There is provided a DAS acquisition device which combines both a coherent OTDR mode of operation and an un-coherent OTDR mode of operation for allowing real-time monitoring of both fiber vibrations and fiber loss variations in a hardware efficient, low-cost and compact manner. The DAS acquisition apparatus comprises a coherent light source consisting of a CW coherent light source followed by a semiconductor optical amplifier (SOA) driven by a pulse generator. When the CW coherent light source is turned on (coherent OTDR mode of operation), a coherent pulsed test light signal is produced, so as to acquire DAS traces for acoustic and vibration measurement. But when the CW coherent laser is turned off (un-coherent OTDR mode of operation), an un-coherent pulsed test light signal is produced, so as to acquire un-coherent reflectometric traces for optical fiber loss measurement.