We report an effectively simple dry silver electromigration technology designed to fabricate low-loss deep channel waveguides on a specially chosen BF450 glass substrate with refractive index of 1.472. The simplicity is achieved by replacing the gold or aluminum film electrodes commonly deposited on the glass substrate with two stainless-steel electrodes to facilitate the electromigration process. In contrast to earlier ion exchange waveguides reported, a relatively high electrical field of 545 V/mm was applied to the glass to speed up the migration and also to prevent the silver ions that were driven into the glass from reducing into silver atoms, a major contributor to waveguide loss. The deep channel waveguides thus fabricated showed no discolors or cracks, of which the attenuation losses of less than 0.1 dB/cm were later measured using our 0.6328 µm He-Ne laser edge-coupling setup. Lastly, the scanning electron microscope equipped with an energy-dispersive X-ray (EDX) detector was adopted to obtain the concentration profile of silver ions distributed in a channel waveguide region after the exchange. The EDX measurements were then utilized along with the Gladstone-Dale relation to deduce the refractive index profile, of which a nearly step-like profile was deduced from every deep channel waveguide fabricated.
Ricky W. Chuang and Chin C. Lee, "Low-Loss Deep Glass Waveguides Produced With Dry Silver Electromigration Process," J. Lightwave Technol. 20, 1590- (2002)