Photonic band gaps structure properties of two-dimensional function photonic crystals

The tunable two-dimensional photonic crystals band gap, absolute photonic band gap and semi-Dirac point are beneficial to designing the novel optical devices. In this paper, tunable photonic band gaps structure was realized by a new type two-dimensional function photonic crystals, which dielectric constants of medium columns are functions of space coordinates. However for the two-dimensional conventional photonic crystals the dielectric constant does not change with space coordinates. As the parameter adjustment, we found that the photonic band gaps structures are dielectric constant function coefficient, medium columns radius, dielectric constant function form period number and pump light intensity dependent, namely, the photonic band gaps position and width can be tuned. we also obtained absolute photonic band gaps and semi-Dirac point in the photonic band gaps structures of two-dimensional function photonic crystals. These results provide an important theoretical foundation for design novel optical devices.     

一维光子晶体禁带的展宽

作为一维光子晶体的应用基础，一维光子晶体的禁带是研究的重点。通过传输矩阵的方法分析了一维光子晶体禁带的特性，讨论了影响带宽的因素。说明了相对带宽对光子晶体设计的重要性。在这个基础上讨论了扩展一维光子晶体带宽的方法，提出了在角域范围内对光子晶体进行叠加的方法，为设计制造一维光子晶体提供了一种行之有效的方法。分别对2个、3个和4个晶体的叠加进行了分析，最后计算了所设计的合成晶体的反射率。其中4个晶体的叠加，相对带宽达到57．52％，极大地展宽了一维光子晶体的禁带，从而证明利用角域的叠加来展宽一维光子晶体的禁带是非常有效的。     

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.     

Synthesis and photonic band gap characterization of high quality photonic crystal heterostructures

High quality photonic crystal heterostructures with a thin titania planar defect layer between its two constitutional photonic crystals were fabricated and their structural and optical properties were analyzed. The results suggest that the thin planar defect layer is beneficial to separate the two constitutional photonic crystals from each other and to reduce the roughness of the interface. The quality of the resulting photonic crystal heterostructures is improved largely and the main features of the photonic band gaps of the two constitutional photonic crystals are inherited. The predominant optical quality of these heterostructures (e.g. deep double photonic band gaps and steep photonic band edges) may afford new flexibility and functionality for engineered photonic behavior in practical devices such as late-model light-operated switches.     

Two-dimensional function photonic crystals

In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.     

二维函数光子晶体

光子晶体是由两种或两种以上不同介电常数材料所构成的周期性光学纳米结构.光子晶体结构可分为一维、二维和三维,其中二维光子晶体已成为研究的热点.可调带隙的二维光子晶体可以设计出新型的光学器件,因此,对它的研究具有重要的理论意义和应用价值.本文提出的二维新型函数光子晶体可以实现光子晶体带隙的可调性.所谓二维函数光子晶体,即组成它的介质柱的介电常数是空间坐标的函数,它不同于介电常数为常数的二维常规光子晶体.二维函数光子晶体是通过光折变非线性光学效应或电光效应使介质柱的介电常数成为空间坐标的函数.运用平面波展开法给出了TE和TM波的本征方程,由傅里叶变换得到二维函数光子晶体介电常数ε(r)的傅里叶变换ε(G),其傅里叶变换比常规二维光子晶体的复杂.计算发现当介质柱介电常数为常数时,其傅里叶变换与常规二维光子晶体的相同,因此二维常规光子晶体是二维函数光子晶体的特例.在此基础上具体研究了二维函数光子晶体TE波和TM波的带隙结构,其介质柱介电常数函数形式取为ε(r)=k·r+b,其中k,b为可调的参数.并与二维常规光子晶体TE波和TM波的带隙结构进行了比较,发现二维函数光子晶体与二维常规光子晶体TE波和TM波的带隙结构有明显的区别,二维函数光子晶体的带隙数目、位置以及宽度随参数k的变化而发生改变.从而实现了二维函数光子晶体带隙结构的可调性,为基于二维光子晶体的光学器件的设计提供了新的设计方法和重要的理论依据.     

Optical properties of one-dimensional photonic crystals obtained by micromatchining silicon (a review)

The theoretical and experimental investigations of photonic band gaps in one-dimensional photonic crystals created by micromatchining silicon, which have been performed by the author as part of his doctoral dissertation, are presented. The most important result of the work is the development of a method of modeling photonic crystals based on photonic band gap maps plotted in structure–property coordinates, which can be used with any optical materials and in any region of electromagnetic radiation, and also for nonperiodic structures. This method made it possible to realize the targeted control of the optical contrast of photonic crystals and to predict the optical properties of optical heterostructures and three-component and composite photonic crystals. The theoretical findings were experimentally implemented using methods of micromatchining silicon, which can be incorporated into modern technological lines for the production of microchips. In the IR spectra of a designed and a fabricated optical heterostructure (a composite photonic crystal), extended bands with high reflectivities were obtained. In a Si-based three-component photonic crystal, broad transmission bands and photonic band gaps in the middle IR region have been predicted and experimentally demonstrated for the first time. Si–liquid crystal periodic structures with electric-field tunable photonic band-gap edges have been investigated. The one-dimensional photonic crystals developed based on micromatchining silicon can serve as a basis for creating components of optical processors, as well as highly sensitive chemical and biological sensors in a wide region of the IR spectrum (from 1 to 20 μm) for lab-on-a-chip applications.     

光控光子晶体偏光片

提出了一种新颖的调节液晶光子晶体光子带隙的方法.光子晶体波导通过往二维三角形光子晶体的介质柱之间填充液晶得到，光诱导液晶取向以改变液晶的折射指数从而改变光子晶体的光子带隙.数值模拟结果表明：通过外界光场控制所填充的向列相液晶的方向可以对这种二维三角形介质柱光子晶体的禁带结构进行调节.与电场调制方法相比，该光控液晶取向技术具有响应速度快、结构简单的优点.这种可调光子晶体可用于制作新颖的光敏偏光片.     

Nonlinear three-wave interaction in photonic crystals

We present a multi-scale analysis of nonlinear three-wave-interaction processes in photonic crystals. Based on photonic Bloch functions as carrier waves, we derive the effective nonlinear coupled wave equations that govern pulse propagation in these systems and obtain the corresponding effective photonic crystal parameters directly from photonic band-structure computations. As an illustration, we show how hitherto inaccessible radiation-conversion processes such as wave-front reversal of optical pulses can be realized. Furthermore, we describe a novel regime of nonlinear three-wave interaction in photonic crystals associated with the nearly degenerate case and show how these results may be utilized to study experimentally certain problems from plasma physics and hydrodynamics in the context of nonlinear photonic crystals.     

Optical Tamm states in one-dimensional magnetophotonic structures

We demonstrate the existence of a spectrally narrow localized surface state, the so-called optical Tamm state, at the interface between one-dimensional magnetophotonic and nonmagnetic photonic crystals. The state is spectrally located inside the photonic band gaps of each of the photonic crystals comprising this magnetophotonic structure. This state is associated with a sharp transmission peak through the sample and is responsible for the substantial enhancement of the Faraday rotation for the corresponding wavelength. The experimental results are in excellent agreement with the theoretical predictions.     

光子晶体可调谐滤波特性的理论研究

用特征矩阵法研究了带缺陷的一维光子晶体的透射性质，并提出了新的可调谐光滤波器的概念.一维光子晶体(L1H1)m带有Lc-H2(L2H2)n形式的缺陷时，在光子晶体中间出现了窄的透射峰，其他级次的干涉峰则随着覆盖层H2(L2H2)n周期数的增大而减弱并消失.当耦合层Lc厚度变化时，在光子晶体禁带边缘附近出现两个高透射率区域.高透射率区域透射峰的特性由光子晶体和覆盖层的性质决定.当光子晶体禁带宽度较小时，两个高透射率区域接近，形成具有约150nm调谐范围的区域，因此可制备以一维光子晶体为基础的新型可调谐光滤波器. 关键词： 光子晶体 可调谐光滤波器 特征矩阵     

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.     

Two-dimensional photonic crystals with pure germanium-on-insulator

We have investigated pure germanium two-dimensional photonic crystals. The photonic crystals which exhibit resonances in the near infrared spectral range were fabricated on germanium-on-insulator substrates using standard silicon-based processing. The germanium-on-insulator substrate consists of a thin layer of pure germanium-on-oxide deposited on a silicon substrate. The optical properties are probed by the direct band gap optical recombination of pure germanium at room temperature. Resonant optical modes are evidenced between 1.68 and 1.53 μm in different type of hexagonal cavities (H1-H5). The spectral position of the modes is controlled by the lattice periodicity and air filling factor of the photonic crystals. Close to the Ge band edge, the quality factors are limited by the bulk material absorption.     

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.     

二氧化硅胶体球自组装光子晶体的研究

光子晶体由于具有光子带隙和光子局域等一系列优异的光学特性而受到了人们广泛的关注。由于采用胶体颗粒自组装法制备光子晶体制备工艺简单,所需要的费用也较低,因此已成为制备可见光至红外波段三维光子晶体的一种简便有效的方法。采用垂直沉积法制得了三维光子晶体薄膜,并用扫描电子显微镜和紫外-可见光-近红外分光光度计对其显微结构和光学特性进行了详细的研究。结果表明,自组装薄膜在三维方向上都具有有序结构,其密排面平行于载波片的表面。制备的光子晶体薄膜具有明显的光子带隙特性,带隙中心波长为956nm。研究了带隙中心波长同入射线与密排面法线夹角之间的变化关系,其结果与理论值吻合得很好。     

Structural and optical characterization of photonic crystals synthesized using the inward growing self-assembling method

We present a systematic analysis of three-dimensionally (3D) ordered photonic crystals fabricated using the recently reported inward growing self-assembling method. The structural and optical characterizations reveal extremely high quality features in these crystals. These include the high reflectance values in the first order stop band and the high energy optical response observed in all the samples, irrespective of the diameter of the spheres, even though the time for fabrication is less than three hours. The photonic stop band is tuned by varying the angle of incidence of light. The peak reflectance and the width of the photonic stop band are unaffected up to an angle of incidence of 45°. At higher angles of incidence, the involvement of other planes in the Bragg reflection is qualitatively demonstrated, emphasizing the extent of ordering and the quality of photonic crystals.     

Novel optical modulator using silicon photonic crystals

We propose a novel compact and integrated optical modulator, which consists of p–i–n silicon photonic crystals with triangular lattice and a line defect waveguide. The device operation is based on a dynamic shift of the photonic band gap (PBG), which induced change in the silicon refractive index by the free carrier injection. We have numerically analyzed and investigated its light modulation performance by using plane wave expansion (PWE) method and finite-difference time-domain method. With small size, rapid response time and high extinct ratio, the designed optical modulator can be used in photonic integrated circuits.     

Selective Excitation of Band Extrema in Valley Photonic Crystals

Flexible control of building blocks of photonic crystals enables achieving desirable band structures. Exploration of photonic band extrema has brought many fantastic features to design artificial optical materials, such as Brillouin‐zone‐corner extrema for valley photonic materials and zone‐center extremum for zero‐index metamaterials. However, two such kinds of extrema are always found independently in different photonic crystals. In this work, a kind of valley photonic crystals possessing both zone‐center and zone‐corner band extrema almost at the same frequency is proposed. Inspired by antennas theory, a three‐antenna array (TAA) source is devoted to individually manipulate each extremum. The correlation coefficient is given to determine the coupling efficiency between the TAA source and extrema eigenmodes. By using a source with a high correlation coefficient, these extrema bulk states are selectively excited consistent with their eigenfields. Furthermore, three control cases are shown that multiple extrema points are simultaneously excited, in order to confirm the validity of the correlation coefficient. Finally, a potential application of a beam‐steering device is proposed through selective excitation of ternary extrema. This work develops binary valley states into ternary mix states, rendering more degrees of freedom for on‐chip optical information transport, particularly for beam steering and mode division multiplexing.     

A colloidal crystal microstructure fiber: fabrication and characterization

A method of fabricating colloidal crystal microstructured fiber is presented. The proposed structure relies on partial etching of the cladding layer of a single-mode fiber and growth of colloidal photonic crystals inside eroded area. The photonic crystal cylindrical annulus embedded in fiber is characterized by optical and scanning electron microscopy. The optical characterization was analyzed by optical transmission spectroscopy. The measurement results show a about 1550-nm band gap. The results also reveal the possibility of cladding cylindrical fibers with three-dimensional photonic crystals.     

Nanostructural effects on optical properties of tungsten inverse opal

Tungsten (W) photonic crystals are very attractive because of their potential applications in the conventional lighting field. In this work we show that W nanostructures have dominative effects on optical properties of W inverse opal. The nanoparticle structure of W phase can cause intensive optical absorption and breakdown of the photonic band gap; on the contrary, W inverse opal made from bulk and compact W phase would have weak absorption and possess a good photonic band gap. The results will throw a new light on the study and application of W photonic crystals and development of other photonic crystal and black-body materials. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.