Slow Light

We demonstrate a technique for generating tunable all-optical delays in room temperature single-mode optical fibers at telecommunication wavelengths using the stimulated Brillouin scattering process. This technique makes use of the rapid variation of the refractive index that occurs in the vicinity of the Brillouin gain feature. The wavelength at which the induced delay occurs is broadly tunable by controlling the wavelength of the laser pumping the process, and the magnitude of the delay can be tuned continuously by as much as 25 ns by adjusting the intensity of the pump field. The technique can be applied to pulses as short as 15 ns. This scheme represents an important first step towards implementing slow-light techniques for various applications including buffering in telecommunication systems.

We theoretically demonstrate the slow light capabilities of 2D silicon carbide based photonic crystal W1 waveguides (SiC-PhC-W1Ws) with numerical simulations. The PhC is assumed to be created by devising air-holes with hexagonal lattice in a standard SiC substrate having oscillator type ordinary refractive index. Numerical simulations show that by means of selective optofluidic infiltration and varying the air-holes radii, SiC-PhC-W1Ws are capable of slowing light down by about 473 times while their group velocity dispersions are tailored to near zero values. Our numerical study also suggests the possibility of slow-light guiding with n g ×∆λ/λ c values as high as 0.42 in SiC-PhC-W1Ws at optical telecommunications wavelengths.

Optical micromanipulation stands for contact-free handling of microscopic particles by light. Optical forces can manipulate non-absorbing objects in a large range of sizes, e.g., from biological cells down to cold atoms. Recently much progress has been made going from the micro-down to the nanoscale. Less attention has been paid to going the other way, trapping increasingly large particles. Optical tweezers typically employ a single laser beam tightly focused by a microscope objective of high numerical aperture to stably trap a particle in three dimensions (3D). As the particle size increases, stable 3D trapping in a single-beam trap requires scaling up the optical power, which eventually induces adverse biological effects. Moreover, the restricted field of view of standard optical tweezers, dictated by the use of high NA objectives, is particularly unfavorable for catching actively moving specimens. Both problems can be overcome by traps with counter-propagating beams. Our 'macro-tweezers' are especially designed to trap highly motile organisms, as they enable three-dimensional all-optical trapping and guiding in a volume of 2 × 1 × 2 mm 3 . Here we report for the first time the optical trapping of large actively swimming organisms, such as for instance Euglena protists and dinoflagellates of up to 70 µm length. Adverse bio-effects are kept low since trapping occurs outside high intensity regions, e.g., focal spots. We expect our approach to open various possibilities in the contact-free handling of 50-100 µm sized objects that could hitherto not be envisaged, for instance all-optical holding of individual micro-organisms for taxonomic identification, selective collecting or tagging.

We demonstrate that fast tunable optical switches and tunable slow-light devices can be designed as optical cavities entangled with quantum dots. We derive the analytical conditions for switching and tuning the filter transmittance, considering both dipole-induced transparency and electromagnetic-induced transparency effects.

We present a planar design of a metamaterial exhibiting electromagnetically induced transparency that is amenable to experimental verification in the microwave frequency band. The design is based on the coupling of a split-ring resonator with a cut-wire in the same plane. We investigate the sensitivity of the parameters of the transmission window on the coupling strength and on the circuit elements of the individual resonators, and we interpret the results in terms of two linearly coupled Lorentzian resonators. Our metamaterial designs combine low losses with the extremely small group velocity associated with the resonant response in the transmission window, rendering them suitable for slow light applications at room temperature.

Slow light, EIT, photonic band gap. (left) Anita R Warrier is a post-doctoral fellow at the Department of Physics, Indian Institute of Technology, Madras. Her research interests are in photothermal effect studies, semiconductors and photonic crystals. (right) C Vijayan is a Professor at the Department of Physics, Indian Institute of Technology, Madras and is interested in the area of nanophotonics. For more information, see http://www.physics.

The phenomenon of slow light is interesting not only from a fundamental physics standpoint, but also because it introduces the possibility of new applications in telecommunications 1 . For a practical slow-light device, the important features are bandwidth, range of wavelength tunability and size, rather than the absolute slowdown factor achieved 2 . Slow light can be achieved in three main ways: through quantum interference effects 3-8 , which can slow the speed of light down to several metres per second, albeit within a very narrow bandwidth; by using photonic crystals 9 , which are able to slow light over large bandwidths but with much smaller slowdown factors 10,11 ; and by using stimulated Brillouin or Raman scattering 12,13 . Surface plasmon polaritons have the advantage that they can overcome the diffraction limit of light in a microchip-sized device . Increases in the propagation lengths of surface plasmon polaritons 18 and the feasibility of all-optical wavelength tunability 19 have been reported. Here we report the observation of slow, femtosecond surface-plasmon-polariton wavepackets. We show that a highly compact (55 mm length) plasmonic structure is able to achieve an effective slowdown factor of two over a 4 THz bandwidth. These results will increase the scope of photonic devices based on surface plasmon polaritons.

A light beam normally incident upon an uniformly moving dielectric medium is in general subject to bendings due to a transverse Fresnel-Fizeau light drag effect. In conventional dielectrics, the magnitude of this bending effect is very small and hard to detect. Yet, it can be dramatically enhanced in strongly dispersive media where slow group velocities in the m/s range have been recently observed taking advantage of the electromagnetically induced transparency (EIT) effect. In addition to the usual downstream drag that takes place for positive group velocities, we predict a significant anomalous upstream drag to occur for small and negative group velocities. Furthermore, for sufficiently fast speeds of the medium, higher order dispersion terms are found to play an important role and to be responsible for peculiar effects such as light propagation along curved paths and the restoration of the spatial coherence of an incident noisy beam. The physics underlying this new class of slow-light effects is thoroughly discussed.

We study the resonant transmission of light in a coupled-resonator optical waveguide interacting with two nearly identical side cavities. We reveal and describe a novel effect of the coupled-resonator-induced reflection (CRIR) characterized by a very high and easily tunable quality factor of the reflection line, for the case of the inter-site coupling between the cavities and the waveguide. This effect differs sharply from the coupled-resonator-induced transparency (CRIT) -- an all-optical analogue of the electromagnetically-induced transparency -- which has recently been studied theoretically and observed experimentally for the structures based on micro-ring resonators and photonic crystal cavities. Both CRIR and CRIT effects have the same physical origin which can be attributed to the Fano-Feshbach resonances in the systems exhibiting more than one resonance. We discuss the applicability of the novel CRIR effect to the control of the slow-light propagation and low-threshold all-optical switching.

We demonstrate that planar metamaterial lacking of mirror symmetry shows asymmetric transmission of terahertz waves and bands of positive, negative and zero phase and group velocities indicating a polarization sensitive negative index and slow-light media.

We study the dispersion and absorption spectra of a weak probe in a ⌳-type three-level atomic system with closely ground sublevels driven by a strong field and damped by a broadband squeezed vacuum. We analyze the interplay between the spontaneous generated coherence and the squeezed field on the susceptibility of the atomic system. We find that by varying the intensity of the squeezed field the group velocity of a weak pulse can change from subluminal to superluminal. In addition we exploit the fact that the properties of the atomic medium can be dramatically modified by controlling the relative phase between the driving field and the squeezed field, allowing us to manipulate the group velocity at which light propagates. The physical origin of this phenomenon corresponds to a transfer of the atomic coherence from electromagnetically induced transparency to electromagnetically induced absorption. Besides, this phenomenon is achieved under nearly transparency conditions and with negligible distortion of the propagation pulse.

Electromagnetically induced transparency (EIT) [1, 2] provides a powerful mechanism for controlling light propagation in a dielectric medium, and for producing slow and fast light. EIT traditionally arises from destructive interference induced by a nonradiative coherence in an atomic system. Stimulated Brillouin scattering (SBS) of light from propagating hypersonic acoustic waves [3] has also been used successfully for the generation of slow and fast light . However, EIT-type processes based on SBS were considered infeasible because of the short coherence lifetime of hypersonic phonons. Here, we report a new Brillouin scattering induced transparency (BSIT) phenomenon generated by acousto-optic interaction of light with long-lived propagating phonons . We demonstrate that BSIT is uniquely non-reciprocal due to the propagating acoustic phonon wave and accompanying momentum conservation requirement. Using a silica microresonator having naturally occurring forward-SBS phasematched modal configuration , we show that BSIT enables compact and ultralow-power slow-light generation with delay-bandwidth product comparable to state-of-the-art SBS systems.

Le ralentissement de la lumière est le résultat d'une forte dispersion de l'indice de réfraction. Nous observons un tel effet obtenu par oscillation cohérente de population dans un cristal dopé aux ions d'Erbium triplement ionisés. La lumière s'y propage avec une vitesse de groupe de 2.7 m/s. La largeur inhomogène de la transition est exploitée comme un paramètre additionnel pour contrôler à la fois cette vitesse de groupe et la transmission.

An integrated configuration is proposed to convert tunable slow light from signal to another frequency in a wide bandwidth by using a 70 m-long highly nonlinear photonic crystal fiber (HN-PCF). A 10 GHz RZ signal is delayed by a 10 Gbit/s 2 31 1 pseudo random bit sequence (PRBS) stimulated Brillouin scattering (SBS) pump, and the slow light is converted to another frequency in a broadband by four-wave mixing (FWM). By this way, not only the slow light is converted, but the idler power is enhanced greatly. In our experiment, all-optical controlled 37.5 ps delay time is converted in a 40 nm bandwidth flatly, and 4.7 dB idler power is enhanced simultaneously. The experimental results are in good agreement with those of the theory.

We present a theoretical model for electromagnetically induced transparency (EIT) in vapor, that incorporates atomic motion and velocity-changing collisions into the dynamics of the densitymatrix distribution. Within a unified formalism we demonstrate various motional effects, known for EIT in vapor: Doppler-broadening of the absorption spectrum; Dicke-narrowing and time-offlight broadening of the transmission window for a finite-sized probe; Diffusion of atomic coherence during storage of light and diffusion of the light-matter excitation during slow-light propagation; and Ramsey-narrowing of the spectrum for a probe and pump beams of finite-size.

The epsilon-near-zero ͑ENZ͒ tunneling phenomenon allows full transmission of waves through a narrow channel even in the presence of a strong geometric mismatch. Here we experimentally demonstrate nonlinear control of the ENZ tunneling by an external field, as well as self-modulation of the transmission resonance due to the incident wave. Using a waveguide section near cut-off frequency as the ENZ system, we introduce a diode with tunable and nonlinear capacitance to demonstrate both these effects. Our results confirm earlier theoretical ideas on using an ENZ channel for dielectric sensing and their potential applications for tunable slow-light structures.

Coupling two lasers of different intensities and wavelengths inside bulk matter, also known as EIT, has applications in slowing down light. EIT essentially transforms an opaque material to a given radiation into a transparent one, and can be applied in new optoelectronic devices, including quantum circuits, and in quantum computing. The main challenge in using this procedure comes from the difficulty in the coherent retrieval of the light signal squeezed inside the bulk matter after the EIT process ceases. We propose an alternative to the EIT mechanism in which we use the interaction between a weak probe laser beam reflected near the Brewster angle and a stronger coupling laser beam directed at normal incidence toward the same dielectric surface. As opposed to a classical EIT-type phenomenon, in our case (1) the dielectric is transparent to both incident lasers, and (2) the coupling between the two beams is realized on the dielectric surface, within one dipole layer in thickness. The signature of the coupling between the two lasers is indicated by (1) a shift in the value of the Brewster angle measured in the direction of the reflected probe beam toward a value associated to the electric permittivity of the dielectric in interaction with the stronger laser alone, and (2) an interference pattern near Brewster angle with several minima, which can be interpreted similarly as for light diffraction patterns. This result indicates that we can lock a laser beam on a dielectric surface.

We study the manipulation of slow light with an orbital angular momentum propagating in a cloud of cold atoms. Atoms are affected by four co-propagating control laser beams in a double tripod configuration of the atomic energy levels involved, allowing us to minimize the losses at the vortex core of the control beams. In such a situation the atomic medium is transparent for a pair of co-propagating probe fields, leading to the creation of two-component (spinor) slow light. We study the interaction between the probe fields when two control beams carry optical vortices of opposite helicity. As a result, a transfer of the optical vortex takes place from the control to the probe fields without switching off and on the control beams. This feature is missing in a single tripod scheme where the optical vortex can be transferred from the control to the probe field only during either the storage or retrieval of light.

We propose a "channelization" architecture to achieve wide-band electromagnetically induced transparency (EIT) and ultra-slow light propagation in atomic 87 Rb vapors. EIT and slow light are achieved by shining a strong, resonant "pump" laser on the atomic medium, which allows slow and unattenuated propagation of a weaker "signal" beam, but only when a two-photon resonance condition is satisfied. Our wideband architecture is accomplished by dispersing a wideband signal spatially, transverse to the propagation direction, prior to entering the atomic cell. When particular Zeeman sub-levels are used in the EIT system, then one can introduce a magnetic field with a linear gradient such that the two-photon resonance condition is satisfied for each individual frequency component. Because slow light is a group velocity effect, utilizing differential phase shifts across the spectrum of a light pulse, one must then introduce a slight mismatch from perfect resonance to induce a delay. We present a model which accounts for diffusion of the atoms in the varying magnetic field as well as interaction with levels outside the ideal three-level system on which EIT is based. We find the maximum delay-bandwidth product decreases with bandwidth, and that delay-bandwidth product ∼ 1 should be achievable with bandwidth ∼ 50 MHz (∼ 5 ns delay). This is a large improvement over the ∼ 1 MHz bandwidths in conventional slow light systems and could be of use in signal processing applications. I. INTRODUCTION Electromagnetically induced transparency (EIT) [1, 2], in which a "pump" field of laser light can allow a weaker "signal" field to propagate through an otherwise opaque atomic gas, has been inspiring a number of applications based on the underlying coherent interaction of laser light with atomic media. These include nonlinear optics at low light levels [3] and ultra-sensitive magnetic field measurements [4]. Of particular interest has been the recent observation of ultra-slow light (USL) [5, 6] in atomic gases, at group velocities on the order of 10 m/s, due to a steep linear dispersion in the index of refraction associated with the narrow EIT feature. This could allow for controllable true-time delay devices for classical light pulses, with applications in fiber-optic telecommunications [7] and radar signal processing [8]. Later extensions of the technique to stored light [9, 10] (for several milliseconds) has also raised the possibility of quantum memory devices [11]. While the narrow frequency feature (below the natural linewidth and Doppler width) of EIT is one of its attractive features for precision applications [4], this has drawbacks in regards to delay and storage applications. Optical communications and radar processing typically desire ∼ 20 GHz bandwidth. Similarly, single photon sources and other tools of potential quantum information technologies may emit photons over a broad band. In USL experiments to date, the width of EIT transparency window is much narrower. EIT and USL work best when the atom can be well described with a Λ energy level structure. The signal field is nearresonant with a stable state (which we label |1) and a radiatively decaying excited state (|3). The pump field is resonant with another stable state |2 and the common excited level |3. We consider two energy level schemes in 87 Rb, shown in Fig.1(a). The schemes are labeled "A" (dashed, blue arrows) and "B" (solid, red arrows). The transparency and slow, distortion-free propagation of the signal pulse that we desire occur only when the frequency difference of the two lasers ω s − ω p matches the energy level difference between levels |1 and |2 to within the narrow EIT width. Frequency components of the signal outside this width are strongly absorbed and distorted. This width is directly proportional to the pump power and practical limits on the pump power (∼ 10 mW/cm 2) limit it to ∼ 1 MHz. The need for a wide-band, controllable true-time delay device inspired us to here consider theoretically a "channelization" geometry utilizing Zeeman shifts in the atoms (see Fig.1(b)). There are a variety of techniques available to spatially separate various frequency components of broadband light. Assume a broadband signal pulse (represented as a dashed, yellow arrow) propagating along the longitudinal (z) dimension is split in the transverse (x) direction, with a transverse displacement proportional to the detuning from some chosen central frequency. In our channelization geometry, this dispersed signal then enters the 87 Rb cell, which is illuminated by a co-propagating, monochromatic pump field. When particular Zeeman sublevels are used, as in Fig.1(a), the two photon resonance condition required for slow light will be a strong function of magnetic field along the quantization axis z due Zeeman shifts of the levels. Thus, applying a longitudinal magnetic field (dotted, green arrows) with a linear gradient along x will allow us to achieve the conditions for EIT and USL for each frequency simultaneously. The components can then be recombined after passing through the cell, resulting in a true time delay device for a broadband signal. USL is a group (rather than phase) velocity effect, meaning it works by applying differential phase shifts to each frequency component in the signal pulse. Maintaining perfect two-photon resonance everywhere would result in no differential phase shift and thus, no delay. Therefore, one should choose the magnetic field gradient such that there is a small, varying detuning across the cell. By choosing this mismatch to be small enough that all components are within the EIT resonance one can obtain the linear frequency dispersion necessary for slow light and still maintain transparency. There is a direct trade-off such that the

We consider two-component "spinor" slow light in an ensemble of atoms coherently driven by two pairs of counterpropagating control laser fields in a double tripod-type linkage scheme. We derive an equation of motion for the spinor slow light (SSL) representing an effective Dirac equation for a massive particle with the mass determined by the two-photon detuning. By changing the detuning the atomic medium acts as a photonic crystal with a controllable band gap. If the frequency of the incident probe light lies within the band gap, the light tunnels through the sample. For frequencies outside the band gap, the transmission probability oscillates with increasing length of the sample. In both cases the reflection takes place into the complementary mode of the probe field. We investigate the influence of the finite excited state lifetime on the transmission and reflection coefficients of the probe light. We discuss possible experimental implementations of the SSL using alkali atoms such as Rubidium or Sodium.

We consider the coupling into a slow mode that appears near an inflection point in the band structure of a photonic crystal waveguide. Remarkably, the coupling into this slow mode, which has a group index n g Ͼ 1000, can be essentially perfect without any transition region. We show that this efficient coupling occurs thanks to an evanescent mode in the slow medium, which has appreciable amplitude and helps satisfy the boundary conditions but does not transport any energy.

We show for the first time that a planar metamaterial, an array of coupled metal split-ring resonators with a unit cell lacking mirror symmetry, exhibits asymmetric transmission of terahertz radiation (0.25-2.5 THz) propagating through it in opposite directions. This intriguing effect, that is compatible with Lorentz reciprocity and time-reversal, depends on a directional difference in conversion efficiency of the incident circularly polarized wave into one of opposite handedness, that is only possible in lossy low-symmetry planar chiral metamaterials. We show that asymmetric transmission is linked to excitation of enantiomerically sensitive plasmons, these are induced charge-field excitations that depend on the mutual handedness of incident wave and metamaterial pattern. Various bands of positive, negative and zero phase and group velocities have been identified indicating the opportunity to develop polarization sensitive negative index and slow light media based on such metamaterials.

Recent experimental results on slow light heighten interest in nonlinear Maxwell theories. We obtain Galilei covariant equations for electromagnetism by allowing special nonlinearities in the constitutive equations only, keeping Maxwell's equations unchanged. Combining these with linear or nonlinear Schrödinger equations, e.g. as proposed by Doebner and Goldin, yields a Galilean quantum electrodynamics.

We demonstrate an all-optical delay line in hot cesium vapor that tunably delays 275 ps input pulses up to 6.8 ns and 740 input ps pulses up to 59 ns (group index of approximately 200) with little pulse distortion. The delay is made tunable with a fast reconfiguration time (100's of ns) by optically pumping out of the atomic ground states.

We calculate electric susceptibility of a laser-dressed atomic medium. The model adopted in this work refers to the experiment with cold 85 Rb atoms, where the states F′ = 1, 2, 3 of the hyperfine manifold 5P 3/2 (F′) are strongly coupled with the ground state 5S 1/2 (F = 2), and the coupling is probed by a weak probing field from the other ground-state component 5S 1/2 (F = 3). We present a five-level model in which the states F = 2, 3 and F′ = 1, 2, 3 are taken into account, while the noncoupled state F′ = 4 is neglected. The model is used as a starting point to reproduce spectral features observed in the absorption of probe light passing through a cold sample of 85 Rb atoms in a magneto-optical trap. Basing on numerical solutions of this model, we have also studied in detail the impact on the probe spectra from the presence of the state F′ = 1 to which probing is forbidden by electric-dipole transition, but coupling is allowed [see, e.g., Proc. of SPIE 8770 (2013) 87700Q].

We demonstrate efficient generation of slow-light in As 2 S 3 single-mode fibers through stimulated Brillouin scattering using a 1548 nm DFB laser. Sinusoidal pulses with a 40-ns period have been delayed 19 ns with only 31 mW of launched power in 10 m of fiber.

Even as we advance the frontiers of physics knowledge, our understanding of how this knowledge evolves remains at the descriptive levels of Popper and Kuhn. Using the Ameri-can Physical Society (APS) publications data sets, we ask in this paper how new knowledge is built upon old knowledge. We do so by constructing year-to-year bibliographic coupling networks, and identify in them validated communities that represent different research fields. We then visualize their evolutionary relationships in the form of alluvial diagrams, and show how they remain intact through APS journal splits. Quantitatively, we see that most fields undergo weak Popperian mixing, and it is rare for a field to remain isolated/undergo strong mixing. The sizes of fields obey a simple linear growth with recombination. We can also reliably predict the merging between two fields, but not for the considerably more complex splitting. Finally, we report a case study of two fields that underwent repeated merging and splitting around 1995, and how these Kuhnian events are correlated with breakthroughs on Bose-Einstein condensation (BEC), quantum teleportation, and slow light. This impact showed up quantitatively in the citations of the BEC field as a larger proportion of references from during and shortly after these events.

Periodic silicon nanostructures can be used for different kinds of gas sensors depending on the analyte concentration. First we present an optical gas sensor based on the classical non-dispersive infrared technique for ppm-concentration using ultra-compact photonic crystal gas cells 1 . It is conceptually based on low group velocities inside a photonic crystal gas cell and anti-reflection layers coupling light into the device. Experimentally, an enhancement of the CO 2 infrared absorption by a factor of 2.6 to 3.5 as compared to an empty cell, due to slow light inside a 2D silicon photonic crystal gas cell, was observed; this is in excellent agreement with numerical simulations. In addition we report on silicon nanotip arrays 2 , suitable for gas ionization in ion mobility microspectrometers (micro-IMS) having detection ranges in principle down to the ppt-range. Such instruments allow the detection of explosives, chemical warfare agents, and illicit drugs, e.g., at airports. We describe the fabrication process of large-scale-ordered nanotips with different tip shapes. Both silicon microstructures have been fabricated by photoelectrochemical etching of silicon.

We demonstrate that the resonance of metallic split-ring resonators can interact with Bragg phase interference effects in a surrounding one-dimensional photonic crystal in such a way that a zero-bandwidth mode arises within the photonic band gap of the crystal. The band can also be designed to exhibit forward or backward slow-light propagation. We present a very simple model to explain these phenomena and verify the results with numerical simulations. The dynamic tuning of the structure has potential for stopping light or time-reversal applications.

We report on the investigation of four-wave mixing (FWM) in a long (1.3 mm) dispersion-engineered Gallium Indium Phosphide (GaInP) photonic crystal (PhC) waveguide. A comparison with a non-engineered design is made with respect to measured FWM efficiency maps. A striking different response is observed, in terms of dependence on the pump wavelength and the spectral detuning. The benefits and the limitations of both structures are discussed, in particular the trade-off between slow-light enhancement of the FWM efficiency and the conversion bandwidth. The time-resolved parametric conversion of short pulses at 10 GHz is also shown. Finally, the transmission capability of a 40 Gbit/s RZ signal is assessed through bit-error rate measurements, revealing error-free operation with only 1dB penalty.

We analyze the resonant linear and nonlinear transmission through a photonic crystal waveguide sidecoupled to a Kerr-nonlinear photonic crystal resonator. First, we extend the standard coupled-mode theory analysis to photonic crystal structures and obtain explicit analytical expressions for the bistability thresholds and transmission coefficients which provide the basis for a detailed understanding of the possibilities associated with these structures. Next, we discuss limitations of standard coupled-mode theory and present an alternative analytical approach based on the effective discrete equations derived using a Green's function method. We find that the discrete nature of the photonic crystal waveguides allows a geometry-driven enhancement of nonlinear effects by shifting the resonator location relative to the waveguide, thus providing an additional control of resonant waveguide transmission and Fano resonances. We further demonstrate that this enhancement may result in the lowering of the bistability threshold and switching power of nonlinear devices by several orders of magnitude. Finally, we show that employing such enhancements is of paramount importance for the design of all-optical devices based on slow-light photonic crystal waveguides.

Large and periodically corrugated optical waveguide structures are shown to possess specific modal regimes of slow-light propagation that are easily attainable. The very multimode nature of the coupling is studied by employing coupled-mode theory and the plane-wave expansion method. Given a large enough light cone, associated with a surrounding medium with low enough refractive index, we notably identify a critical slowdown regime with an interesting bandwidth-slowdown product. Essential features of these original systems are further explored: the nature of the coupled modes, the role of gain, symmetry effects, polarization, and relation with photonic-crystal systems. Practical systems are introduced using finite-difference time-domain methods, which provides first-order rules for the use of the above phenomena and their implementation in devices.

We review the different types of dispersion engineered photonic crystal waveguides that have been developed for slow light applications. We introduce the group index bandwidth product (GBP) and the loss per delay in terms of dB ns −1 as two key figures of merit to describe such structures and compare the different experimental realizations based on these figures. A key outcome of the comparison is that slow light based on photonic crystals performs as well or better than slow light based on coupled ring resonators.

We consider the propagation of slow light with an orbital angular momentum (OAM) in a moving atomic medium. We have derived a general equation of motion and applied it in analysing propagation of slow light with an OAM in a rotating medium, such as a vortex lattice. We have shown that the OAM of slow light manifests itself in a rotation of the polarisation plane of linearly polarised light. To extract a pure rotational phase shift, we suggest to measure a difference in the angle of the polarisation plane rotation by two consecutive light beams with opposite OAM. The differential angle $\Delta\alpha_{\ell}$ is proportional to the rotation frequency of the medium $\omega_{\mathrm{rot}}$ and the winding number $\ell$ of light, and is inversely proportional to the group velocity of light. For slow light the angle $\Delta\alpha_{\ell}$ should be large enough to be detectable. The effect can be used as a tool for measuring the rotation frequency $\omega_{\mathrm{rot}}$ of the medium.

We consider the interaction of two weak probe fields of light with an atomic ensemble coherently driven by two pairs of standing wave laser fields in a tripod-type linkage scheme. The system is shown to exhibit a Dirac-like spectrum for light-matter quasiparticles with multiple dark states, termed spinor slow-light polaritons. They posses an ''effective speed of light'' given by the group velocity of slow light, and can be made massive by inducing a small two-photon detuning. Control of the two-photon detuning can be used to locally vary the mass including a sign flip. Particularly, this allows the implementation of the randommass Dirac model for which localized zero-energy (midgap) states exist with unusual long-range correlations.

PACS 42.50.Gy-Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption PACS 42.25.Bs-Wave propagation, transmission and absorption PACS 42.50.Nn-Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media Abstract-Electromagnetically induced transparency (EIT) is observed in gaseous 4 He at room temperature. Ultra-narrow (less than 10 kHz) EIT windows are obtained for the first time for purely electronic spins in the presence of Doppler broadening. The positive role of collisions is emphasized through measurements of the power dependence of the EIT resonance. The measurement of slow light opens up possible ways to applications.

We analyse the three-colour electromagnetically induced transparency for the D 1 transition in cold 87 Rb atoms. We report an enhancement of the electromagnetically induced emission of a drive field as an exclusive enhancement of the third-and fourth-rank components of the density matrix. Moreover, the gain experienced by the drive field is attributed to the influence of the quantum switching effect on the increased absorption of the probe field. The electromagnetically induced emission effect is employed to generate slow light Gaussian-wave trains with shape preserving. These soliton trains were not only generated in the drive channel as has been designated but also in the switch channel which reveals multiple-light storage phenomenon.

We present an optical gas sensor based on the classical nondispersive infrared technique using ultracompact photonic crystal gas cells. The ultracompact device is conceptually based on low group velocities inside a photonic crystal gas cell and low-reflectivity antireflection layers coupling light into the device. Experimentally, an enhancement of the CO 2 infrared absorption by a factor of 2.6 to 3.5 as compared to an empty cell, due to slow light inside a 2D silicon photonic crystal gas cell, was observed; this is in excellent agreement with numerical simulations. We show that, theoretically, for an optimal design enhancement factors of up to 60 are possible in the region of slow light. However, the overall transmission of bulk photonic crystals, and thus the performance of the device, is limited by fluctuations of the pore diameter. Numerical estimates suggest that the positional variations and pore diameter fluctuations have to be well below 0.5% to allow for a reasonable transmission of a 1 mm device.