Synthesis of a 30-Hz Linewidth Wave Tunable Over 500 GHz

We report on a compact source of 30-Hz linewidth, low-phase noise electrical waves with 500-GHz tunability. These waves are generated by photomixing two distributed feedback laser diodes at 1550 nm, which are frequency stabilized on a fibered cavity. We demonstrate a phase noise suppression down to -90 dBc/Hz at 100-kHz carrier offset frequency of the beat note at 2-, 10-, 18-, 40-, and 92-GHz frequencies. The setup also displays a ~170-kHz frequency drift of the beat note at 10 GHz in the long term over a continuous 7.5-h locking period.