Application of fringes of equal chromatic order for investigating the effect of temperature on optical parameters of a GRIN optical fibre

Multiple-beam white light interference fringes across a GRIN optical fibre immersed in a liquid wedge interferometer placed in front of a grating spectrograph are produced. They are used to investigate the effect of temperature on the optical fibre parameters of both the cladding (pure SiO₂) and the core (GeO₂-doped SiO₂). A two-term Sellmeier dispersion relation is adopted and fitted to the experimental refractive index data. Then a temperature-dependent Sellmeier formula is deduced to study the effect of temperature on the refractive index of the fibre and its dispersion in addition to all of its optical parameters. These parameters are the average energy gap, the variation of the thermo-optic coefficient with photon energy, the refractive index difference, the numerical aperture, the normalized frequency (V-number), the number of modes, the material dispersion and the zero-dispersion wavelength.