Observation of simultaneous fast and slow light

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.PACS numbers: 42.25. Lc,42.25.Ja,42.79.Sz Increasing bandwidth demands are pushing for the development of all-optical circuitry that will be able to quickly and reliably transmit and process vast amounts of data. Precise control of light propagation, such as the ability to advance, delay, or store a pulse transmitted through a waveguide, is a requisite ingredient for optical data processing in photonic circuits [1]. Remarkably, exotic optical phenomena occurring in the presence of strong spectral dispersion such as slow [2] and fast[3] light have been found very useful for achieving these goals, generating a surge of experimental activities aimed at realizing fast or slow light in different media: atomic vapors[2, 3, 4], crystals [5], semiconductors [6,7], and microresonators [8,9,10,11]. These demonstrations have shown either fast or slow light for a given configuration. Here we introduce a microresonator-based system that is capable of simultaneously producing time-advanced and time-delayed pulses, including an experimental proof-of-concept implementation.The ability to simultaneously slow and advance pulses of light brings about a new perspective on photonics: one can easily envision applications involving all-optical processing of data headers and data packets where both fast and slow light may be desirable. Time-advanced signals can be used to compensate time delays inevitable in any complex optical-processing network [12]. The appeal of strong spectral dispersion is not limited to the linear properties of light: the resulting high optical energy compression may lead to extraordinary enhancement of nonlinear effects and, one day, to single-photon applications for quantum computing and communications. Our experimental implementation uses a silica microsphere evanescently coupled to a tapered optical fiber [13,14] as the resonator. Light polarization plays an important role in the experiment as the enabling tool for achieving fast/slow light and also provides an additional degree of freedom available for data storage and/or processing.It has been known for a long time that media with sharp spectral features can modify the group speed of light propagating through them [15], resulting in subluminal or superluminal propagation of pulses. More recently it has also been established that systems where two modes can propagate can also show anomalous dispersion, even in the absence of absorption or reflection [16]. This has been shown in photonic crystals [16,17] and coupled mode systems [18]. Our system combines both appro...

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