JP2599905B2 - Optical fiber cable - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a structure of an optical fiber cable.

2. Description of the Related Art Problems to be solved by the prior art and the invention
FIG. 6 and FIG.

In FIG. 5, 1 is an optical fiber core or an optical fiber unit 1A, 2 is a tensile member, and 3 is a jacket.

Here, the optical fiber unit 1A has a structure in which the optical fiber 1 is directly assembled tightly (Ref. 1, Masaaki Kawase et al. “Design and Characteristics of Subscriber Optical Cable” Research and Application Report, Research Institute of Electrical Communication, 33, No. 3, P517, 1984 ), But loosely housed in a pipe (Ref. 2 P. Patel et al “Compact Lightguid
e Cable Design "Proceeding of IWCS, 34th P21,1985)
But it is good. In such a structure, a difference occurs in the radius of curvature depending on the position of the optical fiber when the drum is wound or bent, and a compressive strain occurs inside the bend and an elongation strain occurs outside the bend. Since these strains may cause an increase in loss or a risk of breaking the optical fiber, the optical fiber unit 1A is twisted around the strength member 2 so as to have a structure in which expansion and contraction due to bending are averaged. I have. However, in the twisting process at the time of cable manufacturing, not only the manufacturing equipment becomes large and complicated, but also
There is a problem that the manufacturing speed is also slow.

FIG. 6 shows an optical fiber unit loosely assembled in a pipe. 1A is an optical fiber unit, 4 is a tensile member uniformly embedded in the jacket 3, and 5 is a hollow portion of the pipe 6.

In a cable with such a structure, the position of the optical fiber cannot be fixed to the center of the cable during manufacturing, so the cross-sectional shape is not point-symmetric, and the radius of curvature of the optical fiber and the radius of curvature of the center of the cable when the drum is wound or bent. The length of the cable does not match the length of the cable when the wire is wound, or the optical fiber is pulled or protruded at the cable end, or the optical fiber is distorted. there were.

Means for Solving the Problems The present invention accommodates an optical fiber unit or an optical fiber in a state of being in contact with the inner surface of a pipe-shaped cavity formed in a plastic jacket, and uses a plastic material in the meat portion of the plastic jacket. When a tensile member having a high Young's modulus is buried and the optical fiber cable is bent, the position of the optical fiber or the optical fiber unit is fixed at a fixed point (neutral point of bending) where expansion and contraction does not occur due to bending in the cross section of the optical fiber cable.
Or a metal pipe-shaped hollow portion by providing a metal layer on the inner surface of the pulp-shaped hollow portion of plastic in which the optical fiber or the optical fiber unit is accommodated, and in the former configuration, Is the maximum allowable value εmax Allowable minimum value of optical fiber extra length εmin In the latter configuration Respectively, and in the above In the description of the other symbols, the description in the claims is cited.

According to the present invention, based on the configuration, the length of the optical fiber and the length of the cable are always equal, and tension is not applied to the optical fiber when the drum is wound or drawn, and no deviation such as pulling in of a terminal occurs. By defining the positional relationship between the position of the optical fiber and the neutral point of bending, there is no increase in loss and the reliability is improved.

FIG. 1 is a sectional view of a first embodiment of the optical fiber cable according to the present invention.

10 is a fiber cable of the present invention, 1 is an optical fiber or an optical fiber unit 1A, 3 is a jacket of PE (polyethylene), 5 is a pipe-shaped hollow portion provided in a jacket 3 containing an optical fiber, 7 Is the metal layer inside the pulp-like cavity,
Reference numeral 8 denotes a tensile strength member eccentrically embedded in the jacket 3.

In the figure, 0 is the center point of the outer diameter (radius R) of the optical fiber cable 10 (hereinafter referred to as cable center point), and 0 'is the center point of the pipe-shaped cavity (hereinafter referred to as cavity center point).
(Inner radius r), d ₁ is the interval of the cable center point 0 and the cavity center point 0 ', d ₂ the distance between the center point of the cable center point 0 and the tension member 8, t is the thickness of the metal layer .

When an optical fiber cable having such a structure is bent, the outside of the bent cable extends, the inside contracts, and a fixed point (hereinafter, a neutral point N) which does not expand and contract exists in the middle. When the neutral point N does not coincide with the cable center point 0, when the cable is wound around a drum having a radius _RD during manufacturing, tension is applied so that the center point of the tension acts inside the bend.

In addition, since a back-tension is applied to the optical fiber during manufacture, the optical fiber is located inside the bend (bottom) in the cavity. Therefore, by defining the position of the neutral point N at the accommodation position of the optical fiber, that is, at the bottom of the pipe-shaped hollow portion 5, the length of the optical fiber can be matched with the length of the cable. Further, if the position of the bottom of the pipe-shaped hollow portion is located outside the neutral point N, the length of the optical fiber can be made longer than the cable length.

When the optical fiber cable of FIG. 1 is raised in the 0-0 ′ direction of the figure, the stress σ in the cross section of the optical fiber cable is increased.
Means that the integral at the total cross-sectional area A becomes 0 from the balance of the force.

_{Ａ A} σdA = 0 (1) Referring to FIG. 1, when the interval between the cable center point 0 and the neutral point N is C, the following equation is obtained.

_{CA P E P + (C +} d 1) (A M E M -A a E P) = (d 2 -C) (A SM E SM -A SM E P) ...... (2) where, E _P, E _M , E _SM is the jacket, metal layer inside the pipe,
It is each Young's modulus of the strength _{members, A P, A M, A} SM, the A _a jacket, a metal layer, strength members, a cross-sectional area of each of the pipe-shaped cavity inside.

 When the equation (2) is arranged for C, the following equation is obtained.

If there is no metal layer 7, that is, if there is only a plastic pipe-shaped cavity, A _M = 0 may be set.

If this is C ' Becomes

When an optical fiber cable having such a structure is wound around a drum having a body radius _RD , the excess length of the optical fiber Is given by

Here, t is the thickness of the metal layer, and in the case of only a plastic pipe-shaped hollow portion, t = 0. r ₀ is the radius of the optical fiber or the optical fiber unit, and when the optical fiber unit is composed of a plurality of optical fibers as in the optical fiber unit 1A, the extra length ratios of the optical fibers located at the innermost and outermost positions of the bending are different. And is expressed by the following equation of the minimum value (innermost) εmin and the maximum value εmax (outermost) of ε.

When an elongation strain is applied to the optical fiber, it causes breakage. Therefore, ε is 0 or more, that is, the length of the optical fiber is the same as the cable length, but it is better to be longer.

However, if the length is too long, the optical fiber meanders inside the pipe of the cable when the wire is drawn, causing bending and increasing the loss.

Now, when the optical fiber has an extra length, if the optical fiber is housed in a spiral manner on the inner wall of the pipe-shaped cavity 5, if the inner radius of the pipe-shaped cavity is r '(r' = rt), the light When the fiber radius is r ₀ and the bending pitch of the optical fiber is P, the extra length ε ₀ of the optical fiber is given by the following equation.

The relationship between the loss increase α due to the bending of the optical fiber having such a shape and the pitch P is described in Reference 3 (Ishihara et al., “Pitch and Optical Loss Increase of Optical Cable,” IEICE Transactions J62-B, No. .10, P956, 1979).

However, _{α; dB / mm r c,} R, P; the unit mm (8) formula calculation result shown in Figure 2.

r 'varies depending on the number of optical fibers, and the allowable value of the increase in loss varies depending on the design of the system. Generally, there is no problem if the value is 0.1 dB / Km or less.

Now, assuming that r '= 5 mm, the allowable margin ratio for suppressing the loss increase to 0.1 dB / Km or less is 45% from FIG. In addition, when r '= 2.5 mm, the remaining length ratio is 2%, which is 0.1 dB / Km or less.
It is.

As described above, if the allowable values of the inner diameter of the pipe-shaped hollow portion and the increase in the loss are set, the maximum allowable length ratio is determined.

In this way, when designing the optical fiber cable, when the maximum value εmax and the minimum value εmin of the allowable surplus length ratio are defined, the tensile strength of the tensile strength member is satisfied from the equations (5) and (6) so as to satisfy the following equation. By setting the structure such as the position, thickness, and cable outer diameter, an optical fiber cable having excellent transmission characteristics and reliability can be realized.

FIG. 3 shows a sectional view of a second embodiment of the present invention.

As shown in the figure, the inner part of the cable outer diameter in the bending direction as shown in FIG. 9 is formed into a plane perpendicular to the 0-0 'axis.

With such a structure, the axis of the optical fiber cable in the cross-sectional direction is stably wound when the optical fiber cable is wound on the drum, and more accurate extra length control is possible.

In the embodiment shown in FIGS. 1 and 3, if the pipe-shaped hollow portion is filled with a waterproof material having fluidity such as dieli, grease, or water-absorbing powder, or the loose is partially or entirely filled with a water-absorbing fiber, the cable becomes Water running can be prevented at the time of cutting or the like, and a highly reliable waterproof optical fiber cable can be realized.

 Next, a design example will be described.

Design example A specific design example is shown below.

As described above, as an example of the design condition, εmin ≧ 0 from the condition that the elongation strain is not applied to the optical fiber, the inner radius of the pipe cavity is set to 5 mm, and εmax ≦ 0.0045 from the condition that the loss increase is 0.1 dB / Km or less. Design as

First, each constant is determined as follows, and then εmin, εmax
There is assumed that the design in procedure for determining the position d ₂ of the strength members so as to satisfy the condition.

R _D = 600 mm R = 10 mm r = 5 mm r ₀ = 1 mm (2 mm diameter optical fiber unit) d ₁ = 3 mm A _SM = 0.785 mm ² (1 mm diameter tensile strength line) E _P = 30 kg / mm ² (PE) E _SM = 21,000 Kg / mm ² (steel wire) A _M = 0 t = 0 First, C that satisfies εmax = 0.0045 is determined from equation (5). When formula (5) is rearranged and calculated for C, Therefore, the neutral point is at a position 2.73 mm from the center of the outer diameter.
By substituting this value into equation (6), εmin = 0.012, and satisfies εmin ≧ 0.

Next, d ₂ is obtained.

(3) expression and to organize for d _2, Substituting the values, d ₂ = 3.47 A cross-sectional view of the cable in this design example is shown in FIG.

1 is an optical fiber unit, 3 is a jacket, 5 is a pipe-shaped cavity, and 8 is a tensile strength member.

In addition to the steel wire, a material having high Young's modulus and high rigidity such as FRP is suitable as the tensile strength member.

Effects of the Invention The optical fiber cable according to the configuration of the present invention has the following advantages. No tension is applied to the optical fiber when the wire is wound or drawn, and no deviation such as pulling in of the terminal occurs. (2) Loss is increased by specifying the positional relationship between the position of the optical fiber and the neutral point of bending. (3) If the pipe cavity is partially or entirely filled with a preventive material, it is possible to prevent water running when cutting the cable.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the optical fiber cable of the present invention, FIG. 2 is a diagram showing the relationship between the extra length of the optical fiber and the increase in loss, and FIG. 2 is a cross-sectional view of an embodiment, FIG. 4 is a cross-sectional view of an example of an optical fiber cable designed based on the present invention, and FIGS. 5 and 6 are cross-sectional views of a conventional cable. 1: Optical fiber core wire, 1A: Optical fiber unit, 2: Tensile body, 3: Jacket, 4: Tensile body evenly embedded in jacket, 5:
Pipe-shaped cavity, 7: Metal layer inside the pipe, 8: Tensile body eccentrically embedded in the jacket, 9: Notch in the jacket

Claims (6)

(57) [Claims] An optical fiber unit or an optical fiber is accommodated in a plastic casing in a state of being in contact with an inner surface of the pipe-shaped cavity, and a plastic material is contained in a flesh portion of the plastic casing. When a tensile member having a high Young's modulus is buried and the optical fiber cable is bent, the position of the optical fiber or the optical fiber unit is fixed at a fixed point (neutral point of bending) where expansion and contraction does not occur due to bending in the cross section of the optical fiber cable. An optical fiber cable, characterized in that the optical fiber cable is configured to conform to the following. 2. A pipe-shaped cavity is formed in a plastic jacket, and an optical fiber unit or an optical fiber core is accommodated in a state of being in contact with an inner surface of the pipe-shaped cavity, and an optical fiber or an optical fiber unit is accommodated therein. A metal layer is provided on the inner surface of the pipe-shaped cavity made of plastic to form a metal pipe-shaped cavity, and a tensile strength member having a Young's modulus higher than that of a plastic material is embedded in the wall of the plastic jacket, and the optical fiber cable is bent. An optical fiber cable, characterized in that the position of the optical fiber or the optical fiber unit coincides with a fixed point (neutral point of bending) where no expansion or contraction occurs due to bending in the cross section of the optical fiber cable. 3. A pipe-shaped cavity is formed in a plastic jacket, and an optical fiber unit or an optical fiber core is accommodated in contact with an inner surface of the pipe-shaped cavity. A tensile strength member having a higher Young's modulus than the material is buried, and the allowable maximum value of the extra length of the optical fiber defined by {(length of optical fiber) − (length of cable)} / (length of cable) is εmax. , When the minimum value is εmin, Where R is the outer radius of the optical fiber cable r is the inner radius of the pipe-shaped cavity r ₀ is the radius of the optical fiber or optical fiber unit R _D is the radius of the drum body around which the optical fiber cable is wound
d ₁ is the distance between the center point of the cable and the center point of the pipe-shaped cavity. Here, E _p and E _SM are the Young's moduli of the jacket material and the tensile strength material, A _P , A _SM , and A _a are the respective cross-sectional areas of the optical fiber cable, the tensile strength material, and the pipe-shaped cavity, and d ₂ is The distance between the center point of the strength member and the center point of the cable. When the above-mentioned two formulas are satisfied and the optical fiber cable is bent, the position of the optical fiber or the optical fiber unit expands and contracts due to bending in the cross section of the optical fiber cable. An optical fiber cable characterized in that it is configured to coincide with a fixed point (neutral point of bending). 4. A pipe-shaped hollow portion is formed in a plastic jacket, and an optical fiber unit or an optical fiber is accommodated in a state of being in contact with an inner surface of the pipe-shaped hollow portion. A tensile strength member having a high Young's modulus is embedded, and a metal layer is provided on the inner surface of the pipe-shaped hollow portion of the plastic jacket in which the optical fiber or the optical fiber unit is housed. When the allowable maximum value of the extra length of the optical fiber defined by (length) − (length of cable)｝ / (length of cable) is εmax, and the minimum value is εmin, Here, R is the optical fiber cable outer radius, r is the inner radius of the metal pipe-shaped cavity, r ₈ is the radius of the optical fiber or fiber unit, t is a metal layer thickness, R _D is set around the cable drum Sinus radius, d ₁ is the distance between the center point of the cable and the center point of the pipe cavity, Here, E _p , E _M , and E _SM are the Young's moduli of the jacket, the metal layer inside the pipe, and the tensile strength member, and A _p , A _M , A _SM , and A _a are the jacket, the metal layer, strength member, the cross-sectional area of each of the pipe-shaped cavity inside, d ₂ the distance between the center point and the center point of the cable strength members, said satisfies two formulas, the optical fiber or optical fiber unit positions the optical fiber cable An optical fiber cable configured to match a fixed point (neutral point of bending) where expansion and contraction does not occur due to bending in a cross section. 5. A waterproof material is partially or wholly filled in a pipe-shaped hollow portion formed in an outer jacket in which an optical fiber or an optical fiber unit is housed. An optical fiber cable according to claim 4. 6. An optical fiber unit or a pipe-shaped hollow portion formed in a jacket in which an optical fiber is housed in contact therewith is partially or entirely filled with a preventive material. 4. The optical fiber cable according to claim 1, 2, or 3.