AAWSAP DIRD, Metamaterials for Aerospace Applications, April 2010

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Figure 24. Example of a Generic Chiral Metamaterial: An Optical Fiber with a Rectangular Cross Section Core
Twisted During the Drawing Process Forms a Double Helix. If the core index is nonlinear, then one can engineer a
variable helix pitch in such a way that the core (localized) modes can be selectively coupled to cladding modes
depending on the direction of propagation.
Under a highly simplified assumption of just two interacting mode (core and cladding),
we have developed a coupled-mode theory describing the evolution of the mode
amplitudes a,0 and ac1 along the fiber axis z. The set of the generic equations for a,0 and
act is given by:
0
a;; - i(/Jo +rI aw 12 -8 I 2)a,·o = iWad,
(8)
aac1 - i(/30 + <5 I 2)ac1 = iW* ac0
ar
where/30 =c(f3co + f3c1)1 2wis the average normalized propagation constant,
o(r) = c(/3co - f3c1 + 2/3,,)I ()) is the distance-dependent mode detuning, r is the
nonlinearity coefficient, Wis the coupling strength between the modes, and r =wz/ c is
the normalized propagation distance.
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