Phase noise of an electro-optic terahertz comb.

Photonic millimeter wave and terahertz frequency generation and detection benefit from a large tunability of several octaves as opposed to electronic frequency generation and multiplication. However, reaching multiple 100 GHz continuous tuning range while simultaneously featuring a 3-dB linewidth in the Hz range and low phase noise is still very challenging. We present an electro-optical comb driving a photomixer with potential usability as an extension module based on side-band generation by an electro-optical phase modulator. This enables a Hz-level 3-dB linewidth from microwaves to terahertz frequencies. We discuss the working principle of the mentioned electro-optical comb, characterize the phase noise of the optical subsystem up to frequencies of 40 GHz where electronic phase noise analyzers are available and draw conclusions on the phase noise at higher frequencies in the THz domain.