Showing papers in "Journal of Optics in 2010"
TL;DR: In this paper, the spaser can perform functions of an ultrafast nanoamplifier in two modes: transient and bistable on the basis of quantum density matrix (optical Bloch) equations.
Abstract: Nanoplasmonics has recently experienced explosive development with many novel ideas and dramatic achievements in both fundamentals and applications The spaser has been predicted and observed experimentally as an active element—a generator of coherent local fields Even greater progress will be achieved if the spaser can function as an ultrafast nanoamplifier—an optical counterpart of the MOSFET (metal–oxide–semiconductor field effect transistor) A formidable problem with this is that the spaser has inherent feedback, causing quantum generation of nanolocalized surface plasmons and saturation and consequent elimination of the net gain, making it unsuitable for amplification We have overcome this inherent problem and shown that the spaser can perform functions of an ultrafast nanoamplifier in two modes: transient and bistable On the basis of quantum density matrix (optical Bloch) equations we have shown that the spaser amplifies with gain with a switching time fs (potentially, ~10 fs) This prospective spaser technology will further broaden both fundamental and applied horizons of nanoscience, in particular enabling ultrafast microprocessors working at 10–100 THz clock speed Other prospective applications are in ultrasensing, ultradense and ultrafast information storage, and biomedicine The spasers are based on metals and, in contrast to semiconductors, are highly resistive to ionizing radiation, high temperatures, microwave radiation, and other adverse environments
372 citations
TL;DR: In this paper, the authors review the fundamentals and applications of nanowires and microwires manufactured from optical fibres and present a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness.
Abstract: Optical fibre nanowires and microwires offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These distinctive features have been exploited in a wealth of applications ranging from telecommunication devices to sensors, from optical manipulation to high Q resonators. In this paper I will review the fundamentals and applications of nanowires and microwires manufactured from optical fibres.
346 citations
TL;DR: In this article, different types of dispersion engineered photonic crystal waveguides have been developed for slow light applications, and the group index bandwidth product (GBP) and the loss per delay in terms of dB ns −1 were compared.
Abstract: 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.
231 citations
TL;DR: In this article, a photonic crystal fiber based surface plasmonic resonance sensor is proposed, which consists of selectively metal-coated air holes containing analyte channels, which enhance the phase matching between the plasmic mode and the core-guided mode.
Abstract: We propose a novel design for a photonic crystal fiber based surface plasmonic resonance sensor. The sensor consists of selectively metal-coated air holes containing analyte channels, which enhance the phase matching between the plasmonic mode and the core-guided mode. Good refractive index sensitivity as high as 5500 nm/RIU (refractive index unit) can be achieved in the proposed structure. Compared with the entirely coated structure, the selectively coated sensor design demonstrates narrower resonance spectral width. Moreover, the greater resonance depth can improve the sensing performance in terms of signal to noise ratio (SNR). The improvements in spectral width and SNR can both contribute to a better detection limit for this refractive index sensor.
207 citations
TL;DR: In this article, the authors present a discussion of the characteristics of pulses containing spatio-temporal couplings, including their sources, a mathematical description and the interdependence of different couplings.
Abstract: The electric field of an ultrashort laser pulse often fails to separate into a product of purely temporal and purely spatial factors. These so-called spatio-temporal couplings constitute a broad range of physical effects, which often become important in applications. In this review, we compile some recent experimental and theoretical work on the understanding, avoidance and applications of these effects. We first present a discussion of the characteristics of pulses containing spatio-temporal couplings, including their sources, a mathematical description and the interdependence of different couplings. We then review different experimental methods for their characterization. Finally, we describe different applications of spatio-temporal couplings and suggest further schemes for their exploitation and avoidance.
202 citations
TL;DR: In this article, the relationship between the size of the dark focal spot and the polarization of the input light beam was investigated, and the results of the analysis provided the theoretical basis and reference for designing a STED system.
Abstract: The size of the dark focal spot directly determines the resolution and stability of stimulated emission depletion (STED) microscopy. This paper investigates the relationship between the size of the dark focal spot and the polarization of the input light beam. The types of fundamental polarization are discussed, their effects on the dark focal spot are compared and the optimized mode for each kind of polarization is proposed. The results of the analysis provide the theoretical basis and reference for designing a STED system.
199 citations
TL;DR: In this paper, the authors review recent work on the development of ultra-broadband OPAs and experimentally demonstrate pulses with durations approaching the single-cycle limit and almost continuous tunability from the visible to the mid IR.
Abstract: Ultrafast optical parametric amplifiers (OPAs) can provide, under suitable conditions, ultra-broad gain bandwidths and can thus be used as effective tools for the generation of widely tunable few-optical-cycle light pulses. In this paper we review recent work on the development of ultra-broadband OPAs and experimentally demonstrate pulses with durations approaching the single-cycle limit and almost continuous tunability from the visible to the mid-IR.
168 citations
TL;DR: In this article, the femtosecond laser-induced multi-photon polymerization of a zirconium-silicon based sol-gel photopolymer was employed for the fabrication of a series of micro-optical elements with single and combined optical functions: convex and Fresnel lenses, gratings, solid immersion lenses on a glass slide and on the tip of an optical fiber.
Abstract: The femtosecond laser-induced multi-photon polymerization of a zirconium–silicon based sol–gel photopolymer was employed for the fabrication of a series of micro-optical elements with single and combined optical functions: convex and Fresnel lenses, gratings, solid immersion lenses on a glass slide and on the tip of an optical fiber. The microlenses were produced as polymer caps of varying radii from 10 to 90 µm. The matching of refractive indices between the polymer and substrate was exploited for the creation of composite glass-resist structures which functioned as single lenses. Using this principle, solid immersion lenses were fabricated and their performance demonstrated. The magnification of the composite solid immersion lenses corresponded to the calculated values. The surface roughness of the lenses was below ~ 30 nm, acceptable for optical applications in the visible range. In addition, the integration of micro-optical elements onto the tip of an optical fiber was demonstrated. To increase the efficiency of the 3D laser polymerization, the lenses were formed by scanning only the outer shell and polymerizing the interior by exposure to UV light.
160 citations
TL;DR: Multiphoton polymerization has been developed as a direct laser writing technique for the preparation of complex 3D structures with resolution beyond the diffraction limit of light as mentioned in this paper, where the combination of two or more hybrid materials with different functionalities in the same system has allowed the extraction of structures with advanced properties and functions.
Abstract: Multiphoton polymerization has been developed as a direct laser writing technique for the preparation of complex 3D structures with resolution beyond the diffraction limit of light. The combination of two or more hybrid materials with different functionalities in the same system has allowed the preparation of structures with advanced properties and functions. Furthermore, the surface functionalization of the 3D structures opens new avenues for their applications in a variety of nanobiotechnological fields. This paper describes the principles of 2PP and the experimental set-up used for 3D structure fabrication. It also gives an overview of the materials that have been employed in 2PP so far and depicts the perspectives of this technique in the development of new active components.
153 citations
TL;DR: In this paper, the authors describe the underlying theory developed for shallow gratings, but whose conclusions can be extended to planar photonic crystal waveguides, in particular the enhancement of third-order nonlinear processes with slow light.
Abstract: We review recent advances related to slow light in periodic structures, where the refractive index varies along one or two directions, i.e. gratings and planar photonic crystals. We focus on how these geometries are conducive to enhancing the nonlinear interaction between light and matter. We describe the underlying theory developed for shallow gratings, but whose conclusions can be extended to planar photonic crystal waveguides, in particular the enhancement of third-order nonlinear processes with slow light. We review some experiments showing how gratings have been used for pulse compression and the generation of slow gap solitons. We then present recent nonlinear experiments performed in photonic crystal waveguides that demonstrate the strong reinforcement of nonlinear third-order optical phenomena with slow light. We discuss the challenges associated with slow light in these 2D structures and their unique advantage—dispersion engineering—for creating broadband nonlinear devices for all-optical signal processing. By breaking down the relation between dispersion and group velocity imposed in gratings, these structures also offer new opportunities for generating soliton-like effects over short length scales, at low powers and with short pulses.
120 citations
TL;DR: In this paper, a review of supercontinuum generation in optical fibres with high power pulse sources in the modulation instability regime is presented, including the use of cascaded and tapered photonic crystal fibres.
Abstract: Supercontinuum generation in optical fibres pumped with high power pulse sources in the modulation instability regime is reviewed. The physical mechanisms and supercontinuum dynamics are described in detail. Routes to optimized output in terms of spectral flatness and particularly blue and ultraviolet spectral extent are presented, including the use of cascaded and tapered photonic crystal fibres.
TL;DR: In this article, a comparative study of lossy mode resonances generated by depositing two different materials, namely indium tin oxide (ITO) and indium oxide, is presented.
Abstract: A comparative study of lossy mode resonances generated by depositing two different materials is presented. The two materials selected are indium tin oxide (ITO) and indium oxide. The two materials present different dielectric dispersion, which leads to the generation of single-peak lossy mode resonances with the ITO coated optical fibers and dual-peak lossy mode resonances with the In2O3 coated optical fibers. The obvious advantage of a dual-peak based measurement in the sensors field is enhanced by a sensitivity increase observed in sensors based on In2O3 if compared with those based on ITO. These characteristics are analyzed both theoretically and experimentally.
TL;DR: In this article, a femtosecond laser-induced photopolymerization is used to construct microlenses for microscopy applications, where the fabrication resolution is not restricted to the diffraction limit for the applied laser excitation wavelength but is determined by the intensity of a focused beam.
Abstract: Light-initiated quasi-instant solidification of a liquid polymer is attractive for its ultra-precise spatial and temporal control of the photochemical reaction. In this paper we present microlenses structured by femtosecond laser-induced photopolymerization. Due to nonlinear phenomena the fabrication resolution is not restricted to the diffraction limit for the applied laser excitation wavelength but is determined by the intensity of a focused beam. Furthermore, pin-point structuring enables one to produce three-dimensional structures of any form from the photopolymer. The smallest structural elements of 200 nm lateral dimensions can be achieved reproducibly by using high numerical aperture oil immersion focusing optics (NA = 1.4). Axial resolution (which is fundamentally a few times worse than lateral resolution due to the distribution of light intensity in the focal region) can be controlled to a precision of a few hundred nanometers by decreasing the scanning step. In our work we applied the commercially available and widely used zirconium–silicon based hybrid sol–gel photopolymer (Ormosil, SZ2080). Arrays of custom-parameter spherical microlenses for microscopy applications have been fabricated. Their surface roughness, focal distance and imaging quality were tested. The obtained results show potential for fast and flexible fabrication of custom-parameter microlenses by the proposed technique.
TL;DR: In this article, a self-consistent computational scheme for one-dimensional and two-dimensional (2D) metamaterial systems with gain incorporated into the nanostructures is presented.
Abstract: A self-consistent computational scheme is presented for one-dimensional (1D) and two-dimensional (2D) metamaterial systems with gain incorporated into the nanostructures. The gain is described by a generic four-level system. The loss compensation and the lasing behavior of the metamaterial system with gain are studied. A critical pumping rate exists for compensating the losses of the metamaterial. There exists a wide range of input signals where the composite system behaves linearly. Nonlinearities arise for stronger signals due to gain depletion. The retrieved effective parameters are presented for one layer of gain embedded in two layers of Lorentz dielectric rods and split ring resonators (SRR) with two different gain inclusions: (1) gain is embedded in the gaps only and (2) gain is surrounding the SRR. When the pumping rate increases, there is a critical pumping rate at which the metamaterial system starts lasing.
TL;DR: Coupled-ring resonator-based slow light structures are reported and discussed by combining the advantages of high index contrast silicon-on-insulator technology with an efficient thermo-optical activation as mentioned in this paper.
Abstract: Coupled-ring resonator-based slow light structures are reported and discussed By combining the advantages of high index contrast silicon-on-insulator technology with an efficient thermo-optical activation, they provide an on-chip solution with a bandwidth of up to 100 GHz and a slowdown factor of up to 16, as well as a continuous reconfiguration scheme and a fine tunability The performance of these devices is investigated in detail for both static and dynamic operation, in order to evaluate their potential in optical signal processing applications at high bit rate The main impairments imposed by fabrication imperfections are also discussed in relation to the slowdown factor In particular, the analysis of the impact of backscatter, disorder and two-photon absorption on the device transfer function reveals the ultimate limits of these structures and provides valuable design rules for their optimization
TL;DR: The stochastic gradient descent approach, which is a useful tool in machine learning, is adopted to train the mask design and simulation shows that the proposed algorithm is effective in producing robust masks.
Abstract: Inverse lithography technology (ILT) synthesizes photomasks by solving an inverse imaging problem through optimization of an appropriate functional. Much effort on ILT is dedicated to deriving superior masks at a nominal process condition. However, the lower k1 factor causes the mask to be more sensitive to process variations. Robustness to major process variations, such as focus and dose variations, is desired. In this paper, we consider the focus variation as a stochastic variable, and treat the mask design as a machine learning problem. The stochastic gradient descent approach, which is a useful tool in machine learning, is adopted to train the mask design. Compared with previous work, simulation shows that the proposed algorithm is effective in producing robust masks.
TL;DR: In this paper, conditions of the light confinement by excitation of the trapped mode resonances in certain structures, both polarization-sensitive and polarization-insensitive, were studied, and the existence of a high-order trapped mode resonance with the greater quality factor than that of the lowest one has been shown.
Abstract: The problem of the near-IR light reflection from and transmittance through a planar 2D periodic metal–dielectric structure with a square periodic cell of two complex-shaped asymmetric metal elements has been solved. Conditions of the light confinement by excitation of the trapped mode resonances in certain structures, both polarization-sensitive and polarization-insensitive, were studied. For the first time, the existence of a high-order trapped mode resonance with the greater quality factor than that of the lowest one has been shown. It was ascertained that the Babinet principle provides a good prediction of the resonance properties of the complementary structures, despite the very high Joule losses in the metal strips in near-IR, a finite thickness of the metal elements and the presence of a dielectric substrate.
TL;DR: An overview over typical medical indications for ultrashort pulse laser surgery, the optics of the tissues involved, the available laser technology, the laser–tissue interaction process, and possible future developments is given.
Abstract: The strongly localized interaction process of ultrashort laser pulses with tissue makes femtosecond lasers a powerful tool for eye surgery. These lasers are now routinely used in refractive surgery and other forms of surgery of the anterior segment of the eye. Several clinical laser systems also offer options for corneal grafting and the potential use of ultrashort pulse lasers in glaucoma surgery has been the object of several recent studies which have shown promising results. While devices aimed for interventions in clear tissue may be based on available solid state or fibre laser technology, the development of tools for surgery in more strongly scattering tissue has to account for the compromised tissular transparency and requires the development of optimized laser sources. The present paper focuses on surgery of clear and pathological cornea as well as sclera. It aims to give an overview over typical medical indications for ultrashort pulse laser surgery, the optics of the tissues involved, the available laser technology, the laser–tissue interaction process, and possible future developments.
TL;DR: In this article, the spatial light modulators (SLMs) in a holographic tweezers system can be used as the principal element of a wavefront sensor and the corrective element in a closed-loop adaptive optics system.
Abstract: Holographic optical tweezers allow the creation of multiple optical traps in 3D configurations through the use of dynamic diffractive optical elements called spatial light modulators (SLMs). We show that, in addition to controlling traps, the SLM in a holographic tweezers system can be both the principal element of a wavefront sensor and the corrective element in a closed-loop adaptive optics system. This means that aberrations in such systems can be estimated and corrected without altering the experimental setup. Aberrations are estimated using the Shack–Hartmann method, where an array of spots is projected into the sample plane and the distortion of this array is used to recover the aberration. The system can recover aberrations of up to ten wavelengths peak–peak, and is sensitive to aberrations much smaller than a wavelength. The spot pattern could also be analysed by eye, as a tool for aligning the system.
TL;DR: In this article, random lasing emission spectra have been collected from both healthy and cancerous tissues, and the two types of tissue with optical gain have different light scattering properties as obtained from an average power Fourier transform of their random LAS spectra.
Abstract: Random lasing emission spectra have been collected from both healthy and cancerous tissues. The two types of tissue with optical gain have different light scattering properties as obtained from an average power Fourier transform of their random lasing emission spectra. The difference in the power Fourier transform leads to a contrast between cancerous and benign tissues, which is utilized for tissue mapping of healthy and cancerous regions of patients.
TL;DR: In this article, the authors studied the stimulated emission in a random laser based on rhodamine 6G dye and TiO2 nanoparticles and found that the threshold reached its maximum at the transition from a weak scattering regime to a strong scattering regime when the transport mean free path lt is approximately equal to the absorption length lt.
Abstract: We have studied stimulated emission in a random laser based on rhodamine 6G dye and TiO2 nanoparticles. At both small and large concentrations of nanoparticles, the minimum threshold was found at ultra-high concentrations of dye, 20?g?L?1. With the increase in concentration of TiO2 nanoparticles, the threshold reaches its maximum at the transition from a weak-scattering regime to a strong-scattering regime, when the transport mean free path lt is approximately equal to the absorption length la. At the same value of lt, the random laser emission qualitatively changes its behavior. The experimental results are in good agreement with the predictions of a heuristic model.
TL;DR: Some numerical simulations have validated the feasibility of the proposed image encryption scheme and the parameters in the affine transform and the gyrator transform are regarded as the key for the encryption algorithm.
Abstract: We propose a kind of double-image-encryption algorithm by using the affine transform in the gyrator transform domain. Two original images are converted into the real part and the imaginary part of a complex function by employing the affine transform. And then the complex function is encoded and transformed into the gyrator domain. The affine transform, the encoding and the gyrator transform are performed twice in this encryption method. The parameters in the affine transform and the gyrator transform are regarded as the key for the encryption algorithm. Some numerical simulations have validated the feasibility of the proposed image encryption scheme.
TL;DR: In this article, the authors review recent extensions of semiclassical multimode laser theory to open systems with overlapping resonances and inhomogeneous refractive index, and discuss applications of the theory, as well as other experimental and numerical results related to random lasing with mode competition.
Abstract: We review recent extensions of semiclassical multimode laser theory to open systems with overlapping resonances and inhomogeneous refractive index. An essential ingredient of the theory is a system of biorthogonal quasimodes that describe field decay in an open passive system and are used as a basis for lasing modes. We discuss applications of the semiclassical theory, as well as other experimental and numerical results related to random lasing with mode competition.
TL;DR: In this article, the authors investigated the normal incidence transmission through periodically and randomly arranged planar split ring resonators (SRRs) in terahertz time-domain spectroscopy.
Abstract: Using terahertz time-domain spectroscopy, we investigate the normal incidence transmission through periodically and randomly arranged planar split ring resonators (SRRs). The introduction of positional disorder in metamaterials has no effect on the quality factor of the fundamental inductive-capacitive (LC) resonance. The dipole resonances undergo broadening and shift in their resonance frequencies. The experiment reveals that the randomly distributed SRR structures interact incoherently at LC resonance but couple coherently at the higher frequency dipole resonance.
TL;DR: The extreme versatility of the internal conical refraction in biaxial crystals in the transformation of Gaussian laser beams is demonstrated and discussed in this article, by means of simple variations in the focusing and polarization of the input beam.
Abstract: The extreme versatility of the internal conical refraction in biaxial crystals in the transformation of Gaussian laser beams is demonstrated and discussed. By means of simple variations in the focusing and polarization of the input beam, various beam configurations like Bessel–Gauss, Hermite–Gauss, Laguerre–Gauss, and others are shown to be produced from a lowest-order Gaussian beam passed through a biaxial crystal along one of its optical axes. Further transformations of the beam profile and formation of more complex light patterns were obtained in a cascaded scheme, when the beam was passed consecutively through two crystals. These observations, together with the known ability of conical refraction to form a variety of other complex light structures, demonstrate the unique properties of the effect in manipulations with the amplitude, phase, and polarization of light beams.
TL;DR: In this article, the authors proposed a new approach that enables full control over the three-dimensional state of polarization and the field distribution near the focus of a high numerical aperture objective lens.
Abstract: We propose a new approach that enables full control over the three-dimensional state of polarization and the field distribution near the focus of a high numerical aperture objective lens. By combining the electric dipole radiation and a vectorial diffraction method, the input field at the pupil plane for generating arbitrary three-dimensionally oriented linear polarization at the focal point with a diffraction limited spot size is found analytically by solving the inverse problem. Arbitrary three-dimensional elliptical polarization can be obtained by introducing a second electric dipole oriented in the orthogonal plane with appropriate amplitude and phase differences.
TL;DR: In this paper, a phase modulation of the surface plasmon provided by the dielectric block with varying geometric parameters located on the interface is proposed, based on a rigorous coupled wave analysis.
Abstract: We present a method of designing diffractive optical elements for transforming and focusing surface plasmons. The method is based on a phase modulation of the surface plasmon provided by the dielectric block with varying geometric parameters located on the interface. The problem of SP diffraction by a dielectric block is solved using the rigorous coupled wave analysis. We demonstrate that the modulation can be implemented not only by changing the length of the dielectric block at fixed height, but also by changing the height at fixed length as well as by simultaneous changing of both parameters. The height modulation and combined height–length modulation are believed to be considered for the first time. As an example, the design of diffractive elements for focusing surface plasmons is considered. It is demonstrated that combining the height and length modulations allows us to increase the diffraction efficiency by more than 10%.
TL;DR: In this article, a review on random lasing properties of organic nanofibers made of oligophenyl nanocrystals grown by molecular epitaxy on polar substrates is presented.
Abstract: We present a review on random lasing in organic nanofibers made of oligophenyl nanocrystals grown by molecular epitaxy on polar substrates. The nanofibers have sub-wavelength cross-sectional dimensions and can extend in length up to the millimeter scale. We report on random lasing properties of nanofibers, under subpicosecond photopumping, both in the coherent and incoherent regimes. With the aid of both optical and morphological studies on individual fibers, we get insight into one-dimensional coherent feedback taking place along the nanofibers' axes. Model calculations of light propagation in disordered media allow us to give a semiquantitative description of one-dimensional coherent random lasing near the lasing threshold. We also report on amplified simulated emission in individual nanofibers and demonstrate that nanoscale linear optical amplifiers can be obtained by molecular self-assembly at surfaces. Photophysical studies of nanofibers resorting to subpicosecond luminescence and pump–probe spectroscopy give us valuable information on temperature-dependent, excited-state nonlinear processes, such as exciton–exciton annihilation and photoinduced absorption. Excited-state effects strongly influence lasing thresholds under quasi-continuous-wave photoexcitation conditions, as demonstrated in photoexcitation experiments performed with nanosecond pulses. Last, we briefly discuss the potential of organic epitaxial nanofibers featuring low-threshold random lasing for photonic sensing applications.
TL;DR: In this paper, the optical properties of active coated spherical nano-particles excited by an arbitrarily located electric Hertzian dipole are investigated, and the spatial near-field distribution as well as the normalized radiation resistance is examined.
Abstract: The present work investigates the optical properties of active coated spherical nano-particles excited by an arbitrarily located electric Hertzian dipole. The nano-particles are made of specific dielectric and plasmonic materials. The spatial near-field distribution as well as the normalized radiation resistance is examined. Both enhanced as well as reduced radiation effects are demonstrated. In particular, it is shown that specific active coated nano-particles can be designed to be resonant, leading to much larger values of the normalized radiation resistance than is the case with the corresponding passive coated nano-particles, thereby overcoming the intrinsic losses present in the plasmonic materials. Moreover, it is shown that other active coated nano-particle designs can significantly reduce the normalized radiation resistance; thus both the resonant as well as non-radiating/transparent states of the active coated nano-particle are identified. Implications of both the resonant and non-radiating states on the previously proposed localized sensors based on the active coated nano-particle will also be considered here.
TL;DR: In this paper, an overview of the experimental methods, based on both linear and nonlinear atom-light interaction, that have produced superluminal propagation in atomic media, and discuss some of the significant theoretical contributions to the issues of pulse preservation and reconciling faster-than-light propagation and the principle of causality.
Abstract: Atomic media have played a major role in studies of fast light. One of their attractive features is the ability to manipulate experimental parameters to control the dispersive properties that determine the group velocity of a propagating light pulse. We give an overview of the experimental methods, based on both linear and nonlinear atom–light interaction, that have produced superluminal propagation in atomic media, and discuss some of the significant theoretical contributions to the issues of pulse preservation and reconciling faster-than-light propagation and the principle of causality. The comparison of storage of light, enhanced Kerr nonlinearity and efficient wave mixing processes in slow and fast light atomic media illustrates their common and distinct features.