Sol-gel preparation of one-dimensional photonic bandgap structures

One-dimensional (1-D) photonic bandgap (PBG) structures remain one of the most practical ways of applying the PBG concepts to the solution of many urgent problems in laser physics and optical technologies. The sol-gel method is an inexpensive and flexible liquid phase processing technique that is suitable for the deposition of multilayer stacks. The multilayer stacks can be designed as 1-D PBG structures, such as distributed Bragg reflectors (DBR), or single and coupled microcavities, as reported in this work. Spin-coated TiO2 and SiO2 layers acted as the high and low refractive index materials, respectively. Each layer was heat-treated at a high temperature (similar to1000 degreesC) for a short period of time (similar to90 s) in order to increase the index contrast, while preserving relatively smooth interfaces between the consecutive layers. Ellipsometry, X-ray diffraction, micro-Raman spectroscopy, transmittance/reflectance spectroscopy, and atomic force microscopy were used to characterize both the individual layers and the whole structures. Strong PBG properties are demonstrated, with an omni-directional stop band for a 5.5-pair DBR (lambda = 550-600 nm, gap to mid-gap ratio 7.6%) and sharp pass bands within the stop bands for the microcavities.