Evolutionary Dynamics Of Asymmetric PT Solitons And Rotating Vortex Solitons

Spatial optical soliton is a kind of self-trapping beam relying on diffraction and nonlinear effect equilibrium,which has potential application value in optical communication,optical capture and other fields.In recent years,soliton dynamics in complex externally-modulated nonlinear systems with Parity-time(PT)symmetry have received extensive attention.So far,all solitons found in PT systems have even symmetric real parts and odd symmetric imaginary parts.In the past decade,many researchers have devoted themselves to the study of vortex beams.Compared with the conventional spherical wave and plane wave,vortex beams have unique structural characteristics of central phase singularity,spiral phase plane and ring intensity,and have good applications in medical diagnosis,optical imaging,particle manipulation and other fields.In recent years,the researches on the dynamics of solitons in rotating systems mainly focus on radially symmetric vortex solitons or vortex solitons limited to external potential.Asymmetric vortex solitons containing one or more eccentric phase singularities are rarely studied.In particular,fully stable beams carrying average fractional angular momentum per photon have not been reported.When an asymmetric vortex soliton propagates in a uniform nonlinear medium,it may exhibit many interesting properties.The research content of this paper is as follows:1.Solitons in non-uniform self-defocusing PT systemThe soliton characteristics of non-uniform self-defocused PT system under local and periodic gain-loss modulation are studied.The morphology distribution and stability of the soliton are analyzed theoretically.There exists a class of bright soliton in both systems.Compared with the traditional PT symmetric soliton,the real and imaginary parts of this kind of soliton do not satisfy the oddeven symmetry,but its amplitude still has the symmetry in the traditional sense.In addition,this kind of soliton has unbroken parity-time symmetry and the merging property of soliton branch pairs.In a periodic gain-loss system,the effect of spatial frequency on solitons is investigated.By increasing the spatial frequency,it is found that the merging of soliton branch pairs depends on the frequency of gain-loss.2.Fractional angular momentum based on rotating vortex solitonsThe propagation dynamics of vortex solitons with fractional angular momentum in competitive cubic-quintic nonlinear media with transverse rotation modulation of refractive index are investigated.The existence,stability,propagation dynamics and the effect of rotation frequency on the propagation characteristics of vortex solitons with one or two eccentric phase singularities are discussed.It is found that the Coriolis force caused by rotation moves the vortex core from the origin to the periphery.In this process,for the vortex soliton with a phase singularity,the angular momentum carried by each photon varies from 1h to 0.For vortex solitons containing two opposite topological exponents,a counterclockwise rotation results in a change in angular momentum per photon from 0 to-1h,and vice versa.Especially for the vortex solitons containing two topological indices of the same sign,when the rotation frequency exceeds the critical value,the vortex solitons with symmetric eccentric nuclei and the vortex solitons with asymmetric eccentric nuclei have two branches co-existing.Linear stability analysis and direct propagation simulation show that the rotational nonlinear state with fractional angular momentum is completely stable under high power.