Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Patent
1983-05-19
1986-06-03
Brown, David H.
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
73657, 350 9629, 356349, 367140, H04R 144, G01B 902
Patent
active
045933855
ABSTRACT:
An optoacoustic hydrophone for detection of acoustic waves in a fluid such as sea water. The hydrophone includes an optical waveguide comprising a fiber optic input lead, a fiber optic sensor, and a fiber optic exit lead, an optical subassembly and a signal processor. A coherent light beam generated by the optical subassembly is transmitted through the input lead and the sensor which is disposed in the fluid. Acoustic waves in the fluid modulate the index of refraction of the fiber optic sensor thereby modulating the transmitted light beam. The modulated light beam is directed through the fiber optic exit lead to a focus on one of two photodetectors. The other photodetector is oriented for receipt of light reflected from a partially reflective mirror disposed between the input fiber optic lead and the fiber optic sensor. The two light beams impinging on respective photodetector are combined with unmodulated light beams of slightly different frequencies to produce an interference pattern at each photodetector. Each photodetectors produces an electrical signal representative of the interference pattern and the respective electrical signals are applied to a phase meter. The phase meter produces an output signal representative of the acoustic wave alone which corresponds to the difference between the two electrical signals provided by respective photodetectors. The disclosed optoacoustic hydrophone effectively cancels common mode lead noise resulting from towage of the optical waveguide through the fluid. Pressure effects in optical fibers created by other physical mechanisms are also sensed by the present apparatus.
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Brown David H.
Griffiths John E.
The Charles Stark Draper Laboratory
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