05-10-2012, 04:17 PM
OPTICAL TIME DOMAIN REFLECTOMETER (OTDR)
OTDR1.ppt (Size: 104 KB / Downloads: 32)
OPERAING PRINCIPLES
One Port Operation.
Works on the Principle of Back Scattering (Raleigh Scattering, see Figure ).
Scattering is the main cause of Fiber Loss
Scattering Coefficient=1/4
An Optical Pulse is launched into one End of Fiber and Back Scattered Signals are detected.
These Signals are approximately 50 dB below the Transmitted level.
Measuring conditions and Results are displayed.
FRESNEL REFLECTION
It happens when there is a great change of Refractive Index:-
Break Fault.
Connecter Loss.
Free Fiber-End.
Received reflected signal depends on surface conditions.
It is normally 14 db below Transmitted signals.
BOX CAR AVERAGER AMPLIFIER
It is provided to improve S/N of the RX. Signal in OTDR
It is done by sampling the signal at each point in Time, starting at time, t=0.
An Arithmetic Average is generated by a Low Pass Filter (LPF). Then a variable delay is used to move to the next point in Time t=1,2,3-------n.
It scans the entire signal. Larger the No. of Samples (n), the smaller the Mean Square Noise Current:-
OTDR1.ppt (Size: 104 KB / Downloads: 32)
OPERAING PRINCIPLES
One Port Operation.
Works on the Principle of Back Scattering (Raleigh Scattering, see Figure ).
Scattering is the main cause of Fiber Loss
Scattering Coefficient=1/4
An Optical Pulse is launched into one End of Fiber and Back Scattered Signals are detected.
These Signals are approximately 50 dB below the Transmitted level.
Measuring conditions and Results are displayed.
FRESNEL REFLECTION
It happens when there is a great change of Refractive Index:-
Break Fault.
Connecter Loss.
Free Fiber-End.
Received reflected signal depends on surface conditions.
It is normally 14 db below Transmitted signals.
BOX CAR AVERAGER AMPLIFIER
It is provided to improve S/N of the RX. Signal in OTDR
It is done by sampling the signal at each point in Time, starting at time, t=0.
An Arithmetic Average is generated by a Low Pass Filter (LPF). Then a variable delay is used to move to the next point in Time t=1,2,3-------n.
It scans the entire signal. Larger the No. of Samples (n), the smaller the Mean Square Noise Current:-