Fiber optic strain sensor and read-out system

An optical sensor with read-out system comprising:

• an optical sensor comprising first and second optical paths differing in length by a predetermined distance, said optical sensor providing an optical signal output at a first wavelength responsive to an environment sensed by said optical sensor;
• an optical source for generating an optical source output at a second wavelength differing from said first wavelength;
• third and fourth optical paths differing in length by a distance substantially equal to said predetermined distance, said optical signal output and said optical source output coupled to said third and fourth optical paths such that a first portion of said optical signal output and a first portion of said optical source output comprise a first optical beam traversing said third optical path and such that a second portion of said optical signal output and a second portion of said optical source output comprise a second optical beam traversing said fourth optical path;
• a modulator for modulating the phase of at least one of said first and second optical beams;
• and
• a controller for sensing a first change in phase relationship between said first and second optical beams at said first wavelength, for sensing a second change in phase relationship between said first and second optical beams at said second wavelength, and for providing a signal to said modulator based on a difference between said first and second changes in phase relationship, said controller returning said phase relationship between said first and second optical beams to a predetermined phase relationship independent of temperature and vibration effects in said read-out system.

A method for linearizing an optical signal output at a first wavelength responsive to an environment sensed by an optical sensor comprising first and second optical paths differing in length by a predetermined distance, said method comprising the steps of:

• coupling said optical signal output of said optical sensor at said first wavelength and an optical source output from an optical source operating at a second wavelength different from said first wavelength to third and fourth optical paths such that a first portion of said optical signal output and a first portion of said optical source output comprise a first optical beam traversing said third optical path and such that a second portion of said optical signal output and a second portion of said optical source output comprise a second optical beam traversing said fourth optical path, said third and fourth optical paths differing in length by a distance substantially equal to said predetermined distance;
• sensing a first change in phase relationship between said first and second optical beams at said first wavelength and a second change in phase relationship between said first and second optical beams at said second wavelength;
• and
• modulating the phase of at least one of said first and second optical beams based on a difference between said first and second changes in phase relationship to return said phase relationship between said first and second optical beams to a predetermined phase relationship independent of temperature and vibration effects in said read-out system.

An optical sensor read-out system for use in connection with an optical sensor comprising first and second optical paths differing in length by a predetermined distance for providing an optical signal output at a first wavelength responsive to an environment sensed by said optical sensor, said optical sensor read-out system comprising:

• an optical source for generating an optical source output at a second wavelength differing from said first wavelength;
• third and fourth optical paths differing in length by a distance substantially equal to said predetermined distance, said optical signal output and said optical source output coupled to said third and fourth optical paths such that a first portion of said optical signal output and a first portion of said optical source output comprise a first optical beam traversing said third optical path and such that a second portion of said optical signal output and a second portion of said optical source output comprise a second optical beam traversing said fourth optical path;
• a modulator for modulating the phase of at least one of said first and second optical beams;
• and
• a controller for sensing a first change in phase relationship between said first and second optical beams at said first wavelength, for sensing a second change in phase relationship between said first and second optical beams at said second wavelength, and for providing a signal to said modulator based on a difference between said first and second changes in phase relationship, said controller returning said phase relationship between said first and second optical beams to a predetermined phase relationship independent of temperature and vibration effects in said read-out system.