Multiplexing of Fiber-Optic Long-Period Grating-Based Interferometric Sensors

Abstract

Two long-period gratings (LPGs) fabricated in series in an optical fiber form a \nMach-Zehnder interferometer, producing a sinusoidal channelled spectrum within \nthe characteristic LPG attenuation bands, which has the appearance of an \ninterference fringe pattern. The phase of the fringes is sensitive to changes in \nthe surrounding environmental parameters, such as refractive index. Fabrication \nof a number of identical cascaded LPG pairs with different separations produces \nindependent fringe patterns of different frequencies within the attenuation \nbands. The application of basic Fourier techniques to analyze the transmission \nspectrum allows the phase of each fringe pattern to be determined independently, \nfacilitating the differentiation of external effects acting on each \ninterferometer