Optical Time domain Reflectometer is used to measure:

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ALP CBT 2 Electronic Mechanic Previous Paper: Held on 21 Jan 2019 Shift 2

Answer 1

Concept:

An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber.
The Optical Time Domain Reflectometer (OTDR) is useful for testing the integrity of fiber optic cables.
OTDR is used to verify splice loss, find faults, and measure the length of optical communication.
The instrument emits short laser pulses, e.g. with pulse durations of some tens of nanoseconds and peak power of a few hundred milliwatts, as can be obtained with a single-mode laser diode.
The pulses are injected through a launch cable into the tested optical fiber.
Any reflected light is extracted with a directional fiber coupler and sent to a fast and sensitive photodetector.
The photodetector allows for the time-resolved measurement of the reflected optical power and thus of the return loss.
One can find the propagation losses and also find whether the loss coefficient is constant along with the fire or changes locally.