Spatial Vector Soliton In Photorefractive Materials And Localized Surface Waves

Spatial optical solitons are special propagation states when the beam diffraction isfully compensated by the nonlinear effect of the material. Because of their broadapplication prospects and profound theoretical significance, they have attracted theattention of many researchers around the world. Generation of spatial optical solitonsby photorefractive effect makes the application of optical solitons have greaterfeasibility. The advantages of photorefractive polymers such as cheapness and ease ofparameter tuning even broaden the application prospects of spatial optical solitons.This thesis will cover the following topics:1．Gray photorefractive polymeric optical spatial solitonsWe show that gray spatial optical solitons are possible in biased photorefractivepolymers under steady-state conditions. We fnd that for a given material parameterthe absolute value of a gray photorefractive polymeric soliton’s phase decreases withan increase in the beam’s grayness, whereas it increases with the material parameterfor a given beam’s grayness and that the full width half maximum (FWHM) of thegray soliton beam’s intensity increases with the beam’s grayness when the normalizedbackground intensity and the material parameter are fxed. On the other hand, we alsoshow that N coupled beam evolution equations in biased photorefractive polymers canexhibit multicomponent gray solitons. These multicomponent gray solitons can beobtained provided that the N coupled beams share the same polarization, wavelength,and are incoherent with one another. The characteristics and stability properties ofthese multicomponent gray solitons are also discussed in detail. 2． Defect modes in optically induced one-dimensional lattices inphotovoltaic-photorefractive crystalsThese defect modes exist in different bandgaps due to the change of defectintensity. For a positive defect, defect mode branches exist not only in thesemi-infnite bandgap, but also in the frst and second bandgaps. When the defectmode branch is fxed, the confnement of defect modes increases with the defectstrength parameter. For a negative defect, defect mode branches exist only in the frstand second bandgaps. On the other hand, when the defect strength parameter is fxed,the most localized defect modes arise in the semi-infnite bandgap for the positivedefect and in the frst bandgap for the negative defect.3． Localized surface waves at the interface between a linear dielectric and aphotovoltaic-photorefractive crystalWe study localized surface waves at the interface between a linear dielectric and aphotovoltaic-photorefractive (PP) crystal. These localized surface waves can beestablished provided that0b2, where is the guiding parameter, b is thepropagation constant, and is the parameter related to the wavelength and the PPcrystal. We show that when0, the part of the energy concentrated in the PP crystalis always higher than that in the linear dielectric and that when0, the part of theenergy concentrated in the linear dielectric decreases with an increase inb. We fndthat the part of the energy concentrated in the linear dielectric for0is bigger thanthat for0.4． Incoherently coupled soliton pairs in nonlocal nonlinear media We show that incoherently coupled soliton pairs can exist in nonlocal Kerr-typenonlinear media. Such solitons can propagate in bright–bright, dark–dark, and gray–gray confgurations. Our analysis indicates that for a self-focusing nonlinearity theintensity full width half maximum (FWHM) of the bright–bright pair componentsincreases with the degree of nonlocality of the nonlinear response, whereas for aself-defocusing nonlinearity the intensity FWHM of the dark–dark and gray–gray paircomponents decreases with the increase in the degree of nonlocality of the nonlinearresponse.