Guest Editorial: Introduction to the Special Issue on Optical Detectors

The objective of this special issue is to document the current state-of-the-art in the area of Optical Detectors and highlight recent progress and trends in innovative optical detector technology and its applications. This issue combines 11 invited and 21 contributed papers, authored byworld-renowned research groups and promising scientists from around the world. The invited papers present extended reviews on recent progress and significant perspectives on future research directions. They cover lownoise linear-mode avalanche photodiodes (APDs) for fiber optic communications, single photon APDs (SPADs) and Si SPAD arrays for photon counting imagers, hybrid integration technologies, waveguide APDs, lowcapacitance nano-photodetector, integrated photodetectors for coherent receivers, and high-speed uni-traveling carrier (UTC) photodiodes (PDs) for THz applications. The contributed papers cover a broad variety of key research areas and emerging technologies in optical detectors including graphene-based detectors, plasmonic structures for current enhancement, phototransistors, and UTC-type PDs on silicon-on-insulator waveguide as well as a UTC PD with type II hybrid absorber. Several papers describe advances in SPADs and CMOS SPAD arrays for UV and visible detection and four papers cover quantum well and quantum dot devices. This special issue also illustrates a wide range of optical detector technology applications including UV, visible, and IR imaging, fiber optic communications, microwave and THz analog applications, and quantum communications. Furthermore, this special issue covers a range of advances on theory and simulation, design and fabrication, and optical detector characterization methodologies.