Patent ID: 6898337

Claim:
A fiber-optic method for making simultaneous multiple parameter measurements, the method comprising the steps of: a) providing an optical fiber sensor comprising at least one optical fiber having at least one long period grating disposed therein and having at least one reactive coating disposed thereon proximate to the at least one long period grating; b) creating an excitation in the optical fiber sensor wherein a plurality of evanescent field sensing depths result, creating at least two long period grating signatures, wherein each long period grating signature is defined by the equation: λ=( ng−ncl )Λ wherein: λ=coupling wavelength for a specific loss band Λ=grating period ng=effective index of the guided mode of the optical fiber ncl=effective index of a cladding mode of the optical fiber; c) exposing the optical fiber sensor to at least one material; and d) identifying changes in the reactive coating as it reacts with the material by measuring and comparing shifts in each long period grating signature; correlating the shifts to the changes in the material; and solving a series of equations that compare changes in the coupling wavelength for a specific loss band wherein the series of equations consist of at least two equations expressed as: [ A]Δ P1 +[B]Δ P2 =Δλ 1 [ C]Δ P1 +[D]Δ P2 =Δλ 2 wherein: [A] is a coefficient for a first parameter that reflects the change in wavelength [δλ] 1 per a change in the first parameter [δP 1 ] 1 at a first sensing depth and is expressed as: [ δ ⁢ ⁢ λ ] 1 [ δ ⁢ ⁢ P 1 ] 1 ; [B] is a coefficient for a second parameter that reflects the change in wavelength [δλ] 1 per a change in the second parameter [δP 2 ] 1 at a first sensing depth and is expressed as: [ δ ⁢ ⁢ λ ] 1 [ δ ⁢ ⁢ P 2 ] 1 ; [C] a coefficient for a third parameter that reflects the change in wavelength [δλ] 2 per a change in the first parameter [δP 1 ] 2 at a second sensing depth and is expressed as: [ δ ⁢ ⁢ λ ] 2 [ δ ⁢ ⁢ P 1 ] 2 ; [D] is a coefficient for a fourth parameter that reflects the change in wavelength [δλ] 2 per a change in the second parameter [δP 2 ] 2 at a second sensing depth and is expressed as: [ δ ⁢ ⁢ λ ] 2 [ δ ⁢ ⁢ P 2 ] 2 ; Δ P1 is a first spacially resolvable density change; Δ P2 is a second spacially resolvable density change; Δλ 1 is a change in a first coupling wavelength for a specific loss band when the optical fiber sensor is exposed to at least one material; and Δλ 2 is a change in a second coupling wavelength for a specific loss band when the optical fiber sensor is exposed to at least one material.