  The detected frequency response range of phase-sensitive optical time domain
reflectometry is limited by the sensing fiber length. In this paper, we
demonstrate an amplitude modulated pulses based phase-sensitive OTDR to detect
vibrations with high spatial resolution and wide frequency response range. The
amplitude modulated pulses consisting of narrow pulses and background light are
injected into the sensing fiber as probe light. The Rayleigh backscattering
generated by the background light interferes at the detection end, presenting a
phase sensitive response to external vibrations. The Rayleigh backscattering of
narrow pulses are tracked to locate vibrations. The frequency information is
obtained from the frequency domain analysis of the interference signal. The
system can realize high frequency response with low repetition rate of probe
pulses by one-end detection.
