Standing-wave Coupling Research Articles

Asymmetric diffraction in anti-parity-time symmetry of non-Hermitian photonic lattice

Non-Hermitian systems based on anti-parity-time (PT) symmetry reveal rich physics beyond the Hermitian regime. Here, the anti-PT-symmetric photonic lattice is effectively achieved in a four-level inverted Y-type 85Rb atomic vapor. Such instantaneously reconfigurable anti-PT-symmetric photonic lattice possessing susceptibility of χ(x)=−χ∗(−x), is established by a one-dimensional standing-wave coupling field under the assist of a standing-wave driving field. The input probe beam experiences a periodic refractive index modulation when traveling through the photonic lattice, the evolution of output diffraction patterns with symmetric, asymmetric, and lopsided intensity distribution is obtained by adjusting the relevant parameters of constructed non-Hermitian system. Moreover, the anti-PT symmetry in two-dimensional case of both square and hexagonal lattices are correspondingly realized. Our work promotes the development of non-Hermitian devices, and also has some important applications in quantum simulation.

Unidirectional and bidirectional photon transport blockade in driven atomic lattices of parity-time antisymmetry

We propose a scheme for realizing exact parity-time ( PT ) antisymmetry of complex susceptibility in a wide range of probe detuning by considering a one-dimensional lattice of cold atoms driven into the simplest three-level Λ configuration. This is attained by modulating the intensity of a standing-wave coupling field with a proper phase shift to counteract the product of a single-photon detuning and a two-photon detuning. Such a dynamically controlled PT -antisymmetric lattice supports the integration of a few nontrivial scattering behaviors including unidirectional light reflectionless, asymmetric perfect absorption, and directional signal quenching. These behaviors, depending in particular on atomic densities and lattice lengths, facilitate the on-demand realization of unidirectional or bidirectional photon transport blockade.

Optomechanically induced grating in a graphene based nanocavity

The optomechanically induced grating (OMIG) in a nanocavity using a bilayer graphene system as the intracavity medium has been proposed. We investigate the effects of different parameters on the Fraunhofer diffraction pattern of the incident probe light. Here, one mirror of the nanocavity is considered coherently driven by the standing wave coupling and probe fields, whereas the second mirror has mechanical oscillation due to the radiation pressure. We consider interaction of bilayer graphene with the optomechanical cavity and show that OMIG can be obtained corresponding to output probe field frequency. Moreover, we find that under specific parametric conditions, most of the probe energy can transfer to the higher orders of the diffraction and only a small portion remains in the zero order.

Investigation of diffraction grating in photothermal cavity

The photothermal effects in an optical cavity driven by a strong control field and a weak probe field have recently been shown to generate an induced transparency phenomenon (Ma et al., 2020). This phenomenon, referred to as photothermally induced transparency (PTIT), arises from the nonlinear behavior of an optical resonator caused by optical heating of the its mirrors. In this study, we investigate the manipulation of PTIT by substituting the strong coupling field in the PTIT scheme with a spatially periodic standing wave (SW) coupling field, resulting in the diffraction of the weak probe field into high-order diffractions. The resulting structure, termed the photothermally induced grating (PTIG), can be effectively controlled by adjusting various system parameters, including the coupling strength, effective detuning, interaction length, and photothermal coefficient. By carefully optimizing the coupling strength, we demonstrate that a significant portion of the probe field energy can be efficiently transferred to the third-order diffraction grating. The introduction of a spatially periodic standing wave coupling field opens up new possibilities for designing and manipulating photothermally induced gratings with enhanced functionalities.

Tunable atom lithography scheme with high resolution in atomic system

We theoretically propose a scheme that utilizes the excited state of a Λ-type three-level atom system for atom lithography. A standing-wave coupling field and a probe field provide localized probability distribution of the excited atoms. Unlike the previous studies in atom localization, we focus on splitting the single-peak structure localized on the node of the standing-wave field to a double-peak structure. The shift distance of double-peak related to the parameters of external laser fields is investigated. The period of lithography pattern could reach λ/4, while the resolution of lithography is promising to be smaller than 0.02λ by adjusting system parameters. This scheme can be extended to form a two-dimensional pattern for lithography.

Phase controlling of electromagnetically induced grating

In this paper, we investigated electromagnetically induced grating in a three-level atomic system via relative phase between applied lights. The three-level atomic system interacts with a weak probe light, a signal light and a strong standing wave coupling light in two-dimensional directions. We realized that Fraunhofer diffraction pattern can be obtained by tuning the intensity and detuning’s of the coupling light. We also use of optical vortex light instead of optical plane wave and found that the asymmetric diffraction pattern can be obtained via orbital angular momentum (OAM), respectively. We also studied the different orders of the diffraction pattern versus relative phase of applied lights for different number of OAM.

Azimuthal modulation of electromagnetically induced grating using structured light

We propose a theoretical scheme for creating a two-dimensional Electromagnetically Induced Grating in a three-level Lambda -type atomic system interacting with a weak probe field and two simultaneous position-dependent coupling fields—a two dimensional standing wave and an optical vortex beam. Upon derivation of the Maxwell wave equation, describing the dynamic response of the probe light in the atomic medium, we perform numerical calculations of the amplitude, phase modulations and Fraunhofer diffraction pattern of the probe field under different system parameters. We show that due to the azimuthal modulation of the Laguerre–Gaussian field, a two-dimensional asymmetric grating is observed, giving an increase of the zeroth and high orders of diffraction, thus transferring the probe energy to the high orders of direction. The asymmetry is especially seen in the case of combining a resonant probe with an off-resonant standing wave coupling and optical vortex fields. Unlike in previously reported asymmetric diffraction gratings for PT symmetric structures, the parity time symmetric structure is not necessary for the asymmetric diffraction grating presented here. The asymmetry is due to the constructive and destructive interference between the amplitude and phase modulations of the grating system, resulting in complete blocking of the diffracted photons at negative or positive angles, due to the coupling of the vortex beam. A detailed analysis of the probe field energy transfer to different orders of diffraction in the case of off-resonant standing wave coupling field proves the possibility of direct control over the performance of the grating.

Electromagnetically induced grating with second field quantization in spherical semiconductor quantum dots

A new approach for diffracting the weak probe beam into higher-order directions is proposed via electromagnetically induced grating in second field quantization formalism, offering a new way for implementations of quantum information with semiconductor quantum dots. The formalism of second field quantization allows describing atoms and photons as a many-body system. An induced diffraction grating is formed based on the electromagnetic induced transparency when a standing-wave coupling field is applied to a spherical quantum dot as a three-level system. Due to phase modulation, the zeroth-order light intensity becomes weak, and the first-order diffraction is improved affectedly. On the contrary, the probe beam is barely diffracted via absorption modulation. The simulation results verify that photon numbers of probe and control fields, as well as other parameters in the QD, can lead to the diffraction efficiency of phase grating to be improved. Phase diffraction grating accompanied with a high transmissivity is demonstrated, and the first-order diffraction efficiency reaches $$30\%$$. Also, the impact of QD dimensions on its optical response is investigated. This model may find potential applications in designing the semiconductor quantum dot-based photonic devices in optical communications and quantum information networks.

Electromagnetically induced grating in semiconductor quantum dot and metal nanoparticle hybrid system by considering nonlocality effects

The optical polarization from a hybrid system including a closely spaced spherical SQD (modeled as a three-level V-type system) and a metal nanoparticle which are considered classically and are connected by the dipole–dipole interaction mechanism is investigated. The interaction between the SQD and the MNP shows an interesting optical response. In the weak probe field regime and MNP nonlocality correction, the absorption spectrum of the hybrid system exhibits an EIT window with two absorption peaks and the plasmon-assisted quantum interference plays an important role in the position and amplitude of these peaks, which are intensely altered by including the nonlocal effects. The probe diffraction grating is created based on the excitons-induced transparency by applying a standing-wave coupling field. The results of this study are useful in numerous areas of all-optical communications.

Synthesized magnetic field of a sawtooth superradiance lattice in Bose\u2013Einstein condensates

Ultracold atoms have become one of the most exciting platforms to synthesize novel condensed matter physics. Here we realize a sawtooth superradiance lattice in Bose–Einstein condensates and investigate its chiral edge currents. Based on one-dimensional superradiance lattice (SL) in standing wave-coupled electromagnetically induced transparency, a far-detuned standing-wave field is introduced to synthesize a magnetic field. The relative spatial phase between the two standing-wave coupling fields introduce a magnetic flux in the sawtooth loop transitions of the lattice. This flux determines the moving direction of excitations created in the SL and results in nonsymmetric reflectivities when the SL is probed in two opposite directions. Our work demonstrates an in situ technique to synthesize and detect artificial gauge field in cold atoms.

Thermal-motion-induced optical switching with standing-wave coupled atom-cavity system

We report an experimental scheme of three-channel all-optical switching based on the conversion between single and double dark states in an atom-ring-cavity system driven by a coherent standing-wave coupling field. By turning on and off the counter-propagating part of the coupling field, the switching for the probe field at three different frequencies is simultaneously achieved. We give a theoretical interpretation to the experimental results via the intracavity susceptibility for thermal atoms at different velocities. The switching performance is experimentally analyzed by introducing an additional coherent pumping light.

Unidirectional and controllable higher-order diffraction by a Rydberg electromagnetically induced grating

A method for diffracting the weak probe beam into unidirectional and higher-order directions is proposed via a novel Rydberg electromagnetically induced grating, providing a new way for the implementations of quantum devices with cold Rydberg atoms. The proposed scheme utilizes a suitable and position-dependent adjustment to the two-photon detuning besides the modulation of the standing-wave coupling field, bringing a in-phase modulation which can change the parity of the dispersion. We observe that when the modulation amplitude is appropriate, a perfect unidirectional diffraction grating can be realized. In addition, due to the mutual effect between the van der Waals (vdWs) interaction and the atom-field interaction length that deeply improves the dispersion of the medium, the probe energy can be counter-intuitively transferred into higher-order diffractions as increasing the vdWs interaction, leading to the realization of a controllable higher-order diffraction grating via strong blockade.

Coupling field dependent quantum interference effects in a Λ-system of 87Rb atom

A Λ-system in D2 line transition of the R87b atom has been investigated for quantum interference effects for different configurations of coupling field. With a traveling wave coupling field (co-propagating with probe field), the probe beam shows the earlier known electromagnetically induced transparency (EIT) effect at the resonance. With a standing wave coupling field (which is co- and counter-propagating with probe beam), the probe EIT gets transformed into an electromagnetically induced absorption (EIA). A variation in coupling beam power has shown that, at high coupling power, EIA signals have much larger amplitude and slope than those of EIT signals with and without applied magnetic field. These EIA signals can be useful for tight laser frequency locking and optical switching.

Controllable photonic crystal with periodic Raman gain in a coherent atomic medium.

With two sets of standing-wave fields built in a thermal rubidium vapor cell, we have established a controllable photonic crystal with periodic gain in a coherently prepared N-type four-level atomic configuration. First, the photonic lattice constructed by a resonant standing-wave coupling field results in a spatially modulated susceptibility and makes the signal field diffract in a discrete manner under the condition of electromagnetically induced transparency. Then, with the addition of the standing-wave pump field, the N-type atomic medium can induce a periodic Raman gain on the signal field, which can be effectively controlled by tuning the pertinent atomic parameters. The experimental demonstration of such a real-time reconfigurable photonic crystal structure with periodic Raman gain can pave the way for realizing desired applications predicted in the gain-modulated periodic optical systems.

Large capacity hydrogen production by microwave discharge plasma in liquid fuels ethanol

In situ hydrogen production technologies have attracted attentions because of hydrogen storage and transportation safety issues. Discharge plasma technology for hydrogen production is of fast response, large capacity, small scale and portability, which is suitable for automobiles and ships. In this paper, a method for producing hydrogen by microwave discharge in ethanol solution was introduced. A microwave discharge reactor of direct standing wave coupling (MDRSWC) was designed, which was suitable for on-board hydrogen production. The characteristics of large capacity hydrogen production by applying MDRSWC in liquid ethanol were investigated. Depending on the experimental conditions of ethanol concentration and microwave power, the flow rate of hydrogen production was achieved ranging from 28.93 to 72.48 g/h. In addition to main hydrogen and carbon dioxide, a small amount of methane and acetylene as by-products were detected. By optimizing the experimental conditions, the experimental results showed that the flow rate of hydrogen, the percentage concentration of hydrogen and the energy yield of hydrogen production were 72.48 g/h, 58.1% and 48.32 g/kWh respectively. This work could provide a potentially effective hydrogen production method for on-board hydrogen utilization device.

Electromagnetically Induced Grating Without Absorption Using Incoherent Pump

We propose a scheme for creating electromagnetically induced grating in a four-level double- Λ atomic system driven by a coupling field and an incoherent pump field. Owing to the incoherent pumping process, large refractivity accompanied with vanishing absorption or even gain across the probe field can be built up in the atoms, thus phase grating or gain-phase grating, which diffracts a probe light into different directions, can be formed with the help of a standing-wave coupling field. The diffraction efficiency of the gratings can be tuned by the coupling field intensity and the incoherent pump rate, hence the proposed gratings should be suitable for beam splitter and optical switching in optical communication and networking.

Effect of Phase Modulation on Electromagnetically Induced Grating in a Five-Level M-Type Atomic System**Supported by the National Natural Science Foundation of China under Grant Nos 11274112 and 11474092, the Key Project of Shanghai Municipal Education Commission under Grant No 14ZZ056, the Shanghai Natural Science Fund Project under Grant No 14ZR1410300, and the Key Research Project of Henan Province Education Department

We theoretically investigate the phenomena of electromagnetically induced grating in an M-type five-level atomic system. It is found that a weak field can be effectively diffracted into high-order directions using a standing wave coupling field, and different depths of the phase modulation can disperse the diffraction light into different orders. When the phase modulation depth is approximated to the orders of , and , the first-, second- and third-order diffraction intensity reach the maximum, respectively. Thus we can take advantage of the phase modulation to control the probe light dispersing into the required high orders.

Wide stopband single‐/dual‐bandpass filters using rotational symmetric composite right/left‐handed resonators

ABSTRACTBoth single‐/dual‐bandpass wide stopband filters with rotational symmetry using composite right/left‐handed resonators are proposed in this study. Designs of this type obtain a single passband at 2.40 GHz as well as dual passbands at 2.40 and 5.20 GHz, and achieve a wide stopband with no additional structures, which are implemented and demonstrated with full‐wave simulations and measurements. Standing wave coupling models are presented to analyze the characteristics of a wide stopband effectively. The proposed single‐bandpass filter (BPF) with rotational symmetry achieves a preferable wide stopband, in which |S21| is mainly <−20 dB below 19.00 GHz; the proposed dual‐BPF also obtains a wide stopband, in which |S21| < −20 dB below 16.90 GHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:49–53, 2017

Control of the probe absorption in coupled quantum wells in two dimensions

We investigate the probe absorption of a weak probe field in two dimensions (the so-called two-dimensional probe absorption) in an asymmetric two coupled quantum wells. It is found that, due to the joint quantum interference induced by the standing-wave and coherent coupling fields, the probe absorption can be easily controlled via adjusting the system parameters in two dimensions. Most importantly, the pattern of probe absorption can be localized at a particular position and the maximal probability of finding the pattern in one period of the standing-wave fields reaches unity by properly adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state optoelectronics and quantum information science.

Ground-state cooling of a trapped ion by quantum interference pathways

We investigate the possibility of enhancement of cooling a trapped ion by combining the electromagnetically induced transparency (EIT) effect with the standing-wave coupling. Our study shows that the quantum destructive interference which is caused by the EIT effect and the standing-wave coupling can cancel all the dominant heating effects if appropriate parameters are chosen. The analytical predictions and numerical simulations show that the final temperature can be much lower than the recoil energy. In addition, this fast-cooling scheme is robust against fluctuations of the strength of the laser beams, which makes it more feasible for experimental realization.