OTDR - How to read the traces

In this article let us have an overview of how to read OTDR traces .As we know OTDR traces are usually used to identify the fibre cuts/losses and reflection events .

When we fire the OTDR we can need to use two types of pulses

-Short pulse (used typically to identify the fibre faults for example losses/reflection events within 10-15 kms)

-Long pulse (used typically to identify the fibre faults for example losses/reflection events which usually occur >10-15 kms range for example 50 kms)

We usually need both these OTDR pulses and in both transmit and receive directions to identify the fault within the span

So in summary both short and long pulse OTDR and on both directions (TX and RX).

Now let us try and read OTDR sample trace as uploaded in the picture

-The start and end of the OTDR traces indicate Fresnel reflection ( named after Augustin-Jean Fresnel who discovered that as light passes from one medium i.e. fibre to another medium i.e air with a different refractive index such reflectiions take place)

-Dynamic range denotes the difference difference between the maximum and levels that an OTDR can measure

-The number indicate the events in the fibre for example as we can see even 32 has more fibre loss