Hello,
I am searching about OTDR (Optical Time Domain Reflectometer) system.
It shows optical length in fiber. It has 3 main parts ; laser diode, photodetector and a proccessor.
First ligth energy is injected by OTDR into the fiber through a laser diode and pulse generator. In the measurement the returning ligth energy is seprated from injected pulse using a Coupler and fed to the photodiode. Then it is converted to electrical energy and the proccessor measure the travel time between outgoing pulse from laser diode and incoming pulse into photodiode. Then calculate the length by knowing the speed of ligth in fiber.
Now what I can not undrestand is that how OTDR measures the travel time of ligth. How it knows the time of injected pulse's time and returning pulse?
Thanks,