偶极子位置及偏振对激发光子晶体H1微腔的影响

光子晶体微腔和量子点的集成是实现量子信息处理非常具有潜力的平台之一,利用微腔和量子点的耦合可以制备纠缠光子对,实现对量子态的操控.因为光子晶体微腔具有品质因子高、模场体积小等优点,可以极大地增强光与物质之间的相互作用,从而易于实现量子态在不同物理体系之间的转换.通过单量子点和光子晶体H1微腔的耦合可以产生纠缠光子对,因为H1微腔具有简并的、模式偏振正交的基态模式.通常微腔模式的激发随着量子点在微腔中的位置变化而改变,本文用时域有限差分方法研究了偶极子光源的位置及偏振对激发光子晶体H1微腔模式的影响.结果表明:通过改变偶极子光源位置可以选择性地激发H1微腔简并模式中的一个;具有某一偏振的偶极子光源只能激发相应偏振的微腔模式;模式激发强度的大小也是由偶极子光源在微腔中的位置决定的.鉴于目前量子点在微腔中的位置尚不能精确控制,所以微腔模式受激发光源位置的影响的研究具有重要意义.     

光子晶体微腔中高偏振单偶极模的研究

三角晶格排列的光子晶体微腔中的偶极模式是简并的,通过改变其晶格的对称性可以消除模式简并.晶格的整体形变破坏了晶格对称性从而影响光场的分布,同时还改变了电磁场的偏振分布.晶格整体形变使得简并的偶极模式分离成x极和y极偶极模式.通过计算分析发现分离后的模式具有良好的偏振特性,从而为实现单偏振光子晶体激光器提供了一种很好的途径.文中针对光子晶体薄板结构的微腔,主要计算了偶极模中x极偶极模式在不同拉伸时以及不同填充因子情况下的Q值,并分别计算了x关键词： 光子晶体 偶极模 品质因子 偏振度     

三能级原子系统中原子偶极压缩和光场压缩间的关联

通过考察三能级原子与单模和双模场相互作用系统中原子偶极压缩和光场压缩随时间的演化规律, 研究了原子偶极压缩与光场压缩之间的关系, 讨论了原子偶极压缩与光场压缩之间相互转换的特征, 并给出了初始处于偶极压缩状态的原子辐射压缩光的条件。     

Cavity‐photon contribution to the effective interaction of electrons in parallel quantum dots

A single cavity photon mode is expected to modify the Coulomb interaction of an electron system in the cavity. Here we investigate this phenomena in a parallel double quantum dot system. We explore properties of the closed system and the system after it has been opened up for electron transport. We show how results for both cases support the idea that the effective electron‐electron interaction becomes more repulsive in the presence of a cavity photon field. This can be understood in terms of the cavity photons dressing the polarization terms in the effective mutual electron interaction leading to nontrivial delocalization or polarization of the charge in the double parallel dot potential. In addition, we find that the effective repulsion of the electrons can be reduced by quadrupolar collective oscillations excited by an external classical dipole electric field.     

两等同双能级原子与三模腔场六光子共振相互作用辐射谱研究

研究了两个偶极－偶极力关联的等同双能级原子与三模腔场六光子共振相互作用的辐射谱，对三模分别处于不同数态时辐射谱的结构特征和物理特性进行了详细分析，从而揭示了一系列重要的新特点。     

Efficient atomic quantum memory for photonic qubits in cavity QED

We investigate a scheme of atomic quantum memory to store photonic qubits of polarization in cavity QED. It is observed that the quantum state swapping between a single-photon pulse and a Λ-type atom can be made via scattering in an optical cavity [T. W. Chen, C. K. Law, P. T. Leung, Phys. Rev. A 69 (2004) 063810]. This swapping operates limitedly in the strong coupling regime for Λ-type atoms with equal dipole couplings. We extend this scheme in cavity QED to present a more feasible and efficient method for quantum memory combined with projective measurement. This method works without requiring such a condition on the dipole couplings. The fidelity is significantly higher than that of the swapping, and even in the moderate coupling regime it reaches almost unity by narrowing sufficiently the photon-pulse spectrum. This high performance is rather unaffected by the atomic loss, cavity leakage or detunings, while a trade-off is paid in the success probability for projective measurement.     

立体耦合光子晶体薄板微腔的高Q值特性研究

利用微腔之间的立体耦合,提出了基于无源材料硅的双层光子晶体薄板H1(DLPCS-H1)腔,薄板之间为空气层.使用三维时域有限差分方法和Padé近似方法分析了DLPCS-H1腔的偶极模的场分布和品质因子.通过对中间空气层高度的优化使DLPCS-H1腔的偶极模的品质因子得到了显著的提高,大约为单层光子晶体薄板H1腔的偶极模的品质因子的4倍.此外,还研究了三层光子晶体薄板H1腔,它的偶极模的品质因子约为单层光子晶体薄板H1腔的偶极模的品质因子的7倍.     

Normal-mode spectroscopy of a single-bound-atom-cavity system

The energy-level structure of a single atom strongly coupled to the mode of a high-finesse optical cavity is investigated. The atom is stored in an intracavity dipole trap and cavity cooling is used to compensate for inevitable heating. Two well-resolved normal modes are observed both in the cavity transmission and the trap lifetime. The experiment is in good agreement with a Monte Carlo simulation, demonstrating our ability to localize the atom to within lambda/10 at a cavity antinode.     

Influence of Doppler broadening on the stability of monomode ring lasers

We consider a single running mode in a ring gas laser where inhomogenous Doppler broadening is dominant. The analytic linear stability analysis of the stationary solution leads to the conclusion that in the bad cavity limit a second threshold exists; a salient property is that it occurs at low intensity in contradistinction to homogeneously broadened media where it occurs at high intensity.     

Polarization control of microwave emission from high powerrectangular cross-section gyrotron devices

Results are summarized of experiments on a gyrotron utilizing a rectangular-cross-section (RCS) cavity region. The major issue under investigation is polarization control of microwave emission as a function of magnetic field. The electron beam driver is the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V=0.8 MV, I_diode=1-10 kA, I_tube=0.1=0.5 kA, and t_e-beam=0.4-1.0 μs. The annular e-beam is spun up into an axis-encircling beam by passing it through a magnetic cusp prior to entering the RCS interaction cavity. Experimental results show a high degree of polarization in either of two orthogonal modes as a function of cavity fields. The RCS gyrotron produced peak powers of 14 MW in one polarization (TE₁₀) and 6 MW in the cross-polarized mode (TE ₀₁). Electronic efficiencies for this device reached as high as 8% with transverse efficiency of 16%. Experimental results on the beam alpha (α=V_⊥/V_∥) diagnostics, where alpha is the ratio of the e-beam's transverse velocity to its parallel velocity, agree well with the single electron trajectory code. MAGIC code results are in qualitative agreement with microwave measurements. Microwave emission shifts from the dominant fundamental mode polarization (TE₁₀□ ), to the next higher order mode polarization (TE₀₁□) as the solenoid magnetic field is raised from 1.4-1.9 kGauss. Frequency measurements using heterodyne mixers support mode identification as well as MAGIC code simulations     

耦合双原子与单模场喇曼相互作用模型的腔场谱

研究了存在偶极-偶极相互作用的两个等同二能级原子与单模光场喇曼耦合过程的腔场谱.结果表明,当两原子处于同一能级时,腔场谱在弱场和强场条件下相应地为五峰和三峰结构.当两原子初态处于不同能级时,交换对称性对谱结构有明显的影响. 原子间的相互作用只在初始场很弱时才会影响谱结构.     

Linear dipole behavior of single quantum dots encased in metal oxide semiconductor nanoparticles films

Understanding of charge/energy exchange processes and interfacial interactions that occur between quantum dots (QDs) and the metal oxides is of critical importance to these QD-based optoelectronic devices. This work reports on linear dipole behavior of single near-infrared emitting CdSeTe/ZnS core/shell QDs which are encased in indium tin oxide (ITO) semiconductor nanoparticles films. A strong polarization anisotropy in photoluminescence emission is observed by defocused wide-field imaging and polarization measurement techniques, and the average polarization degree is up to 0.45. A possible mechanism for the observation is presented in which the electrons, locating at single QD surface from ITO by electron transfer due to the equilibration of the Fermi levels, result in a significant Stark distortion of the QD electron/hole wavefunctions. The Stark distortion results in the linear polarization property of the single QDs. The investigation of linear dipole behavior for single QDs encased in ITO films would be helpful for further improving QD-based device performance.     

Compact, single-frequency all-fiber Q-switched laser at 1 microm

We demonstrate a unique, all-fiber, actively Q-switched laser operating in the 1 microm region. The laser is compact, single mode, single frequency, highly polarized, and exhibits high peak power. The laser cavity is constructed without external coupling, utilizing fiber Bragg gratings that permit feedback at only a single polarization. By using a piezoelectric to press the fiber and modulate the fiber birefringence, the cavity is switched between high and low loss states, permitting Q-switching. We demonstrate this Q-switching at repetition rates up to 700 KHz.     

A hypothetical model of confinement in a dia-electric medium

The assumption of a perfect color dia-electric vacuum in quantum chromodynamics (QCD) led to a reasonable explanation of quark confinement. Along the same lines, a hypothetical dia-electric medium in electromagnetism is shown to lead to charge confinement; although such a medium does not exist, the analysis of this hypothetical problem illuminates in a very simple and straightforward way how this dia property (negative susceptibility) of a medium leads to confinement. It is shown that adding a dipole (particle-antiparticle) charge distribution to such a dia-electric medium would lead the creation of a cavity surrounding the charges; by a simple analysis, using the image problem along with a series expansion in Legendre polynomials, it is shown that the polarization charge distribution on the cavity's surface would lead to an increase in the dipole energy by a finite amount; on the other hand, the increase in the electric energy of a single charge inserted in such a medium would be infinite. It is thus concluded that in such a dia-electric medium, separating the charges of a dipole would require an infinite amount of energy, and thus illustrating in a simple way the confinement concept.     

Properties of laser gain of Li:CdZnO/ZnMgO quantum well

The many-body optical gain in Li:CdZnO/MgZnO quantum well (QW) structures with spontaneous polarization and piezoelectric polarization, and ferroelectric dipole moment is investigated by using the non-Markovian gain model with many-body effects. The CdZnO/MgZnO QW structure with high Cd composition is found to have smaller optical gain because the strain-induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd. The internal field is reduced due to the additional polarization by Li in the CdZnO/MgZnO QW structure. These results show that Li:CdZnO-based QW lasers are promising candidates for optoelectric applications in visible and UV regions.     

Single polarization transmission in pedestal-supported silicon waveguides

In this Letter, properties of a pedestal-supported silicon waveguide are investigated, showing that it supports single polarization transmission. The pedestal is fabricated easily through a wet-etching process on strip waveguides. Theoretical analysis shows that this property is due to the leakage of quasi-TM mode when the pedestal width is small. A polarization extinction ratio larger than 20 dB at 1550 nm is measured in the pedestal waveguide sample, demonstrating single polarization transmission property experimentally. Thanks to its large single polarization transmission bandwidth, robustness in fabrication tolerance, and simple fabrication process, pedestal waveguides will have potential applications as simple silicon-integrated polarizers.     

Switchable dual-wavelength Erbium-doped fiber ring laser with cascaded fiber Bragg gratings

We have experimentally shown wavelength mode switching in a dual-wavelength Erbium-doped single cavity fiber laser where the initial two wavelengths of 1 nm spacing are determined by the cascaded reflection type short-period fiber Bragg gratings having two different centre wavelengths of 1550.5 and 1551.5 nm. The lasing mode depends on the polarization in the ring cavity to migrate from one wavelength to another or operates in both modes in a polarization beam splitter output. To effectively control the polarization in the ring cavity, the polarization controllers were positioned before and after the polarization beam splitter. This method of wavelength switching provides a simple way of mode tuning in dual-wavelength fiber lasers.     

高聚物与光场相互作用的微观机制

分析光场与高聚物相互作用的微观机制，介绍高分子与小分子在光场作用下的极化过程。对在窄束光场作用下，高分子链极化后链上各处极化程度的分布情况进行研究，指出对于高度拉伸的聚合物薄膜，电偶极子模型不适合准确解释高分子与光场相互作用的微观机制。为此，采用符合实际的天线模型分析高分子天线与窄束光场的相互作用，从理论上推导出天线模型高分子链上一小段的极化公式，并用离散变分方法——DVM（discrete variational method）计算一个高分子链的极化分布，验证了文中推导出的分式的合理性。最后，将极化分布看作是电流在天线上的分布，计算了天线的次级辐射在空间中的角分布，得到天线模型对电偶极子模型的修正因子。     

Single polarization, single transverse mode, and widely tunable narrow-linewidth laser from a multimode vertical cavity surface-emitting laser by use of a coupled cavity

A simple method for achieving a widely tunable narrow-linewidth, single polarization state and single transverse mode lasing oscillation from a commercially available multimode vertical cavity surface-emitting laser by use of a coupled cavity is reported. The laser has a wavelength tuning range of more than 5 nm along 850 nm, a side-mode suppression ratio of approximately 15 dB, and an output power of approximately 0.3 mW from a 50-microm multimode optical fiber at a bias current of 15 mA. The laser was operated in a single state of polarization lasing oscillation without any polarization switching.     

Propagator of an electron in a cavity in the presence of a coherent photonic field

In the present paper we consider the case of an electron under the presence of a single mode field in a cavity linearly polarized in the z-direction. We adopt the dipole approximation and we derive the full propagator of the electron. In the present case we suppose that the field is in a coherent state. The parameters of the propagator involve Mathieu functions. Finally we extract the time evolution of an initially Gaussian wavepacket and its probability density. The present theory is applicable to the interaction of strong fields with atoms. Received 17 March 2000 and Received in final form 19 December 2000