USA As Represented by Secretary of the Navy

Gerald L Assard

Antonio L Deus, Iii

Barry A Blakely

David J Moretti

Antonio L Deus

Arthur L Moorcroft

Michael Amaral

Antonio L Deus Iii

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

A digital receiver system is used to recover a signal of interest, such as measurand signal, from a phase modulated signal detected from a system utilizing quadrature carriers, such as a fiber optic interferometer sensor system. The digital receiver system includes a quadrature sampling demodulator that samples the phase modulated signal by using quadrature sampling periods to recover the odd and even components of the signal of interest. The digital receiver system can be used with an interferometer sensor system having an array of sensors that multiplex the measurand signals, e.g., using time or wavelength division multiplexing. Sampling with quadrature time samples provides a spacing in time between the samples that allows additional sensors to be multiplexed.

System and method for recovering a signal of interest from a phase

A demodulation system and method is used in a sensor system, such as a fi optic sensor system, that senses optical signals and modulates a phase generated carrier having a carrier frequency .omega..sub.c to form a modulated carrier. The modulated carrier is preferably undersampled at three times the carrier frequency (3.omega..sub.c), thereby maximizing the sensors' demodulated bandwidth relative to the sensors' sampling frequency. The undersampled, modulated carrier is orthogonally demodulated by multiplying the undersampled, modulated carrier by cos(.omega..sub.c (t.sub.o)) and sin(.omega..sub.c)(t.sub.o)) 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 digital spectral normalizer for subtracting out the mean of an input sil to be normalized to obtain a normalized output signal. The normalizer comprises a variable gain amplifier which adjusts the input level to fall within the dynamic range of an analog to digital converter. The output of the digital converter propagates along two paths, i.e. one path used to drive a first digital to analog converter which provides the analog levels to a first low pass filter to obtain the mean of the input signal and the second path used to delay the output of the digital converter by an amount selected in a digital delay line to match the inherent delay of the mean signal traveling via the first path. The delayed signal drives a second analog to digital converter, the output of which passes through a second low pass filter of relatively high frequency, restoring the quantized waveform back to continuous analog signal. The mean signal is then subtracted from the delayed signal in the output amplifier to obtain the normalized output signal.

Digital spectral normalizer

A cylindrical interferometric hydrophone having an axial hollow free-flooded volume includes an outer fiber wrap for a sensor leg and an inner fiber wrap for a reference leg. Both inner and outer fiber wraps are wound on elastomers and exposed to seawater for sensing acoustic signals. In operation an increased pressure shortens the outer wrap and lengthens the inner wrap. This use of both the sensor and the reference legs to detect signals gives increased sensitivity.

Complementary interferometric hydrophone

An interferometer inhibits a received low frequency acoustic signal that is elow the pass band of interest from appearing in the output. The interferometer has a conventional optical hydrophone in the signal leg to sense both the high and low frequencies of an acoustic signal. The reference leg has means for accepting a low frequency acoustic signal to modulate the coherent light path length while inhibiting the desired high frequency signal. On recombining the signals from both the signal and reference legs the low frequency signal appearing in both legs is canceled and only the high frequency signal appearing in the signal leg reaches the output. In an alternate embodiment the reference leg mandrel is placed internal to the sensor mandrel and provides a low frequency compensation chamber.

Interferometric hydrophone reference leg low frequency compensation

A pseudo-random noise generator (PRNG) or a hard clipped tonal is remotely mployed as an acoustic signal simulator for calibrating individual hydrophone channels of an acoustic array. The PRNG is employed to present a complete measurement of the channel gain and phase vs. frequency characteristics. The circuitry provides for synchronizing a channel hydrophone PRNG's to obtain gain and phase comparison of a single channel measurement. The hard clipped tonal provides the gain vs. frequency of the channel transfer function. In addition a binary signal is provided for changing the gain of the channel.

Pseudo-random noise generator calibration for acoustic hydrophones

A relatively solid mounting surface, which may be part of a leveling gimb supports a piezoelectric bearing mount which has the properties of an acoustic transducer. The transducer has electrodes thereon which are powered from multi-phase electrical sources causing the bearing mount, and a bearing jewel which is rigid therewith, to move so as to dither the jewel in a rotary or other preselected fashion, thereby reducing bearing friction. Bandwidth, level and phasing sequence of the power sources are adjustable permitting optimized average dynamic motion and corresponding increased readout accuracy.

Precise bearing support ditherer with piezoelectric drive means

A target simulator tests the characteristics of a multi-element array witt the use of large memories and long delay line storage. The simulator includes a master clock which provides the count frequency to a binary counter. The reading of the binary counter is compared in a comparator with a stored number in a sequence from a programmable readable memory (PROM). On agreement the comparator feeds an output to an appropriate member of a group of hydrophone counters. Upon receipt of the signal from the comparator the counter provides a signal to the PROM. The PROM then provides its next synchronizing binary number to the comparator. The hydrophone counter also provides a signal to the channel selector reset which resets an appropriate pseudo-random noise generator (PRNG) to produce an output of the target simulator.

Pseudo-random noise generated target simulator

A system for analog-to-digital conversion provides a dynamic range in exc of 120 dB yet requires an output of only 9 bits. These bits are utilized to transmit a companded digital word format including sign information. Use of this companded output format results in significant transmit bandwidth reduction compared with transmit bandwidths required for conventional linear bit formats. This companding results in a worse case error of 3.125%.

Gain-step companding analog to digital converter

A system for increasing the dynamic range of a digital device. This is acplished by enhancing a serial N bit Bipolar Return to Zero (BPRZ) transmitter so as to employ an inherently hidden degree of freedom. This enables the receiver to extract N+1 bits of digital code from an N bit transmitted code.

A/D Dynamic range enhancing technique

A synthesized sinusoid generator for delivering to an acoustic driver high ower of a discrete spectral component from a spectrum including the discrete spectral component and its harmonics. The generator uses a plurality of unity gain switching amplifiers and involves summing various stages thereof at full power. This is accomplished by switching on and off various unity gain switching amplifiers as a function of time of the fundamental, thus necessitating only generation of the fundamental frequency and a delay network to switch on and off the designated unity gain switching amplifiers.

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Waterford, CT, United States of America

Gerald L Assard