Abstract
Light traversing a hollow-core photonic band-gap fiber may experience multiple reflections and thereby a slow-down and enhanced optical path length. This offers a technologically interesting way of increasing the optical absorption of an otherwise weakly absorbing material which can infiltrate the fibre. However, in contrast to structures with a refractive index that varies along the propagation direction, like Bragg stacks, the translationally invariant structures studied here feature an intrinsic trade-off between light slow-down and filling fraction that limits the net absorption enhancement. We quantify the degree of absorption enhancement that can be achieved and its dependence on key material parameters. By treating the absorption and index on equal footing, we demonstrate the existence of an absorption-induced saturation of the group index that itself limits the maximum absorption enhancement that can be achieved.
Highlights
Media supporting slow-light propagation of electromagnetic waves are presently receiving tremendous attention in the context of enhanced light-matter interactions
In contrast to structures with a refractive index that varies along the propagation direction, like Bragg stacks, the translationally invariant structures studied here feature an intrinsic trade-off between light slow-down and filling fraction that limits the net absorption enhancement
We quantify the degree of absorption enhancement that can be achieved and its dependence on key material parameters
Summary
Media supporting slow-light propagation of electromagnetic waves are presently receiving tremendous attention in the context of enhanced light-matter interactions. A one-dimensional Bragg stack [8] is one example of a structure that can enhance the net absorption experienced by a beam traversing the structure In this case, the picture of a beam propagation path that is effectively prolonged by multiple back-and-forth scattering in the propagation direction offers a simple physical interpretation. The physical picture offered above for one-dimensional structures has to be modified to take into account that part of the effective propagation path may lie outside the region containing the material with which the interaction is to be increased Taking into account this issue of reduced modal overlap it is not immediately clear whether translationally invariant stuctures, which realize slow light effects by a strongly guiding index structure that feature multiple scattering effects in the transverse direction, would offer net absorption enhancement.
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