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Conference on Lasers and Electro-Optics

Observation of negative pulse delay in a microsphere

Kouki Totsuka, Makoto Tomita

Published Jan 1, 2006• 0 citations
Publisher

Abstract

We observed −4.9 ns negative delay in optical pulse propagation associated with a single Mie scattering process. The observed fast light can well be explained by a directional coupling theory on the under coupling condition.
DOI
10.1109/cleo.2006.4628808

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Journal of the Optical Society of America B•Sep 28, 2006•50 citations
We discuss the mechanism of fast and slow light generation when optical pulses propagate through a fiber taper coupled to an ultrahigh-Q microsphere system in the time domain. Fast and slow light are explained as interference effects between ballistic light through the fiber and circulated light within the sphere. One of the striking effects predicted by this model is dynamic pulse splitting in the transmitted pulse at the critical coupling condition, where the coupling strength between the sphere and fiber equals the round-trip loss in the sphere. By realizing this critical coupling condition experimentally, we observed this dynamic pulse splitting effect.
The dispersion relation in a system of a fiber taper coupled with a microsphere is investigated. On the undercoupling condition, in which the coupling strength between the sphere and the fiber is weak compared with the round-trip loss in the sphere, the system shows anomalous dispersion. On the other hand, on the overcoupling condition, in which the coupling strength is strong compared with the loss, the system shows normal dispersion. We performed pulse propagation experiments and observed both the slow light and the fast light relevant to the normal and anomalous dispersions in the single microsphere-fiber taper system, controlling the coupling strength between the sphere and the fiber. The observed pulse propagation times show good agreement with theoretical calculations based on a directional coupling theory.