Defect modes tuning of one-dimensional photonic crystals with lithium niobate and silver material defect

In this paper, a novel PCs defect mode is designed by inserting a Ag/LiNbO₃/Ag sandwich structure into periodically stacked TiO₂/MgF₂ dielectric superlattice. The band gap calculation is conducted using transfer matrix method. An emergence of defect mode around 525 nm is demonstrated. By applying an external voltage on this defect mode, remarkable wavelength tuning can be achieved. At normal incidence, a tuning bandwidth up to 70 nm is obtained by moderate change of external voltage from −250 to 250 V. This feature can be employed to fabricate practical tunable filters in visible region.     

两种新型芴类衍生物的三光子吸收特性研究

研究了两种新型芴类衍生物9，9_二（2_乙基已基）_2，7_二咔唑_9H_芴（简记为DCZF）和9 ，9_二（2_乙基已基）_2，7_二（2_（4_甲氧基）苯_2，1_乙烯基）芴（简记为BMOSF）在N ，N_二甲基甲酰胺（DMF）中的线性吸收和单光子荧光行为，并用脉冲宽度为38ps，重复 频率为10 Hz的1064 nm Nd：YAG脉冲激光研究了两种化合物的三光子吸收性质.结果表明： 两种新材料的最大线性吸收峰分别位于330和380nm，吸收区域覆盖了270—420 nm波段. 两种化合物的荧光带位于蓝_紫区，中心波长为369和442 nm，都具有较小的斯托克斯位移. 化合物DCZF和BMOSF的三光子吸收系数分别为γ_DCZF=678×10^{- 20} cm3/W²和γ_BMOSF=592×10^-20 cm³/W². 同时， 两种新材料还表现出明显的三光子吸收光限幅效应，当入射光强分别为8和6GW/cm²时，非线性透过率分别达到30%和45%. 关键词： 芴类衍生物 三光子吸收 光限幅 非线性透过率     

用量子隧穿法研究带质量四极矩静态黑洞的Hawking辐射

对带质量四极矩的静态黑洞Hawking辐射的隧穿过程进行了简单直接的推导，得到了热谱.因推导过程应用了能量守恒定律，故真正的辐射不一定是纯热的.这一结果支持了这样一种观点：隧穿的辐射携带信息是可能的. 关键词： 黑洞 辐射 隧穿 能量守恒     

Highly efficient Cherenkov radiation generation in the irregular point of hollow-core photonic crystal fiber

Highly efficient Cherenkov radiation(CR) is generated by the soliton self-frequency shift(SSFS) in the irregular point of a hollow-core photonic crystal fiber(HC-PCF) in our laboratory.The impacts of pump power and wavelength on the CR are investigated,and the corresponding nonlinear processes are discussed.When the average power of the 120 fs pump pulse increases from 500 mW to 700 mW,the Raman soliton shifts from 2210 nm to 2360 nm,the output power of the CR increases by 2.3 times,the maximum output power ratio of the CR at 539 nm to that of the residual pump is calculated to be 24.32:1,the width of the output optical spectrum at the visible wavelength broadens from 35 nm to 62 nm,and the conversion efficiency η of the CR in the experiment can be above 32%.     

Deterministic Bidirectional Remote State Preparation of a- and Symmetric Quantum States with a Proper Quantum Channel

We present a new scheme for deterministically realizing the mutual interchange of quantum information between two distant parties via selected quantum states as the shared entangled resource. We first show the symmetric bidirectional remote state preparation (BRSP), where two single-qubit quantum states will be simultaneously exchanged in a deterministic manner provided that each of the users performs single-qubit von Neumann measurements with proper measurement bases as well as appropriate unitary operations, depending essentially on the outcomes of the prior measurements. Then we consider to extend the symmetric protocol to an asymmetric case, in which BRSP of a general single-qubit state and an arbitrary two-qubit state is investigated successfully. The necessary quantum operations and the employed quantum resources are feasible according to the present technology, resulting in that this protocol may be realizable in the realm of current physical experiment.     

Photovoltaic effect of TiO2 thick films with an ultrathin BiFeO3 as buffer layer

The photovoltaic (PV) effect of a bilayer anatase TiO₂/BiFeO₃ (BFO) film has been studied. The 20-nm ultrathin BFO layers were deposited on the fluorine-doped tin oxide (FTO) glass substrates by the chemical solution deposition method. An anatase TiO₂ layer is deposited subsequently on the BFO surface via a screen-printing technique. It is found that the FTO/TiO₂/Au cell exhibits negligible PV effect under solar exposure, while the one after introducing an ultrathin BFO film between TiO₂ and FTO leads to a considerable PV effect with an open-circuit voltage of ?0.58 V and a photocurrent density of 18.27 µA/cm². The FTO/BiVO₄ (BVO)/TiO₂/Au cell was constructed to investigate the underlying mechanism for the observed effect. A negligible PV effect of the FTO/BVO/TiO₂/Au cell indicates that the PV effect of the FTO/BFO/TiO₂/Au cell arises mainly from a built-in electric field in the BFO film induced by the self-polarization. Our work opens up a new path to utilize TiO₂ and may influence the future design of solar cells.     

Fabrication of widely tunable ridge waveguide DBR lasers for WDM-PON

We report the fabrication of widely tunable ridge waveguide distributed Bragg reflector(DBR) lasers with InGaAsP butt-joint as grating material. The shape of the butt–joint interface is found to have significant effect on the properties of the lasers. It is shown that irregular mode jumps during wavelength tuning can be avoided by a V-shaped butt–joint interface. From the fabricated device, 23 channels with 0.8 nm spacing and greater than 35 dB side mode suppression ratios are obtained. The different tuning characteristics of the ridge waveguide and the previously reported buried ridge stripe DBR lasers are discussed. Combined with the wide tuning range and the simple structure, the ridge waveguide DBR lasers are promising for use in wavelength division multiplexing passive optical networks(WDM-PONs).     

Symmetric bursting of focus-focus type in the controlled Lorenz system with two time scales

By employing a special feedback controlling scheme, a hyperchaotic Lorenz system with the structure of two time scales is constructed. Two kinds of bursting phenomena, symmetric fold/fold bursting and symmetric sub-Hopf/sub-Hopf bursting, can be observed in this system. Their respective dynamical behaviors are investigated by means of slow-fast analysis. In particular, symmetric fold/fold bursting is of focus-focus type, namely, both the up-state and the down-state are stable focus, which is different from the usual fold/fold bursting; Symmetric sub-Hopf/sub-Hopf bursting is also of focus-focus type, which has not been reported in previous work. Furthermore, phase plane analysis has been introduced to explore the evolution details of the fast subsystem for symmetric sub-Hopf/sub-Hopf bursting. With the variation of the parameter, symmetric sub-Hopf/sub-Hopf bursting can evolve to symmetric chaotic bursting or even hyperchaos.     

Influence of the illumination on the subband structure and?occupation in AlxGa1?xN/GaN heterostructures

The subband structure and occupation in the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well at Al _x Ga_1−x N/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination.