**7. Conclusions**

In this chapter the digital holographic phase shifting interferometric method is used to investigate and characterize GRIN optical waveguide samples. Phase shifting digital holography has the advantages of no dc term and no twin image in the reconstructed field as well as high accuracy due to the redundant data in the multiple holograms. The optical interference phase differences due to the variation of refractive indices of GRIN optical waveguides are extracted. A simple algorithm is used to recover the tilting of the extracted optical interference phase differences along the GRIN optical wavegide, to avoid the errors of the calculated mean values of optical phase differences due to the GRIN optical waveguides. The broadening of optical waveguide radius or width is also reduced.

The advances of accurate reconstructed interference phase differences in combination of multilayer model are used to calculate the refractive index profiles of GRIN optical waveguide. Also, a simple algorithm based on the assumptions of the multilayer model is used to reconstruct the 3D refractive index profile of GRIN optical fibre.

The refractive index profiles of symmetric and asymmetric GRIN optical waveguides and their associated modes are calculated. The propagation coefficient *β* and hence the effective indices *neff* associated with every mode are determined.
