No abstract

The effects of fourth-order dispersion (FOD) on modulation instabilities in the twin-core optical fibers with the asymmetric CW state are studied systematically. When the product of the group velocity dispersion and FOD is negative, in the anomalous dispersion regime, two new MI bands in the high frequency are generated with one band either having the equivalent gain with that of original band or dominating the MI depending on the FOD value; in the normal dispersion, a new dominant MI band in the high frequency is always generated, and the original MI bands vanish in the presence of FOD at total power above a critical value. When the product of the group velocity dispersion and FOD is positive, the main effect of FOD is to shift the MI band to the low frequency and reduce the bandwidth simultaneously with minor effects on the instability gain. We also find that the effects of linear coupling coefficient dispersion can be significantly suppressed in the presence of FOD especially for the case of negative product of the group velocity dispersion and FOD. Finally, the effects of FOD on MI are verified numerically by launching continuous waves with the wave propagation method. Our results should provide very benificial information for successfully observing MI in TCFs or MI related applications with TCFs.