A Photonic Spectrum Analyzer for Waveguide-Coupled Sources in the Terahertz Range

Signals in the terahertz range are mainly wireless, waveguide-bound or on-chip signals. To measure their spectral power, linewidth and harmonics, usually spectrum analyzers are used. Here we present a photonic spectrum analyzer for waveguide-bound signals for the frequency range from 450 GHz to 1.05 THz with the possibility to extend its operation to on-chip signals. Therefore, a photonically generated local oscillator frequency is used to downconvert the signal under test within a photoconductor. A Vivaldi antenna feeds the signal from a dielectric waveguide to the photoconductor. This allows the measurement of any signal that can be transported via a dielectric waveguide. We show details on the transition from a rectangular metallic hollow waveguide to a dielectric waveguide and spectral measurements of a rectangular metallic hollow waveguide source. The same transition can also be used to attach metallic waveguide-coupled ground-source-ground probes in order to characterize on-chip sources.