Distributed fiber optic acoustic sensor

A coherent optical time domain reflectometer device, comprising:

• a coherent light source that produces coherent probe light pulses at an optical wavelength;
• an optical coupling unit coupled to one end of a fiber link under test to direct the coherent probe light pulses into the fiber link under test and to receive reflected probe light pulses from the fiber link under test;
• an optical detection unit coupled to the optical coupling unit to receive the reflected probe light pulses and structured to include an optical interferometer to process the reflected probe light pulses along two different optical paths to generate different optical output signals from the reflected probe light pulses along different optical paths, and optical detectors respectively in the different optical paths to receive the optical output signals from the optical interferometer;
• and
• a device controller coupled to the optical detection unit to receive detector output signals from the optical detectors and to process the detector signals to extract information on spatial distribution of acoustic—or vibration—or strain-dependent characteristics as a function of distance along the fiber link under test.