Phase noise mitigation of the microwave-to-photonic conversion process using feedback on the laser current

The generation and transfer of ultra-stable microwave signals are of paramount importance in numerous applications spanning from radar systems to communications and metrology. We demonstrate residual phase noise mitigation at 10 GHz of a directly modulated laser system through active control of the laser bias current. The latter is tuned to a finely selected point, where the current-to-phase dependence, measured at several microwave power and frequency values, is maximized. A residual phase noise of − 113 d B r a d 2 / H z at 1 Hz offset frequency from a 10 GHz carrier, with a fractional frequency stability of 1.2 × 10 − 16 at 1 s and below 10 − 19 at 10 5 s , is measured. These performances are compliant with the transfer of the most stable microwave signals available to date, obtained with cryogenic sapphire oscillators or combs locked to cavity-stabilized lasers. This approach is of interest for the distribution of ultra-stable microwave signals in a very simple photonic configuration.