USA As Represented by Secretary of the Navy

Antonio L Deus, Iii

Gregory H Ames

Gerald L Assard

David J Moretti

Michael Amaral

Christopher M Hansen

Paul D Curry

The present invention relates to a system for sensing the curvature of a towed hydrophone array and a curvature sensor used in the system. The system has at least two curvature sensors positioned along the length of the array. Each of the curvature sensors comprises a bend member which bends as the array bends, at least one optical fiber within the bend member, and at least one detection device embedded within the at least one optical fiber to detect a change in the strain in the at least one optical fiber.

Fiber optic curvature sensor for towed hydrophone arrays

A system for digitally demodulating optical hydrophone signals is provided. The system includes an optical hydrophone connected to an analog-to-digital converter and further connected to a digital signal processor. Within the digital signal processor, a demodulator is calibrated by a preferred automatic calibration circuit such that mixer frequencies are coherently mixed with the incoming acoustic signals received by the hydrophone. The automatic calibration circuit preferably determines an extreme case of phase offset by following a programmable routine including a series of tests. After the extreme case is detected, the precise phase calibration is known and provided to the demodulator mixer tables. The automatic calibration circuit can be utilized for automatic calibrations of multisensor systems containing large numbers of hydrophones.

Digital signal demodulator calibration system and method for optical hydrophones

A demodulation system and method is used in a sensor system, such as a fiber optic sensor system, that senses optical signals and modulates a phase generated carrier having a carrier frequency &ohgr; to form a modulated carrier. The modulated carrier is preferably undersampled at two times the carrier frequency (2&ohgr; ), thereby maximizing the sensors' demodulated bandwidth relative to the sensors' sampling frequency. The undersampled, modulated carrier is orthogonally demodulated by multiplying the modulated carrier by cos(2&ohgr; (t )) and sin(2&ohgr; (t )) to extract even and odd harmonic components of the signal of interest. The even and odd harmonic components of the signal of interest are further demodulated by taking the square root of the sum of squares of the even and odd harmonic components, normalizing the even and odd harmonic components, and differentiating, cross-multiplying and differencing the normalized even and odd harmonic components to recover the signal of interest.

Demodulation system and method for recovering a signal of interest from a modulated carrier sampled at two times the phase generated carrier frequency

A system for digitally demodulating optical hydrophone signals is provided. The system includes an optical hydrophone connected to an analog-to-digl converter and further connected to a digital signal processor. Within the digital signal processor, a basic demodulator has a first and second mixing tables, the first table operating at a modulating frequency, .omega., injected into reference legs of the hydrophone, and a second table operating at 2.omega.. The mixer frequencies are coherently mixed with the incoming acoustic signals received by the hydrophone. An automatic calibration circuit which adjusts the phase of the mixers is connected to the basic demodulator.

Optical hydrophone with digital signal demodulation

An interlink for connecting hydrophone elements that allows a single sens fiber to transition from a first hydrophone element, across the interlink, to a second hydrophone element, while providing a secure connection between hydrophone elements without the disadvantages of mechanical resonances produced by a rigid interlink material. The interlink has a first end connected to a first hydrophone element, and a second end connected to a second hydrophone element. The interlink may be composed entirely of open cell foam, or a more rigid structure that is covered by open cell foam. Sensing fiber transitions from a first hydrophone element, onto the foam interlink, and thence onto a second hydrophone element, with only a change in winding angle. The sensing fiber is not susceptible to a rigid interlink structure and undesirable mechanical resonances.

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Saunderstown, RI, United States of America

Antonio L Deus, Iii