JP2016206396A - Optical cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical cable that can be bent by 180 degrees without breaking optical fibers stored inside thereof.SOLUTION: An optical cable 10 comprises: optical fiber ribbons 20 formed with parallelly arranged optical fiber core wires 21 integrated by being covered by a resin; tensile strength fibers 11; and a tubular jacket 12 storing the optical fiber ribbons 20 and the tensile strength fibers 11. The jacket 12 stores a plurality of the optical fiber ribbons 20. The total value of a width Wof the optical fiber ribbons 20 is larger than the inner diameter D2 of the jacket 11 when the cable is in a straight state, and the total value of the width Wof the optical fibers 20 is smaller, when the optical cable 10 is bent by 180 degrees, than the major axis of the inner diameter of the jacket 12 at a portion bent by 180 degrees.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical cable used for connection between devices, for example.

  For example, Patent Document 1 includes a single optical fiber tape core wire in which a plurality of parallel optical fibers are integrated, a tensile body, and an outer sheath that covers the optical fiber tape core wire and the tensile body. An optical cable is disclosed.

JP2013-109003A

  When an optical cable as described in Patent Document 1 is bent 180 degrees (so-called cable pinching), the optical fiber of the optical fiber ribbon accommodated in the optical cable may be broken or cracked.

  An object of the present invention is to provide an optical cable in which an optical fiber accommodated therein is not broken even if it is bent by 180 degrees.

An optical cable according to the present invention comprises:
An optical cable comprising: an optical fiber ribbon in which the periphery of parallel optical fibers is coated and integrated with a resin; a tensile fiber; and a tube-shaped jacket that houses the optical fiber ribbon and the tensile fiber. ,
A plurality of optical fiber ribbons are stored in the jacket,
The total value of the widths of the plurality of optical fiber ribbons is larger than the inner diameter of the jacket in a straight cable state,
When the optical cable is bent 180 degrees, the total value of the widths of the plurality of optical fiber ribbons is smaller than the major diameter of the inner diameter of the portion of the jacket that is bent 180 degrees.

  According to the present invention, it is possible to provide an optical cable in which an optical fiber accommodated therein is not broken even when bent 180 degrees.

(A) is sectional drawing which shows an example of the optical cable of this embodiment, (b) is sectional drawing which shows an example of the optical fiber ribbon accommodated in the optical cable. (A) is a figure which shows an example of the optical fiber which comprises the optical fiber ribbon shown in FIG. 1, (b) is a figure which shows an example of the refractive index distribution of the said optical fiber. (A) is a figure which shows the state which bent the optical cable of this embodiment 180 degree | times, (b) is the II sectional view taken on the line of (a). It is a figure which shows the relationship between the bending radius of an optical fiber, and a fracture probability. It is a figure which shows the relationship between the bending radius and bending loss of an optical fiber. It is a figure which shows the relationship between the fiber length of an optical fiber, and numerical aperture (NA).

[Description of Embodiment of Present Invention]
First, the contents of the embodiments of the present invention will be listed and described.
An optical cable according to an embodiment of the present invention is
(1) An optical cable comprising an optical fiber ribbon in which the periphery of parallel optical fibers is coated and integrated with a resin, a tensile fiber, and a tube-shaped outer casing that houses the optical fiber ribbon and the tensile fiber. Because
A plurality of optical fiber ribbons are stored in the jacket,
The total value of the widths of the plurality of optical fiber ribbons is larger than the inner diameter of the jacket in a straight cable state,
When the optical cable is bent 180 degrees, the total value of the widths of the plurality of optical fiber ribbons is smaller than the major diameter of the inner diameter of the portion of the jacket that is bent 180 degrees.
According to this configuration, it is possible to provide an optical cable in which the optical fiber accommodated therein is not broken even when bent 180 degrees.

(2) It is preferable that the inner diameter of the outer cover in the linear state is a value of 45% or more and 61% or less of the outer diameter of the outer cover.
According to this configuration, it is possible to bend the jacket easily, and even if the jacket is bent 180 degrees, the jacket is not kinked (broken and crushed), and the optical fiber can be sufficiently prevented from being broken. .

(3) It is preferable that the breaking probability of the optical fiber is 10 ⁻⁵ or less when the optical fiber is bent 180 degrees with a bending radius of 1.75 mm and held for 1 minute.
The optical cable according to the present embodiment can keep the optical fiber breaking probability low even when the optical cable is pinched under the above conditions.

(4) It is preferable that the outer diameter of the glass part of the said optical fiber is 100 micrometers or less.
According to this configuration, the breaking probability of the optical fiber can be further reduced.

(5) It is preferable that the coating layer which adhere | attaches the said glass part around the said glass part is provided.
According to this configuration, by providing a coating layer that is not easily peeled around the glass portion of the thinned optical fiber, it can be used for connection terminals of various diameters, for example, a general optical fiber having a glass diameter of 125 μm. Can be attached to the connector.

(6) It is preferable that the core of the optical fiber is made of glass and the clad is made of resin.
According to this configuration, since the glass portion of the optical fiber is further reduced in diameter, the probability of breakage can be further reduced.

(7) It is preferable that the fatigue coefficient of the optical fiber is 21 or more.
According to this configuration, since the optical fiber is resistant to distortion and the like, it is further difficult to break.

(8) The tensile strength fiber is accommodated at an accommodation density of 1270 denier / mm ^{2 to} 1600 denier / mm ^{2 with} respect to the sectional area of the inner space of the jacket and including the optical fiber ribbon portion. It is preferable that
According to this configuration, the tensile strength of the optical cable can be satisfied and the optical cable can be easily bent by 180 degrees.

(9) The resin for covering and integrating the optical fibers arranged in parallel in the optical fiber ribbon is formed in a corrugated shape along the outer periphery of the optical fibers arranged in parallel. The thickness of the thinnest part is preferably 10 μm or more and 20 μm or less.
According to this configuration, since the optical fiber ribbon is thinned, the optical cable can be easily bent.

(10) It is preferable that a change in transmission loss of the optical fiber when the optical cable is bent by 180 degrees is 2.0 dB or less as compared with a transmission loss before the optical cable is bent.
The optical cable according to the present embodiment can suppress the transmission loss of the optical fiber within the above range even when the optical cable is pinched.

(11) Preferably, a trench having a refractive index lower than that of the cladding is provided around the core of the optical fiber, and the cladding is provided around the trench.
According to this configuration, the optical fiber has a refractive index distribution strong against bending, and bending loss can be suppressed.

(12) A weight in which a portion in contact with the optical cable is a spherical surface having a radius of 12.5 mm from a direction orthogonal to the length direction of the optical cable in the extended state, and the product of the weight of the weight and the height to be dropped The increase in transmission loss of the optical fiber in an impact resistance test for evaluating impact resistance by dropping a weight set so as to be 0.74 N · m is 0.5 dB or less, and the jacket is cracked. It is preferable that no occurs.
The optical cable according to the present embodiment has sufficient strength against an impact.

(13) An increase in transmission loss of the optical fiber in a lateral pressure test performed by applying a load of 3.5 N per 1 mm of the optical cable to the stretched optical cable for 10 minutes is 0.5 dB or less, and It is preferable that there is no crack in the outer jacket.
The optical cable according to the present embodiment has sufficient strength against the side pressure.

(14) The numerical aperture (NA) of the optical fiber is preferably 0.22 or less when the optical fiber length is 2 m.
Since the NA of the optical cable according to the present embodiment is suppressed within the above range, for example, transmission loss of an optical signal can be suppressed when coupled with a light receiving element.

[Details of the embodiment of the present invention]
Hereinafter, an example of an optical cable according to the present invention will be described with reference to the drawings.
FIG. 1A is a cross-sectional view showing an example of the optical cable 10 of the present embodiment, and FIG. 1B is a cross-sectional view showing an example of the optical fiber ribbon 20 accommodated in the optical cable 10.
As shown in FIG. 1A, an optical cable 10 includes a plurality (here, two) of optical fiber ribbons 20, tensile strength fibers 11 arranged along the plurality of optical fiber ribbons 20, and an optical fiber. And a tube-shaped outer covering 12 covering the periphery of the ribbon 20 and the tensile strength fiber 11. The optical cable 10 according to the present embodiment is used for connection between devices in a data center, for example. For this reason, the optical cable 10 is often used with a length of 10 to 100 m, preferably 10 to 20 m.

The tensile strength fiber 11 is composed of a large number of aramid fibers, staple yarns, and the like. The tensile strength fiber 11 is accommodated at an accommodation density of 1270 denier / mm ² or more and 1600 denier / mm ² or less with respect to the cross-sectional area of the inner space of the jacket 12 (including the portion where the optical fiber ribbon 20 is present). When the accommodation density of the tensile strength fiber 11 is less than 1270 denier / mm ² , the tensile strength of the optical cable 10 cannot be satisfied. On the other hand, when the accommodation density of the tensile strength fibers 11 is higher than 1600 denier / mm ² , it is difficult to bend the optical cable 10 by 180 degrees.

  The tube-shaped outer casing 12 has, for example, an outer diameter D1 of 3.5 ± 0.1 mm and an inner diameter D2 of 2.0 ± 0.1 mm. The inner diameter D2 of the outer jacket 12 is preferably 45% or more and 61% or less of the outer diameter D1. When the inner diameter D2 of the jacket 12 is less than 45% of the outer diameter D1, it is difficult to bend the optical cable 10 by 180 degrees. On the other hand, if the inner diameter D2 of the outer sheath 12 is larger than 61% of the outer diameter D1, the outer sheath 12 may be broken and kinks may occur when the optical cable 10 is bent 180 degrees.

  The jacket 12 is made of polyvinyl alcohol (PVA), polyethylene, or the like. The resin material of the outer cover 12 is preferably a material that does not contain halogen. This is because there is little environmental pollution during incineration. Moreover, it is preferable that the outer cover 12 is comprised from the flame-retardant resin material. This flame-retardant material is a material that passes the riser combustion test (applicable safety standard UL1666). In detail, it is preferable that the jacket 12 is made of a material corresponding to the fact that the flame does not propagate up to 12 feet even if the cable is laid vertically and burned in a predetermined gas burner for 30 minutes. In order to constitute such a material, the jacket 12 is made by adding various flame retardants (nitrogen flame retardant, phosphorus flame retardant, etc.) to the PVA or polyethylene resin.

  As shown in FIG.1 (b), the optical fiber ribbon 20 which concerns on this embodiment has arranged the optical fiber core wire 21 (an example of an optical fiber) of the multiple pieces (here, for example, 4 pieces) in parallel on a plane, These optical fiber core wires 21 are formed by collectively covering with a coating layer 30.

  As the coating layer 30 for integrating the optical fiber cores 21 arranged in parallel, it is preferable to use an ultraviolet curable resin or the like. The covering layer 30 is formed along the outer periphery of the optical fiber cores 21 arranged in parallel, and has a corrugated shape. In the coating layer 30, a recess 30 a is formed according to the recess between the adjacent optical fiber core wires 21. The thickness of the thinnest portion of the corrugated coating layer 30 is, for example, 10 μm or more and 20 μm or less. If the thickness is less than 10 μm, the strength and durability of the coating layer 30 are inferior, and if the thickness is greater than 20 μm, the optical fiber ribbon 20 is difficult to bend. This affects the ease of bending when bending.

Width _{W R} of the direction along the parallel direction of the optical fiber core wire 21 of the optical fiber ribbon 20 is, for example, 1.1 ± 0.1 mm. In this embodiment, two total values for example 2.2mm next width W _R of the optical fiber ribbon 20, the inside diameter of the envelope 12 in a state where no optical cable 10 is bent (cable straight state) D2 (2 0.0 mm).

FIG. 2A is a diagram illustrating an example of the optical fiber core wire 21 constituting the optical fiber ribbon 20 illustrated in FIG. 1, and FIG. 2B is an example of a refractive index distribution of the optical fiber core wire 21. FIG.
As shown in FIGS. 1B and 2A, the optical fiber core wire 21 has an optical fiber strand 22 and a resin coating layer 25. The optical fiber 22 has a core 22a, a clad 22b around the core 22a, and an adhesion coating layer 23 around the clad 22b. The outer diameter of the core 22a is, for example, 50 ± 3 μm, and the outer diameter of the cladding 22b is, for example, 100 μm or less. The outer diameter of the adhesion coating layer 23 is, for example, 125 ± 2 μm. In the present embodiment, in order to keep the probability of breakage of the optical fiber 22 low, the outer diameter of the glass portion (the outer diameter of the cladding 22b) is set to 100 μm or less, which is thinner than the general outer diameter of 125 μm. As the optical fiber 22, an optical fiber (AGF: All Glass Fiber) in which the core 22 a and the clad 22 b are both quartz glass can be used.

  The adhesion coating layer 23 is made of an ultraviolet curable resin or the like, and is adhered and coated around the clad 22 b that is a glass portion of the optical fiber strand 22. Since the diameter (cladding diameter) of the glass portion of the optical fiber core wire is usually 125 μm, a connector or the like to which an optical fiber core wire with a glass diameter of 125 μm is generally attached is manufactured. In the present embodiment, the glass portion of the optical fiber strand 22 is made thinner than a normal optical fiber. Therefore, an adhesion coating layer 23 is provided around the clad 22b of the optical fiber 22 so that it can be attached to a general connector for an optical fiber having a diameter of 125 μm, and the diameter of the adhesion coating layer 23 is set to 125 ± 2 μm. . The adhesion coating layer 23 is adhesively coated on the cladding 22b so that the adhesion coating layer 23 is not peeled off from the cladding 22b even if the resin coating layer 25 coated around the adhesion coating layer 23 is peeled off from the adhesion coating layer 23. . For example, the adhesion coating layer 23 has a peeling force of 3 N / m or more, preferably 15 N / m or more when the adhesion coating layer 23 is peeled from the clad 22b by a 90-degree peel test.

  The resin coating layer 25 is made of an ultraviolet curable resin or the like. The resin coating layer 25 preferably has a structure in which a plurality of layers are laminated in the radial direction. In this embodiment, the resin coating layer 25 includes a primary coating layer 25a that covers the periphery of the optical fiber 22 and a secondary coating layer 25b that covers the periphery of the primary coating layer 25a. The outer diameter of the secondary coating layer 25b (that is, the outer diameter of the optical fiber core wire 21) is, for example, 250 ± 15 μm.

As shown in FIG. 2B, in this embodiment, a trench 22c is provided between the core 22a and the clad 22b of the optical fiber 22. That is, a trench 22c is provided around the core 22a, and a cladding 22b is provided around the trench 22c. The trench 22c is a portion having a lower refractive index than the cladding 22b, and its width _Wt is, for example, 3 μm. The relative refractive index difference Δ1 between the core 22a and the clad 22b is, for example, 1.1%. The relative refractive index difference Δ2 of the trench 22c with respect to the cladding 22b is −0.5% or less, preferably about −0.6%. That is, the refractive index _{n t} of the trench 22c, the refractive index of the cladding 22b is taken as _{n c,} it is preferable to satisfy the _{Δ2 = (n t -n c)} / n c <-0.5%.

FIG. 3A shows a state where the optical cable 10 of the present embodiment is bent by 180 degrees, and FIG. 3B is a cross-sectional view taken along the line II in FIG. A cross-sectional view of the optical cable 10 is shown.
The optical cable 10 according to the present embodiment is used for, for example, connection between devices. At this time, the optical cable 10 may be bent to accommodate or arrange the optical cable 10 in a narrow place. Even in such a case, it is required that the optical fiber in the optical cable does not break or the signal is not interrupted due to an increase in transmission loss. It should be ascertained that if the optical cable 10 is deliberately bent 180 degrees, the optical fiber does not break or the transmission loss does not increase so much that the signal is lost. As shown in FIG. 3A, when the optical cable 10 is bent 180 degrees by a finger F or the like, as shown in FIG. 3B, the portion where the optical cable 10 is most deformed (the pinched portion) is the optical cable. Ten outer coverings 12 spread laterally and become oval. Diameter D3 of the inner diameter of a portion 180 degree bend was of the envelope 12, for example, a 3.0mm approximately, larger than the total value of the width _{W R} of the two optical fiber ribbons 20 2.2 mm.

As described above, the optical cable 10 according to the present embodiment, is greater than the inner diameter D2 of the envelope 12 of the cable straight state sum of the width W _R of the two optical fiber ribbons 20 accommodated in the envelope 12 on the other hand, when the bent optical cable 10 180 degrees, the two sum values of the width W _R of the optical fiber ribbon 20 is set to be smaller than the diameter D3 of the inner diameter of the portion bent by 180 degrees of the envelope 12 Yes. Therefore, as shown in FIG. 3 (b), at the location where the outer sheath 12 is bent by 180 degrees, the two optical fiber ribbons 20 are formed in the inner space of the outer sheath 12 which spreads horizontally and becomes oval. It becomes possible to be accommodated in parallel in a horizontal row without overlapping.

If the optical fiber ribbon 20 overlaps at the bent portion, the probability of breakage increases. However, according to the present embodiment, the two optical fiber ribbons 20 do not overlap in parallel at the portion where the optical cable 10 is bent 180 degrees. The fracture probability can be greatly reduced. Specifically, the optical cable 10 of this embodiment has a fracture probability of 10 ⁻⁵ or less when the optical fiber core 21 is bent by 180 degrees with a bending radius of 1.75 mm and held for 1 minute. Furthermore, according to this embodiment, the transmission loss change of the optical fiber core wire 21 when the optical cable 10 is bent 180 degrees is 2.0 dB or less compared to the transmission loss before the optical cable 10 is bent. Therefore, the optical cable 10 according to the present embodiment can not only break the optical fiber core 21 even when pinched, but can also reduce the transmission loss of the optical fiber core 21.

  In addition, if the optical fiber core wires are put in the outer casing one by one without being ribboned, they are easily overlapped at the bent portion. However, in the present embodiment, since a plurality of optical fiber cores 21 are integrated and formed as the optical fiber ribbon 20, the optical fiber core wires 21 do not overlap inside the optical fiber ribbon 20. Furthermore, for example, if one optical fiber ribbon in which eight optical fiber cores are made multi-core is formed, the width of the optical fiber ribbon becomes wide, and the diameter of the cable jacket that accommodates the optical fiber ribbon becomes large. . On the other hand, in the present embodiment, four optical fiber cores 21 are formed as two optical fiber ribbons 20 by four, and the two optical fiber ribbons 20 are accommodated in the jacket 12 so that an optical cable is obtained. The diameter of 10 can be made as small as possible.

  In the present embodiment, the ratio of the inner diameter to the outer diameter of the outer cover 12 in the linear state is not less than 45% and not more than 61%. As a result, the outer cover 12 can be easily bent, and the outer cover 12 is not kinked even if bent 180 degrees. When the jacket is kinked, a bending force is also applied to the optical fiber core in the jacket, and the optical fiber core is easily broken. However, in the present embodiment, since the jacket 12 is not kinked, the optical fiber core wire 21 can be prevented from being broken.

  Furthermore, in the present embodiment, the outer diameter of the glass portion of the optical fiber core wire 21 (the outer diameter of the cladding 22b) is 100 μm or less. Since the glass portion of the optical fiber core wire 21 is made thinner than usual, the probability of breakage of the optical fiber core wire 21 can be further reduced.

  Furthermore, in the present embodiment, an adhesion coating layer 23 that is in close contact with the cladding 22b is provided around the cladding 22b (glass portion) of the optical fiber core wire 21. By providing an adhesion coating layer 23 that does not easily peel around the thinned cladding 22b and setting the outer diameter of the adhesion coating layer 23 to 125 μm, it can be attached to a general connector corresponding to 125 μm.

Furthermore, in the present embodiment, the tensile strength fiber 11 is 1270 denier / mm ² or more and 1600 denier / mm ² or less with respect to the cross-sectional area of the internal space (including the portion where the optical fiber ribbon 20 is present) in the jacket 12. It is housed at a housing density. As a result, the tensile strength of the optical cable 10 can be satisfied, and the optical cable 10 can be easily bent 180 degrees.

  Furthermore, in this embodiment, the resin coating layer 25 which integrates the optical fiber core wire 21 and constitutes the optical fiber ribbon 20 has a corrugated shape along the outer periphery of the optical fiber core wire 21. The thickness of the thinnest part of the coating layer 25 is 10 μm or more and 20 μm or less. Thereby, since the optical fiber ribbon 20 is thinned and the optical fiber ribbon 20 is easily bent, the optical cable 10 can be easily pinched.

  Furthermore, in the present embodiment, a trench 22c having a refractive index lower than that of the cladding 22b is provided around the core 22a of the optical fiber core wire 21, and the cladding 22b is provided around the trench 22c. Thereby, the optical fiber core wire 21 has a refractive index distribution strong against bending, and bending loss can be suppressed.

In the case of a cable based on the premise that bending stress is applied like the optical cable 10 according to the present embodiment, it is important to have fatigue characteristics that can withstand severe use conditions. This fatigue coefficient (hereinafter referred to as n value) is one of the parameters representing the strength related to the growth rate of cracks on the optical fiber surface. The n value is used as an index indicating the reliability of the optical fiber when the optical fiber (optical fiber core wire) is subjected to repeated stress fluctuations. There is a correlation between the n value and the fracture probability. The larger the n value, the lower the fracture probability (that is, the less likely it is to break). There are several methods for measuring the n value. In this embodiment, as an example, the n value is measured based on the wound static fatigue characteristics. (See Japanese Published Patent Application No. 2011-154107.)
It should be noted that the n value can also be obtained by a 180-degree bending test in order to approach an actual usage pattern.

  In the optical fiber core wire 21 according to the present embodiment, the required n value is, for example, 21 or more. That is, the optical fiber core wire 21 of this embodiment can achieve an n value of 21 or more. As described above, according to the present embodiment, since the optical fiber core wire 21 having a high fatigue coefficient and strong against strain or the like is used, the optical fiber core wire 21 is more difficult to break even when the optical cable 10 is bent 180 degrees. ing.

[Evaluation]
Table 1 shows an example of the structure of the optical cable according to the present embodiment and the evaluation results of the mechanical characteristics of the optical cable.

The impact characteristics [dB] in Table 1 indicate an increase in transmission loss of the optical fiber core when an impact resistance test based on the US TIA / EIA FOTP-25C standard is performed. This impact resistance test is performed by dropping a weight of a stretched optical cable having a spherical surface with a radius of 12.5 mm in contact with the optical cable. At this time, the weight and the drop height are set so that the product of the weight and the drop height is 0.74 N · m. For example, if the weight is 500 g, it is dropped from a height of 15 cm.
As shown in Table 1, the increase in transmission loss of the optical fiber core when such an impact resistance test was performed was 0.5 dB or less. Moreover, there was no crack in the outer jacket. Thereby, it has confirmed that the optical cable which concerns on this embodiment had sufficient intensity | strength with respect to an impact.

The side pressure characteristic [dB] in Table 1 shows an increase in transmission loss of the optical fiber core when a side pressure test based on the US TIA / EIA FOTP-41A standard is performed. This side pressure test is performed by placing an iron plate on an optical cable in a stretched state and applying a load of 3.5 N per 1 mm of the optical cable for 10 minutes.
As shown in Table 1, the increase in transmission loss of the optical fiber core when such a side pressure test was performed was 0.5 dB or less, and no crack was generated in the jacket. Thereby, it has confirmed that the optical cable which concerns on this embodiment had sufficient intensity | strength also with respect to a side pressure.

  Next, an evaluation test was performed on the optical fiber cores according to Examples 1 to 3 shown in Table 2. Example 1 is an optical fiber core (clad diameter: 100 μm) of the optical cable according to the present embodiment, and Examples 2 and 3 are optical fiber cores (clad diameter) that are thicker than the optical fiber core according to the present embodiment. : 125 μm). The results are shown in FIGS.

FIG. 4 shows the relationship between the bending radius R of the optical fiber core and the fracture probability when the optical fiber core is bent at the bending radius R.
As shown in FIG. 4, the smaller the bending radius R, the higher the breaking probability of the optical fiber core wire. The target value of the breaking probability is a value that is 10 ⁻⁵ or less when the optical fiber core wire is bent 180 degrees with a bending radius R of 1.75 mm and held for 1 minute. In Example 1, when the optical fiber core was bent 180 degrees with a bending radius R of 1.75 mm and held for 1 minute, the breaking probability of the optical fiber core was 10 ⁻⁵ or less. On the other hand, in Examples 2 and 3 having a glass diameter larger than that of Example 1, the breaking probability of the optical fiber core wire under the same conditions was higher than 10 ⁻⁵ . Therefore, in Example 1, it was confirmed that the breaking probability when the optical fiber core wire was bent could be maintained lower than that of Examples 2 and 3 as the conventional examples and the target value could be achieved.

FIG. 5 shows the relationship between the bending radius R of the optical fiber core and the bending loss when the optical fiber core is bent at the bending radius R.
As shown in FIG. 5, the bending loss of the optical fiber core increases as the bending radius R decreases. The target value of the bending loss is 2. compared to the transmission loss before the optical fiber core is bent when the optical fiber core is bent 180 degrees with a bending radius R of 1.75 mm and held for 1 minute. The value is 0 dB or less. In Example 1, the transmission loss change when the optical fiber core is bent 180 degrees with a bending radius R of 1.75 mm and held for 1 minute is 2.0 dB compared to the transmission loss before the optical fiber core is bent. It was the following. On the other hand, in Example 2 having a larger glass diameter than Example 1, the transmission loss change was higher than 2.0 dB. In Example 3, the change in transmission loss was 2.0 dB or less, but higher than Example 1. Therefore, in Example 1, it was confirmed that the bending loss when the optical fiber core was bent was suppressed more than in Examples 2 and 3, and the target value could be achieved.

FIG. 6 is a diagram showing the relationship between the fiber length of the optical fiber core wire and the numerical aperture (NA).
As shown in FIG. 6, the longer the optical fiber core wire, the lower the NA value. The target value of NA is a value that is 0.22 or less when the optical fiber length is 2 m (optical fiber length defined by NA measurement). The NA of the optical fiber core of Example 1 was 0.22 or less when the length was 2 m, and it was confirmed that the NA was kept low. By setting the numerical aperture of the optical fiber in this range, for example, optical signal transmission loss can be reduced when coupled with a light receiving element such as a photodiode (PD), and the optical cable is suitable for connection to a PD or the like. It will be.

  While the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. In addition, the number, position, shape, and the like of the constituent members described above are not limited to the above-described embodiments, and can be changed to a number, position, shape, and the like that are suitable for carrying out the present invention.

  In the said embodiment, although the optical fiber whose core 22a and the clad | crud 22b are quartz glass is used as the optical fiber strand 22, it is not restricted to this example. For example, as the optical fiber, an optical fiber (HPCF: Hard Plastic Clad Fiber) in which the clad 22b is made of hard plastic can be used. HPCF has superior fracture resistance compared to AGF having the same cladding diameter because the glass portion of the optical fiber is thinner than AGF.

In the above embodiment, the trench 22c, which is a portion having a lower refractive index than the cladding 22b, is provided between the core 22a and the cladding 22b of the optical fiber strand 22, but the present invention is not limited to this example. For example, a structure in which a cladding is formed directly around the core without providing a trench may be adopted.
Further, the clad may be formed directly around the core, the trench may be formed around the clad, and the clad may be formed around the trench. That is, a trench may be provided between the first layer clad and the second layer clad. Also with this configuration, the optical fiber core wire has a refractive index distribution strong against bending, and bending loss can be sufficiently suppressed.

10: Optical cable 11: Tensile fiber 12: Outer sheath 20: Optical fiber ribbon 21: Optical fiber core wire (an example of an optical fiber)
22: Optical fiber 22a: Core 22b: Clad 22c: Trench 23: Adhesive coating layer 25: Resin coating layer 25a: Primary coating layer 25b: Secondary coating layer 30: Coating layer D1: Outer diameter of jacket D2: Jacket Inner diameter D3: major diameter of inner diameter of jacket when bent 180 degrees W _R : width of fiber ribbon W _t : width of trench

Claims (14)

An optical cable comprising: an optical fiber ribbon in which the periphery of parallel optical fibers is coated and integrated with a resin; a tensile fiber; and a tube-shaped jacket that houses the optical fiber ribbon and the tensile fiber. ,
A plurality of optical fiber ribbons are stored in the jacket,
The total value of the widths of the plurality of optical fiber ribbons is larger than the inner diameter of the jacket in a straight cable state,
An optical cable in which, when the optical cable is bent 180 degrees, the total value of the plurality of optical fiber ribbons is smaller than a major axis of an inner diameter of a portion where the outer cover is bent 180 degrees.   2. The optical cable according to claim 1, wherein an inner diameter of the jacket in the linear state is a value that is not less than 45% and not more than 61% of an outer diameter of the jacket. 3. The optical cable according to claim 1, wherein the optical fiber has a breaking probability of 10 ⁻⁵ or less when the optical fiber is bent at 180 degrees with a bending radius of 1.75 mm and held for 1 minute.   The optical cable of Claim 3 whose outer diameter of the glass part of the said optical fiber is 100 micrometers or less.   The optical cable according to claim 4, wherein a coating layer that is in close contact with the glass portion is provided around the glass portion.   The optical cable according to claim 3, wherein a core of the optical fiber is made of glass and a clad is made of resin.   The optical cable according to any one of claims 3 to 6, wherein the fatigue coefficient of the optical fiber is 21 or more. The tensile strength fiber is accommodated at an accommodation density of 1270 denier / mm ² or more and 1600 denier / mm ² or less with respect to a sectional area of the inner space of the outer jacket and including a portion of the optical fiber ribbon. The optical cable according to any one of claims 1 to 7.   The resin for covering and integrating the optical fibers arranged in parallel in the optical fiber ribbon is formed in a corrugated shape along the outer periphery of the optical fibers arranged in parallel, and the thinnest portion of the corrugated resin The optical cable according to claim 1, wherein the thickness of the optical cable is 10 μm or more and 20 μm or less.   The transmission loss change of the optical fiber when the optical cable is bent by 180 degrees is 2.0 dB or less as compared with the transmission loss before the optical cable is bent. The optical cable described.   The optical cable according to claim 10, wherein a trench having a refractive index lower than that of a clad is provided around the core of the optical fiber, and the clad is provided around the trench.   From the direction perpendicular to the length direction of the optical cable in the stretched state, the portion that contacts the optical cable is a weight having a spherical surface with a radius of 12.5 mm, and the product of the weight of the weight and the height to be dropped is 0. An increase in transmission loss of the optical fiber in an impact resistance test for evaluating impact resistance by dropping a weight set to 74 N · m is 0.5 dB or less, and a crack occurs in the jacket. The optical cable according to claim 1, wherein the optical cable is not provided.   The increase in the transmission loss of the optical fiber in the lateral pressure test performed by applying a load of 3.5 N per 1 mm of the optical cable to the stretched optical cable for 10 minutes is 0.5 dB or less, and The optical cable according to any one of claims 1 to 12, wherein no crack is generated.   The optical cable according to claim 13, wherein a numerical aperture (NA) of the optical fiber is 0.22 or less when the optical fiber length is 2 m.

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