Photonically-Enabled Low Phase Noise Multi-Octave RF Synthesizer

RF synthesizers using microwave photonics are typically limited in terms of tunability or noise. Highly tunable architectures can be constructed by heterodyning two lasers onto a photodetector, however drift between these lasers generates noise on the RF tone. Ultra-low phase noise optical combs have been generated using frequency division methods; however, they are banded and lack tunability. In this paper a photonically enabled RF synthesizer known as a Tunable Optical Paired Source (TOPS) is presented. A pair of lasers are heterodyned to generate an RF tone and noise is reduced by means of optical injection locking. The system achieves a continuously tunable output frequency ranging from 6 GHz to 110 GHz without the need for frequency extenders. When generating a 100 GHz RF tone the system demonstrates a phase noise of -106 dBc/Hz at a 100 kHz offset.