Focus on silicon photonics

E-mail: y-ishikawa@material. t.u-tokyo.ac.jp Si photonics has attracted much interest over the last decade as it allows integration of photonic and electronic devices on a small Si chip, providing highcapacity, energy-efficient, and cost-effective optical interconnects. Active optical cables based on Si photonics are now commercially available for rack-to-rack interconnects in supercomputers and data centers. Shorter reach optical interconnects, i.e., interand intra-chip optical interconnects, have been studied as the next challenge for higher speed computing. Science and technology of advanced materials is essential for rapid development in this field, and therefore it is very appropriate to publish this focus issue in STAM. This focus issue introduces state-of-the-art material and device technologies in Si photonics. The topics cover not only technologies for the optical interconnects but also optical sensing as a novel application. We are grateful to the authors who contributed to this focus issue, and hope that it will help researchers understand the frontiers of Si photonics, stimulating novel concepts in material and device technologies, as well as novel developments in and applications of Si photonics.