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