WO2009034667A1

WO2009034667A1 - Loose tube optical fiber cable

Info

Publication number: WO2009034667A1
Application number: PCT/JP2008/001370
Authority: WO
Inventors: Yoshio Hashimoto; Naoki Okada; Takayuki Kubo
Original assignee: Fujikura Ltd.
Priority date: 2007-09-12
Filing date: 2008-05-30
Publication date: 2009-03-19
Also published as: JP2009086637A

Abstract

A loose tube optical fiber cable 1 includes: a centered tension member 3; a cable core 7 including a plurality of loose tubes 5 collected on the circumference of the centered tension member 3; and a sheath 9 that covers the outer periphery of the cable core 7. Each of the loose tubes 5 houses at least one optical fiber and a water absorptive optical fiber 15. The water absorptive optical fiber 15 has a single core optical fiber 23, and has a powdered absorbent 27 substantially uniformly applied and fixed on the outermost layer thereof by use of a water soluble UV resin 25 as a binder.

Description

Description LOOSE TUBE OPTICAL FIBER CABLE

Technical Field

[0001] The present invention relates to a loose tube optical fiber cable, particularly to a loose tube optical fiber cable that suppresses water infiltration into the cable to a minimum extent in a longitudinal direction when the cable is immersed in water. 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 optical fiber core wire, 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] US Patent No. 7099542 discloses a loose tube optical fiber cable having loose tubes each accommodating a yarn, which is applied by a water-absorbing material thereon.

[0006] US Patent No. 7200307 discloses a loose tube optical fiber cable having an optical fiber bundle, which is applied by talc thereon.

[0007] US Patent No. 6483971 discloses a loose tube optical fiber cable housing having loose tubes each accommodating calcium carbonate, talc, ultra water absorptive polymer, and the like.

[0008] US Patent No. 5630003 discloses a loose tube optical fiber cable having loose tubes each housing a linear waterproof member . Patent Citation 1 : JP-A-3- 137607 Patent Citation 2: US Patent No. 7099542 Patent Citation 3 : US Patent No. 7200307 Patent Citation 4: US Patent No. 6483971 Patent Citation 5 : US Patent No. 5630003 Disclosure of Invention

Technical Problem

[0009] Recently, the development of a loose tube with the dried inside is advanced. In addition, reduction in diameter and weight of fiber cables is advanced for the purpose to improve the installation workability. For example, when conventional water absorbing materials as a water-stop material instead of jerry, as described in the above- mentioned patent documents, are used in a loose tube, it is difficult to reduce the diameter of an optical fiber cable for the reasons below.

[0010] (1) Conventional water absorbing materials use material produced by entangling a water absorptive polymer with fibers. However, the linear expansion coefficient of the material differs from that of an optical fiber such as an jacketed optical fiber to be housed in a loose tube. In other words, because a contraction of the water absorbing material at low temperature is larger than that of the optical fiber, the optical fiber meanders at the low temperature, thereby increase a transmission loss. Also, when the inner diameter of a loose tube decreases, the effect of the contraction of a water absorbing material enlarges. Therefore, it is difficult to reduce the diameter of the loose tube.

[0011] (2) 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 this regard, the present invention is directed to provide a loose tube optical fiber cable including a loose tube whose inside is completely dried without use of jerry, the loose tube having a reduced diameter and good waterproof and temperature characteristics. Technical Solution

[0013] For solving the problems described above, a loose tube optical fiber cable of the present invention includes: a centered tension member; a water absorptive optical fiber having: a single core optical fiber; a water soluble UV resin covering the single core optical fiber; and a powdered absorbent applied on an outermost layer of the single core optical fiber and fixed by the water soluble UV resin as a binder; a plurality of loose tubes, each housing at least one optical fiber and the water absorptive optical fiber; a cable core including the plurality of loose tubes collected on the circumference of the centered tension member; and a sheath covering the outer periphery of the cable core.

[0014] In addition, in the loose tube optical fiber cable of the present invention, the water absorptive optical fiber preferably has substantially the same mechanical properties such as a linear expansion coefficient, strength, and Young's modulus as those of other optical fibers housed in each loose tube.

[0015] Additionally, in the loose tube optical fiber cable of the present invention, the loose tubes may have an inner diameter of 1.4 mm to ensure a transmission loss of the optical fiber between 0.18 and 0.25 dB/km in the temperature range from -45 to 80 degrees Celsius.

[0016] Moreover, the loose tube optical fiber cable of the present invention may have a tube structure applicable to a microduct cable. The tube structure has the inner diameter of the loose tube of about 1.3 mm to ensure a transmission loss of the optical fiber between 0.19 and 0.28 dB/km in the temperature range from -30 degrees Celsius to 80 degrees Celsius.

Advantageous Effects

[0017] According to the present invention, use of a water absorptive optical fiber as a water absorbing material within a loose tube reduces the diameter while maintaining good the waterproof and temperature characteristics of the optical fiber cable. In addition, in usual temperature and humidity environments, a water absorbing powder of the water absorptive optical fiber is hardly detached, thereby being capable of rendering the loose tube and the inside of the optical fiber cable be in a completely dry state.

[0018] Additionally, since a water absorptive optical fiber can be achieved that reduces the diameter to a diameter substantially the same as that of other optical fibers within a loose tube, the diameters of the loose tube and the optical fiber cable can be made small.

[0019] Moreover, use of a water absorptive optical fiber having mechanical characteristics such as a linear expansion coefficient, strength, and Young's modulus equivalent to those of other optical fibers within a loose tube renders it easy to handle the loose tube during its production.

[0020] Furthermore, the application of a water absorptive optical fiber as a water absorbing material within a loose tube can offer added values as a water immersion detection optical fiber for position determination during water immersion to a water absorbing material or as a communication optical fiber for arrangements of operators to each other at the time of operation. Brief Description of the Drawings [0021] [fig.1] Fig. 1 is a sectional view of a loose tube optical fiber cable according to an embodiment of the present invention.

[fig.2]Fig. 2 is a sectional view of a loose tube housed in the optical fiber cable of Fig. 1.

[fig.3]Fig. 3 is a sectional view of a water absorptive optical fiber housed in the loose tube of Fig. 2.

[fig.4]Fig. 4 shows a graph of transmission loss, in the temperature range of from -45 to 80 degrees Celsius, of the optical fiber cable of Fig. 1.

[fig.5A] Fig. 5 A is a schematic depiction diagram when the immersion position is determined by making use of a water absorptive optical fiber housed in the loose tube of the optical fiber cable of Fig. 1.

[fig.5B]Fig. 5B illustrates a schematic diagram indicating the transmission loss variation of a water immersion site in an OTDR screen.

[fig.6] Fig. 6 is a sectional view of a microduct cable serving as a loose tube optical fiber cable according to another embodiment of the present invention. [fig.7]Fig. 7 illustrates a graph of transmission loss of the optical fiber cable of Fig. 6 in the temperature range of from -30 to 80 degrees Celsius. Best Mode for Carrying Out the Invention

[0022] Embodiments of the present invention will be described below with reference to the drawings.

[0023] As shown in Fig. 1, a loose tube optical fiber cable 1 according to an embodiment of the present invention (hereinafter, simply referred to as an "optical fiber cable") includes: a centered tension member 3; a cable core 7 including a plurality of loose tubes 5 collected in the circumference of the centered tension member 3; and a sheath 9 applied on the outer periphery of the cable core 7. In the present embodiment, the optical fiber cable 1 houses six loose tubes 5 , and two rip cords 11 along the longitudinal direction thereof near the border between the sheath 9 and the cable core 7.

[0024] As shown in Fig. 2, the loose tube 5 is configured by a tube 17. The tube 17 houses at least one optical fiber 13 and at least one water absorptive fiber 15. In the present embodiment, the tube 17 (the coat) is made of a thermoplastic material such as PBT (polybutylene terephthalate) or PP (polypropylene). The inner diameter di of the tube 17 is about 1.4 mm. In the present embodiment, the optical fiber 13 is a jacketed optical fiber. In a case shown in Fig. 2, twelve optical fibers 13 are housed. In addition, a talc 21 is provided within the tube 17 to prevent the optical fibers 13 from sticking to the tube 17. The talc 12 includes magnesium silicate hydrate (3MgO 4SiO₂ H₂O), for example.

[0025] Meanwhile, the optical fiber 13 may be an optical fiber wire, an optical fiber cord, or an optical fiber of another form, in place of the above-mentioned jacketed optical fiber.

[0026] As shown in Fig. 3, the water absorptive optical fiber 15 includes: a single core optical fiber 23; a water soluble UV resin 25 substantially uniformly applied on the outer periphery of the single core optical fiber 23; and a powdered absorbent 27 substantially uniformly fixed onto the outermost layer using the water soluble UV resin 25 as a binder.

[0027] The single core optical fiber 23 has an optical fiber wire 29 and a secondary coat 31 such as a polyamide resin covering the outer periphery of the optical fiber wire 29. This structure is uniformly formed in the longitudinal direction. Moreover, in the present embodiment, the single core optical fiber 23 is a jacketed optical fiber having the diameter of 250 micrometers. Furthermore, the single core optical fiber 23 may be an optical fiber wire, an optical fiber cord, or a single core optical fiber of another form, in place of the above-mentioned jacketed optical fiber.

[0028] The water-soluble UV resin 25 is a UV resin to fixate an absorbent (a binder), and the outer diameter of the water-soluble UV resin 25 is 300 micrometers. Additionally, the water-soluble UV resin 25 is uniformly applied in the longitudinal direction. As the absorbent, for example, a high water absorbing powder (a particulate or powdered water absorbing material) is used. Here, a particle diameter ofthe powder is from 10 to 50 micrometers.

[0029] The water absorptive fiber 15 is manufactured as follows. Firstly, the water-soluble UV resin 25 prior to curing is applied on the outer periphery of the single core optical fiber 23. The powdered absorbent 27 is substantially uniformly distributed on the outer periphery of the water-soluble UV resin 25. Thereafter, the water-soluble UV resin 25 is cured by ultraviolet-ray irradiation. This makes it possible to fix the powdered absorbent 27 to the outermost layer using the water-soluble UV resin 25 as a binder.

[0030] Moreover, the waterproof performance of the tube 17 conforms to IEC60794-1

(pouring of tap water into the end face and then not leaking of water at its water head height of 1 m after 24 hours). In other words, the waterproof performance test of the loose tube 5 evaluates waterproof characteristics by using tap water as a medium at ambient temperature and immersing a sample of the loose tube 5 having a length of 3 m (meters) in the water with a water head height of 1 m (meter) for 24 hours.

[0031] In the waterproof test, a sample of 3 m is substantially horizontally oriented, and a water head tube is connected from one end of the sample in order to apply water pressure. The water head tube is a cylinder stood perpendicular to the sample, and tap water at ambient temperature is filled in the water head tube so that the water head height would be 1 m. The sample is left for 24 hours after the tap water has been filled, and then the length of the sample wetted with water is measured.

[0032] Because of the above configuration, in usual temperature and humidity en- vironments, the water soluble UV resin 25 functions as a binder that fixes the water absorbing powder 27 by sufficient gripping force. Accordingly, the water absorbing powder 27 is hardly detached from the single core optical fiber 23. In other words, the insides of the loose tube 5 and the optical fiber cable 1 are in a dry state.

[0033] On the other hand, when the optical fiber cable 1 and the loose tube 5 are immersed in water, the water soluble UV resin 25 is dissolved in the water, and the water absorbing powder 27 is easily detached from the jacketed optical fiber 23. In addition, the detached water absorbing powder 27 swells with maintaining a suitable gel viscosity and deposits in a downstream direction of the water, thus filling the clearance in the tube 17 and stopping the water. Thereby waterproof performance of the loose tube 5 is improved.

[0034] In order to adapt the water absorptive fiber 15 to environmental changes as the optical fiber 13 housed in each loose tube 5 is adapted thereto, the water absorptive fiber 15 desirably has the mechanical characteristics such as a linear expansion coefficient, strength and Young's modulus, which are almost equivalent to those of the optical fiber 13. In other words, conventionally, the contraction of a water absorbing material is larger than that of the jacketed optical fiber at low temperature, thereby meandering of an jacketed optical fiber is caused and the transmission loss increases. Therefore, reduction of the diameter could not be achieved. On the other hand, the use of the water absorptive optical fiber 15 according to the embodiment does not cause meandering even though environmental changes occur, whereby the transmission loss does not increase. As a result, the small-diametered loose tube 5 can be achieved. In addition, the outer diameter of the water absorptive optical fiber 15 is almost equivalent to that of the optical fiber 13, so the diameters of the loose tube 5 and the optical fiber cable 1 can be made small.

[0035] Fig. 2 shows the loose tube optical fiber cable 1 configured by 72-core cable with 1-6 sequence. That is, in the present embodiment, one water absorptive optical fiber 15 and six loose tubes 5 are used. In the present embodiment, as a result, use of the water absorptive optical fiber 15 makes it possible to reduce the inner diameter U₁ of the loose tube 5 to about 1.4 mm. Additionally, the outer diameter D₁ of the optical fiber cable 1 can be 9.0 mm or less.

[0036] Additionally, even in a state where the diameters of the loose tube 5 and the optical fiber cable 1 are small, the transmission loss of the optical fiber 13 in the temperature range from -45 to 80 degrees Celsius is between 0.18 and 0.25 dB/km as shown in Fig. 4. Thus, the variation of the transmission loss well becomes 0.1 micrometers or less. In other words, this means that an operation of the optical fiber cable 1 is ensured in the temperature range of from -45 to 80 degrees Celsius.

[0037] In addition, the single core optical fiber 23 is an jacketed optical fiber with a single core. The water absorptive optical fiber 15 itself is not used as a medium of a usual optical communication line, but is used as a second grade optical fiber (an optical fiber for secondary testing). For example, the water absorptive optical fiber 15 can be used as a contact line during cable installing operation. In other words, if a pair (two units) of optical talk sets or the like is utilized, operators present in both ends of the loose tube 5 can use the water absorptive optical fiber 15 as a contact line for emergency communication.

[0038] Additionally, as shown in Fig. 5, if the terminal of the water absorptive fiber 15 is connected to an OTDR (Optical Time Domain Reflectometer) 37 set in a monitoring room 35 in a telephone station after cable installing operation, the water immersion position can be easily determined. At this time, the transmission loss of the water absorptive optical fiber 15 is desirably, for example, 5.0 micrometers or less. If the optical fiber cable 1 is immersed into water, the water absorbing powder 27 is detached from the water absorptive optical fiber 15and the transmission loss in the water immersion varies. The water immersion site can be detected with a combination of monitoring the variation of the transmission loss and using OTDR 37. Accordingly, the water absorptive optical fiber 15 is utilizable also as a fiber for water immersion detection.

[0039] As a result, the loose tube optical fiber cable 1 of the present embodiment offers the following advantages.

[0040] (1) The use of the water absorptive optical fiber 15 as a water absorbing material within the loose tube 5 reduces the diameter while well maintaining the waterproof and temperature characteristics of the optical fiber cable 1. In addition, in usual temperature and humidity environments, the water absorbing powder 27 of the water absorptive optical fiber 15 is hardly detached, thereby being capable of rendering the loose tube 5 and the inside of the optical fiber cable 1 be in a completely dry state.

[0041] (2) In the embodiment of the present invention, the water absorptive optical fiber 15 is used as a water absorbing material within the loose tube 5. The fiber 15 has mechanical characteristics such as a linear expansion coefficient, strength, and Young's modulus equivalent to those of the optical fiber 13 housed within the loose tube 5. The use of the fiber 15 renders it easy to handle the loose tube 5 during its production. Additionally, the water absorptive optical fiber 15 can have its diameter which is reduced to about 300 micrometers, and the diameter is almost equivalent to that of the optical fiber 13. Therefore, the diameters of the loose tube 5 and the optical fiber cable 1 can be made small.

[0042] (3) The water absorptive optical fiber 15 as a water absorbing material within the loose tube 5 can have additional functions as a water immersion detection optical fiber detecting a position where a water absorbing material is immersed to water, or as a communication optical fiber used for operators in the fiber installing operation.

[0043] Next, a loose tube optical fiber cable 39 of another embodiment of the present invention will be described. Note that the fiber cable is substantially the same as the optical fiber cable 1 of the above-described embodiment, so like members are assigned with the same reference numerals, and their detailed descriptions are omitted.

[0044] As shown in Fig. 6, the optical fiber cable 39 is used as a microduct cable specialized in pneumatic feeding to a duct. As such, the optical fiber cable 39 is a 72 core cable in 1-6 sequence including one water absorptive optical fiber 15 and six loose tubes 41. Each of the loose tubes has a structure similar to that of the loose tube 5 of Fig. 2. As same as the above-described embodiment, in the optical fiber cable 39 of the present embodiment, the water absorptive optical fiber 15 makes it possible to reduce the inner diameter d₂ of the loose tube 41 to about 1.3 mm. With this, the outer diameter D₂ of the optical fiber cable 39 has been made to be 6.0 mm.

[0045] In addition, even where the diameters of the loose tube 5 and the optical fiber cable 39 are made small. As shown in Fig. 7, the transmission loss in the temperature range from -30 to 80 degrees Celsius is between 0.19 and 0.28 dB/km. Hence, the variation of the transmission loss is 0.1 micrometers or less. This means that the loose tube 41 ensures an operation of the optical fiber cable 39 inthe temperature range of from -30 to 80 degrees Celsius.

[0046] Additionally, the operation and advantages of the optical fiber cable 39 are substantially the same as those of the above-described optical fiber cable 1, whereby detailed descriptions thereof are omitted. Industrial Applicability

[0047] According to the present invention, a water absorptive optical fiber is used as a water absorbing material within a loose tube. The water absorptive optical fiber reduces the diameter while well maintaining the waterproof and temperature characteristics of the optical fiber cable. In addition, in usual temperature and humidity environments, a water absorbing powder of a water absorptive optical fiber is hardly detached, thereby being capable of rendering the loose tube and the inside of the optical fiber cable be in a completely dry state.

Claims

[1] A loose tube optical fiber cable comprising: a centered tension member; a water absorptive optical fiber including: a single core optical fiber; a water soluble UV resin covering the single core optical fiber; and a powdered absorbent applied on an outermost layer of the single core optical fiber and fixed by the water soluble UV resin as a binder; a plurality of loose tubes, each housing at least one optical fiber and the water absorptive optical fiber; a cable core including the plurality of loose tubes collected on the circumference of the centered tension member; and a sheath covering the outer periphery of the cable core. [2] The loose tube optical fiber cable according to claim 1, wherein the water absorptive optical fiber has substantially the same mechanical properties such as a linear expansion coefficient, strength, and Young's modulus as those of the optical fiber housed in each loose tube. [3] The loose tube optical fiber cable according to claim 1, wherein each of the loose tubes has an inner diameter of about 1.4 mm to ensure variation of a transmission loss of the optical fiber between 0.15 micrometers or less in the temperature range from -45 to 80 degrees Celsius. [4] The loose tube optical fiber cable according to claim 1, wherein the loose tube optical fiber cable has a tube structure applicable to a microduct cable, the tube structure having the inner diameter of the loose tube of about 1.3 mm to ensure variation of a transmission loss of the optical fiber between 0.15 micrometers or less in the temperature range from -30 degrees Celsius to 80 degrees Celsius.