Distributed, spatially resolving optical fiber strain gauge

Claim 1

A strain sensor for measuring strain in a region within a rigid body comprising: an optical fiber, having a single core, disposed in a predetermined path passing through said region of said rigid body, said single core having at least one periodic optical grating, having a predetermined grating length along said fiber and a predetermined grating spacing in the visible region of the optical spectrum, formed within and throughout said core, whereby said fiber has at least one grating region containing said optical grating and said region comprises at least one discrete measurement region having a measurement region length substantially equal to said grating length; means for passing broadband optical radiation in a predetermined wavelength range of the spectrum into said single core; and means for processing optical radiation emerging from said at least one core to form a measurement representative of strain within said region, including means for analyzing the spectrum of radiation reflected from said at least one grating and emerging from said single core to identify a characteristic wavelength corresponding to said predetermined grating spacing and means for comparing said characteristic wavelength with a stored corresponding reference wavelength to derive therefrom a measurement of the strain within said at least one discrete region, characterized in that: said at least one grating region has two gratings having first and second grating spacings formed therein, whereby the spectrum of radiation emerging from said core contains two characteristic wavelengths corresponding to each of said first and second grating spacings; and said means for processing optical radiation compares said two characteristic wavelengths with two corresponding reference wavelengths to derive therefrom a temperature-corrected measurement of the strain within said at least one discrete measurement region.