Abstract
Crystallization behaviors in Ge-doped SiO2 fiber preforms fabricated by vapor-phase axial deposition (VAD) method have been investigated. Since X-ray diffraction (XRD) peaks at around 2θ=22° in the crystallized glasses are reported to be strongly related with the induced second- and third-order optical nonlinear effects in poled glasses, enhancement of such crystalline phases is quite important and useful for fabrication of nonlinear functional glasses. It has been found that crystallization behaviors are drastically affected by thermal annealing and ultraviolet (UV) laser irradiation performed prior to heat-treatments for crystallization. In particular, it has been clarified that a crystalline phase, which is known to be highly effective for increase of induced optical nonlinearity, can be increased by pre-treatments of UV-laser irradiation at λ=193nm wavelength. These results suggest that modification of initial defect states in Ge-doped SiO2 fiber preforms could lead to fabricate crystallized glasses with optical nonlinearity induced by poling and/or crystallization.
