Fast Light Effects Research Articles

Plasmonically Induced Absorption and Transparency Based on Stub Waveguide with Nanodisk and Fabry-Perot Resonator

A novel metal-insulator-metal (MIM) plasmonic waveguides structure, which is composed by stub waveguide with nanodisk and Fabry-Perot (F-P) resonator, has been proposed and numerically simulated with the finite-difference time-domain (FDTD). Based on the three-level system, the extreme destructive interference between bright and dark resonators gives rise to the distinct plasmonically induced absorption (PIA) response with the abnormal dispersion and novel fast-light feature. Simultaneously, the dramatic double plasmonically induced transparency (PIT) effect with slow-light characteristic can also be achieved in the system. The relationship between the transmission characteristics and the geometric parameters is studied in detail. By optimum design, the modulation depth of the PIA transmission spectrum of 90 % with 0.145 and 0.14 ps fast-light effect can be gained simultaneously, and the peak transmissivity of the double PIT system of 75.2 and 72.8 % with −0.38 ps slow light-effect can be achieved. The simulated transmission features are in agreement with the temporal-coupled mode theory (CMT). The characteristics of the system indicate an important potential application in integrated optical circuits such as slow-light and fast-light devices, high-performance filter, and optical storage.

Coherent optical propagation and ultrahigh resolution mass sensor based on photonic molecules optomechanics

We theoretically demonstrate the coherent optical propagation properties based on a photonic molecules optomechanics. With choosing a suitable detuning of the pump field from optomechanical cavity resonance, both the slow- and fast-light effect of the probe field appear in the system. The coupling strength of the two cavities play a key role, which affords a quantum channel and influences the width of the transparency window. Based on the photonic molecules optomechanical system, a high resolution mass sensor is also proposed. The mass of external nanoparticles deposited onto the cavity can be measured straightforward via tracking the mechanical resonance frequency shifts due to mass changes in the probe transmission spectrum. Compared with the single-cavity optomechanics mass sensors, the mass resolution is improved significantly due to the cavity–cavity coupling. The photonic molecules optomechanics provide a new platform for on-chip applications in quantum information processing and ultrahigh resolution sensor devices.

Weak-value amplification of the fast-light effect in rubidium vapor

We use weak-value amplification to enhance the polarization-sensitive fast-light effect from induced Raman absorption in hot rubidium vapor. We experimentally demonstrate that projecting the output signal into an appropriate polarization state enables a pulse advancement of 4.2 {\mu}s, which is 15 times larger than that naturally caused by dispersion. More significantly, we show that combining weak-value amplification with the dispersive response of an atomic system provides a clear advantage in terms of the maximum pulse advancement achievable for a given value of loss. This technique has potential applications for designing novel quantum-information-processing gates and optical buffers for telecommunication systems.

Tunable fast and slow light in a hybrid optomechanical system

We explain the probe field transmission spectrum under the influence of a strong pump field in a hybrid optomechanical system, composed of an optical cavity, a mechanical resonator, and a two-level atom. We show fast (superluminal) and slow (subluminal) light effects of the transmitted probe field in the hybrid system for suitable parametric regimes. For the experimental accessible domain, we find that the fast light effect obtained for the single optomechanical coupling can further be enhanced with the additional atom-field coupling in the hybrid system. Furthermore, we report the existence of a tunable switch from fast to slow light by adjusting the atomic detuning with the anti-Stokes and Stokes sidebands, respectively, as $\Delta_a=+\omega_m$ and $-\omega_m$. The reported characteristics are realizable in state-of-the-art laboratory experiments.

Fast-light-assisted four-wave mixing in the photonic bandgap.

In this Letter, the enhanced four-wave mixing (FWM) in the photonic bandgap of fiber Bragg grating (FBG) has been achieved with an extra phase introduced by fast-light effect in the bandgap. The experiment for phase-matched FWM generation in the bandgap in a special-designed FBG was carried out, as well as simulations. The enhanced energy conversion with such a FWM in the bandgap has been demonstrated but the transmissivity has not. The experimental results show agreement with the simulations.

Photonic coherence effects from dual-waveguide coupled pair of co-resonant microring resonators.

We theoretically describe photonic manifestations of electromagnetically induced transparency (EIT) and absorption (EIA) using co-resonant coupled microresonators (CMRs) as opposed to detuned CMRs explored previously. Here the coherent optical interactions between the two resonators are mediated via two adjacent waveguides and the photonic EIT and EIA are achieved by coupling two identical resonators to the waveguides with equal strength, although this coupling is distinct for each waveguide. Using co-resonant CMRs based on either identical or distinct intrinsic quality factor (Q) resonators, these effects may be obtained in both transmission and reflection. We elucidate origin of the sharp features in the spectra of co-resonant CMRs. Furthermore, we demonstrate tunability of these features using Q-tunable resonators, which may lead to tunable slow and fast light effects. The theoretical model described here greatly simplifies accurate numerical studies of coupled-resonator effects, as no additional calculations are required to account for the waveguide dispersion.

基于石墨烯光机械系统的光学三极管和相干光学存贮

原子尺寸厚度的二维纳米材料——石墨烯，由于它对于研究其量子运动行为的独特性质，石墨烯也许是构成纳米机械振子的最终纳米材料。本文在红边带条件下，通过用一个强的微波泵浦场和一个弱的信号场驱动石墨烯纳米机械振子–微波腔耦合系统，理论证明了系统中的光机械诱导透明。在蓝边带条件下，通过计算信号场的透射谱，发现信号场可以实现有效地减弱和放大取决于栅极场(泵浦场)的功率强度。这样在蓝边带下石墨烯光机械系统呈现出类似一个光学三极管实现弱微波信号的放大。此外通过控制强泵浦场，石墨烯光机械系统可以实现快光和慢光效应，并且通过调节腔场与泵浦场之间的失谐能实现快光和慢光效应之间的转换。石墨烯光机械系统对于光的存储将会是一个很有希望的方案，同时对于在通讯和量子信息技术上的应用也指出了一个方向。 Graphene, atomically thin two-dimensional nanomaterials, may be considered as the ultimate nanomaterial for fabricating nanomechanical resonator due to its unique properties for studying its quantum behavior of the motion. In this work, we theoretically demonstrate optomechanically induced transparency based on the coupled graphene nanomechanical resonator-microwave cavity system with a strong microwave pump field and a weak signal field under the condition of red sideband. At the blue sideband, the signal field can be efficiently attenuated or amplified with calculating the transmission spectrum of the signal field, depending on the power of a second “gating” (pump) field which can behave as an optical transistor to amplify a weak microwave field. In addition, the graphene optomechanics can obtain the slow and fast light effect with controlling the strong pump field, and the slow and fast light effect can be switched via adjusting the detuning between the cavity field and the pump field. This scheme may be a promising candidate for light storage and pave the way for numerous applications in telecommunication and quantum information technologies.

Tunable slow and fast light in an atom-assisted optomechanical system

We theoretically investigate the slow and fast light effects of a probe laser in an optomechanical double-ended cavity filled with a bunch of identical two-level cold 87Rb atoms. It is shown that the presence of atoms can transfer the optomechanically induced transparency (OMIT) window into the steeper Fano shapes and the broader normal-mode splitting shapes. We find that the transmission group delay related to the Fano resonance is much greater than that of the OMIT and normal-mode splitting at the resonances, meanwhile, with the growing of the atomic number, the slow light becomes increasingly significant. The value of reflection group delay related to the OMIT and normal-mode splitting is positive, while the value related to the Fano resonance is significantly negative. This indicates that the reflection parts of output field contain both slow light and fast light. Therefore, via changing the atomic number and detuning, we can realize not only the manipulation of the magnitudes of the group delay and advance, but also a tunable switch from slow light to fast light.

Controlling single-photon transport properties with asymmetrical waveguide-whispering-gallery resonator couplings

Asymmetrical waveguide-whispering-gallery resonator (WGR) couplings are proposed to manipulate single-photon transport properties in a hybrid system composed of a linear waveguide, a WGR and two separated two-level atoms. Tri-frequency/quadri-frequency photon attenuators and all-pass filters (caused by decoupling effects) are realized via the symmetrical/asymmetrical waveguide-WGR couplings and the phase difference induced by two atoms. The study of group delay shows slow-light and fast-light effects in this hybrid system, and dissipation effects imposing on the transmitted single photon are also analyzed.

Microwave field controlled slow and fast light with a coupled system consisting of a nanomechanical resonator and a Cooper-pair box

We theoretically demonstrate an efficient method to control slow and fast light in microwave regime with a coupled system consisting of a nanomechanical resonator (NR) and a superconducting Cooper-pair box (CPB). Using the pump-probe technique, we find that both slow and fast light effects of the probe field can appear in this coupled system. Furthermore, we show that a tunable switch from slow light to fast light can be achieved by only adjusting the pump-CPB detuning from the NR frequency to zero. Our coupled system may have potential applications, for example, in optical communication, microwave photonics, and nonlinear optics.

Coherent control of optical precursors in a warm atomic system with Doppler effects

We theoretically study coherent control of optical precursors via active Raman gain (ARG) in an N-type warm atomic system. When a step pulse passes through an ARG window, main fields are advanced due to fast-light effect and constructively interference with optical precursors, then an enhanced transient pulse appears. As the control field decreases, the interference effect is strengthened, and the transient pulse builds up and becomes narrow. Moreover, its peak intensity is inverse to the system temperature and also determined by the input-pulse form. The scheme may be useful in designing optical devices in optical communication.

From fast light to slow light in resonantly driven quantum dot systems

In this article, we study the resonantly driven quantum dot systems. Based on the density matrix approach, we theoretically investigate the absorption and refractive index near the quantum dot resonance energy. We find that the systems show fast light effect at smaller incident light intensity due to the first order absorption, and show slow light effect at larger incident light intensity due to the third order absorption. It can be tuned by the incident light intensity, and be interpreted in terms of absorption saturation. It operates under normal environmental conditions and at telecommunication wavelengths, and may really be applied.

Electrically Tunable Slow and Fast Light using Coherent Population Oscillations in Quantum Dot Semiconductor Optical Amplifier

Coherent population oscillations (CPO) in quantum dots (QDs) have been utilized in this article to achieve slow and fast light effects in a semiconductor optical amplifier. These phenomena have been achieved based on a pump-probe scheme and tuning the input current source. Coupled rate equations have been developed to determine the carrier dynamics and occupation probabilities. The effects of barrier, wetting layer and excited state densities have been included for CPO phenomenon occurring between the ground states. A quantum disc model embedded in another disc has been assumed for modeling the QDs and density matrix elements are used to obtain induced polarization at the signal frequency after determining the energy states and state probabilities. Tunable absorption dip, corresponding refractive index variation and group index, exhibit widely tunable slow and fast light characteristics by changing the bias condition.

Magnetically induced separation and enhancement of optical precursors via electromagnetically induced transparency

Based on magnetically-induced coherence, a scheme for separating and enhancing optical precursors is proposed in a four-level atomic system. An rf field induces a magnetic dipole transition, which consists of a loop system with other optical fields. Under conditions of electromagnetically induced transparency, optical precursors could be separated from the delayed main signal when the relative phase of the system is 0. While, by changing the phase from 0 to π, the phase-dependent dispersion strengthens the constructive interference between the precursors and main signal, thus the precursor pulse is much enhanced. This is attributed to the competition between magnetically induced slow- and fast-light effects.

Tunable microwave photonic phase shifter based on slow and fast light effects in a tilted fiber Bragg grating

A continuously tunable microwave phase shifter based on slow and fast light effects in a tilted fiber Bragg grating (TFBG) written in an erbium/ytterbium (Er/Yb) co-doped fiber is proposed and experimentally demonstrated. By optically pumping the TFBG, the magnitude and phase responses of the cladding mode resonances are changed, which is used to introduce a tunable phase shift to the optical carrier of a single-sideband modulated signal. The beating between the phase-shifted optical carrier and the sideband will generate a microwave signal with the phase shift from the optical carrier directly translated to the generated microwave signal. A tunable phase shifter with a tunable phase shift of 280° at a microwave frequency tunable from 24 to 36 GHz is experimentally demonstrated.

Enhanced coupled-resonator-induced transparency and optical Fano resonance via intracavity backscattering

We look into the use of the intracavity backscattering in twin-coupled traveling wave microresonators (TWMRs) to generate enhanced coupled-resonator-induced transparency (CRIT) and optical Fano resonance (OFR). Intracavity backscattering makes it possible to either generate a single CRIT peak or a pair of CRIT peaks within one free spectral range in the transmission spectrum. The distance between the twin-CRIT peaks can be tuned by controlling the intracavity backscattering strength. Also, the use of intracavity backscattering allows the simultaneous production of both fast and slow light effects. In addition, it is found that the symmetric CRIT peaks can be reshaped into asymmetric OFR line shapes either by using TWMRs with different intracavity backscattering strengths when one input is launched into the circuit or by modulating the phase/amplitude difference between the dual contrapropagating inputs, which are launched into the circuit in the presence of intracavity backscattering. These allow switching between CRIT and OFR to be realized in the absence of gain or phase tuning elements in the cavities, unlike conventional twin-coupled TWMR systems.

Recent Breakthroughs in Microwave Photonics

We present a brief review of recent accomplishments in the field of Microwave Photonics (MWP). Recent research across a broad range of MWP applications is summarized, including photonic generation of microwave, millimeter, and Terahertz waves; broadband optical beamforming for phased array antennas; tunable, reconfigurable, and adaptive microwave photonic filtering, as well as the application of slow and fast light effects to the implementation of tunable microwave phase shifting and true time delay operations.

Slow and Fast Light Effects and Their Applications to Microwave Photonics Using Semiconductor Optical Amplifiers

We provide a comprehensive review of the application of slow and fast light (SFL) techniques to the field of microwave photonics. Basic principles leading to the implementation of phase shifting and true time delay operations which are instrumental in this field are first considered. We then focus on the description of the main results obtained by our groups in the implementation of broadband, full 360 phase shifting using coherent population oscillations in semiconductor waveguides. Next, attention is given to the evaluation of the system impairments implied by these devices when included in analog links. Finally, the main results obtained for several microwave photonic applications such as filtering, arbitrary waveform generation and optoelectronic oscillators (OEOs) are reviewed, and other directions for future research in the field are discussed.

Slow and fast light associated with polariton interference

Propagation times of optical pulses through a medium near an absorptive resonance with and without spatial dispersion are studied and contrasted. When spatial dispersion is not present, a light pulse is expected to traverse a medium in a time inversely proportional to its group velocity. In a medium with spatial dispersion, where two polariton modes exist (here, bulk GaAs as an example), a similar description is obtained if the losses are such that light propagates primarily in one mode. However, we show that, when the broadening of the resonance (dephasing rate) is below a critical value, a frequency range exists near resonance where the transit times are determined by interference between copropagating polaritons and deviate strongly from expectations based on the group velocities of the polariton branches. When the interference is constructive at the samples end face, the transit times are determined by the average of the inverse group velocities; when it is destructive, we find abrupt transitions between very slow (long positive) and very fast (large negative) transit times. We present quantitative criteria for the resolution of these features and for distortion-free propagation in the spectral vicinity of them. Our analysis puts the well-known slow- and fast-light effects in systems without spatial dispersion into a broader context by illustrating that they are a limiting case of systems with spatial dispersion.

Practical tests for distinguishing slow light from saturable absorption

A series of practical tests of slow light (light with reduced group velocity) in saturable absorbers is proposed. These include experimental tests for saturable absorption, which can mimic slow light effects in saturable media, the dependence of slow light on the mutual coherence of pump and probe, since both slow and fast light effects can be simulated with incoherent sources, and the influence of polarization. The principal requirements for practical observation of spectral hole burning are reviewed and shown to be achievable for a wide range of saturable media with the narrow line sources now available.