OFC Splicing jointing |Jointing (Splicing) of Optical Fibre Cable

 OFC Splicing jointing |Jointing (Splicing) of Optical Fibre Cable

Jointing (Splicing) of Optical Fibre Cable

Optical fibre cable jointing or Splicing is a permanent connection of two pieces of fibres. Optical fibre cable splicing Techniques is of two types.

1. Mechanical splicing
2. Fusion Splicing

Read also: OFC Cable jointing Tools and Equipments  

1. Mechanical Splicing

Mechanical splicing is perform with a small mechanical splicer which joints permanently the two optical fibres.

 Mechanical splicer is a small fibre connector that aligns the axis of the two bare fibres to be joined

and physically hold them together.

 A snap-type cover, an adhesive cover, or both, are used to permanently fasten the splice. Insertion loss

per joint is less than 0.5dB.

 Mechanical splicing is used for temporary splicing of fibres or where fusion splicing is impractical or undesirable.

This is done by applying localized heating (i.e. by electric arc or flame) at the interface between the butted, pre-aligned fibre end, causing them to soften and fuse together.

 Mechanical Splicing Process

The splicing process is basically the same for all types of mechanical splices. The first step is to strip, clean & cleave the fibres to be spliced.

Strip the primary buffer coating to expose the proper length of bare fibre. Clean the fibre with appropriate wipes. Cleave the fibre using the directions appropriate to the cleaver being used. Using a high quality cleaver such as those provided with fusion splicers will yield more consistent and lower loss splices.

 Making the Mechanical Splice

Insert the first fibre into the mechanical splicer. Most splicers are designed to limit the depth of the fibre insertion by the stripped length of buffer coating on the fibre. Clamp the fibre in place if fibres are held

separately. Some splicers clamp both fibres at once. Repeat these steps for the second fibre.

You can optimize the loss of a mechanical splice visually using a visual fault locator, a visible laser test source if the fibre ends being spliced are visible. Gently withdraw one of the fibres a slight amount, rotating it slightly and reinserting it until the visible light is minimized, indicating lowest loss.

2 Fusion Splicing

Fusion splicing involves the melting and jointing of optical fibres using

heat generated by an electric arc between electrodes. Fusion splicing is

classified into the two methods, as follows.

i. Core Alignment Method

Optical fibre cores observed with a microscope are positioned with the

help of image processing so that they are concentrically aligned. Then,

an electric arc is applied to the fibre cores. The fusion splicer used has

cameras for observation and positioning in two directions

ii. Stationary V-groove Alignment Method

This fusion splicing method uses V-grooves produced with high precision

to position and orient optical fibres and utilizes the surface tension of

melted optical fibres for alignment effects (cladding alignment).

Splices made by this method achieve low loss, which has improved the

dimensional accuracy regarding the placement of core.

This method is primarily used for splicing a multi-fibre cable in a single

action.

Optical fibre cable fusion splicing provides the lowest insertion loss less

than 0.1dB. Special equipment called fusion splicer is used for it. The

fusion splicer performs optical fibre fusion splicing in two steps.

 Precisely align the two fibres

 Generate a small electric arc to melt the fibres and weld them together

Fusion splicing is perform by Fusion splicer, a machine used to weld

(fuse) two optical fibres together. The fibre ends are prepared, cleaved, and placed in alignment fixtures on the fusion splicer. At the press of a

button, the fibre ends are heated with electrodes, brought together,

and fused. We can preset the splicing parameters or choose factory

recommended settings that will control the splicing process itself. Each

manufacturer's product is slightly different and requires somewhat

different procedures. A photograph of typical splicer is shown below:

Preparation of cable for jointing

 During the installation, a minimum of 10 meter of cable at each end is

coiled in the jointing pit to provide for jointing to be carried out at

convenient location as well as spare length to be available for future

use in case of failures.

 The pit size shall be so as to ensure the length of the wall on which

joint is mounted is greater than closure length plus twice the

minimum bending radius of the cable. A pit length of 1 meter is

sufficient for most of the cable and joint closures. Bracket to support

eh cable coil are also fixed on the wall of the pit. Details of cable pit

are given in Drawing No.RDSO/TCDO/COP-21.

 The cable is then coiled on to the pit wall in the same position as

required after the joint is complete. The marking is done on all the

loops so that it will be easier to install it later

 The distance from the last centre to the end of the cable must be at

least 1.8 meters. This is the minimum length to be stripped for

preparation of joint.

 Sufficient cable length at both ends up to the jointing

vehicle/enclosure is then uncoiled from the pit for jointing.

 Stripping/Cutting of the Cable

 The cable is stripped of outer and inner sheath with each sheath

staggered approximately 10mm from the one above it.

 Proper care must be taken when removing the inner sheath to

ensure that the fibres are not scratched or cut with the stripping

knife or tool. To prevent this, it is better to score the inner sheath

twice on opposite sides of the cable, rather than cutting completely

through it. The two scores marking on either side of the cable can be

easily stripped of the inner sheath by hand.

 The fibres shall be then removed from cable one by one and each

fibre is cleaned individually using kerosene oil to remove the jelly.

 Armouring shall remain outside the gland and will not be connected

through.

Preparation of Cable Joint Closure for Splicing

 The type of preparation work performed on the cable prior to splicing

differs on the type of joint closure and fibre organizer used. However,

the following steps shall be usually common for different types of

joint closure.

(a) The strength member of each cable shall be joined to each

other and/or the central frame of the joint closure.

(b) The joint closure shall be assembled around the cable.

(c) The sealing compound or heat shrink sleeve shall be applied to

the cables and closure, or prepared for application after splicing

is complete.

(d) Tags which identify the fibres number shall be attached at

suitable location on the fibres.

(e) Splice protectors shall be slipped over each fibre in readiness

for placing over the bare fibre after splicing.

Stripping and Cleaving of Fibre

 (a) Prior to splicing, primary protective coating of each fibre shall be

stripped off up to length of 50 mm. by using fibre stripper. Fibre

strippers shall be manufactured to fine tolerances and only score the

coating without contacting the glass fibre.

 The bare fibre shall be then wiped with a lint tissue paper rinsed with

ethyl alcohol.

 Cleaving of the fibre shall then be performed to obtain as close as

possible to a perfect 90 degree face on the fibre.

 Fusion splicing of fibre

 Some of the general steps with full automatic micro processor

control splicing machines shall be as under:

 (a) Hands shall be thoroughly washed prior to commencing this

procedure.

 (b) The clean bare fibre shall be dipped in the beaker of ethyl

alcohol of the ultrasonic cleaver and ultrasonic clever switched

on for 5-10 seconds.

 (c) The bare fibre shall then be placed inside ‘V’ groove of the

splicing machine by opening clamp handle, in such a way so that

1 mm gap is available between the electrodes and the end of

fibre being spliced and heat shrink protector inserted

 (d) The same procedure shall be repeated for other fibre.

 (e) The start button on the splice controller shall be pressed.

 (f) The machine shall pre-fuse set align both in ‘X’ and ‘Y’

direction and then finally fuse the fibre.

 (g) The splice shall be inspected on monitor provide on the

fusion splicing machine, there shall be no nicking, bulging and

cores are adequately aligned. The above procedure shall be

repeated if the splice is not visually good looking.

 (h) The heat shrink protector shall be slid over the splice and

tube shall be placed in tube heater. Heating shall be considered

complete when soft inner layer is seen to be ‘oozing’ out of the

outer layer of the protector.

 (i) The steps a) to (h) above shall be repeated for other fibres.

 Organising fibre and finishing joints

 (a) After each fibre has been spliced, the heat shrink protection

sleeve shall be slipped over the bare fibre before any handling of

fibre takes place as uncoated fibres are very brittle and cannot

withstand small radius bends without breaking.

 (b) The fibre shall then be organized into its tray by coiling the

fibres on east side of the protection sleeve using the full tray side

to ensure the maximum radius possible for fibre coils.

 (c) The tray then shall be placed in the position.

 (d) OTDR reading shall be taken for all splices in this organized

state and recorded on the test sheet to confirm that of all fibres

attenuation is within specified limits. The OTDR test confirms

that fibres were not subjected to excessive stress during the

organizing process. Care should be taken that the fibres are not

interchanged while jointing.

 (e) The joint shall then be closed with necessary sealing etc. and

considered ready for placement in the pit.

Placing of completed joint in pit

 (a) Joint shall be taken out from the vehicle and placed on the

tarpaulin provided near the pit.

 (b) The cable is laid on the ground and looped according to the

marking done in the beginning. These loops shall then be tied

together with the tape.

 (c) The joint shall be permanently closed and sealed by heating

heat shrinkable sleeve, etc.

 (d) The joint closure shall be fixed to the bracket on the pit wall

and pit closed.

Some guidelines for splicers are given below.

 Follow the applicable equipment manufacturer’s guidelines

through operating manual for setup and maintenance of all splice

equipment. Besides cleaning regularly, they require electrode

alignment and occasional replacement.

 Maintain clean equipment and a clean splice environment, being

especially wary of windy and/or dusty conditions.

 Splice loss specifications should be set with the total link power

budget in mind and be based on average splice loss.

Testing of Splicing

 Good Splicing

Visually inspect the splice after the program has run, using both X and Y

views. Some flaws that do not affect optical transmission are

acceptable, as shown below. Some fibres (e.g. fluorine-doped or

titanium coated) may cause white or black lines in splice region that are

not faults. Some graphics of a typical splicer “Sumitomo” manual are

given below.

Fusion splices provide a high-quality joint with the lowest loss (in the

range of 0.01 dB to 0.10 dB for single-mode fibres) and are practically

non- reflective.

Bad Splicing

Some flaws are unacceptable and require starting the splicing process

over. Some, like black spots or lines, can be improved by repeating the

ARC step, but never more than twice. For large core offsets, bubbles or

bulging splices, always redo. 

Read also: OFC Cable jointing Tools and Equipments