Abstract: Results obtained from m-line spectroscopy experiments were used to calculate optogeometric parameters (the refractive indices and thickness) of Al2O3 thin film by solving the conventional prism waveguide coupler mode dispersion equations. These equations were solved using graphical and numerical methods. The numerical method is based on the Newton-Raphson algorithm. The solution to one mode of propagation was obtained by solving the zero order transverse electric (TE0) mode and transverse magnetic (TM0) mode. The values of 1.61±0.02 and 253.00±0.05 nm were obtained for the refractive index and thickness respectively from the graphical solution while the Newton-Raphson algorithm gave 1.6200±0.0007 for the refractive index and 240.1100±0.0005 nm for the film thickness. For two modes of propagation, two TE and two TM modes were considered. The graphical solution for the two TE modes gives a refractive index of 1.5995±0.0002 and a thickness of 772.526±0.001 nm with the Newton-Raphson algorithm giving 1.5995±0.0003 for the refractive index and 767.850±0.005 nm as film thickness. The two modes of propagation for the TM modes gives the graphical results for the refractive index and thickness as 1.6010±0.0002 and 774.671±0.004 nm respectively while the result of the Newton-Raphson algorithm is 1.6010±0.0002 and 773.336±0.003 nm respectively. In comparison with the experimental values obtained, the percentage uncertainty is less than ±5% for both parameters. The results generally, showed a higher uncertainty in determining the film thickness than the refractive index for both TE and TM polarization.