JP2022101280A - Optical fiber cable - Google Patents

Abstract

To provide an optical fiber cable capable of suppressing an increase in transmission loss especially at a high temperature.SOLUTION: An optical fiber cable 1 is a slotless type cable not using a slot, and mainly consists of a tension member 9, a sheath 13, a cable core 15, and so on. The optical fiber cable 1 consists of a plurality of coated optical fibers 3. An optical fiber unit 5 is constituted by twisting the plurality of coated optical fibers 3. Further, the cable core 15 is constituted by twisting a plurality of optical fiber units 5. In this case, the plurality of optical fiber units 5 are twisted into a plurality of layers. The actual twisting ratio of optical fiber units 5 in each layer is larger than the reference twisting ratio calculated from the core diameter of each layer and the twisting pitch of optical fiber units 5 in the layer.SELECTED DRAWING: Figure 1

Description

The present invention particularly relates to an optical fiber cable capable of suppressing an increase in transmission loss at high temperatures.

In recent years, with the spread of the Internet, FTTH (Fiber To The Home), which realizes a high-speed communication service by directly drawing an optical fiber into a general household, is rapidly expanding. Generally, an optical fiber cable used for FTTH contains an aggregate of optical fibers for large-capacity data communication.

As such an optical fiber cable, there is a cable in which an intermittent tape core wire is twisted to form an optical fiber unit, and the optical fiber unit is further twisted to form a cable core, which is covered with an outer cover in which a tension member is embedded (. Patent Document 1).

Japanese Unexamined Patent Publication No. 2019-109400

In this way, in a general optical fiber cable, optical fiber core wires are twisted together to form an optical fiber unit, and a plurality of optical fiber units are arranged to form concentric circles while forming layers from the inside to the outside. It is twisted into a shape. Further, a presser winding is wound around the outer side of the outermost layer optical fiber unit, and the outer cover is extruded around the outer circumference thereof.

When such an optical fiber cable is laid in an outdoor environment, the optical fiber cable is stretched at a high temperature and contracted at a low temperature due to the linear expansion of the constituent material of the optical fiber cable. At this time, the coefficient of linear expansion of the jacket, which is a composite of a jacket made of plastic such as polyethylene and a tension member made of steel wire or FRP, is generally higher than that of an optical fiber made of glass and an ultraviolet curable resin. Is big. Therefore, the expansion and contraction due to a temperature change differs between the outer cover and the optical fiber, and the optical fiber receives tensile strain in a high temperature environment and compression strain in a low temperature environment.

FIG. 5 is a conceptual diagram showing a state in which a plurality of optical fiber units 100 are twisted together. In the illustrated example, the optical fiber unit 100 is twisted at a twisting pitch _p0 . Further, FIG. 6A is a diagram showing a state in which the twisted optical fiber unit is unfolded. As shown in the figure, where d ₀ is the layer core diameter of the optical fiber unit (the center diameter of the layer around which the optical fiber unit is wound in the cross section), the length of the 1-pitch optical fiber unit is represented by l ₀ . .. At this time, how long the length l ₀ of the optical fiber unit is with respect to the pitch p ₀ is defined as the twisting ratio. That is, the twisting ratio (%) = ((l ₀ / p ₀ ) -1) × 100 is defined.

When the optical fiber cable having the optical fiber unit in such a state is arranged in a low temperature environment, the outer cover portion shrinks as described above. FIG. 6B is a developed view showing _a state in which the outer cover portion contracts and the pitch changes from _p0 to p1. In this case, the optical fiber unit (internal optical fiber) is compressed, but the compression strain is released by bending the optical fiber so as to undulate. At this time, if the space inside the outer cover is narrow, the optical fiber cannot be bent uniformly, and the optical fiber is locally bent with a small bending diameter, which causes an increase in macrobend loss. On the other hand, by securing a certain void inside the outer cover, it is possible to reduce the increase in transmission loss at low temperature.

On the other hand, when the optical fiber cable is arranged in a high temperature environment, the outer cover portion expands as described above. _FIG . 7A is a development view showing a state in which the outer cover portion is expanded and the pitch is changed from _p0 to p2. In this case, the optical fiber unit (internal optical fiber) is pulled. In this case, as shown in FIG. 7B, the tensile strain of the optical fiber is released by reducing the layer core diameter of the optical fiber unit (that is, by winding from the layer core diameter d ₀ to d ₁ ). Will be done. However, if the core diameter of the layer changes significantly, it may receive lateral pressure from the adjacent optical fiber or bundle tape, causing an increase in microbend loss.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical fiber cable capable of suppressing an increase in transmission loss particularly at a high temperature.

In order to achieve the above-mentioned object, the present invention is an optical fiber cable composed of a plurality of optical fiber core wires, wherein the plurality of the optical fiber core wires are twisted to form an optical fiber unit, and the plurality of the optical fibers are formed. The unit is twisted into a plurality of layers, and the twisting ratio of the optical fiber unit in each layer is larger than the reference twisting ratio calculated from the twist pitch and the layer core diameter of the optical fiber unit in each layer. It is an optical fiber cable.

It is desirable that the difference between the twisting ratio of the optical fiber unit in each layer and the reference twisting ratio in each layer increases from the outer layer to the inner layer.

It is desirable that the difference between the twisting ratio of the optical fiber unit in the innermost layer and the reference twisting ratio in the innermost layer is 0.04% or more.

It is desirable that the difference between the twisting ratio of the optical fiber unit in the outermost layer and the reference twisting ratio of the outermost layer is 0.015% or less.

According to the present invention, the actual twisting ratio of the optical fiber unit is set to be larger than the standard twisting ratio calculated from the twisting pitch and the core diameter of the optical fiber unit in each layer in advance, so that the twisting ratio of the actual optical fiber unit is increased at high temperature. Also, it is possible to follow the increase in the twist pitch of the optical fiber unit. Therefore, it is possible to suppress the tensile strain of the optical fiber unit and the increase in loss due to the increase in lateral pressure due to winding tightening.

Further, by increasing the difference between the entwining ratio of the optical fiber unit and the standard entwining ratio in each layer from the outer layer to the inner layer, the loss increase of the optical fiber unit on the inner layer side, which is a stricter condition, is dealt with. It is effective.

In particular, by setting the difference between the twisting ratio of the optical fiber unit in the innermost layer and the reference twisting ratio in the innermost layer to 0.04% or more, it is possible to more reliably suppress the increase in loss.

Further, since the outermost circumference is held down by the outer cover, if the twisting ratio of the outermost circumference is increased, the transmission loss may increase due to the lateral pressure from the outer sheath. By setting the difference in the reference twisting ratio of the outermost layer to 0.015% or less, the influence can be suppressed.

According to the present invention, it is possible to provide an optical fiber cable capable of suppressing an increase in transmission loss particularly at a high temperature.

Sectional drawing of an optical fiber cable 1. It is sectional drawing of optical fiber cable 1, and is the figure which shows the dimension of each part. (A) is a diagram showing a twisted state of the optical fiber unit 5, and (b) is a developed view of the optical fiber unit. The figure which shows the relationship between the layer core diameter and the twisting ratio (reference twisting ratio) in an ideal state in the case of a pitch of 750mm. The figure which shows the twisted state of an optical fiber unit 100. (A) is a development view of an optical fiber unit, and (b) is a development view of an optical fiber unit at a low temperature. (A) is a development view of the optical fiber unit at a high temperature, and (b) is a development view of the optical fiber unit in a wound state.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the optical fiber cable 1. The optical fiber cable 1 is a slotless cable that does not use a slot, and is mainly composed of a tension member 9, an outer cover 13, a cable core 15, and the like.

The cable core 15 is formed by twisting a plurality of optical fiber units 5. The optical fiber unit 5 is formed by, for example, twisting a plurality of optical fiber core wires 3 together. That is, the optical fiber cable 1 is composed of a plurality of optical fiber core wires 3. The optical fiber core wire 3 is, for example, an intermittently bonded optical fiber tape core wire that is intermittently bonded in the longitudinal direction.

A presser winding 7 is provided on the outer circumference of the cable core 15. The presser roll 7 is a tape-shaped member, a non-woven fabric, or the like, and is arranged so as to collectively cover the outer periphery of the cable core 15 by, for example, vertical attachment. That is, the longitudinal direction of the presser winding 7 substantially coincides with the axial direction of the optical fiber cable 1, and the width direction of the presser winding 7 is vertically attached to the outer periphery of the cable core 15 so as to be the circumferential direction of the optical fiber cable 1.

In the cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 1, tension members 9 are provided on both sides of the cable core 15 (press winding 7). That is, a pair of tension members 9 are provided at positions facing each other with the cable core 15 interposed therebetween. Further, a tear string 11 is provided so as to face the tension member 9 with the cable core 15 (holding winding 7) interposed therebetween in a direction substantially orthogonal to the facing direction of the tension member 9.

An outer cover 13 is provided on the outer periphery of the cable core 15. The tension member 9 and the tear string 11 are embedded in the outer cover 13. That is, the outer cover 13 is provided so as to cover the cable core 15, the tension member 9, and the like. The outer shape of the outer cover 13 is substantially circular. The jacket 13 is, for example, a polyolefin-based resin. The tension member 9, the tear string 11, and the outer cover 13 may be collectively referred to as an outer cover portion.

Next, the cable core 15 will be described in detail. As described above, the plurality of optical fiber core wires 3 are twisted together to form the optical fiber unit 5. Further, a plurality of optical fiber units 5 are twisted together to form a cable core 15. At this time, the plurality of optical fiber units 5 are twisted into a plurality of layers.

FIG. 2 is a conceptual diagram of a cable core 15 formed in a plurality of layers. In the illustrated example, the cable core 15 has a four-layer structure of a first layer 17a, a second layer 17b, a third layer 17c, and a fourth layer 17d. If the cable core 15 is formed into a plurality of layers, the number of layers of the cable core 15 is not particularly limited.

In each layer, a plurality of optical fiber units 5 are twisted together. At this time, the boundary between the layers is approximately divided into a circle, and the center line of each divided layer is defined as the layer center diameter of each layer. In the illustrated example, the layer core diameter of the first layer 17a is D1, the layer core diameter of the second layer 17b is D2, the layer core diameter of the third layer 17c is D3, and the layer of the fourth layer 17d. The core diameter is D4. That is, the layer core diameter of each layer is calculated by (outer diameter + inner diameter) / 2 of each layer (however, the inner diameter of the first layer 17a, which is the innermost layer, is 0). Further, the thickness of each layer is substantially the same as the diameter of the optical fiber unit (however, the outer diameter of the innermost layer is substantially the same as the diameter of the optical fiber unit × 2).

FIG. 3A is a diagram showing a twisted state of the optical fiber unit 5, and FIG. 3B is a developed view of the optical fiber unit 5. In the illustrated example, the twisting pitch of the optical fiber unit 5 is P, and the layer core diameter is D. At this time, in the ideal state, the length of the optical fiber unit 5 at one pitch is the length _L0 of the hypotenuse of a right triangle having a base P and a height πD. The twisting rate at this time is the twisting rate (%) = ((L ₀ / P) -1) × 100 = (√ (P ² + π ² · D ² ) / P-1) × 100. That is, the ideal twisting ratio is simply calculated for each layer.

FIG. 4 is a diagram showing, as an example, the relationship between the core diameter of the layer and the twisting ratio in the ideal state in the case of a pitch of 750 mm. Here, the twisting ratio in the ideal state is the twisting ratio when the twisting pitch and the twisting diameter (layer core diameter) are constant without variation and are wound without any slack. It is called the twisting ratio.

As shown in FIG. 4, for example, when the layer core diameter is 4 mm, the standard twisting rate is about 0.014%, and when the layer core diameter is 3 mm, the standard twisting rate is about 0.008%, and the layer core is about 0.008%. When the diameter is 2 mm, the standard twisting ratio is about 0.0035%. Here, in the present invention, the actual twisting ratio of the optical fiber unit 5 in each layer of the cable core is larger than the reference twisting ratio calculated from the twist pitch P and the layer core diameter D of the optical fiber unit in each layer. Specifically, as shown by the dotted line A shown in FIG. 3B, the length of the optical fiber unit 5 is set longer than the length _L0 of the hypotenuse of the right triangle, and the optical fiber unit 5 is slightly loosened. To form.

As described above, when the outer cover portion expands at a high temperature, the pitch P becomes large, so that a tensile force is applied to the optical fiber unit 5. Further, in order to relax this tensile force, the layer core diameter of the optical fiber unit 5 tries to be reduced (see FIGS. 7 (a) and 7 (b)).

On the other hand, by forming a slack in the optical fiber unit 5 in advance at room temperature to make the actual twisting rate larger than the standard twisting rate, even if the pitch P becomes large at high temperature, , It is possible to suppress an increase in the tensile force applied to the optical fiber unit 5. Therefore, even a slight change in the core diameter of the layer can alleviate the tensile strain.

Here, as shown in FIG. 4, when the layer core diameter is 4 mm, the reference twist rate decreases by about 0.006% when the layer core diameter changes by 1 mm, but when the layer core diameter is 3 mm, the reference twist rate decreases. Even if the core diameter of the layer changes by 1 mm, the standard twisting rate decreases by only about 0.0045%. That is, if the pitch is constant, when the layer core diameter is large (that is, on the outer layer side), even a slight change in the layer core diameter causes a reference twist rate (that is, the required length of the optical fiber unit). ), But when the layer core diameter is small (that is, on the inner layer side), the reference twist rate (that is, the required length of the optical fiber unit) changes even if the layer core diameter changes. The amount is small.

In other words, in the optical fiber unit on the outer layer side, the tensile strain is alleviated by slightly moving the optical fiber unit toward the center side of the cable core 15 so as to reduce the core diameter of the layer. On the other hand, in the inner optical fiber unit, even if the optical fiber unit moves slightly toward the center of the cable core 15 so as to reduce the layer core diameter, the amount of relaxation of tensile strain is small. Therefore, the tensile strain cannot be alleviated unless the optical fiber unit moves significantly to the center side of the cable core 15.

That is, in the optical fiber unit on the outer layer side, even if the difference between the actual twisting ratio and the reference twisting ratio is small, the tensile strain is alleviated by slightly changing the layer core diameter of the optical fiber unit. On the other hand, in the optical fiber unit on the inner layer side, if the difference between the actual twisting ratio and the reference twisting ratio is small, the tensile strain cannot be alleviated even if the layer core diameter of the optical fiber unit is slightly changed. Therefore, it is desired that the optical fiber unit on the inner layer side has a large difference between the actual twisting rate and the reference twisting rate.

As described above, it is desirable that the smaller the core diameter of the layer, the larger the difference between the actual twisting rate and the reference twisting rate. That is, it is desirable that the difference between the twisting ratio of the optical fiber unit in each layer and the reference twisting ratio in each layer increases from the outer layer to the inner layer.

Further, it is desirable that the difference between the twisting ratio of the optical fiber unit in the innermost layer and the reference twisting ratio of the innermost layer is 0.04% or more, and more preferably, the twisting ratio of the optical fiber unit in the innermost layer. The difference in the standard twisting ratio of the innermost layer is 0.09% or more. If the difference between the twisting ratio of the optical fiber unit in the innermost layer and the reference twisting ratio in the innermost layer is too small, the effect of suppressing the increase in loss is small.

On the other hand, if the difference between the actual twisting rate and the reference twisting rate is increased, the amount of slack in the optical fiber unit from the reference state becomes large. Normally, this slack is absorbed by the slack in the longitudinal direction and the slack toward the adjacent outer layer. However, in the optical fiber unit of the outermost layer, since the outer layer side is the outer layer 13, the outer layer 13 suppresses the slack, which causes an increase in loss especially at a low temperature. Therefore, in the outermost layer, it is desirable that the difference between the actual twisting rate and the standard twisting rate is small.

Therefore, it is desirable that the difference between the twisting rate of the outermost layer optical fiber unit and the reference twisting rate of the outermost layer is 0.015% or less, and more preferably, the twisting rate of the outermost layer optical fiber unit. The difference in the standard twisting ratio of the outermost layer is 0.010% or less. If the difference between the twisting ratio of the optical fiber unit in the outermost layer and the reference twisting ratio in the outermost layer is large, the lateral pressure due to the outer cover increases and the transmission loss increases.

As described above, according to the present embodiment, by setting the twisting ratio of the optical fiber unit 5 of each layer to be larger than the standard twisting ratio of each layer, an increase in transmission loss is suppressed especially at high temperature. can do. At this time, the difference between the twisting ratio of the optical fiber unit in each layer and the reference twisting ratio in each layer is configured to increase from the outer layer to the inner layer, thereby ensuring an appropriate amount of slack in each layer. Can be done.

Various optical fiber cables were made, and it was confirmed that the transmission loss increased at high temperature and low temperature. First, 12 optical fibers having a diameter of 200 um were intermittently bonded to create a 12-core intermittent tape core wire. Further, 12 of the obtained intermittent tape core wires were twisted and wound with a plastic tape having a width of 2 mm to form a 144-core optical fiber unit.

A total of 48 144-core optical fiber units were twisted in 4 layers in order from the inner layer side so as to form an arrangement of 2-9-15-22. The twist pitch of the optical fiber unit of each layer was set to 750 mm. Here, when twisting the optical fiber units, the twisting ratio of each layer was adjusted by changing the balance of the supply tension of each optical fiber unit. At the site where 48 optical fiber units were supplied, a water-absorbent non-woven fabric was vertically attached, rolled with a forming jig, and a nylon presser thread was wound around it to create a 6912-core cable core.

The cable core thus prepared, a tension member using a glass fiber reinforced resin having a diameter of 2.0 mm, and a tear string for tearing the outer cover were sheathed in a cylindrical shape with the outer cover material to prepare an optical fiber cable. The outer cover material was LLDPE. The outer diameter of the optical fiber cable was 29 mm, and the inner diameter of the outer cover was 22 mm.

For each of the manufactured optical fiber cables, run along 20 m, remove the outer cover, take out each optical fiber unit, measure the length, measure the difference from the cable length of 20 m, and calculate the average value for each layer. did. The twist ratio was calculated by (√ (P ² + π ² · D ² ) / P-1) × 100 (%) when the twist pitch of the optical fiber unit was P and the layer core diameter of the unit was D. ..

The standard value of the twisting ratio is 2.85 mm for the outer diameter of the optical fiber unit, 2.85 mm for the core diameter of the first layer, and 2.85 + 2.85 × 2 = 8. The core diameter of the third layer was 8.55 + 2.85 × 2 = 14.25 mm, and the core diameter of the outermost layer was 14.25 + 2.85 × 2 = 19.95 mm.

The temperature characteristics of each optical fiber cable were measured. For temperature characteristics, an optical fiber cable is wound around a drum with a body diameter of 1800 mm, the drum is placed in a large constant temperature bath, the temperature inside the constant temperature bath is changed, and the transmission loss is measured by OTDR at a wavelength of 1550 nm. The difference from the measured value of was calculated. Table 1 shows the evaluation results of the twisting ratio of each optical fiber unit and the temperature characteristics of the transmission loss.

In Examples 1 to 4, the twisting ratio of each layer is large with respect to the reference value, and the maximum loss increase at high temperature (70 ° C.) and low temperature (-30 ° C.) is 0.15 dB / km or less. Was done. On the other hand, in the comparative example manufactured according to the substantially standard value, the maximum loss increase at high temperature (70 ° C.) exceeded 0.15 dB / km.

More specifically, Examples 1 to 3 are configured such that the difference from the reference value of the twisting ratio of the optical fiber unit in each layer increases from the outer layer to the inner layer. On the other hand, in Example 4, the twisting rate was increased by about 0.05% as a whole as compared with the reference value. In Example 4, the increase in loss at high and low temperatures could be suppressed to 0.15 dB / km or less, but the increase in loss at low temperatures (-30 degrees) was higher than in the comparative example, reaching 0.10 dB / km. Beyond.

In Example 3, the twisting ratio is increased by giving a gradient of 0.001 to 0.046% from the innermost layer to the outermost layer. In Example 3, the increase in loss at high temperature was reduced as compared with the comparative example, but it could not be less than 0.10 dB / km. However, since the difference from the standard twisting ratio of the outermost layer was 0.001%, which was 0.01% or less, the increase in loss at low temperature was only a slight increase compared to the comparative example.

In Example 2, by setting the difference from the reference twisting ratio of the innermost layer to 0.09% or more, the increase in loss at high temperature could be suppressed to 0.10 dB / km or less. Since the difference in the standard twisting ratio of the outermost layer was 0.01% or less, the increase in loss at low temperature was only a slight increase compared to the comparative example.

In Example 1, by setting the difference in the reference twisting ratio of the innermost layer to 0.1% or more, it was possible to suppress an increase in loss at a higher temperature than in Example 2. On the other hand, since the difference from the standard twisting rate of the outermost layer exceeds 0.01%, the increase in loss at low temperature slightly increased as compared with Example 2, but the standard twisting rate of the outermost layer. Since the difference from the above was 0.015% or less, the increase in loss at low temperature could be suppressed to 0.10 dB / km or less.

Although the embodiments of the present invention have been described above with reference to the attached drawings, the technical scope of the present invention does not depend on the above-described embodiments. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs to.

1 ………… Optical fiber cable 3 ………… Optical fiber core wire 5 ………… Optical fiber unit 7 ………… Press winding 9 ………… Tension member 11 ………… Tear string 13 ………… Cover 15 ………… Cable core 17a ………… 1st layer 17b ………… 2nd layer 17c ………… 3rd layer 17d ………… 4th layer 100 ………… Optical fiber unit

Claims (4)

An optical fiber cable consisting of multiple optical fiber core wires.
A plurality of the optical fiber core wires are twisted to form an optical fiber unit, and the plurality of the optical fiber units are twisted into a plurality of layers.
An optical fiber cable characterized in that the twisting ratio of the optical fiber unit in each layer is larger than the reference twisting ratio calculated from the twist pitch and the layer core diameter of the optical fiber unit in each layer. The optical fiber cable according to claim 1, wherein the difference between the twisting ratio of the optical fiber unit in each layer and the reference twisting ratio in each layer increases from the outer layer to the inner layer. The optical fiber cable according to claim 1 or 2, wherein the difference between the twisting ratio of the optical fiber unit in the innermost layer and the reference twisting ratio of the innermost layer is 0.04% or more. The optical fiber according to any one of claims 1 to 3, wherein the difference between the twisting ratio of the optical fiber unit in the outermost layer and the reference twisting ratio of the outermost layer is 0.015% or less. cable.

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