Tunneling leaky modes in fiber-optic waveguides

It is shown that the absolute value of the refractive index may be measured at various points in the cross section of a fiber-optic waveguide with a fairly high degree of accuracy. The results are reported of measurements made by using a prism coupling-in element and monitoring tunneling leaky modes at the output end of the waveguide. Comparative results are presented for various samples of fiber-optic waveguides.