Investigation On Copper Ion Exchange Glass Planar Waveguides And Their Photoluminescence Properties

Ion exchange technique is an important method for fabricating glass waveguides. The ion exchange glass waveguides have many advantages, such as low production cost, low transmission loss, good matching with optical fiber and easy integrating into system, with wide range of applications. Among so many ion exchange techniques, copper ion exchange is a later developed and valuable glass waveguides fabrication technique. Copper ion exchange technology is different from the traditional Ag⁺-Na⁺ and K⁺-Na⁺ ion exchange technology, because the doped copper in copper ion exchange waveguides not only results in refractive index change for ion exchange layer which comes into being waveguide, but also produces blue-green luminescence properties. So it is clear that copper ion exchange can change the passive waveguide into active one, therefore the research for the technology will have very good application prospects. This paper studies the refractive index distribution and photoluminescence properties of copper ion exchange glass planar waveguides. The ion exchange technology, the mechanism of refractive index changes, as well as the measurement and characterization of waveguides are introduced.For copper ion exchange glass waveguides, Cu⁺, Cu²⁺ will diffuse into different regions; and their contributions to the refractive index change are different. Some studies have considered Cu⁺ play a leading role, and Cu²⁺ can be ignored. If this is the case, then the refractive index distribution of copper ion exchange planar waveguide should be "buried-shape", however, the refractive index distribution is of monotonously decreasing shape. As the above analysis reveals, the contribution of Cu²⁺ for the refractive index change can not be ignored, so the concentration distribution and refractive index distribution of two types of ions should be considered together. In this paper, copper ion exchange technology was used to prepare planar Soda-lime glass waveguides, and prism coupled technique was applied to measure the effective index of waveguides. The refractive indices of TE and TM mode are more or less the same, indicating that the stress fields are small and the birefringence can be negligible. The refractive index profiles of multi-mode waveguides were fitted by IWKB method. The diffusion equation of copper ion exchange was solved. In the process of calculating, the surface concentration of Cu⁺, Cu²⁺ can be gained through X-ray absorption spectra methodology with the assumption that the surface concentrations of Cu⁺, Cu²⁺ are constants, and the normalized surface concentration of Cu²⁺ is about 2 times as many as Cu⁺ for the samples. The diffusion depths of Cu⁺ and Cu²⁺ increase as the ion exchange time increases. However, Cu⁺ spreads with deeper depth and the maximum concentration is not in the surface of glass; Cu²⁺ diffuses with relatively shallower depth, concentrates near the surface and decreases monotonously. For copper ion exchange waveguides, the refractive index changes can be mainly caused by polarizability changes between Cu⁺, Cu²⁺ and Na+, as the radius difference is small. The equation of Cu⁺ concentration changes and the refractive index changes was educed by polynomial fitting, which isâ–³n=kâ–³c_Cu, and the refractive index profile was calculated as well. Then the equation was modified by the normalized weighing of Cu⁺ and Cu²⁺ compared with Na+ in accordance with their polarizability changes, which isâ–³n=k (0.636â–³c_Cu++0.364â–³c_Cu²⁺. The equation indicated the same profile as that by IWKB method basically. The results show that the refractive index changes in copper ion exchange process are caused by the combined effect of both Cu⁺ and Cu²⁺ and the contribution of Cu²⁺ can not be ignored, especially in the vicinity of the glass surface.During the preparation of copper ion exchange waveguides, there existences Cu⁺ and Cu²⁺, so the preparation conditions will affect the concentration distribution of Cu⁺ and Cu²⁺, and waveguide luminescence properties as well. There have been some researches focusing on the research of luminescence properties of copper ions for silicate glasses hosts, however, there were few reports considering ion exchange time and ion exchange temperature as controllable parameters simultaneously, which can affect the photoluminescence properties of waveguides; as the copper state is very sensitive to the doping route, making it unable to reflect preparation parameters'effect on the photoluminescence properties of copper ion exchange glass waveguides. Copper ion exchange technology was used to prepare planar Soda-lime and BK7 glass waveguides, and prism coupled technique was applied to measure the mode refractive index of waveguides. The refractive index profiles of waveguides were fitted by IWKB method as well. Then the photoluminescence spectra were analyzed on their spectral intensity and peak wavelength respectively. For Soda-lime glass waveguides, the peak wavelength of excitation spectra was 300-330nm. Emission spectra were centered between 500-550nm. For BK7 glass waveguides, excitation spectra were of peak wavelength at 280-320nm. Emission spectra were 480-600nm. The peak and intensity of emission spectra depend on the changes of ion exchange time and temperature. The emission bands are typical for the emission of Cu⁺ ions that undergo the transition 3d94s1â†'3d10. For BK7 glass waveguides: when ion exchange temperature is 570℃,wavelength red shift of the emission band peak with ion exchange time increases is mainly attributed to the energy level splitting of Cu⁺; when ion exchange time is 20 minutes, wavelength blue shift of the emission band peak with ion exchange temperature increases may arise from copper nano-clusters coagulation, causing the copper cluster enlarging to form bigger ones, so the symmetry of the local electric field around the Cu⁺ ions in the matrix can be partially influenced, indicating a blue shift of emission band. Through the ion exchange time and temperature parameters changes, the glass waveguides can be prepared for specific luminescence properties.