EXFO MAX-700 - Manual (Page 21)

Introducing the MAX-700
MAX-700 9
OTDR Basic Principles
OTDR Basic Principles
An OTDR sends short pulses of light into a fiber. Light scattering occurs in
the fiber due to discontinuities such as connectors, splices, bends, and
faults. An OTDR then detects and analyzes the backscattered signals. The
signal strength is measured for specific intervals of time and is used to
characterize events.
The OTDR calculates distances as follows:
where
c = speed of light in a vacuum (2.998 x 10
8
m/s)
t = time delay from the launch of the pulse to the reception of the
pulse
n = index of refraction of the fiber under test (as specified by the
manufacturer)
Distance
c
n
---
t
2
---  =