Optical fibre reflective diffraction grating devices

Claim 1

An optical system for sensing variable deformation of an optical fibre, said system comprising means for producing coherent light signals for propagation along the optical fibre, reflective means located at distributed points along the optical fibre for partially reflecting said propagating coherent light signals back along the optical fibre so that the partially reflected light combines with the light propagating along the fibre to produce interference signals and demodulation means for receiving said interference signals to provide an output indicative of deformation forces acting on the optical fibre at the distributed points therealong, in which the distributed reflective means are formed along an optical fibre wound around a grooved mounting block having curved grooves formed thereon which receive spaced apart relatively short lengths of the optical fibre which are secured in the curved grooves, the grooved surface of the mounting block being pared away so that parts of the outer convex surfaces of the short lengths of the optical fibre are removed thereby to provide flat surfaces at least closely adjacent the core of the optical fibre, in which a diffraction grating is formed on each of said flat surfaces of the optical fibre to provide reflective means along the fibre and in which the mounting block is divisible into a plurality of parts each of which includes a portion of the optical fibre having a diffraction grating associated with it to define one of the said distributed reflective means along the optical fibre.