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arXiv:0803.1216 · Physical Review A

Observation of simultaneous fast and slow light

Pablo Bianucci, Chris R. Fietz, John W. Robertson, Gennady B. Shvets, Chih-Kang Ken Shih

Published May 19, 2008• 19 citations
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Abstract

We present a microresonator-based system capable of simultaneously producing time-advanced and time-delayed pulses. The effect is based on the combination of a sharp spectral feature with two orthogonally-polarized propagating waveguide modes. We include an experimental proof-of-concept implementation using a silica microsphere coupled to a tapered optical fiber and use a time-domain picture to interpret the observed delays. We also discuss potential applications for future all-optical networks.

DOI
10.1103/physreva.77.053816

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Two Speeds at Once

In the seemingly never-ending quest to speed up data transfer, light constitutes the ultimate communications carrier. However, the speed of light through a medium is generally constant, making photon storage and on-chip optical signal processing difficult tasks to implement. To slow things down, coupling microring resonators to an optical waveguide can effectively delay the propagation of photons. It has also been shown that the dispersion properties of these devices can distort the pulse profile so that the speed of light appears to be exceeded, providing so-called fast-light. From a practical viewpoint, it would be desirable to combine both of these properties in a single optical device. Recent work has found that these microring resonators are birefringent with respect to the polarization of the propagating light; i.e., one polarization simultaneously propagates faster than its orthogonal counterpart. From calculations, Fietz and Shvets show that by using light of mixed polarization and adjusting the mixing angle of that light and the number of microring resonators along the waveguide, a tunable delay time between polarized wave packets of incoming light should be readily achieved. — ISO

Science•Jan 3, 2008•1 citation
We present a microresonator-based system capable of simultaneously producing time-advanced and time-delayed pulses. The effect is based on the combination of a sharp spectral feature with two orthogonally-polarized propagating waveguide modes. We include an experimental proof-of-concept implementation using a silica microsphere coupled to a tapered optical fiber and use a time-domain picture to interpret the observed delays. We also discuss potential applications for future all-optical networks.
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.
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.
We report controllable manipulation of slow and fast light in a whispering-gallery-mode microtoroid resonator fabricated from Erbium (Er3+) doped silica. We observe continuous transition of the coupling between the fiber-taper waveguide and the microresonator from undercoupling to critical coupling and then to overcoupling regimes by increasing the pump power even though the spatial distance between the resonator and the waveguide was kept fixed. This, in turn, enables switching from fast to slow light and vice versa just by increasing the optical gain. An enhancement of delay of two-fold over the passive silica resonator (no optical gain) was observed in the slow light regime. Moreover, we show dynamic pulse splitting and its control in slow/fast light systems using optical gain.
In the seemingly never-ending quest to speed up data transfer, light constitutes the ultimate communications carrier. However, the speed of light through a medium is generally constant, making photon storage and on-chip optical signal processing difficult tasks to implement. To slow things down, coupling microring resonators to an optical waveguide can effectively delay the propagation of photons. It has also been shown that the dispersion properties of these devices can distort the pulse profile so that the speed of light appears to be exceeded, providing so-called fast-light. From a practical viewpoint, it would be desirable to combine both of these properties in a single optical device. Recent work has found that these microring resonators are birefringent with respect to the polarization of the propagating light; i.e., one polarization simultaneously propagates faster than its orthogonal counterpart. From calculations, Fietz and Shvets show that by using light of mixed polarization and adjusting the mixing angle of that light and the number of microring resonators along the waveguide, a tunable delay time between polarized wave packets of incoming light should be readily achieved. — ISO