USA As Represented by Secretary of the Navy

George H Sigel, Jr

Kee P Koo

Henry F Taylor

Thomas G Giallorenzi

Anthony Dandridge

Frank Bucholtz

Alan B Tveten

Michael E Gingerich

A three-axis fiber optic vector magnetometer is provided for measuring both he direction and magnitude of a DC or low frequency magnetic field. The magnetometer includes an optical interferometer system including a sensing fiber arm disposed with three respective sensing portions perpendicular to one another and attached to a uni-directional sensor material. The interferometer system also includes a reference fiber arm and a laser light source for generating and introducing a laser light into both of the arms. Respective biasing devices generate a reference AC magnetic bias and a respective reference frequency in the three sensing portions. A detecting device detects a reference light signal from the reference fiber arm and the magnetically altered sensing light signal from the sensing fiber arm and forms an interferometer output signal. Respective separating devices then separate the respective magnetically induced interferometer signals at respective ones of the frequencies and produce a respective output signal indicative thereof. This output signal is thus indicative of the magnetic field strength in the respective direction and a vector sum of the strengths shows the magnetic field direction. Preferably, the sensor material is an annealed amorphous metallic glass strip and the separating means are lock-in amplifiers in their phase sensitive detection modes. The biasing devices are also preferably respective Helmholtz coils and a feedback system is provided for feeding back the output of the respective separating devices to the respective biasing devices.

Three-axis fiber optic vector magnetometer

A device and method for interconnecting multiterminal electronic devices. e device and method combine the use of input light sources, output light detectors and an optical waveguide matrix device for routing the signals from various preselected input terminals to various other output terminals. The optical waveguide matrix device includes a number of intersecting optical waveguides formed on a base. The intersecting waveguides are optically coupled by means of reflecting surfaces formed at the nodes of intersection.

Optical waveguide apparatus and method for manufacturing

A fiber optic magnetometer for detecting DC magnetic fields includes a first optical fiber having a magnetostrictive jacket thereon which defines a sensing arm, and a second fiber defining a reference arm. A first AC magnetic field of frequency .omega..sub.o and a second AC field of frequency .omega..sub.s are imposed on the magnetostrictive jacket so as to cause a time varying optical path length change, having .omega..sub.o, (.omega..sub.o +.omega..sub.s), and (.omega..sub.o -.omega..sub.s) components in the sensing arm fiber. This induces a corresponding time varying phase shift, also having the above components, in light transmitted through the sensing arm fiber which is detected by a phase detector. The phase detector produces a signal proportional to the phase shift, this signal being passed to a lock-in amplifier set to amplify at .omega..sub.o. .omega..sub.s is sufficiently small such that the lock-in amplifier filters all components other than the .omega..sub.o, (.omega..sub.o +.omega..sub.s), and (.omega..sub.o -.omega..sub.s) components. The sum of these components changes in magnitude upon exposure of the magnetostrictive jacket to a DC field, thereby indicating the presence of a DC field. The lock-in amplifier output is plotted on an oscilloscope versus the second AC field of frequency .omega..sub.s to give a loop which shifts in position when the device is exposed to an external DC field.

Fiber optic DC magnetometer without hysteresis ambiguity

A fiber optic magnetometer for detecting DC magnetic fields includes a first optical fiber having a magnetostrictive jacket thereon which defines a sensing arm, and a second fiber defining a reference arm. An AC magnetic field of frequency .omega..sub.o and constant amplitude is imposed on the magnetostrictive jacket so as to cause a time varying optical path length change, having an .omega..sub.o component, in the sensing arm fiber. This induces a corresponding time varying phase shift, also having an .omega..sub.o component, in light transmitted through the sensing arm fiber which is detected by a phase detector. The phase detector produces a signal proportional to the phase shift, this signal being passed to a lock-in amplifier set to amplify at .omega..sub.o. The lock-in amplifier produces an output signal proportional to the amplitude of the .omega..sub.o component, wherein this amplitude is proportional to any DC magnetic fields to which the device is exposed.

Fiber optic magnetometer for detecting DC magnetic fields

A fiber optic magnetic gradiometer for measuring both ac and dc magnetic field gradients. The gradiometer utilizes an optical interferometer with magnetostrictive magnetic field sensing elements in each of the interferometer arms. Ac and dc magnetic field biasing is achieved by disposing each of the magnetic field sensing elements within its own magnetic field coil and utilizing a variable dc current source for applying dc current to each magnetic coil. An ac current source at frequency w.sub.o connected across the circuits for the dc current sources is used in conjunction with a variable attenuator to control the ac bias to the respective magnetic coils. The detected output from the interferometer is processed either by bandpass filters or a spectrum analyzer to obtain the signal component at w.sub.o, which is proportional to the external dc gradient magnetic field, and at w.sub.o +w.sub.s, (where w.sub.s is external ac magnetic field frequency), which is proportional to the external ac magnetic field gradient.

Fiber-optic magnetic gradiometer with variable magnetic biasing fields

A sensing element of magnetostrictive material associated with an optical fiber of an interferometer arm defining apparatus for detecting magnetic fields. The magnetostrictive material is adhered in close co-extensive adjacency with the optical fiber and in the presence of a magnetic field undergoes responsive longitudinal dimension changes which strains the optical fiber and induces a strain related phase shift in an optically propagating beam in the fiber detectable by interferometry.

Growing community of inventors

Great Falls, VA, United States of America

George H Sigel, Jr