In the coherent PHI-OTDR system, the phase
signal is retrieved based on the reference point and the observation point
which are off and closer to the two sides of step of the phase change. In the
experiment, the optical pulse with the changed peak power, width or shape is
injected into the fiber for interrogating the change of the quantitative
characteristic of the measured phase signal. When the pulse width is fixed at
200 ns and its peak power is adjusted from 14 dBm to -23 dBm, the amplitude is
slightly increased from 17.3575 rad to 17.4411 rad as long as the Rayleigh
backscattering signal can be found in the electrical signal. Changing the pulse
width from 260 ns to 80 ns when the peak power is fixed at 14 dBm, the maximum
amplitude and the minimum amplitude of the measured phase signal are 17.4625
rad to 17.4509 rad, respectively. When the arbitrary shape of the optical pulse
generated from the MZI structure with a changed delay fiber from 3 m to 6 m,
the amplitude varies from 17.4558 rad to 17.4819 rad. For every measurement,
the change of frequency is also small. And the small value of standard
deviation supports the accuracy of the measurement. All the measurements show
that the changed pulse nearly has no impact on the quantitative characteristic
of the measured phase signal in the coherent PHI-OTDR system. Moreover, we also find that the phase signal of
external event can be correctly extracted as long as the Rayleigh
backscattering signal can be detected.<br>
Time division control optical pulse width method of distributed optical vibration sensing system in smart power plant
