A dry silver electromigration process to fabricate optical waveguides on glass substrates

Abstract

We present an improved method to fabricate low-loss waveguides on glass without the use of molten salts or liquid solutions. Preliminary results obtained so far are reported. This technique encompasses a dry silver ion migration process assisted by applied electric field. The waveguides thus fabricated showed no discolors or cracks, a well-known problem commonly incurred if molten nitrate process was used. The fabrication principle is based on driving silver ions from a solid source into the glass using an applied electric field, and at the same time moving the sodium ions out of substrate along the direction of the applied electrical field to maintain charge neutrality inside the glass. As a result, sodium ions are replaced by silver ions. In this experiment, high quality silver films approximately 1 /spl mu/m thick were electron-beam deposited on sodalime slide glass in high vacuum (/spl sim/10/sup -7/ Torrs). An electromigration process was then initiated by applying the voltage between the top and bottom surfaces of glass that was heated to about 230/spl deg/C. After a while, the silver film showed sign of being depleted during the diffusion/drift process as the ionic current started to decrease. This is a clear indication that silver ions were indeed driven into the glass. Based on the measurements and calculation of the current, the time, along with the sodium concentration, the waveguide depth is estimated to be 6 /spl mu/m. The optical characterization of the waveguide was conducted with a 0.6328 /spl mu/m He-Ne laser. The laser beam was coupled into and out of the waveguide using two prisms of high index of refraction. Data subsequently obtained from the prism coupling technique includes propagation mode patterns and index change associated with the waveguide region. Both the fabrication process as well as waveguide properties will also be presented. Fabrication of waveguides on BK7 optical glass is also underway.