Polarization modulation instability in a Manakov fiber system

The Manakov model is the simplest multicomponent model of nonlinear wave theory: It describes elementary
stable soliton propagation and multisoliton solutions, and it applies to nonlinear optics, hydrodynamics, and
Bose-Einstein condensates. It is also of fundamental interest as an asymptotic model in the context of the
widely used wavelength-division-multiplexed optical fiber transmission systems. However, although its physical
relevance was confirmed by the experimental observation of Manakov (vector) solitons in a planar waveguide in
1996, there have in fact been no quantitative experiments confirming its validity for nonlinear dynamics other than
soliton formation. Here, we report experiments in optical fiber that provide evidence of passband and baseband
polarization modulation instabilities in a defocusing Manakov system. In the spontaneous regime, we also reveal
a unique saturation effect as the pump power increases. We anticipate that such observations may impact the
application of this minimal model to describe and understand more complicated phenomena in nature, such as
the formation of extreme waves in multicomponent systems.