A theoretical and experimental investigation of power transmission in a large diameter optical fiber

The effect of varying the angle of incidence of a Gaussian beam from a He-Ne laser incident upon a large radius optical fiber is theoretically and experimentally investigated. The modes in a weakly-guiding, step index fiber were determined by using an analytical approximation technique to calculate the corresponding eigenvalues. An expression was developed for the fractional power per mode as a function of the angle of incidence for such a fiber. This expression was used to calculate the fractional power per mode for the lowest order 171 modes. This allowed the calculation of the fractional power per order and total power. By comparing these theoretical results to our experiment results, it is shown that the theoretical method is accurate at normal incidence and gives qualitative but not quantitative agreement at larger angles.