JPH0588059A - Optical cable and production thereof - Google Patents

Abstract

PURPOSE:To raise the upper limit value of the input power to optical fibers determined by Brillouin scattering. CONSTITUTION:The optical fibers 2 are twisted around a tension member 1 and twists are applied to the respective optical fibers 2. The size of the twists changes periodically with the longitudinal direction of the cable. A distribution of strains is imparted in the longitudinal direction of the optical cable, by which the Brillouin gain band width is widened and the upper limit value of the input power can be raised. The twists applied to the optical fibers is fixed by a resin 3 and a sheath 4 is applied thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical cable structure and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing an example of the structure of a conventional optical cable. In the figure, 1 is a tension member, 4
Is a sheath, 12 is an optical fiber, and 13 is a press winding.
Such an optical cable is manufactured by gathering the coated optical fibers 12 around the tension member 1, applying the press winding 13, and coating the sheath 4 thereon.

When the optical fibers 12 are assembled, the optical fibers 12 are usually assembled with twisting back, so that the optical fibers 12 are not twisted. Therefore, the strain that the optical fiber receives after making it into a cable is only the fiber stretching strain due to the supply tension when the optical fibers are assembled,
There is a constant strain in the length direction of the optical cable.

Even when the optical fibers are assembled without twisting back, the twisting pitch of the optical fibers becomes equal to the twisting pitch of the optical fibers and takes a constant value. + Twisting strain) has a constant value in the length direction.

Since such an optical cable has a characteristic of wide band and low loss as compared with the conventionally used copper cable, it is possible to greatly extend the interval between the repeaters. In particular, the advantages of the optical cable can be utilized to the fullest extent in applications such as submarine cables that require longer relay spans.

On the other hand, in the system using the optical cable, factors that give the upper limit of the non-repeatered transmission distance are the transmission loss and the transmission capacity of the optical fiber itself, and the upper limit value of the signal level that can be input to the optical fiber. .. In general, as the power of the light source is increased, the power that can be input to the optical fiber also increases in proportion. However, if it exceeds a certain threshold, stimulated Brillouin scattering occurs, and even if the power of the light source is increased, There is a phenomenon that the input power is saturated and it becomes impossible to input more power.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the upper limit value of the input power determined by the above-mentioned Brillouin scattering is not uniform in the longitudinal direction of the cable. The purpose is to raise by giving a twist distortion.

[0008]

According to a first aspect of the present invention, in an optical cable in which the optical fiber is twisted and accommodated in the cable, the degree of twist of the optical fiber is the length of the optical cable. According to the invention of claim 2, in the method for manufacturing an optical cable, the supply bobbin of the optical fiber is rotated with respect to the optical fiber being fed out. The optical fiber is characterized in that the optical fiber is aggregated while periodically changing the rotational speed or the rotational direction or both to give a twist distribution to the optical fiber.

[0009]

The upper limit value P _C of input power determined by Brillouin scattering is expressed by the following equation. P _C = Aα / G where A is a constant, α is a transmission loss of the optical fiber, and G is a Brillouin gain coefficient. Also, the Brillouin gain coefficient G
Is inversely proportional to the Brillouin gain bandwidth ΔV as shown in the equation. G∝1 / ΔV Therefore, in order to increase the upper limit value P _C of the input power, it is understood that it is sufficient to increase ΔV.

On the other hand, it is known that the Brillouin gain bandwidth ΔV is increased by giving a strain distribution in the length direction of the optical fiber. For example, the coordinate in the length direction of the optical fiber is x, and the strain distribution is Strain distribution ε
Where ε = ε ₀ cos (2πx / P), the Brillouin gain bandwidth ΔV _S after distortion is given by
It is approximately expressed by the following formula. ΔV _S = ΔV + Bε _{0 In} the above equation, B is a constant.

As described above, the present invention proposes a method of giving a strain distribution to an optical fiber contained in a cable in order to raise the upper limit of the power that can be input to the optical fiber. The distribution of strain is imparted by giving a torsional strain that periodically changes in the depth direction, and as a result, it is possible to widen the Brillouin gain bandwidth ΔV _S and raise the upper limit of the input power. By twisting the optical fiber, shear strain γ represented by the following equation is generated. γ = (d / 2) (dφ / dx) where (d / 2) is the distance from the center and φ is the twisting angle of the optical fiber.

For example, if φ = a · cos (2πx / P), then γ = − (d / 2) · (2πa / P) · sin (2πx / P), and the maximum strain ε ₀ = dπa / P, The strain distribution of the pitch P is provided in the cable length direction.

[0013]

1 is a sectional view of an optical cable according to an embodiment of the present invention. In the figure, 1 is a tension member, 2 is an optical fiber, 3 is a resin, and 4 is a sheath. The optical fiber 2 is
Although twisted around the tension member 1, each optical fiber is twisted. The size of the twist
It changes periodically in the longitudinal direction of the cable. As a result, a strain distribution is given in the length direction of the optical cable. The twist given to the optical fiber is fixed by the resin 3, and the sheath 4 is applied thereon. Therefore, the twisted state does not change during or after the installation of the optical cable.

A specific example of a prototype optical cable will be described. An optical fiber 2 coated with an ultraviolet curable resin so as to have an outer diameter of 400 μm was twisted around a tension member 1 while imparting a periodically changing twist on a single mode optical fiber having an outer diameter of 125 μm. After that, the ultraviolet effect resin 3 was applied and cured to fix the optical fiber 2, and then the sheath 4 was applied.

FIG. 2 is a schematic configuration diagram of a collecting apparatus for manufacturing this optical cable. In the figure, 1 is a tension member, 2 is an optical fiber, 5 is a supply bobbin, 6 is a rotating mechanism, 7 is a collecting die, 8 is a resin supply device, 9 is a curing furnace, 10 is a tension member supply reel, and 11 is winding. It is a device. The tension member 1 is pulled out from the tension member supply reel 10 toward the assembly die 7. On the other hand, the optical fiber 2 is paid out from the supply bobbin 5 whose rotational speed or rotational direction changes periodically by the rotating mechanism 6, and is arranged around the rotating tension member 1 by the assembly die 7 and twisted. It
The tension member 1 is rotated by synchronizing the tension member supply reel 10 and the winding device 11 with each other.

Further, a resin supply device 8 is provided by the assembly die 7.
The ultraviolet curable resin supplied from the above is applied and cured in the curing furnace 9 so that the twisting strain applied to the optical fiber is fixed so as not to be relaxed in the length direction, and then synchronized with the tension member supply 10. Revolving winding device 1
It is wound up to 1. In this embodiment, a winding and rotating type collecting device is used, but instead of rotating the tension member supply 10 and the winding device 11, the supply bobbin 5 is used.
May be rotated around the tension member 1. Although the step of applying the sheath is a separate step, the sheath is covered in a series of steps, and the winding device 1
It is also possible to wind up with 1.

As a method of fixing the optical fiber so that the twisting strain applied thereto is not relaxed, a method of pressing and winding with a tape may be used in addition to the method of fixing with a resin.
By intermittently applying a brake to the rotating supply bobbin 5, the rotational speed was periodically changed, and the optical cable of FIG. 1 having a torsional strain distribution in the length direction was prototyped. The maximum strain due to the twist was 0.03%, and the strain distribution pitch was 1 m. When the Brillouin gain bandwidth ΔV was measured using this cable, the bandwidth expanded from ΔV = 40 [MHz] before cabling to ΔV = 70 [MHz] after cabling, and the upper limit of input power It was also confirmed that it could be improved by about 2.4 dB.

Brillouin gain can also be obtained by distributing the torsional strain on the step in the length direction of the cable, instead of giving a continuously varying strain distribution such as ε = ε ₀ cos (2πx / P). The bandwidth ΔV _S can be increased.

In the optical cable shown in FIG. 1, 1 km of an optical cable having a portion where a twist is applied to an optical fiber and a portion where a twist is not applied is alternately formed every 100 m, and the Brillouin gain bandwidth ΔV is measured. The twist distortion is 0.
When 04% was added and the Brillouin gain bandwidth ΔV was measured, it was ΔV = 80 [MHz], and it was confirmed that the upper limit value of the input power could be improved by about 3 dB.

In these prototypes, the twisting directions of the twist imparting portions are the same, but it is not necessary to make the directions the same, and either the right twisting or the left twisting may be performed.
Further, as a method of applying the twist distortion, twists of two or more stages may be applied on the steps in the length direction of the optical fiber.

[0021]

As is clear from the above description, by imparting a cyclically changing torsional strain to the optical fiber contained in the optical cable, the Brillouin scattering gain bandwidth peculiar to the fiber is widened, and as a result, It is possible to raise the upper limit of the power that can be input to the optical fiber. Therefore, since larger power can be input to the optical fiber, there is an effect that the non-repeatered transmission distance of the optical fiber becomes long and the required number of repeaters can be reduced.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram of an embodiment of an assembling apparatus for manufacturing the optical cable of the present invention.

FIG. 3 is a cross-sectional view of an example of a conventional optical cable structure.

[Explanation of symbols]

 1 Tension member 2 Optical fiber, 3 Resin 4 Sheath 5 Supply bobbin 6 Rotation mechanism 7 Assembly die 8 Resin supply device 9 Curing furnace 10 Tension member supply reel 11 Winding device

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shigeru Tanaka 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Nobuyuki Yoshizawa 1-6, Uchiyuki-cho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. An optical cable in which an optical fiber is twisted and accommodated in the cable, and the magnitude of the twist of the optical fiber is periodically changed in the length direction of the optical cable. .. 2. The optical fiber supply bobbin is rotated with respect to the optical fiber fed out, and the rotational speed and / or the rotational direction are periodically changed to gather the optical fibers while giving a twist distribution. And a method for manufacturing an optical cable.