This PDF file contains the front matter associated with SPIE Proceedings Volume 7226, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

This paper reports two advances in a slow light device consisting of chirped photonic crystal slab coupled waveguide on SOI substrate. One is concerning the delay-bandwidth product, indicating the buffering capacity of the device. We experimentally evaluated a record high value of 57 (a 40 ps delay and a 1.4 THz bandwidth). We also observed a few picosecond wide optical pulse transmission in the cross-correlation measurement. Regarding the pulse as a signal and considering the broadening of the pulse width due to the imperfect dispersion compensation in the device, storage of more than 12 signal bits was confirmed. The other is a widerange tuning of the pulse delay. We propose a technique for externally controlling the chirping to permit variable delay. We demonstrate tuning of the pulse delay up to 23 ps, maintaining the average pulse width to be 3.3 ps. It corresponds to the tunable time shift of 8 bits and a ~7 mm extension of the free space length.

Slow-light techniques are promising for obtaining tunable delay lines which are potential candidates for bit synchronization and buffer applications in optical packet switching networks. We describe a theoretical study on slowlight in optical fibers based on stimulated Brillouin scattering (SBS). A general model for resonant three-wave nonlinear interactions between a pump beam, an acoustic wave and a counterpropagating signal pulse is proposed. Analytic and numerical solutions of the three-wave coupled equations are obtained for the steady-state and the transient regimes, respectively. Space-time evolutions of a generating slow-light pulse for both small-signal and pump-depletion (or gainsaturation) cases in the above two regimes are given and compared, for different pump powers and signal pulse widths. The physical origin of broadening and distortion of slow-light pulse is discussed. Optimum design considerations for undistorted slow-light signal propagation also are discussed.

It has been shown that doubly resonant microcavities can be used to obtain miniaturized parametric devices leading for example to efficient second-harmonic generation (SHG). First we will briefly recall the basic properties of SHG in III-V semiconductor whispering gallery mode microdisks or microrings. Then we will show theoretically that by coupling such microresonators and by using the artificial dispersion of a side-coupled integrated spaced sequence of resonators (SCISSOR) it is possible to adapt the Fresnel phase-matching technique to the case of highly confining waveguides or to enhance the second order nonlinear properties of a semiconductor waveguide by slowing fundamental and second-harmonic waves.

Reduced density matrix descriptions are developed for linear and non-linear interactions in electromagnetically induced transparency and related pump-probe optical phenomena involving moving atomic systems. Applied magnetic fields as well as atomic collisions, together with other environmental decoherence and relaxation processes, are taken into account. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. The standard Born (lowest-order perturbation-theory) and Markov (short-memory-time) approximations are systematically introduced within the framework of the general non-perturbative and non-Markovian formulations. A preliminary semiclassical treatment of the electromagnetic interaction is adopted. However, the need for a fully quantum mechanical approach is emphasized. Compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear macroscopic electromagnetic-response tensors within the framework of a perturbation-theory treatment of the semiclassical electromagnetic interaction. These expressions can be evaluated for coherent initial atomic excitations and for the full tetradic-matrix form of the Liouville-space self-energy operator representing the environmental interactions in the Markov approximation. Collisional interactions between atoms can be treated in various approximations for the self-energy operator, and the influence of Zeeman coherences on the electromagnetic-pulse propagation can be investigated.

Cold atoms confined inside a hollow-core photonic-crystal fiber with core diameters of a few photon wavelengths are a promising medium for studying nonlinear optical interactions at extremely low light levels. The high electric field intensity per photon and interaction lengths not limited by diffraction are some of the unique features of this system. Here, we present the results of our first nonlinear optics experiments in this system including a demonstration of an all-optical switch that is activated at energies corresponding to few hundred optical photons per pulse.

Application of slow light linear delay to squint-free (true-time delay) steering of phased array radar antennae is discussed. Theoretical analysis is provided on true-time delay radar requirements, including delay precision, amplitude precision, and bandwidth. We also discuss an improvement to the slow light technique based on stimulated Brillouin scattering by using a Faraday rotator mirror that provides temporally stable, linear (with pump power) delay, applicable to practical implementations. Future directions are considered.

The ubiquitous role of optical fibers in modern photonic systems has stimulated research to realize slow and fast light devices directly in this close-to-perfect transmission line. Recent progress in developing optically-controlled delays in optical fibers, operating under normal environmental conditions and at telecommunications wavelengths, has paved the way towards real applications for slow and fast light. Advanced schemes can be realized thanks to the extremely flexible possibility to shape the gain spectrum to make it optimized for applications. Ultra wide bandwidth, delaying with flat amplitude response and lower distortion were successfully demonstrated this way.

We demonstrate numerically that acoustooptic interaction between two co-propagating modes in an optical fiber can be utilized to obtain positive and negative delays. A single acousto-optic interaction region, and a configuration based on two acousto-optic interaction regions, separated by a section of unperturbed fiber, are simulated. It is found that the delays and advancements can be several pulse lengths in the configuration with two acoustooptic coupling regions separated by a section of unperturbed fiber. These results are not in conflict with relativistic causality, but are a consequence of the difference in group velocity between the two coupled modes.

We report a preliminary experimental study of EIT and stored light in the high optical depth regime. In particular, we characterize two ways to mitigate radiation trapping, a decoherence mechanism at high atomic density: nitrogen as buffer gas, and a long, narrow cell geometry. Initial results show the promise of both approaches in minimizing radiation trapping, but also reveal problems such as optical pumping into trapped end-states. We also observe distortion in EIT lineshapes at high optical depth, a result of interference from four-wave mixing. Experimental results are in good qualitative agreement with theoretical predictions.

We present a realistic theoretical treatment of a three-level Λ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. We take into account a dynamic rate of influx of atoms in the two lower levels of the Λ, and an outflux from all the three levels. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. Our predictions are in excellent agreement with the reported experimental results for ⁴He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

In a Λ-type atomic system with electromagnetically-induced transparency, we probe the fidelity of the storage and retrieval of an electromagnetic signal, as the control laser field is varied with time. We study numerically the adiabatic transfer problem for an isolated atom, and show that for a weak signal, even the slowest variations of the control field take the system out of the dark state, which is a coherent superposition of the two lower levels of the Λ system. Following this, we incorporate the effect of dissipation on system dynamics by allowing for spontaneous decay of the system to the lower levels in a wavefunction approach. We conclude that dissipation definitely aids the retrieval process but not so much the storage. Further, for storing the signal, the control field should be switched off as slowly as possible, but while retrieving it, the faster we switch on the control field, the better the signal is retrieved. Also, for a given system there is an optimal control power for the best retrieval. Our results find partial support in the reported experimental observations.

One fundamental aspect of photonic technology has always been the quest for the perfect light-guiding system, which would exhibit, over a large frequency bandwidth, subwavelength modes of controllable (with special interest lately on small [1]) group velocity and small attenuation, both devoid of frequency dispersion [2]. If this were possible, a temporally and spatially tiny wavepacket would basically propagate without changing shape but only with slowly uniformly decreasing size. Such a system is yet not known to exist in nature, as none of the existing material platforms can achieve simultaneously all of the above attributes, but at most only a subset. All-dielectric structures [3] cannot support highly-subwavelength light propagation, which can be attained by exploiting (bulk or surface) polaritons in plasmonic [4-14] or other resonant-material (e.g. atomic, excitonic, phononic [15, 16]) waveguiding structures, which typically suffer though from high absorption losses. The one problem, however, that is commonly shared among all existing photonic systems is modal dispersion. In particular, for slow- [17-25] and stopped- [26-28] light systems, dispersion is the major reason there is a limitation on their achievable so-called 'bandwidth-delay product' [29-34]. This fact has thus motivated the recent invention of a few advanced dispersion-cancellation schemes, which make use of coupled geometric [35] or gain-material [36] resonances or a fine balance of dispersion with nonlinearities [37]. It was also pointed out recently [38] that layered axially-uniform plasmonic-dielectric-hybrid waveguiding systems can guide broadband slow and subwavelength light, but the proposed systems were still dispersion-limited. In this Article, we show that such multilayered Surface-PlasmonoDielectric-Polaritonic (SPDP) systems allow for a new physical mechanism, which enables their inherently-single-polarization surface-polaritonic modes to additionally have - for small positive, negative or zero group-velocity - the dispersion coefficients of simultaneously both the group velocity and the attenuation systematically cancelled to unusually high orders, thus leading to the first linear passive system in nature, known to us, that essentially is dispersionless and breaks the 'bandwidth-delay product' limitation. By arguing [38] that, in the absence of disorder, attenuation may also, in principle, be reducible by cooling, these material systems approach the ideal slow-light-guiding system. Furthermore, they can also be tailored to invent a variety of novel intricate dispersion relations with multiple points of zero group velocity. The applications of this class of guiding systems in the technological realm of nanophotonics could be substantial.

Surface Plasmon polaritons are unique waves propagating on metal interfaces and exhibiting special dispersion characteristics which include wave slowing (phase velocity) light slowing (group velocity), fast light (negative group velocity) and even stopped light. Here we track the mechanisms for the light slowing and reversing (backward propagation) in a plasmonic structure based on a dielectric gap between two metal plates. Three major driving forces - which are determining the dispersion characteristics were identified and the role of the unique circular light flow in plasmonic structure is discussed

Recently there has been a considerable interest in metamaterial waveguide structures capable of dramatically slowing down or, even, completely stopping light. Here, we shall explain in some detail the working principle behind the deceleration and/or stopping of light in metamaterial structures, and review the various, metamaterial-enabled, methods that have been proposed thus far towards achieving such a goal. Further, we will concisely describe how one can construct zero-loss metamaterials over a continuous and broad (but not infinite) range of frequencies, which is an essential prerequisite for any slow-light system. Moreover, it will be explained that inside such waveguide structures light can in principle be stopped (zero group velocity, v_g = 0) even in the presence of losses. By nature, metamaterialenabled schemes for stopping/storing light invoke solid-state materials and, as such, are not subject to low-temperature or atomic coherence limitations. Furthermore, these methods simultaneously allow for broad bandwidth operation, since they do not rely on group index resonances; large delay-bandwidth products, since a wave packet can, in principle, be completely stopped and buffered indefinitely; and (for the case, in particular, where a negative-index metamaterial is used) high, almost 100%, in/out-coupling efficiencies. Thus, we conclude that these methods for trapping photons, which can be realised using existing technology, could open the way to a multitude of hybrid optoelectronic devices to be used in 'quantum information' processing, communication networks and signal processors and may conceivably herald a new realm of combined metamaterials and slow light research.

We theoretically and experimentally study the Rabi splitting induced by photon tunneling modes in a paired structure composed of a permittivity-negative medium and a permeability-negative medium. It is shown that a tunneling mode will appear at the frequency where the paired structure is equivalent to a media with effective (near) zero refractive index. A cavity may be realized with features: subwavelength cavity size and exponentially increasing of the optical field. Therefore, the photon tunneling mode in a metamaterial with effective (near) zero refractive index may be used as a cavity with highly localized field and small volume.

We propose a new scheme for manipulating optical information by trapping and releasing optical pulses propagating in an array of coupled semiconductor lasers. The manipulation of the optical pulses is achieved directly by changing the pump parameter of the individual lasers. Applications such as optical routing, delay lines and memories are studied in detail.

We describe a dynamically-tuned system capable of capturing light pulses incident from a waveguide in a pair of microcavities. We use coupled mode theory to design a method for determining how to tune the microcavity resonant frequencies. The results show that pulses can be captured almost completely, with arbitrarily small reflected power. We optimize the pulse capture bandwidth by varying the cavity coupling constants and show that the maximum bandwidth is comparable to the resonant-frequency tuning range. We demonstrate near complete pulse capture in FDTD simulations of a two cavity 2D photonic crystal implementation of the system. Current technology would allow for capture of pulses with widths as low as ~100ps, with a holding time limited only by cavity loss rates.

We present a simple method to determine simultaneously the transmission and dispersive properties of passive or active high Q-factor optical resonators. The method is based on cavity ring down spectroscopy where the probe wavelength is rapidly swept across the resonance. It has already been shown that this technique allows the loaded cavity lifetime of passive resonators to be obtained. Here we show that we can also infer the dispersion introduced by the resonator and the resonant gain in the case of active resonators. The method is tested on a model system consisting of fiber resonators. We applied the method to measure the intrinsic Q-factor of a passive MgF₂ whispering gallery mode resonator. We also used it to characterize the high Q-factor of a system of coupled fiber resonators. Finally we show that the method can be used to determine the gain and dispersive properties of selective amplifiers such as Er³⁺ doped fiber resonators.

We reveal that the reduction of the group velocity of light in periodic waveguides is generically associated with the presence of vortex energy flows. We show that the energy flows are gradually frozen for slow-light at the Brillouin zone edge, whereas vortices persist for slow-light states having non-vanishing phase velocity inside the Brillouin zone. We also demonstrate that presence of vortices can be linked to the absence of slow-light at the zone edge, and present calculations illustrating these general results.

We demonstrate and explain interesting dynamics of both a pair of gap solitons or a single gap soliton in a resonant photonic crystal whusing both analytical and numerical methods. The most important result is the fact that we are able to show that the oscillating gap soliton created either by the presence of an inversion inside the crystal or by the Bragg resonance mismatch can be manipulated by means of a proper choice of bit rate, phase and amplitude modulation, or even by the resonance detuning We manage to obtain qualitatively different regimes of the resonance photonic crystal operation. A noticeable observation is that both the delay time and amplitude difference must exceed a certain level to ensure effective control over soliton dynamics. The modification of the defect that accomplishes the soliton trapping can make the dynamics of N soliton trains in the resonant photonic crystal with defects even more interesting and is a subject of the future work.

Two of the key aspects for operating photonic crystal waveguides in slow light regime are discussed: coupling and propagation losses. We show that a variety of techniques exist that allow coupling into the slow light regime with high efficiency and highlight that the nature of the slow mode (being a Bloch mode) needs to be taken into account. As to propagation losses, we show that the commonly accepted square dependence of the losses on the group velocity does not universally hold, and that a regime of low loss operation up to group indices of 30-40 exists.

We review the theory of slow and fast light effects due to coherent population oscillations in semiconductor waveguides, and potential applications of these effects in microwave photonic systems as RF phase shifters. In order to satisfy the application requirement of 360° RF phase shift at different microwave or millimeter-wave frequency bands, we present several schemes to increase the achievable RF phase shift by enhancing light slow-down or speed-up. These schemes include integrating gain and absorption sections, optical filtering and the exploitation of the initial chirp effects. As a real application in microwave photonics, a widely tunable microwave photonic notch filter with 100% fractional tuning range is also proposed and demonstrated.

By balancing the steep linear and nonlinear dispersions of an intracavity electromagnetically induced transparency medium, the cavity transmission spectra can be significantly modified and controlled. As the cavity input intensity increases, the cavity linewidth changes from far below to above the empty cavity linewidth, corresponding to the photon propagation in the cavity from "subluminal" to "superluminal", respectively. A "white-light cavity" condition has been achieved under certain experimental conditions.