Time delay limits of stimulated-Brillouin-scattering-based slow light systems

We discuss the maximum achievable time delay of stimulated-Brillouin-scattering-based systems that rely on the superposition of gain and loss spectra. As we will show, the time delay can be enhanced up to 8.5 times if the gain is superimposed with a broad loss and 9.5 times if two narrow losses are superimposed at the wings of the gain. Furthermore, we show that the parametric interaction between the different pump waves is negligibly small. Our theoretical analysis does not include pulse distortions that are accompanied by the delay.     

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.     

Precise relative rotation sensing using slow light

A novel relative rotation sensor based on slow light is proposed and analysed. A theoretical analysis shows that the high sensitivity of the proposed rotation sensor is achieved through an electromagnetically-induced-transparency medium. Unlike the tradition detection method, the idea of rotation sensing is to detect group delay between counterpropagating wave packets. It can be used to realize an ultra-precise rotation sensor.     

Expansion of the relative time delay by switching between slow and fast light using coherent population oscillation with semiconductors

The slow-light effect based on free-carrier population oscillation in semiconductors is analyzed using generalized macroscopic Bloch equations. Using this model, we are able to investigate the relation between the fractional time delay and the intensity of control laser beams for semiconductors. It is found that although increasing the control-beam intensity can enlarge the fractional time delay, the maximum delay that can be achieved is limited and determined by a critical value of the separation between the quasi-Fermi levels of electrons and holes. We also show that there is an intensity threshold for the control beam above which the probe signal becomes gain-assisted fast light rather than slow light. We therefore suggest a method to expand the relative time delay by switching between the fast-light region and the slow-light region through changing the intensity of the control laser beams. PACS 42.25.Bs; 42.70.Nq; 42.79.-e     

Spectrally efficient slow light using multilevel phase-modulated formats

A phase-preserving and spectrally efficient slow-light scheme has been proposed and demonstrated by utilizing advanced multilevel phase-modulated formats. A 60 ps symbol delay with error-free demodulation of both I and Q channels for 10 Gbit/s return-to-zero differential-quadrature-phase-shift-keyed (DQPSK) signals via a broadband stimulated Brillouin scattering-based slow-light medium is achieved experimentally. Simulation results on 20 Gbit/s DQPSK and 30 Gbit/s D8PSK propose to transmit very high spectrally efficient multilevel formats through a bandwidth-limited slow-light element.     

All-optical switching at ultralow light levels

We report an experimental demonstration of all-optical switching at ultralow light levels in coherently prepared Rb atoms. A signal light pulse is switched on and off by a control light pulse at different frequencies in a four-level atomic system based on multiphoton interferences. We observed a switching efficiency of 55% with the signal and control light pulses containing approximately 20 photons each, corresponding to a control energy density of approximately 10(-5) photons per atomic cross section lambda(2)/(2pi).     

All-optical magnetic recording with circularly polarized light

We experimentally demonstrate that the magnetization can be reversed in a reproducible manner by a single 40 femtosecond circularly polarized laser pulse, without any applied magnetic field. This optically induced ultrafast magnetization reversal previously believed impossible is the combined result of femtosecond laser heating of the magnetic system to just below the Curie point and circularly polarized light simultaneously acting as a magnetic field. The direction of this opto-magnetic switching is determined only by the helicity of light. This finding reveals an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.     

Low power penalty tunable slow light using vertical-cavity surface-emitting laser amplifier

A tunable slow light of 2.5-Gb/s pseudo-random binary sequence signal using a 1550-nm vertical-cavity surface-emitting laser (VCSEL) is experimentally demonstrated. The influences of the bias current and the gain saturation on the slow light are investigated. With bias current increasing, tunable optical group delay up to 98 ps is obtained at room temperature. Demonstration of the time delay between 16 and 24 ps by signal intensity change is reported. Under an appropriate bias current, by tuning the input signal to track the peak gain wavelength of the VCSEL, slow light of a power penalty as low as 1 dB is achieved. With such a low power penalty, the VCSEL has a great potential application as a compact optical buffer.     

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.     

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.     

高灵敏度色散型慢光干涉仪的仿真研究

设计了一种基于慢光介质色散特性的新型干涉装置,研究其物理过程,证明利用慢光介质可以有效提高干涉仪的光谱灵敏度,并且光谱灵敏度与慢光介质的群折射率成正比。同时,进一步具体分析慢光介质GaAs的色散特性,给出研究色散型慢光干涉仪的一般性方法,并证明使用慢光介质GaAs在近红外区域可以提高光谱灵敏度2倍左右。     

Two-photon and two-photon-assisted slow light

We show that light pulses propagating in two-photon absorbing systems may present time delays like slow light produced via coherent population oscillations in one-photon interactions. Two regimes are numerically studied for a simplified two-level system: (a) a light pulse at frequency ω/2 undergoes two-photon absorption (TPA) and is delayed by the absorbing system (two-photon slow light) and (b) a light pulse at frequency ω is delayed in a system prepared by TPA of a light pulse at frequency ω/2 (two-photon-assisted slow light). The study carried out in solutions of dyes and dendrites shows significant delays, low distortion, and good transmission for easily reachable experimental conditions. The working principle can be applied to other media and can be used in telecommunications technology.     

Uniform silicon slow light waveguide

An uniform silicon waveguide is proposed featuring ultralow-dispersion slow light. The core of the waveguide consists of one silicon trip and two pairs of air/silicon strip and the cladding is composed of several alternative silicon and air strips, which form a transverse band gap to confine propagating light in the core. The waveguide has several nearly linear photonic bands in a large frequency range, which can support broadband slow modes with a group velocity of 0.03–0.08c and tolerable group velocity dispersion.     

Pondermotive forces with slow light

This work describes atomic processes which result from the greatly enhanced longitudinal gradient force which is inherent to the propagation of slow light. These processes are (1) ballistic atom motion and atom surfing, and (2) a type of local pondermotive nonlinearity or scattering which results from free-particle sinusoidal motion and the density variation caused by this motion.     

All-optical signal regeneration using fiber nonlinearity

All-optical signal processing requires the use of nonlinear optical materials. One promising candidate for this purpose for operation at speeds faster than a few tens of Gbit/s is the optical fiber. In this paper, we describe all-optical signal regeneration using the self-phase modulation (SPM) in nonlinear fibers. Our recent experimental work on high-speed on-off keying signal regeneration using a two-stage SPM-based regenerator in bidirectional fiber configuration and on its application to differential phase-shift-keying signal regeneration is described in detail.     

All-optical quaternary circuits using quaternary T-gate

In multi-valued logic (radix>2), quaternary multiplexer (also known as T-gate) places a significant role for data transmission and signal processing. Four valued multiplexer transmit one data (from 4-input) to the output corresponding to the one selected input. Any four-valued logic can be implemented using T-gate. So it is called ‘universal’ element. In this paper some all-optical quaternary logical operations, quaternary half-adder, quaternary multiplier and quaternary comparator is proposed and described using only all-optical quaternary T-gate.     

Slow light and slow current

It is shown that the effect of hole-burning under conditions of coherent population oscillations as well as the light pulse delay in a saturable absorber (a modification of the so-called slow light effect) can be interpreted, in a comprehensive way, in terms of the intensity spectrum of the light and intensity-related susceptibility of the medium. The physical content of these effects is illustrated by a simple electric circuit with a non-linear resistor which realizes a full analog of the saturable absorber. In this case the effect of hole-burning in the absorption spectrum of the medium is converted into the effect of hole-burning in the frequency dependence of resistance of the resistor and the effect of slow light into the effect of slow current.     

高灵敏度色散型慢光干涉仪的仿真研究

设计了一种基于慢光介质色散特性的新型干涉装置,研究其物理过程,证明利用慢光介质可以有效提高干涉仪的光谱灵敏度,并且光谱灵敏度与慢光介质的群折射率成正比。同时,进一步具体分析慢光介质GaAs的色散特性,给出研究色散型慢光干涉仪的一般性方法,并证明使用慢光介质GaAs在近红外区域可以提高光谱灵敏度2倍左右。     

Ultra slow light propagation without any control light field

Without need of another control light, this paper analyses in a time-dependent way a new scheme to achieve ultraslow propagation of the input probe field through a medium composed of two-level atoms where their upper level is split into two hyperfine sub-levels via some applied static field such as a DC magnetic or a DC electric field or whatever other static field.[第一段]