Method and apparatus of distributed acoustic sensing

A fiber optic distributed acoustic sensing (DAS) acquisition device for performing acoustic and vibration measurements as well as optical fiber loss measurement, the DAS acquisition device comprising:

• a light generating assembly to be coupled to the optical fiber link for generating and propagating in the optical fiber link a test light signal comprising test light pulses, the light generating assembly comprising:
• a coherent light source to produce continuous wave coherent light;
• a semiconductor optical amplifier receiving light from said coherent light source;
• a pulse generator connected to the semiconductor optical amplifier to drive it to generate said test light pulses;
• and
• a detection module for detecting corresponding return light from the optical fiber link so as to acquire a reflectometric trace representing backscattered and reflected light as a function of distance along the optical fiber link;
• wherein in a coherent OTDR mode of operation, said coherent light source is turned on so that said light generating assembly produces a coherent pulsed test light signal, so as to acquire DAS traces for acoustic and vibration measurement;
• and
• wherein in an un-coherent OTDR mode of operation, said coherent light source is turned off so that said light generating assembly produces an un-coherent pulsed test light signal, so as to acquire un-coherent reflectometric traces for optical fiber loss measurement.