3 October 1997 Geometric beam phenomena in large-diameter illumination fiber and light guide
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The recent development of large core diameter (5 to 25 mm) flexible illumination fiber raises some interesting questions about the properties and theory of geometric illumination beams. Examples are shown of the peculiar beam properties of light from large diameter, large numerical aperture fibers focused by a lens. It is demonstrated that the axial position for the tightest beam focus does not occur at the location predicted by the conventional geometric imaging equation. This focus shift is very similar to that found with coherent laser beams and described by the Gaussian Beam Propagation Equations. In fact in the geometric illumination beam case it is found that nearly identical beam focus equations apply. Furthermore the illumination beam equations can be derived entirely from geometric optics, independent from wave optics, and are simply the refraction equations for a paraxial skew ray. These theoretical considerations are shown to have a significant impact on the design of fiber coupling and other beam handling optics for use with the new large core fiber. Examples, such as 90 degree bend optics and other optical `plumbing' are given.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
John F. Forkner, John F. Forkner, } "Geometric beam phenomena in large-diameter illumination fiber and light guide", Proc. SPIE 3139, Nonimaging Optics: Maximum Efficiency Light Transfer IV, (3 October 1997); doi: 10.1117/12.279222; https://doi.org/10.1117/12.279222


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