Ultrahigh enhancement in absolute and relative rotation sensing using fast and slow light
TL;DR: In this paper, the authors describe a resonator-based optical gyroscope whose sensitivity for measuring absolute rotation is enhanced via use of the anomalous dispersion characteristic of superluminal light propagation.
Abstract: We describe a resonator-based optical gyroscope whose sensitivity for measuring absolute rotation is enhanced via use of the anomalous dispersion characteristic of superluminal light propagation. The enhancement is given by the inverse of the group index, saturating to a bound determined by the group velocity dispersion. We also show how the offsetting effect of the concomitant broadening of the resonator linewidth may be circumvented by using an active cavity. For realistic conditions, the enhancement factor is as high as ${10}^{6}$. We also show how normal dispersion used for slow light can enhance relative rotation sensing in a specially designed Sagnac interferometer, with the enhancement given by the slowing factor.
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TL;DR: In this article, the physical basics of slow light propagation in atomic media, photonic structures, and optical fibers are considered and a set of criteria are then used to compare different media.
Abstract: I consider the physical basics of slow light propagation in atomic media, photonic
structures, and optical fibers. I show similarities and differences between all of
the above media and develop set of criteria that are then used to compare different
media. Special attention is given to dispersion of group velocity and loss, which are
shown to limit the bandwidth and delay capacity of all the slow light schemes.
157 citations
TL;DR: In this paper, a method based on non-Hermitian singularities, or exceptional points, was used to increase the Sagnac scale factor and enhance the sensitivity of ring-laser gyroscopes.
Abstract: Gyroscopes are essential to many diverse applications associated with navigation, positioning and inertial sensing1. In general, most optical gyroscopes rely on the Sagnac effect—a relativistically induced phase shift that scales linearly with the rotational velocity2,3. In ring laser gyroscopes (RLGs), this shift manifests as a resonance splitting in the emission spectrum, which can be detected as a beat frequency4. The need for ever more precise RLGs has fuelled research activities aimed at boosting the sensitivity of RLGs beyond the limits dictated by geometrical constraints, including attempts to use either dispersive or nonlinear effects5–8. Here we establish and experimentally demonstrate a method using non-Hermitian singularities, or exceptional points, to enhance the Sagnac scale factor9–13. By exploiting the increased rotational sensitivity of RLGs in the vicinity of an exceptional point, we enhance the resonance splitting by up to a factor of 20. Our results pave the way towards the next generation of ultrasensitive and compact RLGs and provide a practical approach for the development of other classes of integrated sensor. A method based on non-Hermitian singularities, or exceptional points, is established and used to increase the Sagnac scale factor and enhance the sensitivity of ring-laser gyroscopes.
148 citations
TL;DR: A survey of methods for establishing extreme values of the group velocity, concentrating especially on methods that can work in room temperature solids, can be found in this article, where the authors also describe some of the applications of slow and fast light that are currently under development.
Abstract: We review progress in the development of methods for controlling the group velocity of light. These methods allow one to create situations in which the group velocity of light is much smaller than the velocity of light in vacuum c, in which the group velocity is greater than c, or in which the group velocity is negative. We present a survey of methods for establishing extreme values of the group velocity, concentrating especially on methods that can work in room temperature solids. We also describe some of the applications of slow and fast light that are currently under development.
141 citations
TL;DR: A method based on non-Hermitian singularities, or exceptional points, is established and used to increase the Sagnac scale factor and enhance the sensitivity of ring-laser gyroscopes.
Abstract: Gyroscopes play a crucial role in many and diverse applications associated with navigation, positioning, and inertial sensing [1]. In general, most optical gyroscopes rely on the Sagnac effect -- a relativistically induced phase shift that scales linearly with the rotational velocity [2,3]. In ring laser gyroscopes (RLGs), this shift manifests itself as a resonance splitting in the emission spectrum that can be detected as a beat frequency [4]. The need for ever-more precise RLGs has fueled research activities towards devising new approaches aimed to boost the sensitivity beyond what is dictated by geometrical constraints. In this respect, attempts have been made in the past to use either dispersive or nonlinear effects [5-8]. Here, we experimentally demonstrate an altogether new route based on non-Hermitian singularities or exceptional points in order to enhance the Sagnac scale factor [9-13]. Our results not only can pave the way towards a new generation of ultrasensitive and compact ring laser gyroscopes, but they may also provide practical approaches for developing other classes of integrated sensors.
126 citations
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...In this respect, attempts have been made in the past to use either dispersive or nonlinear effects [5-8]....
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TL;DR: It is shown here that the effective dispersion experienced by the lasing frequency is still sensitive to the spectral profile of the unsaturated gain, leading to a versatile sensor of hyper sensitivity.
Abstract: The group velocity of light becomes superluminal in a medium with a tuned negative dispersion, using two gain peaks, for example. Inside a laser, however, the gain is constant, equaling the loss. We show here that the effective dispersion experienced by the lasing frequency is still sensitive to the spectral profile of the unsaturated gain. In particular, a dip in the gain profile leads to a superluminal group velocity for the lasing mode. The displacement sensitivity of the lasing frequency is enhanced by nearly five orders of magnitude, leading to a versatile sensor of hyper sensitivity.
96 citations
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TL;DR: In this paper, an experimental demonstration of electromagnetically induced transparency in an ultracold gas of sodium atoms, in which the optical pulses propagate at twenty million times slower than the speed of light in a vacuum, is presented.
Abstract: Techniques that use quantum interference effects are being actively investigated to manipulate the optical properties of quantum systems1. One such example is electromagnetically induced transparency, a quantum effect that permits the propagation of light pulses through an otherwise opaque medium2,3,4,5. Here we report an experimental demonstration of electromagnetically induced transparency in an ultracold gas of sodium atoms, in which the optical pulses propagate at twenty million times slower than the speed of light in a vacuum. The gas is cooled to nanokelvin temperatures by laser and evaporative cooling6,7,8,9,10. The quantum interference controlling the optical properties of the medium is set up by a ‘coupling’ laser beam propagating at a right angle to the pulsed ‘probe’ beam. At nanokelvin temperatures, the variation of refractive index with probe frequency can be made very steep. In conjunction with the high atomic density, this results in the exceptionally low light speeds observed. By cooling the cloud below the transition temperature for Bose–Einstein condensation11,12,13 (causing a macroscopic population of alkali atoms in the quantum ground state of the confining potential), we observe even lower pulse propagation velocities (17?m?s−1) owing to the increased atom density. We report an inferred nonlinear refractive index of 0.18?cm2?W−1 and find that the system shows exceptionally large optical nonlinearities, which are of potential fundamental and technological interest for quantum optics.
3,438 citations
TL;DR: Gain-assisted linear anomalous dispersion is used to demonstrate superluminal light propagation in atomic caesium gas and is observed to be a direct consequence of classical interference between its different frequency components in an anomalously dispersion region.
Abstract: Einstein's theory of special relativity and the principle of causality imply that the speed of any moving object cannot exceed that of light in a vacuum (c) Nevertheless, there exist various proposals for observing faster-than-c propagation of light pulses, using anomalous dispersion near an absorption line, nonlinear and linear gain lines, or tunnelling barriers However, in all previous experimental demonstrations, the light pulses experienced either very large absorption or severe reshaping, resulting in controversies over the interpretation Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light propagation in atomic caesium gas The group velocity of a laser pulse in this region exceeds c and can even become negative, while the shape of the pulse is preserved We measure a group-velocity index of n(g) = -310(+/- 5); in practice, this means that a light pulse propagating through the atomic vapour cell appears at the exit side so much earlier than if it had propagated the same distance in a vacuum that the peak of the pulse appears to leave the cell before entering it The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region
1,211 citations
TL;DR: Low group velocities of light in an optically dense crystal of Pr doped Y2SiO5 are reported by using a sharp spectral feature in absorption and dispersion that is produced by resonance Raman excitation of a ground-state spin coherence.
Abstract: We report ultraslow group velocities of light in an optically dense crystal of Pr doped ${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 \ensuremath{\mu}s. Deceleration and ``stopping'' or trapping of the light pulse was also observed. These reductions of the group velocity are accomplished by using a sharp spectral feature in absorption and dispersion that is produced by resonance Raman excitation of a ground-state spin coherence.
791 citations
TL;DR: It is observed that ions in mirror sites are inversely saturable and cause superluminal light propagation, whereas ions in inversion sites experience conventional saturable absorption and produce slow light.
Abstract: We have observed both superluminal and ultraslow light propagation in an alexandrite crystal at room temperature. Group velocities as slow as 91 meters per second to as fast as -800 meters per second were measured and attributed to the influence of coherent population oscillations involving chromium ions in either mirror or inversion sites within the crystal lattice. Namely, ions in mirror sites are inversely saturable and cause superluminal light propagation, whereas ions in inversion sites experience conventional saturable absorption and produce slow light. This technique for producing large group indices is considerably easier than the existing methods to implement and is therefore suitable for diverse applications.
753 citations