Optoelectronic down-conversion by four-wave mixing in a highly nonlinear   fiber for millimeter-wave and THz phase-locking
  Optoelectronic down-conversion of a THz optical beatnote to a RF intermediate frequency is performed with a standard Mach-Zehnder modulator followed by a zero dispersion-slope fiber. The two interleaved optical spectra obtained by four-wave mixing are shown to contain more than 75 harmonics enabling to conveniently recover the phase noise of a beatnote at 770 GHz at around 500 MHz. This four-wave mixing down-conversion technique is implemented in a two-frequency solid-state laser in order to directly phase-lock its 168 GHz beatnote to a 10 MHz local oscillator. 
Antoine Rolland, Lucien Pouget, Marc Brunel and Mehdi Alouini
physics.optics