Micromachined wide-band lithium-niobate electrooptic Modulators

We present our detailed study of a micromachined substrate approach for a wide-band lithium-niobate modulator and other ultra-wideband RF interconnection applications. Resonant substrate mode coupling often results in large RF loss that affects the frequency performance in LiNbO₃ modulators. Using the micromachining approach, we demonstrated significantly reduced resonant mode coupling loss in LiNbO₃ modulator electrodes. In this paper, the effects of substrate geometry and material combination on microwave transmission are experimentally investigated. Our investigation showed that the RF launch of the coplanar-waveguide circuit is a major contributor to the resonant mode coupling. Micromachining the launch area allows us not only to suppress resonant couplings, but also to retain substrate mechanical strength for high-yield production. Two micromachined modulator die configurations were proposed and experimentally demonstrated.