Ultra-Low Phase Noise Frequency Synthesis for THz Communications Using Optoelectronic PLLs

Recently it has been demonstrated that an optoelectronic phase-locked loop (OEPLL) using a mode-locked laser as a reference oscillator achieves significantly lower phase noise than conventional electronic frequency synthesizers. In this paper a concept for an OEPLL-based frequency synthesizer is presented and it is investigated how it can be used as a local oscillator (LO) for THz transceivers in order to improve the signal quality in THz wireless communications. The concept of the OEPLL is presented and it's measured phase noise is compared to the phase noise of a laboratory-grade electronic frequency synthesizer. The measured phase noise spectra of both synthesizers at 10 GHz are then used to model LO phase noise at 320 GHz. Based on models of generic zero-IF transmit and receive frontends, THz signals with different modulation formats and Baud rates are simulated at system level using the modeled LO phase noise for the two LO approaches. Finally, the results are compared.