Modulation instabilities in twin-core fibers with self-steepening effects

Abstract Effects of self-steepening (SS) on modulation instabilities (MIs) are systematically studied in twin-core optical fibers with the asymmetric continuous wave (CW) state. In anomalous dispersion, there is one MI band. SS can reduce the instability gain significantly, shrink the MI band dramatically, and moves the instability band to low frequency. MI never vanishes for any incident total powers above a required minimum total power, being contrary to the case in single core fibers that MI disappears at total powers above a threshold value in relation to SS. In normal dispersion, there are two MI bands. With SS, the high frequency band vanishes for incident total powers above a threshold value, and the low frequency band enhances with gain increasing and moves to the lower frequency. We also discover that SS can significantly suppress (enhances) the high frequency band that appears due to coupling coefficient dispersion and fourth-order dispersion (Raman scattering).