Continuous-wave terahertz photonics

Terahertz (100 GHz–10 THz) photonics combines semiconductor technology and optical concepts to powerful, high-performance systems. It became an established technique and is now at a competitive level as compared to previously dominating electronic and purely optical approaches. This Perspective provides an overview of the state of the art and latest developments in sources, detectors, and systems for terahertz key applications. Photonic spectroscopic systems achieve Hz-level linewidth, tunability, and frequency coverage over more than 6 THz in a single system and a dynamic range beyond 90 dB/Hz at 1 THz. This article points out mixed photonic–electronic wireless communication systems with data rates beyond 1 TBit/s and first industrially deployed purely photonic systems in non-destructive testing and carves out integration perspectives using photonic integrated circuits as well as promising future directions, including domains that were covered solely by electronic systems in the past, such as radar, spectrum analysis, and vector network analysis.