JPH0519148A - Optical fiber cable - Google Patents

Abstract

PURPOSE:To set the pulse arrival time of each coated optical fiber to the same with regard to plural coated optical fibers in which coated optical fiber length of an optical fiber cable is different. CONSTITUTION:With regard to a coated optical fiber 41 and the other coated optical fiber 42 whose coated optical fiber length is different from each other, when a specific refractive index difference of a coated optical fiber and a clad of one coated optical fiber 41, length of one coated optical fiber 41, and a difference of length of one coated optical fiber 41 and the other coated optical fiber 42 are denoted as DELTA0, L, and DELTAL, respectively, optical path length of each coated optical fiber is set to the same by increasing or decreasing by DELTAL/L from the specific refractive index difference DELTA0 of the coated optical fiber and the clad of the other coated optical fiber 42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-fiber optical fiber cable, and more particularly to an optical fiber cable including a plurality of optical fiber core wires having different core wire lengths and having a problem of a pulse arrival (propagation) time difference. is there.

[0002]

2. Description of the Related Art In a multi-fiber optical fiber cable,
Due to the structure, the length of the optical fiber inside may be different. For example, in the case of a tape spacer type optical fiber cable, since the multi-core tape fiber is arranged in a layer in the groove of the spacer and is wound at a predetermined pitch in the longitudinal direction to give an extra length, the length of the multi-fiber tape fiber is increased. Is different between the upper layer and the lower layer, so that the core length of the optical fiber constituting the multi-core tape fiber is also different.

Conventionally, when optical transmission is carried out by such an optical fiber cable, if a difference in the arrival time of pulses between the optical fiber cores poses a problem, a delay line (delay line) is inserted. By cutting off the extra length part of, the difference in arrival time was eliminated.

[0004]

However, in the method of the prior art, the pulse arrival time may not be the same in each optical fiber core wire, for example, because the remaining length of the optical fiber core wire is small. Further, even if the delay line is inserted, there is a problem that there is no space for it and the cost is high. For this reason, in an extreme case, it is necessary to replace the optical fiber cable itself with one suitable for use.

An object of the present invention is to solve the above-mentioned problems and to provide an optical fiber cable in which the pulse arrival time of each optical fiber is the same regardless of the optical fiber optical fiber at low cost.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to an optical fiber cable including a plurality of optical fiber core wires having different core wire lengths, and one core wire and another core wire having different core wire lengths from each other. When the length of the core wire differs from the length L of the core wire by ΔL, the relative refractive index difference between the core and the clad of the other core wire is calculated as follows. ΔL than ₀
/ L is different, and the optical path length of each core is the same.

[0007]

For example, if the core length of another core is longer than the core length L of 1 by ΔL, the other core is
The core and the relative refractive index difference delta _x of the cladding, and the first core wire core and a value reduced from the relative refractive index difference delta ₀ only [Delta] L / L of the cladding (Δ ₀ -ΔL / L). In this way, the optical path length (optical length) of each core wire can be made equal by adjusting the relative refractive index difference (core refractive index) of the optical fiber core wires used according to the difference in core wire length. ..

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the formula will be briefly described.

Let L be the length of a certain optical fiber core and n _{0 be} the refractive index of the core of the optical fiber used. Then, when the length of the optical fiber of interest changes from L to L + ΔL, let n _{x be} the refractive index of the core of the optical fiber to be used to equalize the optical path lengths (optical lengths).

[0010]

## EQU1 ## From n ₀ L = n _x (L + ΔL) (1)

[0011]

[Equation 2]

To obtain This is the relative refractive index difference between the core and the clad

[0013]

[Equation 3]

[0014]

[Equation 4]

[Equation 2] Substituting equation 2 into n _x in equation 4

[0016]

[Equation 5]

[0017]

[Equation 6]

To obtain That if cord lengths differ by [Delta] L, it may be changed relative refractive index difference from the delta ₀ to Δ ₀ -ΔL / L.

As a concrete example, the tape spacer type optical fiber cable of FIG. 1 will be described.

In the tape spacer type optical fiber cable of FIG. 1, multifilamentary tape fibers 3 of 8 cores are arranged in layers in four twisted grooves 2 provided around the spacer 1 in four layers, whereby a long length is obtained. Wrap at a predetermined pitch in the direction,
The optical fiber core wire 4 forming the multi-core tape fiber 3 has a structure in which an extra length is added. That is, when the optical fiber core wire 4 is formed into a cable, the core wire 41 belonging to the lowest layer of the multi-core tape fiber laminate has the shortest length and the core wire 42 belonging to the top layer has the shortest length in each groove. Have the longest relationship.

Here, as a representative example, consider the case where the optical path lengths of the core wire 41 of the lowermost layer and the core wire 42 of the uppermost layer are matched. Assuming that the radius to the lowest layer of the spacer 1 is 4 mm, the radius to the highest layer is 5.5 mm, and the winding pitch of the tape fiber 4 is 500 mm, at a cable length of 100 m,
The length of each of the core wire 41 and the core wire 42 is L = 100126.25 mm (= 100.12625 m) L + ΔL = 100242.98 mm (= 100.24298 m). In other words, ΔL = 116.
The length of 73 mm becomes uneven. Therefore, the ratio is ΔL / L = 0.0011658 = 0.11658%.

Now, assuming that the relative refractive index difference of the core wire 41 of the lowermost layer is Δ ₀ = 0.35%, the relative refractive index difference of the core wire 2 of the uppermost layer is Δ _x = 0. 35-0.11658 = 0.233% may be set. Similarly, with respect to the core wires belonging to other intermediate layers, the optical path length can be made the same for all the optical fiber core wires 3 by adjusting the relative refractive index difference of the optical fiber to be used.

Actually, when a cable was prototyped using the optical fiber whose relative refractive index difference was adjusted as described above and the pulse arrival time (propagation time) was measured, it was confirmed that the pulse arrival times were exactly the same. It was

The multi-fiber optical fiber cable having the above structure is
It can be applied as an optical fiber cable for data transmission between computer devices, and the speed and quality of transmitted data are greatly improved. Therefore, the distance between devices is long, and it works particularly effectively when transmitting an ultra-high speed parallel signal.

[0025]

As described above, according to the present invention, the difference in the lengths of the core wires is adjusted by changing the relative refractive index difference (refractive index of the core) of the optical fiber core wires to be used. Since the optical path lengths (optical lengths) of the wires are made equal, compared to methods such as cutting the extra length of the optical fiber core wire and inserting a delay line,
It is possible to align the pulse arrival time (propagation time) between the cores at a lower cost. When applied to data transmission between computer devices, the speed and quality of data to be transmitted can be greatly improved.

[Brief description of drawings]

FIG. 1 shows a cross section of an optical cable to which the present invention is applied.

[Explanation of symbols]

 1 spacer 2 twist groove 2 3 multi-core tape fiber 4 optical fiber core wire 41 core wire belonging to the lowest layer (L) 42 core wire belonging to the highest layer (L + ΔL)

Claims (1)

Claim: What is claimed is: 1. An optical fiber cable including a plurality of optical fiber core wires having different core wire lengths, wherein one core wire and another core wire having different core wire lengths are different from each other. When the length of the wire differs from the length L of the core wire by ΔL, the relative refractive index difference between the core and the cladding of the other core wire is calculated from the relative refractive index difference Δ ₀ between the core and the cladding of the core wire of 1. Also, the optical fiber cable is characterized in that the optical path length of each core wire is made the same by differentiating by ΔL / L.