Self-Assembled Colloidal Crystals in Capillary with Its Fiber Junction

Silica microspheres self-assembled in glass capillary are investigated. Monodisperse silica microsphere dispersions in diameter 320 nm are self-organized into a bulk cylindrical colloidal crystal by evaporation induced nucleation and crystallization. The resulting colloidal crystals are characterized by optical microscopy and scanning electronic microscopy (SEM), and the SEM images show these crystals dominate in fcc lattice with its (111) crystallographic axis as longitudinal. The colloidal crystal filled capillary is packaged into a heat-shrink plastic tube and a fiber measurement system is designed to measure the optical property of colloidal bulk in capillary. It is found that an appreciable bandgap appears at wavelength 686 nm from the transmission spectroscopy, which is consistent with the theoretical estimation. A considerable photonic band gap of up to -10 dB and a steep photonic band edge of up to 0.25 dB/nm indicate that silica microspheres are promising for implementing optical filter applications in fiber systems.