Terahertz-wave generation in a conventional optical fiber

We theoretically propose surface-emitted and collinear phase-matched terahertz (THz)-wave generation in a conventional optical fiber. The third-order nonlinear effect, four-wave mixing (FWM), is used to generate THz waves in an optical fiber. Surface-emitted THz-wave generation via FWM is realized using a single-mode fiber. Perfect phase matching is obtained at ~800 nm and 1.5 microm pumping, and it follows that third-order polarization in an optical fiber has the same phase at any point. In this situation, the optical fiber acts like a phased array antenna of the THz wave. Collinear phase-matching THz waves are obtained under the same conditions as for surface-emitted THz waves, and the THz wave is propagated in the silica cladding of the optical fiber. This is a promising method for realizing a reasonable THz-wave source.     

Controllable four-wave mixing based on quantum dot-cavity coupling system

We theoretically study the four-wave mixing(FWM) response in a quantum dot-cavity coupling system, where a two-level quantum dot(QD) is placed in an optical cavity while the cavity mode is coupled to the nanomechanical resonator via radiation pressure. The influences of the QD-cavity coupling strength, the Rabi coupling strength of the QD, and the power of the pump light on the FWM intensity are mainly considered. The numerical results show that the FWM intensity in this hybrid system can be significantly enhanced by increasing the QD-cavity coupling strength. In addition, the FWM intensity can be effectively modulated by the Rabi coupling strength and the pump power. Furthermore, the effects of the cavity decay rate and the cavitypump detuning on the FWM signal are also explored. The obtained results may have potential applications in the fields of quantum optics and quantum information science.     

An equivalent circuit model for terahertz quantum cascade lasers:Modeling and experiments

Terahertz quantum cascade lasers(THz QCLs) emitted at 4.4 THz are fabricated and characterized. An equivalent circuit model is established based on the five-level rate equations to describe their characteristics. In order to illustrate the capability of the model, the steady and dynamic performances of the fabricated THz QCLs are simulated by the model.Compared to the sophisticated numerical methods, the presented model has advantages of fast calculation and good compatibility with circuit simulation for system-level designs and optimizations. The validity of the model is verified by the experimental and numerical results.     

Characterization of the pairwise correlations in different quantum networks consisting of four-wave mixers and beamsplitters

We investigate the performances of the pairwise correlations(PCs) in different quantum networks consisting of fourwave mixers(FWMs) and beamsplitters(BSs). PCs with quantum correlation in different quantum networks can be verified by calculating the degree of relative intensity squeezing for any pair of all the output fields. More interestingly, the quantum correlation recovery and enhancement are present in the FWM+BS network and the repulsion effect phenomena(signal(idler)-frequency mode cannot be quantum correlated with the other two idler(signal)-frequency modes simultaneously)between the PCs with quantum correlation are predicted in the FWM + FWM and FWM + FWM + FWM networks. Our results presented here pave the way for the manipulation of the quantum correlation in quantum networks.     

基于λ/4相移分布反馈半导体激光器四波混频的THz波长转换特性研究

利用耦合模方程，分析了基于λ/4相移分布反馈半导体激光器四波混频的波长转换特性.数值模拟表明：增大偏置电流、减小失谐量有利于扩展转换效率及消光比的动态范围，同时恶化了频率啁啾的动态范围; 受激射效应影响，消光比及频率啁啾在弛豫振荡频率处达到极大值.通过合理选择系统参量，可以获得较理想的波长转换效果.该方案无需抽运光输入，可实现高速、宽带波长转换，在光通信系统中有一定的应用前景. 关键词： λ/4相移分布反馈半导体激光器')" href="#">λ/4相移分布反馈半导体激光器 四波混频 波长转换     

利用微扰法分析两个相互耦合的参量四波混频过程

利用微扰法在旋转波近似下分析了铷原子中两个独立的参量四波混频过程和一个耦合的参量四波混频过程.当用超短激光脉冲相干激发这两个参量四波混频过程时,两个过程就会同时出现并且存在相互耦合作用.微扰分析表明,耦合的参量四波混频信号中可以观察到量子拍,量子拍幅度的大小不仅取决于超短脉冲的特性,而且依赖于两个耦合的参量四波混频过程中的相位匹配.     

Optical Bloch equations with dual photon excitation explain the polarization dependence of four wave mixing quantum beats

We explain the polarization dependence of four wave mixing (FWM) quantum beats for semiconductors as essentially due to the spin phase correlations of photo-excited electrons, rather than to Coulomb interaction between the electrons. A theoretical analysis is given within the framework of optical Bloch equations for the light–semiconductor interactions and the Luttinger–Kohn model for the band structure. Residual Coulomb interactions between charge carriers are ignored. The results suggest that the polarization dependence of FWM quantum beats is a purely coherent effect of dual photon excitations, rather than, e.g., exciton–exciton Coulomb interaction. We show that the coherence transfer between the excited states is responsible for the FWM in a configuration with orthogonally polarized pump and probe.     

High Efficiency Four-Wave Mixing with Relaxation Coupling of Longitude-Optical Phonons in Semiconductor Quantum Wells

The time-dependent analysis of four-wave mixing(FWM) has been performed in four-level double semiconductor quantum wells(SQWs) considering the cross-coupling of the longitude-optical phonons(LOP) relaxation. It is shown that both the amplitude and the conversion efficiency of the FWM field enhance greatly with the increasing strength of cross-coupling of LOP relaxation. Interestingly, a double peak value of the conversion efficiency is obtained under a relatively weak single-photon detuning considering the LOP coupling. When the detuning becomes stronger,the double peaks turn into one peak appearing at the line respect to the about equality two control fields. The results can be interpreted by the effect of electromagnetically induced transparency and the indirect transition. Such controlled high efficiency FWM based on the cross-coupling LOP may have potential applications in quantum control and communications.     

Quantum cascade structure for mid-IR four-wave mixing

The design and modeling of a quantum cascade optical amplifier (QCOA) using intra-cavity non-linear interactions to achieve wavelength conversion is proposed. The model is based on the nonlinear equation coupled with Maxwell wave equations for different emission modes. In the proposed structure, four wave mixing (FWM) output exhibits a peak as a function of pump and probe frequency if they are tuned to the energy levels of the QC structure subbands. Results demonstrate that the FWM output signal power significantly depends on how subbands are engineered and interact with optical pulses which propagate in multi layer medium. In addition, we show that by adjusting pump and probe signal frequencies, FWM output power can be tuned.     

Rabi Oscillations and Coherence Dynamics in Terahertz Streaking-Assisted Photoelectron Spectrum

We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_1/2 and 5P_3/2 in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.     

Fully quantized theory of four-wave mixing with bosonic matter waves

We solve exactly a set of fully quantized coupled equations that describe the quantum dynamics, including the evolution of quantum fluctuations, entanglements, and correlations, of four-wave mixing (FWM) with matter waves. The analytical solution reveals Rabi oscillations, collapses and revivals, and agrees with FWM experiments. It also applies to optical FWM and the Rayleigh superradiance in Bose-Einstein condensates.     

Quantum cascade lasers operating from 1.4 to 4 THz

The development of teranertz (THz) quantum cascade lasers (QCLs) has progressed considerably since their advent almost a decade ago.THz QCLs operating in a frequency range from 1.4 to 4 THz with electron-phonon scattering mediated depopulation schemes are described.Several different types of GaAs/AlGaAs superlattice designs are reviewed.Some of the best temperature performances are obtained by the so-called resonant-phonon designs that are described.Operation above a temperature of 160 K has been obtained across the spectrum for THz QCLs operating at ν > 1.8 THz.The maximum operating temperature of previously reported THz QCLs has empirically been limited to a value of ～ω/k B.A new design scheme for THz QCLs with scattering-assisted injection is shown to surpass this empirical temperature barrier,and is promising to improve the maximum operating temperatures of THz QCLs even further.     

Phase-conjugation in two-level atoms: comparison of quantum interference theory to exact results

The analytically derived predictions of a recently developed theory on phase conjugate four wave mixing (FWM) in two-level atoms [Phys. Rev. A 60, 1672 (1999)], which interprets many of the signal features as a consequence of quantum interference between the probability amplitudes for photon emission from relevant dressed states, is compared to the results that one obtains from a non-perturbative, numerical calculation of the density matrix equations. The results delineate the regimes and assumptions under which the perturbative results are valid, and it is shown that despite the simplifying assumptions that are invoked for the dressed state theory, many of its predictions are in qualitative agreement with the exact, numerical results.     

A New Bosonization Method for Photoexcited Electronic States and Its Application to Nonlinear Optical Responses

We derive a bosonized Hamiltonian for a semiconductor quantum well with a light field by a new bosonization method taking exactly into account the composite-particle effects of excitons. Then we apply the bosonized Hamiltonian to the four-wave-mixing (FWM) processes. The obtained Hamiltonian describes two-boson states corresponding to bound and unbound two-exciton states and guarantees exclusion of unphysical states, which cannot exist in the fermionic space due to the Pauli exclusion principle. Calculated results of the FWM signals are in good agreement with the experimental ones, and therefore, the bosonized Hamiltonian turns out to be able to describe two-exciton correlations effectively.     

Interaction of valence band excitations and terahertz TE-polarized cavity modes

The strong coupling of THz radiation and material excitations has potential to improve the quantum efficiency of THz devices. In this paper, we investigate a simple structure delivering THz polaritons and antipolaritons based on valence band transitions. The approach can improve the quantum efficiency of THz based devices based on TE mode in the strong coupling regime of THz radiations and intervalence bands transitions in a GaAs/AlGaAs quantum well. A Nonequilibrium Many Body Approach for the optical response beyond the Hartree–Fock approximation is used as input to the effective dielectric function formalism for the polariton/antipolariton problem. The energy dispersions relations in the THz range are obtained based on simplified analytical approximation.     

加偏置电场的双曲线量子阱中线性与三阶非线性光学吸收系数的计算

利用紧致密度矩阵近似方法,研究了加偏置电场双曲线量子阱中的线性与三阶非线性光学吸收系数. 得到了该系统中的线性与三阶非线性光学吸收系数的解析表达式.分析了势阱的形状、外加电场的大小以及入射光场的强度对吸收系数的影响规律. 文章以典型的AlxGa1－xAs/ GaAs双曲线量子阱为例作了数值计算.结果表明：随着势阱宽度的增加,系统的吸收系数将减小;随着外加电场的增加,系统的非对称性增加,系统的吸收系数将增加;随着外加光场强度的增加,系统的吸收系数将减小,并且当光强增加到一定值时会出现明显的饱和吸收现象,这一结论为进一步的实验研究提供了相应的理论依据.     

非对称量子阱中的二阶非线性光学极化率

本文主要研究了一个特殊非对称量子阱中的二阶非线性光学极化率,并且利用量子力学中的密度矩阵算符理论和迭代方法导出了二次谐波极化率的解析表达式.最后,以典型的GaAs/AlGaAs非对称量子阱为例作了数值计算.数值结果表明,较大的二次谐波极化率与系统的非对称性有关,系统的非对称性越大,二次谐波极化率越大.     

Optimized all-optical amplitude reshaping by exploiting nonlinear phase shift in fiber for degenerated FWM

We describe a novel performance optimization method for all-optical amplitude reshaping via degenerated four-wave mixing(FWM) in highly nonlinear optical fiber.The proposed optimization method is achieved by judiciously configuring the FWM operational condition and exploiting the nonlinear phase shift induced by self-and cross-phase modulations to properly influence the FWM conversion efficiency.Through the proposed scheme,fully functional and prevailing reshaping performance,including significant amplitude jitter suppression and extinction ratio improvement,is obtained within a single FWM stage.Results of the present theoretical calculation and numerical simulation verify the feasibility and advantages of the proposed scheme.     

Optimization of Quantum Correlation in Cascaded Four-Wave Mixing

We propose a measurement strategy that can be used to optimize quantum correlation for a cascaded four-wave mixing (FWM) structure. By calculating the covariance matrix of a cascaded FWM structure, we can get all the correlations between any two parties in the outputs. We then calculate the eigenvalues and corresponding eigenmodes of the covariance matrix to find the squeezing degrees of the squeezed modes. Our theoretical model can explain our previous experimental results very well and is useful to optimize the squeezing degree in the cascaded FWM structure.     

半导体光放大器中垂直双抽运四波混频效应的理论研究

建立了输入信号光偏振方向任意情况下的半导体光放大器(SOA)中 垂直双抽运四波混频(FWM)效应的完整宽带理论模型. 以基于SOA的垂直双抽运FWM型全光波长转换器为例, 通过数值模拟的方法, 理论研究了输入信号光与两抽运光功率、两抽运光与信号光之间的波长失 谐量和输入信号光偏振方向等工作参数对SOA的垂直双抽 运FWM效应及基于SOA的垂直双抽运FWM型波长转换器特性的影响.