JPH11174289A - Cable for optical fiber parallel transmission and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a skew mutually between optical fibers in an optical fiber parallel transmission cable in which the plural optical fibers are inserted into the inside of a coating tube. SOLUTION: In this cable for optical fiber parallel transmission in which the plural optical fibers 1 are inserted into the inside of the coating tube 5, the plural optical fibers 1 inside the coating tube 5 are separated from each other and inserted into the inside of the coating tube 5 with waviness. Then, a slack ratio is respectively adjusted for each optical fiber 1 so as to turn the skew mutually between the optical fibers 1 to be less than the allowable skew value of an optical device connected to the cable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber cable, and more particularly to an optical fiber parallel transmission cable and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in an optical fiber communication system for a multimedia society, time multiplex transmission or wavelength multiplex transmission has been adopted in consideration of economy. Particularly in large-capacity, long-distance transmission, time multiplex transmission is mainly used. Either way, it is a serial signal, and the main focus of research and development is to increase the transmission speed as the required transmission capacity increases.

When a large capacity for consumer such as the Internet is required, a high-speed metal signal line is required for an ATM switch or a parallel computer which requires a large capacity.
High density has become a problem, and expectations for optical fiber parallel transmission using parallel signals are increasing. When a serial signal is used, transmission over 100 km is possible with one single mode optical fiber signal line. In the case of a parallel signal, since multiple signal lines are required,
Skew between each signal line becomes a problem. Skew is
It refers to the shift between the optical fibers in the signal transmission time from one end of the optical fiber to the other end, that is, the difference between the maximum value and the minimum value of the signal arrival time of a plurality of optical fibers in the cable. Therefore, if the skew is large, normal data transmission becomes impossible. This skew becomes more serious as the transmission distance becomes longer. Currently 100 Mb / s
At present, it is possible to transmit only up to about 100 m at the transmission speed. This is because the skew of an optical fiber used for an optical fiber parallel transmission cable has a variation of about 2 ps / m (in the case of a single mode optical fiber), and the allowable skew value of an optical device (for example, a connection device for optical parallel transmission) is small. Due to 200 ps. In some cases, a multimode optical fiber is used, but there is the same limitation of the applicable distance due to skew.

If an optical fiber cable with a reduced skew can be made, it is possible to extend the distance in parallel transmission of optical fibers. 8 as a signal line in an optical fiber parallel transmission cable
In the case where there are eight optical fibers and eight-bit parallel transmission is performed, the eight signal lines are taped and integrated in a cable as an integral unit in order to keep the distance constant. In the case of a single mode optical fiber, the skew of these eight signal lines is about 2 ps / m. This is about 0.04% in terms of the transmission speed of light in a fiber (assuming the speed of light in a fiber is 200,000 km / s).
It is presumed that the cause of this variation is the residual stress, bending degree, absolute length, and the like when the optical fiber is taped.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to reduce skew between optical fibers in an optical fiber parallel transmission cable in which a plurality of optical fibers are inserted in a cladding tube.

[0006]

Means for Solving the Problems Conventionally, tapes have been implemented to keep the length of each optical fiber of an optical fiber parallel transmission cable constant. In order to suppress the skew between them, we considered adjusting the length of each optical fiber.

That is, according to the optical fiber parallel transmission cable of the present invention, in a cable for optical fiber parallel transmission in which a plurality of optical fibers are inserted into a cladding tube, the plurality of optical fibers in the cladding tube are separated from each other and undulated. The extra length is adjusted for each optical fiber so that the skew between the optical fibers is equal to or less than the allowable value of the optical device connected to the cable.

In the present invention, the lengths of the optical fibers, that is, the surplus length ratio, are adjusted according to the skew between the optical fibers, instead of making the lengths of the optical fibers equal. Therefore, the skew between the optical fibers can be reliably and easily reduced to a required skew value or less.
By finely adjusting the extra length ratio for each optical fiber, the skew between the optical fibers can be reduced to, for example, about 10 ps. By reducing the skew, the distance between the optical devices can be increased.

It is desirable that the lengths of the optical fibers exposed from both ends of the cladding tube be substantially equal. In this way, terminal processing such as connector processing and fusion processing can be collectively performed for a plurality of optical fibers. For each optical fiber, a connector is not required, so that the mounting density is increased, or in order to arrange terminals. There is an advantage that a protective box for storing the longer optical fiber is not required.

According to the method for manufacturing an optical fiber parallel transmission cable of the present invention, a plurality of optical fibers separated from each other are inserted into a cladding tube so as to form undulations, and then the skew between the optical fibers is measured. The extra length ratio of each optical fiber is adjusted according to the measured skew value so that the skew is equal to or less than the allowable skew value of the optical device connected to the cable.

In the method for manufacturing an optical fiber parallel transmission cable according to the present invention, the extra length of each optical fiber is adjusted based on the skew measurement value of each optical fiber inserted in the cladding tube. Therefore, an optical fiber parallel transmission cable with small skew between optical fibers can be easily manufactured. Further, once the skew is adjusted by the method of the present invention, the skew between the optical fibers can be further reduced by repeating the measurement of the skew and the adjustment of the excess length ratio.

An arbitrary one of a plurality (n) of optical fibers inserted into the cladding tube is used as a reference optical fiber, and an adjustment length C of the remaining (n-1) optical fibers with respect to the reference optical fiber. _i (m) can be determined using the following formula. C _i = (b / a) × S _i where i: 1 to n−1 a: Group refractive index of optical fiber b: Speed of light in vacuum (m / s) S _i : Skew with respect to reference optical fiber (s) If the skew with respect to the reference optical fiber is negative, that is, if the signal arrives earlier than the reference optical fiber, the optical fiber is lengthened based on the above equation so that the signal arrives almost simultaneously with the reference optical fiber. If the skew is positive, the optical fiber is shortened based on the above equation.

[0013]

FIG. 1 shows an optical fiber parallel transmission cable according to the present invention. As shown in the drawing, a plurality of optical fibers 1 form undulations and are inserted into a cladding tube 5 so as to be separated from each other. The optical fiber 1 is
It is a bare optical fiber or an optical fiber or a core, and may be either single mode or multimode. The number of inserted optical fibers is, for example, 8 to 16
It is a book. The material of the cladding tube 5 into which the optical fiber 1 is inserted is selected according to the conditions of use of the cable. For example,
Stainless steel, titanium, inconel (Cr-Ni alloy, trade name of International Nickel) and the like as materials having excellent corrosion resistance, and Kovar (N
i-Co-Fe alloy, trade name of Stupakoff) and the like are used. Further, plastics such as vinyl chloride resin, polyethylene, and fluororesin can also be used.

The skew between the optical fibers is equal to or less than the allowable skew value of the optical device. The allowable skew value of an optical device is, for example, 20 m for a cable having a length of 200 m.
It is 0 ps (1 ps / m). The skew between the optical fibers depends on the use conditions of the optical fiber itself and the cable. However, as described above, the skew can be set to 200 ps or less, for example, about 10 ps by finely adjusting the extra length. is there. Factors affecting the skew between optical fibers include cable length, applicable communication wavelength, bending state of optical fiber in the cable, absolute length of bending, core diameter between optical fibers, group refractive index, numerical aperture, etc. There are differences in structural factors, residual stress due to optical fiber tape, and the like. The inner diameter of the cladding tube is about 0.8 to 10 mm. The extra length ratio (%) is defined as {(length of optical fiber−length of cladding tube) / length of cladding tube} × 100, and is about 0 to 1.5%.

In the method for manufacturing an optical fiber parallel transmission cable according to the present invention, the optical fiber is inserted into the cladding tube by using vibration or fluid flow, or by welding the opening edge of the tubular body. A method of inserting an optical fiber from the opening is used. The vibration insertion method (for example, see Japanese Patent Application Laid-Open No. 62-44010) is suitable because the adjustment of the excess length ratio is easy, and it can be inserted into a long and small-diameter tube.

FIG. 2 shows an example of an apparatus used for vibration insertion. The vibration table 11 is supported on the gantry 15 via a coil spring 16. Two vibration motors 18 are mounted on a holding frame 13 extending downward from the bottom of the vibration table 11. The vibration motor 18 is mounted on the vibration table 11 symmetrically with respect to the table center axis C. The vibration motor 18 has an unbalanced weight (not shown), and is inclined in directions opposite to each other with respect to the table center axis C. When the vibration motor 18 is driven, the vibration table 11 vibrates along the spiral path S around the center axis of the table.

In the apparatus configured as described above, the metal tube 5 is wound around the bobbin 21 in a coil shape,
Is fixed to the vibration table 11 with the stopper 23. The required number of optical fibers 1 with the tip 2 bundled with a tape 25 is inserted in advance by about 1 to 50 m from the tube inlet 6. Then, the vibration motor 18 is driven to vibrate the metal tube coil 9, and the optical fiber 1 is inserted into the metal tube 5. When the optical fiber 1 is inserted into a long tube, the optical fiber 1 is wound on a reel (not shown), and the reel is driven to rotate and supplied to the metal tube 5. The optical fiber 1 travels in the tube while undulating due to vibration. The optical fiber 1 is inserted until the tip 2 of the optical fiber is exposed to an appropriate length from the tube outlet 7. After insertion, the skew is measured for each optical fiber. The excess length ratio is adjusted according to the skew measurement result, and the skew is set to a predetermined value or less.

In order to adjust the extra length, as shown in FIG. 3, the front end 2 of the optical fiber is fixed with a fixture 27, and the rear end 3 of the optical fiber other than the optical fiber for which the extra length is to be adjusted. It is fixed with the fixing bracket 28. In such a state, the optical fiber 1 is moved forward or backward by vibrating the metal tube coil 9. To increase the extra length, the optical fiber 1 is advanced, and to decrease, the optical fiber 1 is advanced. For forward and backward travel of the optical fiber 1,
The rotation direction of the vibration motor 18 is switched. When the adjustment of the excess length, that is, the skew, is completed, the metal tube 5 of the optical fiber 1 is
The front end portion 2 and the rear end portion 3 that are exposed from are trimmed to have substantially the same length. The length L of the optical fiber 1 exposed from the metal tube 5 is about 0.1 to 5 m.

When adjusting the extra length after inserting the optical fiber into the cladding tube, a reference optical fiber is arbitrarily determined in advance, and the skew with respect to the reference optical fiber is measured. Then, the extra length ratio is adjusted based on the measured or minimum optical fiber of the skew. By doing so, the work of adjusting the margin ratio to make the skew equal to or less than the required skew value becomes easy.

[0020]

EXAMPLE Eight optical fibers (SM10 / 125, coating outer diameter: 0.25 mm, length: 1020 m), and a metal tube (SUS 316, outer diameter: 2.0 mm, inner diameter: 1.6 mm,
(Length: 1000 m 2) was prepared, the ends of the optical fibers were bundled, and inserted into a metal tube by the vibration insertion method. The insertion was stopped when the optical fiber came out about 5 m from the tip of the metal tube. About 9 to 12 m of optical fiber remained on the entrance side. At this time, the skew of each optical fiber was measured, a serial number was assigned based on the optical fiber having the largest skew, and the extra length ratio was adjusted.

Table 1 shows the skew immediately after insertion.

[Table 1]

Next, the speed of the optical fiber in a vacuum 2.9.
98 × 10 ⁸ m / s is divided by 1.474 of the group refractive index of the optical fiber, and the light velocity in the optical fiber is 2.034 × 10 ⁸ m / s.
Get. Based on this speed, the fiber No. Two or less additional insertions are sequentially performed (hereinafter, refer to FIG. 3). Table 1 shows the additional insertion length. The tips of the eight optical fibers are fixed so as not to be ejected any more, and no. 1 is fixed so that it is not inserted any more. In such a state,
Fiber No. 2 is additionally inserted. At this time, No. 3
-No. Since the optical fiber of No. 8 is not fixed, the fiber No. 8 is not fixed. Inserted with 2. When the insertion of these optical fibers is completed, 1 to No. No. 2 optical fiber was fixed. 3-No. 8 is inserted.
Thereafter, insertion of a predetermined length is sequentially performed in the same manner, and the optical fiber after the insertion is fixed. After all additional insertions were completed, all eight pieces were cut to make the length 5 m at the entrance side. Table 1 shows the skew measurement results in this state.
The skew variation is -190 to +20 ps, which is significantly improved. Conversely, a similar effect can be expected even if another optical fiber is returned to the tube inlet side on the basis of the one with the smallest skew (the optical fiber of No. 8). In that case, the vibration direction may be reversed.

Table 1 shows the skew when a 1 km optical cable is divided into about 500 m. The skew variation was stable even after the division of 500 m, and it was confirmed that there was no problem in practice.

[0024]

According to the optical fiber parallel transmission cable of the present invention, since the difference in signal arrival time between optical fibers is small, information can be transmitted in parallel to a remote place accurately.
For long-distance optical fiber parallel transmission, which will increase in the future,
The optical fiber cable of the present invention is expected to be widely used. In addition, in the case of the optical fiber parallel transmission cable in which the exposed length of each optical fiber is substantially the same, the workability is improved when the collective connector is finished.

[Brief description of the drawings]

FIG. 1 is a drawing schematically showing an optical fiber parallel transmission cable of the present invention.

FIG. 2 is a drawing showing an example of an apparatus used for inserting an optical fiber through vibration.

FIG. 3 is a diagram illustrating a method of adjusting a surplus length rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 5 Clad tube 9 Metal tube coil 11 Vibration table 15 Mount 16 Coil spring 18 Vibration motor 21 Bobbin 27 Fixture 28 Fixture

Claims (4)

[Claims] An optical fiber parallel transmission cable in which a plurality of optical fibers are inserted into a cladding tube, wherein the plurality of optical fibers in the cladding tube are separated from each other and inserted into the cladding tube with undulations. An optical fiber parallel transmission cable, wherein the extra length ratio is adjusted for each optical fiber such that the skew between the fibers is equal to or less than the allowable skew value of an optical device connected to the cable. 2. The optical fiber parallel transmission cable according to claim 1, wherein the lengths of the optical fibers exposed from both ends of the cladding tube are substantially equal. 3. After a plurality of optical fibers separated from each other are inserted into a cladding tube so as to form a swell, skew between the optical fibers is measured, and the skew is measured for an optical device connected to a cable. A method of manufacturing a cable for parallel transmission of optical fibers, wherein the extra length ratio of each optical fiber is adjusted according to the measured value of the skew so as to be equal to or less than an allowable skew value. 4. An arbitrary one of a plurality of (n) optical fibers inserted into the cladding tube is set as a reference optical fiber,
The remaining optical fibers (n-1) according to claim 3 a method of manufacturing an optical fiber parallel transmission cable according to the adjustment length C _i (m) is determined according to the following calculation equation with respect to the reference optical fiber for the present. C _i = (b / a) × S _i where i: 1 to n−1 a: Group refractive index of optical fiber b: Speed of light in vacuum (m / s) S _i : Skew with respect to reference optical fiber (s) )