WO2009034666A1

WO2009034666A1 - Water absorptive optical fiber and method for manufacturing the same

Info

Publication number: WO2009034666A1
Application number: PCT/JP2008/001369
Authority: WO
Inventors: Yoshio Hashimoto; Naoki Okada; Yukiko Sato
Original assignee: Fujikura Ltd.
Priority date: 2007-09-12
Filing date: 2008-05-30
Publication date: 2009-03-19
Also published as: JP2009086636A

Abstract

A water absorptive optical fiber 1 includes: a single core optical fiber 3; a water soluble UV resin 5 substantially uniformly disposed on the outer periphery of the single core optical fiber 3; and a powdered absorbent 7 substantially uniformly fixed in/on the water soluble UV resin 5 by use of the water soluble UV resin 5 as a binder.

Description

WATER ABSORPTIVE OPTICAL FIBER AND METHOD FOR MANUFACTURING THE SAME

Technical Field

[0001] The present invention relates to an optical fiber cable and particularly to a water absorptive optical fiber for suppressing water infiltration into the cable in a longitudinal direction to a minimum extent by its accommodation in a loose tube optical fiber cable when the optical fiber cable is immersed in water and a method for manufacturing the same. Background Art

[0002] A mainstream optical fiber cable in Europe and the United States is a loose tube optical fiber cable. The loose tube optical fiber cable has a centered tension member, optical fibers, a tube and a sheath. The optical fibers is covered with the tube made of a thermoplastic material such as PBT, and are collected surrounding the centered tension member in the SZ direction. Further, the sheath is applied therearound. Moreover, a jerry is commonly used as a water-stop material to fill in the tube. However, the jerry is adhesive, thus it degenerates a connection workability. Accordingly, a structure without the jerry, that is, a tube structure having dry space is attractive for the purpose to improve the connection workability.

[0003] As exemplary dry water-stop materials within tubes in place of the jerry, there is a material configured by a yarn, which is made of plastics such as polyester, on which a water absorbing material is applied. The material is already commercially available.

[0004] As other optical fibers and optical fiber cables having dry space for improvement of water-stop, JP-A-3- 137607 discloses a structure that is produced by sheathing a UV resin onto the outer periphery of a single-core jacketed optical fiber, as a primary coat layer, and further sheathing a water absorbing material of a UV resin onto the outer periphery of the primary coat layer.

[0005] JP-A 11-311725 discloses a structure produced by coating, with a UV resin, the outer periphery of an optical fiber unit and fixing a particulate water absorptive powder thereonto.

[0006] US Patent No. 5817713 discloses a structure produced by coating, with PVC, the outer periphery of a bundle fiber and fixing a particulate water absorbing polymer thereonto. Its manufacturing method is also disclosed in this document.

[0007] US Patent No. 6087000 discloses a structure produced by coating, with a hydrophobic polymer serving as a primary layer, the outer periphery of a glass fiber- bundle, and by coating the primary layer with a hydrophilic polymer as a secondary layer.

[0008] US Patent No. 7180000 discloses a structure produced by burying a glass fiber- bundle in a primary layer, and by further coating, with a water absorptive coat, the outer periphery of the above primary layer. Patent Citation 1 : JP- A-3- 137607 Patent Citation 2: JP-A 11-311725 Patent Citation 3 : US Patent No. 5817713 Patent Citation 4: US Patent No. 6087000 Patent Citation 5 : US Patent No. 7180000 Disclosure of Invention Technical Problem

[0009] Recently, along with the development of a loose tube in which it is dry, reduction in diameter and weight of optical fiber cables is advanced for improvement of installation workability. In this case, a water-absorbing material is desired to have a diameter as small as possible in the normal hygrothermal environment, and to have a large coefficient of volume expansion and high swelling speed when the optical fiber cable is immersed in water.

[0010] A conventional water absorbing yarn is produced by intertwining a particulate high water absorbing polymer with fibers and fixing them with a binder resin, or by applying a water absorbing layer to fibers. With this configuration, a large content of a high water absorbing material and sufficient water absorbing performance can be obtained. However, with this yarn, it is difficult to satisfy a small diameter, a low contraction, and a high strength. Hence, use of water absorbing yarn, for example, as a water-stop material of the inside of a loose tube poses a problem in that it is difficult to reduce the diameter of a loose tube.

[0011] Additionally, JA- A-3- 137607 discloses an optical fiber having a sheath with hygroscopic swelling properties. If the jacketed optical fiber is used as a water-stop agent to be installed in the loose tube, the maximum clearance between an inside wall of the loose tube and the sheath is limited, because the content of water absorbing material in the optical fiber is limited. Consequently, there is a problem in that it is difficult to design the inner size of a loose tube meeting waterproof properties while satisfying sufficient low-temperature characteristics.

[0012] In addition, the structure described in JP-A- 11-311725 is for protecting the optical fiber unit itself from water infiltration, but not for stopping water infiltration by accommodating the optical fiber unit inside the optical fiber cable when the optical cable is immersed in water. For this reason, it is difficult to reduce the diameter of the optical fiber cable. [0013] Moreover, because the water absorbing materials disclosed in US Patent Nos.

5817713, 6087000, and 7180000 are directed to waterproofing of bundled fibers or glass fiber bundle themselves, it is difficult to reduce the diameter of an optical fiber cable including the materials due to the same reason as for JA-A 11-311725.

[0014] The object of the present invention is to provide, a water absorptive fiber drying an inside of a loose tube disposed in an optical fiber cable, without use of jerry inside the loose tube, and the water absorptive fiber improving waterproof properties of the optical fiber cable and satisfying a small diameter, a low contraction, and a high strength of an optical fiber cable. Technical Solution

[0015] For solving the above problems, a water absorptive optical fiber according to a first aspect of the present invention includes: a single core optical fiber; a water soluble UV resin disposed on the outer periphery of the above single core optical fiber; and a powdered absorbent fixed in/on the water soluble UV resin by use of the water soluble UV resin as a binder.

[0016] In addition, the water absorptive optical fiber according to the present invention may have an uneven surface formed by the powdered absorbent.

[0017] Additionally, in a water absorptive optical fiber according to the present invention, the single core optical fiber preferably has a transmission loss of 5.0 dB/km or less.

[0018] A method for manufacturing a water absorptive optical fiber according to a second aspect of the present invention includes the following steps. A water soluble UV resin is substantially uniformly disposed onto the outer periphery of a single core optical fiber. A powdered absorbent is substantially uniformly disposed onto the outer periphery of the water soluble UV resin. Thereafter, the water soluble UV resin is irradiated with ultraviolet rays for curing. In the method, the powdered absorbent is fixed in/on the water soluble UV resin by use of the water soluble UV resin as a binder.

Advantageous Effects

[0019] According to a water absorptive optical fiber of the present invention, the inside of an optical fiber cable housing a water absorptive optical fiber is placed in a completely dry state in the usual hygrothermal environment. A water absorptive optical fiber of the present invention is not directed to protect itself from water, but to improve the waterproof performance of an optical fiber cable or the like. In other words, when a loose tube having accommodated therein a water absorptive optical fiber or the inside of an optical fiber cable is immersed in water, a water soluble UV resin is dissolved in the water. At this time, a powdered absorbent fixed onto the outer peripheral surface of the water absorptive optical fiber is readily detached. Then this detached absorbent absorbs water and swells to thereby prevent further water wetting in the longitudinal direction as much as possible. That is, this makes it possible to restrain the deterioration of the optical transmission characteristics or the breakage of an optical fiber for optical communication line other than a water absorptive fiber. Therefore, the waterproof performance of an optical fiber cable can be improved.

[0020] In addition, a water absorptive optical fiber of the present invention can be used as a short-distance contact line during cable installing operation by utilization of an optical talk set or the like. Moreover, after cable installing operation, the terminal of a water absorptive optical fiber can be connected to an OTDR (Optical Time Domain Re- flectometer) placed in a telephone station, rendering it possible to easily determine a water immersion position.

[0021] According to a method for manufacturing a water absorptive optical fiber of the present invention, because a water soluble UV resin is used as a binder, a powdered absorbent can be readily substantially uniformly applied onto the outer periphery of the water soluble UV resin prior to curing. Thereafter, the irradiation of the water soluble UV resin with ultraviolet rays for curing enables the powdered absorbent to be readily fixed. Brief Description of the Drawings

[0022] [fig.1] Fig. 1 is a sectional view of a water absorptive optical fiber according to an embodiment of the present invention.

[fig.2]Fig. 2 is a sectional view of a loose tube having accommodated therein a water absorptive optical fiber according to the embodiment of the present invention. [fig.3]Fig. 3 shows a graph indicating waterproof performance study results of an example and comparative example on the basis of the loose tube of Fig. 2. [fig.4A]Fig. 4A is a schematic diagram explaining a case where a water immersion position is determined by utilization of a water absorptive fiber accommodated in a loose tube.

[fig.4B]Fig. 4B shows a schematic graph indicating the transmission loss variation of a water immersion site in an OTDR screen. Best Mode for Carrying Out the Invention

[0023] An embodiment of the present invention will be described below with reference to the drawings.

[0024] As shown in Fig. 1, a water absorptive optical fiber 1 according to the present embodiment includes: a single core optical fiber 3; a water soluble UV resin 5 substantially uniformly disposed on the outer periphery of the single core optical fiber 3; and a powdered absorbent 7 substantially uniformly fixed in/on the water soluble UV resin 5 by use of the water soluble UV resin 5 as a binder. In other words, the powered absorbent 7 substantially uniformly fixed in/on the outermost layer of the water absorptive optical fiber 1 by the binder.

[0025] In the present embodiment, the above single core optical fiber 3 is a jacketed optical fiber produced by application of a secondary coat 11 such as a polyamide resin onto the outer periphery of an optical fiber 9. The diameter of the single core optical fiber 3 is 250 micrometers. In addition, the single core optical fiber 3 may also be an optical fiber, an optical fiber cord, or a single core optical fiber of another form.

[0026] Additionally, the absorbent 7 is a high water absorptive particulate or powder having a particle diameter of, for example, from 10 to 15 micrometers. Moreover, the thickness of the water soluble UV resin 5 serving as a binder between the single core optical fiber 3 and the high water absorptive powder 7 is, for example, 30 micrometers.

[0027] The water absorptive optical fiber 1 is manufactured as follows. Firstly, the water soluble UV resin 5 prior to curing is substantially uniformly disposed onto the outer periphery of the single core optical fiber 3. Onto the outer periphery of the water soluble UV resin 5, the powdered absorbent 7 is substantially uniformly disposed. Thereafter, the water soluble UV resin 5 prior to curing is irradiated with an ultraviolet ray for curing to fix the powdered absorbent 7 in/on the water soluble UV resin 5. That is, the water soluble UV resin 5 is used as a binder.

[0028] Since the water soluble UV resin 5 is used as a binder, the powdered absorbent 7 can be readily substantially uniformly dispersed and applied onto the outer periphery of the water soluble UV resin 5 before curing. Thereafter, the resulting material is irradiated with an ultraviolet ray to cure the water soluble UV resin 5, whereby the powdered absorbent can be readily fixed in/on the water soluble UV resin 5 around the outer periphery of the single core optical fiber 3. Therefore, the working efficiency becomes good.

[0029] Next, a loose tube 15 having the water absorptive optical fiber 1 therein according to the embodiment will be described.

[0030] As shown in Fig. 2, in the present embodiment, the loose tube 15 has a tube (a jacket) 17 made of PBT, and twelve jacketed optical fibers 19 provided in the tube 17, talc 21 constituted of magnesium silicate hydrate (3MgCMSiO₂-H₂O) and one water absorptive optical fiber 1 according to the embodiment described above. The inner diameter of the tube 17 is about 1.4 mm.

[0031] Waterproof performance testing was carried out on the above-described loose tube 15 by using samples A and B, as described below. Sample A is the water absorptive optical fiber 1 according to the present embodiment. As described above, the water absorptive optical fiber 1 has the single core optical fiber 3, the water soluble UV resin 5 and the water absorptive powder 7 fixed in/on the water soluble UV resin 5. On the other hand, Sample B is an optical fiber as a comparative example, which has the single core optical fiber 3, a water insoluble UV resin disposed on the outer periphery of the single core optical fiber 3, and the water absorptive powder 7 fixed in/on the water insoluble UV resin by use of water insoluble UV resin as a binder. Waterproof performance tests were carried out on the loose tube 15 housing Sample A of the example described above and a loose tube housing Sample B of the comparative example.

[0032] In addition, the waterproof performance test evaluates the loose tube 15 in accordance with IEC60794-1 (Pouring tap water to end face, and then checking the water wetted length at a water head height of 1 m after 24 hours).

[0033] In other words, the waterproof characteristics were evaluated under the conditions where tap water of ambient temperature is used as a medium, a water head height is 1 m, sample lengths of Samples A and B are 3 m and they are immersed in the water for 24 hours.

[0034] Describing it in more detail, Samples A and B of 3 m are substantially horizontally oriented in the waterproof performance test. One end of each of Samples A and B is connected to a water head tube so that the water pressure can be loaded. The water head tube is a cylinder, and perpendicularly stands from the ends of Samples A and B. Ambient temperature tap water is introduced into the water head tube so that the water head height would be 1 m. Twenty-four hours after the tap water is introduced, the water wetted length of each of Samples A and B is measured.

[0035] The results of the waterproof performance test are shown in Fig. 3. In Sample A, when the amount of adhesion of a water absorbing powder is about 0.006 g/m, the water wetted length becomes about 300 cm. In this case, the water-stop property is thus not good. On the other hand, when the amount of adhesion of a water absorbing powder is about 0.013 g/m or more, the water wetted length becomes roughly from 20 to 30 cm. The water-stop property is thus extremely good. In addition, in Sample B as the comparative example, even though the amount of adhesion of a water absorbing powder is about 0.02 g/m, the water wetted length becomes about 300 cm. Even though the amount of adhesion of a water absorbing powder is from about 0.025 to about 0.028 g/m, the water wetted length becomes about 150 to 190 cm. The water stop property is thus not good. As a result, it is realized that the waterproof performance is improved in Sample A.

[0036] In the water absorptive optical fiber 1 according to the present embodiment, the water soluble UV resin 5 fixes the water absorptive powder 7 by sufficient gripping force to thereby serve as a binder. Accordingly, the water absorptive powder 7 is hardly detached from the single core optical fiber 3 in the usual hygrothermal environment. In other words, the inside of the loose tube 15 is completely in a dry state.

[0037] When the loose tube 15 is immersed in water, the water soluble UV resin 5 of the water absorptive optical fiber 1 is dissolved in water, so the water absorptive powder 7 is readily detached from the single core optical fiber 3. Also, the detached water absorptive powder 7 deposits in a downstream direction of the water immersion while swelling and maintaining a suitable gel viscosity, thereby sufficiently filling the clearance in the tube 17 and stopping the water.

[0038] Hence, the use of the water soluble UV resin 5 as a binder more readily detaches the water absorptive powder 7 during water immersion than the use of a usual UV resin or thermoplastic resin as a binder. For this reason, the waterproof performance of the loose tube 15 is improved. In addition, the mechanical characteristics such as a linear expansion coefficient, strength, and Young's modulus of the water absorptive optical fiber 1 are desirably substantially equivalent to those of the jacketed optical fiber 19 housed within the loose tube 15. This is because the water absorptive optical fiber can be adapted to environmental changes as the other optical fire core wire 19 does. Moreover, the outer diameter of the water absorptive optical fiber 1 is substantially the same as that of the jacketed optical fiber 19, so that it is possible to reduce the diameter of the loose tube 15 or of the optical fiber cable 1.

[0039] In addition, because the water absorptive powder 7 is fixed in/on the water soluble UV resin 5, an uneven surface is formed by the presence of the water absorptive powder 7. Accordingly, the difference between the water absorptive optical fiber 1 and the jacketed optical fiber 19 can be easily recognized by hand feeling.

[0040] The primary role (function) of the water absorptive optical fiber 1 is to perform the waterproof of the cable by absorbing water and expanding during water immersion. In other words, the water absorptive optical fiber 1 itself is not used as a medium of a usual optical communication line, but prevents water running to the longitudinal direction of the cable as much as possible when the loose tube 15 is immersed in water.

[0041] Furthermore, its secondary role (function) is to be used as a short distance communication line at cable installing operation. In other words, when a pair (2 units) of optical talk sets or the like is connected via the water absorptive optical fiber 1, the operators, each is at both ends of the loose tube 15, can communicate each other for emergency communication, for example.

[0042] As described above, the water absorptive optical fiber 1 of the present embodiment offers the following effects.

[0043] (1) When the water soluble UV resin 5 is used as a binder between the water absorptive powder 7 and the single core optical fiber 3, the water absorptive powder 7 becomes to be hardly detached in the usual hygrothermal environment. For this reason, it is possible to render the inside of the loose tube 15 having accommodated the water absorptive optical fiber 1 therein, in a complete dry state. On the other hand, if the loose tube 15 is immersed in water, the water soluble UV resin 5 dissolves in water, whereby the water absorptive powder 7 is detached from the single core optical fiber 3 and swollen and certainly deposits within the loose tube 15.

[0044] (2) Use of the jacketed optical fiber as the single core optical fiber 3 of the water absorptive optical fiber 1 achieves the water absorptive optical fiber 1 in which the linear expansion coefficient is substantially equivalent to that of the jacketed optical fiber 19 accommodated within the loose tube 15 and in which the diameter is reduced, at about 300 micrometers. As a result, the diameter of the loose tube 15 or the optical fiber cable can be reduced while the optical transmission characteristics are ensured at low temperature.

[0045] (3) Use of the jacketed optical fiber as the single core optical fiber 3 of the water absorptive optical fiber 1 makes it possible to use also the water absorptive optical fiber 1 as a detecting material for water immersion or a communication line. Industrial Applicability

[0046] A water absorptive optical fiber according to the present invention contributes to improve the waterproof performance of the optical fiber cable and to reduce the diameter thereof.

Claims

[1] A water absorptive optical fiber, comprising: a single core optical fiber; a water soluble UV resin substantially uniformly disposed on the outer periphery of the single core optical fiber; and a powdered absorbent substantially uniformly fixed in/on the water soluble UV resin by use of the water soluble UV resin as a binder. [2] The water absorptive optical fiber according to claim 1, wherein the water absorptive optical fiber has an uneven surface formed by the powdered absorbent. [3] The water absorptive optical fiber according to claim 1, wherein the single core optical fiber has a transmission loss of 5.0 dB/km or less. [4] A method for manufacturing a water absorptive optical fiber, comprising: substantially uniformly applying a water soluble UV resin onto the outer periphery of a single core optical fiber; substantially uniformly applying a powdered absorbent onto the outer periphery of the water soluble UV resin; and thereafter irradiating the water soluble UV resin with ultraviolet rays for curing; wherein the powdered absorbent is fixed in/on the water soluble UV resin by use of the water soluble UV resin as a binder.