This PDF file contains the front matter associated with SPIE Proceedings Volume 7949, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We evaluated the nonlinear enhancement in slow-light photonic crystal waveguides. The devices butt-joined to Si wire waveguides were fabricated on SOI substrate using CMOS-compatible process. Integrating spot size converter to the device allows high input power and clear enhancement. The coupling loss between lensed fiber and the wire was 3 - 4 dB. We observed two-photon absorption, self-phase modulation and four-wave mixing in the low power regime of less than 1 W, which is assisted by low-dispersion slow light. Such slow light can be exploited for compact functional components such as optical limiters and wavelength converters.

We develop a perturbation theory for slow-light photonic-crystal waveguides engineered to suppress group-velocity dispersion, and predict that weak material loss (gain) is enhanced proportionally to the slow-down factor, whereas the attenuation (amplification) rate saturates for loss (gain) exceeding a certain threshold. This happens due to hybridization of propagating and evanescent modes which allows significant intensity enhancement observed in our numerical simulations for photonic crystal waveguides even under strong material losses.

Optofluidics, the marriage of photonics and microfluidics, uses the inherent flexibility of confined fluids to reversibly tune photonic structures beyond traditional fabrication methods. Photonic crystals (PhCs) are well suited to optofluidic tuning; their periodic air-hole microstructure is a natural candidate for housing liquids. This microstructure enables PhCs to strongly control light on the wavelength scale. Defects purposefully introduced during PhC fabrication can support guided optical modes, forming waveguides or cavities; their dispersion can be engineered by fine alteration of individual PhC holes in or around the structure. This engineering requires very high fabrication tolerances and is irreversible once performed. Optofluidic tuning of PhC waveguides, however, is completely reversible and only limited by the properties of available fluids. Infiltration of the PhC microstructure surrounding a waveguide modifies the local refractive index profile through the liquid used and the amount of microstructure filled. In this paper we demonstrate experimentally for the first time, optofluidics dispersion engineer of photonic crystals waveguides. We have modified the group velocity dispersion using a technique based on selective liquid infiltrations to precisely and reversibly change our structures. We also present how the amount of fluid infiltrated into the photonic crystal microstructure strongly influences the waveguide dispersion.

Nonlinear photonic crystal (PhC) waveguides are being developed for ultrafast modulators. To enable phase velocity matching we have investigated one- and two-dimensional structures. Photonic crystal (PhC) waveguides based on epitaxial barium titanate (BTO) thin film in a Si₃N₄/BTO/MgO multilayer structure were fabricated by electron beam lithography or focused ion beam (FIB) milling. For both one- and two-dimensional PhCs, simulation shows that sufficient refractive index contrast is achieved to form a stop band. For one-dimensional Bragg reflector, we measured its slow light properties and the group refractive index of optical wave. For a millimeter long waveguide a 27 nm wide stop band was obtained at 1550 nm. A slowing of the light was observed, the group refractive indices at the mid band gap and at the band edges were estimated to be between 8.0 and 12 for the transverse electric (TE) mode, and 6.9 and 13 for the transverse magnetic (TM) mode. For TE optical modes, the enhancement factor of EO coefficient ranges from 7 to 13, and for the TM mode, the factor ranges from 5.9 to 15. Measurements indicate that near velocity phase matching can be realized. Upon realizing the phase velocity matching condition, devices with a small foot print with bandwidths at 490 GHz can be attained. Two-dimensional PhC crystal with a hexagonal lattice was also investigated. The PhCs were fabricated from epitaxial BTO thin film multilayers using focused ion beam milling. The PhCs are based on BTO slab waveguide and air hole arrays defined within Si₃N₄ and BTO thin films. A refractive index contrast of 0.4 between the barium titanate thin film multilayers and the air holes enables strong light confinement. For the TE optical mode, the hexagonal photonic crystal lattice with a diameter of 155 nm and a lattice constant of 740 nm yields a photonic bandgap over the wavelength range from 1525 to 1575 nm. The transmission spectrum of the PhC waveguide exhibits stronger Fabry Perot resonance compared to that of conventional waveguide. Measured transmission spectra show a bandgap in the ΓM direction in the reciprocal lattice that is in agreement with the simulated results using the finite-difference time-domain (FDTD) method. Compared to polarization intensity EO modulator with a half-wave voltage length product of 4.7 V•mm. The PhC based EO modulator has a factor of 6.6 improvement in the figure of merit performance. The thin film PhC waveguide devices show considerable potential for ultra-wide bandwidth electro-optic modulators as well as tunable optical filters and switches.

A photonic microcell (PMC) is a length of gas-filled hollow core-photonic crystal fiber (HC-PCF) which is hermetically sealed at both ends by splicing to standard single mode fiber. We describe advances in the fabrication technique of PMCs which enable large core Kagome-lattice HC-PCFs to be integrated into PMC form. The modified fabrication technique uses fiber-tapering to accommodate the large dimensions of the fiber and enables low loss splices with single mode fiber by reducing mode field mismatch. Splice losses as low as 0.6 dB are achieved between 1-cell defect Kagome HC-PCF and single mode fiber. Relative to the previously reported PMCs, which were based on photonic bandgap HC-PCF, the present Kagome HC-PCF based PMC provides broad optical transmission, surface mode-free guidance and larger core at the cost of slightly increased fiber attenuation (~0.2 dB/m). Therefore, the integration of this fiber into PMC form opens up new applications for PMC-based devices. The advantage of the large core dimensions and surface mode free guidance for quantum optics in gas-filled HC-PCF are demonstrated by generation of narrow sub-Doppler features in an acetylenefilled large core PMC.

Recent advances in tunable optical delays and their applications are discussed. Conversion/Dispersion based delays are highlighted including recent delays in excess of 3.6 μs for a 100-Gb/s signal and the application of delays towards optical buffering and signal processing. Limiting factors of achieving large conversion/dispersion delays are discussed as well as the techniques being used to overcome them. Finally, recent applications of these delays towards the implementation of optical tapped-delay-lines for optical equalization and correlation of amplitude and phase based signals is presented.

We study the slow light effect via stimulated Brillouin scattering (SBS) using broadly-tunable frequency-swept sources, such as that used in optical coherence tomography. Slow light can be achieved, in principle, over the entire transparency window of the optical fiber (many 100's of nm at telecommunication wavelengths). We demonstrate a SBS slow light delay of more than 1 ns over a wide bandwidth at 1.55 μm using a 2-km-long highly nonlinear fiber with a source sweep rate of 20 MHz/μs and a delay of 10 ns using a 10-m-long photonic crystal fiber with a sweep rate of 400 MHz/μs. We also find that, for a given sweep rate R, there is an optimum value of fiber length L to obtain the largest delay.

The polarization-related properties of stimulated Brillouin scattering (SBS) processes in long, randomly birefringent, standard optical fibers are examined. Evolution equations for the pump and signal waves, in the presence of both birefringence and SBS, are provided in Jones and Stokes spaces. It is shown that in the undepleted pump regime, the amplification of the SBS signal wave is equivalent to that of a linear medium with polarization-dependent gain. The process is associated with a pair of orthogonal states of polarizations (SOPs) of the signal wave, which undergo maximum and minimum amplification. In long, standard fibers, the Jones vector of the probe SOP which corresponds to maximum amplification is aligned with the complex conjugate of the pump wave Jones vector. The maximum and minimum SBS gain coefficients in such fibers equal two-thirds and one-third of the gain coefficient that is predicted by scalar theory, respectively. The large differential gain of the SBS process gives rise to an effective pulling of the amplified Stokes probe wave SOP, towards that of maximum amplification. Lastly, Stokes wave pulses that are aligned for maximum and minimum amplification experience different group delays, which manifest as polarization-related distortions in SBS slow light setups.

Slow light systems are particularly attractive for analog signal processing, since their inherent limitation to a delay-bandwidth product of 1 is less critical for analog systems such as those used in microwave photonics. We present here the implementation of two basic functions - phase shifting and true time delaying - fully optically controlled using stimulated Brillouin scattering in optical fibers. The combination of these two functions makes possible the implementation of true time delays without limitation on the microwave carrier frequency using the separate carrier tuning technique. This is illustrated by the implementation of the delaying system for the realization of a microwave tunable notch filter.

We demonstrate through numerical simulations that a fiber Bragg grating operated in transmission can support much slower light than previously anticipated. This is accomplished by increasing the grating's index modulation, reducing its loss, optimizing its length, and apodizing its index profile. With current fiber Bragg grating loss and index modulation, we predict that group velocities lower than c/1000 are attainable. We validate this concept with a record measured group index of 130 in a strong apodized grating (index modulation of ~1.1 10^-3) with a nearly optimized length of 1.2 cm and an inferred loss coefficient of 1 m^-1.

It is well-known that a transfer function method is useful to predict the profile of a pulse after it propagates through an intracavity fast-light medium. However, by using this technique, a behavior of the pulse inside the medium cannot be determined. In this paper, we describe a new theoretical approach to deal with this constraint. In the new method, we find an analytical solution for a monochromatic field of infinite spatial and temporal extents, and add the waves with the weighted amplitude and with the tailored phase to embody a Gaussian input pulse moving toward the cavity. At different time frames, the sum of these waves produces a spatial profile of the pulse before, inside and after the cavity. In particular, the pulse profile can be visualized during a superluminal propagation through the intracavity fast-light medium with zero group index. This model allows us to understand the physical process behind the superluminal propagation through a white light cavity, which is significant to realize a high bandwidth data buffer system overcoming conventional delay bandwidth product(DBP) problem.

The talk consists of two parts. In the first, we have demonstrated enhancement of nonlinear signals and suggested a new approach that extends Raman spectroscopy to media which has a high level of scattering. The stimulated Raman scattering has an advantage of relaxing phase-matching condition which is difficult or even impossible to meet under condition of strong scattering. The second topic is related to enhanced optico-mechanical coupling that occurs when the group velocity of light is ultra-slow. We show theoretically that, due to dragging of the light by the mechanical motion of the medium, it is possible to control phase-matching condition.

We study theoretically slow light structures exhibiting zero group velocity in middle of the Brillouin zone. We find that in order to exhibit a mid-band group velocity point in its dispersion relation, a slow-light structure must possess two distinct optical paths supporting counter-propagating power flows. This is in contrast to conventional slow-light structures which exhibit zero group velocity only at the edge of their Brillouin zone, which indicates the emergence of a standing wave.

Recently, we have demonstrated slow light propagation in coupled-resonator optical waveguides consisting of upto 235 directly-coupled silicon microrings. High resolution spectral measurements of light transmission and the scaling of transport statistics with increasing length reveal that resonator excitations are mutually correlated, as expected from theory. Successful light transmission through coherently-coupled resonator chains that are several hundreds of resonators long is promising for future large-scale silicon photonic circuitry.

We outline the theory of slow-light propagation in waveguides featuring negative electromagnetic parameters (permittivity, permeability and/or refractive index). We explain the mechanism by which these heterostructures can enable stopping of light even in the presence of disorder and, simultaneously, dissipative losses. Using full-wave numerical simulations and analytical transfer-matrix calculations we show that the incorporation of thin layers made of an active medium adjacently to the core layer of a negative-refractive-index waveguide can completely remove dissipative losses - in a slow- or stopped-light regime where the effective index of the guided lightwave remains negative. We also review and compare several 'trapped rainbow' schemes that have recently been proposed for slowing and stopping waves.

Optically tunable pulse delays in cesium vapor were demonstrated by pumping several D₂ transitions and burning holes in the D₁ absorption spectrum. A modified sub-Doppler absorption spectroscopy setup was used with counter propagating beams with a Gaussian 7-ns full-width at half-maximum probe pulse is scanned across the D₁ absorption spectrum. Probe laser optical delays followed Kramers-Kronig model prediction for Cs D₁ without D₂ pump laser. Optical control of pulse delay was demonstrated by varying pump intensity. Localized delay effects in agreement with model predictions were observed in the neighborhood of a burnt hole.

Pulsed coherent population trapping in atomic vapor provides a convenient method for generating frequency narrowed atomic resonance using Ramsey interference. Here, we present our experimental results showing high-contrast and sub-kilohertz Ramsey interference fringes produced by coherently prepared ⁸⁵Rb atoms using Raman excitation formed in D1 line transitions. A test system for atomic clock has been constructed to measure light shift for both continuous and pulsed Raman excitation cases. Our measurements show that light shift measured using pulsed Raman excitation, is reduced compared to the continuous excitation case. Our ability to measure light shift is currently limited by the resolution of the frequency counter, and performance of the locking electronics used.

We describe an enhanced rotation sensor involving an active helium-neon (HeNe) ring laser coupled to a passive enhancement resonator, which has been named a fast-light-enhanced HeNe ring-laser gyroscope (RLG). Theoretical rotation sensitivity enhancements as large as two orders of magnitude are presented. The physical effect responsible for the increased rotational sensitivity is the anomalous dispersion of the enhancement resonator, which produces a larger beat frequency as compared to a standard HeNe ring-laser gyroscope (RLG) as the laser cavity is rotated. We present the layout of the fast-light enhanced HeNe RLG, and we provide the theoretical modeling of the enhanced rotational sensitivity. A design is presented for the red HeNe (632.8 nm). The beat frequency is calculated with respect to rotation rate, which defines the useful range of operation for this highly sensitive RLG. Considerations for practical issues including laser-mirror reflectivity precision, unsaturated laser gain, and cavity-length stability are discussed.

By performing two-beam coupling experiments in a liquid crystal light-valve, a large slow-light effect is obtained, with group velocity as slow as a few tenths of mm/s. According to the anisotropic character of the wave-mixing process in liquid crystals, the interactions are accompanied by different behaviors on the different polarization states, with high response to phase changes on the extraordinary wave and the ordinary wave traveling unaffected. Different types of enhanced sensitivity phase detection systems are realized based on the slow-light features of wave-mixing in light-valves, such as common-path polarization interferometers exploiting different polarization states, adaptive holography and nonlinear Sagnac detection.

We demonstrate a Mach-Zehnder(M-Z) interferometer coupled with a nested fiber ring resonator. The numerical results shows that the sensitivity of the M-Z interferometer is enhanced by its strong dispersive response at resonance. Large enhancement factor will be get nearing critical coupling.

Stimulated Brillouin scattering (SBS) based slow light is considered for application to squint-free (true time delay) steering of phased array radar antennae. Results are presented on true time delay radar requirements, including delay precision and bandwidth. We experimentally investigated the level of delay precision that exists in actual slow-light systems (based on Brillouin scattering). The practical use of SBS to meet the necessary requirements for radar use is discussed.

We study analytically pulse distortion in linear slow light systems, and provide some useful limits on these devices. Additionally, we also show that the contributions of phase and amplitude broadening can be de-coupled and quantified. It is observed that phase broadening is generally smaller than amplitude broadening in conventional slow light media (lorentzian gain profile) except for very large fractional delays, where it becomes larger. Upon these expressions, we may envisage new strategies to minimize the distortion in the delaying of pulses, depending on the specific application and the required fractional delay. To overcome the residual distortion, we show that nonlinear systems can lead to a resharpening of the pulses and a re-generation of the filtered frequencies.

Non-linear interactions involving pump-probe optical phenomena, such as electromagnetically induced transparency, in quantized many-electron systems are investigated using a reduced-density-matrix approach. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner and self-consistent 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 perturbation-theory treatment of the electromagnetic interaction is adopted. However, it is emphasized that a quantized-electromagnetic-field approach is essential for a self-consistent quantum-mechanical formulation. Our primary result is the derivation of compact Liouville-space operator expressions for the linear and the general (n'th order) non-linear macroscopic electromagnetic-response tensors for moving many-electron system. These expressions can be evaluated for coherent initial electronic excitations and for the full tetradic-matrix form of the Liouville-space self-energy operator representing the environmental interactions in the Markov approximation. Environmental interactions can be treated in various approximations for the self-energy operator, and the influence of Zeeman coherences on electromagnetic-field propagation can be investigated by including an applied magnetic field on an equal footing with the electromagnetic fields.