Wide-band frequency modulation of a terahertz intrinsic Josephson junction emitter of a cuprate superconductor

Communication using terahertz (∼10 12 Hz) electromagnetic waves is critical for developing sixth-generation wireless network infrastructures. Conflictions between stable radiation and frequency modulation of terahertz sources impede the superposing of transmitting signals on carrier waves. The Josephson junctions included in a cuprate superconductor radiate terahertz waves with frequencies proportional to the bias voltages. Thus, the modulation of the bias voltage leads to the modulation of the Josephson plasma emission (JPE) frequency. This study aims to demonstrate the generation of frequency-modulated (FM) terahertz continuous waves from Josephson junctions. A FM bandwidth of up to 40 GHz was achieved when 3 GHz sinusoidal waves were superimposed on 840–890 GHz carrier waves radiated by a JPE. The results verify that the instantaneous JPE frequency follows the gigahertz-modulated bias voltage. The wide-band FM terahertz generation by a monolithic device shows a sharp contrast to the mode-lock frequency comb constructed using highly sophisticated optics on a bench. A further increase of the modulation amplitude facilitates up- or downconversion of frequencies over more than one octave. The obtained FM bandwidth exhibited an improvement of two orders of magnitude in the demodulation signal-to-noise ratio compared with the amplitude-modulated waves. The demonstrated FM JPE stimulates further research on terahertz communication technology and metrology using superconducting devices.