Continuously Tunable Ultra-Broadband Low-Phase Noise Photonic Terahertz Oscillator

In this paper, we present the lowest phase noise of a continuously tunable terahertz oscillator reported so far. The terahertz wave is generated using the concept known as photomixing. Two slightly detuned diode lasers are superimposed in a fiber-combiner to create an optical beat signal that oscillates at the desired terahertz frequency. An ultrafast PIN photodiode converts the optical beat signal into a terahertz wave that is radiated into free space. To achieve extremely low phase noise, the two diode lasers are locked to a single frequency-comb based on a mode-locked femtosecond laser. The carrier-envelope-offset frequency and the repetition rate of the frequency-comb are compensated and well stabilized, respectively. We measure the phase noise at 500 GHz using a dedicated electronic cross-correlation detection scheme. The results are compared to a state-of-the-art commercially available electronic signal generator.