Geometric phase in cavity QED containing a nonlinear optical medium and a quantum well

The geometric phase (GP) in cavity QED filled with a nonlinear medium and containing a quantum well is analyzed. We observe collapses and revivals. The optical nonlinearity leads to high frequency oscillations of the GP. The GP is very sensitive not only to the dissipation rates but also to the amplitude of the laser pump.     

Optical force and friction of a V-type three-level atom in a driven high-Q cavity

A model is presented to calculate the optical force and friction for a three-level atom in a V-type configuration in a weakly driven high-finesse cavity. Analytical expressions for the force and friction are derived using Heisenberg equations. It is demonstrated that the cooling rate can be increased by one order of magnitude over that of a two-level atomic system, which would stimulate further experimental investigations.     

Two different regimes in a V-type three-level atom trapped in an optical cavity

In this paper two different behaviors of a V-type three-level atom which is driven by a classical field in an optical cavity are shown. We show that the behavior of an atom depends on the values of the critical photon number. The system treatment for large enough values of the critical photon number is described by the semiclassical laser theory. In contrast, for small enough values of the critical photon number, the system shows new quantum properties. In the former case, it is shown that the system performs like a conventional laser and in the latter one, the system acts as an effective two-level model. The behaviors of the system are investigated both in the semiclassical approximation and full quantum theory. For comparing the results, computer simulations are implemented.     

The nonlinear effects over time evolution of a three-level atom confined in a single mode optical cavity

A single atom is trapped in an optical cavity in the presence and absence of a nonlinear mirror corresponding to the nonlinear and linear regimes, respectively. The time evolutions of both systems are derived. The resultant equations are numerically solved by a fourth-order Runge–Kutta method. The effect of the nonlinear mirror over time evolution of the population inversion, the mean photon number and the second-order coherence function is investigated. It is shown that in the presence of the nonlinear effects, the time average of the population inversion is increased. As the time evolution proceeds, the mean photon number is decreased as well as the light exhibiting sub-Poissonian photon distributions. Under specific conditions and in a weak-driving limit, these systems can be well approximated by an effective two-level atom. The result of the calculations confirms the predictions of the two-level model.     

Enhanced gain and narrow linewidth of an optical cavity by the Doppler effect in a four-level atomic system

Abstract

A scheme for high gain and narrow linewidth of an optical cavity with a four-level atomic system is proposed by the Doppler effect via active Raman gain (ARG) process. Atomic motion leads to Doppler frequency shift which induces constructive interference for the linear susceptibility. The enhanced normal dispersion greatly narrows the cavity linewidth, and the amplified gain gives rise to a high cavity transmission. Simulation results show that the cavity linewidth based on ARG is about one order of magnitude narrower than that based on electromagnetically-induced transparency under the same conditions, and the cavity transmission intensity could be enhanced by nearly 30 times.     

Performance of line codes in optical direct detection continuous phase frequency shift keying transmission system impaired by polarization mode dispersion

Small deviations from perfect circular symmetry in the core region of single mode fiber (SMF) cause optical pulses to become broadened as they propagate. This phenomenon is referred to as polarization mode dispersion (PMD), which leads to intersymbol interference and becomes a major impediment for the high speed long-haul fiber-optic links. We present here the theoretical complement for evaluating the performance of a line-coded continuous phase frequency shift keying (CPFSK) optical transmission system with a direct detection receiver. The analysis is carried out for two different line-coding schemes, i.e. alternate mark inversion (AMI) and order-1 coding, to investigate the effectiveness of the line coding in counteracting the effect of PMD in a CPFSK direct detection transmission system in the presence of group velocity dispersion (GVD) and receiver noise in a single mode fiber. The average bit error rate (BER) performances are evaluated without and compared to that of line codes at a bit rate of 10 Gb s^?1 considering Maxwellian distribution for the mean differential group delay (DGD). We found that the amount of power penalty improvement of line-coded systems is within 0.65 to 2.25 dB with respect to NRZ data at a BER of 10^?9.     

Optical Frequency Metrology of an Iodine-Stabilized He-Ne Laser Using the Frequency Comb of a Quantum-Interference-Stabilized Mode-Locked Laser

We perform optical frequency metrology of an iodine-stabilized He-Ne laser using a mode-locked Ti:sapphire laser frequency comb that is stabilized using quantum interference of photocurrents in a semiconductor. Using this technique, we demonstrate carrier-envelope offset frequency fluctuations of less than 5 mHz using a 1 s gate time. With the resulting stable frequency comb, we measure the optical frequency of the iodine transition [¹²⁷I₂ R(127) 11-5 i component] to be 473 612 214 712.96 ± 0.66 kHz, well within the uncertainty of the CIPM recommended value. The stability of the quantum interference technique is high enough such that it does not limit the measurements.     

Analysis and observation,on an atomic resonance,of the frequency shift due to the length modulation of an optical cavity

The frequency shift of the light owing to a cavity length modulation has been observed with the spectroscopy of the 1S-3S two-photon transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm. One produces this radiation by frequency doubling a 410-nm radiation in an enhancement ring cavity. The length modulation of this cavity induces frequency shifts and a splitting of the observed 1S-3S line. We obtain a good agreement between the experiment and the theoretical analysis.     

基于辐射噪声强度和线谱多普勒的目标运动参数估计

提出了一种利用辐射噪声强度和线谱多普勒频移联合估计匀速直线运动目标的速度和正横距离的方法。该方法基于单水听器观测,首先在球面波近似下利用目标辐射噪声强度估计出正横时刻并确定目标速度和正横距离之间满足的线性关系;然后利用线谱多普勒频移,通过对一个新定义的代价函数进行一维搜索的方法估计出目标速度和正横距离。与现有各种基于噪声强度和线谱多普勒频移进行测距测速的方法相比,该方法具有以下优点：（1）要求更少的先验知识,易于确定参数搜索范围;（2）参数估计过程中仅需一维搜索,并且算法可应用于需对目标参数进行预报的场合。数值仿真给出了不同参数条件下目标运动参数估计结果的统计误差。湖试结果验证了该方法的有效性。     

On the quantum core of an optical vortex

An optical vortex is a line around which the phase increases by an integer multiple of 2π. It follows that the phase on the line itself is undefined and hence the field must have zero amplitude there. Berry and Dennis have suggested that this line of darkness is smoothed by a ‘quantum core’ with a radius proportional to ?^1/2 and have illustrated this idea by considering the competition between stimulated and spontaneous emission by an excited atom placed in the vicinity of the vortex. We show here that a similar phenomenon may be seen in absorption when the quantum state of motion of the absorbing atom is taken into consideration. There is, however, an underlying quantum singularity in which the absorption events for an atom centred on the vortex core can take place only if accompanied by a transfer of angular momentum to the atomic motion. The nature of this singularity relies on the evolution of an entangled state between the electronic and motional degrees of freedom of the trapped atom. We comment briefly on the effects of field quantisation on this quantum core of the optical vortex.     

理论研究垂直腔半导体光放大器脉冲放大特性

从速率方程和薄膜光学理论出发,对垂直腔半导体光放大器(Vertical Cavity Semiconductor Optical Amplifiers,简称VCSOAs)在脉冲工作情况下的动态增益进行了数值模拟.在计算中考虑了载流子和光强沿光轴方向的不均匀性,以及腔内介质折射率的不连续性对光波传输的影响.详细分析了反射模式下VCSOA在脉冲通过时载流子密度和瞬时增益的变化、输出光脉冲的畸变以及抽运光功率、分布布拉格反射镜(Distributed Bragger Reflector,简称DBR)周期数、输入脉冲能量以及脉冲宽度等参量对脉冲放大中的能量增益的影响.结果表明,能量增益随抽运光功率增大而增加;在峰值功率一定时输入脉冲宽度的增加将减小能量增益;输入脉冲能量的增加也会引起能量增益的下降,而适当减少顶部DBR的周期数可以改善这种脉冲放大的能量增益饱和特性.     

Entropy generation due to natural convection of a nanofluid in a partially open triangular cavity

A numerical analysis of laminar natural convection with entropy generation in a partially heated open triangular cavity filled with a Cu-water nanofluid has been carried out. Mathematical model including partial differential equations and boundary conditions has been solved by using finite difference method. Particular efforts have been focused on the effects of Rayleigh number, nanoparticles volume fraction and position of the local heater on streamlines, isotherms, local entropy generation as well as local and average Nusselt number, average Bejan number, average entropy generation and fluid flow rate. Obtained results have demonstrated that the heat transfer enhancement and fluid flow attenuation with nanoparticles volume fraction, mainly for high values of Rayleigh number.     

External-Field Shifts of the 199Hg+ Optical Frequency Standard

Frequency shifts of the ¹⁹⁹Hg⁺ 5d¹⁰6s ²S_1/2 (F = 0, M_F = 0) to 5d⁹6s^{2 2}D_5/2 (F = 2, M_F = 0) electric-quadrupole transition at 282 nm due to external fields are calculated, based on a combination of measured atomic parameters and ab initio calculations. This transition is under investigation as an optical frequency standard. The perturbations calculated are the quadratic Zeeman shift, the scalar and tensor quadratic Stark shifts, and the interaction between an external electric field gradient and the atomic quadrupole moment. The quadrupole shift is likely to be the most difficult to evaluate in a frequency standard and may have a magnitude of about 1 Hz for a single ion in a Paul trap.     

Controllable optical bistability and Fano line shape in a hybrid optomechanical system assisted by kerr medium: possibility of all optical switching

We theoretically analyse the optical and optomechanical nonlinearity present in a hybrid system consisting of a quantum dot(QD) coupled to an optomechanical cavity in the presence of a nonlinear Kerr medium, and show that this hybrid system can be used as an all optical switch. A high degree of control and tunability via the QD-cavity coupling strength, the Kerr and the optomechanical nonlinearity over the bistable behaviour shown by the mean intracavity optical field and the power transmission of the weak probe field can be achieved.The results obtained in this investigation has the potential to be used for designing efficient all-optical switch and high sensitive sensors for use in Telecom systems.     

Enhancement of discord and entanglement with detuning for two coupled quantum dots in a driven cavity

We study the quantum discord for a system of two identical coupled quantum dots interacting with quantized cavity field in the presence of cavity as well as dot decay and detuning. The cavity is externally driven by a coherent light. These results are compared with the entanglement of the quantum dots in various parameter regimes in which system may or may not show bistability. We show that the discord in the steady state is nonzero for any nonzero cavity field amplitude. The system has higher discord in the upper branch of the bistability curve where the entanglement is zero. We also find many other interesting results including high discord and entanglement in the presence of detuning, a phenomenon which we further examine by approximating the density matrix in the appropriate limit.     

Method of Measuring the Fundamental Frequency of a Complex Periodic Signal

A simple method is suggested for measuring the fundamental frequency of a complex periodic signal for various spectral amplitudes. The experimental results reported prove that the method is accurate.     

红外空芯光纤辐射温度计的研制及应用

为了对冲击发电机的轴套温度进行监测,设计并研制了一种新型的红外光纤辐射温度计.温度计主要由红外空芯玻璃光纤、红外探测器、放大电路及80C552单片机组成.在分析各部分实现功能的基础上,重点研究了环境温度变化对探测器的影响,并实现了数学建模.温度计的工作波长是8~14μm,测量温度范围是60~400℃,测试环境温度范围是25~60℃.利用可精确控温的实物标定炉和环境模拟箱对温度计进行了标定,测量误差小于2%.经过几个月的在线监测,取得了较好的测量结果.     

全固态飞秒光学频率梳研究进展及展望

自1999年至今,光学频率梳（Optical Frequency Comb,OFC）经历了二十多年的快速发展。基于飞秒激光的光学频率梳在频率计量学、超快光谱学、光学频率标准、阿秒脉冲的产生、多脉冲时域合成等众多前沿研究领域中发挥了不可替代的作用。特别是继飞秒钛宝石激光频率梳、飞秒光纤激光频率梳之后,基于二极管激光直接泵浦的全固态飞秒激光频率梳由于兼具钛宝石激光噪声低、重复频率高,光纤激光结构紧凑、电光效率高的共同优势,引起了许多研究组的兴趣,并取得系列有意义的进展。本文综述了全固态光学频率梳的发展和已取得的典型应用,并结合笔者所在课题组取得的研究成果,对全固态光学频率梳未来的发展方向进行展望,为促进全固态飞秒锁模振荡器的发展提供借鉴。     

Tunable ultranarrow linewidth of a cavity induced by interacting dark resonances

A scheme for obtaining a tunable ultranarrow linewidth of a cavity due to an embedded four-level atomic medium with double-dark resonances is proposed. It is shown that the steep dispersion induced by double-dark resonances in the transparency window leads to the ultranarrow transmission peak. Compared with the case of a single-dark resonance system, the linewidth can be narrowed even by one order under proper conditions. Furthermore, the position of the ultranarrow peak can be engineered by varying the detuning of the control field.     

法拉第滤光器在法拉第激光器领域研究进展

法拉第激光器是一种利用法拉第反常色散原子滤光器作为选频元件的新型外腔半导体激光器,原理上法拉第激光的输出波长随着激光二极管驱动电流及工作温度的变化,始终与原子跃迁谱线相对应,可以将激光频率有效地锁定至原子跃迁谱线,实现窄线宽的激光输出信号,并且短期与长期频率稳定性均较好。本文详细介绍了自1845年法拉第旋光效应提出以来,法拉第反常色散原子滤光器的发展历程,法拉第激光器的工作机理、发展历程以及性能优越性,并结合国内外的研究进展,介绍了法拉第激光发展各个阶段的技术瓶颈及相应的解决办法,同时展望了法拉第激光器未来在量子领域特别是量子精密测量领域的重要价值。