Kerr frequency comb generation in the normal dispersion regime of dispersion oscillating telecom fiber

The generation of optical frequency combs has a variety of applications from optical metrology to spectroscopy and wavelength division multiplexing. Nonlinear methods to generate frequency combs are based on multiple four-wave mixing (FWM) in highly nonlinear waveguides [1]. The mechanism for the generation of a wideband comb from a CW pump is Kerr-induced phase-matching of the FWM interaction or modulation instability (MI), which requires operating in the anomalous dispersion regime. Such restriction can be circumvented with a cavity geometry, where MI [2] and comb generation [3] may also be observed in the normal dispersion region. Alternatively, one may obtain MI and unequally spaced Kerr frequency combs with average normal, periodically varying dispersion, so that the FWM process is quasi-phase-matched (QPM) [4]. QPM-FWM and supercontinuum generation were recently observed in a photonic crystal fiber [5] and in a highly nonlinear fiber (HNLF) at telecom wavelengths [6], respectively.