实现全反射镜功能的光子晶体禁带特性

用传输矩阵法研究一维光子晶体G(AB)mC(AB)mH的能带特性及电场分布,结果发现:随着m的增大,在830—883nm波长范围内,光子晶体G(AB)mC(AB)mH禁带中的导带透射率逐渐趋于零,即光被禁止通过,实现全反射镜功能,且随着入射角的增大,光子晶体的禁带逐渐向短波方向移动。随着介质层G、H的折射率增大,光子晶体在833.6—879.1nm波长范围内出现大的禁带,亦实现全反射镜功能。光子晶体G(AB)5C(AB)5H内部存在很强的局域电场,即在光子晶体内传输的光,被强烈局域在禁带范围内,并在缺陷层C处达到极大值,而且随着m的增大,局域强度增强。这些光学传输特性,为研究、设计新型光学器件全反射镜、滤波器等提供指导。     

Near-infrared tunable narrow filter properties in a 1D photonic crystal containing semiconductor metamaterial photonic quantum-well defect

The near-infrared (NIR) narrow filter properties in the transmission spectra of a one-dimensional photonic crystal doped with semiconductor metamaterial photonic quantum-well defect (PQW) were theoretically studied. The behavior of the defect mode as a function of the stack number of the PQW defect structure, the filling factor of semiconductor metamaterial layer, the polarization and the angle of incidence were investigated for Al-doped ZnO (AZO) and ZnO as the semiconductor metamaterial layer. It is found that the frequency of the defect mode can be tuned by variation of the period of the defect structure, polarization, incidence angle, and the filling factor of the semiconductor metamaterial layer. It is also shown that the number of the defect mode is independent of the period of the PQW defect structure and is in sharp contrast with the case where a common dielectric or metamaterial defect are used. The results also show that for both polarizations the defect mode is red-shifted as the number of the defect period and filling factor increase. An opposite trend is observed as the angle of incidence increases. The proposed structure could provide useful information for designing new types of tuneable narrowband filters at NIR region.     

Anisotropy of light propagation in thin opal films

Thin opal films are prepared by crystallization in a moving meniscus, and their optical transmission spectra are recorded in polarized light and studied. It is shown that the anisotropy of light propagation in the films is unambiguously related to the photonic band structure of opal and depends on the angle of incidence, the orientation of the incidence plane with respect to the opal lattice, and the wavelength and polarization of the incident light. Azimuthal diagrams of transmitted polarized light are constructed in the range of photonic band gaps of three orders for oblique incidence of a light beam. The anisotropy is found to vary with the light wave-length independently in perpendicular polarizations. A model of the band structure of opal wherein opal is represented as an fcc lattice of close-packed spheres adequately describes the optical transmission of opal films only in the range of the first-order photonic band gap.     

Giant and negative bistable shifts for one-dimensional photonic crystal containing a nonlinear metamaterial defect

In this Letter, we investigate giant and negative bistable lateral shifts for a light beam transmitted through a one-dimensional photonic crystal containing a nonlinear metamaterial defect. It is shown that there exists a typical S-shaped curve of the normalized input-output intensity. The hysteresis of lateral shift, resulting from the reshaping effect (constructive and destructive interferences of each plane wave components undergoing different phase shifts) is dependent on the nonlinear defect, the incident intensity and incidence angle. Numerical simulations are also made for the validity of stationary phase approach. All these phenomena lead to potential applications in integrated optics and optical switches.     

Defect mode properties in a one-dimensional photonic crystal

Based on the transfer matrix method (TMM), the interaction of electromagnetic waves with one-dimensional (1D) defective photonic crystal in ultraviolet (UV) frequency region had been studied. With the calculated transmittance characteristics in the wavelength domain, it can be found that the defect mode can be generated within the photonic band gap (PBG) at the central wavelength. Also the effects of many parameters such as the angle of incidence, the state of polarization and the defect layer thickness have been taken in account. A significant effect in generating multiple defect peaks within the PBG has been illustrated.     

An acoustic model for microresonator in on-beam quartz-enhanced photoacoustic spectroscopy

The effect of air impurity layer on the reflection spectrum of one-dimensional holographic photonic crystals was investigated in two forms. One form is the band-edge oscillation phenomenon when the air impurity layer is near the surface of the structure; the other form is the defect mode appearing in the band gap when the air impurity layer is near the center of the structure. For the defect mode, its central wavelength will nonlinearly change with some repeatability with the defect size, not as the result of the step-index photonic crystal. Moreover, the depth of the defect mode in the band gap can be modulated by the intensity ratio of the two construction beams. And the reflectance at the central wavelength of the defect mode can be almost zero with appropriate optical intensity ratio. The corresponding experimental results were also demonstrated.     

Anisotropic photonic crystals and microcavities based on mesoporous silicon

A technique to prepare one-dimensional anisotropic photonic crystals and microcavities based on anisotropic porous silicon exhibiting optical birefringence has been developed. Reflectance spectra demonstrate the existence of a photonic band gap and of an allowed microcavity mode at the photonic band gap center. The spectral position of these bands changes under rotation of the sample about its normal and/or under rotation of the plane of polarization of the incident radiation. The dependence of the shift of the spectral position of the photonic band gap edges and of the microcavity mode on the orientation of the polarization vector of incident electromagnetic wave with respect to the optical axis of the photonic crystals and microcavities was studied.     

单轴应力对一维镜像光子晶体光子局域态透射峰的影响

利用传输矩阵法研究了镜像异质三周期一维光子晶体中的光子局域态随单轴应力发生变化的特性. 对于镜像异质三周期光子晶体, 由于其镜像结构, 破坏了光子晶体的有序性, 产生了一个缺陷态, 使其在较宽的光子禁带中心有一个光子局域态透射峰. 研究表明: 当对镜像异质三周期光子晶体施加单轴应力时, 其中的光子局域态透射峰会随着应力的改变而发生剧烈的变化. 当外部微弱的机械应力施加到光子晶体上时, 对光子晶体形成一个拉伸应变, 拉伸应变引起光子晶体结构的变化, 进而大幅度影响光子局域态透射峰的透射率.结果表明: 透射峰的透射率明显受单轴应力的影响. 这些特性可为用此结构的光子晶体设计超高灵敏度压力传感器提供理论参考. 关键词： 光子晶体 单轴应力 光子局域态 传输矩阵     

Finite size effects on structure and magnetism in mass-selected CoPt nanoparticles

In this paper, the one-way absorption property in one-dimensional dielectric/metal photonic crystal structure with a dielectric defect layer is studied. The effects of incident angle and state of polarization on one-way absorption behaviour of the anti-resonant (AR) mode are investigated. The normally incident wave from left to right propagation is totally allowed to penetrate to the structure but right to left propagation totally reflected at the same wavelength. It is found that, with increasing of the incident angle, the AR mode shifts to the lower wavelengths and its intensity decreases. Simultaneously, another AR mode with reversed one-way property appears at higher wavelength. The one-way behaviour on absorption is observed at the both states of polarizations but is localized on different wavelengths. Those effects, are suggesting that the proposed structure can be used as a direction sense polarization splitter or reflector/antireflector device.     

Position calculation of the frequency band gap in the finite photonic crystal with multiple alternations using boundary element method

In this paper, the wave transmission from finite photonic crystals with multiple alternations is investigated using boundary element method (BEM). Since that, in these structures the alternation is not in all directions of space; the investigations of the frequency band gap with desired accuracy are not practical by analytical methods. Also, the frequency dispersion of dielectric rods is an effective parameter in photonic crystals, which this effect in our calculations has been considered. Due to the high capabilities of the BEM, the transmitted wave spectrum in the photonic crystal is calculated by changing the geometrical and optical parameters of the photonic crystal and applying more alternation in its structure and the position and width of the frequency band gap is investigated. Then, it is assumed that the photonic crystal with an arbitrary angle is rotated around the axis which is perpendicular on the crystal cross section and then, it is irradiated with a plan wave. The band gap of the photonic crystals with the desired structure, desired rotation angle and multiple alternations have been solved. Very low information volume, high speed and accuracy during the calculation and useable for any desired structures are the characteristics of this method.     

一维液晶光子晶体透射谱的研究

一维液晶光子晶体在光滤波器、低阈值激光器和光开关等领域有着很好的应用前景。研究了一维液晶光子晶体的透射谱,电压范围在0～10V内,光谱调谐范围约为50nm,透射峰半高宽为18nm,禁带宽度近400nm。进一步提出了非偏振光型液晶光子晶体,设计了相互垂直0°扭曲取向的双液晶层一维液晶光子晶体器件。双液晶层起到了对各向偏振光光程的补偿作用,使得禁带中的两个透射峰合并为一个透射峰,加强了光强度,增强了滤波性能。     

Multiband Terahertz Photonic Band Gaps of Subwavelength Planar Fractals

Optical transmission properties of subwavelength planar fractals in terahertz （THz） frequency regime are studied by means of time-domain spectroscopy. The transmission spectra with multiple pass bands and stop bands are observed. The tunable photonic band gaps are realized by changing the angle between the principle axis of planar fractal and the polarization of THz wave. The possible application of the subwavelength optical component is discussed. We attribute the detected transmittance from subwavelength fractals to localized resonances.     

Two-dimensional photonic crystals with a lattice defect: Spectrum of defect modes, localization of light, and formation of evanescent waves

Properties of an electromagnetic field localized in the defect modes of two-dimensional photonic crystals are studied. The defect-mode spectrum of these structures is calculated, electromagnetic field localization and channeling effects are analyzed, and the properties of the field inside and beyond a photonic crystal with a lattice defect are also studied. The calculations show that the electromagnetic field is localized in the defect mode of a photonic crystal in a region smaller than the wavelength. The dependence of the defect-mode spectrum on the parameters of the photonic crystal is investigated and possibilities for controlling the spectrum of defect modes are indicated. It is shown that the optical field leaving a photonic crystal possesses the properties of a evanescent wave, which means that spatial resolution substantially greater than the wavelength of the radiation can be achieved in the near field and opens up possibilities for using photonic crystals with a lattice defect in near-field optical microscopy. The possibility of externally controlling an optical field localized in the defect modes of a photonic crystals is demonstrated.     

Broad band polarizing beam splitter with a dielectric layer embedded in the groove of metal grating

We described the use of a metal grating embedded with a dielectric layer in the grating groove as a highly efficient polarizing beam splitter (PBS), to reflect s-polarized light and transmit p-polarized light in a wide spectrum band. This novel structure is designed at a wavelength of 1550 nm to be used in the optical communication wavelength band. High polarization efficiency and extinction ratio for both reflected and transmitted light are obtained by optimization of the designed structure. Moreover, it is shown that this structure can exhibit extremely high extinction ratio in the optical communication band with less dependence on the grating parameters and on the incidence angle, which greatly ease the fabrication of such kind of gratings.     

二维点缺陷正方光子晶体的微腔结构

通过平面波展开法对由Al₂O₃介质棒在空气背景介质中构成含有点缺陷的二维正方光子晶体微腔结构进行研究,计算得出缺陷态能带以及缺陷态模场分布。缺陷模对应的电磁波波长为470~476nm。对该微腔结构的品质因数的求解,得出缺陷态光谱曲线。在光谱曲线中,随着传输波长的增大,将产生几个峰值,并且在475nm处的波动最为明显,反映出在475nm附近的电磁波段在缺陷处的光强较大。进一步利用全矢量等效折射率法研究该结构缺陷模频率的稳定性,得出等效折射率的变化曲线。从等效折射率变化曲线可以看出,当传输波长达到475nm时,该结构已经达到稳定传输的区域。含缺陷模的二维光子晶体微腔结构在光子晶体发光二极管以及高阈值半导体激光器等方面有着重要的应用价值。     

Single channel tunable wavelength demultiplexer using nonlinear one dimensional defect mode photonic crystal

Transmission characteristics of nonlinear one dimensional photonic crystal with a defect have been studied. GaAs/Si multilayer structure with a single defect has been simulated using transfer matrix method. In this study refractive indices of both layers have been taken to be dependent on intensity and wavelength simultaneously. It is found that central wavelength of defect mode change with intensity of wave. Average change in central wavelength of defect mode is 0.02 nm/(1 GW/cm²). This property can be exploited in the design of a single channel tunable wavelength division demultiplexer for optical communication.     

On transmittance and localization of the electromagnetic wave in two-dimensional graphene-based photonic crystals

Two-dimensional graphene-based photonic crystal (GPC) formed by a periodic array of the homogeneous dielectric cylinders etched in the alternating graphene and dielectric layers and its inverse counterpart are considered. The transmittance of the photonic crystal is obtained. The waveguide due to the localization of the electromagnetic wave on the lattice defect that breaks the translational symmetry of the GPC of two different topologies is studied. The different topologies of GPC are characterized by different photonic band structures with different widths of photonic band gaps (PBG) and provide different frequencies for the localized electromagnetic wave due to the defect. The frequencies of the localized mode for both type of the GPC, located inside the lowest PBG, are in the range of THz or tens of THz depending on the topology of the GPC. It is shown that the photonic band gap always can be tuned by changing the chemical potential of graphene to provide formation of the localized photonic mode due to the defect. The technological advantages of the GPC, as well as the opportunity to tune the PBG and the frequency of the localized electromagnetic wave in the terahertz region of spectrum for the GPC are discussed.     

红外区二维光子晶体偏振分光镜透射谱分析

采用时域有限差分（Finite-Difference Time-Domain,FDTD）法模拟了垂直入射红外波段二维光子晶体偏振分光镜的透射谱,从而验证了用平面波展开方法计算的二维光子晶体能带结构.用电子束蒸发方法在光栅基板上制备了Ge/BaF2多层膜,实现了二维光子晶体偏振分光镜.实验初步证明了这种光子晶体在垂直入射时具有偏振特性,分析了实验结果与理论计算之间偏差的产生原因.     

Super Narrow Bandpass Filter Using Fractal Cantor Structures

In this paper, we present a new photonic crystal structure, which is composed of fractal Cantor multilayer with a defect embedded in its middle. Optical transmission matrix method is used to calculating the transmittance and reflectance. Compared with general Cantor multilayer, we find the new structure has wider stopband and shows a super narrow band in the middle of wider stopband. It can be served as a super narrow bandpass filter. The pass band obtained can be less than 0.6nm near the infrared 1530 nm. The optical transmission is the center wavelength is higher than 99 %. This means a very low insert loss. It is more superior to other kind narrow band filters. This kind of photonic crystal super narrow band optical filter may find applications in super dense wavelength division multiplexing for optical communications and precise optical measurement.     

Properties of Defect Modes in Periodic Lossy Multilayer with Negative-Index-Materials

Employing the characteristic matrix method, this study investigates transmission properties of onedimensional defective lossy photonic crystals composed of negative and positive refractive index layers with one lossless defect layer at the center of the crystal. The results of the study show that as the refractive index and thickness of the defect layer increase, the frequency of the defect mode decreases. In addition, the study shows that the frequency of the defect mode is sensitive to the incidence angle, polarization, and physical properties of the defect layer, but it is insensitive to the small lattice loss factor. The peak of the defect mode is very sensitive to the loss factor, incidence angle, polarization, refractive index, and thickness of the defect layer. This study also shows that the peak and the width of the defect mode are affected by the numbers of the lattice period and the loss factor. The results can lead to designing new types of narrow filter structures and other optical devices.