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Research On Theoretical And Experimental Properties Of Photorefractive Spatial Solitons Induced By Shifting Beam

Posted on:2014-02-25Degree:MasterType:Thesis
Country:ChinaCandidate:J QiuFull Text:PDF
GTID:2230330398961301Subject:Optics
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With low power, fast response and strong nonlinear effects, photorefractive spatial solitons are easily formed in experiments. We can achieve either the purpose of a light to control another which is called all-optical manipulation by taking advantage of interaction between solitons to, or the output of light beam at an arbitrary position by using solitons’own inherent characteristics. Its potential application in optical switches, optical waveguides and optical interconnection has been concerned about.Research on theoretical and experimental properties of photorefractive spatial solitons induced by shifting beam has been done in pure LiNbO3and Ce:SBN crystals.Without background illumination and external field, the incident beam is self-diffracted when propagating in photovoltaic photorefractive LiNbO3crystal. When the beam is shifting with the direction paralleled with c-axis, the space charge field is rebuild and can reverse at certain shifting speed. The optical nonlinearity will be changed and the beam will be swiched from self-defocusing to self-focusing. Bright spatial solitons are possible. At the edges of the illumination area along c axis, the spatial charge field is antiparallel to the one in the central illumination area. Within relaxation time, this edge of illumination area tends to decrease and be replaced by a new illumination area because of the beam shifting, the superposition of the two spatial charge fields tend to be inversed. In the steady state of inversed spatial charge fields, band transport model can be used and the propagation prosperities can be obtained.Steady-state bright screening solitons induced by beam shifting can be formed and bend in Ce:SBN crystals with applied external field. The outside transversely shifting velocity influences the free-carrier diffusion speed and spatial electric field creation time. A higher shifting velocity can effectively shorten the time of the saturable refractive index change. The light excites charges, which migrate in the presence of the external electric field as well as velocity field, and are captured (recombined) by deep (ionized donors or acceptors) traps. Just as in photorefractive screening solitons’ formation. the formed spatial electric field modifies the refractive index via the linear electro-optic (Pockel’s) effect and traps the beam. Moreover, the nonlinear relaxation effect excited by the shifting governs the saturable refractive index change, which results in the bending of the soliton. The bending amplitude of the soliton in propagation is studied and simulated in relation with the shifting velocity.
Keywords/Search Tags:shifting beam, photorefractive spatial solitons, photovoltaic brightspatial solitons, soliton bending
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