S-matrix pole trajectories in quantum wires with resonantly coupled cavities

We consider a T-shaped, one-dimensional quantum waveguide containing an attractive or repulsive impurity in the lateral stub, and study how the resonance poles move in the complex k-plane when the strength or the position of the defect changes. Similarities and differences with respect to standard potential scattering problems are highlighted.     

Nonstationary Casimir effect in cavities with two resonantly coupled modes

We study the peculiarities of the nonstationary Casimir effect (creation of photons in cavities with moving boundaries) in the special case of two resonantly coupled modes with frequencies ω₀ and (3+Δ)ω₀, parametrically excited due to small amplitude oscillations of the ideal cavity wall at the frequency 2ω₀(1+δ) (with |δ|,|Δ|⪡1). The effects of thermally induced oscillations in time dependences of the mean numbers of created photons and the exchange of quantum purities between the modes are discovered. Squeezing and photon distributions in each modes are calculated for initial vacuum and thermal states. A possibility of compensation of detunings is shown.     

Modification of photon states in photonic molecules with semiconductor nanocrystals

We report on the coherent coupling of whispering gallery modes (WGMs) in a photonic molecule formed from two melamine formaldehyde spherical microcavities coated with a thin shell of CdTe nanocrystals. Utilizing different excitation conditions, the splitting of the WGM resonances originating from bonding and antibonding branches of the photonic states is observed and a fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Observation of optical wavelength switching with controllable spectral position and separation is reported.     

One-dimensional coupled cavities photonic crystal filters with tapered Bragg mirrors

The performance of one-dimensional (1D) coupled cavities photonic crystal (PC) filters has been analyzed by finite-difference time-domain (FDTD) simulation. It is shown that the addition of tapered Bragg mirrors at each side of the cavities, to create near-Gaussian field profiles for the cavity modes, results in the prediction of near flat-top passband filters with high out-of-band rejection ratio and near unity transmission. The tapered structures suppress the vertical radiation loss to allow optimization of the number of mirror periods for the best filter response whilst guaranteeing high transmission. A critical coupling condition (k = 2L_out/L_in = 1) for flat-top responses in doubly coupled cavities filters is proposed in the tapered structures. An optimized filter for 100 GHz optical communication system are demonstrated with 1 dB bandwidth of 0.17 nm, roll-off of 0.6 dB/GHz, out-of-band signal rejection of 33 dB and transmission of 95%. Further improvement of roll-off and out-of-band rejection is demonstrated in a triply coupled cavities filter.     

Density of states in coupled chains with off-diagonal disorder

We compute the density of states rho(varepsilon) in N coupled chains with random hopping. At zero energy, rho(varepsilon) shows a singularity that strongly depends on the parity of N. For odd N, rho(varepsilon) approximately 1/|varepsilonln (3)varepsilon|, with and without time-reversal symmetry. For even N, rho(varepsilon) approximately |lnvarepsilon| in the presence of time-reversal symmetry, while there is a pseudogap, rho(varepsilon) approximately |varepsilonlnvarepsilon|, in the absence of time-reversal symmetry.     

渐变折射率光量子阱对束缚态能级的调整

在对称的均匀电介质材料光子晶体体系中插入另一折射率渐变的光子晶体可构成光量子阱结构.利用时域有限差分法计算了不同折射率分布光量子阱结构的传输谱.研究表明：束缚态是对处于垒光子晶体禁带中的阱光子晶体导通带的离散化,束缚态能级个数等于阱光子晶体结构单元的重复周期数；以渐变方式调整阱区折射率分布,可在特定频率范围内得到新的互不交叠的束缚态.这样在有限的禁带区域可以成倍增加光子束缚态而无需增大光量子阱结构的尺寸,使信道密度最大化、光波有效带宽的使用最优化.这种量子阱结构可用于制作超窄带滤波器和多通道窄带滤波器,有望在光通信超密集波分复用和光学精密测量技术中获得广泛应用. 关键词： 光量子阱 光子束缚态 渐变折射率 光子晶体     

Wavelength switching by mode interference of coupled cavities with photonic crystal reflectors

We report the development of current-controlled widely tunable laser diodes based on InP with photonic crystal reflectors. The lasers consist of two longitudinally coupled and individually contacted segments that are coupled through photonic crystal sections. Two designs are presented, one based on a gain-coupled distributed feedback mechanism, the second based on contra-directional coupling of two photonic crystal waveguides. The emission wavelength can be switched quasi-continuously over a range around 53 nm for the first design. PACS 42.55.Px; 42.60.Da; 42.60.Fc; 42.25.Hz; 42.70.Qs     

Observation of nanojet-induced modes with small propagation losses in chains of coupled spherical cavities

Nanojet-induced modes (NIMs) and their attenuation properties are studied in linear chains consisting of tens of touching polystyrene microspheres with sizes in the 2-10 micro m range. To couple light to NIMs we used locally excited sources of light formed by several dye-doped fluorescent microspheres from the same chain of cavities. We directly observed the formation and propagation of NIMs by means of the scattering imaging technique. By measuring attenuation at long distances from the source, we demonstrate propagation losses for NIMs as small as 0.5 dB per sphere.     

Ultra-fast all-optical switching in MEH-PPV photonic crystals with resonantly enhanced nonlinearity

Photonic crystal all-optical switching is realized in two-dimensional nonlinear photonic crystals made of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]. Organic polymer films are fabricated by a slow evaporation method. Under resonant excitation, the organic matrix provides very large third-order nonlinear optical susceptibility. An operating pump energy as low as 514 pJ/cm² and a high switching efficiency of 70% are achieved for the photonic crystal optical switching. A switching time of 45.6 ps is maintained due to fast Forster transfer of excitons.     

Quasiclassical dynamics of resonantly driven Rydberg states

We present a semiclassical analysis of the dynamics of Rydberg states of atomic hydrogen driven by a resonant microwave field of linear polarization. The semiclassical quasienergies of the atom in the field are found to be in very good agreement with the exact quantum solutions. The ionization rates of individual eigenstates of the atom dressed by the field reflect their quasiclassical dynamics along classical periodic orbits in the near integrable regime, but exhibit a transition to nonspecific rates when global chaos takes over in phase space. We concentrate both on the principal resonance where the unperturbed Kepler frequency is equal to the driving field frequency and on the higher primary resonance The latter case allows for the construction of nondispersive wave packets which propagate along Kepler ellipses of intermediate eccentricity. Received: 23 June 1998 / Accepted: 10 November 1998     

High-Q cavities in photosensitive photonic crystals

We propose a novel concept for creating high-Q cavities in photonic crystal slabs (PCSs) composed of photosensitive material. To date, high-Q cavities have been realized through the use of double heterostructures where the lattice geometry is altered via nanolithography. Here, we show that selective postexposure to light of a uniform PCS composed of photosensitive material, altering the refractive index permanently, can also yield high-Q microcavities. We show theoretically that high-Q cavities (up to Q = 1 x 10(6)) can be achieved with photoinduced index changes that are well within what can be achieved in chalcogenide glasses.     

弱相干场耦合腔系统中的纠缠特性

研究由三个全同的二能级原子与耦合腔构成的系统, 考虑腔场处于弱相干态的情况. 采用Negativity熵度量两子系统间的纠缠, 利用数值计算方法研究了两个原子之间和两个腔场之间的纠缠性质. 讨论了腔场间的耦合系数和腔场的强度对纠缠特性的影响. 研究结果表明: 随光场强度增大, 原子间纠缠和腔场间纠缠均增强. 另一方面, 随耦合腔的耦合系数增大, 两原子间的纠缠减弱, 腔A和腔B间的纠缠增强; 而腔B和腔C间的纠缠, 以及腔A和腔C间纠缠与腔场间的耦合系数间存在非线性关系.     

NOON states in entangled cavities

We show how NOON states may be generated entangling two cavities by passing atoms through them. The atoms interact with each cavity via two-photon resonant transitions. We take advantage of the fact that depending on the state the atom enter (excite or ground), it leaves or takes two photons per interaction and leaves the cavities in a pure state.     

Bound states of three and four resonantly interacting particles

We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonance bound state of two fermions in a spin-singlet state, with corresponding scattering length a _F . Applying this approach to the calculation of the dimmer-dimer scattering length a _B , we recover exactly the already known result a _B = 0.6 a _F . We use the developed approach to obtain new results in 2D for fermions and bosons. Namely, we calculate bound state energies for three bbb and four bbbb resonantly interacting bosons in 2D. For the case of resonance interaction between fermions and bosons, we exactly calculate bound state energies of the following complexes: two bosons plus one fermion bbf, two bosons plus two fermions bf↑bf↓, and three bosons plus one fermion bbbf.     

Enhanced single photon emission in silicon carbide with Bull's eye cavities

The authors demonstrate a Bull's eye cavity design that is composed of circular Bragg gratings and micropillar optical cavity in 4H silicon carbide (4H-SiC) for single photon emission. Numerical calculations are used to investigate and optimize the emission rate and directionality of emission. Thanks to the optical mode resonances and Bragg reflections, the radiative decay rates of a dipole embedded in the cavity center is enhanced by 12.8 times as compared to that from a bulk 4H-SiC. In particular, a convergent angular distribution of the emission in far field is simultaneously achieved, which remarkably boost the collection efficiency. The findings of this work provide an alternative architecture to manipulate light—matter interactions for achieving high-efficient SiC single photon sources towards applications in quantum information technologies.