Enhanced bandwidth distributed acoustic sensing using a frequency multiplexed pulse train and micro-machined point reflector fiber

In this Letter, we present an enhanced bandwidth distributed acoustic sensor (DAS) that uses a frequency multiplexed interrogation system to probe a micro-machined point reflector fiber. The fiber contains a series of discrete point reflectors with reflectance as high as -48 dB, while the frequency multiplexed interrogator allows us to increase the effective pulse repetition rate by a factor of 10. Together, this enables a phase noise as low as -101 dB (re rad(2)/Hz) for a 2.5 km fiber with 10 m spatial resolution, corresponding to a strain noise of 0.095 p epsilon / root Hz. This scheme also enables a 10-fold increase in the sensor bandwidth without introducing noise due to interference fading. Finally, we demonstrate sensing at ranges up to 10 km using a fiber containing 1000 point reflectors, illustrating the scalability of this approach. (C) 2022 Optica Publishing Group