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.
We show that anomalous dispersion characteristic of fast-light can be used to enhance the sensitivity of optical interferometry under certain conditions. In particular, we show that a dual-chamber Fabry-Perot interferometer with a shared mirror-pair can be used in a way so that its sensitivity is increased by operating near the critically anomalous dispersion condition where the group index is much less than unity. The enhancement factor can be as high as 10 8 for realistic conditions. The process of bi-frequency pumped Raman gain in a Λ-type atomic medium can be used to achieve this effect. PACS Codes: 0.37.-a, 0.07.-a, 45.40.Cc Metrological applications deal with ultra-precision standards that require measurements using optical interferometers with extremely high sensitivity [1-4]. Recent experiments have shown that 'slow' or 'fast' group velocities in different kinds of material medium can drastically enhance the dispersion property under resonance condition [5-9]. It has been predicted that nonlinear Kerr index change of an active material in a photonic crystal based waveguide Mach-Zehnder interferometer (MZI) system can be dramatically enhanced using slow group velocity of light [10].
Abstract:We report on experimental observation of electromagnetically induced transparency and slow-light (v g ≈ c/607) in atomic sodium vapor, as a potential medium for a recently proposed experiment on slow-light enhanced relative rotation sensing [11]. We have performed an interferometric measurement of the index variation associated with a two-photon resonance to estimate the dispersion characteristics of the medium that is relevant to the slow-light based rotation sensing scheme. We also show that the presence of counter-propagating pump beams in an optical Sagnac loop produces a backward optical phase conjugation beam that can generate spurious signals, which may complicate the measurement of small rotations in the slow-light enhanced gyroscope. We identify techniques for overcoming this constraint.Key Words: Rotation sensing, optical gyroscope, slow light, electromagnetically induced transparency, sodium vapor, Mach-Zehnder interferometer Extreme dispersion induced by electromagnetically induced transparency (EIT) can reduce the speed or group velocity of light by many orders of magnitude compared to the speed of light in vacuum [1][2][3][4]. Recently, there has been a significant interest in the physics and applications of slow light. Typical applications include schemes where a controllably varied group velocity is used to realize optical delay lines, buffers, etc. [5,6], as well as techniques where reversible mapping of photon pulses in atomic medium are used for quantum state storage [7][8][9]. Recent proposals have also envisioned using slow light to enhance the rotational sensitivity of an interferometric optical gyroscope [10,11]. Such an interferometer may use slow light induced dispersive drag for enhanced sensitivity in relative rotation sensing. In this case, the rotational fringe shift is augmented by the group index or the dispersion in the medium, which, for realistic conditions, can yield many orders of magnitude improvement in the sensitivity of the gyroscope [11].An experimental implementation of the interferometric gyroscope relies on using an EIT medium, so that the counter-rotating optical fields experience resonant dispersion along the entire optical path. A relative motion between the medium and interferometer is also needed [11]. This gives rise to a rotational fringe shift that depends on the magnitude of the dispersion in the medium. We have considered Na atoms in a dilute vapor as an example of an experimental medium for this purpose. We have studied EIT in Doppler-broadened optical transitions of the D 1 line in Na vapor, and experimentally measured its dispersion characteristics that are relevant to its use in a slow-light enhanced Sagnac interferometer. In particular, magnitudes of the index change and the dispersion, under a narrow EIT resonance, have been measured by a phase delay obtained using a homodyne detection scheme. Precise measurements of these values help us infer the dynamic range as well as the magnitude of the sensitivity enhancement [11]. An excellent agreement...
We have recently proposed [9], the use of 'fast-light' media to obtain ultrahigh precision rotation sensing capabilities. The scheme relies on producing a critically anomalous dispersion (CAD), in a suitable dispersive medium, which is introduced in the arms of a Sagnac interferometer. We present here an experimental investigation of the anomalous dispersion properties of bi-frequency Raman gain in Rb vapor, with the goal of using this medium for producing the CAD condition. A heterodyne phase measurement technique is used to measure accurately the index variation associated with the dispersion. The slope of the negative linear dispersion (or group index) is experimentally varied by more than two orders of magnitude while changing the frequency separation between pump fields, responsible for producing gain. Using this result, we have identified the experimental
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