An optical time-domain reflectometer is test equipment used to evaluate the loss of signal inside an optical fiber by transmitting laser pulses inside the fiber and measures the scattered light signal.
As we can see in the figure shown above the OTDR Machine contains a light source (mainly a laser) and a
receiver along with a coupler or circulator. The coupler is connected with the
fiber under test through a front panel connector.
The laser produces a short and intense light beam. These pulses
are directed into the fiber link under test through a fiber optic coupler. A
coupler splits the transmitted light pulse into two halves. Due to this, not
all the transmitted pulse is directed inside the fiber.
However, despite using a coupler if we use a circulator then this
wastage of transmitted signal can be avoided. As circulators are highly directional
devices that direct the overall light signal into the
fiber as well as sends the reflected or scattered light signal into the detector.
By inserting circulators in the operational unit of fiber optic tester, the dynamic range
of the equipment can be improved. However, it also causes the overall cost of
the system to increase considerably as the circulator is highly expensive in
comparison to couplers.
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