Method and apparatus for sensing strain

Claim 1

A strain sensor comprising: (a) at least two optical waveguides separated by an air gap in a colinear relationship; (b) a splice for fixing said waveguides in said relationship with said gap; (c) means for generating optical pulses into the optical waveguides; and (d) a structure in which localized strains are to be sensed; (e) said optical waveguides and said splice being imbedded in said structure; (f) means for sensing localized strain in said structure by determining shifts in arrival times of the optical pulses reflected at said splice by the sensing means that correspond to the localized strain.

Claim 8

A method of sensing strain in a structure comprising: (a) arranging portions of at least two optical waveguides in substantially colinear relationship with ends of said optical waveguides in spaced relationship; (b) fixing said portions within a splice to maintain said optical waveguides in said relationship; (c) imbedding said splice and said optical waveguides in said structure with a portion of at least one waveguide exposed; (d) imparting optical pulses to the exposed portion of said optical waveguide; (e) a portion of said pulse being reflected at said splice (f) sensing the reflected portion of said pulse at said exposed portions; and (g) measuring time intervals between said pulse and said reflected pulse.

Claim 9

A method of sensing strain in a structure comprising: (a) arranging portions of at least two optical waveguides in substantially colinear relationship with ends of said optical waveguides in spaced relationship; (b) fixing said portions within a splice to maintain said optical waveguides in said relationship; (c) imbedding said splice and said optical waveguides in said structure with a portion of at least one waveguide exposed; (d) imparting optical pulses to the exposed portion of said optical waveguide; (e) a portion of said pulse being reflected at said splice (f) sensing the reflected portion of said pulse at said exposed portions; and (g) measuring time intervals between said pulse and said reflected pulse.

Claim 19

A method for sensing strain in a structure comprising: (a) arranging a number of optical fibers in substantially colinear relationship with the ends of said fibers in spaced relationship from adjacent fibers wherein said space is less than about 50 microns; (b) fixing said ends within a splice to maintain said fibers in said spaced relationship and surrounding said ends within said splice with material to maintain substantially total internal reflection; (c) imbedding said optical fibers in a structure with at least one of the ends of said fibers not fixed in a splice exposed; (d) imparting optical pulses to said exposed portion of said fiber from a laser source; (e) reflecting a portion of said pulse at each of said splices; (f) splitting at least a portion of reflected pulses and said optical pulse from said laser; (g) sensing said optical pulses and said reflected pulses from said splitting step; and (h) measuring the time intervals between said imparting step and said reflecting step as sensed from said splitting step.

Claim 20

A method for sensing strain in a structure comprising: (a) arranging a number of optical fibers in substantially colinear relationship with the ends of said fibers in spaced relationship from adjacent fibers wherein said space is less than about 50 microns; (b) fixing said ends within a splice to maintain said fibers in said spaced relationship and surrounding said ends within said splice with material to maintain substantially total internal reflection; (c) imbedding said optical fibers in a structure with at least one of the ends of said fibers not fixed in a splice exposed; (d) imparting optical pulses to said exposed portion of said fiber from a laser source; (e) reflecting a portion of said pulse at each of said splices; (f) splitting at least a portion of reflected pulses and said optical pulse from said laser; (g) sensing said optical pulses and said reflected pulses from said splitting step; and (h) measuring the time intervals between said imparting step and said reflecting step as sensed from said splitting step.

Claim 21

An apparatus for measuring strain in a structure comprising: (a) a number of optical fibers, with each fiber having ends, said ends of said fibers being held together in spaced relationship by a splice wherein space between said ends is less than about 50 microns and at least one end of said fibers being exposed; (b) said splice including an outer tube, an alignment sleeve within said outer tube for aligning said ends in said colinear and spaced relationship and an epoxy for securing said sleeve and said fibers within said tube, said epoxy and said alignment sleeve being of a material to maintain substantially total internal reflection; (c) said fibers forming a string of predetermined length, said string being imbedded in said structure with said one exposed end exposed for launching optical pulses into said string; (d) laser means arranged adjacent to said exposed end for launching optical pulses into said string; (e) means for sensing pulses from said laser means end reflected pulses from said exposed end of said string; (f) a beam splitter located between said laser means for directing at least a portion of said reflected pulse and said optical pulse to said sensing means; and (g) measuring means connected to said sensing means for measuring the time intervals between said optical pulse and said reflected pulse.

Claim 22

An apparatus for measuring strain in a structure comprising: (a) a number of optical fibers, with each fiber having ends, said ends of said fibers being held together in spaced relationship by a splice wherein space between said ends is less than about 50 microns and at least one end of said fibers being exposed; (b) said splice including an outer tube, an alignment sleeve within said outer tube for aligning said ends in said colinear and spaced relationship and an epoxy for securing said sleeve and said fibers within said tube, said epoxy and said alignment sleeve being of a material to maintain substantially total internal reflection; (c) said fibers forming a string of predetermined length, said string being imbedded in said structure with said one exposed end exposed for launching optical pulses into said string; (d) laser means arranged adjacent to said exposed end for launching optical pulses into said string; (e) means for sensing pulses from said laser means end reflected pulses from said exposed end of said string; (f) a beam splitter located between said laser means for directing at least a portion of said reflected pulse and said optical pulse to said sensing means; and (g) measuring means connected to said sensing means for measuring the time intervals between said optical pulse and said reflected pulse.

Claim 24

The apparatus according to claims 17, 18 or 19 wherein each optical fiber includes a coating, a portion of said coating being removed at said ends in said splice; said alignment sleeve in said splice being configured to align said exposed portions of adjacent fibers in colinear relationship.