Optical Fiber Communication Systems

• Optical Fiber Communication Systems are covered

Section I: OFC Usage Guidelines

• Use 24/48 fiber OFC with 6 quad jelly-filled quad cable
• All OFC should be laid in HDPE pipe via the blowing method
• Install an IP-MPLS network for both short and long haul distances

Section II

• Cable pits near OFC rooms should be 1.25 meters deep
• Two RCC pipes, each 100mm in diameter, are needed separately for OFC and quad cable
• Pipes should extend up to 2 meters from the cable pit, outside with a suitable slope; cable entry into the cable must be as smooth as possible

Section III: Route Plan

• Detailed surveying is needed to finalize the OFC route plan

Procedures (for "5 km charts")

• "5 km charts covering a 5 km length of the route should be prepared (Scale: 10 cm = 1 km)

• Start the cable route from the control office using a 30-meter steel tape

• Maintain a minimum distance of 5.75 meters between ONE masts and the cable for OFC

• Maintain Imtr from ONE masts in yards using HDPE pipes

• Use 1 km to 1.2 km tapping for the emergency control circuit

Cable Length (for OFC System)

• Route length is determined as per actual measurement plus a contour allowance of 2.5%
• Extra length for track crossing is required, including 2.5 meters loop on each side
• 10 meters extra length is required on approaches/crossing the bridges and culverts on each side
• Maintain 5 meters of cable on either side of a major steel bridge
• Maintain 2.5 meters of cables on short bridges
• Keep a loop of 10 meters at every joint on either side
• A loop of 10 meters should be kept in the cable pit

Section VIII: Work Flow Diagram

• Preparation of Materials, Tools & Equipment → Digging → Trenching → Laying of HDPE Duct → Sieved Earth Filling → Backfilling & Protective Covers (if any) → DIT (Duct Integrity Test) → Blowing of Cable → Completion

• A Caterpillar tractor can be used for laying cable along the cable route, using an adjustable ripper, allowing a typical preparation of 1.20 meter depth

• DIT should be carried out once laying is completed, per block section (8-10 km)

Paying Out Cable

• Under tension during a pull, the OFC bend radius is always at least 20 times the cable's diameter
• For armored OFC, the bending radius under tension during pulling should always be greater than 30 times the OFC's diameter

Laying Cable by Winch

• Pulling Tension: (1.1 times w) kg
• Bending Radius = 30 times D
• Pulling Speed: Max, 15 mtr./min.
• 10 to 15 meters of OFC should be kept in the next pit

Section IX: Cable Protection

• The chapter or section covers arrangements to prevent damage to the cable and to protect staff

Protection of Cables Crossing Bridges/Culverts

• Separate troughs should be used for laying 6 quad cable and OFC
• For smaller culverts/bridges, HDD should be adopted, with DWC pipe protection, ensuring the cable is minimum 2 mtrs below the bed of culverts/bridges.
• At major culverts & bridges use steel troughing, GI pipe, box/pipe, or channels
• Use bitumen to prevent theft

Measures Against Theft of Steel Troughs

• To prevent theft of optic fiber cable steel troughs filled with OFC, apply a bitumen compound to IS specification, supervised by a senior supervisor
• Bitumen should be poured when the temperature is 18°C or less
• Accurately measure and ensure the pouring temperature of the bitumen compound is not more than 140°C
• Fill the bitumen compound up to a height of approximately 60mm

Arrangement for Laying Fiber Optic Cable Across Girder Bridges

• For girder bridges up to a span length of 12 meters, use GI pipe
• For girder bridges of span length more than 12 meters, use steel trough
• Always use a separate trough for laying 6 quad cable
• Bricks are provided in cable trenching

Protection Arrangement on Cable Route

• B-class bricks must be placed after covering the cable duct
• Cable markers indicating route changes should be provided every 50 meters on the cable route
• Joint indicators shall be provided at all joints
• Standard stone and RCC type cable and joint markers must be provided

Cable Crossing Tracks and Level Crossing Gates

• Lay the cable in RCC/DWC ducts, maintaining the same depth as normal routes
• For cable road crossings, RCC/DWC ducts should be laid on the road for at least 2 meters from either side
• Depth at any track crossing should not be less than 1.2 meters with RCC/DWC duct
• Ensure the cable's bend radius is not less than 600mm when crossing a track
• When trenchless HDD is adopted, the minimum depth should be 1.2 meter/120 cm, * 120 cm for OFC and 100 cm for quad cable
• Use GI pipe in rocky areas, culverts, girder bridges, and PSC girder bridges; always keep 5 meters of cable at the ends
• OFC cables must be run through Class B GI pipes of 80 mm diameter, also for funnels

Back Filling of Trenches

• Maintain at least 120 mm from the surface of the last cable
• A PVC warning tape should be continuously laid at a depth of 500mm
• In case of labor shortage, make a video recording of the cable and its trench

Section X: Jointing and Termination

• Two techniques for jointing OFC: Mechanical splice and Fusion splice

• Mechanical splice aligns the axis of the two fibers and physically holds them together

• Mechanical splicing may only be used to temporarily splice fibers

• Fusion splicing applies localized heating (e.g., electric arc/flame) at the interface between butted, pre-aligned fiber ends, causing them soften and fuse together

• Only use the fusion splicing technique now

Steps Involved in Jointing Cables

• Prepare the Cable for jointing
• Strip/cut the Cable
• Prepare cable and joint closure for splicing
• Strip and clean fibers
• Organize fibers and finish joint
• Seal joint closure
• Place the joint it a pit

Preparation of Cable for Jointing

• During installation, coil a minimum of 10 meters of cable at each end in the jointing pit to provide slack for jointing

• The pit must have sufficient length of the wall that the joint is mounted.

• Subtract the closure length and add twice the minimum bending radius of the cable

• A pit length of 1 meter is sufficient for most cables and joint closures

Stripping/Cutting the Cable

• Strip the cable's outer and inner sheath, staggering each sheath approximately 10mm from the one below

Stripping and Cleaning of Fiber

• Before splicing, strip each fiber's primary protective coating up to 50mm, using a fiber stripper
• After stripping, clean the fiber as close as possible to a perfect 90° face.

Splicing of the Fiber

• Ensure that it is fully automatic with microprocessor splicing machine

Fusion Splicing of Fiber

• Dip the clean bare fiber in ethyl alcohol from the ultrasonic cleaner, and switch for 5 to 10 seconds

• Then placing it a "v" groove of the splicing machine, ensure that there is I mm gap between

• Then heat shrink the insulator

• Precision alignment is also required for better connectivity

Mechanical Splicing of the Fiber

• Align the fiber in vi groove
• Using Index matched adhesive can help to seal the fibre ends

Other Factors Notes

• End to End tests
• 1310 nm = 0.40 db/km
• 1550nm = 0.25 db/km

For RCC Cable Route Marker

• All sides above ground to be painted in RED

For OFC Joint

• All sides above ground to be painted GREEN

For QUAD Joint:

• All sides above ground to be painted YELLOW

Duct Integrity Test (DIT)

• Carry out DIT before OFC cable blowing
• Determine that it is suitable for fitting
• Cable is set to a pressure of 10 Bar
• Leakage or a puncture can lead to failure in pressure testing
• Air should flow freely and have no discontinuities
• The test should also use a shuttle and Sponge twice the size of inner duct, passed with pressurized air.

The DIT test steps are

• Ensure no discontinuities by using pressurized air
• Ensure the duct inside the diameter of 150mm
• Conduct five bar pressure for 30 minutes, drop no more than 0.5 Bar

Shuttle Test

• A Diameter of 80% passed, diameter and the length should be recorded

Sponge Test

• Ensure to clean the surface of the area

Pressure Loss Test

• Measure pressure is 5 bar during loss