Fibre-optic long period gratings for sensing applications

Long period gratings (LPGs) are formed by inducing a permanent periodic modulation of the refractive index (RI) of the core of an optical fibre. The transmission spectrum of the LPG contains a series of attenuation bands centered at discrete wavelengths. The exact form of the transmission spectrum and the central wavelengths of the attenuation bands, are sensitive to the period and the length of the LPG and to the local environment. The sensitivity of a LPG to a particular measurand is dependant upon the composition of the fibre and upon the order of the cladding mode to which the guided mode is coupled to and is thus different for each attenuation band. Cont/d.