JP2001051168A - Plastic optical fiber cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-core plastic optical fiber cable superior in the flexibility while keeping the necessary transmittability. SOLUTION: This optical fiber cable is manufactured by stranding up two plastic optical fiber codes 1 respectively formed by forming a coating 3 on a plastic optical fiber strand 2, and forming a sheath 5 outside the plastic optical fiber codes 1. On this occasion, a lay ratio defined by the formula. Where, P mm is a stranding pitch of two plastic optical fiber codes 1, 1, and D mm is a pitch diameter is within a range of 0.01%-1%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical fiber cable used for short-distance communication between devices in a home or an automobile.

[0002]

2. Description of the Related Art A plastic optical fiber is an optical fiber in which both a core and a clad are made of plastic. As plastic fibers that have been put into practical use,
For example, the core is formed of PMMA (polymethyl methacrylate), PC (polycarbonate), PS (polystyrene) or the like, and the clad is formed of a fluoropolymer such as a tetrafluoroethylene / vinylidene fluoride copolymer or a fluoroalkyl methacrylate polymer. Some are formed by coalescence. Such a plastic optical fiber is free from the problem of radiated electromagnetic noise and satisfies high-speed broadband transmission characteristics as optical fiber communication characteristics. In addition, it is advantageous in that it is not necessary to pay attention to the allowable bending radius as much as the quartz optical fiber during the wiring operation. However,
Plastic optical fibers have a transmission loss about three orders of magnitude higher than quartz optical fibers and are not suitable for long-distance transmission. Therefore, their use for short-distance data transmission has been studied.

For example, ATM forums and IEEE13
94. b, etc., the use of plastic optical fiber for serial transmission in a wide band has been studied. The ATM Forum has standardized the transmission of 50 m at a transmission rate of 155 Mbps, and IEEE1394. 100Mbp for b
A standard for transmitting 50 m at a transmission rate of s, 200 Mbps is being studied.

[0004] Plastic optical fibers have been studied and standardized for the following reasons in addition to being suitable for short-range communication as described above.
That is, the fiber diameter of the plastic optical fiber is 0.
5 mm to 1.0 mm, which is much larger than a quartz optical fiber, easy to couple with a light emitting element or a light receiving element, and a large tolerance of a connector can be obtained.
Furthermore, the terminal processing is easy, visible light LED,
The fact that a Si-PD can be used means that the system can be formed at low cost.

[0005] For such a reason, the use of plastic optical fiber cables for short-distance connections between devices in homes and automobiles has been studied. The shape of the cable used for this is a multi-core plastic optical fiber formed into a cable.
As described in Japanese Patent No. 171003, four or more optical fibers are twisted to form a unit, and a plurality of the units are twisted to form a cable.

[0006] As a cable used for connection between devices, for example, since IEEE1394 is a full-duplex transmission system, at least two cables are required. In addition, when a plurality of devices are connected by a plastic optical fiber cable and networking is considered in a home or the like, flexible wiring is required with respect to expandability of devices and layout changes. In order to cope with this, the above-mentioned multi-core plastic optical fiber cable is laid, and it is not suitable for use such as branching in the middle.
Expanding is the most suitable wiring method.

On the other hand, as a conventional two-core plastic optical fiber cable, there is a two-core parallel type as shown in FIG. The two-core parallel type plastic optical fiber cable is obtained by arranging two plastic optical fiber wires 10 having a coating 11 in parallel, and connecting the two in a line by a connecting portion 12. If such a plastic optical fiber cable is used, flexible wiring can be performed for scalability of equipment, layout change, and the like.

[0008]

However, the above-mentioned 2
With a parallel-core type plastic optical fiber cable,
There is a problem in that the flexibility is low and a problem occurs in wiring work, for example, the bending direction is restricted such that it is difficult to bend in the width direction.

An object of the present invention is to solve such a problem and to provide a two-core plastic optical fiber cable having excellent flexibility while maintaining necessary transmission characteristics.

[0010]

In order to solve the above-mentioned problems, a plastic optical fiber cable according to the present invention comprises two twisted plastic optical fiber cords each of which is coated on a bare plastic optical fiber, and a sheath is provided on the outside thereof. In the formed plastic optical fiber cable, when the twist pitch of the two plastic optical fiber cords is Pmm, the layer core diameter is Dmm, and the twisting rate is defined by the following equation:

(Equation 2) The twist ratio is in the range of 0.01% to 1%. This improves flexibility while maintaining necessary transmission characteristics.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of the plastic optical fiber cable of the present invention, and FIG.
FIG. 4 is a diagram showing a state of an optical fiber cord inside the cable of FIG. 1 and 2, reference numeral 1 denotes an optical fiber cord composed of an optical fiber 2 and a coating layer 3, reference numeral 4 denotes a holding layer, and reference numeral 5 denotes a sheath.

The optical fiber 2 is made of a transparent plastic for both the core and the clad, and has a coating layer 3 made of plastic on the outside thereof. In the plastic optical fiber cable of the present invention, two optical fiber cords 1 each composed of such an optical fiber 2 and a coating layer 3 are used, and as shown in FIG. Good flexibility is provided.

Two twisted optical fiber cords 1,
On top of 1, a restraining winding layer 4 such as a polyester tape, a low-density polyethylene tape, a foamed polyethylene tape or the like is applied, and a sheath 5 is formed thereon by extruding plastic or the like. There is no particular limitation on the thickness of the suppression winding layer 4, but in order not to impair the flexibility of the cable,
A thickness of about 12 μm to 200 μm is desirable. Further, the winding pitch of the restraining winding layer 4 is not limited as long as the twist of the optical fiber cord 1 can be maintained. However, the winding pitch is not wrapped so as not to impair the flexibility of the cable. Is desirable. Furthermore, in the case of employing a tandem line that enters the sheathing step immediately after the twisting step, the sheath 5 can be formed before the twisting returns, so that the restraining winding layer 4 is not necessarily required.

In general, it is known that the transmission loss of an optical fiber increases due to bending. Therefore, even when the two optical fiber cords 1 are twisted, if the twist is given too much, the bending applied to the optical fiber 2 becomes large, and the transmission loss increases. Therefore, the relationship between the twist pitch and the increase in loss was examined by changing the outer diameter of the optical fiber cord 1 to be twisted variously.

As a result, a result as shown in FIG. 4 was obtained. As shown in FIG. 4, the loss of each optical fiber cord increases sharply from a certain twist pitch. The twist pitch at which the loss starts to increase sharply differs considerably depending on the diameter of the optical fiber cord to be twisted. The larger the diameter of the optical fiber cord, the more the loss starts to increase at a large twist pitch.

Analysis and examination based on these results revealed that there is a unique relationship between the twisting rate and the increase in loss when twisting optical fiber cords. The twist rate is used as an index indicating the degree of twist in a metal conductor cable or the like, and is defined by the following equation (3).

[0017]

(Equation 3)

Here, P is a twist pitch, as shown in FIG. 2, and refers to a length from the position where one optical fiber cord 1 has a stranded wire to the next same position. Also, D
Is the diameter of the layer core, as shown in FIG. 1, refers to the diameter of a circle connecting the centers of the optical fiber cords with the center of the stranded wire as a fixed point in the cross section of the stranded wire. In the case of a stranded wire, it is the distance between the centers of the two optical fiber cords 1.

FIG. 5 shows the relationship between the twisting rate and the increase in the loss by variously changing the outer diameter of the optical fiber cord 1 to be twisted. As is clear from FIG. 5, in any of the optical fiber cords having different diameters, the loss sharply increases when the twisting ratio exceeds 1%. Also, the smaller the twisting rate, the smaller the loss increase, but if the twisting rate is less than 0.01%, the twist pitch becomes relatively long, which is different from the case where the flexibility of the cable is two-core parallel. Not bad.

On the other hand, the theoretical aperture coefficient NA (= Numerical Aperture) is determined by the refractive index n _{1 of the} plastic used for the core and the refractive index n _{2 of the} plastic used for the cladding.
ture) can be obtained by the following equation (4).

[0021]

(Equation 4)

In general, when the NA is large, the loss increase due to bending is small, but the transmission band is narrow. Conversely, it is known that when the NA is small, the loss due to bending increases, but the transmission band becomes wide. When the two optical fiber cords 1 and 1 are twisted as in the plastic optical fiber cable of the present invention, the bending is applied to the optical fiber strands 2 and 2 of the optical fiber cords 1 and 1, so that the NA and the band are not changed. It is necessary to consider the twist ratio.

The NA of the SI type plastic optical fiber cord currently on the market is generally 0.3 to 0.75. Among them, 0.3 to 0.6 are approximately 2
It satisfies the transmission speed of 00 Mbps to 50 Mbps and is mainly used for communication purposes. On the other hand, when NA is 0.
The ones from 6 to 0.75 are used for sensors and decorations that do not require high transmission rates. Therefore, when twisting an optical fiber cord having an NA of 0.3 to 0.6 used for communication, the twisting rate is about 0.01 to 0.45%,
It is desirable to make it smaller. For example, if an optical fiber cord having an NA of 0.3 is twisted at a twist rate of more than 0.45%, the loss increase exceeds 0.2 dB / m, and the IEEE 1394 transmits at 50 m at a transmission rate exceeding 100 Mbps. . It does not meet the standard of b.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
Plastic optical fiber cables of various fiber diameters and cord diameters were manufactured by changing the twisting ratio. In FIG. 3, “excellent” in the flexibility column means that it is bendable in all directions, “good” means that it is bendable but has a somewhat high rigidity, and “impossible” means This means that there is a restriction on the bending direction.

As is apparent from FIG. 3, in all of the cord diameters, in Examples 1 to 3 in which the twisting ratio is within the range of 0.01% to 1%, the flexibility is not increased in terms of the loss increase. But satisfactory results were obtained. On the other hand, in the comparative example, the twisting rate is too small, and there is a problem in the flexibility of the cable. In the comparative example, the twisting rate is too large, the loss increases, and exceeds 100 Mbps. IEEE 1394. that transmits 50 m at a transmission rate.
It does not meet the standard of b.

[0026]

According to the present invention, as described above, two plastic optical fiber cords are twisted and the twisting rate at that time is set in the range of 0.01% to 1%. Thus, a plastic optical fiber cable having excellent flexibility while maintaining necessary transmission characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a plastic optical fiber cable of the present invention.

FIG. 2 is a diagram showing a state of an optical fiber cord inside the cable of FIG. 1;

FIG. 3 is a diagram illustrating characteristics of an example and a comparative example.

FIG. 4 is a diagram showing a relationship between twist pitch and loss increase.

FIG. 5 is a diagram showing the relationship between the twisting rate and the increase in loss.

FIG. 6 is a view showing a two-core parallel type plastic optical fiber cable.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber cord 2 ... Optical fiber wire 3 ... Coating layer 4 ... Holding layer 5 ... Sheath 10 ... Optical fiber wire 11 ... Coating 12 ... Connecting part

Claims (1)

[Claims] 1. A plastic optical fiber cord obtained by coating a plastic optical fiber strand with two wires,
A plastic optical fiber cable having a sheath formed outside thereof, wherein the twist pitch of the two plastic optical fiber cords is P mm, the layer core diameter is D mm, and the twisting rate is defined by the following equation: 1) A plastic optical fiber cable having a twist rate in a range of 0.01% to 1%.