Local modes bent fibers

Criterion for slow variation Local modes of bent fibers Multimode fibers and rays References... 

Fig. 19-4 (a) Two tapered fibers with equal core radii p at z = z, while at zi and Z2 the core radii are reversed, (b) Qualitative behavior of the local-mode propagation constants along fibers 1 and 2 of (a) in isolation, (c) Coupler consisting of bent fibers of constant core radius, (d) Schematic representation of an arbitrary tapered coupler consisting of fibers 1 and 2 of increasing and decreasing core radii, respectively. 

We are primarily interested in radiation from the fundamental modes of bent, single-mode fibers. Within the weak-guidance approximation, the power radiated is insensitive to polarization, since p. Thus we can conveniently assume that the transverse electric field is parallel to the Z-axis in Fig. 23-2(a), i.e. orthogonal to the plane of the bend. Close to and within the core, the magnitude of the electric field on the bend is given by aj Fo (R) exp (ifiz), using the local-mode approxinution, where is the modal amplitude, Fq (R) is the... 

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