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US 5,633,748 AGranted
Fiber optic Bragg grating demodulator and sensor incorporating same
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorsIgnacio M. Perez, Thomas F. A. Bibby, Jr.
Life of this patent
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Abstract
A tapped Bragg grating is used to demodulate optical signals reflected by ber optic Bragg gratings in a sensor in which the line spacings in the fiber optic Bragg gratings vary in response to a mechanical stress. A light detector, or light detector array is used to detect variation in the angular pattern of the light scattered by the tapped Bragg grating. Arrangements of mirrors, or alternatively arrangements of lenses, are used to concentrate the scattered light toward the light detectors and to enhance the angular changes in the scattered light.
Claims19
A demodulator for use in conjunction with a fiberoptic Bragg grating comprising:
- an optical fiber capable of receiving and conducting light reflected by a fiberoptic Bragg grating;
- means, comprising a tapped Bragg grating formed in the core of said optical fiber, for scattering light conducted by the optical fiber at angles varying in dependence on the wavelength of the reflected light;
- and
- means for detecting shifts in the pattern of the light scattered by the tapped Bragg grating.
1 more element
A sensor comprising:
- a first Bragg grating with grating lines arranged to reflect selected wavelengths of light incident on the first grating;
- means responsive to a measurand for inducing variations in the spacing of the lines of first grating;
- means for directing light to the first Bragg grating;
- means comprising a second Bragg grating with grating lines, the second grating being arranged to scatter light reflected by the first Bragg grating;
- and
- light-detecting means, adjacent to the second grating, for detecting shifts in the pattern of the light scattered by the second grating, and thereby detecting variations in the spacing of the lines of the first grating induced by the means responsive to the measurand.
3 more elements
A sensor comprising:
- a source of light consisting of a band of wavelengths;
- an optical fiber arranged to conduct light from said source, the optical fiber having a core with at least two sensing Bragg gratings formed therein, each grating having grating lines spaced so that it reflects a selected subband of wavelengths within a band of wavelengths of the light incident thereon, the line spacing for each of said gratings being different from the line spacing for each of the other ones of said gratings, so that the subband of wavelengths reflected by each grating is different as a whole from the subband of wavelengths reflected by each of the other gratings;
- means responsive to a measurand for inducing variations in the spacing of the lines of each of said gratings;
- means comprising at least one tapped Bragg grating with grating lines, each tapped Bragg grating being arranged to scatter light reflected by at least one of the sensing Bragg gratings;
- and
- light-detecting means, adjacent to each tapped Bragg grating, for detecting shifts in the pattern of the light scattered by each tapped Bragg grating, and thereby detecting variations in the spacing of the lines of the sensing Bragg gratings induced by the means responsive to the measurand.
3 more elements
A sensor comprising:
- a first length of optical fiber having a first light-conducting path extending along an axis, the first light-conducting path having a region with a periodic spatial variation in its refractive index along the direction of the axis, forming a first Bragg grating with grating lines disposed substantially transverse to said axis whereby the first grating is adapted to reflect selected wavelengths of light along the first light-conducting path;
- means, comprising a source of light, for directing light along said light-conducting path;
- a second length of optical fiber having a second light-conducting path extending along a second axis, the second length of optical fiber being arranged to receive light reflected by the first Bragg grating in the first length of optical fiber, the second length of optical fiber having a region with a periodic spatial variation in its refractive index along the direction of the second axis, forming a second Bragg grating having grating lines disposed oblique to the second axis, whereby said reflected light in the second light conducting path reaching the second grating is scattered transverse to said second axis at the location of the second grating;
- means responsive to a measurand for inducing variations in the spacing of the lines of first grating;
- and
- light-detecting means disposed adjacent to the second grating, for detecting shifts in the pattern of the light scattered by the second grating, and thereby detecting variations in the spacing of the lines of the first grating induced by the means responsive to the measurand.
3 more elements
Dependencies are inferred from the claim text.