Nonuniform fibers multimode

The above analysis is readily generalized to describe the redistribution of power due to slight nonuniformities within multimode fibers by including all... 

Fiber optics are commonly used for delivering Ar-ion beams conveniently and safely. Single-mode polarization-preserving fibers can be used for dehvering up to 1 W of input power, whereas multimode fibers can accept up to 10 W. Although use of multimode fibers produces nonuniform intensity in the light sheet, they have been used in some PIV apphcations. 

At each position z along a nonuniform, multimode fiber, a high-order local mode is equivalent to a single family of rays, as is clear from Section 36-2. Each ray follows a path which changes slowly over the local half-period Zp(z) of Eq. (5-12). This is the ray analogue of the multimode-fiber discussion in Section 19-2. Furthermore, the equivalence of mode and ray transit times, which is demonstrated in Section 36-9, is readily extended to slowly varying fibers, for which the transit time is given by Eq. (5-11). 

When light propagates along a fiber and impinges on nonuniformities due to imperfections in the fiber, some of its power is scattered, as shown schematically in Fig. 22-1 (a). Part of the scattered power is distributed into forward-and backward-propagating modes, while the remainder is radiated. For multimode fibers, the distribution of scattered power is best treated by the ray methods of Chapter 5. Here we are primarily interested in fibers that propagate only one or a few modes. We treat the nonuniformities of the perturbed fiber as induced current sources within the unperturbed fiber. The results of the previous chapter can then be used to describe excitation of bound modes and the radiation field [1-3]. 

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