Effect of sintering condition on the attenuation of silica glasses fabricated by additive manufacturing

Over the past few years, additive manufacturing (AM) of silica glasses and silica optical fibers has received great attention, mainly due to the high manufacturing flexibility and low manufacturing cost. However, compared with the traditional methods, the silica material made by AM technology is sintered at temperature below the melting point and has not gone through the long-time fusing or melting, so it has more defects, leading a higher attenuation. Due to the large amount of hydroxyl groups in the raw materials used in AM technology, it directly affects strong hydroxyl absorption. In this work, the influence of sintering pressure (SP) and temperature (ST) on the attenuation of printed and sintered silica glasses, including Rayleigh scattering, intrinsic point defects at characteristic wavelengths and hydroxyl absorption, was studied. The defects in silica glasses fabricated by AM technology were analyzed and discussed against sintering conditions. On one hand, we found that lower SP significantly reduced Rayleigh scattering and the intrinsic point defects due to moisture in the air and that the stress caused by densification in sintering process could further increase the intrinsic point defects. On the other hand, in the absence of crystallization, higher ST also reduced Rayleigh scattering, and the stress affected the inherent point defects. Hydroxyl absorption was determined by the diffusion of water and the amount of intrinsic point defects. The optimization of the SP and ST increased the glass transmittance at 600 nm by nearly 30% and 19% compared with non-vacuum and 1170 °C sintering conditions, respectively.