Study Of The Photorefractive Medium Surface Solitons

When beam propagating in photorefractive crystals, the self-bending phenomenon may exist due to the diffusion effect, when the deflection is balanced by the internal reflection on the surface of the medium, stable su rface wave can be generated over the surface of the photorefractive crystal. Photorefractive surface wave is a kind of self-induced surface wave mainly by means of the deflection or self-focusing of the induced beam, it can draw energy constraints in photorefractive crystal layer near the surface of the narrow space. The light energy is efficiently focused in photorefractive crystal surface, which has the characteristics of high energy density and can be transmitted along a straight line, so that a lot of surface nonlinear optical effect was significantly enhanced. In this paper, the theoretical analysis and numerical simulation has been carried on based on the diffusion mechanism of photorefractive surface vector solitons. Related content and conclusions are as follows:The research background and significance of photorefractive surface solitons were briefly introduced, also introduces the general situation of photorefractive surface wave, and the research progress of photorefractive surface wave is stated from the three aspects of theoretical study, experimental research and application.From the principle of photorefractive effect and the band transport model, deduce the space charge field in photorefractive medium. Simply introduced the common photorefractive material, and shows that the formation mechanism of photorefractive surface wave by the soliton self-bending dynamic process. The vector solitons are briefly discussed in the last.The basic theory of photorefractive surface solitons is studied. The normalized evolution equation which meeting the photorefractive surface dark soliton is deduced, and gives the analytical solution of steady state under the condition of dark soliton. The simulation analysis and research the influence of the applied electric field and light intensity to the surface dark soliton propagation properties. Results show that the surface dark soliton can keep no deformation in the transmission process, meanwhile, the full width at half maximum of the soliton is severely changed along with the change of light intensity while the light intensity is quite small. Applied electric field will affect the attenuation speed of soliton at the interface, and the light power impact the energy of soliton.Photorefractive surface nonlinear vector solitons is studied. The normalized evolution equation satisfies the photorefractive surface nonlinear vector soliton is obtained through the slowly varying envelope approximation and paraxial approximation of the vector soliton. The bright soliton and dark soliton solutions is achieved without any loss of generality, and theoretically analysed the influence to the transmission characteristics of bright soliton and dark soliton through the difference of light intensity and applied electric field, respectively. Results showed that the bright soliton and dark soliton can maintain original and stable transmission. The difference of light intensity and applied electric field impact the soliton energy and attenuation speed, respectively, and with the increase of light intensity and applied electric field, soliton decay rate increases.Numerical simulation shows the intensity distribution of photorefractive surface vector solitons at focal plane in tight focusing system. Discussed the influence of the numerical aperture, the applied electric field, and light intensity difference to the intensity distribution of photorefractive surface vector solitons at focal plane in tight focusing system. Results show that the focused mode can be modulated along with the applied electric field, light intensity difference and numerical aperture of the tight focusing system. Numerical analysis results show that after the tight focusing, focused mode will be broadening. At the same time, the results also showed that the focused mode on the focal plane will depend on the numerical space aperture.