Selectable microwave-frequency doubling and quadrupling via optical path-length tuning

A technique to selectively double or quadruple the frequency of a microwave signal is experimentally demonstrated based on a commercial single-output Mach-Zehnder modulator (MZM). Selectability is achieved by only a change in optical path length in a post-MZM optical subsystem, without filtering and without changing the MZM drive voltage. This path length controls the synchronisation of two similarly shaped optical signals that are incoherently combined. Multiplication from 2 GHz (S-band) to 4 GHz (C-band, doubling) and to 8 GHz (X-band, quadrupling) is demonstrated with side-tone suppression greater than 24 dB. At a 10-kHz offset from the quadrupled frequency, the phase-noise degradation is only 7.9 dB, a 4.1-dB improvement over traditional quadrupling techniques.