3.OFC

 SM fibre ( Single mode fibre)-

It is a type of fibre optics cable that has smaller core diameter compared to multimode fibre.

This means only a single mode of light can travel through it,resulting less signal loss and higher bandwidth.

It transmits a single ray of light,which has higher bandwidth capabilities and preferred in longer distance applications.

Multi mode Fibre Optic Cable-

Large diameter core that allows multiple modes of light to propogate.

As the core increases,more data passes through a given time.

Quality of signal reduced over long distances.

Typically used for short distances,data and audio/video applications in LANs.

Windows of OFC -

1 st window - 850 nm - Short wavelength region

2 nd window - 1310 nm - Medium wavelength (O band)

3rd window - 1550 nm - Long Wavelength (C band)

Attenuation is minimum at 3 rd window.

2nd and 3rd window are used in Single Mode Fibre.

1st and 2nd in Multi mode Fibre.

Max speed of Cable laying in OFC - 15 meter/ min.

Link power budget analysis in OFC Link performed to ensure 

1. Sufficient System operations margin 

2. Link operational feasibility 

3. Minimum power available at receiver. 

10 m of ofc is to be coiled on each end in the jointing pit.

Dead Zone in OTDR - Distance along ofc cable where OTDR can not detect or measure events such as splices or connectors.

Excessive pulse width in OTDR causes increase in dead zone length.

Numerical Aperture of an OFC is its light gathering ability.

LSPM - ( Light Source Power Meter)

This meter is superior to OTDR for  measures power loss.

only.

Overall OTDR is much superior because it power loss,location of faults or faulty connectors.

Counter allowance in OFC laying- 2.5 %

Extra length for track cross in OFC - 2.5 m on each side

Bridge and culvert - 10 m each side 

Major Steel bridge - 5 m both sides.

Short Bridge - 2.5 m both side

At every cable joint - 10 m 

Telecom cable laying - 01 m inside Railway boundary 

Minimum bending radius is 30 time the radius of OFC diameter 

Pulling tension - 1.1 times of weight of OFC.

Pulling speed - 15 m/second.

After OFC laying,bitumen compound is poured in early hours or late hours when Ambient temperature is around 18 degrees or less so that temperature of cable does not increase beyond 55 degrees Celsius.

Bitumen compound should be filled upto height of 60 mm.

Cable marker should be placed at 50 m and at places where route ranges.

At track crossing depth should not less than 1.2 mm.

At 500 depth a PVC warning tape shall be provided continuously running in trench.

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