Photonic Synthesis of Continuously Tunable (5–170 GHz) Microwave Signals with Frequency Independent Phase Noise

We propose and demonstrate continuously tunable frequency synthesis over 5–170 GHz using phase locked narrow linewidth lasers. Phase locking over a wide frequency range is achieved by detecting the high-order harmonic components generated by modulating the continuous wave (CW) lasers. This harmonic based phase lock loop significantly reduces the phase noise within the locking bandwidth. Due to the low fundamental linewidth of the lasers, the high frequency (> 1kHz) components of synthesized RF signals exhibit a constant phase noise irrespective of the RF frequency. Such behaviour leads to a decreased jitter as the frequency increases, achieving a jitter of 27 fs at 170 GHz, outperforming commercially available electronic high-end frequency synthesizers. We demonstrate low phase noise RF signal generation from 5 GHz to 170 GHz with 1-MHz-step tunability using low-speed control electronics for cost-effective implementation.