Preparation of opal-based PBG crystals to develop multiple stop bands
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Preparation of opal-based PBG crystals to develop multiple stop bands Yen-Tai Chen and Leo Chau-Kuang Liau Department of Chemical Engineering, Yuan Ze University, 135 Yuan-Tung Rd., Chung-Li, Taiwan 320 email: [email protected] ABSTRACT Opal-based photonic band gap (PBG) crystals with multiple stop bands were prepared utilizing a sol-gel method. The fabricating procedure includes colloidal crystal syntheses, dispersion, sedimentation, coating, and thermal treatments. Each of the steps can affect the PBG properties, such as stop band locations and ranges. Different stop bands of the photonic crystals can be produced by controlling the particle sizes prepared by the colloidal crystal syntheses. A PBG crystal film with a certain stop band was formed using a particular size of the colloidal crystals coated on glass substrates. In this study, two layers of different particle sizes of PBG crystal were fabricated by different deposition conditions to demonstrate the feasibility of producing multiple stop bands. These conditions can affect the stack layers and structural regularity for forming the PBG layers. In addition, the stop band intensity of the PBG layer can be further improved by the step of thermal treatments. Results imply that multiple stop bands can be feasibly designed and produced as multiple PBG layers coating with a certain SiO2 particle size for each layer.
INTRODUCTION Nowadays, photonic band gap (PBG) technology has been paid attention to many researchers, especially the field of opto-electronics. This technology has been applied on promoting the modern optical communication and improving efficiencies of light emitted diode (LED) and laser devices. Furthermore, the PBG elements have been designed as photonic integrated circuits developed to take part in the conventional microelectronics for the purpose of miniaturizing devices [1]. The theory of PBG is that certain frequency ranges of light wave propagation can be forbidden due to the periodical crystal structure of PBG materials. The ability of PBG to control the propagation of certain light frequency described as a photonic stop band is similar to manipulating electrons in semiconductor as an on-off signal. The structure of PBG materials were first proposed by Yablonovitch [2] to improve an efficiency of laser device and John [3] to create light localization both in 1987. The typical photonic crystals are fabricated with face-centered cubic (fcc) structure of silica as called opal PBG. However, more different photonic crystal materials, such as
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PS [4], CdSe [5], ZnO [6], TiO2 [7], and structures were successfully established, i.e. rod-matrix structure [8], inverse opal structure [9] in recent years. There are many methods to produce photonic crystals with different structures, such as such as bar-matrix structure using a lithography method [8]. One of the practical methods adopts sol-gel technique to synthesize colloidal crystals as materials to fabricate PBG crystals. The fabricating procedure of this method starts from a st
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