Preparation technology of low loss nanoporous glass based on fluoride doping

Abstract

The nanoporous silica with silica content more than 96% can be obtained, which based on the glass phase separation technology, the boron rich phase can be removed by acid leaching which according to control the stable and uniform phase separation of borosilicate glass (SiO₂-B₂O₃-Na₂O). The porous glass has strong adsorption capacity and large surface area, in particular, the abundant broken bonds on the surface of porous glass channels provide enough non-bridging oxygen bonds. So that a new active fiber with high gain and uniformity can be obtained by drawing the rare earth doped nanoporous glass which is potential for fiber amplifiers and fiber lasers. However, nanoporous glass is doped in solution, hydroxyl groups will be retained after the sintering, which will increase the background loss of the material. Because Si-F bond energy is greater and bonding is stronger than Si-OH, F-bonds with Si replaced OH- by fluoride doping so as to reduce the loss caused by hydroxyl. In this paper, nanoporous glass is soaked in the solution with a certain concentration of fluoride, and sintered it at high temperature in helium atmosphere to reduce loss. The experimental results show that the hydroxyl content in porous glass gradually decreases with the increase of fluoride concentration, the raman peak at 935 cm-1 in the raman spectrum also confirms the existence of Si-F bond, and the lowest hydroxyl content is only 3.31ppm. In this case, the refractive index of glass will decrease uniformly with the increase of fluoride doping concentration, which provides a new method for preparing low loss nanoporous glass fiber materials.