Study On The Propagation And Control Of The Beam In The Photorefractive Crystals

In the recently 10 years, the researches of the photorefractive spatial solitons have attracted more and more attention of researchers for their wide potential application in many fields such as optical communication, optical interconnection, design of optical storage devices and optical computation. When studying the deflection government of the spatial solitons, this dissertation puts forward a concept of travellingwave-like and mainly investigates their propagating properties and control in the photorefractive crystal.Based on systemically studying the fundamental theories of photorefractive spatial solitons, a simplified nonlinear equation of the biased photovoltaic photorefractive crystal is deduced. It is convenient to study the beam propagation in photorefractive media.The algorithms of Crank-Nicholson-like finite difference and improved split Fourier transform are developed. By using these numerical methods, the propagating properties of the separate variable spatial solitons are investigated.Travellingwave-like spatial soliton is advanced and the form condition is represented. It has unique format of the bright soliton and whose amplitude and phase are the function of a complex variable. The results show that the soliton departs from initial incidence direction when propagating in photorefractive crystal. The angle and direction of deflection depend on the transverse phase modulation coefficient. The properties can control beam deflection.For the coherent interaction of travellingwave-like, the magnitude of interaction force is relative to the relative intensity and the distance of solitons and the electric field biased in the photorefractive crystal. The higher the intensity of solitons, the smaller the distance between two solitons, and the stronger the biased electric field, the bigger the interaction force between two solitons. The quality of the force is relative to the initial phase difference. Interaction of the in-phase solitons appears to attract each other, and interaction of theπout of phase solitons appears to repel each other. When their distance is smaller they would experience only a few times collision and then depart from each other and obviously transfer some energy. The interaction of the multiple solitons may be use in optical computation. For incoherent interaction of the travellingwave-like, the interaction force takes on attraction. Its magnitude depends on their distance and the electric field biased in the photorefractive crystal. When the distance is smaller the interaction solitons would cross and wrap.The evolution of the Gaussian beam in the photorefractive crystal is researched. The amplitude and width of Gaussian beam varies exponentially or vibrates periodically. But the product of the amplitude square by width remains unchanged. Under the certain condition, the Gaussian soliton can be formed in the photorefractive crystal. The approximate matching condition of Gaussian beam with bright soliton is represented. The evolution of the Gaussian beam in the photorefractive crystal biased space-modulation electric field is also researched. The step field can substitute for linear one. When the Gaussian beam propagates in the photorefractive crystal, the beam width would be modulated by biased field. This property can be use for reshaping the beam. The interactions of Gaussian beam pair in the photorefractive crystal biased space-modulation electric field put up attraction in in-phase or repellence in out-phase. Because the modulation field affect on the propagating properties, one can control beam deflection by adjusting the field and control the distance of parallel propagation of two beam. These are importance in the soliton lattice and waveguide array formed by coherent beam.In the end of the dissertation, the partial incoherent spatial dark soliton is investigated experimentally. The waveguide induced by dark soliton can guide the coherent and partial spatial incoherent beam. A directional energy coupler formed by two partially spatially incoherent photovoltaic dark spatial solitons is realized. The coupling efficiency can be changed by adjusting the distance of two dark solitons.