Effectively modulating spatial vortex four-wave mixing in a diamond atomic system

Due to the spatial characteristics of orbital angular momentum,vortex fields can be applied in the fields of quantum storage and quantum information.We study the realization of spatially modulated vortex fields based on four-wave mixing in a four-level atomic system with a diamond structure.The intensity and spiral phase of the vortex field are effectively transferred to the generated four-wave mixing field.By changing the detuning of the probe field,the phase and intensity of the generated vertex four-wave mixing field can be changed.When the probe field takes a large detuning value,the spatial distribution of the intensity and phase of the vertex four-wave mixing field can be effectively tuned by adjusting the Rabi frequency or detuning value of the coupled field.At the same time,we also provide a detailed explanation based on the dispersion relationship,and the results agree well with our simulation results.

Wavelength dependence four-wave mixing spectroscopy in a micrometric atomic vapour

This paper presents a theoretical study of wavelength dependence four-wave-mixing （FWM） spectroscopy in a micrometric thin atomic vapour. It compares three cases termed as mismatched case I, matched case and mismatched case II for the probe wavelength less, equal and greater than the pump wavelength respectively. It finds that Dicke- narrowing can overcome width broadening induced by Doppler effects and polarisation interference of thermal atoms, and high resolution FWM spectra can be achieved both in matched and mismatched wavelength for many cases. It also finds that the magnitude of the FWM signal can be dramatically modified to be suppressed or to be enhanced in comparison with that of matched wavelength in mismatched case I or II. The width narrowing and the magnitude suppression or enhancement can be demonstrated by considering enhanced contribution of slow atoms induced by atom-wall collision and transient effect of atom-light interaction in a micrometric thin vapour.

Influence of degenerate four-wave mixing on the performance of supercontinuum-based multiwavelength optical source

The influence of degenerate four-wave mixing （FWM） on the performance of supercontinuum-based multiwavelength optical source has been investigated in detail experimentally and theoretically. Numerical simulation results show that the degenerate FWM effect has a deteriorative influence on the spectral uniformity and the optical signal-to-noise ratio （OSNR） of supercontinuum-based optical source, and by suppressing degenerate FWM effect the performance enhancement of the supercontinuum can be achieved successfully. These results are also confirmed by our experiments. Experimentally, by suppressing degenerate FWM the crosstalk of adjacent channels to the filtered channel can be reduced by as much as 15 dB, and consequently the measured receiver sensitivity at 10 Gbit/s for the filtered optical source is improved from -1.7 to -17.8 dBm.

Phase-matching analysis of four-wave mixing induced by modulation instability in a single-mode fiber

Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will provide guidance for fiber communication and sensing systems using wavelength division multiplexing technology.

Characterize and optimize the four-wave mixing in dual-interferometer coupled silicon microrings

By designing and fabricating a series of dual-interferometer coupled silicon microrings, the coupling condition of the pump, signal, and idler beams can be engineered independently and then we carried out both the continuous-wave and pulse pumped four-wave mixing experiments to verify the dependence of conversion efficiency on the coupling conditions of the four interacting beams, respectively. Under the continuous-wave pump, the four-wave mixing efficiency gets maximized when both the pump and signal/idler beams are closely operated at the critical coupling point, while for the pulse pump case, the efficiency can be enhanced greatly when the pump and converted idler beams are all overcoupled. These experiment results agree well with our theoretical calculations. Our design provides a platform for explicitly characterizing the four-wave mixing under different pumping conditions, and offers a method to optimize the four-wave mixing, which will facilitate the development of on-chip all-optical signal processing with a higher efficiency or reduced pump power.

Microcrack localization using a collinear Lamb wave frequency-mixing technique in a thin plate

A novel Lamb wave frequency-mixing technique is proposed for locating microcracks in a thin plate,which does not require the resonance condition of Lamb wave mixing and can accurately locate the microcracks through only one-time sensing.Based on the bilinear stress-strain constitutive model,a two-dimensional finite element(FE)model is built to investigate the frequency-mixing response induced by the interaction between two primary Lamb waves and a microcrack.When two primary Lamb waves of A0 and S0 modes with different frequencies excited on the same side of the plate simultaneously impinge on the examined microcrack,under the modulation of the contact acoustic nonlinearity,the microcrack itself can be deemed as the secondary sound source and it will radiate the Lamb waves of new combined frequencies.Based on the time of flight of the generated A0 mode at difference frequency,an indicator named normalized amplitude index(NAI)is defined to directly locate the multi-microcracks in the given plate.It is found that the number and location of the microcracks can be intuitively visualized by using the NAI based frequency-mixing technique.It is also demonstrated that the proposed frequency mixing technique is a promising approach for the microcrack localization.

Analysis of Radio over Fiber system for mitigating four-wave mixing effect

In this paper,an efficient 8-channel 32Gbps RoF(Radio over Fiber)system incorporating Bessel Filter(8/32 RoFBF)has been demonstrated to reduce the impact of non-linear transmission effects,specifically Four-Wave Mixing(FWM).The simulation results indicate that the proposed 8/32 RoF-BF system provides an optimum result w.r.t.channel spacing(75 GHz),input source power(0 dBm)and number of input channels(8).In comparison with the existing RoF system,the proposed 8/32 RoF-BF system has been validated analytically and it is found that the performance of the proposed system is in close proximity particularly in FWM sideband power reduction of the order of 4 dBm for the 8-channel 32Gbps RoF system.

Photon statistics of pulse-pumped four-wave mixing in fiber with weak signal injection

We study the photon statistics of pulse-pumped four-wave mixing in fibers with weak coherent signal injection by measuring the intensity correlation functions of individual signal and idler fields. The experimental results show that the intensity correlation function of individual signal（idler） field g_（s（i））^（2） decreases with the intensity of signal injection. After applying narrow band filter in signal（idler） band, the value of g_（s（i））^（2） decreases from 1.9 ± 0.02（1.9 ± 0.02） to 1.03 ± 0.02（1.05 ± 0.02） when the intensity of signal injection varies from 0 to 120 photons/pulse. The results indicate that the photon statistics changes from Bose–Einstein distribution to Poisson distribution. We calculate the intensity correlation functions by using the multi-mode theory of four-wave mixing in fibers. The theoretical curves well fit the experimental results.Our investigation will be useful for mitigating the crosstalk between quantum and classical channels in a dense wavelength division multiplexing network.

Coherent 420 nm laser beam generated by four-wave mixing in Rb vapor with a single continuous-wave laser

We demonstrate the generation of the coherent 420 nm laser via parametric four-wave mixing process in Rb vapor.A single 778 nm laser with circular polarization is directly injected into a high-density atomic vapor,which drives the atoms from the 5S1/2 state to the 5D5/2 state with monochromatic two-photon transition.The frequency up-conversion laser is generated by the parametric four-wave mixing process under the phase matching condition.This coherent laser is firstly certified by the knife-edge method and a narrow range grating spectrometer.Then the generated laser power is investigated in terms of the power and frequency of the incoming beam as well as the density of the atoms.Finally,a 420 nm coherent laser with power of 19μW and beam quality of Mx^2=1.32,My^2=1.37 is obtained with optimal experimental parameters.This novel laser shows potential prospects in the measurement of material properties,information storage,and underwater optical communication.

Phase dispersion of Raman and Rayleigh-enhanced four-wave mixings in femtosecond polarization beats

Based on color-locking noisy field correlation in three Markovian stochastic models, phase dispersions of the Raman- and Rayleigh-enhanced four-wave mixing （FWM） have been investigated. The phase dispersions are modified by both linewidth and time delay for negative time delay, but only by linewidth for positive time delay. Moreover, the results under narrowband condition are close to the nonmodified nonlinear dispersion and absorption of the material. Homodyne and heterodyne detections of the Raman, the Rayleigh and the mixing femtosecond difference-frequency polarization beats have also been investigated, separately.

Online Inter-Modal Dispersion Monitoring Based on Four-Wave Mixing

A novel online Differential Mode Group Delay(DMGD)monitoring method based on four-wave mixing(FWM) in few mode fiber(FMF) transmission system is proposed, and the DMGD monitoring is achieved on the whole range of 15-50 ps/km. Detection principle is deduced and relationship of the power of idler waves and DMGD is analyzed. With various chromatic dispersion(CD)values, different line widths and different optical signal noise ratio(OSNR) values, the simulations are carried out. The simulation results show that this new DMGD monitoring method is less affected by different line widths and has a high tolerance for OSNR.

Enhancement of multiple four-wave mixing via cascaded fibers with discrete dispersion decreasing

Cascaded fiber geometry with the dispersion of each fiber decreasing is proposed to enhance the multiple four-wave mixing（FWM） generation. The first fiber with relatively large dispersion initiates and accelerates the expansion of multiple FWM, and the second fiber with small dispersion would allow the phase-matching process（thus the spectrum broadening）to keep going. Numerical and experimental results show that with this geometry not only multiple FWM expansion can be accelerated, but also the efficiency of multiple FWM products can be effectively improved with shorter fibers.

Enhancement and suppression of spatial splitting four-wave mixing in atomic medium

We experimentally report on the evolution from singly-dressed to doubly-dressed four-wave mixing （FWM） process by controlling the powers of the probe, the pump and the dressing fields respectively. The differences in the enhancement and the suppression of FWM signal between the two-level and cascade three-level atomic systems are observed and explained by the multi-dressed effect theoretically. Both the x direction and the y direction spatial splittings of the degenerate-FWM （DWFM） beams are obtained. We also investigate the switch between the enhancement and the suppression of the DWFM signals and between its spatial splittings in x direction and y direction. The spatial splittings in x direction and y direction can be controlled by the relative position and the intensity of the involved laser beams. Such a study can be useful for optimizing the efficiency of the FWM process and providing potential applications in spatial signal processing.

Multi-component optical azimuthons of four-wave mixing

We report the multi-component optical azimuthons of four-wave mixing （FWM） composed of several modulated vortex beams, the so-called azimuthons, in V-type three-level and two-level atomic systems. We analyze the formation mechanisms of the FWM azimuthons theoretically and experimentally. In addition, we illustrate the interactions between the co-propagating azimuthon components. Finally, we also compare the stabilities of azimuthons in V-type three-level and two-level atomic systems.

Electro-optomechanical switch via tunable bistability and four-wave mixing

We investigate the tunable bistable behavior of a hybrid nano-electro-optomechanical system(NEOMS) composed of S-shaped in the presence of two-level atoms, trapped inside a Fabry–Pérot cavity, and driven by a strong driving field and a weak probe field. The bistable behavior of the steady-state photon number and the mechanical steady-state positions are discussed. Further, we tune bistability by tuning all the coupling frequencies involved in the system and amplitude of the driving field. The present study provides the possibility of realization of a controllable optical switch depending on atom-field coupling, optomechanical coupling, electrostatic Coulomb coupling, and threshold power. In addition, we discuss that the non-linear effect of the hybrid NEOMS generates the four-wave mixing(FWM) process. Moreover, we show that the FWM process can be suppressed by the atom-field detuning and cavity-field detuning, which exhibits low photon transmission.

Measurement of the argon-gas-induced broadening and line shifting of the barium Rydberg level 6s24d 1^D2 by two-photon resonant nondegenerate four-wave mixing

We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state to the obser-vation of the broadening and shifting of the barium Rydberg level 6s24d 1^D2 by collision with argon. The collision broadening and shifting cross sections are measured. This technique is purely optical, and can investigate the pressure dependence of the transverse relaxation rate-P21 between the Rydberg state and an intermediate state, as well as the transverse relaxation rate F20 between the Rydberg state and the ground state.

Controllable four-wave mixing response in a dual-cavity hybrid optomechanical system

We systematically investigate the four-wave mixing(FWM)spectrum in a dual-cavity hybrid optomechanical system,which is made up of one optical cavity with an ensemble of two-level atoms and another with a mechanical oscillator.In this work,we propose that the hybrid dual-cavity optomechanical system can be employed as a highly sensitive mass sensor due to the fact that the FWM spectrum generated in this system has a narrow spectral width and the intensity of the FWM can be easily tuned by controlling the coupling strength(cavity-cavity,atom-cavity).More fascinatingly,the dual-cavity hybrid optomechanical system can also be used as an all-optical switch in view of the easy on/off control of FWM signals by adjusting the atom-pump detuning to be positive or negative.The proposed schemes have great potential applications in quantum information processing and highly sensitive detection.

Dynamical effects of the four-wave mixing enhancement induced by constructive quantum interference

In a four-level system of ultracold STRb atoms, through analytical and numerical calculations we propose an efficient scheme to achieve the enhanced four-wave mixing process and demonstrate its dynamical control by various parameters such as the travel distance z, probe detuning δ and the probe pulse width T. In particular, we find that the maximal intensity of the nonlinearly generated signal pulse can be about 80% of the initial input probe under the optimal condition. This greatly enhanced conversion efficiency occurs due to the constructive quantum interference between two different components of the generated signal pulse.

Controllable optical mirror of cesium atoms with four-wave mixing

The controllable optical mirror is experimentally accomplished in a A-type three-level atomic system coupled with standing wave. It is shown that the reflection of probe light results from electromagnetically-induced-transparency-based four-wave mixing, therefore the reflection efficiency is highly dependent on the angle for phase matching condition between the probe and coupling fields. The measured reflection spectra show good agreement with dispersion compensation theory.

Slow light via four-wave mixing in a hot rubidium vapour

In this work, we report on an off-resonant four-wave mixing experiment via a ladder-type configuration in a hot rubidium atomic vapour. We find for the first time, to the best of our knowledge, that the generated light is delayed compared with the reference. At the same time, the seeded signal beam is also delayed, though the delay time is not as so large as the one that the generated light has. Both delayed times can be adjusted experimentally by controlling the two-photon detuning. The experimental results are in good agreement with our theoretical predictions. Our results may be important for storing telecom-band photons.