The very high nonlinearity of silicon nanophotonic waveguides motivates research into chip-scale nonlinear optics e.g., wavelength conversion via four-wave mixing (FWM). We demonstrate FWM in silicon coupled microrings with a slow light enhanced effective nonlinear parameter γ_eff ~ 3700 (Wm)^-1 at a pump wavelength of 1570 nm. Impairments on the wavelength conversion efficiency of these structures, such as linear and nonlinear loss, waveguide and coupler dispersion as well as fabrication imperfections are discussed. Evaluation of the performance of optimized waveguide designs shows coupled resonator waveguides to be a promising platform for highly efficient wavelength converters.

We study the dynamics of coupled arrays of Vertical Cavity Surface Emitting Lasers (VCSELs) under optical injection of light into on of the VCSEL in the array In spite of a theoretical expectation for slow light propagation exhibiting resonance tunneling of the injected pulse to its adjacent lasers we observed the opposite effect - the light was first observed in the VCSEL furthest away from the injection point. These rather surprising results are presented and several possible explanations are discussed.

In this manuscript we present calculations that consider the propagation of a squeezed vacuum signal field through a resonant atomic medium under electromagnetically induced transparency (EIT). We show that squeezing is degraded due to four-wave mixing processes at high optical depth of the atomic medium. We also present some preliminary results for degenerate Zeeman EIT resonances.

Reflections from movable, dynamic acoustic gratings in polarization maintaining (PM) fibers are employed in the long variable delay of periodic, isolated pulses. The gratings are introduced by stimulated Brillouin scattering (SBS) interaction between two counter-propagating pump waves, which are spectrally detuned by the Brillouin frequency shift of the PM fiber and are both polarized along one of its principal axes. The gratings are interrogated by the reflections of read-out signals that are polarized along the orthogonal principal axis. High-rate phase modulation of both pump waves by a pseudo-random binary sequence introduces dynamic gratings that are both localized and stationary, at specific locations in which the modulated pumps are correlated. The separation between adjacent correlation peaks can be made arbitrarily long. Long variable delays are readily obtained by scanning the grating along the fiber, via changing either the length or the rate of the modulation sequence. At the same time, the short length of the gratings, on the order of a cm, accommodates the delay of broadband pulses. The technique is therefore free of the delay-times-bandwidth product limitation that undermines the performance of SBS-based 'slow light' delay: we report the delay 1-ns long pulses by as much as 770 ns. In addition, the combined reflections from two dynamic gratings with a variable separation are used to implement radio-frequency photonic filters of tunable free spectral range. At the current stage, the technique is restricted by noise from residual scattering that takes place outside of the correlation peaks. Hence, it is thus far limited to the processing of repetitive signals, for which the noise may be effectively averaged out.

We present a novel superluminal fiber laser based super-sensor employing Brillouin gain. The white light cavity condition is attained by introducing an additional ring cavity into the main cavity. By adjusting the parameters of the laser cavity and those of the phase component it is possible to attain sensitivity enhancement of more than two orders of magnitude compared to conventional laser sensors. The tradeoffs between the attainable sensitivity enhancement, the cavity dimensions and the impact of the cavity roundtrip loss are studied in details providing a set of design rules for the optimization of the super-sensor.

We theoretically demonstrate possibility of detecting rotation by measurement of frequency of generated field via wave mixing. It potentially allows one to "enhance" the rotation frequency by several order of magnitude. Using an ultra-dispersive medium here takes advantage of strong nonlinear properties of the coherent medium as well as steep dispersion that provides frequency shift.

We have measured the dispersion for a 632.8nm probe beam in helium neon vapor in the presence of a strong pump. Our measurements show an average index of refraction variation of 1.27 * 10^-6 per GHz. This degree of dispersion could provide up to a 33% scale factor enhancement if implemented in a Ring Laser Gyroscope (RLG), and our measurements indicate enhancements of >100% are possible. With some modifications in this approach, the same dispersion should be achievable in a compact system which can be integrated with existing RLGs at a reasonable cost and without drastic increases in size, weight, or power. Further theoretical modeling is required in order to determine the maximum achievable scale factor enhancement, and the effects on rotational measurement noise and bias stability.

Phenomenon of slow light has long been a hot research topic due to its promising and potential applications in communication networks, signal processing, optical sensors and nonlinear interactions. Particularly, photonic crystal devices, being capable of supporting slow-light propagation, are much attractive owing to its room-temperature operation and tunable dispersion features. Among them, photonic crystal waveguides (PCWs) are specially used in compact devices, while photonic band-gap fibers (PBGFs) are usually used in short-distance propagation and high sensitive interferometers. In this paper, dispersion tailoring schemes for obtaining a high group index with the wide band and low group velocity dispersion (GVD) are reviewed in both PCWs and PBGFs. For the same purpose, we propose schemes for the slow-pulse propagation in PCWs based on the air-hole shifting method and in PBGFs based on the microfluid infiltration method, respectively. Simulation results using 2D plane wave expansion method and finite-difference timedomain (FDTD) method are given. Pulse distortion and design optimization are also discussed in some detail with the consideration of the practical fabrication errors. Slow-light pulse propagation in photonic crystal fiber is also demonstrated in the experiment based on stimulated Brillouin scattering.

We report on progress in different hollow core photonic crystal fiber (HC-PCF) design and fabrication for atomic vapor based applications. We have fabricated a Photonic bandgap (PBG) guiding HC-PCF with a record loss of 107dB/km at 785nm in this class of fiber. A double photonic bandgap (DPBG) guiding HC-PCF with guidance bands centred at 780nm and 1064nm is reported. A 7-cell 3-ring Kagome HC-PCF with hypocycloid core is reported, the optical loss at 780nm has been reduced to 70dB/km which to the best of our knowledge is the lowest optical loss reported at this wavelength using HC-PCF. Details on experimental loading of alkali metal vapours using a far off red detuned laser are reported. This optical loading has been shown to decrease the necessary loading time for Rb into the hollow core of a fiber. The quantity of Rb within the fiber core has been enhanced by a maximum of 14% through this loading procedure.

We motivate the study of an 'N-scheme' atomic system for the case of a bi-directional probe field. We derive the equations of motion. The equations were expanded in order of the counter-propagating field strength over the co-propagating field strength. We solve the equations numerically in steady state in a perturbative manner. The zeroth order solutions describe the dispersion and absorption of the co-propagating field, while the first order solutions describe the dispersion and absorption of the counter-propagating field. We investigate the solutions in two temperature regimes for a variety of field strengths. Regimes of similar dispersion for the co- and counter-propagating fields were found, as well as regimes of opposite behavior. In most cases, absorption of the fields is still a problem.

In several applications such as optical gyroscopes, gravitational wave detection, and vibrometry, the precision sensing of the effective length of the optical cavity is key. In this work we show how an active single mode laser with a negatively dispersive medium can enhance the sensitivity of measuring the alteration of the length of the cavity in the practical case of a warm medium. We also state how a Rubidium based Diode Pump Alkali Laser satisfies the requirements of the proposed model.

We have measured mode pushing by the dispersion of a rubidium vapor in a Fabry-Perot cavity and have shown that the scale factor and sensitivity of a passive cavity can be strongly enhanced by the presence of such an anomalous dispersion medium. The enhancement is the result of the atom-cavity coupling, which provides a positive feedback to the cavity response. The cavity sensitivity can also be controlled and tuned through a pole by a second, optical pumping, beam applied transverse to the cavity. Alternatively, the sensitivity can be controlled by the introduction of a second counter-propagating input beam that interferes with the first beam, coherently increasing the cavity absorptance. We show that the pole in the sensitivity occurs when the sum of the effective group index and an additional cavity delay factor that accounts for mode reshaping goes to zero, and is an example of an exceptional point, commonly associated with coupled non- Hermitian Hamiltonian systems. Additionally we show that a normal dispersion feature can decrease the cavity scale factor and can be generated through velocity selective optical pumping.

We present the nonlinear optical properties of liquid crystal light-valves and wave-mixing experiments from which slow-light effects are obtained. Group velocities as low as fractions of mm/s are achieved, the corresponding group index becoming very large. We show how this property that can be exploited to realize interferometric systems, for instance, an enhanced sensitivity Mach-Zehnder interferometer containing the light-valve as a slowlight medium is shown. Then, we present a common-path polarization interferometer based on the anisotropic character of the slow-light process occurring in the light-valve. Finally, we present a nonlinear optical cavity where a Doppler shift is introduced by the controlled displacement of one of the mirrors. Self-pulsing is obtained in the cavity due to the strongly dispersive response of the light-valve.

This paper examines the sensitivity improvements that have been achieved by making use of slow light in a variety of fiber sensors. We show in particular that slow light can have dramatically different impacts depending on its nature (material or structural) and on the parameter that is being sensed. In a fiber optic gyroscope measuring an absolute rotation for example, structural slow light does not enhance the maximum sensitivity achievable for a given loss and sensing area compared to a non-resonant structure such as a Sagnac-based fiber optic gyroscope. However, it does reduce the length of fiber required to achieve this sensitivity. For fiber sensors relying on the measurement of absorption, such as gas detectors, structural slow light improves the sensitivity because it increases the effective path length through the absorber and therefore the level of absorption. Material slow light, on the other hand, has been measured to have no impact on the sensitivity. For many other parameters besides rotation and absorption, the sensitivity is expected to be enhanced by either type of slow light, by orders of magnitude with suitable configurations. We illustrate this enormous potential with two configurations of strain sensors utilizing a fiber Bragg grating (FBG) as the sensing and slow-light medium. In properly designed FBGs supporting light with a group index in the range of 50 to 130, we measured a maximum sensitivity of 1.7-3.14 10⁵ strain^-1 and a record minimum detectable strain of 820-880 fε/√Hz. This value is ~730 lower than the previous record using conventional light in a passive FBG sensor, in accord with predictions. Further enhancements are expected with straightforward improvements in FBG design.

We experimentally demonstrate that the spectral resolution of Fourier transform interferometer could be greatly enhanced by utilizing the dispersive property of semiconductor GaAs in the near infrared region and it is inversely proportional to the maximum group delay time that can be achieved in the system. The spectral resolution could be increased 6 times approximately by using GaAs contrast with conventional FT interferometer under the same conditions.

Microscopic and macroscopic descriptions of electromagnetic-field propagation relevant to resonant pumpprobe optical phenomena, such as electromagnetically induced transparency, in quantized many-electron systems are formulated within the framework of a general reduced-density-matrix approach. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified and self-consistent manner. A semiclassical perturbation-theory treatment of the electromagnetic interaction is adopted, in which the electromagnetic field is described as a classical field satisfying either the microscopic form or the macroscopic form of the Maxwell equations. However, it is emphasized that a quantized-field approach is essential for a fully self-consistent quantummechanical formulation. Compact Liouville-space operator expressions are obtained for the linear and the general (n'th order) non-linear electromagnetic-response tensors for moving many-electron systems. These expressions can be evaluated for coherent initial electronic excitations and for the full tetradic-matrix form of the Liouville-space selfenergy operator in the Markov (short-memory-time) approximation. Environmental interactions can be treated in terms of the Liouville-space self-energy operator, and the influence of Zeeman coherences on electromagnetic-field propagation can be investigated by including an applied magnetic field together with the electromagnetic field.

Kerr effect accounts for the change in refractive index of a material with the light intensity and appears in all known optical materials. In this work we analyze Kerr effect in structured superluminal media (e.g some specific types of resonators). We show that Kerr effect in these structures can be cancelled or even reversed (in comparison with the Kerr effect of the material composing the structure) depending on the group index of the structure. We also discuss some possible realizations of structured superluminal media.

We discuss potential advantages of slow-light waveguides compared to cavity-based structures for enhancing opto-mechanical interactions. Then, we reveal that slow-light enhanced optical forces between side-coupled photonic-crystal nanowire waveguides can be flexibly controlled by introducing a relative longitudinal shift. We predict that close to the photonic band-edge, where the group velocity is reduced, the transverse force can be tuned from repulsive to attractive, and the force is suppressed for a particular shift value. Additionally the shift leads to symmetry breaking that can facilitate longitudinal forces acting on the waveguides, in contrast to unshifted structures where such forces vanish.

Si photonics enables the integration of photonics with electronics, making it to be an attractive platform for compact and highly functional devices. By incorporating photonics crystal waveguides (PCWs) and other slow-light nanostructures, optical devices can be made compact as well as having additional functionality. Furthermore, fabricating these devices using existing CMOS process is crucial for their low-cost mass production. In this paper, we report our recent results on CMOS-fabricated, integrated PCW and other slow-light devices, including tunable delays, high-nonlinearity devices, optical modulators and DQPSK receivers.

Photonic crystal defect waveguides with embedded active layers containing single or multiple quantum wells or quantum dots have been fabricated. Spontaneous emission spectra are enhanced close to the bandedge, consistently with the enhancement of gain by slow light effects. These are promising results for future compact devices for terabit/s communication, such as miniaturised semiconductor optical amplifiers and mode-locked lasers.

A couple of experiments are here presented to clarify the impact of slow light on light-matter interaction. The experiments are designed, so that the process generating slow light and the probed light-matter interaction only present a marginal cross-effect. The impact of slow light on simple molecular absorption could be separately evaluated under either material or structural slow light propagation in the same medium and led to an entirely different response.

Recent advance in controlling optical forces using nanostructures suggests that nanoscale optical waveguides are capable of generating coherent acoustic phonons efficiently through a combination of radiation pressure and electrostriction. We discuss the critical roles of group velocity in such processes. This photon-phonon coupling would allow an acoustic intermediary to perform on-chip optical delay with a capacity 10⁵ greater than photonic delay lines of the same size.