Nonuniform fibers single-mode

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. 

Single-mode fibers of arbitrary profile 22-7 Weakly guiding single-mode fibers 22-8 Example Isolated nonuniformity 22-9 Example Sinusoidally perturbed interface... 

We now examine the scattering of power into bound modes when an x-polarized HEj j mode is incident on an isolated nonuniformity within a single-mode, step-profile fiber. Within the weak-guidance approximation, we deduce from Eq. (22-26) and Table 14-3, page 313, that... 

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). 

In Section 22-5 we determined the attenuation of the fundamental mode on a weakly guiding, step-profile fiber due to radiation from a sinusoidal perturbation of the interface, using free-space antenna methods and correction factors. Here we consider the situation when the radiation field is well approximated by a single leaky mode, which can be realized by having an on-axis sinusoidal nonuniformity of the form of Eq. (22-14). The azimuthal symmetry ensures that only HEi leaky modes are excited. Further, the direction of radiation should coincide with the direction of the leaky-mode radiation [23]. If we represent the nonuniformity and the incident fundamental-mode fields by the induced current method, as in Section 22-5, the direction condition is satisfied by setting C = in Eq. (24-43), whence... 

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