D.M. Dagenais

Detection of low-frequency magnetic signals in a magnetostrictive fiber-optic sensor with suppressed residual signal

A correlation is presented between experimental data obtained under various operating conditions and a modified coherent rotation model which predicts the behavior of the residual signal and the sideband noise. The authors identify an operating regime that eliminates the residual signal and gives rise to a reduction in noise levels by a factor of five over previously reported results. Minimum detectable fields of 11+or-2pT/ square root Hz at 1 Hz and 38+or-8 pT/ square root Hz at 0.2 Hz are achieved. >

Wavelength stability characteristics of a high-power, amplified superfluorescent source

This paper demonstrates a stable, broad-band two-stage superfluorescent source at 1.55 /spl mu/m consisting of an erbium-doped fiber (EDF) seed source and a high-power Er-Yb fiber amplifier. The source exhibited from 140 to 220 mW of power, 18 to 28 nm bandwidth, with an estimated mean wavelength stability from 1 to 10 ppm. Operating conditions for the seed source and amplifier required to achieve these performance characteristics are described.

Multichannel fiber-optic magnetometer system for undersea measurements

We have designed, fabricated, and operated an undersea array of eight fiber-optic vector magnetometers. Each magnetometer consists of three magnetostrictive transducers aligned on orthogonal axes and incorporated in a single Michelson interferometer. During undersea operation, each interferometer exhibited less than 1 /spl mu/rad//spl radic/ Hz phase noise, and the self-noise of each magnetic transducer was less than 0.2 nT//spl radic/ Hz at 0.1 Hz. We discuss the design and performance of the optical system including noise mechanisms. We present the results of magnetic measurements of the geomagnetic field and the magnetic tracking of ships. >

Elimination of residual signals and reduction of noise in a low‐frequency magnetic fiber sensor

Low‐frequency sensitivities of interferometric magnetic fiber optic sensors have been limited by the presence of a large residual signal at the dither frequency which limits the dynamic range and upconverts low‐frequency noise into sideband noise around the carrier. We present an operating regime that enables us to eliminate residual signals associated with the ac carrier. By choosing the proper carrier frequency and amplitude we obtain a nulled residual signal, strong magnetomechanical coupling, and an increase in signal‐to‐noise ratio of approximately 13 dB over previously reported results. A minimum detectable field of 45 pT/(Hz)1/2 at 0.1 Hz is demonstrated.

Effects of parasitic Fabry–Perot cavities in fiber-optic interferometric sensors

We show theoretical and experimental evidence for increased quadrature point fluctuations and amplitude and phase noise in interferometric fiber sensors owing to the presence of parasitic Fabry-Perot cavities. We demonstrate greater than 2 orders of magnitude reduction of such effects.

Low-frequency Intensity Noise Reduction for Fiber-Optic Sensor Applications

Fiber sensors have recently taken advantage of the 1.3µm diode-pumped laser technology, which offers high output power in a single frequency and orders of magnitude improvement in frequency stability over semiconductor devices [1]. The small frequency jitter [2] of Nd:YAG lasers enables one to attain submicron phase noise in interferometric sensors with as much as 10 meters of optical path difference. Because non-linear fiber sensors, such as magnetic fiber sensors, which make use of a carrier to upconvert low-frequency signals to be detected, are often limited by intensity noise upconverted around the carrier [3], we have measured the intensity stability of those devices . The intensity noise in fiber sensors originates from both the laser instabilities and the drifts in the fiber launch.

Recent developments in fiber optic magnetostrictive sensors

We review developments over the past five years in fiber optic magnetometry based on magnetostriction. Recent work has demonstrated detection of magnetic fields from dc to over 1 MHz with resolution of 10 pT P1Hz at 1 .0 Hz and 0.07 pTpIHz at35 kHz in laboratory devices. We present the basic device operating principles and discuss factors which limit the resolution of fiber optic interferometric magnetic sensors. Results are presented for a number of configurations including a ruggedized, compact, three-axis magnetometer for dc and low-frequency measurements, a single-axis gradiometer, a single-axis heterodyne configuration for narrowband detection of fields in the frequency range 0.01 Hz to 1 MHz, and a magnetostrictive oscillator which exhibits period doubling bifurcations and chaos.

Direct observation of dynamic strain bifurcations and chaos in magnetostrictive amorphous ribbons

Period doubling, quasiperiodicity, phase locking, and chaos are observed in the strain dynamics of a magnetically driven magnetostrictive ribbon (Metglas 2605S‐2). The dynamic strain response of the ribbon was measured with a fiber‐optic Mach–Zehnder interferometer. The predicted universal behavior was characterized with power spectral density measurements and by phase‐space flow. The nonlinearity responsible for observing universal behavior in the system does not involve the ΔE effect.

Demonstration of a fiber optic array of three-axis magnetometers for undersea application

We describe an undersea array of eight magnetic sensors. The employ magnetostrictive the transducer elements. ting principles and the ~orm~nce of the system during actual undersea

Fiber optic magnetic sensor technology for undersea applications

An array of eight fiber optic vector magnetometers was designed and constructed for use in undersea applications such as harbors, ports, and waterways. We describe the design and performance characteristics of the array including the single-mode fiber optic system and magnetostrictive transducers. Data is presented from both laboratory measurements and from actual undersea operation.