Investigation On Evolutional Characteristic And Experimental Observation Of Spatial Light Solitons In A Photorefractive Dissipative System

Photorefractive spatial optical soliton means that it is a non-diffracting beam when itevolves forward inside the PR material maintaining its shape, amplitude unchanged. It may bewidely used in many fields, such as optical information technology, integrating optics, opticalsignal processing and optical communications. With the development of material technol-ogy, the photorefractive materials have been developed from nonlinear crystals to the easilyintegrated materials, such as semiconductor, thin film and liquid crystal, etc. The new photore-fractive materials offer a good foundation for future application. For dissipative holographicsoliton (DHS), a new type of spatial optical soliton, with different advantages from the PR soli-ton in Hamiltonian system, it has attracted more and more attentions of scientists. In theory,we have completely investigated the evolution (including de?ection) characteristic of the DHSin the thesis. In experiment, we have observed the bright DHS in photorefractive dissipativecrystal and carbazole photorefractive film.Based on the Kukhtarev-Vinestskii model, we have derived the forming mechanism ofspace-charge field and its in?uence on the refractive index of nonlinear materials. Also, therelevant theories of photorefractive spatial solitons have been presented. Generally, spatialsolitons are originated from the self-phase modulation self-focusing mechanism and the holo-graphic focusing mechanism that arises from the nonlinear phase coupling. Normally, we callthe spatial solitons arising from the holographic focusing mechanism as holographic solitons.Judged by whether the asymmetric energy exchange between two beams takes place or notduring the forming of the holographic solitons, the holographic solitons can be divided intoHamiltonian holographic solitons (HHS) and DHS. For the DHS model, one beam can actas pump beam to supply energy for the other beam, which behaves as the signal beam. Insmall-signal condition, the intensity of pump beam has been considered as constant,and itsevolution is ignored.The evolution and de?ection characteristics of the DHS have been investigated by numer-ical simulation method. A fully study is performed on the evolution and stability propertiesof DHS through discussing the role of every system parameter. The results indicate that theDHS can stably propagate along a straight line in the dissipative system with unchanged pro-file. When the diffusion effect is taken into account, the DHS beam will move almost ona parabolic trajectory, and the spatial shift of the DHS's center depends completely on theparameters of the dissipative system. The results from the further study by perturbation tech-nique are good agreement with the results obtained from numerical method. The dynamical evolution and de?ection of the DHS are strongly dependent on the system temperature, and itscentral de?ection distance increases with the temperature rising up. Numerical results showthat the input DHS beam can evolve into a stable soliton and propagate in the dissipative sys-tem when the temperature drift is quite small. The incidence DHS can experience a large cycleof expansion or compression when the temperature change isn't large enough. Whereas it willnot evolve into a stable state if the temperature departure is big enough. The dynamical evolu-tion and stability of the DHS in?uenced by the various system parameters are similar as thosein?uenced by temperature change. By increasing the applied electric field, photovoltaic elec-tric field, the angle of two beams, or decreasing the linear loss of the dissipative system, theangle between polarization directions of two beams, the incidence DHS is on the"over-gain"status, so its intensity increases and width narrows, which can be realized light amplification.Contrariwise, it is in reverse. The input DHS is on the"over-loss"status, thus its intensityweakens or is completely absorbed, which can be realized the optical switches. Furthermore,some changes of the system parameters can result in that the incidence DHS becomes a"di-verging"wave, it can be used for optical interconnection. In a word, the incidence DHS isstable against small perturbation. Its evolution (including de?ection) is affected by systemparameters and can be controlled by adjusting the parameters.Based on CCD technology and software processing, we have experimentally observedthe bright Hamiltonian photovoltaic soliton in KNSBN crystal. Also, it is confirmed thatthe intensity of the input light and the background illumination, can affect its evolution. InCu:KNSBN without a biasing field, the dissipative holographic photovoltaic soliton (DHPS)has been observed via the two-beam coupling, moreover, it is validated that the evolutionof the DHPS is in?uenced by the system parameters. Furthermore, we have found that thecarbazole photorefractive film can produce holographic focusing effects obviously via two-beam coupling in 632.8nm wavelength without a biasing field. At the same time, the DHPS isobserved in the organic PR film above, without applying an external field, and it is affected bythe system parameters.