Frequency comb generation by four-wave mixing: the role of fiber dispersion

Summary form only given. Optical frequency comb generators (OFCGs) are important for a number of applications in optical communications. They enable difference-frequency measurements and frequency calibration over a several THz range as well as low-chirp short-pulse synthesis. A fiber-optic comb generator (F-OFCG) was recently demonstrated that utilizes four-wave mixing (FWM) in an optical fiber to expand a modulated CW lightwave into a frequency comb. The standard OFCG design encloses a sinusoidally driven electro-optic modulator (EOM) within an optical cavity resonant on the input laser frequency and all-modulation sidebands. The F-OFCG eliminates the demands of a high-finesse, resonant cavity. It requires no active controls to lock the cavity to the laser frequency and allows continuous tuning of the comb frequency spacing. As indicated by coupled-wave simulations, interference among FWM interactions is the principle mechanism governing F-OFCG sideband generation. By means of the varying phase mismatches, positive dispersion draws the different FWM interactions into phase. Their constructive addition yields strong resultant nonlinear polarizations, which drive comb expansion. Conversely, negative dispersion pulls FWM interactions out of phase such that the low resultant nonlinear polarizations deter comb expansion. Widest F-OFCG bandwidths are achieved using dispersion-mapped fiber links.