Design and packaging of ultra broadband lithium niobate modulator for millimeter-wave applications

Macario, Julien
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University of Delaware
Millimeter-waves have grown in popularity for imaging applications in recent years due to their unique properties. In the electromagnetic spectrum, millimeter-waves can be seen as the frontier between radio waves and optics and thus benefit to some extent from both worlds. On one hand, they are long enough to penetrate through obscurant and thin dielectric and experience low atmospheric attenuation. On the other hand, they are small enough to be relatively convenient for imaging by providing good resolution for a manageable aperture size. In addition, millimeter-wave imaging has also benefited directly from the recent emergence of new components in the millimeter-wave region, an effort mainly driven by the booming of the telecommunication market and the quest for bigger and faster networks. At the University of Delaware, we have spent the last decade developing passive millimeter-wave imaging systems at 35 GHz and in W band at 77 GHz and 94 GHz. The architecture of these systems is based on the optical upconversion of the native blackbody radiations emitted by the scene and detected by an antenna or a distributed aperture antenna array. The modulator converting the detected millimeter-wave radiations into the optical domain on a carrier is considered the heart of the detection technique. However, they are no commercially available modulators capable of operating in W band, which led us to develop our own. In this regard, I present an ultra broadband LiNbO3 electro-optic phase modulator based on ridge coplanar waveguide capable of operating in W band and well beyond. In addition to the modulator's design and fabrication process, I introduce a novel LiNbO3 micromachining process that eliminates substrate mode coupling in the millimeter-wave region. As results, optical modulation sidebands were observed over the full millimeter-wave spectrum. Modulation in the millimeter-wave region is interesting not only for imaging applications but also for the telecommunication industry. In that regard, I integrated the ultra broadband LiNbO3 modulator with a 1 mm coaxial connector in a fully packaged, low RF insertion loss, module for modulation operation over the 0-110 GHz band.