Some models for quantum gravity (QG) violate Lorentz invariance and predict an energy dependence of the speed of light, leading to a dispersion of high-energy gamma-ray signals that travel over cosmological distances. Limits on the dispersion from short-duration substructures observed in gamma-rays emitted by gamma-ray bursts (GRBs) at cosmological distances have provided interesting bounds on ...

We demonstrate evanescent coupling between a strip waveguide and a periodically-patterned ring resonator in the slow light regime. Resonances with a group index > 22 are efficiently coupled with an extinction ratio of > 20 dB. This result opens up the possibility of new applications in compact device integration in wavelengthdivision multiplexing (WDM) systems while reducing the in-band four-wa...

We demonstrate a method of preparation of broadband sign-reversible dispersion in alkali vapour based on velocity-selective optical pumping. The refractive index in Rb vapour has been measured using a heterodyne method. The magnitudes of the normal and anomalous dispersion, which are almost constant over a spectral region of approximately 40 MHz, can lead to a reduced (V(g) approximately c/230)...

Four-wave mixing is observed in a silicon W1 photonic crystal waveguide. The dispersion dependence of the idler conversion efficiency is measured and shown to be enhanced at wavelengths exhibiting slow group velocities. A 12-dB increase in the conversion efficiency is observed. Concurrently, a decrease in the conversion bandwidth is observed due to the increase in group velocity dispersion in t...

We consider phonon polariton states which may arise in disordered dielectrics due to a random light-phonon coupling. We show that these states can be described within the model of disorder-induced crossing resonance (DICR). The dispersion laws and relaxation rates of these states have been explored. Polaritons are shown to be good candidates for the experimental observation of the effects of DI...

The numerical dispersion relation that governs the propagation of fields in a finite-difference time-domain (FDTD) grid was derived several years ago. In this letter a different interpretation is given for the governing equation. It is shown that the dispersion relation predicts faster-than-light propagation for coarsely resolved fields. Additionally, some spectral components that were previous...

Keck spectroscopy is presented for four dwarf elliptical galaxies in the Virgo Cluster. At this distance, the mean velocity and velocity dispersion are well resolved as a function of radius between 100 to 1000 pc, allowing a clear separation between nuclear and surrounding galaxy light. We find a variety of dispersion profiles for the inner regions of these objects, and show that none of these ...

Dispersive approaches provide model independent description of meson-meson scattering. We first review here the use of dispersion relations to obtain a model independent unitarization of Chiral Perturbation Theory amplitudes, that establish the existence of light scalar mesons and whose leading 1/Nc behavior suggest they ahve a non q̄q dominant component. We also review the forward dispersion re...

Slow light with a markedly low group velocity is a promising solution for optical buffering and advanced time-domain optical signal processing. It is also anticipated to enhance linear and nonlinear effects and so miniaturize functional photonic devices because slow light compresses optical energy in space. Photonic crystal waveguide devices generate on-chip slow light at room temperature with ...

Asbestos fibers as small as 1 mum in diameter can be uniquely identified by light microscopy by employing dispersion staining methods. The technique described herein involves suspension of fibers in liquids of known refractive indices and observation of color display by means of a dispersion staining objective. Wavelengths or indices of refraction may be determined at right angles to and parall...