Fiber Optic Gradient Hydrophone.
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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A laboratory study has been made of the characteristics of an interferometric type optical fiber pressure gradient hydrophone. The optical system is configured as an all-fiber Mach-Zehnder interferometer excited by a single mode gallium arsenide diode laser. A pair of identical fiber coils, one in each arm of the interferometer, forms the sensing portion of the gradient hydrophone. Each coil consists of 10 meters of polyethylene jacketed, single mode fiber, wound in a doughnut shaped element of mean diameter 4 cm and thickness 3 mm. An acoustic calibrator, similar in design to the USRD type G40 shipboard calibrator used by the U.S. Navy, was constructed for use in obtaining single and dual dipole coil sensitivities. The acoustic sensitivity of each coil was determined separately and then the pair was aligned coaxially and separated by 10 cm to operate as a pressure gradient device. Details of the construction of the system, calibration procedure, lock-in demodulator, and hydrophone sensitivity data are presented. The system has demonstrated a 14 dB sensitivity advantage over the USRD type G63 standard piezoelectric pressure gradient hydrophone. Author
- Acoustic Detection and Detectors
- Fiber Optics and Integrated Optics