Optical spatial soliton supported by photoisomerization nonlinearity in a polymer with a background beam

f T f a m t o q t . INTRODUCTION n the past decade, spatial solitons (SSs) supported by hotorefractive effect have attracted much attention. he photorefractive effect is a saturable nonlinearity that an support oneor two-dimensional optical SSs at a very ow (microwatts) power level. Interesting discoveries, uch as self-trapping of incoherent white light, interacion of the SSs, self-trapping of incoherent light beams, otating SSs, multiple composite SSs, and discrete olitons have been reported in photorefractive crystals. n a polymer material, several nonlinear effects have een exploited to form SSs and waveguides. The photoreractive effect has been suggested by Shih and Sheu and heu and Shih to form a SS in a polymer, which has een realized by Chen et al. and Asaro et al. In 1995, onro et al. predicted that the photopolymerization proess can be exploited to form waveguides and SSs; Keitsch and Yariv realized this idea in 1996. Interacions of the SSs in this type of material have been iscussed by Shoji et al. and Dorkenoo et al. Recently, he three-dimensional waveguide in which the refractive ndex can be accurately controlled was formed in photoensitive materials by Dorkenoo et al. Upconverted dye hotobleaching is another nonlinear effect that can be exloited to form SSs. Nakanishi et al. and Sarkisov et l. have formed SSs with this type of nonlinearity and ave studied the interaction of the SSs. More recently, we ave shown that the photoisomerization nonlinearity an support SSs and that a circularly polarized 14.5 nm beam in a dye-doped poly(methyl methacrylate) PMMA) bulk polymer can form spontaneous SSs. Bian nd Kuzyk have formed SSs in the same material using linearly polarized beam of 647 nm wavelength. In our revious paper, we presented the formation of SSs with linearly polarized signal beam and an unpolarized back-