JPS63301911A - Optical fiber cable - Google Patents

Abstract

PURPOSE:To suppress the increase of a transmission loss depending on the bending direction, by setting an inversion angle for showing a rotational angle in the grooved spacer peripheral direction in which the spiral direction of a spiral groove reaches the next inversion position from one inversion position, to a specific range. CONSTITUTION:In an optical fiber cable of a structure which has contained an optical fiber 4 in groove of a grooved spacer 3 having a spiral groove whose direction is inverted periodically, on the outside periphery, an inversion angle for showing a rotational angle in the groove spacer peripheral direction in which the spiral direction of the spiral groove reaches the next inversion posi tion F2 from one inversion position F1 is set between 230 deg. and 330 deg.. Also, an angle which has added has added 360 deg.X(n) (n is an integer multiple >='0') to the inversion angle of this range is set as an inversion angle, and especially desirably, the inversion angle is set to about 275 deg. or 275 deg.+360 deg.X(n) (n is integer multiple >='0'). In such a way, an increase of a transmission loss depending on the bending direction of the optical fiber cable, as well can be suppressed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical fiber cable, and particularly to a structure in which an optical fiber is housed in a groove of a grooved spacer having a spiral groove whose direction is periodically reversed on the outer periphery. This invention relates to improvements to optical fiber cables.

[Conventional technology]

In contrast to the conventional optical fiber cable structure in which optical fibers are twisted in one direction and housed in the groove of a spiral grooved spacer, a structure that can improve the manufacturability of optical fiber cables has been proposed, for example, in Japanese Patent Laid-Open No. 52 As disclosed in Japanese Patent No. 126238, an optical fiber cable has been proposed in which an optical fiber is housed in a groove of a spiral grooved spacer in which the spiral direction is reversed at appropriate intervals.

[Problem that the invention seeks to solve]

The above-mentioned optical fiber cable has a structure in which the optical fiber is housed in the groove of a spiral grooved spacer in which the helical direction is reversed, which has improved manufacturability, but on the other hand, transmission due to bending of the optical fiber cable Problems that did not exist with conventional optical fiber cables having a structure twisted in one direction have arisen in that the increase in loss is large and the increase in transmission loss also depends on the direction of bending of the optical fiber cable. For example, if an optical fiber cable is structured such that an optical fiber is housed in a groove of a grooved spacer with an outer diameter of 9 mmφ and the helical direction reverses every 360 degrees, and the optical fiber is bent to a radius of 100 mm, a problem will occur in the optical fiber housed in the groove. It has been found from theory and experiments that the strain is as much as 1%. This 1% distortion is
This already exceeds the screening level of 0.7% during normal optical fiber manufacturing, which is unacceptable in terms of optical transmission loss and optical fiber life. However, the reason why this type of optical fiber cable is inferior in terms of bending properties is currently unresolved.

! No matter which direction an octopus-type optical fiber cable is bent, the study and design of the inversion angle that minimizes the strain on the optical fiber remains unresolved.

Note that the reversal angle here refers to the rotation angle in the circumferential direction of the grooved spacer from one reversal position to the next reversal position of the groove of the spiral grooved spacer whose direction is reversed at appropriate intervals. FIG. 2 shows the rotation angle ψ in the circumferential direction of the central member 1 corresponding to the grooved spacer from the starting point, for example Fl, of the reversal to the end point, ie, the point F2 at which the next reversal occurs.

[Means for solving problems]

The present invention solves the conventional unresolved problems and provides an optical fiber cable with an optimal reversal angle. In an optical fiber cable having a structure in which a fiber is housed, the reversal angle ψ, which indicates the rotation angle in the circumferential direction of the grooved spacer from one reversal position to the next reversal position, is from 230° to 330°. The inversion angle is preferably about 275°.
or 275°+360°Xn (n is an integer multiple of 0 or more)
It is characterized by setting.

[Effect]

The effects of the configuration of the present invention will be explained below. FIG. 3 is a diagram showing an outline of the structure of an optical fiber cable having a structure in which the twist directions are periodically reversed. 3 is a central member corresponding to a grooved spacer, and 4 is an optical fiber housed in a spiral groove with its direction reversed; the spiral groove is also shown. FIG. 4 is a diagram developed on a plane centered on point A in FIG. 3.

Note that FIGS. 3 and 4 are diagrams modeled assuming that the optical fiber 4.2 has a tight structure.

In the coordinate system shown in FIG. 3, for example, the center member 3 is
- When bent so that the bending center is on the -z plane and in the positive direction of X, the B of the optical fiber 2 is
-A shrinkage strain occurs in the A and A-D portions, and an elongation strain occurs in the C-B and D-C portions of the optical fiber 2. If the reversal angle ψ shown in FIG. 2 is set to less than 180°, shrinkage distortion will occur in the entire optical fiber.

That is, this is the reason why the inversion angle ψ is not normally set to 180° or less in an optical fiber cable having this type of structure.

We attempted to develop a theory as detailed below for the case where the inversion angle is 360°, which is conventionally employed in optical fiber cables having this type of structure. As a result, even when the optical fiber is bent in the same direction as in the case shown in Figure 3 above, even in a state where it can move freely, the strain that occurs in the optical fiber, that is, the difference between the elongation strain and the contraction strain, is substantially reduced. It has become clear that this will remain to an extent that cannot be ignored. Therefore, the cause of the poor bending properties of conventional optical fiber cables with this type of structure has been clarified.

The inventors first theoretically studied the reversal angle at which when an optical fiber cable with this structure is bent, the stretching strain and the contraction strain occurring in the optical fiber are equal in amount.

Based on the model shown in FIG. 3, the shape of the optical fiber between point F1 and point F2 in the figure can be expressed by the following equation (1).

In equation (1), a is the distance between the OAs shown in Figure 3, θ is the angle that the radius vector in the x-y plane makes with the X axis, ψ is the inversion angle,
P is the pitch of the helix. From equation (1), the line length from point F1 to point F2 of the optical fiber. can be found.

Next, the central member 3, which is a model of an optical fiber cable, is
When bent with radius R in the direction where the angle with the X axis is α,
Although the detailed calculation process is omitted, equation (1) can be calculated as follows (
2) It is derived from Eq.

From equation (2), the line length LR from the point F1 to the point F2 of the optical fiber 40 when the central member 3 is bent with a radius R in the direction where the angle with the X axis is α can be determined.

Further, the strain ε (%) of the optical fiber 4 from point F1 to point F2 can be calculated from the following equation (3).

Here, as shown in FIG. 3, the sense of distortion is the distortion at half a pitch of the optical fiber 40, that is, P/2, and the most desirable inversion angle is such that this distortion becomes zero.

As an example of calculation, for example, P=400mm+a=
4mm, R=100mm and R=300
FIG. 5 shows the results of determining the relationship between ε in equation (3) and the reversal angle, assuming mm.

The solid line portion in FIG. 5 is the calculation result when the bending radius R=100 mm, and the dotted line portion is the calculation result when the bending radius R=300 mm. The vertical axis in FIG. 5 is the strain from the F1 point to the F2 point of the optical fiber 4 shown in FIG.
It is. In addition, in Figure 5, the numerical values shown on the short solid lines at the ends of each strain characteristic showing the calculation results are the 6th
FIG. 3 shows an angle representing the bending direction shown in the diagram that defines the bending method of the optical fiber cable in the diagram.

From the results shown in FIG. 5, it can be seen that under the above-mentioned conditions, no matter which direction the optical fiber is bent and regardless of the bending radius, the reversal angle at which the recognition or rejection occurring in the optical fiber becomes zero is around 275°. In addition, since the outer periphery of the cylindrical grooved spacer has a spiral groove structure that periodically reverses direction, the preferred reversal angle determined by the above calculation is 275° to 360°.
It is clear that the same result can be obtained by adding .

Next, an example will be shown in which the calculation results shown in FIG. 5 are verified through the following experiment. Outer diameter 9mmφ, reversal pitch 400mm 1 reversal angle 180°, 250°, 275°, 310°, 360
Prepare one each of five types of helical grooved spacers, store the optical fiber tightly in the grooves of these grooved spacers, fix both ends of the optical fiber to the grooved spacers, and then This method, which measures the elongation of an optical fiber by injecting light from one end of the optical fiber and detecting the phase change of the received light at the other end, can reduce the distortion of the optical fiber shown in Figure 5. The strain of the optical fiber was measured when the optical fiber was bent in the direction in which it was thickest.

Figure 7 shows the experimental results. The solid line shows the bending radius R
=100mm, the dotted line shows the bending radius R=
This is the result for 300mm. From FIG. 7, it can be seen that the experimentally measured results are in close agreement with the theoretical calculation results shown in FIG.

Normally, optical fiber cables are allowed to be bent to a radius of 20 to 100% of the diameter of the optical fiber cable in a long-term use environment. Furthermore, in a short-term use environment, bending with a radius of about 10 times the diameter of the optical fiber cable is permissible. Therefore, from the perspective of optical fiber transmission loss and lifespan, in the long term, the distortion of the optical fiber should be reduced to 0.2% or less, and in the short term, the normal screening level of the optical fiber, that is, the strength guarantee level, should be reduced to 0. It is necessary to keep it below .7%.

Currently, the outer diameter of the optical fiber cable in the calculation model is 10 mm.
Since it is φ, the bending radius R, which is I times the outer diameter, is 30
0 mm, and the 10x bending radius R is 100 mm. Therefore, from the calculation results shown in Figure 5 and the experimental results shown in Figure 7, the permissible range for acceptance or rejection of optical fibers in the usage environment described above is 0.2% or less in the long-term case and 0.7% in the short-term case. The reversal angle that satisfies the tolerance range less than or equal to 2
A range between 40° and 310° is found to be suitable. Furthermore, when optical fibers are collected and housed in the groove of a grooved spacer, an extra length of about 0.1% is usually provided, so even if the inversion angle is increased from 230° to 330°, the optical fiber It was found that the distortion could be suppressed within an acceptable range. In addition, for an optical fiber cable with this type of structure, as explained in the calculation results shown in FIG.
230°+360°×n to 330°+360°Xn (
It is clear that almost the same results can be obtained even if the range is set to (n is an integer greater than or equal to 0).

Moreover, when the outer diameter of the optical cable is changed, the above-mentioned results can be applied by appropriately selecting the helical pitch.

In order to verify the above results, the inventors conducted a theoretical verification using mathematical calculations. The contents will be explained below.

In the schematic diagram of the optical fiber cable structure shown in Fig. 3, which has a structure in which the multiple twisting directions are reversed, when first considering the case where it is bent on the x-z plane, the three-dimensional space curve expressed by equation (1) is The factors that cause distortion due to bending on the When the line segment dz is bent by the radius R, the length of the line segment is (R+X)dξ. However, at that time, the length of the center line does not change, so Rdξ=dz...
- The relationship (4) holds true. Therefore, the relationship (R+x)dξ=dz+T=(5) is induced.

From equation (5), the elongation (
If X is negative, shrinkage) dΔlz is given by the following equation (6).

d△lz=-xdz ・・・・・・
(6) In proceeding with the calculation, the variable θ shown in equation (1) is converted into the variable t shown by the following function.

, -1u ・Song interval (7) 1=stn ψ Substituting equation (7) into equation (1) and then into equation (6), the sum of the elongations from point 21 to point F2 shown in Figure 3 is obtained. can be expressed by the following equation (8).

It is clear that the reversal angle ψ at which the integral value of equation (8) becomes zero is the optimal reversal angle.

Direction where the angle made with any X axis is α (shown in Figure 6)
When bent with radius R, the sum of elongations from point 21 to point F2, also shown in FIG. 3, can be expressed by the following equation (9), although the detailed calculation process will be omitted.

It can be seen from equation (9) that when bent on α-0, that is, the xz plane, it becomes the same as equation (8).

When finding the next zero point, ”-=2.4...
...α]) is obtained. When ψ is expressed as an angle, ψ
=275°. Furthermore, 2 or more zero points are
It has been clarified that the optimal inversion angle is close to the value obtained by adding an integral multiple of 360° to 5°.0 The above theoretical verification has shown that the optimal inversion angle is 360° regardless of the pitch P, radius R2, and bending radius of the inversion helix.
It has been proven that within the following range it is 275°. Specific examples will be described below.

〔Example〕

FIG. 1 shows a cross section of a prototype optical fiber cable according to the present invention having a structure in which an optical fiber is accommodated in a grooved spacer in which the helical direction of the spiral groove is periodically reversed.

The grooved spacer 6 has four grooves with an inversion angle ψ of 280°, a helical pitch P of 400 mm, and an outer diameter of 9 mmφ. This optical fiber cable has a structure in which optical fiber units 7 are housed one by one in the grooves of this grooved spacer 6, and the outer periphery of which is wrapped with a presser winding 8 is coated with a LAP sheath 5. Note that 9 is the central tensile strength member.

A prototype optical fiber cable according to the present invention has a radius of 10
When bent to 0 mm, the strain produced in the optical fiber is 0.
It was less than 2%. Also, when bent to a radius of 300mm,
The strain generated in the optical fiber was 0.1% or less.

Although the above embodiment has been described for the case where n is zero, the present invention is not limited to this embodiment.

In the present invention, n may be an integer greater than or equal to zero, for example,
Normally, in order to make the total processing length of the terminal as long as possible for a branch optical cable, the S direction twist is repeated several times, the twist direction is reversed once, and the two direction twist is continued several times. Grooved spacers may be used.

As an example of the cable, for example, a grooved spacer type optical fiber cable with n=10 was manufactured as a prototype (not shown). The spacer has four grooves with an outer diameter of 9 mmφ, and the shape of the grooves is S with a pitch of 200 mm.
The direction twisting continues 10 times, and then the twisting direction is reversed,
The inversion angle is 275°, and the two-way twist is 1
It lasted 0 times. Three optical fiber strands were housed in the grooves of this grooved spacer, and the fibers were further pressed and wound to cover the outer periphery with a LAP sheath to form a cable. When the cable was bent to a radius of 100 mm around the reversed portion, the strain produced in the optical fiber was 0.15% or less. However, when the same grooved spacer cable with n=10 and the inverted angle of the inverted part is 360 degrees is bent to the same radius, the strain generated in the optical fiber is about 0.
It was measured to be 25%.

The specific number of n varies depending on the use of the cable, the outer diameter of the cable, the number of fibers to be stored, the scale of the collective equipment, etc., but the gist of the present invention is that regardless of the number of n, it is possible to For example, it describes the optimal angle of the reversal angle.

〔Effect of the invention〕

As described above, the optical fiber cable according to the present invention has a structure in which an optical fiber is housed in a groove of a grooved spacer having a spiral groove whose direction is periodically reversed on the outer periphery. The optimal reversal angle ψ of the helical direction is 230° + 360°Xn × ψ≦330°
By setting the cable in the range of +360° This solves the problem of increased transmission loss depending on the bending direction of the optical fiber cable, which was a problem with this type of optical fiber cable with a structure in which the optical fiber is housed in the groove of a spiral grooved spacer whose helical direction is reversed. and the effect is great.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional structural diagram of the optical fiber cable of the present invention, Fig. 2 is a diagram defining the reversal angle, Fig. 3 is a structural schematic diagram of an optical fiber cable with a structure in which the twist direction is reversed, and Fig. 4 is Figure 3 is expanded on a plane, Figure 5 is the theoretical calculation result of the relationship between the reversal angle and optical fiber strain, Figure 6 is a diagram defining the bending direction of the cable, and Figure 7 is the relationship between the reversal angle and the strain of the optical fiber. Figure 8 is a diagram illustrating the experimental results of the relationship between optical fiber strain and bending strain. 1.3... Central member 2.4... Optical fiber 5... LAP sheath 6... Grooved spacer 7... Optical fiber unit 8... Presser winding 9... Central tensile strength body patent Applicant Sumitomo Electric Industries Co., Ltd. Agent Patent Attorney Tama Mushi Fifth theoretical calculation result of the relationship between the Kugobe reversal angle and the distortion of the fiber
Fig. 6 Defining the bending direction of the cable Fig. 7 Experimental results of the relationship between the reversal angle and optical fiber strain Fig. 7

Claims (1)

[Scope of Claims] An optical fiber cable having a structure in which an optical fiber is housed in a groove of a grooved spacer having a spiral groove whose direction is periodically reversed on the outer periphery, wherein the spiral direction of the spiral groove is one reverse. The reversal angle φ, which indicates the rotation angle in the circumferential direction of the grooved spacer from one position to the next reversal position, is 230° + 360° x n≦φ≦330°+360°×n
(n is an integer greater than or equal to 0).