The speed of information in a ‘fast-light’ optical medium

Stenner, Michael D.; Gauthier, Daniel J.; Neifeld, Mark A.

doi:10.1038/nature02016

Cited by 321 publications

(241 citation statements)

References 24 publications

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“…This velocity cannot exceed c [5]. The fact that no modification of the group velocity can increase the speed at which information is transmitted has been directly demonstrated in a recent experiment [6]. Superluminal (or even negative) and, on the other extreme, exceedingly small group velocities, have been observed in several media [7].…”

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confidence: 99%

Direct Measurement of Superluminal Group Velocity and Signal Velocity in an Optical Fiber

et al. 2004

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We present an easy way of observing superluminal group velocities using a birefringent optical fiber and other standard devices. In the theoretical analysis, we show that the optical properties of the setup can be described using the notion of "weak value". The experiment shows that the group velocity can indeed exceed c in the fiber; and we report the first direct observation of the so-called "signal velocity", the speed at which information propagates and that cannot exceed c.The physics of light propagation is a very timely topic because of its relevance for both classical [1] and quantum [2] communication. Two kind of velocities are usually introduced to describe the propagation of a wave in a medium with dispersion ω(k): the phase velocity v ph = ω k and the group velocity v g = ∂ω ∂k . Both of these velocities can exceed the speed of light in vacuum c in suitable cases [3]; hence, neither can describe the speed at which the information carried by a pulse propagates in the medium. Indeed, since the seminal work of Sommerfeld, extended and completed by Brillouin [4], it is known that information travels at the signal velocity, defined as the speed of the front of a square pulse. This velocity cannot exceed c [5]. The fact that no modification of the group velocity can increase the speed at which information is transmitted has been directly demonstrated in a recent experiment [6]. Superluminal (or even negative) and, on the other extreme, exceedingly small group velocities, have been observed in several media [7]. In this letter we report observation of both superluminal and delayed pulse propagation in a tabletop experiment that involves only a highly birefringent optical fiber and other standard telecom devices.Before describing our setup, it is useful to understand in some more detail the mechanism through which anomalous group velocities can be obtained. For a light pulse sharply peaked in frequency, the speed of the center-of-mass is the group velocity v g of the medium for the central frequency [3]. In the absence of anomalous light propagation, the local refractive index of the medium is n f , supposed independent on frequency for the region of interest. The free propagation simply yields v g = L/t f where L is the length of the medium and t f = n f L/c is the free propagation time. One way to allow fast-and slow-light amounts to modify the properties of the medium in such a way that it becomes opaque for all but the fastest (slowest) frequency components. The center-of-mass of the outgoing pulse appears then at a time t = t f + t , with t the mean time of arrival once the free propagation has been subtracted; obviously t < 0 for fast-light, t > 0 for slow-light. If the deformation of the pulse is weak, the group velocity is still the speed of the center-of-mass, now given by( 1) This can become either very large and even negative ( t → −∞) or very small ( t → ∞) -although in these limiting situations the pulse is usually strongly distorted, so that our reasoning breaks down.We can now move to our setu...

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confidence: 99%

Direct Measurement of Superluminal Group Velocity and Signal Velocity in an Optical Fiber

et al. 2004

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“…These platforms offer the possibility of a generation of highly-sensitive sensors, which are able to detect (for example) weak forces, with a precision limited only by quantum uncertainties [39]. Fano resonances [40,41], optomechanically induced transparency [42] with single [43] and multiple windows [41,44,45], superluminal and subluminal effects [46][47][48][49][50][51][52][53][54][55][56][57][58][59] have also been observed in optomechanical systems, where nano dimensions and normal environmental conditions have paved the new avenues towards stateof-the-art potential applications, such as imaging and cloaking, telecommunication, interferometry, quantumoptomechanical memory and classical signal processing applications [60][61][62][63].…”

Section: Introductionmentioning

confidence: 99%

Control of Fano resonances and slow light using Bose-Einstein condensates in a nanocavity

et al. 2017

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In this study, a standing wave in an optical nanocavity with Bose-Einstein condensate (BEC) constitutes a one-dimensional optical lattice potential in the presence of a finite two bodies atomic interaction. We report that the interaction of a BEC with a standing field in an optical cavity coherently evolves to exhibit Fano resonances in the output field at the probe frequency. The behaviour of the reported resonance shows an excellent compatibility with the original formulation of asymmetric resonance as discovered by Fano [U. Fano, Phys. Rev. 124, 1866(1961]. Based on our analytical and numerical results, we find that the Fano resonances and subsequently electromagnetically induced transparency of the probe pulse can be controlled through the intensity of the cavity standing wave field and the strength of the atom-atom interaction in the BEC. In addition, enhancement of the slow light effect by the strength of the atom-atom interaction and its robustness against the condensate fluctuations are realizable using presently available technology.

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“…2b, where it can be clearly seen that the leading edge of the pulse is reshaped, so that the peak of the pulse is apparently simultaneously present at the input and the output of the fibre. This situation is of course possible only at the expense of a severe distortion of the pulse to satisfy all the principles given by causality and relativity for the transfer of information, as fully and elegantly described by Leon Brillouin in the 1910's (refs [19][20][21]. These results were the first demonstration that a negative group velocity can actually be achieved in optical fibres.…”

Section: Review Article | Focusmentioning

confidence: 57%

Slow and fast light in optical fibres

2008

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The ubiquitous role of optical fibres in modern photonic systems has stimulated research to realize slow and fast light devices directly in this close-to-perfect transmission line. Recent progress in developing optically controlled delays in optical fibres, operating under normal environmental conditions and at telecommunication wavelengths, has paved the way towards real applications for slow and fast light. This review presents the state-of-the-art research in this fascinating field and possible outcomes in the near future. The development of high-quality silica optical fibres with excellent transmission capabilities has directly contributed to the tremendous expansion of the global communication network. The success is due to their unrivalled low-loss performance (typically 50% of light is still present after a 15-km transmission distance), their wide bandwidth, which allows terabits per second of information to be transmitted over more than 1,000 km, and also their extremely low production cost. Realizing tunable delays for optical data signals directly in fibres, as well as integrating such devices into existing communication networks, is certainly a very attractive approach for optimizing the flow of data traffic in future networks. The approach may also enhance the capabilities of optical and microwave-on-optical-carrier signal processing. Given the limited possibilities for engineering the dispersion curve of standard single-mode fibres without creating complex photonic-crystal structures (see pages 448 and 465 of this issue 1,2 ), much research on fibre-based delays has been directed towards solutions based on spectral resonances to generate slow and fast light. The initial pioneering demonstrations of slow and fast light in various media all exploited narrow spectral resonances, typically created by electromagnetically induced transparency 3 or coherent population oscillation 4 . Narrow spectral resonances have a dramatic effect on optical propagation, as any sharp spectral change in the medium's transmission curve results in a steep quasi-linear variation of the effective refractive index with wavelength in the narrow spectral region near the resonance. This in turn results in a strong change in the group velocity at the exact centre of the resonance 5 . The velocity change is strongest for narrower spectral resonances (as explained in detail below) and for this reason, the early experiments were all carried out in special media, such as ultracold atomic gases or atomic transitions in a crystalline solid at a well-defined wavelength. Luc ThévenazWithin the resonance, the relationship between the change in the optical transmission and the delay can be determined as follows. The refractive-index change, Δn, as a function of the optical frequency, ν, is calculated using the Kramers-Kronig transformation, and the index change associated with the group velocity, Δn g , is then found using the relationship Δn g = Δn + ν(dΔn/dν) (ref. 5). Finally, the delay, ΔT, added to the normal transit time in the medium...

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The speed of information in a ‘fast-light’ optical medium

Cited by 321 publications

References 24 publications

Direct Measurement of Superluminal Group Velocity and Signal Velocity in an Optical Fiber

Direct Measurement of Superluminal Group Velocity and Signal Velocity in an Optical Fiber

Control of Fano resonances and slow light using Bose-Einstein condensates in a nanocavity

Slow and fast light in optical fibres

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