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Reconstruction of 3D refractive index distribution across the graded index optical fibre using digital holographic interferometry

Digital holographic interferometric phase shifting method is used to calculate the refractive index profile of graded index (GRIN) optical fibre and the 3D refractive index distribution across the GRIN fibre. GRIN optical fibre sample is immersed in a suitable liquid and then Mach-Zehnder-like arrangement phase shifting digital holographic system is used. The optical phase difference due to the graded index optical fibre can be extracted by digital holographic interferometric phase shifting technique. The problem of the tilted GRIN optical fibre with respect to the reference axis is solved, since the fibre must be perpendicular to the reference axis according to symmetry considerations. The optical phase difference map along the GRIN optical fibre is used to calculate the mean values of the optical phase difference across the fibre. The refractive index profile of GRIN optical fibre is calculated using the multilayer mathematical model, where the refraction of the incident rays through the fibre layers is considered. The shape parameter of the investigated optical fibre is determined. The mode field distributions can be analyzed for the used GRIN optical fibre. The calculated refractive index profile is used to reconstruct the 3D refractive index distribution across the fibre sample.