Preparation Of GeO₂ Reflective Film For Hollow Waveguide Application

The properties and applications of CO2 laser and hollow optical waveguide were introduced in this work. GeO2 ceramic films were deposited onto the inner wall of silica glass capillary tube via an acid-induced liquid phase deposition (LPD) method. By sintered at a temperature slightly higher than the melting point of hexagonal GeO2 (1115℃), the as-deposited GeO2 ceramic film was transformed into a compact GeO2 reflective film for hollow waveguide application. The composition, morphologies and thickness of the LPD-derived GeO2 ceramic film and the compact reflective film were investiguated. The transmission properties of the GeO2 coated hollow waveguides were evaluated.The experimental results show that transparent and stable germanate ion aqueous solution could be obtained by reaction between hexagonal GeO2 powders and ammonia aqueous solution. Germanate ions were decomposed with acid addition and GeO2 ceramic films could grow on the substrate surface through a LPD process. The dissolving time of GeO2 in ammonia aqueous solution decrease with temperature increase and prolong with rising solid content. The optimal dissolving temperature and solid content are 70℃and 5~6%, respectively. The LPD growth of GeO2 is accelerated under low pH condition. The proper pH value of precursor solution for occurrence of LPD process is 1~2. GeO2 film prepared by acid-induced LPD method has hexagonal crystal structure. Using polybasic acid to adjust the pH value of precursor solution would lead to formation of films with larger particle size.GeO2 films with cube-like particles could be obtained by increasing the deposition temperature. Thickness and compactness of the film could be improved by cycles of LPD operations. GeO2 ceramic film was melted and adhered to the substrates after annealed at 1130℃for 30min. The obtained film is crack-free and dense. Films with the thickness beyond 4μm were prepared by several cycles of LPD operations. Optical transmission spectrum analyses demonstrate that the GeO2 film has a high transmisstance at the wavelength of CO2 laser (10.6μm). The transmission loss of samples decreases with increasing film thickness. The lowest loss value is 0.65dB/m and GeO2 hollow waveguide exhibits potential applications such optical detect device, etc. GeO2/Ge composite film could be fabricated after annealing the sample under H2 atmosphere for 5~20min at 600℃. Nano pores were formed on the film surface. GeO2 was reduced to Ge completely after 30min. This composite film is expected to decrease the transmission loss according to the theory of total reflection type of hollow waveguide.