含复介电常量一维光子晶体量子阱结构研究

利用传输矩阵法研究了实介电常量和含复介电常量时一维光子晶体的透射谱.结果表明:两种情况下均构成光量子阱结构,并且光量子阱结构的透射能带谱位置和结构相同,但在含复介电常量负虚部情况下共振透射峰出现很强的增益现象,而在含复介电常量正虚部情况下共振透射峰则呈现明显的衰减现象.     

复介电常量双缺陷层的镜像对称光子晶体特性

利用传输矩阵法研究了两个复介电常量缺陷层镜像对称一维光子晶体的带隙结构和光传输特性。重点讨论了缺陷层的复介电常量的虚部为负值且光学厚度为λ0/4的情形时对传输特性的影响。研究发现:当在光子晶体的两端加入具有负虚部的复介电常量缺陷层后,多处出现了较强的透射峰增益。随着缺陷层复介电常量的虚部与实部比值的增加,各处透射峰增益变化规律不同。但中心波长处的缺陷膜的位置和高度不变。这为光子晶体同时实现多通道超窄带滤波器和不同放大倍数的光放大微器件的设计提供了理论基础。而在光子晶体的两端加入具有正虚部的复介电常量缺陷层后,各透射峰都出现了吸收现象,且随着其正虚部值I的增加,吸收越明显,这给光子晶体实现放大功能提供了理论指导。     

激活材料对镜像对称一维光子晶体透射谱的影响

利用传输矩阵法理论,研究了激活杂质材料对镜像对称结构一维光子晶体（ABCB）m（BCBA）m的透射谱的影响。结果表明：当介质无掺入激活杂质,即介质的介电常量为一实数时,禁带中心出现一条透射率为100%的透射峰;当在镜像对称结构的任一介质中掺入激活杂质,即介质的介电常数为一带有负虚部的复数时,透射峰的透射率均出现增益现象,且随着各介质复介电虚部大小的增大,透射增益出现一极大值后又减小;各介质复介电虚部大小的变化对光子晶体透射谱的影响存在各异,其中介质A掺入激活杂质时增益幅度最大,其次为C,B相对较小,但透射率的增益对B介质的复介电虚部响应最为灵敏,其次为C,A相对较为迟钝。这些特性对新型光学器件的设计具有指导意义。     

左手介质对一维光量子阱透射谱的影响

通过传输矩阵法理论研究左手介质对一维光子晶体量子阱(AB)m(CBAABC)n(BA)m透射谱的影响,结果发现:当C层为双正介质时,光量子阱透射谱中出现2n+1条窄透射峰,当C层为左手介质时,呈现简并现象,光量子阱透射峰中仅出现2n-1条窄透射峰;当C层左手介质折射率负值增大时,光量子阱透射谱向禁带中心两侧移动,同时透射峰快速变窄;当C层左手介质光学厚度负值减小时,光量子阱透射谱向禁带中心靠拢,同时透射峰迅速变窄;光量子阱透射变窄对左手介质光学厚度的响应灵敏度高于对折射率负值的响应。左手介质对光量子阱透射谱特性的影响规律,可为光子晶体理论研究及新型量子光学器件设计提供参考。     

基于含单负材料光量子阱结构的全向多通道滤波器

分析了含单负材料的光量子阱结构中的振荡透射模的性质.用两种单负（负介电常量或负磁导率）材料交替周期堆叠形成的两个光子晶体构造了一维光量子阱结构,该结构中仅其中一个光子晶体含有零有效位相带隙.数值计算结果发现,在零有效位相带隙内存在振荡透射模.通过改变井区域光子晶体内单负材料层的厚度及周期数,振荡透射模的数目、频率及频率间隔均可调节.振荡透射模对入射角度的依赖均很弱;随着入射角度的改变,缺陷模频率的相对改变量保持在0.02以下.该研究结果可用于设计多通道全向滤波器.     

基于含单负材料光量子阱结构的全向多通道滤波器

分析了含单负材料的光量子阱结构中的振荡透射模的性质.用两种单负(负介电常量或负磁导率)材料交替周期堆叠形成的两个光子晶体构造了一维光量子阱结构,该结构中仅其中一个光子晶体含有零有效位相带隙.数值计算结果发现,在零有效位相带隙内存在振荡透射模.通过改变井区域光子晶体内单负材料层的厚度及周期数,振荡透射模的数目、频率及频率间隔均可调节.振荡透射模对入射角度的依赖均很弱;随着入射角度的改变,缺陷模频率的相对改变量保持在0.02以下.该研究结果可用于设计多通道全向滤波器.     

二维光量子阱共振隧穿光谱特性的改善

用时域有限差分法研究了光子晶体量子阱中的量子化能态.研究发现,开腔与闭腔光量子阱结构共振透射峰的数目相同,位置几乎不变,但闭腔光量子阱出射光强更强,透射率更大,频率选择性更好,品质因子Q值更高.同时计算了开腔和闭腔光量子阱光场分布,结果表明,开腔光量子阱为行波阱,闭腔光量子阱为驻波阱,充分证实了闭腔光量子阱更能束缚光场的设想,对其作用机理进行了探讨.     

双重势垒一维光子晶体量子阱的光传输特性研究

利用传输矩阵法,研究单势垒和双重势垒一维光子晶体量子阱结构的光传输特性.结果表明:垒层折射率总和大的单势垒光量子阱的透射峰更加精细,内部局域电场更加强;双重势垒光量子阱的透射峰比单势垒光量子阱的透射峰精细,内部局域电场也比单势垒光量子阱的强;随着垒层光子晶体周期数增大,双重势垒光量子阱内部局域电场增强,而且垒、阱层折射率总和之比越大,双重势垒光量子阱的内部局域电场增强速度越快,当双重垒层光子晶体周期数同时增大时,双重势垒量子阱内部局域电场增强速度最快,透射峰越加精细.随着阱层光子晶体周期数的增大,单势垒或双重势垒光量子阱的内部局域电场强度均下降,但透射峰的透射率不随之改变.该特性为设计新型可调高品质的量子光学器件提供指导.     

具有三量子阱结构的一维光子晶体透射谱研究

在适当选择结构参数基础上,通过传输矩阵法计算模拟光子晶体(AB)m(CD)n(BA)m结构模型的透射谱,当光子晶体(CD)n的三个导带分别处于光子晶体(AB)m(AB)m相邻的三个禁带中时,构成光子晶体三量子阱结构,在光量子阱透射谱的归一化频率1.0(ωa/2πc),2.0(ωa/2πc)和3.0(ωa/2πc)三处周围,分布着三套具有规律的局域共振峰,出现明显的量子化效应,且三套透过峰数目都可以通过光子晶体(CD)n的重复周期数n来调节,这一现象可用于设计可调性多通道滤波器。     

可实现奇数通道滤波功能的光量子阱透射谱

针对光子晶体(AB)_m(CD)_n(BA)_m模型,选择适当的结构参数,通过传输矩阵法对其透射谱进行计算模拟发现,在归一化中心频率0.5(ωa/2πc)处,当光子晶体(CD)_n的导带处于光子晶体(AB)_m(BA)_m的禁带中,且两者均以中心频率处为对称中心时,构成镜像对称的光子晶体量子阱结构。在光量子阱透射谱的中心频率处及对称的两侧,分布着具有规律的奇数局域共振峰,出现明显的量子化效应,透射峰数目和位置都可以通过光子晶体(CD)_n的重复周期数n来调节,这一现象可用于设计可调性奇数通道滤波器。     

具有复介电常量二维光子晶体的特性研究

采用平面波展开法,通过数值模拟研究了具有复介电常量的二维光子晶体的能带结构和光传输特性,重点讨论介电常量的虚部为负值情形时对传输特性的影响。研究表明由于光子带隙的存在有效地抑制了频率位于带隙内光的自发辐射。当在介质中掺入具有增益特性的杂质时,即使两种介质的介电常量相差很小,在靠近光子带隙边缘,出现了较强的受激辐射放大。通常在带隙的边缘处,光子晶体的群速度较小,而激光阈值正比于群速度的平方,当群速度很小时,激光阈值将大大减小。这为实现零阈值激光器提供了基础,也为制作光放大微器件提供了一个有益的理论参考。     

含有吸收材料对称结构一维三元光子晶体的透射谱

利用传输矩阵法理论,研究含吸收材料对称结构一维三元光子晶体的光传输特性。结果表明:当各层介质无吸收时,在较宽的禁带范围内出现一条透射率为100%的透射峰;当介质的折射率为带有正虚部的复数,即介质存在吸收时,禁带中的透射峰出现明显的透射衰减,且随着复折射率虚实比β的增大透射率出现单调衰减规律;当单个介质存在吸收时,随着各介质折射率虚实比的增大,透射率的衰减速度存在各异,其中以C介质的折射率虚实比βc对透射峰透射率的影响较大,其次为B,A的影响相对较小;当所有介质同时存在吸收时,透射衰减最为明显。这些特性为光学衰减器的设计提供理论指导意义。     

具有复介电常量一维光子晶体的特性研究

利用传输矩阵法计算了一维光子晶体的能带结构和光传输特性,重点讨论了介电常量的虚部为负值时对传输特性的影响。当在介质中掺入具有增益特性的介质时,靠近光子带隙边缘就会出现较强的受激辐射放大。同时,光子晶体的长度和介电常量虚部的大小都会影响晶体的受激辐射。随着虚部数值的增加,受激增强并不是单调递增,而是存在一极值点。     

Extremely low optical transmittance in the stopbands of photonic crystals

We demonstrate extremely low transmittance characteristics of photonic crystals (PhCs) with a finite thickness in specific photonic bandgaps (PBGs) through numerical simulation, and clarify its origin. Some of the PhCs support decaying Bloch eigenmodes, whose propagation constant (real part of the Bloch wavenumber) as well as their decay constant (imaginary part) changes with frequency inside the bandgap. Such a class of modes can interfere destructively at the exit end of the crystal depending on their round-trip phase change, which creates comb-like valleys in their transmission spectra.     

Effects of dielectric core and embedding medium on plasmonic coupling of gold nanoshell arrays

The effects of the dielectric core and the dielectric embedding medium separately on transmission spectra and plasmon resonance properties of gold nanoshell arrays were investigated by using the finite-difference time-domain (FDTD) theory. It is found that when the hollow nanoshell arrays are placed in air, the wide photonic band gap becomes narrower as the core dielectric constant increases. On the contrary, when the nanoshell arrays with dielectric core are placed in the dielectric medium, the photonic band gap becomes wider. Furthermore, increasing core or medium dielectric constant leads to a redshift of the transmission spectra due to the polarization of the dielectric. Based on the electric field distributions, we also clearly show that the plasmon properties of the nanoshell arrays are strongly influenced by the presence of the dielectric.     

Measurement of the complex dielectric constant of a single gold nanoparticle

A differential interference contrast microscopy technique that employs a photonic crystal fiber as a white-light source is used to measure both the real and the imaginary part of the complex dielectric constant of single 10 and 15 nm gold nanoparticles over a wavelength range of 480 to 610 nm. Noticeable deviations from bulk gold measurements are observed at short wavelengths and for individual particles even after taking into account finite-size surface damping effects.     

Band gap extension in honeycomb lattice two-dimensional plasma photonic crystals in the presence of dissipation

We investigate two types of honeycomb lattice two-dimensional plasma photonic crystals that possess large photonic band gaps in the presence of dissipation. We obtain a clear insight into the band structures and find imaginary parts of the eigenvalue band structure at the symmetry points display discontinuous behaviour when the filling factor of plasma in type-1 structure is low. Further more, we show how the photonic band gaps are affected by the normalized plasma frequency, radius of cylinder, dielectric constant and collision frequency. Our results demonstrate the band gap extension by increasing normalized plasma frequency in both type structures and radius of plasma cylinders in type-1 structure. The width of band gaps could also be enlarged by decreasing dielectric cylinder's radius. The bands shift toward lower frequencies when relative dielectric constant increases in both two types. These results may provide theoretical instructions to design new optoelectronic devices.     

Applications of the expanded basis method to study the behavior of light in polaritonic photonic crystal slab with losses

We apply the expanded basis method (EBM) to investigate the behavior of light in polaritonic photonic crystal (PC) slabs with losses. The influence of losses on transmissivity is studied. It is found that the transmissivity is significantly lowered with the increase of losses, in particular, it is abruptly decreased in the vicinity of transverse-optical-phonon frequency. The electromagnetic (EM) dissipation is mainly dominated by the imaginary part of dielectric constant of PC. The larger the imaginary part of the dielectric constant, the more the EM energy depletion is. The variation of EM dissipation with the number of period layers in the PC slab is approximately linear or oscillatory increase with the number of period layers.     

Applications of the expanded basis method to study the properties of photonic crystals with frequency-dependent dielectric functions and dielectric losses

Band structures of two-dimensional photonic crystals (PCs) made of polar material with frequency-dependent dielectric constant are calculated by using an expanded basis method. The effect of the polariton gap (PG) of polar material on the photonic band gaps (PBGs) is explored. It is found that the PBGs are significantly modified near the PG, where the abrupt change of the dielectric constant appears. The feature of electromagnetic (EM) field is revealed when the frequency is located in the flat band. We display the equifrequency-surface configuration of the localized field and the spacial distributions of field. We observe the existence of several equi-ω curves for a specified frequency and the localized field distribution exhibiting various different patterns, dependent of the mode index. We also study the influence of the dielectric losses of the polar material on dispersion and find that the change of the real part of the Bloch wave vector is crucially related to the real part of the dielectric constant and the attenuated length is determined by its imaginary part.     

分数Poynting-Thomson模型对E7复介电常数的应用

基于分数阶微积分理论和介电分数单元,建立了分数Poynting-Thomson模型,给出了复介电常数的表达式.利用遗传算法结合共轭梯度法,分别求得复介电常数实部和虚部的最优参数,并对E7（主要是氰基联苯化合物）复介电常数实部和虚部的实验数据进行拟合.结果表明能对E7的复介电常数给出很好的描述.另外,由于该法对研究聚合物的复介电常数有广泛的适用性,故该法对研究与E7性质相差很大的聚合物同样适用.