Optical frequency comb sources based on three-wave-mixing in quadratic nonlinear materials allow for reduced pump power threshold and extended spectral coverage. We review recent progress on quadratic optical frequency combs based on second-harmonic generation and optical parametric oscillation.
Funding Agencies|Ministero dellIstruzione, Universita e RicercaMinistry of Education, Universities and Research (MIUR) [2015KEZNYM-NEMO]; H2020 European Research Council (ERC)European Research Council (ERC) [757800]