Recent progress of continuous-wave terahertz systems for spectroscopy, non-destructive testing, and telecommunication

Within the last decade, photoconductive terahertz (THz) systems have become well-established tools in scientific laboratories and industrial R&D departments. In particular, the exploitation of telecommunication technology around 1.5 mm wavelength enabled this development. Continuous wave (cw) THz systems benefit especially from telecom technology since the required optical components are already available. As no femtosecond fiber-laser is needed, photonic integration may lead to extremely compact cw THz devices. We present a fully fiber-coupled cw THz system in combination with optimized InGaAs-based emitter and detector antennas and an optical phase modulator. This system can be employed as both, a highly precise spectroscopic tool and a high-speed measurement system for non-destructive testing. In addition, we present recent results on heterodyne cw THz spectroscopy. This is a prerequisite for future broadband, wireless telecommunication systems using THz carrier frequencies. The fiber-coupled heterodyne receiver is able to detect THz signals up to 1 THz with an intermediate frequency of 2.2 GHz. These are the highest values reported for photoconductive heterodyne receivers so far.