Ray Optical Analysis Of Backscattering By An Obliquely Illuminated Doubly Clad Fiber

We examine the far-field intensity distribution arising from the backscattering of a plane wave by a step-index fiber. Our calculations are based on the assumption that light scattered in a specified direction is the superposition of rays reflected in that direction. This geometrical optical description of scattering is extended to the case of oblique illumination and multiply clad fibers. Comparison of the computed and measured intensity shows that the ray optical treatment of scattering yields reasonable results even for a diameter to wavelength ratio as low as 20, as it is the case of an image transmitting fiber illuminated by He-Ne laser light.