Enhanced bandwidth distributed acoustic sensing using a frequency multiplexed pulse train and micro-machined point reflector fiber
Hannah M. Ogden, Martynas Beresna, Timothy Lee, Brandon Redding
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>0.095</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mi>p</mml:mi> <mml:mi>ε</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:msqrt> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>Hz</mml:mtext> </mml:mrow> </mml:msqrt> </mml:math> . 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.