Enhanced Sensitivity High Spatial Resolution Distributed Acoustic Sensing Using Optical Frequency Domain Reflectometry and a Point Reflector Array Sensor

Abstract

Acoustics can be sensed with high spatial resolution by analyzing fiber Rayleigh scatter with optical frequency domain reflectometry, but signal-to-noise levels are low. Writing an array of discrete reflectors in fiber with a fs-pulsed laser increases returned light and leads to significant improvements in signal-to-noise levels and dynamic range.

Enhanced-Backscattering and Enhanced-Backreflection Fibers for Distributed Optical Fiber Sensors

“…ULEB fibers were used with OFDR for increased spatial resolution measurements: using an inexpensive tunable laser diode with a 1 nm tuning range and an ULEB fibers with over 40 dB enhancement reflectors spaced by 4.8 cm, strain measurements with a root mean square accuracy of fewer than 2.70 με were achieved when 10-50 με was exerted to the sensing fiber [122]. An ULEB fiber containing 48 reflectors with a reflectivity level of -50.5 dB spaced by 20 cm was interrogated with a commercial Luna OBR 4600 OFDR system [123], tuning over 10 THz at 25 THz/s, resulting in a DAS with 0.02 rad phase noise, 24 kHz range with 2.32 Hz sample spacing.…”