Optical fiber sensor with localized sensing regions

A fiber optic sensing cable for guiding electromagnetic waves and for sensing physical parameters comprising:

• a first single-mode core having a first refractive index;
• a second single-mode core proximately disposed with respect to said first core and having a second refractive index, said first and said second cores having unequal propagation constants;
• cladding surrounding each of said cores and having a third refractive index, said third refractive index being lower than either of said first or said second refractive indices;
• and
• coating means disposed on the outer surface of said cladding for communicating to said cores a pattern of elastic deformation having a periodic variation that is at a spatial periodicity which resonantly matches the difference in core propagation constants, thereby inducing a resonant exchange of optical power between said cores in proportion to the strength of the elastic deformation at the surface of said cladding.

A multiple cored optic fiber article having at least two single-mode cores in sufficiently close proximity to one another so that they would normally experience evanescent wave coupling had they identical propagation constants, said two cores having different refractive indices with respect to each other such that the two cores have unequal propagation constants, and said cores having mismatched optical phase fields wherein evanescent wave coupling is substantially suppressed, and whereby optical power launched into one of said two cores remains propagating within that core alone over an extended length of said optic fiber article, and

• sensitizing means disposed along at least one portion of a length of said optic fiber article for sensitizing said optic fiber article to a predetermined parameter or environmental field and causing said optic fiber article to undergo a physical or mechanical alteration in response to said predetermined parameter or environmental field,
• said sensitizing means comprising a given length of coating disposed about said fiber optic article, said coating having a pattern, the spatial frequency of which resonantly matches the difference in core propagation constants, whereby a resonant exchange of optical power is induced between said first and second cores in response to said predetermined parameter or environmental field, said coating having materials chosen from a group consisting of:
• magnetostrictive material, piezoelectric material, electrostrictive material, heat conductive material, and pressure sensitive material.

A system for guiding electromagnetic waves and sensing physical parameters comprising:

• a first single-mode core having an input end and a first refractive index, said first core being proximately disposed with respect to a second single-mode core having an output end and having a second refractive index, said first and second refractive indices being unequal, said first and second cores having unequal propagation constants;
• a light source operatively disposed with respect to said input end of said first core for producing optical energy;
• a cladding surrounding each of said cores and having a third refractive index lower than the lesser of said first or said second refractive indices;
• coating means disposed on the outer surface of said cladding for communicating to said cores a pattern of elastic deformation having a periodic variation that is at a spatial periodicity which resonantly matches the difference in core propagation constants to induce a resonant exchange of optical power between said cores in proportion to the strength of the elastic deformation at the surface of said cladding;
• and
• detecting means operatively disposed with respect to said output end of said second core for detecting optical power.