US Patent 11867855 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: an interface between a fluid reservoir and a fluid body, the interface including a flexing member attached to an optical medium, the pressure transducer configured to convert an acoustic pressure signal within a nominal borehole pressure incident on the pressure transducer to an alternating strain on the optical medium along an axis of the medium via movement of the flexing member, the acoustic pressure signal propagated via the fluid body; a detector configured to generate acoustic measurement information responsive to received electromagnetic radiation transmitted through the medium along the axis, at least one optical property of the medium being responsive to the alternating strain on the medium; and at least one coupled oscillator displacing a volume of the fluid reservoir responsive to the acoustic pressure signal to modify conversion by the flexing member of signal components of the acoustic pressure signal having a frequency within a predefined frequency range into strain of the optical medium, so that the electromagnetic radiation received by the detector represents a modified acoustic signal.