US Patent 10444063 Downhole fiber optic hydrophone

Methods, systems, devices, and products for acoustic detection in a borehole. Apparatus embodiments comprise an acoustic sensor including: a pressure transducer comprising a flexing member attached to an optical medium, the transducer configured to convert a low-amplitude, high-frequency acoustic pressure signal within a nominal borehole pressure incident on the transducer to an alternating strain on the optical medium along an axis of the medium via movement of the flexing member while suppressing conversion of low-frequency signals and constant pressure into strain of the optical medium, the acoustic pressure signal propagated via a downhole fluid coupled with the transducer; and a detector configured to generate acoustic measurement information responsive to received electromagnetic radiation transmitted through the medium along the axis, the at least one optical property of the medium being responsive to the alternating strain on the medium such that the electromagnetic radiation received by the detector represents the acoustic signal.