一维受限反铁磁光子晶体的性质

采用传输矩阵法计算了一维受限反铁磁光子晶体的带结构和透射比.研究结果表明:除来源于结构周期性的光子带隙外,体系还存在一种频率带隙,与反铁磁材料的共振性质以及受限尺寸有关.适当调节反铁磁各向异性轴的方向和受限尺寸,在反铁磁共振频率处可以出现比大块反铁磁材料的带隙宽约15倍的频率带隙.一定条件下,在大块反铁磁材料带隙的频率区间上,一些电磁波模式是可以在受限光子晶体中传播的.最后分析了几种典型的透射谱,与带结构吻合.     

光子晶体对太赫兹波的调制特性研究

利用传输矩阵方法研究了掺杂半导体n-GaAs/聚碳酸脂一维光子晶体的太赫兹波透射谱.研究结果发现,与一般由两种介电材料组成的一维光子晶体不同,由于掺杂半导体中自由载流子对太赫兹波存在较强的吸收,所以这种材料组成的一维光子晶体除可形成光子带隙外,还可以增强n-GaAs对太赫兹波的透射.同时还提出了一种基于这种一维光子晶体的太赫兹波调制器,通过外加电压控制半导体中电子浓度的大小可实现对太赫兹透射波幅度的调制. 关键词： 掺杂半导体光子晶体 太赫兹波 太赫兹波的调制     

双包层太赫兹光子晶体光纤的传输特性

为了在太赫兹波段实现远距离宽频带传输,设计了一种具有低吸收损耗的环烯烃共聚物(COC)作为基底材料双包层太赫兹光子晶体光纤。利用全矢量有限元法及模式选择理论,数值模拟了该光纤的单模传输范围、限制损耗、色散以及有效模场面积等特性。结果表明:优化结构参数可使在1~10 THz范围内基模限制损耗小于0.1 dB/m,二阶模限制损耗大于1 dB/m。因此可以获得1~10 THz的宽频带单模传输并且在1.5~10 THz内群速度色散可以控制在±0.1 ps/(THz·cm)。     

太赫兹波探测光子晶体涂层覆盖目标的可行性

覆盖于高温目标表面的光子晶体红外涂层可实现对目标红外辐射的抑制,而太赫兹波所具有的强穿透特性使其对该类目标的探测成为可能。以相关文献中设计的光子晶体涂层为例,采用特征矩阵理论对0.3~3 THz频率范围内的太赫兹波在该类涂层中的传输特性进行理论计算和分析,重点研究了不同入射角度的太赫兹波在该类涂层中的传输特性。研究发现,上述太赫兹波段处于光子晶体的带隙之外,0.3~0.5 THz频率范围内的太赫兹波对该类红外涂层具有较强的穿透特性,其光谱透过率大于90%;而在2.4~3 THz范围内,其在涂层上具有较强的反射,且整个波段内的吸收率小于0.2%。当入射角小于60°时,其对太赫兹波的传输特性影响较小;进一步增大入射角,其透过率逐渐降低,而反射率逐渐增大。研究结果证明了利用太赫兹波进行涂层覆盖目标探测的可行性,有望利用太赫兹雷达探测弥补红外探测系统的不足。     

含复折射率介质一维准周期光子晶体的透射特性

用Si和复折射率介质构成了(AB)N型一维准周期光子晶体,在考虑Si色散关系的基础上,利用传输矩阵法研究了其透射特性.数值计算表明其TE波的透射谱有如下特征:电磁波垂直入射时,在相对频率0～4的范围内存在4个等间距的尖锐的透射主峰,各主峰低频端相距0.148 (ω/ω0)处都有一透射副峰.入射角增加,主峰的透射率下降,副峰的透射率上升.周期数N增加,各主、副峰位置都有蓝移,但主峰透射率逐渐减小,而各副峰的半峰全宽度变小.当两介质厚度为定值时,从第一主峰到第四主峰,其透射率依次减小,两介质厚度增加时,各主峰的透射率下降.复折射率虚部增加时,各透射峰的位置保持不变,主峰的透射率变大,而副峰的透射率变小,反之亦然.     

太赫兹波段三角晶格二维光子晶体的传输特性

用平面波展开法研究了太赫兹(THz)波在二维三角晶格光子晶体中的传输特性。数值计算了以硅为背景的空气圆柱构成的二维三角晶格光子晶体的能带结构和态密度,计算表明在介质圆柱半径r=0.47a(a为空气介质柱的晶格常数)出现最大完全光子带隙,带隙宽度为0.070 1 THz;当r=0.49a和r=0.45a时,E偏振和H偏振分别出现最大光子带隙,带隙宽度分别0.102 2,0.192 3 THz。光子晶体能态密度的分布也表明了存在光子带隙的范围。研究结果为THz器件的开发提供了理论依据。     

一维反铁磁光子晶体光学双稳态效应研究

基于传递矩阵方法和光局域化原理, 本文研究了一维反铁磁光子晶体共振频率附近光学双稳态效应随电磁波入射角、 外磁场强度及电介质层数的变化.研究发现, 当外磁场为1.0 kG(1 G=10^-4 T)、电磁波小角度入射时, 反铁磁材料高低共振频率附近均可探测到光学双稳态效应; 当电磁波大角度入射时, 仅在高共振频率附近探测到光学双稳态效应. 然而, 当外磁场强度增加到2.0 kG时, 由于反铁磁材料的高低共振频率向两侧移动, 低共振频率附近缺失的光学双稳态频率窗口又被有效激发. 此外, 电磁波小角度入射时, 电介质层数在低共振频率附近对双稳态效应影响较明显.     

含左手材料的一维准周期光子晶体的透射特性研究

利用传输矩阵法,计算了含左手材料的一维准周期光子晶体的透射谱,并分析了其变化规律.结果表明:nR/ηL的比值对其透射谱影响较大,当比值为1时,透射率T恒为1,与N和△dR、△dL均无关;而当nR/ηL的比值在1.7～2.0之间、N=10时,透射谱的通带呈尖峰状,且通带中心在偶数倍频处有红移,通带峰值不变;而当nR/ηL的比值大于2.0时,在高频处的通带峰值变小,两介质的递增厚度△dR、△dL越大,nR越大,这种变化越明显,改变周期数N,对透射谱有较大的影响.     

太赫兹波光子晶体光纤传输特性分析

利用矢量有限元法分析了太赫兹波光子晶体光纤单模截止频率和波导色散随光纤结构的变化特性．结果表明，太赫兹波光子晶体光纤的单模截止频率随着光纤空气孔占空比的变大而降低，零波导色散点频率随着空气孔占空比变大而增加，约束损耗随着空气孔的圈数增加而降低．     

基于光子晶体的双波长太赫兹波功分器研究

太赫兹波技术和光子晶体技术相结合为设计太赫兹波功能器件提供了新的思路和方法.本文提出了一种基于二维光子晶体的双波长太赫兹波功分器.在光子晶体中引入由三个相互平行的单模波导形成的定向耦合型分束器和Y型结构的1×2型分束器,同时,在Y型结构的分支处分别引入两个介质柱.利用平面波展开法和定向耦合原理计算了在不同入射波频率下,耦合波导的耦合长度,并采用时域有限差分法对功分器的传输特性进行了模拟仿真分析.结果表明,在频率f1=1.0THz时,实现了端口1和端口2的能量均分输出;在频率f2=0.893THz时,通过非对称改变两个介质柱的折射率,可以实现端口3和端口4输出能量的自由分配.     

光子晶体增强石墨烯THz吸收

研究了光子晶体表面石墨烯在应力赝磁场作用下的太赫兹(THz)吸收.由于应力赝磁场的存在使得石墨烯中电子出现朗道能级并对THz波呈现出一个较强的吸收.而光子晶体和石墨烯形成了表面微腔结构使得石墨烯对THz波的吸收比无光子晶体时增强了将近四倍.且可以通过改变应力赝磁场和间隔层厚度来调控石墨烯的THz吸收.     

Wave propagation inside one-dimensional photonic crystals with single-negative materials

The propagation of light waves in one-dimensional photonic crystals (1DPCs) composed of alternating layers of two kinds of single-negative materials is investigated theoretically. The phase velocity is negative when the frequency of the light wave is smaller than the certain critical frequency ω_cr, while the Poynting vector is always positive. At normal incidence, such 1DPCs may act as equivalent left-handed materials. At the inclined incidence, the effective wave vectors inside such 1DPCs do refract negatively, while the effective energy flows do not refract negatively. Therefore, at the inclined incidence, the 1DPCs are not equivalent to the left-handed materials.     

Asymmetric light propagation based on semi-circular photonic crystals

A new structure based on a semi-circular photonic crystal is proposed to achieve asymmetric light propagation. The semi-circular photonic crystal structure proposed in this paper is a deformation of a two-dimensional conventional square photonic crystal. Through the directional bandgap of the semi-circular photonic crystal, the light from one direction can transfer to the other side, but the light from the opposite direction cannot. A high contrast ratio is obtained by designing the constitutive parameters of the photonic crystal and choosing the suitable light frequency. This structure promises a significant potential in optical integration and other areas.     

Ultra-short pulse propagation in 3D GaAs photonic crystals

We have investigated ultra-short pulse propagation through 3D GaAs photonic crystals with a complete photonic band gap in the optical wavelength region. The pulse propagation was calculated by using the finite-differential time-domain (FDTD) method. This is the first time pulse shape measurements have been made using femtosecond pulses. From the experimental results, the shapes of the ultra-short pulses were found to change when the frequency was above the photonic band-gap after the propagation through the photonic crystal, corresponding to the simulation results.     

A comparative study of dispersion relation of EM waves in ternary one-dimensional plasma photonic crystals having two different structures

In this paper, a rigorous theoretical analysis has been made to study the dispersion relation of EM waves in periodic ternary one-dimensional photonic crystal having two different structures. In one case we have chosen glass-plasma and ZnS in one unit cell and in other case we have considered glass-plasma and M_gF₂ in one unit cell. Using Kronig-Penney model the dispersion relation for proposed structures has been obtained and numerical results are presented in the form of dispersion curves. The dependence of photonic band gap (PBG) characteristics on plasma frequency, plasma width and the width of dielectric media are discussed in the light of frequency gap and cutoffs of binary one-dimensional plasma photonic crystal. An attempt has been made to show how the PBG characteristic of a particular structure changes when the dielectric materials of its unit cell is changed by the other dielectric material. It is found that the structure having glass-plasma-ZnS in unit cell is more useful for broad band filtering and other plasma functioning devices compared to the structure having glass-plasma-MgF₂ in one unit cell.     

Study of superluminal-pulse propagation in one-dimensional photonic crystals by the FDTD method

We study the pulse propagation in a one-dimensional photonic crystal using the finite-difference time-domain method. The wave propagation inside the crystal is the result of superposition of forward and backward waves. We observed the superluminal phenomena and negative values of the velocity of the energy-density maximum. The energy velocities within the crystal never exceed the speed of light in vacuum. We hope that our study contributes to a further understanding of the superluminal phenomena.     

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.