the bending radius of fiber optic cable rev5

7/31/2019 The Bending Radius of Fiber Optic Cable Rev5

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Report 311006

Edward Lavides

October 2006

Topic: Minimum Bend Radius Requirements For SM Fibre Optic Cable


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Minimum Bend Radius Requirements For SM fibre Optic Cable

Introduction

Fibre optic waveguides yield normally very low losses in an inline installedposition. Unfortunately this medium also has some limitations in the form ofbending losses due to internal refraction. These losses can be substantial andare dependant on the bending radius and the wavelength. It is also wellunderstood that the longer wavelength induces greater losses for a givenbending radius.

There has been much discussion recently on the bending capability of fibre dueto the introduction of longer wavelength systems in DWDM (Dense WavelengthDivision Multiplexing) systems. The wavelength in use can be as high as1615nm. This represents a substantial increase in wavelength and possibly an

increase in loss beyond the normal capability of current fibre managementsystems.

Scope

The scope of this paper is limited to the MBR study on the following cable typeswhich were indoor type: Cable types on the market - single mode. These includethe 0.9mm, 2mm, 3mm diameter, 4 fibers and 12 fibers internal riser.

The paper provides actual results of each type of Fiber Optic Cables under both

1270nm and 1650nm Wavelength and compares it to the industry standard indetermining the bending radius of Fiber Optic Cable.

Procedure or Materials and Methods

The materials/equipment needed for the experiment included the following:

Agilent Equipment (Model Number: 86140B) or any similar test equipment

Length of FO Cable: 10 meters

0.9mm, 2mm and 3mm diameter of FO Cables

4 and 12 Fibers of Internal FO Cables Number of turns: 10 turns

Cylindrical Object: From 100mm to 20mm in diameter (adjustable eitherby 10s or 5s depending on the test required)


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The figure below showed what the test proper looks like.

Agilent Equipment

Fiber Optic Cable(Length)

Number of Turns

Diameter of

Cylindrical ObjectD

The following were the steps for the testing of the Fiber Optic Cables:

1. The testing for the 0.9mm diameter of the FO Cable started from 50mmdiameter of cylindrical object down to 20mm diameter with decrements of5mm diameter for every test of each FO Cables. The test included the1270nm and 1650nm wavelength and 10 turns on the cylindrical object.

2. For the 2mm and 3mm diameter of FO Cable, repeat step 1.

3. The testing for the 4 Fibers of FO Cables started from 80mm diameter ofcylindrical object down to 20mm diameter with decrements of 5mmdiameter for every test of each FO Cables. Each test included the 1270nmand 1650nm wavelength and 10 turns on the cylindrical object.

4. The testing for the 12 Fibers of FO Cables started from 100mm diameterof cylindrical object down to 50mm diameter with decrements of 10mmdiameter for every test of each FO Cables. But from 50mm diameter downto 20mm diameter the decrements would be 5mm. Each test included the1270nm and 1650nm wavelength and 10 turns on the cylindrical object.


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Results

Based on the experiment, the 1270nm wavelength bending radius loss wasinsignificant for the 2mm, 3mm diameter and 4 fibers for FO Cables until they getto a diameter of 40mm. They surpassed the 0.02 dB loss in the 40mm diameter

(20.0mm radius) of the cylindrical object (see Figure 1). For the 1650nmwavelength bending radius, it showed a significant change in the 60mm diameter(30.0mm radius) of the cylindrical object (see Figure 2).

All fiber cables displayed a common trend of an increase in loss and as expectedthe bending diameter at 1650 nm was larger for the same loss incurred. In factthe power loss of the fiber, at this wavelength, was actually higher. However theMBR that is imposed today on modern fiber optic raceway systems, which is30mm, was still maintained and well within the limit.

At the most sensitive wavelength the MBR that showed a trend upwards for all

fibre cable types was approximately 30.0mm (note graph is in diameter units).

Another very interesting observation was the fact that the multifibre cables whichwere expected to be of consistently more sensitive nature are actually morerobust and can withstand much more bending before common losses areincurred. In addition these cables have a natural tendency to be more effective atconstraining edge bend losses due to the various buffer layers within theconstruction of the cable. In fact they can be effectively cable tied to variousstructures without additional affects on system loss.


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Figure 1.

Bending Radius for 1270nm Wavelength

0

5

10

15

20

25

30 35 40 45 50 55 60 65 70 75 80 85 90

Diameter of Cylindrical Object

Bending

Loss 12 Fibers

4 Fibers

3mm Diameter

2mm Diameter

0.9mm Diameter

Figure 2.

Bending Radius for the 1650nm Wavelength

0

1

2

3

4

5

6

7

8

9

10

40 45 50 55 60 65 70 75 80 85 90

Diameter of Cylindrical Object

Bending

Loss 12 Fibers

4 Fibers

3mm Diameter

2mm Diameter

0.9mm Diameter

Note: 12 Fibers Could not entirely roll because the LSZH material is stiff.


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Discussion

The study showed that the bending radius of each type of Fiber Optic Cablesvaries from one another for both 1270nm and 1650nm wavelength. The moresensitive region was definitely the longer wavelength 1650 nm. All cable types

meet and surpassed current 30mm MBR requirements for ducting systems andsplice trays.

Comparing the result to the Fiber Optic Cable industry standard, we can see thatthe results were not consistent with the industry standard (see Table 1). As anexample, if one were to design a ducting system on the basis of such data therule of thumb imposed below 20 X MBD of the cable would yield a MBR of80mm.

These tests were performed in order to come to terms with the kind of minimumbending radius that would be proposed for a system that would effectively carry

various kinds of SM and MM cables and cords. In addition to the bendingrequirements there were other issues which could not have been effectivelymeasured in this paper. Some of these were:

The loading effects of fibres in the tray

The installation of various types of cables and their interaction with eachother, eg 2mm cord and Multifibre cord together

Ageing effects and the eventual relaxation of the buffer sheath

Temperature variations

PMD variations etc

In making a practical recommendation with the results of this paper andconstraints above taken into account the MBR for a fibre management systemwas recommended as greater than 30mm. Where high bit rate systems weredeployed and these are affected by PMD (Polarization Mode Dispersion) testshave not been performed to verify the limits and affects on transmissionequipment.

Based on these findings W&BT would recommend the use of the current fibreoptic ducting system for cables up to 12 F indoor riser, as tested.

Cable TypeMinimum Bending Radius

As a Multiple of Overall Cable DiameterFiber Optic Cable 10 times overall diameter for multimode cables,

20 times overall diameter for singlemode cables

For future study, repeat the trials with MM cable and verify the limit of thismedium.

End of Paper

the bending radius of fiber optic cable rev5

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