Feature issue introduction: mid-infrared optical materials and their device applications

The mid-infrared (mid-IR, 2 to 10 μm) is a technologically important spectral regime for sensing, imaging, and communications.In the past few years, there has been a surge of interest in novel mid-IR optical materials as well as their device implementations to address the increasing demands from these applications.The 22 papers in this feature issue represent a diverse cross-section of the latest technological advances in this field, spanning mid-IR light generation, propagation, manipulation, and detection functions in free-space, fiber, and planar platforms.In terms of material systems, semiconductors, glasses, plasmonic metals, as well as nanostructures specifically engineered for the mid-IR band, are all extensively covered.We hope that the readers will enjoy the kaleidoscopic view of the burgeoning field of mid-IR optics and photonics through this feature issue.