The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jul. 31, 2001
Filed:
Oct. 29, 1999
Craig W. Hodgson, Thousand Oaks, CA (US);
Donald A. Frederick, Simi Valley, CA (US);
Litton Systems, Inc., Woodland Hills, CA (US);
Abstract
A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, each emitting light at different frequencies; a plurality of subterranean optical sensors, receiving and altering the light in response to acoustic waves; at least one optical detector, receiving the altered light and outputting an electrical signal; and electronics, receiving the electrical signal and converting it into seismic data format. Light from the optical sources is modulated at a plurality of modulation frequencies. The electronics can demodulate the signal by mixing the signal with periodic waveforms having frequencies corresponding to one and two times the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies, and preferably such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The hydrophone for sensing the acoustic signals is able to operate at pressures and temperatures of at least 5,000 psi and 130° C., respectively. The hydrophone may be housed in a cable having a diameter less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry cam, which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. The mandrels have hemispherically-shaped endcaps and are joined by flexible interlinks having grooves for receiving optical fiber.