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1.
This paper predicts that gray spatial solitons can exist in biased two-photon photovoltaic photorefractive crystals. Under appropriate conditions and in the steady state, the gray spatial solitons solution of the optical evolution equation is obtained. The properties associated with these solitons, such as their intensity profile, intensity full width at half-maximum, width, transverse velocity and phase distribution, are discussed as functions of their normalized intensity and degree of “grayness”. Relevant examples are provided. 相似文献
2.
The coupling of two mutually incoherent optical beams with the same polarization and wavelength in two-photon photorefractive media is studied; it is shown that incoherently coupled grey-grey spatial soliton pairs are possible due to two-photon photorefractive effect under appropriate bias conditions. The relevant example is presented. The grey-grey spatial soliton pairs reduce to dark-dark spatial soliton pairs when the greyness is zero. 相似文献
3.
Self-Deflection of Dark Screening Spatial Solitons Based on Higher-Order Space Charge Field
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The effects of higher-order space charge field on the self-deflection of dark screening spatial solitons in biased photorefractive crystals are numerically investigated under steady-state conditions. The expression for an induced space-charge electric field including higher-order space-charge field terms is obtained. Numerical results indicate that dark solitons possess a self-deflection process during propagation, and the solitons always bend in the direction of the c axis of the crystal. The self-deflection of dark solitons can experience considerable increase especially in the regime of high bias field strengths. 相似文献
4.
The propagation of multiple mutually incoherent spatial solitons in biased photovoltaic–photorefractive crystals is investigated
under steady-state conditions. It is shown that incoherently coupled bright–dark hybrid screening–photovoltaic soliton families
can be established in the crystals provided that the mutually incoherent incident beams have the same polarization and the
same wavelength. Relevant examples are presented where the photovoltaic–photorefractive crystal is taken to be lithium niobate.
Received: 15 May 2000 / Revised version: 27 July 2000 / Published online: 5 October 2000 相似文献
5.
The modulational instability of broad optical beams in two-photon photorefractive (PR) photovoltaic materials under open circuit conditions has been investigated. Under linear stability framework, the one dimensional modulational instability growth rate has been estimated by considering the space charge field. Gain of the instability is shown to exist only when the photovoltaic fields orients in the same direction with respect to the optical c-axis of the medium. It is found that the behavior of the gain spectrum is different in low and high power regions. We have found by numerical simulations that the evolution of the soliton induced by the modulational instability at low photovoltaic field show the dynamical behaviors similar to those of the localized beam as the initial profile. However, it has been shown that increasing photovoltaic fields produce traveling, breathing, and mutually interacting solitons. 相似文献
6.
We report on the formation of spatial optical solitons in photorefractive media using picosecond laser pulses. Solitons are
generated with laser pulses in the visible and infrared wavelength region using photorefractive strontium barium niobate.
The dynamics of the soliton formation and the region of existence is studied in detail. 相似文献
7.
Efficient frequency-doubling is experimentally demonstrated in presence of beam self-trapping in congruent lithium niobate crystal. The self-trapping is induced by the generated second harmonic beam via photorefractive effect under an external applied field. The local space charge field distribution, formed by the second harmonic beam, is shown to efficiently trap both wavelengths. The dynamics of self-focusing is studied along with the power evolution of the second harmonic beam. Fast tuning of phase matching conditions in the written waveguide is realized by an externally applied voltage also used for the photorefractive confinement. 相似文献
8.
The coupling of two mutually incoherent optical beams with the same polarization and wavelength in two-photon photovoltaic photorefractive crystal is studied, it is predicted theoretically that incoherently coupled bright-dark photovoltaic spatial soliton pairs are possible due to two-photon photorefractive effect. The existing conditions of these soliton pairs in the crystal are discussed in detail. The intensity profile of these soliton pairs is shown by numerical calculation under the parameters of relevant crystal. 相似文献
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We show that the time-dependent nonlinear wave equation in closed-circuit photovoltaic media can exhibit quasi-steady-state and steady-state spatial solitons. We demonstrate that the formation time of open-circuit quasi-steady-state and open-circuit steady-state dark solitons decreases with an increase in the intensity ratio of the soliton, which is the ratio between the soliton peak intensity and the dark irradiance. We find that for the time-dependent nonlinear wave equation that exhibits only an open-circuit steady-state dark soliton, changing the electric current density J0 does not generate quasi-steady-state dark solitons and affects the formation time of steady-state dark solitons and that for the time-dependent nonlinear wave equation that exhibits an open-circuit quasi-steady-state dark soliton, changing J0 gives rise to three different time evolution regimes of the full width half maximum of the soliton’s intensity. The first regime shows that the formation time of steady-state dark solitons increases with J0 whereas the formation time of quasi-steady-state dark solitons is independent of J0. The second regime shows that the formation time of steady-state dark solitons decreases with an increases in J0 and the formation time of quasi-steady-state dark solitons increases with J0. The third regime shows that changing J0 enables only steady-state dark solitons in the time-dependent nonlinear wave equation, of which the formation time increases with J0. 相似文献
12.
Keqing Lu Wei Zhao Meizhi Zhang Lei Zhang Yongzhuang Chen Jingjun Xu 《Optics Communications》2008,281(1):49-54
We carry out a theoretical investigation of the properties of waveguides induced by photorefractive one-dimensional steady-state gray spatial solitons (i.e., screening solitons, photovoltaic solitons, and screening-photovoltaic solitons). We demonstrate that waveguides induced by photorefractive steady-state gray spatial solitons are only a single guided mode for both all soliton graynesses and all values of ρ, where ρ is the ratio between the soliton peak intensity and the dark irradiance, and moreover, waveguides induced by gray photovoltaic solitons for closed-circuit condition are also only a single guided mode for all electric current densities. We find that the confined energy near the center of a photorefractive steady-state gray spatial soliton increases with ρ and decreases with an increase in the soliton grayness. We also find that the confined energy near the center of a gray photovoltaic soliton for closed-circuit condition increases with the electric current density. On the other hand, waveguides induced by gray screening-photovoltaic solitons are gray screening soliton-induced waveguides when the bulk photovoltaic effect is neglectable and are gray photovoltaic soliton-induced waveguides when the external bias field is absent. 相似文献
13.
有偏压中心对称光折变晶体中的屏蔽孤子 总被引:7,自引:6,他引:1
给出了中心对称光折变晶体中屏蔽孤子的高阶空间电荷场.当高阶项可以忽略时,这个电荷场就变为早前在中心对称光折变晶体中研究的屏蔽孤子的空间电荷场.研究了中心对称光折变晶体中屏蔽孤子的高阶非线性波动方程.在适当的条件下,这个非线性波动方程能够展示明暗空间光孤子.这类晶体不同于非中心对称晶体,其非线性折射率的改变来源于二次电光效应,而不是一般的线性电光效应.应用光束传播的方法,对这些孤子的稳定性进行了讨论.表明在小的微扰下这类孤子是稳定的,不会发生分裂. 相似文献
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By considering the effect of background light and diffusion, the self-deflection process of partially spatially incoherent (PSIC) beams and photovoltaic (PV) solitons in open-circuit PV photorefractive crystals has been investigated by employing numerical method and the perturbation technique, respectively. The results from the two approaches are in good agreement: the center of PSIC PV solitons moves on a parabolic trajectory, which is similar to those of coherent solitons. In addition, we also discuss that the dependence of self-deflection effect on the coherent parameter θ0 and find it is slight relative to θ0 for quasi-soliton but decreases monotonously with θ0 for PSIC beam. 相似文献
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We investigate the backscattering for converging beams in iron-doped lithium niobate crystals. Due to the nonlinear properties of the crystal, backscattering exhibits temporally fluctuating speckles that make a transition to the phase conjugate of the incident beam under certain circumstances. Our observation seems to point to a new kind of self-pumped phase conjugation in photorefractive media. 相似文献
18.
Solitary Wave Evolution of Optical Planar Vortices in Self-Defocusing Photorefractive Media
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Solitary wave evolution of optical planar vortices in isotropie self-defoeusing photorefractive media is investigated in detail. We demonstrate that the formation of a planar vortex soliton intensively depends on the diameter and maximum intensity of the input vortex Seam. The exact solutions of planar vortex solitons are obtained due to the Petviashvili iteration method. It is found that, with the increasing soliton maximum intensity, the soliton core will be gradually diminished to a minimum value. 相似文献
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Analytical and numerical investigation of the propagation of optical beams in Kerr-like saturable photorefractive media is carried out, utilizing a novel model for the local isotropic part of the space-charge field generated in the medium. Using a variational technique, optimal propagation parameters for the most stable propagation of otherwise unstable single Gaussian, single vortex, and optical soliton cluster beams are determined. Analogy between a ring of identical weakly overlapping solitons and a vortex of the same topological charge is explored. 相似文献