A dry electromigration process for fabricating deep optical channel waveguides on glass and their characterization

A dry electromigration technique was developed to fabricate deep multimode channel and planar waveguides on BK7 optical glass. In contrast to earlier ion exchange processes based on thermal diffusion, a relatively high electric field (∼440 V/mm) was applied on the glass to accelerate the field-driven ion exchange process by expeditiously replacing host sodium ions in the glass with silver ions. As a result, the process temperature is significantly reduced, leading to lower optical attenuation on the waveguides. Lowest optical loss was achieved on waveguides fabricated at 320 °C. The increase on the index of refraction for the planar waveguide was determined to be 0.076 using the prism coupling method. The optical loss for channel waveguides was measured using the edge coupling technique with a 0.6328 μm He–Ne laser. Loss of 2 dB/cm was obtained for channel waveguides of 25 μm in depth, relatively low for waveguides of such depth at red wavelength. The scanning electron microscope (SEM) with energy-dispersive X-ray (EDX) spectroscope was utilized to obtain the concentration profile of silver ions in the waveguide region. A modified Huggins–Sun model with Gladstone–Dale relation was employed to deduce the refractive index profile from the silver ion concentration profile. A nearly step-like profile was observed from every deep multimode waveguide fabricated.