One-dimensional photonic crystal fabricated by the photochemical etching of silicon

The formation of periodic wall arrays on an n-type (100) Si substrate with V-shaped seed grooves on the surface was investigated. The influence of silicon sidewall roughness on the optical properties of onedimensional (1D) of photonic crystals obtained on the basis of the arrays was studied. The reflection spectra of the 1D photonic crystals exhibit a high modulation level of up to 95% and photonic band gaps of a high order that are in good agreement with calculations over a wide spectral range (1.5—15 μm).     

Tuning the band gap of self-assembled superparamagnetic photonic crystals in colloidal magnetic fluids using external magnetic fields

The model of tunable superparamagnetic photonic crystals self-assembled in colloidal magnetic fluids under externally applied magnetic fields is established. The mechanisms, which are in charge of the tunability of the band gaps with magnetic fields are clarified. The band structures of the triangularly-arrayed two-dimensional photonic crystals with limited heights of magnetic columns are calculated with the experimental data of structures and refractive indices in the literatures. The field-dependent properties of the first band gaps are gained for the z-odd and z-even modes, respectively. Simulation results indicate that the mid frequencies of the first band gaps of the z-odd modes can be easily tuned by the external magnetic fields, while those of the z-even modes bear relatively weak dependence on the external magnetic fields. Simultaneously, the first band gaps of both kinds of modes become wide along with the increase of the magnetic fields. The results presented in this work give a guideline for realizing the tunable photonic crystals with magnetically colloidal materials and magnetic stimuli.     

Si-based two-dimensional photonic crystals coupled to one-dimensional Bragg mirrors

Planar two-dimensional photonic crystals can be combined with a one-dimensional Bragg mirror to control the quality factor and out-of-plane coupling of optical Bloch modes. We have investigated the optical properties of such structures fabricated on silicon. The photonic crystals are fabricated in the upper Si layer deposited on top of quarter-wave thick SiO₂-polycrystalline Si layers. The optical properties are probed by the room-temperature photoluminescence of Ge/Si self-assembled islands as an internal source. We show that an enhancement of the quality factor can be obtained by controlling the thickness of the silicon upper layer in which the two-dimensional photonic crystal is etched and by controlling the air filling factor of the photonic crystal. Quality factors of 2200 around 1100 nm are obtained by this method for defect-free photonic crystals with a square lattice pattern. The experimental results are supported by three-dimensional finite-difference time-domain (FDTD) calculations of the radiated modes for the investigated structures.     

Applications of the finite difference mode solution method to photonic crystal structures

The finite difference waveguide mode solution method, which has been popularly employed in the study of waveguide modes on various optical and dielectric waveguides, is utilized to calculate the modal characteristics of photonic crystal fibers (PCFs) and planar photonic crystal waveguides and the band diagrams of two-dimensional photonic crystals. Vector guided modes on both PCFs based on the total internal reflection guiding mechanism ('holey fibers') and those resulting from photonic band gap effect are accurately computed, with their effective indexes and field distributions compared with other methods. Calculated dispersion of a single-core holey fiber and coupled-power behavior of a two-core holey fiber are found to agree with measured results. For applications to band diagram calculation and planar photonic crystal waveguide analysis, the finite difference scheme is modified simply by imposing suitable periodic boundary condition. Numerical results for air-column crystals and dielectric-rod crystals are both found to agree well with calculations using other methods.     

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.     

含负折射率材料1维光子晶体的偏振无关非全向的缺陷模

运用光学传输矩阵理论,研究了含负折射率材料1维光子晶体缺陷模的偏振特性。结果显示,零均折射率带隙中缺陷模对入射角和偏振有较强的依赖。通过对缺陷层参数的优化设计,得到了一系列的偏振无关非全向缺陷模,这是传统1维光子晶体中不能出现的。应用这些缺陷模,设计了低通、高通、带通空间滤波器。与传统光子晶体空间滤波器相比,这些空间滤波器具有偏振无关的优点。     

Propagation of light through localized coupled-cavity modes in one-dimensional photonic band-gap structures

We report on the observation of a new type of propagation mechanism through evanescent coupled optical cavity modes in one-dimensional photonic crystals. The crystal is fabricated from alternating silicon-oxide/silicon-nitride pairs with silicon-oxide cavity layers. We achieved nearly full transmission throughout the guiding band of the periodic coupled cavities within the photonic band gap. The tight-binding (TB) parameter κ is determined from experimental results, and the dispersion relation, group velocity and photon lifetime corresponding to the coupled-cavity structures are analyzed within the TB approximation. The measurements are in good agreement with transfer-matrix-method simulations and predictions of the TB photon picture. Received: 21 August 2000 / Revised version: 22 August 2000 / Published online: 9 November 2000     

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.     

Analysis of ultra-small photonic large scale integrated circuits

A detailed study of a platform of ultra-small photonic large-scale integrated circuits was conducted. Bandgap structure calculations of silicon-on-insulator (SOI) based photonic crystals have been investigated. The photonic crystal consists of dielectric cylinders in air. Using the band structure calculations we obtained design parameters for the proposed structures. The coupling between the photonic crystal and a waveguide fabricated from SOI system has been analysed. It is shown that the optical coupling is improved by interfacing different types of spot-size converters (SSCs) between the SOI waveguide and the photonic crystal. Also, the possibility and limitations of silicon doped germanium and SOI photonic crystals to analyse the light guiding in the third dimension is discussed.     

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.     

Uncoupled photonic band gaps

We theoretically investigated the symmetry properties of the modes in two-dimensional square lattice photonic crystals in order to study phenomena that would enable new frontiers in the applications of photonic crystals. Using group theory, symmetry analysis of the photonic crystals bands has been done. Particular attention was given to the search for the uncoupled B modes that cannot be excited by the external plane wave because they are symmetry forbidden. The existence of the uncoupled modes enabled to define new physics phenomena: uncoupled photonic band gaps. For the frequency ranges inside the uncoupled photonic band gaps, zero transmission is obtained. Therefore, there are two different types of photonic gaps in the photonic crystals: photonic band gaps and uncoupled photonic band gaps. The appearance of uncoupled photonic band gaps in photonic crystals could at least improve the application of the existing photonic materials and structures or even enable the usage of new ones for devices like waveguides, filters, and lasers.     

Resonant modes in quantum well structure of photonic crystals with different lattice constants

The resonant modes in a quantum well (QW) structure composed of three slabs of two dimensional (2D) photonic crystals with different lattice constants are analyzed with plane-wave-based transfer matrix method (TMM). It is found that the energy band of the well slab submerged into the band gap of barrier slab is discretized into quantized modes and the number of the resonant modes changes with the well slab thickness. A model structure of asymmetrical photonic QW consisting of two slabs of 2D photonic crystals with different lattice constants and one uniform dielectric slab in between is proposed and the resonant modes in it are investigated with the same method. A useful numerical simulation method for theoretical discussion as well as for practical application about photonic QW structure of photonic crystals with different lattice constants is proposed.     

Growth of InAs/GaAs quantum dots on germanium-on-insulator-on-silicon substrate for silicon photonics

We report the growth of self-assembled InAs/GaAs quantum dots (QDs) on germanium-on-insulator-on-silicon (GeOI/Si) substrate by antimony-mediated metal organic chemical vapor deposition. The influence of various growth procedures for the GaAs buffer layer on the QD formation and optical quality was investigated. We obtained QDs with density above 10¹⁰ cm⁻², and ground state emission in the 1.3 μm band at room temperature. These results demonstrate the promising suitability of germanium-on-insulator for the monolithic integration of QD-based and other GaAs-based photonic devices on silicon.     

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。     

Transient-mode excitation, terahertz generation and wavelength shifting in a photonic band gap

Dynamic responses of photonic crystal microcavities in nonlinear media are analyzed via both a finite-difference code and coupled-mode theory in the time domain. Optical frequency generation in both second- and third-order nonlinear materials is demonstrated based on the transient evolution of cavity modes. Terahertz waves can be generated in quadratically nonlinear crystals by optical rectification, whereas state generation inside the band gap can be linked to a Rabi-like splitting in cubic media. An all-optical ultra-fast wavelength shifter is proposed.     

低压化学气相沉积技术制备锗反蛋白石三维光子晶体

采用溶剂蒸发对流自组装法将单分散SiO2微球组装形成三维有序胶体晶体模板,用低压化学气相沉积法填充高折射率材料锗,酸洗去除SiO2模板,获得了锗反蛋白石三维光子晶体.通过扫描电镜、X射线衍射仪和紫外-可见-近红外光谱仪对锗反蛋白石的形貌、成分、结构和光学性能进行了表征.结果表明：锗在SiO2微球空隙内具有较高的结晶质量,填充致密均匀.通过改变沉积工艺,可控制锗的填充率;制备的锗反蛋白三维光子晶体具有明显的光学反射峰,表现出光学带隙效应.测试的光学性能与理论计算基本吻合.     

The theory of cylindrical photonic wires

The energy modes for a photonic nanowire have been studied and calculated. We model our photonic crystals after Noda et al. (1999) [18] where logs of semiconductor material are stacked to produce photonic band gaps in both the near and far infrared regions. A nominal dispersion relation was adopted in order to achieve qualitatively useful results. Photonic wires were modeled in two schemes, each with two specific geometries. In the first scheme, a pillar of one photonic crystal is embedded in a larger photonic crystal to produce a wire. This pillar was modeled as having either a square or a circular cross-section. The photonic crystals considered consisted of varying proportions of Ga_xAl_1−xAs, so that the wire could be adjusted. The second scheme investigated was a dielectric material for the central pillar, rather than a photonic crystal. Again, circular and square cross sections were considered. It was found that many more modes fit into the near infrared band gap than the far infrared band gap, and that a circular cross-section permits fewer modes. Finally, a dielectric pillar allows for a wire which is physically much smaller than a wire with a photonic crystal in the middle. As many photonic devices include such wires, these qualitative results could be useful in their design.     

Waveguide plasmon polaritons in metal-dielectric photonic crystal slabs

The optical properties of arrays of metallic (gold) nanowires deposited on dielectric substrates are studied both theoretically and experimentally. Depending on the substrate, Wood’s anomalies of two types are observed in the transmission spectra of such planar metal-dielectric photonic crystals. One of them is diffraction (Rayleigh) anomalies associated with the opening of diffraction channels to the substrate or air with an increase in the frequency of the incident light. The other type of Wood’s anomaly is resonance anomalies associated with excitation of surface quasi-guided modes in the substrate. Coupling of the quasi-guided modes with individual nanowire plasmons brings about the formation of waveguide plasmon polaritons. This effect is accompanied by a strong rearrangement of the optical spectrum and can be utilized to control the photonic bands of metal-dielectric photonic crystal slabs.     

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.     

光子晶体表面光波导的特性研究

采用平面波展开法和时域有限差分法,研究了光子晶体表面光波导的色散及光传输特性。研究结果表明,表面模的出现及其色散特性与表面介质柱的半径相关,色散曲线的斜率保持单调变化,并在最低或最高频率附近展现低群速度频率区。由于光子带隙和全内反射的共同影响,光场将沿晶体表面高效率地传输。研究结果为探索在光子晶体外部控制光传输具有重要的理论意义。