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Physical Review E

Dynamics of fast and slow pulse propagation through a microsphere–optical-fiber system

Kouki Totsuka, Makoto Tomita

Published Jan 19, 2007• 24 citations
Publisher

Abstract

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.

DOI
10.1103/physreve.75.016610

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Conference on Lasers and Electro-Optics•May 4, 2008•0 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.
We performed optical pulse propagation experiments in a system in which two ultrahigh-Q silica microspheres of different diameters were coupled in tandem to a fiber taper to yield coupled-resonator-induced transparency. Nearly Gaussian-shaped optical pulses propagated with a large positive delay of 8.5 ns through a transparent frequency window, without significant attenuation, amplification, or pulse deformation, demonstrating classical analogy of the extremely slow light obtained with electromagnetically induced transparency.