Controllable time delay using slow/fast light in active fiber ring resonators with gain manipulation

We propose to generate controllable time delay using slow/fast light in fiber ring resonators with gain manipulation.The dispersion and group delay of active fiber ring resonator can be controlled by manipulating its gain level below the lasing threshold.Controllability of the negative group delay in the undercoupled regime and the positive group delay in the overcoupled regime is theoretically demonstrated.Besides,large group delay can be obtained accompanied by signal gain in active ring resonators.In addition,we describe wide bandwidth and large group delay in 4-stage cascaded ring resonators.     

All-optical delay of images using slow light

Two-dimensional images carried by optical pulses (2 ns) are delayed by up to 10 ns in a 10 cm cesium vapor cell. By interfering the delayed images with a local oscillator, the transverse phase and amplitude profiles of the images are shown to be preserved. It is further shown that delayed images can be well preserved even at very low light levels, where each pulse contains on average less than one photon.     

A saturable absorber, coherent population oscillations, and slow light

The paper presents a critical analysis of publications on one of the methods of creating so-called slow light (light with an anomalously low group velocity) arising due to a high steepness of the refractive index dispersion curve. The method employs, for this purpose, the effect of coherent population oscillations accompanied by burning of a narrow spectral hole in the homogeneously broadened absorption spectrum. The interpretation of the experimental data in the studies under consideration is based on the analysis of the response of a nonlinear medium to a low-frequency intensity modulation of the propagating light beam. We show that all the observations of these papers can be easily interpreted in the framework of the simplest model of a saturable absorber and have nothing to do with the hole burning effect or group velocity reduction.     

Enhancing the sensitivity of fiber Mach-Zehnder interferometers using slow and fast light

We demonstrate theoretically and experimentally that the sensitivity of a fiber Mach-Zehnder (M-Z) interferometer can be enhanced by coupling fiber ring resonators with it. The experimental results agree well with theoretical predications that combining slow light with fast light will further increase the sensitivity of a fiber M-Z interferometer.     

Low distortion, continuously tunable, positive and negative time delays by slow and fast light using stimulated Brillouin scattering

We demonstrate a single optical timing module that can provide both tunable delay and advancement with low distortion using a reconfigurable gain medium based on stimulated Brillouin scattering. Dual-stage intensity modulation method is used to achieve optimized gain profiles for both slow- and fast-light operation. Using 6.5 ns Gaussian pulses, we demonstrate a continuous temporal adjustment from a fractional advancement of 0.31 to a fractional delay of 0.82, giving more than a full pulse width of total tunability.     

Parametric oscillation with the cavity mode driven by coherent light and coupled to a squeezed vacuum reservoir

We seek to investigate, employing stochastic differential equations, the squeezing and statistical properties of the cavity mode of a degenerate parametric oscillator driven by coherent light and coupled to a squeezed vacuum reservoir. Contrary to the case of the squeezed vacuum reservoir, it is found that the driving coherent light has no effect on the squeezing properties of the cavity mode. However, both the squeezed vacuum reservoir and the driving coherent light increase the mean photon number of the cavity mode.     

Analysis of quantum well size alteration effects on slow light device based on excitonic population oscillation

In this paper we investigate the effects of quantum well size changes on slow light device properties. The principle properties such as center frequency and slow down factor of a slow light device are affected by changing the size of quantum well. In this way, the effects of quantum well size on Oscillator Strength and binding energy of exciton are considered separately. First, we investigate the variations in oscillator strength of exciton due to different quantum well size. Second, exciton binding energy level shift due to size of quantum well is investigated. According to this analysis, we have developed a new method for tuning slow light device bandwidth center frequency and slow down factor. Analysis and simulation of a basic GaAs/AlGaAs quantum wells optical slow light device based on excitonic population oscillation shows that size of quantum wells could tune both of the frequency properties and slow down factor of an optical slow light device. Simulation results show that slow down factor and oscillation strength of exciton are proportional to each other in direct manner. Moreover, decreasing the quantum well width, causes enhancement in binding energy of excitons. These achievements are useful in optical nonlinearity enhancements, all-optical signal processing applications and optical communications.     

From slow to fast light in amplified negative refraction using atomic coherence assisted by an incoherent pump

We propose and demonstrate a scheme to realize large negative refraction dispersion when a probe field is amplified by cooperation between a coherent field and an incoherent pump. The probe pulse can propagate either subluminally or superluminally in the left-handed amplification medium by modulating parameters of the coherent and incoherent fields.     

Perturbation method of studying the EI Nifio oscillation with two parameters by using the delay sea-air oscillator model

The EI Nio-southern oscillation (ENSO) is an interannual phenomenon involved in tropical Pacific oceanatmosphere interactions. In this paper, we develop an asymptotic method of solving the nonlinear equation using the ENSO model. Based on a class of the oscillator of the ENSO model, a approximate solution of the corresponding problem is studied employing the perturbation method.     

Stopping and time reversing a light pulse using dynamic loss tuning of coupled-resonator delay lines

We introduce a light-stopping process that uses dynamic loss tuning in coupled-resonator delay lines. We demonstrate via numerical simulations that increasing the loss of selected resonators traps light in a zero group velocity mode concentrated in the low-loss portions of the delay line. The large dynamic range achievable for loss modulation should increase the light-stopping bandwidth relative to previous approaches based on refractive index tuning.     

利用白光干涉谱测定云母片的快慢轴

白光照射到透明云母薄片时,后侧内表面产生的反射光与入射光会在云母片的前表面发生干涉.利用光谱仪可以观察到由于干涉而形成的条状光谱.改变入射光的偏振方向,可以观察到由于云母薄片双折射特性引起的干涉条纹的移动.根据条纹移动的方向,可以判定出云母片两正交的光轴方向上折射率的差异,从而判定出其快轴和慢轴.     

Beam collimation light deflection and time delay in the Kerr spacetime

By using an alternative method valid in weak and strong gravitational fields, we study beam collimation, light bending and time delays in the equatorial Kerr spacetime. Three applications are carried out. First, it is shown that the interaction spin-orbit could collimate a beam only if the particle or photon moves in a opposite direction to the compact object's spin. Secondly, the deflection angles of light rays grazing a quasar, a pulsar (PSR 1937+214), and a rotating black hole are computed and compared with approximate solutions. Finally, we calculate the photon's time delay traveling from SN1987A to Earth. The result of this undertaking is compared with a similar calculation using the PPN formalism.     

In situ accurate determination of the zero time delay between two independent ultrashort laser pulses by observing the oscillation of an atomic excited wave packet

We propose a novel method that uses the oscillation of an atomic excited wave packet observed through a pump-probe technique to accurately determine the zero time delay between a pair of ultrashort laser pulses. This physically based approach provides an easy fix for the intractable problem of synchronizing two different femtosecond laser pulses in a practical experimental environment, especially where an in situ time zero measurement with high accuracy is required.     

Nonlinear phase shifts of modulated light waves with slow and superluminal group delay in stimulated Brillouin scattering

Brillouin amplification with counterpropagating modulated pump and Stokes light leads to nonlinear modulation-phase shifts of the interacting intensity waves. This is due to a partial transformation of the nonmodulated light component at the input into modulated light at the output as a result of a mixing process with the counterpropagating modulated component of the pump and results in an advance or delay of the input modulation. This occurs for interactions over less than half of a modulation wavelength. Milliwatts of power in a kilometer of standard single-mode fiber give significant tunability of the modulation phase.     

Stability and Neimark-Sacker bifurcation analysis of a food-limited population model with a time delay

In this paper,a kind of discrete delay food-limited model obtained by the Euler method is investigated,where the discrete delay τ is regarded as a parameter.By analyzing the associated characteristic equation,the linear stability of this model is studied.It is shown that Neimark-Sacker bifurcation occurs when τ crosses certain critical values.The explicit formulae which determine the stability,direction,and other properties of bifurcating periodic solution are derived by means of the theory of center manifold and normal form.Finally,numerical simulations are performed to verify the analytical results.     

Enhancement and generation of sum squeezing in two-mode light in mixing with coherent light using a beam splitter

Recently, we showed [J. Phys. B: At. Mol. Opt. Phys. 38, 665 (2005)] that the `amplitude-squared squeezing', a non-classical feature, can be enhanced in mixing with a coherent light beam using a beam splitter. Here, we show that the sum squeezing in a two-uncorrelated-mode light beam (one mode is in Gaussian state and the other one is in coherent state), which is degenerate limit of amplitude-squared squeezing, may be generated or enhanced in mixing with a two-mode coherent light beam using a beam splitter.     

Degenerate three-level cascade laser with the cavity mode driven by coherent light

We present the quantum statistical properties of the light produced by a degenerate three-level cascade laser with the cavity mode driven by coherent light. In this system three-level atoms in a cascade configuration, initially prepared in a coherent superposition of the top and bottom levels, are injected into a cavity coupled a vacuum reservoir. We find that although the driving coherent light has no effect on the degree of squeezing, it increases the mean photon number considerably. Therefore, this quantum optical system can be taken as a source of a bright squeezed light.     

Two-photon coherent control of atomic collisions by light with entangled polarization

We describe a new method of coherent optical control of internal dynamics of atomic collisions by means of two correlated light beams having entangled polarizations. We show that, if excitation of a colliding pair of atoms is by two photons having entangled polarizations, it is possible to redirect the output fragments of the collision into certain channels with a selected type of internal transition symmetry. The transition symmetry is defined in the body-fixed coordinate frame which has random and originally unknown orientation in space.     

Diffraction of coherent light with sinusoidal amplitude by a thin-slit grid

We report on the experimental findings of a thin-slit grid diffraction of a coherent light beam with sinusoidal amplitude. We produce diffraction of a field with sinusoidal amplitude by placing a thin-slit grid at the center of the dark fringes of an interference pattern resulting from laser light passing through a dual pinhole. The experimental results show good agreement with diffraction calculations of a thin-slit grid placed at the center of the dark fringes produced by two coherent beams that intersect at small angle. The results are applied to wire-grid diffraction in the Afshar experiment.     

A novel method of measuring coherent ultrashort light pulses using diffraction by a grating

We propose a novel method of measuring coherent ultrashort light pulses in a single shot by monitoring the ratio of the energy of a pulse, diffracted by a grating, to the energy of the incident pulse. In the case of a gaussian pulse we present numerical calculations which allow easy determination of the pulse width. The proposed method is extremely versatile with respect to wavelength regions and pulse duration.