Experimental observation of polarization modulational instability in isotropic fibers

Summary form only given. Modulational instability refers to a parametric four-wave-mixing process in which dispersive waves are phase matched through the compensation of dispersion by the nonlinearity. Owing to the self-focusing Kerr nonlinearity of silica, this purely nonlinear phase-matching process is only possible in the anomalous dispersion regime. However, since the pioneering work of Berkhoer and Zakharov (1970) it is well-known that, when taking into account the additional degree of freedom offered by the polarization of light, purely nonlinear phase matching can be achieved in normally dispersive self-focusing Kerr media. As a result, modulational instability can occur in fibers in the normal dispersion regime. Due to the role of polarization, this instability has been called polarization modulational instability (PMI). We have demonstrated for the first time PMI in isotropic Kerr media. The remarkable and unexpected result is that effective isotropy is achieved over 50 meters of fiber without particular care. This shows that spun fibers can be used for observing the large range of phenomena that have been predicted for isotropic Kerr media such as polarization domain walls or rotating vector solitons. These observations could lead to the development of new applications in the field of all-optical signal processing in fibers.