Free-Space Terahertz Spectrum Analysis with an Optoelectronic Hybrid System

We present an optoelectronic hybrid system to perform high-resolution spectrum analysis in the terahertz regime. The concept is based on phase-locking of the difference frequencies of at least three continuous-wave (CW) distributed-feedback diode lasers by mixing the laser light with the radiation from a high-power electronic narrow-band source. Unlike for state-of-the-art spectrum analysis, no additional frequency extenders are required, keeping the system less complex and more cost-effective. Following our concept, we can generate laser difference frequencies from 0 to more than 1 THz with several hertz precision, which can be easily expanded to even higher frequencies, e.g., by cascading more lasers within our synchronization scheme. We demonstrate the systems frequency resolution and stability by measuring the first five harmonics of an electronic W-band source, and the first three of an active multiplier chain millimeter-wave source, using a CW gallium arsenide (GaAs) photoconductive antenna as a receiver.