One way to improve the reliability of a network is through physical diversity, i.e., via

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Within the framework of perturbation theory, we explore in detail the mixing of orbital angular (OAM) modes due to a fiber bend in a step-index multimode fiber. Using scalar wave equation, we develop a complete set of analytic expressions for mode-mixing, including those for the 2π walk-off length, which is the distance traveled within the bent fiber before an OAM mode transforms into its negative topological charge counterpart, and back into itself. The derived results provide insight into the nature of the bend effects, clearly revealing the mathematical dependence on the bend radius and the topological charge. We numerically simulate the theoretical results with applications to a few-mode fiber and a multimode fiber, and calculate bend-induced modal crosstalk with implications for mode-multiplexed systems. The presented perturbation technique is general enough to be applicable to other perturbations like ellipticity and easily extendable to other fibers with step-index-like profile as in the ring fiber. OCIS codes: 060.2330, 050.4865 O l,m (r, θ ) = 1 N l,m J l (p l,m r)e ilθ f or r ≤ a = 1 N l,m J l (p l,m a) K l (q l,m a) K l (q l,m r)e ilθ f or r ≥ a.N l,m is the normalization constant which can be determined analytically from the properties of the Bessel functions [18]; p l,m = k 2 n 2 1 − β 2 l,m and q l,m = β 2 l,m − k 2 n 2 2 . O l,m (r, θ ) characterized by an exponential azimuthal dependence, is referred to as the amplitude (or the field profile) of an OAM mode corresponding to a topological charge l and a radial mode number m; hereafter we denote such a mode by OAM l,m . The wave solution is continuous at the boundary r = a; the further requirement of the continuity of the first (radial) derivative at r = a then gives the characteristic equation from which the wave propagation constants β l,m are computed [14]. The amplitude O −l,m (r, θ ) of the degenerate −l solution (β −l,m = β l,m ), is also given by Eq. 3, except that e ilθ is replaced with e −ilθ .Within WGA, as discussed above, the vector modes reduce to scalar modes, which are the products of the spatial mode, the OAM l,m defined above and the polarization, ε ± . The impact of a bend is then the product of the impact on the spatial mode and the impact on the polarization (birefringence), evaluated separately. The latter has

Recent, precise analyses of p-p and n~p scattering data up to 800 MeV by Arndt et at. have provided the strongest evidence to date for the existence of dibaryon states in the 7 = 1, D 2 and 3 F 2 nucleon-nucleon channels. Model fits to their new phases reveal poles located near the "NA" threshold (2.15 -0.05i GeV). Because of their strong coupling to this channel, these dibaryon resonances are highly inelastic.