| Photonic crystal consisted of periodic well-ordered arrangement of two materials with different dielectric constants or refractive indices is a novel optoelctronic materials. Colloidal photonic crystals and their ordered porous materials have photonic band gaps and are usually regarded as a type of optical materials or photonic crystals, such as optical filters, switches, and materials with photonic band gap. They also have potential applications in the fields of molecular separation, membrane reactors and biomaterials engineering. A colloidal self-assembly approach can produce complex and regular three-dimensional (3D) structures including channel-like, spherical, ellipsoidal, and rectangular shapes as well as more complex forms such as star-shaped assemblies. Such shape-controlled colloidal crystals are of critical importance for practical use of bulk colloidal crystals. Therefore, significant efforts have been devoted to fabricating3D colloidal photonic crystals and their ordered inverse opals on the non-planar substrates such as the microcapillary and optical fiber, as well as the structure of particle arrangement and the optical properties. These cylindrical colloidal crystals and their inverse opals can be applied to photonic devices such as fiber Bragg grating for optical communications and as supporting materials for catalysis, separation and chromatography. The colloidal crystals based on substrates such as optical fiber are promising to form3D micro-structure fibers.Based on the Maxwell wave equation of the photonic crystal, using the plane wave expansion (PWE) method, we calculate the photonic band gap structure of the opals and inverse opals and obtain the parameters such as the diameter and the refractive index of colloidal sphere. We introduce the generalized finite-difference time-domain (FDTD) method and simulate the reflection/transmission spectra from colloidal crystals, as well as the transmission mode of the electromagnetic wave in the colloidal crystals. The position and depth of the photonic band gap is analyzed and the parameters such as the diameter of colloidal spheres, the refractive index of the material and the number of the crystal layers have been discussed.The mechanism of self-assembly of colloidal crystals is studied and pressure controlled isothermal heating vertical deposition method has been developed. By controlling the pressure and temperature simultaneously, we can obtain high-quality colloidal crystal films at low temperature. The colloidal crystals have the face-centered-cubic (FCC) structure with few defects and the growth.time is reduced to several hours. The novel method can be widely applied because it is free of the limitations of materials and diameters of colloidal spheres. We also utilize the modified vertical deposition to fabricated cylindrical colloidal crystal films on non-planar substrates such as the microcapillary and optical fibers. Inside or outside of the capillaries, the colloidal spheres self-assemble to FCC structure with different [111] crystalline directions. One is perpendicular to the axis of the capillary in a hollow circular annular, while the other is parallel in a solid cylindrical column. Also, the colloidal crystal annular is investigated to have excellent cylindrical symmetry with the (111) plane of FCC structure parallel to the surface of the optical fiber. Transmission spectra have demonstrated deep photonic band gap (PBG) of up to76%and steep photonic band edge (PBE) of up to5.2%/nm. With the angles of out-of-plane incident light increasing from0to60degrees, the peak position and transmittance decreases gradually which agreed well with the Bragg formula. The excellent optical properties not only affirm the success of the assembly method but also introduce PBG materials to meet with the practical application of optical fiber communication, optical switching and sensors.A cooperative assembly method with the confinement by two close substrates is developed to fabricate large area silica inverse opals with open surface pores and no overlayers in large domains. Using this simple, fast and relatively inexpensive method, we have successfully fabricated large-area, highly ordered macroporous structures with different pore sizes. The mechanical stability of the porous structures is enhanced by not only the sol-gel precursor cooperatively assembled in the voids of the colloidal templates but also the limited space confined by two substrates. SEM characterization and transmission spectra affirm the high quality of these porous structures. The excellent photonic properties with deep PBG up to60%and steep PBE up to6%/nm combined with their precisely defined shape should make these porous structures attractive candidates for emerging applications of photonic crystals, electro-catalysts, sensors, photo-catalysts and so on.High quality of nanostructure colloidal crystal-fiber structure is obtained by modified gravity sedimentation method. A tunable3D colloidal photonic crystal based on the reflection peak position shift with increasing the refractive index infiltrated in the voids of the crystal is fabricated on the end face of an optical fiber. The morphology of the colloidal crystal examined by the SEM illustrates the (111) plane parallel to the substrate of the fiber end face. Optical characterization with reflection and transmission spectra is also analyzed with an all-fiber network system. Reflection and transmission spectra show the existence of photonic band gap, which affirming the high quality of the colloidal crystals. As the liquid refractive index filled in the interspaces of the sample increases, the tunable wavelength of reflected maximum predicted by Bragg’s equation considering the effect of PBG shows a good agreement with experimental results. These excellent properties are promising to apply in the field of fiber sensors.Combining with pressure controlled isothermal heating vertical deposition and sol-gel cooperatively assembly method,3D ordered porous structures coated on the outside of the macrocapillary and optical fiber have been successfully obtained. The arrangement of the air spheres possesses FCC structure, i.e. inverse opals, and the (111) plane is parallel to the surface. The effect of the parameters such as the diameter of colloidal spheres, the diameter of optical fiber and the ratio of colloidal suspension concentration to sol-gel precursor concentration have been discussed to fabricate high quality inverse opals. This method is promising to fabricate3D ordered porous microstructure fiber. |
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