Modulation instability in nonlinear complex parity-time (PT) symmetric periodic structures

摘要

We carry out a modulation instability (MI) analysis in nonlinear complexparity-time (PT) symmetric periodic structures. All the three regimes definedby the PT-symmetry breaking point or threshold, namely, below threshold, atthreshold and above threshold are discussed. It is found that MI exists evenbeyond the PT-symmetry threshold indicating the possible existence of solitonsor solitary waves, in conformity with some recent reports. We find that MI doesnot exist at the PT-symmetry breaking point in the case of normal dispersionbelow a certain nonlinear threshold. However, in the case of anomalousdispersion regime, MI does exist even at the PT-symmetry breaking point.