Since I spent ~25 years in underwater acoustics I’m slightly partial to measuring sound. Here are three examples using fiber optics to measure acoustic signals, all related to medical applications:
ULTRASONIC FIBRE OPTIC-HYDROPHONE - uFOHS
a specific application is the in situ measurement of ultrasound fields produced by diagnostic and therapeutic medical ultrasound equipment.
http://www.medphys.ucl.ac.uk/research/mle/fibre_optic.htm
Fiber Optic Probe Hydrophone FOPH 500
A great number of possible applications are in the medical field, in general ultrasonic calibration and measurement as well as in technical ultrasonic equipment:
Absolute pressure measurement in the focus and the extended wave field of medical instruments for extracorporal shock wave lithotripsy, e.g. for the destruction of kidney and gall stones.
Absolute pressure measurement in the focus and the extended wave field of ultrasonic instruments for medical diagnosis.
Characterisation and certification of medical instruments for diagnosis and therapy (IEC 1157).
Underwater shock wave studies.
http://www.pi1.uni-stuttgart.de/link/hydrophon.en.html
Heart sound sensor
US 4672976 A
ABSTRACT
A heart sound sensing device for placement on the body of a patient and for the detection of low frequency sound waves. The device is for use with medical diagnostic devices, and comprises a cylindrical housing structure for retaining the remaining elements of the device, a strap for holding the device to the body of the patient, a fluid ingress/egress aperture, an open end for receiving sound waves, and a hydrophone assembly centrally fixed within the housing structure for producing electrical signals in response to transmitted heart sound waves. The device of this invention is further provided with a flexible diaphragm which is vibratingly sensitive to sound waves generated by the patient's heart and being for placement in direct contact with the patient body surface to conform to the body contours. A bubble free fluid medium is provided to fill the remaining interior volume of the housing structure to transmit sound waves from the diaphragm to the hydrophone assembly. The device further includes a cable means communicatively connected to the hydrophone assembly for transmitting electrical output signals to medical diagnostic devices. The sound sensing device is further used in a method for sensing heart sound waves.
http://www.google.com/patents/US4672976