A fiber-optic interferometric accelerometer/geophone system.

Abstract

A variety of transducers presently exists for geophysical exploration, ranging from suites of land-based geophones, seismometers, and accelerometers to towed hydrophone arrays for off-shore surveying. Miles of electrical cabling are required to implement these systems. To exploit the advantages of long-distance fiber-optic communication technology and to avoid temperature sensitive electronics in warm down-hole applications, several intrinsically optical fiber-optic acoustic and acceleration/geophone transducers have been developed within the NPS Physics Dept. Recent advances at NPS in the development of low-cost interferometric signal demodulators permit the implementation of an economical measurement system, whereby the fiber-optic transducer output may be made indistinguishable from a similar electrical transducer. Push–pull fiber-optic accelerometer/geophone designs employing an all-fiber Mach–Zehnder interferometer, a 3×3 coupler, and a demodulator system will be described. [Work supported by the Naval Postgraduate School Direct Funded Research Program and the Naval Sea Systems Command.]