Modulation of Photonic Bandgap and Localized States by Dielectric Constant Contrast and Filling Factor in Photonic Crystals

The band structure of 2D photonic crystals (PCs) and localized states resulting from defects are analyzed by finite-difference time-domain (FDTD) technique and Padé approximation.The effect of dielectric constant contrast and filling factor on photonic bandgap (PBG) for perfect PCs and localized states in PCs with point defects are investigated.The resonant frequencies and quality factors are calculated for PCs with different defects.The numerical results show that it is possible to modulate the location,width and number of PBGs and frequencies of the localized states only by changing the dielectric constant contrast and filling factor.

Fabrication of BaTiO_3 Inverse Opal Photonic Crystal

The colloidal crystal template or opal with a closed-packed face centered cubic (fcc) lattice, was prepared from monodisperse polystyrene (PS) spheres by gravity sedimentation. The template was used for the generation of photonic crystal. The template provided void space for infiltration of liquid precursor composed of titanium butyloxide, barium acetate, ethanol, and acetic acid. The opal composite was hydrolyzed, dried, sintered by heating for completely removing PS spheres to form BaTiO3 photonic crystals with inverse opal structure. The PS spheres were replaced by air spheres, which interconnected each other through the windows on the BaTiO3 wall. So both the BaTiO3 wall and air void constitute continuous phases.

PAM-PAA microgel inverse opal photonic crystal and pH response

The colloidal crystal template or opal with a closed-packed face-centered cubic （fcc） lattice was prepared from monodisperse polystyrene （PS） spheres by vertical sedimentation. The template provided void space for infiltration of monomer precursor composed of acrylate acid, acrylamide and ammonium-persulfate, as well as microgel from the subsequent copolymerization. The sample was immersed in dimethylbenzene for completely removing PS spheres to form PAM inverse opal hydrogels （IOHPAM） or PAM/PAA inverse opal hydrogels （IOHPAM/PAA） photonic crystals. The PS spheres were replaced by air spheres, which interconnected each other through the windows. The study of responses to pH show that there are two peaks for both IOHPAM and IOHPAM/PAA films, but the IOHPAM/PAA peaks shift to higher pH, and the peaks are independent with the AA content.

Photonic Bandgap Properties of Atom-lattice Photonic Crystals in Polymer

The present paper covers the various photonic crystals（PhCs） structures mimicking real atom-lattice structures in electronic crystals by using the femtosecond laser-induced two-photon photopolymerization of SU-8 resin. The bandgap properties were investigated by varying the crystal orientations in 〈111 〉, 〈110〉 and 〈100〉 of diamond-lattice PhCs. The photonic stop gaps were present at λ=3.88 um in 〈111〉 direction, λ=4.01 um in 〈110〉 direction and λ=5.30 um in 〈100〉 direction, respectively. In addition, defects were introduced in graphite-lattice PhCs and the strong localization of photons in this structure with defects at λ=5 um was achieved. All the above work shows the powerful capability of femtosecond laser fabrication in manufacturing various complicated threedimensional photonic crystals and of controlling photons by inducing defects in the PhCs samples.

Thermal-responsive Photonic Crystals based on Physically Cross-linked Inverse Opal Nanocomposite Hydrogels

A thermal-responsive photonic crystal material was fabricated by forming an inverse opal nanocomposite hydrogel of poly(N-isopropylacrylamide)(IONHPNIPAm)within the interstitial space of a polystyrene photonic crystal template.In IONHPNIPAm,PNIPAm were physically cross-linked with two kinds of nanoparticles(carbon dots and laponite clays).The integration of carbon dots and laponite clays for physical crosslinking endowed IONHPNIPAm sufficient strength and self-healing property.IONHPNIPAm films can be completely peeled from the substrates to be utilized as an independent photonic crystal material.The structural color and optical diffraction of the IONHPNIPAm exhibits a rapid reversible change in response to external thermal stimuli due to its physical cross-linking feature.Moreover,the IONHPNIPAm shows clear fluorescence due to the introduction of carbon dots,which enables a convenient way for chemical detection(such as the detection of silver ions).This stimuli-responsive photonic crystal materials based on physically cross-linked inverse opal nanocomposite hydrogels with fast response and good mechanical stability are promising for applications in the fields of smart optical detectors,thermal-responsive sensors and chemical detectors.

Controlling the Bandgaps of One-Dimensional TiO2/SiO2, TiO2/SnO2, and SiO2/SnO2 Photonic Crystals Using the Transfer Matrix Method

One-dimensional photonic crystals (1D PhCs) have a unique ability to control the propagation of light waves, however certain classes of 1D oxides remain relatively unexplored for use as PhCs. Specifically, there has not been a comparative study of the three different 1D PhC structures to compare the influence of layer thickness, number, and refractive index on the ability of the PhCs to control light transmission. Herein, we use the transfer matrix method (TMM) to theoretically examine the transmission of 1D PhCs composed of layers of TiO2/SiO2, TiO2/SnO2, SiO2/SnO2, and combinations of the three with various top and bottom layer thicknesses to cover a substantial region of the electromagnetic spectrum (UV to NIR). With increasing layer numbers for TiO2/SiO2 and SiO2/SnO2, the edges became sharper and wider and the photonic bandgap width increased. Moreover, we demonstrated that PhCs with significantly thick TiO2/SiO2 layers had a high transmittance for a wide bandgap, allowing for wide-band optical filter applications. These different PhC architectures could enable a variety of applications, depending on the properties needed.

Application of Padé Approximation in Simulating Photonic Crystals

To save finite-difference time-domain（FDTD） computing time, several methods are proposed to convert the time domain FDTD output into frequency domain. The Pad6 approximation with Baker＇s algorithm and the program are introduced to simulate photonic crystal structures. For a simple pole system with frequency 160THz and quality factor of 5000, the intensity spectrum obtained by the Padé approximation from a 2^8-item sequence output is more exact than that obtained by fast Fourier transformation from a 2^20-item sequence output. The mode frequencies and quality factors are calculated at different wave vectors for the photonic crystal slab from a much shorter FDTD output than that required by the FFT method, and then the band diagrams are obatined. In addition, mode frequencies and Q-factors are calculated for photonic crystal microcavity.

A photonic crystal waveguide with silicon on insulator in the near-infrared band

A two-dimensional （2D） photonic crystal waveguide in the Г-K direction with triangular lattice on a silicon-on-insulator （SOI） substrate in the near-infrared band is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. Its transmission characteristics are analysed from the stimulated band diagram by the effective index and the 2D plane wave expansion （PWE） methods. In the experiment, the transmission band edge in a longer wavelength of the photonic crystal waveguide is about 1590 nm, which is in good qualitative agreement with the simulated value. However, there is a disagreement between the experimental and the simulated results when the wavelength ranges from 1607 to 1630 nm, which can be considered as due to the unpolarized source used in the transmission measurement.

Numerical study on characteristic of two-dimensional metal/dielectric photonic crystals

An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional（2D） metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of flat bands and photonic bandgaps on two parameters（dielectric constant and filling factor） are investigated for two types of 2D metal/dielectric（M/D） photonic crystals,hole and cylinder photonic crystals.The simulation results show that band structures are affected greatly by these two parameters.Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters.It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones,and the frequency ranges of bandgaps also depend strongly on these parameters.Besides,the photonic crystals containing metallic medium can obtain more modulation of photonic bands,band gaps,and large effective refractive index,etc.than the dielectric/dielectric ones.According to the numerical results,the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.

A ministop band in a single-defect photonic crystal waveguide based on silicon on insulator

This paper reports that a two-dimensional single-defect photonic crystal waveguide in the Г-K direction with triangular lattice on a silicon-on-insulator substrate is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. A ministop band （MSB） is observed by the measurement of transmission characteristics. It results from the coupling between the two modes with the same symmetry, which is analysed from the stimulated band diagram by the effective index and the two-dimensional plane wave expansion methods. The parameter working on the MSB is the ratio of the radius of air holes to the lattice constant, fla. It is obtained that the critical τ/a value determining the occurrence or disappearance of MSB is 0.36. When τ/a is larger than or equal to 0.36, the MSB occurs. However, when τ/a is smaller than 0.36, the MSB disappears.

Zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres

This paper investigates the zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres （PBGFs） by using a full-vector finite element method. By simulation we found that theoretically the zero dispersion wavelength can be tailored by respectively changing the rounded diameter of air holes, pitch, refractive index, normalized thickness of core rings, and hole diameter to pitch ratio. At the same time the tailoring of dispersion slope can also be realized by changing the rounded diameter of air holes or pitch or normalized thickness of core rings. To illustrate the reasonability of fibre designs, this paper also gives the variance of normalized interface field intensity which measures the scattering loss relatively versus wavelength for different designs. From the viewpoint of loss, varying the rounded diameter and the thickness of core ring could shift zero wavelength but it is difficult to get the required parameters within so tiny range in practical drawing of PBGFs, on the other hand, it is possible in practice to respectively alter the pitch and refractive index to shift zero wavelength. But varying hole diameter to pitch ratio is not worthwhile because they each induce large increase of loss and narrowness of transmission bandwidth. The zero dispersion wavelength can be engineered by respectively varying the rounded diameter of air holes, pitch, refractive index, and normalized thickness of core rings without incurring large loss penalties.

Applied electric field to fabricate colloidal crystals with the photonic band-gap in communication waveband

The macropore silica colloidal crystal templates were assembled orderly in a capillary glass tube by an applied electric field method to control silica deposition. In order to achieve the photonic band gap （PBG） of colloidal crystal in optical communication waveband, the diameter of silica microspheres is selected by Bragg diffraction formula. An experiment was designed to test the bandgap of the silica crystal templates. This paper discusses the formation process and the close-packed fashion of the silica colloidal crystal templates was discussed. The surface morphology of the templates was also analyzed. The results showed that the close-packed fashion of silica array templates was face-centered cubic （FCC） structure： The agreement is very good between the experimental data and the theoretical calculation.

Treating temperature effect on bandgap in polymer opal photonic crystals

The optical reflective spectra and microstruc-tures of polystyrene opal photonic crystals treated with different temperatures have been investigated. With temperature increasing, the polystyrene spheres in opal structure transform to dodecahedrons, and the peak of reflective spectrum moves to shorter wavelength. The experiment result testifies the effect of the effective refractive index and the filling ratio to the bandgap position, and it corresponds to the theoretical simulative result.

类Opal光子晶体红外区安德森定域化理论研究

本文根据Mie散射理论和低浓度近似下,对在中红外区高折射率半导体材料AlP等做为散射体的类Opal光子晶体的安德森定域化进行了理论研究,发现在浓度为10%,折射率比值大于3.8,无吸收状态下,此类晶体将出现两个定域化区.同时为此类晶体的定域化研究提供了一个比较理想的处理方法.

SiO_2 Opal光子晶体结构周期数对TiO_2染料敏化太阳能电池光电性能的影响

通过在N719敏化的纳米晶二氧化钛膜上耦合SiO_2 Opal光子晶体,以此复合膜为光阳极,以敏化二氧化钛与无序SiO_2的复合膜为参比膜,考察了SiO_2 Opal光子晶体结构周期数对电池光电性能的影响。SiO_2 Opal光子晶体的结构周期数由制备光子晶体时的沉积液浓度控制。实验结果表明复合光子晶体后,电池的短路电流密度ISC和能量转化效率Eff明显提高,且光子晶体周期数越多,提高率越大,当SiO_2 Opal结构周期数增加至20层时,ISC和Eff与参比膜相比分别增加了91%和164%。IPCE分析表明光电性能提高的原因在于当光子晶体带隙与N719吸收峰重合时,利用光子带隙反射与光局域效应可提高N719对波长530nm光的吸收率。即光子晶体可有效提高吸光材料在光子带隙处的吸光率,且随着光子周期数增加,提升效果越显著。

ZnS-opal与反opal结构ZnS光子晶体的组装

以单分散SiO2微球为基元,在75%～80%湿度、30～45℃恒温密闭烘箱中垂直快速组装opal模板;以Zn(NO3)(20.035mol/L)、TAA乙醇溶液(0.05mol/L)为前体,通过溶剂热法充填形成ZnS-opal复合光子晶体;ZnS-opal复合光子晶体在2%～5%的HF溶液中浸泡4～5h后卸载模板,制得反opal结构ZnS基光子晶体;采用XRD、SEM、UV-Vis测试手段对反opal结构ZnS基光子晶体形貌、物相和光学性能进行了表征。结果表明:溶剂热法多次充填可使ZnS纳米晶在模板密堆积形成的空隙中均匀成核;经过酸处理的ZnS-opal中SiO2微球溶解、坍塌,形成蜂窝状三维有序介孔和反opal结构ZnS基光子晶体;相同粒径SiO2微球组装的opal模板、ZnS-opal以及反opal结构ZnS光子晶体均表现出光子带隙特性,但反opal结构ZnS光子晶体带隙位置相比前两者发生了蓝移。

在单晶硅片上直接电化学沉积制备镍反opal光子晶体

采用电化学沉积工艺直接向组装在单晶硅片上的聚苯乙烯胶体晶体中填充金属Ni,成功制备了Ni的反opal光子晶体。采用线性扫描伏安法研究了单晶硅表面的化学刻蚀对Ni的电化学沉积过程的影响,并采用扫描电子显微镜(SEM)、X射线衍射等对Ni反opal光子晶体的形貌和结构进行了观察分析,对其光学性能进行了初步研究。研究结果表明,对单晶硅片表面进行化学刻蚀有利于金属Ni的电化学沉积;在PS胶体晶体模板中电化学生长的金属Ni呈多晶状态,去除模板后形成了金属Ni的有序多孔结构。

反Opal及二维非线性光子晶体的研究(英文)

通过向SiO2 Opal模板中填充钛酸乙酯制备TiO2光子晶体，观测到光子晶体带隙位置的移动达62nm，并发现光子晶体的有序度随填充率的升高而下降．向聚苯乙烯Opal模板中填充钛酸乙酯，制备成当时填充率最高、带隙最短的紫外波段TiO2反Ova光子晶体（中心波长～380nm），并根据测量的其透射谱估算出其填充率约为12％，即Opal模板孔隙的50％被填充．本文还对二维PPLN光子晶体进行了研究．建立了一套高压极化装置和电压数据采集装置，通过外加电场极化法成功制备出了具有正方形和矩形两种晶格形状二维PPLN光子晶体．利用二维PPLN的二阶准相位匹配，测量了其对1．064μm激光的二次谐波转换效率，并研究了晶体的温度、激光的入射角度及占空比对二次谐波转换效率的影响．利用矩形晶格实现了多方向、多波长倍频高效输出．

Design of a ZnO/Poly(vinylidene fluoride)inverse opal film for photon localization-assisted full solar spectrum photocatalysis

Owing to its photonic band gap(PBG)and slow light effects,aniline black(AB)-poly(vinylidene fluoride)(PVDF)inverse opal(IO)photonic crystal(PC)was constructed to promote the utility of light and realize photothermal synergetic catalysis.As a highly efficient reaction platform with the capability of restricting heat,a microreactor was introduced to further amplify the photothermal effects of near infrared(NIR)radiation.The photocatalytic efficiency of ZnO/0.5AB-PVDF IO(Z0.5A)increases 1.63-fold compared to that of pure ZnO film under a full solar spectrum,indicating the effectiveness of synergetic promotion by slow light and photothermal effects.Moreover,a 5.85-fold increase is achieved by combining Z0.5A with a microreactor compared to the film in a beaker.The photon localization effect of PVDF IO was further exemplified by finite-difference time-domain(FDTD)calculations.In conclusion,photonic crystal-microreactor enhanced photothermal catalysis has immense potential for alleviating the deteriorating water environment.

SnO_2反opal光子晶体的制备及表征

以PS opal膜为模板制得了SnO2反opal光子晶体膜。采用浸渍提拉法和Sol-LPD法对PS opal模板进行填充,450℃焙烧除去PS模板得到SnO2反opal光子晶体。SEM和UV-Vis透射表征显示,两种填充方式都能得到三维有序的SnO2反opal光子晶体;以相同的PS opal膜为模板,通过Sol-LPD填充法得到的SnO2反opal膜的禁带位置向长波移动(以浸渍提拉法制得的光子晶体的禁带位置为基准)。这证实Sol-LPD填充法比浸渍提拉法有更高的填充率。通过Sol-LPD填充法还能够制备具有多重禁带的SnO2反opal异质复合膜。