  The round trip time of the light pulse limits the maximum detectable
frequency response range of vibration in phase-sensitive optical time domain
reflectometry ({\phi}-OTDR). We propose a method to break the frequency
response range restriction of {\phi}-OTDR system by modulating the light pulse
interval randomly which enables a random sampling for every vibration point in
a long sensing fiber. This sub-Nyquist randomized sampling method is suits for
detecting sparse-wideband-frequency vibration signals. Up to MHz resonance
vibration signal with over dozens of frequency components and 1.153MHz single
frequency vibration signal are clearly identified for a sensing range of 9.6km
with 10kHz maximum sampling rate.
