Temporal behavior of spatial solitons in centrosymmetric photorefractive crystals

We investigate theoretically the time behavior of spatial solitons in biased centrosymmetric photorefractive crystals. A one-dimensional time-dependent wave propagation equation in biased centrosymmetric photorefractive crystals is presented. It is shown that the bright solitons exist in both quasi-steady-state and steady-state regimes for high saturation values. When the intensity ratio is smaller than unity, the bright soliton width decreases monotonically to a minimum value toward steady state. Moreover, the time-dependent nonlinear wave equation exhibits only steady-state screening dark spatial solitons.     

有偏压的光伏光折变晶体中的空间孤子

证明了有偏压的光伏光折变晶体中存在着明、暗稳态的空间孤子.它源于对外电场的非均匀空间屏蔽和光伏效应.与已报道的稳态光折变空间孤子相比,它具有不同的特性.当外电场为某一特定值时,用改变外电场的极性和旋转光的偏振方向可以实现明孤子与暗孤子的相互转换.当外电场足够强可以忽略光伏效应时,它类似于屏蔽孤子;当不存在外电场时,它类似于开路条件下的光伏孤子. 关键词：     

Self-deflection of steady-state bright spatial solitons in biased centrosymmetric photorefractive crystals

The effects of diffusion on self-deflection of steady-state bright spatial solitons in biased centrosymmetric photorefractive crystals are investigated systematically by both numerical and perturbation methods. The results show that the soliton propagates along a parabolic trajectory and the central spatial frequency component shifts linearly with the propagation distance. Both the deflection effects vary cubically with applied external bias field.     

中心对称双光子光折变低振幅灰孤子时间特性

为了得到中心对称双光子光折变晶体中低振幅灰空间孤子时间特性的结果,基于中心对称光折变晶体中双光子光折变效应的理论模型,推导出了含时间参量的空间电荷场和光波动态演化方程.采用数值方法,得到了低振幅灰孤子强度包络和强度半峰全宽的时间演化特性.结果表明:初始阶段形成宽度较宽的孤子,其宽度随时间单调递减到一个最小值直至稳态孤子的形成;在相同的演化时间内,孤子半峰全宽随着孤子峰值强度与暗辐射比值的增大而变小.研究了不同时间下低振幅灰孤子动态演化特性.     

加外电场的光伏光折变晶体中的空间孤子波

证明了在加外电场的光伏光折变晶体中存在着明、暗稳态空间孤子波.它源于对外电场的非均匀空间屏蔽和光伏效应.同已报道的稳态光折变空间孤子相比，它具有不同的特性和物理根源.当外电场足够强时，它类似于屏蔽孤子；当外电场为零时，它退化成闭路条件下的光伏孤子. 关键词：     

温度对中心对称光折变稳态暗孤子演化的影响

为了得到温度对中心对称光折变晶体中空间暗孤子影响的结果,数值研究了中心对称光折变暗孤子动态演化的温度特性。结果表明,孤子强度包络演化强烈地依赖于晶体的温度和介电常数的温度特性。在290-320K的温度变化范围内,暗孤子的宽度随温度的增加而变大,孤子的峰值强度随温度的增加而变小。在300K的温度下,中心对称光折变介质中可以形成稳定的暗空间孤子,当温度从300K升高或降低时,孤子将克服较小的扰动而保持稳定的传播。通过调整温度可以改变孤子的空间形态。     

低振幅中心对称光折变暗和灰空间孤子的时间特性

为了研究中心对称光折变晶体中低振幅暗和灰空间孤子的时间特性,推导出了含时间参量的空间电荷场和光波的动态演化方程.采用数值方法,得到了中心对称光折变晶体中低振幅空间暗和灰孤子强度包络和强度半峰全宽的时间演化特性.结果表明,初始阶段形成的宽度较宽的孤子,其宽度随时间单调递减到一个最小值直至稳态孤子的形成;在相同的演化时间内...     

Temporal behavior of low-amplitude dark spatial solitons in two-photon centrosymmetric photorefractive media

We investigate the temporal behavior of low-amplitude dark spatial solitons in biased centrosymmetric crystals with two-photon photorefractive effects. The expressions of time-dependent space-charge field and dynamical evolution equation are derived. The temporal behaviors of the intensity profiles and the intensity full width at half maximum (FWHM) of dark solitons are investigated by numerical method. The results indicate that a broad soliton is generated at the beginning, and as time evolves, the intensity width of solitons decrease monotonously to a minimum value toward steady state. Within the same propagation time, the higher the ratio of soliton peak intensity to the dark irradiation intensity is, the shorter the FWHM of dark solitons is.     

有偏压中心对称光折变晶体中的屏蔽孤子

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.     

Effects of the temperature on steady-state bright spatial solitons in biased centrosymmetric photorefractive crystals

We provide a theoretical investigation of effects of the temperature on the steady-state bright solitons in centrosymmetric photorefractive crystals. Three physical factors related to the effects of the temperature, i.e., the dielectric constant, diffusion process and dark irradiance, are considered. Our results show that both the intensity profile and self-deflection of solitons strongly depend on the crystal temperature and the dielectric constant temperature dependence dominates the process.     

双光子光折变晶体串联回路中独立全息屏蔽空间孤子对

为了得到双光子独立全息屏蔽空间孤子对的结果,基于光折变晶体中的两波耦合和双光子光折变效应,证明在由两块双光子光折变晶体和一个电压源通过导线连接组成的串联回路中存在全息亮(暗)屏蔽孤子。每块晶体中能支持一个全息屏蔽孤子,这两个孤子称为双光子独立全息屏蔽孤子对,有明-明、暗-暗和明-暗三种类型。数值计算结果表明,在光束的空间展宽远小于晶体宽度的极限条件下,孤子对中的两孤子通过光电流和相互耦合能影响到这些孤子的空间包络和动态演化特性。     

Separate spatial holographic and two-photon-Hamiltonian soliton pairs in an unbiased series photorefractive crystal circuit

This paper presents calculations for an idea in photorefractive spatial solitons, namely, a dissipative holographic soliton and a two-photon-Hamiltonian spatial soliton in one dimension form in an unbiased series photorefractive crystal circuit consisting of a single-photon photorefractive crystals and a two-photon one of which at least one must be photovoltaic. The two solitons are known collectively as a separate Holographic–Hamiltonian spatial soliton pair and there are two types: dark–dark and bright–dark if only one crystal of circuit is photovoltaic. The results show that the two-photon-Hamiltonian soliton in a soliton pair can affect the holographic one by light-induced current and the holographic soliton cannot affect the two-photon-Hamiltonian one.     

有偏压的光伏光折变晶体中的空间灰孤子

修正和完善了有偏压的光伏光折变晶体中空间孤子的非线性波动方程的理论.当光伏效应可忽略时,它转化为屏蔽孤子的非线性波动方程;当外电场为零时,它转化为闭路和开路光伏孤子的非线性波动方程.证明了有偏压的光伏光折变晶体中存在着空间灰孤子.它起源于对外电场的非均匀空间屏蔽和光伏效应.当光伏效应可忽略时,它转化为屏蔽灰孤子;当外电场为零闭路时,它预言了在光伏光折变晶体中存在着光伏灰孤子.     

One-dimensional modulational instability of broad optical beams in biased centrosymmetric photorefractive crystals

We study the one-dimensional modulational instability of broad optical beams in biased centrosymmetric photorefractive crystals under steady-state conditions. The one-dimensional modulational instability growth rates are obtained by globally and locally treating the space-charge field, which depend on the external bias field and the ratio of the intensity of optical beam to that of the dark irradiance. Our analysis indicates that the modulational instability growth rate in local effects can be determined from that in nonlocal effects.     

光折变有机聚合物中的空间孤子

给出了稳态情况下光折变聚合物中光波演化方程的亮、暗及灰孤子解,并讨论了不同孤子态的偏振特性及孤子宽度与外加电场的关系. 关键词： 光折变 聚合物 空间孤子     

Separate holographic screening soliton pairs in a biased series photorefractive crystal circuit

Holographic dark (bright) screening solitons are predicted in one dimension for a series circuit consisting of two photorefractive crystals connected electronically by electrode leads in a chain with a voltage source. Each crystal can support a holographic screening soliton. The two solitons are known collectively as a separate holographic screening soliton pair with three types: bright--bright, bright--dark and dark--dark. The numerical results show that the two solitons in a soliton pair can affect each other through a light-induced current and their coupling can affect their spatial profiles under the limit in which the optical wave has a spatial extent much less than the width of the crystal.     

非对称光折变全息空间光孤子的存在曲线

证明了在加外电场的光折变晶体中存在非对称全息空间光孤子对，其特征是孤子对中的两个 孤子具有相同的宽度、不同的振幅.给出了这种孤子对的存在曲线，其中存在三个具有不同 特征的区域：对于给定的外加电场来说，当孤子对中两个孤子的入射峰值强度之和与背景光 强度之比足够大或者足够小时，孤子宽度强烈依赖于这个比值，而在此中间的一段区域，孤 子宽度几乎不随这个比值而变化.非对称情况下这个中间区域的范围比对称情况的窄. 关键词： 空间光孤子 光折变非线性光学 全息光栅     

双光子光折变介质中非相干耦合亮-暗混合屏蔽孤子族

 根据光波耦合方程及亮-暗孤子对解,对稳态情况下多束互不相干的光束在有外加电场的双光子非光伏光折变晶体中的传播进行分析,给出产生亮-暗双光子光折变屏蔽光伏孤子族需满足的条件。证明有外加电场双光子非光伏光折变晶体中存在非相干耦合亮-暗混合屏蔽孤子族,孤子族由偏振态和波长都相同的多束互不相干的光形成。当外加电场方向和晶体光轴方向相同时,双光子光折变晶体可支持亮孤子族总峰值光强稍大于暗孤子族总峰值光强的的非相干耦合亮-暗混合孤子族,当外加电场方向与晶体光轴方向相反时,双光子光折变晶体可支持亮孤子族总峰值光强稍小于暗孤子族总峰值光强的非相干耦合亮-暗混合孤子族。     

Evolution and stability of spatial solitons in a photorefractive two-wave mixing system

The dynamical evolution and stability of bright dissipative holographic solitons in biased photorefractive materials in which the self-trapping beam obtains a gain from the pump beam via two-wave mixing has been investigated numerically. Results show that these solitons are stable relative to small perturbations. Adjusting some system parameters, such as the bias field and the angle between beams, can easily control the generation of such solitons. Potential applications in optical switches or repeaters are discussed.     

Manakov solitons in biased photorefractive crystals with both the linear and quadratic electro-optic effect

It is shown theoretically that the dark–dark, bright–bright and dark–bright Manakov soliton pairs can exist in biased photorefractive materials with both the linear and quadratic electro-optic effect under steady-state conditions. These soliton pairs can be generated provided that the total intensity of the two mutually inherent, with the same wavelength optical beams is much lower than the sum of the background intensity and the dark irradiance. It is also found that the intensity full width at half maximum of these Manakov solitons is inversely proportional to the square root of a quadratic polynomial of the external bias field. Moreover, the linear and quadratic electro-optic effects can be enhanced, decreased, even offset under appropriate conditions.