polished end surface in which the pores in the end surface are filled with the filler composition and foreign matter such as polishing debris is prevented from entering the pores by the above-described configuration. Can be realized.
(6) The optical fiber of the present invention is a hole assist fiber having a polished end face in which the holes in the end face are filled with the filler composition and the entry of foreign matters such as polishing dust into the holes is prevented by the above-described configuration. is there.
Hereinafter, the present invention will be described in detail.

  The filler composition of the present invention comprises a compound (A) represented by the above general formula (I), a compound (B) represented by the above general formula (II), a monofunctional or bifunctional aliphatic chain acrylate compound , An alicyclic acrylate compound, an aliphatic chain glycidyl compound, an alicyclic glycidyl compound, an aliphatic chain oxetane compound, and an alicyclic oxetane compound (C), and Contains a photopolymerization initiator (D). In the said general formula (I) and general formula (II), several a is the same and represents 0 or 1. Several b is the same and represents 0 or 1. Among these, a is 0, a is 1, and in each of these cases, b is 0 and b is 1. Needless to say, a, b and m in the formula (I) and a, b and m in the formula (II) are independent of each other.

Specific examples of the compound (A), if illustrate only structure excluding Tf1 both _{ends, - (CF 2) m -} , - (CH 2) - (CF 2) m - (CH 2) -, - _{O- (CF 2) m -O -} , - O- (CH 2) - a _(CH 2) -O- such as - _(CF 2) m. m represents an integer of 4 to 12, preferably 6 to 10.

As a specific example of the compound (B), if only the structure excluding Tf2 at both ends is illustrated, — (CF ₂ ) _m —, — (CH ₂ ) — (CF ₂ ) _m — (CH ₂ ) —, — _{O- (CF 2) m -O -} , - O- (CH 2) - a _(CH 2) -O- such as - _(CF 2) m. m represents an integer of 4 to 12, preferably 6 to 10.

  Among these, those in which a is 1 are preferable from the viewpoint of polymerization rate. In the filler composition of the present invention, only one of these compounds can be used, or two or more can be used in combination.

  The compounding weight ratio of the compound (A) to the compound (B) is compound (A) / compound (B) = 5/95 to 95/5. It is preferable from the viewpoint of balance.

The filler composition of the present invention further contains at least one compound represented by the following general formula (III) instead of a part of the compound (A) and / or the compound (B) as necessary. Can be contained.
_{Tf3- (O) c - (CH} 2) d - (CF 2) n -A (III)
In the formula, c represents 0 or 1. d represents an integer of 0-2. n represents an integer of 1 to 11. Tf3 represents a glycidyl group or CH ₂ ═CH—C (O) —. A represents H or F.

  Examples of the compound represented by the general formula (III) include 2,2,2-trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 1H, 1H, 5H-octafluoro. Pentyl (meth) acrylate, heptadecane fluorodecyl acrylate, 3- (1H, 1H, 9H-hexadecafluorononiloyl) -1,2-epoxypropane, 3- (perfluorooctyl) -1,2-epoxypropane, etc. Is mentioned. These compounds may be used alone or in combination of two or more.

When used in place of the compound (A), the compound represented by the general formula (III) preferably has a glycidyl group, and when used in place of the compound (B), the general formula The compound represented by formula (III) preferably has CH ₂ ═CH—C (O) —.

  The compounding amount of the compound represented by the general formula (III) is less than 50 parts by weight per 100 parts by weight in total of the compound (A), the compound (B) and the compound represented by the general formula (III). Is preferable from the viewpoint of photopolymerizability and heat resistance of the composition. More preferably, it is less than 35 parts by weight.

For example, the compound (A) and the compound (B) may be produced by reacting a perfluoro group-containing di- or monoalcohol with a halogenated epoxy propyl, for example, in which the terminal Tf is an epoxy group. Alternatively, after reacting a perfluoro group-containing di- or monoalcohol with an allyl halide, it may be oxidized with a peracid such as formic acid, peracetic acid or perpropionic acid. Tf is _{CH 2 = CH-C (O} ) - in which are, for example, a perfluoro group-containing di- or monoalcohol it is sufficient to esterification reaction of acrylic acid.

  The compound (C) is a monofunctional or bifunctional aliphatic chain acrylate compound, alicyclic acrylate compound, aliphatic chain glycidyl compound, alicyclic glycidyl compound, aliphatic chain oxetane compound, and alicyclic. Selected from the group consisting of oxetane compounds. In the present specification, a monofunctional or bifunctional compound refers to a compound having one or two acrylic groups, glycidyl groups, and oxetanyl groups in the molecule. In the acrylate compound, glycidyl compound and oxetane compound, the compound having an aromatic ring in the molecule is a phase with the compound (A) represented by the general formula (I) and the compound (B) represented by the general formula (II). The solubility is poor and the viscosity and refractive index tend to be high, so they are not used in the present invention. In addition, in the case of an alicyclic epoxy group-containing compound, for example, an epoxy compound described in Patent Document 1, the compatibility with the compound (B) represented by the general formula (II) is poor, and a large amount is used. I can't. In addition, the cured product tends to be fragile, and when it is left in a high temperature and high humidity state, the adhesive strength is greatly reduced, so it is not used in the present invention.

  Examples of the aliphatic chain acrylate compound and the alicyclic acrylate compound include tetrahydrofurfuryl acrylate, isobornyl acrylate, cyclohexyl acrylate, lauryl acrylate, stearyl acrylate, 1,6-hexanediol diacrylate, 1,9 -Nonanediol diacrylate, dimethylol tricyclodecane diacrylate, dimethylol dicyclopentane diacrylate, etc. can be mentioned. Examples of the aliphatic chain glycidyl compound and the alicyclic glycidyl compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1 , 6-hexanediol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether, glycerol diglycidyl ether, trimethylolpropane diglycidyl ether, and the like. Examples of the aliphatic chain oxetane compound and the alicyclic oxetane compound include 3-ethyl-3-hydroxymethyloxetane, di [1-ethyl (3-oxetanyl)] methyl ether, 3-ethyl-3- (2 -Ethylhexyloxymethyl) oxetane and the like.

  Among these, from the viewpoint of high Tg of the cured product and good polishing processability, heat resistance, and adhesiveness, a bifunctional compound is preferable, and an alicyclic compound is more preferable compared to an aliphatic chain compound. In addition, diacrylate compounds and dioxetane compounds are preferred from the viewpoint of being hard to be colored after curing and easy to balance polishing processability, heat resistance, and adhesion, and aliphatic chain and alicyclic diacrylate compounds and aliphatic More preferred are chain dioxetane compounds

  The blending weight ratio of the compound (C) to the total of the compound (A) represented by the general formula (I) and the compound (B) represented by the general formula (II) is determined by the refractive index of the cladding material. From the viewpoint of consistency, the total of compound (A) and compound (B) / compound (C) is preferably 10/90 to 99/1, and more preferably 30/70 to 95/5.

  Moreover, as for the compounding weight ratio of monofunctional compound / 2 bifunctional compound in a compound (C), 0/100-50/50 are preferable from a viewpoint of Tg of hardened | cured material.

  As the photopolymerization initiator used in the filler composition of the present invention, a radical photopolymerization initiator and a cationic photopolymerization initiator are used in combination from the viewpoint of curability. Examples of the photo radical polymerization initiator include acetophenones, aminoacetophenones, benzophenones, Michler ketones, benzyls, benzoins, benzoin ethers, benzyl dimethyl ketals, thioxanthones, and the like. Examples of the cationic photopolymerization initiator include a diazonium salt, a sulfonium salt, and an iodonium salt. Specific examples thereof include, for example, 1-hydroxy-cyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, benzophenone, benzoin isobutyl ether, 2-hydroxy-2-methyl-1-phenylpropane, α , Α-Dimethoxy-α-hydroxy-acetophenone, 1- [4- (2-hydroxyethoxy) phenyl] -2-hydroxy-2-methyl-propan-1-one, α-hydroxyisobutylphenone, 2,4,6 -Photo radical polymerization initiators such as trimethylbenzoyldiphenylphosphine oxide; benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, benzenediazonium hexafluoroborate, aromatic diazonium salt, diallyl Doniumu salt, triarylsulfonium salt, triallyl selenium salt, triallyl pyrylium salts, benzyl pyridinium thiocyanate, dialkyl phenacyl sulfonium salts, dialkyl hydroxyphenyl sulfonium salts, and the like cationic photopolymerization initiator metallocene compounds. These radical photopolymerization initiators and cationic photopolymerization initiators can be used alone or in combination of two or more. In addition, with a sulfonium salt, sufficient hardness may not be obtained only by UV irradiation. On the other hand, the iodonium salt can be cured quickly by using alone or in combination with a sensitizer, and sufficient hardness can be obtained only by ultraviolet curing.

  The addition amount of the photopolymerization initiator is preferably 1 to 10 parts by weight, particularly preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the photopolymerizable compound in the composition.

  Furthermore, if necessary, as a sensitizer, for example, anthracene, 9,10-dimethoxyanthracene, 9,10-dipropoxyanthracene, 9,10-dibutoxyanthracene, 2-ethyl-9,10-dimethoxyanthracene, 2 -Ethyl-9,10-dibutoxyanthracene, 2-ethyl-9,10-dipropoxyanthracene and the like can be used.

  The addition amount of these sensitizers is preferably 1 to 200 parts by weight, particularly preferably 10 to 100 parts by weight with respect to 100 parts by weight of the photopolymerization initiator.

  Other additives can be used in the filler composition of the present invention as long as the object of the present invention is not impaired. Examples of such additives include silane coupling agents, leveling agents, and antifoaming agents. In particular, the addition of a silane coupling agent has the effect of improving the familiarity with inorganic optical fibers. Examples of the silane coupling include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4- Epoxycyclohexyl) ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane and the like. Such other components can be used as long as the following properties such as refractive index, Tg, and viscosity are not impaired.

  The blending amount of the other additives is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, in 100 parts by weight of the filler composition of the present invention.

  In the filler composition of the present invention, the refractive index of the cured product after polymerization is 0.94 to 1.0 times the refractive index of the cladding. When the refractive index is higher than that of the cladding, light leaks toward the filler having a high refractive index. If the refractive index is less than 0.94 times the refractive index of the cladding, the difference in refractive index increases, the non-circularity of the mode shape increases, and the loss during connection increases. Preferably, they are 0.95-1.0 times, More preferably, it is 0.96-0.99 times. The refractive index varies depending on the temperature and wavelength, but is preferably within the above range in the operating temperature range and wavelength range. The use temperature range is usually −10 ° C. to 40 ° C., and the use wavelength range is usually 1000 to 1700 nm, for example, 1310 nm, 1550 nm, 1650 nm, and the like. Since the refractive index of quartz used for the clad is 1.447 (25 ° C., nD) at 18 ° C. and 1310 nm, the refractive index of the cured product after polymerization is 1.447 or less, 1.360 at 18 ° C. and 1310 nm. It must be more than that. Further, it is known that the refractive index of the cured product after polymerization is generally about 0.025 higher than the liquid refractive index. From such a viewpoint, the refractive index at 18 ° C. measured in the liquid before curing is preferably 1.33 to 1.42 at 1310 nm. Further, the refractive index at 25 ° C. and sodium D line (589 nm) measured in the liquid state before curing generally tends to increase slightly as the wavelength becomes shorter (about 0.01 to about 600 to 1600 nm). In view of the fact that a difference of about 0.015 occurs), it is preferably 1.34 to 1.43, more preferably 1.36 to 1.43. The refractive index can be measured with an Abbe refractometer according to JIS K 0062.

  In the filler composition of the present invention, the addition of the silane coupling agent exhibits an effect of increasing the refractive index. On the contrary, the addition of the compound represented by the general formula (III) exhibits an effect of lowering the refractive index. Accordingly, by appropriately using these components, the refractive index of the filler composition of the present invention can be adjusted within the above-mentioned range.

  The filler composition of the present invention preferably has a viscosity at 25 ° C. of 3 mPa · s or more and 500 mPa · s or less. If the viscosity is lower than this range, if the fiber is placed sideways during UV irradiation, the filler will flow out, and it will be difficult to control the length to be filled. Conversely, if the viscosity is too high, the pores will be filled. It takes a long time. For example, when a 125 μm diameter fiber (hole diameter 4.6 μm) is used and the viscosity at 25 ° C. is 2500 mPa · s, it takes 1 hour or more to fill 5 mm. The upper limit is more preferably 200 mPa · s or less, further preferably 100 mPa · s or less, and still more preferably 50 mPa · s or less.

  As for the filler composition of this invention, it is preferable that Tg of the hardened | cured material is 70-150 degreeC. When it is less than 70 ° C., the end face seems to have melted when polished, and when cut, the cut face seems to be broken, not broken, and the uniformity of the end face is lost, and when connected The fibers are not connected to each other, and the fiber interval is opened due to the presence of the broken resin, so that light is reflected at that portion. On the contrary, if Tg exceeds 150 ° C., it is too hard and cracks are generated in the pores during cutting. More preferably, it is 80-100 degreeC.

The filler composition of the present invention preferably has an adhesive strength of 4.0 N / mm ² or more after 6 J / cm ² UV irradiation and 80 ° C./1 hour thermosetting treatment. When the adhesive strength is low, the filler is peeled off when polishing is performed, and the filler is pressed down by the polishing dust that has entered the pores. Furthermore, if the adhesive strength is lower than the shearing force at the time of cutting, the filler will come off. From such a viewpoint, the above range is preferable, and more preferably 5.0 N / mm ² or more.

  There is no limitation in particular in the manufacturing method of the filler composition of this invention, What is necessary is just to mix so that a raw material may mix uniformly. For example, the glycidyl compound of the compound (A), the acrylate compound of the compound (B), at least one of the compound (C), the photopolymerization initiator (D), and, if necessary, the epoxy of the general formula (III) A compound, an acrylate compound, a coupling agent, and other necessary components are blended and mixed, and the mixture is stirred and mixed under a heating and reduced pressure according to a conventional method to perform a defoaming treatment. As conditions, stirring and mixing are performed for 30 minutes to 2 hours under reduced pressure of 40 to 80 ° C and 1 to 20 torr.

The filler composition of the present invention can be suitably cured by UV irradiation. The acrylate compound of the general formula (II), the acrylate compound of the compound (C), and the acrylate compound of the general formula (III) have good polymerizability, for example, by irradiation of less than 6.0 J / cm ² Even if it exists, it is fully curable. The epoxy compound of the general formula (I), the glycidyl compound of the compound (C), the oxetane compound, and the epoxy compound of the general formula (III) also have good polymerizability and are irradiated with 6.0 J / cm ² . Even if it exists, it is fully curable. However, in the case of a glycidyl compound and an epoxy compound, the curability can be further improved by using a thermosetting treatment in combination thereafter. In this case, for example, a thermosetting treatment of about 80 ° C./1 hour is used as desired. be able to.

  The filler composition of the present invention has good compatibility between components, the photo radical polymerization initiator component of the acrylic compound exhibits the catalytic action of the epoxy compound component, and is expected to be fast-curing. . Therefore, a synergistic effect is exhibited by the combined use of the two, the heat resistance of the epoxy resin and the adhesiveness of the acrylic resin are exhibited, and the hardness of the epoxy resin is relaxed by the softness of the acrylic resin, and the low refractive index. Can be adjusted.

  The hole sealing method of the present invention includes a step of filling the holes in the end face of the hole assist fiber having holes in the cladding, a step of irradiating the filled filler composition with ultraviolet rays, and further, if necessary. And a thermosetting process. The blocking method can be suitably applied to the method for producing the hole assist fiber of the present invention described in detail below.

The method for producing a hole assist fiber having a polished end face according to the present invention includes the step of filling the filler composition into the holes in the end face of the hole assist fiber having holes in the cladding, and the filler composition filled. And a step of subjecting the end face to polishing after passing through the ultraviolet irradiation step or, if applicable, the thermosetting treatment step. In the step of filling the pores in the end surface of the hole assist fiber with the filler composition, since the diameter of the pores is about a micron, the capillary phenomenon is used to apply the filler from the end surface, for example, from several millimeters. What is necessary is just to introduce about 10 several millimeters into a void | hole. This filling can be performed in about 10 seconds, for example, and the working efficiency is good. Next, in the step of irradiating the filled filler composition with ultraviolet light, it may be irradiated with an irradiation energy of about 50 mW / cm ^{2 for} about 60 seconds with a UV lamp or the like. After this, if necessary, the end face is subjected to a thermosetting treatment of about 80 ° C./1 hour, and the end face is optically polished to produce a hole assist fiber whose end face is polished while preventing foreign matter from entering the pores. Can do.

  The hole assist fiber having holes in the clad according to the present invention is filled with the filler composition and partially blocked in the longitudinal direction in which the holes coincide with the axial direction of the optical fiber. Such an optical fiber is preferably manufactured by the above manufacturing method. The hole assist fiber thus completed has pores filled with filler at the end face, but does not exceed the refractive index of the cladding and has a refractive index close to the refractive index of the cladding. The mode shape becomes close to a circle at. Accordingly, the end surfaces of the hole assist fibers whose end surfaces are sealed with the filler composition and polished in this way, the end surfaces of the hole assist fiber and the conventional optical fiber, or the end surfaces of the hole assist fiber and the connector are connected. By fixing the ferrule end face against each other, there is no mode shape deviation, the end faces closely contact each other, and the optical waveguide connection can be achieved. Connection can be easily achieved.

  The connection method between optical fibers or between an optical fiber and an optical connector may be an appropriate applicable connection method. For example, an applicable method among methods such as fusion, butting and fixing, and an adhesive is adopted. do it.

  The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

Examples 1-3, Comparative Examples 1-3
Each component was mixed in the formulation (parts by weight) shown in Table 1 and the filler was mixed by a conventional method.
In addition, the symbol of the component in a table | surface is as follows.
FA-16: An acrylate compound manufactured by Kyoeisha Chemical Industry Co., Ltd. (in general formula (II), a = 1, b = 1, m = 8 acrylate compound).
H022: An epoxy compound manufactured by Tosoh F-Tech Co., Ltd. (epoxy compound having a = 0, b = 0, m = 4 in the general formula (I)).
IC651: Irgacure 651 (trade name), photoradical polymerization initiator manufactured by Ciba Specialty Chemicals IC184: Irgacure 184 (product name), photoradical polymerization initiator A2074 manufactured by Ciba Specialty Chemicals, photoinitiator 2074 (product name), Rhodia -Japan photocationic polymerization initiator DCP-A: Light acrylate DCP-A (trade name) (dimethylol tricyclodecane diacrylate), Kyoeisha LA: lauryl acrylate V260: 1,9-nonanediol diacrylate OXT- 221: Product name (di [1-ethyl (3-oxetanyl)] methyl ether), Toa Gosei Co., Ltd. DEX-212: Denacol EX-212 (trade name) (1,6-hexanediol diglycidyl ether), Nagase Chem Tech Company Ltd. CEOX2021: Celloxide 2021 (trade name) (alicyclic epoxy compound), manufactured by Daicel Chemical Industries, Ltd.

Evaluation Method Viscosity: The viscosity of a liquid filler whose temperature was adjusted to 25 ° C. was measured with an E-type (L type) rotary viscometer at a rotation speed of 5 rpm (unit: mPa · s).
Refractive index: Using a digital refractometer RX-5000 manufactured by Atago Co., Ltd., the refractive index of the liquid filler composition was measured at 25 ° C. using sodium D-line (589 nm).
Tg: A DMS manufactured by Seiko Instruments Inc. was used to set a peak value of Tan δ using a 100 μm-thick test piece in a shear mode.
Hue of cured product: Visually evaluated.
Adhesive strength: The filler was applied to an alkali glass plate with a thickness of about 20 μm, and after both were combined, irradiation was performed with a UV lamp at an irradiation energy of 50 mW / cm ² for 60 seconds, followed by heat treatment at 80 ° C./1 hour. Thereafter, the tensile shear bond strength (N / mm ² ) of both was measured with a tensile tester.
Filling time: A hole assist fiber having a hole diameter of 11.6 μm and whose end face was cut perpendicularly was dipped in a filler, and the possibility of filling the hole by capillary action and the filling time up to 10 mm were measured. A filling time of 10 seconds or less was evaluated as ◎, 60 seconds or less as ◯, and 1 hour or more as ×.
Filling situation: The filler was filled in the hole assist fiber and UV cured. The fiber was cut leaving about 2 mm of the filling portion, and the filling state of the cut surface was observed with an optical microscope. A case where there was no peeling and no change in the shape of the filler was evaluated as ◎, a case where there was a slight gap at the interface with the pores, a case where it was not cut evenly, or a case where it was torn.
Processing situation: After attaching an optical connector to a hole assist fiber having pores filled with a filler and optically polishing it, the state of the filler in the pores of the polished end face was observed and evaluated with an optical microscope. The case where a favorable plane was formed in the pore filling portion was evaluated as ◎, and the case where the plane was non-uniform was evaluated as ×.
Work scraping amount: The scraping amount of the filler in the hole portion of the fiber portion with respect to the ferrule was measured by interference fringes on the end face (unit: μm). In addition, as evaluation of a numerical value, when it is + 0.1-0.05 micrometer, it is (double-circle), and when smaller than -0.05 micrometer, it is x.
Optical / insertion loss: Inserted according to JIS C 5961 optical connector test method 6.1 using a hole assist fiber having a hole diameter of 11.6 μm and a filler filled in a hole of about 5 mm. Method (B) and insertion method (C) were measured (in dB). The acceptance standard (standard) is 0.5 dB or less in the insertion method (B) and 1.0 dB or less in the insertion method (C).
Mode shape: Measure the near-field pattern of the light emitted from the end face of the hole-filled fiber with a hole diameter of 11.6μm filled with resin, and the beam width at 1 / e ² from the intensity distribution. The non-circularity was calculated from the difference between the major axis and the minor axis of the beam width, and judged based on whether or not the non-circularity was improved over the hole assist fiber not filled with resin. The case where the hole assist fiber not filled with the resin was improved was evaluated as ◯, and the case where the mode was generated in the resin filled portion was evaluated as x when the hole assist fiber was not improved.

  From Examples 1 to 4, the filler composition of the present invention does not exceed the quartz refractive index (nD) of 1.45 (1.43 as the corresponding liquid refractive index), and the liquid refractive index is 1. .43, low viscosity, moderate Tg, not only has excellent curability, but also particularly excellent adhesive strength, processing status, processing scraping amount, optical / It can be seen that excellent performance with balanced insertion loss is exhibited. On the other hand, Comparative Example 1 which is an acrylic resin composition has a large amount of work scraping, and Comparative Example 2 which is an epoxy resin has a low Tg, poor heat resistance, insufficient filling property, and an acrylic resin. A certain comparative example 3 has a high refractive index, a comparative example 4 has a refractive index that is too low, and a mode shape is insufficient. In either case, although the viscosity is low, it cannot be used as a filler.

  As described above, the viscosity of the acrylic adhesive composition that is usually used is typically about 2500 mPa · s, the Tg is about 56 ° C., the adhesive strength is about the same as the comparative example, and the viscosity is particularly high. Was a problem. However, in general, when the viscosity is lowered, the adhesive strength and the like are lowered, and it is difficult to ensure the required performance in a balanced manner. On the other hand, as described above, it has been found that the composition of the present invention satisfies all of the required performance.

The filler composition of the present invention does not exceed the refractive index of the cladding, can be adjusted to the refractive index of the cladding, and satisfies various performances such as low viscosity, heat resistance, and adhesive strength. It is possible to perform the end face processing of the hole assist fiber, and provides a technology indispensable for laying the hole assist fiber with improved bending characteristics, and is extremely useful for realizing an optical communication network.

Claims (10)

A composition for filling the holes of a hole assist fiber, which is an optical fiber having holes in the clad, (A) a compound represented by the following general formula (I),
(B) a compound represented by the following general formula (II),
(C) Monofunctional or bifunctional aliphatic chain acrylate compound, alicyclic acrylate compound, aliphatic chain glycidyl compound, alicyclic glycidyl compound, aliphatic chain oxetane compound and alicyclic oxetane compound At least one compound selected from the group, and
(D) A filler composition containing a photopolymerization initiator and having a refractive index after curing of 0.94 to 1.0 times the refractive index of the cladding.
_{Tf1- (O) a - (CH} 2) b - (CF 2) m - (CH 2) b - (O) a -Tf1 (I)
_{Tf2- (O) a - (CH} 2) b - (CF 2) m - (CH 2) b - (O) a -Tf2 (II)
(In formula (I) and formula (II), a plurality of a are the same and represent 0 or 1, a plurality of b are the same and represent 0 or 1, and m is an integer of 4 to 12, respectively. Tf1 represents a glycidyl group, and Tf2 represents CH ₂ ═CH—C (O) —.) The compounding weight ratio of the total of the compound (A) represented by the general formula (I) and the compound (B) represented by the general formula (II) and the compound (C) is the compound (A) and the compound (B 2) / compound (C) = 10/90 to 99/1. The filler composition according to claim 1 or 2, having a viscosity at 25 ° C of 3 to 500 mPa · s. Tg of hardened | cured material is 70-150 degreeC, The filler composition in any one of Claims 1-3. A step of filling the filler composition according to any one of claims 1 to 4 into the holes in an end face of a hole assist fiber having holes in the cladding, and a step of irradiating the filled filler composition with ultraviolet rays. A method for sealing holes of a hole assist fiber, comprising: Furthermore, the sealing method of Claim 5 including the process of carrying out the thermosetting process of the said filler composition with which it filled. A step of filling the filler composition according to any one of claims 1 to 4 into the holes in an end face of a hole assist fiber having holes in the cladding, a step of irradiating the filled filler composition with ultraviolet rays, and A method for producing a hole-assist fiber having a polished end face, comprising a step of polishing the end face after the ultraviolet irradiation step. Furthermore, the manufacturing method of Claim 7 including the process of carrying out the thermosetting process of the said filler composition with which it filled. The manufacturing method according to claim 7 or 8, wherein the filler composition is filled in the holes in the end face of the hole assist fiber having holes in the clad within 60 seconds. In the end surface of the hole assist fiber which has a hole in a clad, the hole is filled with the filler composition according to any one of claims 1 to 4, and the hole coincides with an axial direction of the optical fiber. A hole assist fiber that is partially sealed.