Characteristics of local photonic state density in an infinite two-dimensional photonic crystal

The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit “mountain chain” structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electricdisplacement vector at the interface. In the frequency range of the pseudo-PBG （photonic band gap）, the LDPS keeps very low value over the whole Wiger-Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.

Photonic Band Modulation in a Two-Dimensional Photonic Crystal with a One-Dimensional Periodic Dielectric Background

A two-dimensional photonic crystal with a one-dimensional periodic dielectric background is proposed. The photonic band modulation effects due to the periodic background are investigated based on the plane wave expansion method. We find that periodic modulation of the dielectric background greatly alters photonic band structures, especially for the E-polarization modes. The number, width and position of the photonic band gaps （PBGs） sensitively depend on the structure parameters （the layer thicknesses and dielectric constants） of the one-dimensional periodic background,

Band gaps structure and semi-Dirac point of two-dimensional function photonic crystals

Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , are proposed and studied numerically. The band gaps structures of the photonic crystals for TE and TM waves are different from the two-dimensional conventional photonic crystals. Some absolute band gaps and semiDirac points are found. When the medium column radius and the function form of the dielectric constant are modulated, the numbers, width, and position of band gaps are changed, and the semi-Dirac point can either occur or disappear. Therefore,the special band gaps structures and semi-Dirac points can be achieved through the modulation on the two-dimensional function photonic crystals. The results will provide a new design method of optical devices based on the two-dimensional function photonic crystals.

Comment on “Band gaps structure and semi-Dirac point of two-dimensional function photonic crystals” by Si-Qi Zhang et al.

Recently, Zhang et al. （Chin. Phys. B 26 024208 （2017）） investigated the band gap structures and semi-Dirac point of two-dimensional function photonic crystals, and the equations for the plane wave expansion method were induced to obtain the band structures. That report shows the band diagrams with the effects of function coefficient k and medium column ra under TE and TM waves. The proposed results look correct at first glance, but the authors made some mistakes in their report. Thus, the calculated results in their paper are incorrect. According to our calculations, the errors in their report are corrected, and the correct band structures also are presented in this paper.

Implementation of all-optical tristate Pauli X, Y and Z gates based on two-dimensional photonic crystal

In this paper, we have designed and simulated all-optical tristate Pauli X, Y and Z gates using 2D photonic crystal. Simple line and point defects have been used to design the structure. The performance of the structure has been analyzed and investigated by plane wave expansion(PWE) and finite difference time domain(FDTD) methods. Different performance parameters, namely contrast ratio(CR), rise time, fall time, delay time, response time and bit rate, have been calculated. The main advantage of the proposed design is that all the Pauli gates have been realized from a single structure. Due to compact size, fast response time, good CR and high bit rate, the proposed structure can be highly useful for optical computing, data processing and optical integrated circuits.

Two-dimensional near-infrared photonic crystal fabrication by generation of void channels in solid resin

Two-dimensional (2D) triangular void channel photonic crystals with different lattice constants stacked in two different directions were fabricated by using femtosecond laser micro-explosion in solid polymer material. Fundamental and higher-order stop gaps were observed both in the infrared transmission and reflection spectra. There is an approximately linear relationship between the gap position and the lattice constant. The suppression of the fundamental gap is as high as 70% for 24-layer structures stacked in the T-M direction.

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures （CCSs） in two-dimensional （2D） photonic crystals （PCs） are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain （FDTD） method, and the results show that within a very short coupling distance of about 3λ, where ）, is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.

Absolute band gaps in two-dimensional graphite photonic crystal

The off-plane propagation of electromagnetic (EM) waves in a two-dimensional (2D) graphite photonic crystal structure was studied using transfer matrix method. Transmission spectra calculations indicate that such a 2D structure has a common band gap from 0.202 to 0.2035 c/a for both H and E polarizations and for all off-plane angles form 0° up to 90°. The presence of such an absolute band gap implies that 2D graphite photonic crystal, which is much easier and more feasible to fabricate, can exhibit some properties of a three-dimensional (3D) photonic crystal.

Enhancement of light extraction efficiency in OLED with two-dimensional photonic crystal slabs

Light extraction efficiency of organic light emitting diode （OLED） based on various photonic crystal slab （PCS） structures was studied. By using the finite-difference time-domain （FDTD） method, we investigated the effect of several parameters, including filling factor and lattice constant, on the enhancement of light extraction efficiency of three basic PCSs, and got the most effective one. Two novel designs of ＂interlaced＂ and ＂double-interlaced＂ PCS structures based on the most effective basic PCS structure were introduced, and the ＂interlaced＂ one was proved to be even more efficient than its prototype. Large enhancement of light extraction efficiency resulted from the coupling to leaky modes in the expended light cone of a band structure, the diffraction in the space between columns, as well as the strong scattering at indium-tinoxide/glass interfaces.

Design and analysis of superlens based on complex two-dimensional square lattice photonic crystal

We theoretically demonstrate the imaging properties of a complex two-dimensional(2D) face-centered square lattice photonic crystal(PC) made from germanium cylinders in air background. The finitedifference time-domain(FDTD) method is employed to calculate the band structure and simulate image construction. The band diagram of the complex structure is significantly compressed. Negative refraction occurs in the second energy band with negative phase velocity at a frequency of 0.228(2πc/a), which is lower than results from previous studies. Lower negative refraction frequency leads to higher image resolution. Numerical results show that the spatial resolution of the system reaches 0.7296λ, which is lower than the incident wavelength.

Enhanced absorption of solar cell made of photonic crystal by geometrical .design

In this paper, via numerical simulation we designed the geometry of solar cell made by onedimensional （1D） and two-dimensional （2D） photonic crystals with two kinds of materiel （silicon （Si） and hydrogenated amorphous silicon （a-Si：H）） in order to enhance its absorption. The absorption characteristics of light in the solar cell structures are simulated by using finite-difference time-domain （FDTD） method. The calculation results show that the enhancement of absorption in patterned structure is apparent comparing to the unpatterned one, which proves the ability of the structure to produce photonic crystal solar cell. We found solar cell geometries as a 2D photonic crystal enable to increase the absorption between 380 and 750 nm.

二维圆柱层状复周期光子晶体的透射谱

提出由圆柱柱体粗细及介电常数差异间隔构成层状复合周期结构的二维光子晶体,用平面波展开方法数值研究其传输特性,数值结果表明,在不同二维圆柱半径层状复周期结构光子晶体透射谱中,禁带位置、宽度,传导模的出现与间隔层柱体的粗细差异有关,差异越大,光子禁带越小,中心频率位置向低频方向移动;在不同介电常数构成的层状复周期结构中,介电常数差异越大,光子禁带宽度越小,同样中心频率向低频方向移动;当间隔的层状柱体层数达到一定值时,没有传导模式出现,在相同差异条件下,禁带与传导模式相关,还与晶格结构的类型、电磁波入射面柱体的摆放顺序相关。相关结论为扩展二维光子晶体的应用提供新的理论依据。

二维介质柱光子晶体波导的优化设计(英文)

通过改变靠近导光区域介质柱的直径和周期，优化设计了二维介质柱光子晶体波导．结果表明：单独增大和减小柱的直径以及增大柱的周期不能提高波导的传输特性；单独减小柱的周期能提高波导的传输特性，获得传输系数小于1dB，带宽80nm的波谱；同时减小柱的直径及周期能够极大的提高波导的传输特性，得到了带宽为150～250nm，传输系数小于1dB的波谱．

光子带隙型光子晶体光纤温度传感特性分析

为了提高光子带隙型光子晶体光纤的温度灵敏度,提出了在纤芯环上并入高折射率液体圆柱的新结构,并利用全矢量有限元法对提出的结构进行了仿真,得到了温度对光纤有效折射率、纤芯能量和有效模面积等传输特性的影响。结果表明,随着温度的升高,光纤的有效折射率和有效模面积会减小,纤芯能量会增加,且零群速率色散点向短波长方向移动,尤其在短波长条件下光纤传输特性随温度变化趋势更加明显。该研究提高了光子带隙型光子晶体光纤传输特性的温度灵敏度,使其更加适合于温度传感方面的应用。

二维光子晶体的负折射现象

研究了由多层周期圆柱阵构成的二维光子晶体对电磁波的散射,并通过算例从数值上证实了负折射现象的存在。采用的是有效而精确的T-矩阵方法。首先利用单个圆柱的T-矩阵和体现层阵列周期性的栅和得到每一层周期阵的空间谐波散射与透射矩阵,再将每一层的散射与透射矩阵级联起来而得到多层周期圆柱阵的广义散射与透射矩阵。给出了具体的算例,画出了该光子晶体上部空间和下部空间的场的幅值分布,还给出了晶体内部和外部坡印亭矢量的分布图。这些图清楚地显示了负折射现象的存在。

掺杂二维三角圆柱光子晶体传输特性研究

为了研究掺杂对二维光子晶体传输特性的影响,应用时域有限差分方法数值模拟了各种掺杂情况下二维三角圆柱光子晶体的透射率即光传输函数随频率的变化。数值结果表明,对于一定的入射方向,光子晶体中的带隙的宽度、中心位置都受到掺杂所处的位置、掺杂物的折射率、掺杂柱的粗细不同程度的影响。该结论为该类光子晶体的应用提供了理论依据。

五筒晶格光子晶体的带隙分析!

在三角晶格和六角晶格基础上设计了一种五筒型光子晶体,分析了空气孔型和介质柱型两种类型光子晶体的带隙与晶格半径、介电常数和形状之间的关系:随着介电常数的增大,两种类型光子晶体的带隙所对应的归一化频率都逐渐减小;随着晶格半径的增大,介质柱型光子晶体带隙所对应的归一化频率逐渐减小,而空气孔型光子晶体则逐渐增大;对于介质柱型光子晶体,圆形晶格其归一化频率最大,方形晶格最小,而空气孔型光子晶体与之相反。

二维椭圆介质柱光折变光子晶体的制作

对6个点光源进行光学傅里叶变换,在自散焦光折变掺铁铌酸锂晶体中成功制作了具有100余条椭圆柱阵列波导。研究表明,这些阵列波导构成了大带隙的椭圆柱光子晶体。测得沿着椭圆长轴、短轴方向的晶格常数分别26um和15um。

太赫兹波在二维椭圆金属光子晶体的传输特性

研究了一种由金属椭圆柱构成的二维正三角晶格的光子晶体结构,并应用有限积分法对太赫兹波段TE模的传输特性进行了仿真分析。通过改变晶格常数和椭圆的长、短半轴,分析了太赫兹波段TE模在金属光子晶体中的传输特性。结果表明,椭圆柱比圆柱更容易得到大的禁带带隙,通过分组优化组合,得到了对TE模禁带带隙最宽且最佳的光子晶体结构。这为太赫兹波段的光子晶体带阻滤波器的开发与制作提供了参考依据。

基于Y缺陷的改进型光子晶体光分路器

提出一种Y缺陷的改进型光子晶体光分路器,以提高输出端的透射率。在完整的二维光子晶体中引入线缺陷,构成1×4的Y型光子晶体光分路器。通过调节第一分支处的4个介质柱的半径,使其每个输出端口具有更高的透射率。同时,通过改变第二分支处的1个介质柱的半径,可以实现输出端口的高透射率和输出光能量的灵活调节。Y缺陷光子晶体光分路器可以广泛应用于未来的光路集成、集成光学、微光信息处理和光通信领域。