Laser densification of channel waveguides in gel-silica substrates

Channel waveguides are important components in optical signal processing. A new method is described for producing such waveguides with high design flexibility. The channel waveguides are produced using CO₂ laser densification of partially densified gel-silica matrices (Type VI optical silica). Critical processing conditions include pore size and initial density of the matrix, laser power, translational speed of the sample, distance between sample and focusing lens, and ambient humidity.Channel waveguides less than 500 µm wide were produced in gel-silica substrates of different pore sizes and bulk densities throgh laser densification. Optically transparent waveguides were obtained for speeds of the sample over 1.4 cm/s and laser power settings ranging between 12 and 16 mA. Substrates with three different pore sizes were analyzed, i.e, 12, 30 and 45 Å, with densities varying from 1.1 g/cc to 2.1 g/cc. Fourier transform infrared microspectrometry of the densified regions showed that IR shifts ranging from 1 to 38 cm^–1 in the peak position of the Si-O-Si stretching vibrational mode were achieved. This corresponds to changes of index of refraction ranging from 0.01 to 0.20. The experiments show also that the larger the pore size the wider is the range of parameters for producing effective waveguides.