Silicon photonic devices for mid-infrared applications

The mid-infrared (IR) wavelength region (2–20 µm) is of great interest for a number of applications, including trace gas sensing, thermal imaging, and free-space communications. Recently, there has been significant progress in developing a mid-IR photonics platform in Si, which is highly transparent in the mid-IR, due to the ease of fabrication and CMOS compatibility provided by the Si platform. Here, we discuss our group’s recent contributions to the field of silicon-based mid-IR photonics, including photonic crystal cavities in a Si membrane platform and grating-coupled high-quality factor ring resonators in a silicon-on-sapphire (SOS) platform. Since experimental characterization of microphotonic devices is especially challenging at the mid-IR, we also review our mid-IR characterization techniques in some detail. Additionally, pre- and post-processing techniques for improving device performance, such as resist reflow, Piranha clean/HF dip cycling, and annealing are discussed.