Temporal behavior of dark spatial solitons in closed-circuit photovoltaic media

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.     

低振幅双光子屏蔽光伏孤子的时间特性

为了得到低振幅双光子屏蔽光伏孤子时间特性的结果,采用数值模拟的方法对低振幅双光子屏蔽光伏孤子的时间特性进行了理论分析,得到了明和暗孤子时间特性的演化方程。结果表明:孤子的宽度随时间的演化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,孤子的半峰全宽随着孤子峰值强度和暗辐射比值的增大而变窄。     

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.     

Temporal Behavior of Low-Amplitude Grey Spatial Solitons in Biased Two-Photon Photorefractive Crystals

The temporal property of grey screening spatial solitons due to two-photon photorefractive effect in low-amplitude regime is analyzed. The results indicate that a broad solitons is generated at the beginning, and as time evolves, the intensity width of grey solitons decreases monotonically to a minimum value toward steady state. In the same propagation time, the FWHM of solitons decreases with ρ increasing or m decreasing. Moreover, the formation time of solitons is independent of ρ and m. The time isclose to a constant determined by the dielectric relaxation time.     

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.     

Temporal development of open-circuit bright photovoltaic solitons

This paper investigates the temporal behaviour of open-circuit bright photovoltaic spatial solitons by using numerical techniques. It shows that when the intensity ratio of the soliton, the ratio between the soliton peak intensity and the dark irradiance, is small, the quasi-steady-state soliton width decreases monotonically with the increase of τ-, where τ- is the parameter correlated with the time, that when the intensity ratio of the soliton is big, the quasi-steady-state soliton width decreases with the increase of τ- and then increases with τ, and that the formation time of the steady-state solitons is not correlated with the intensity ratio of the soliton. It finds that the local nonlinear effect increases with the photovoltaic field, which behaves as that the width of soliton beams is small and the self-focusing quasi-period is short. On the other hand, we also discuss that both the time and the temperature have an effect on the beam bending.     

对数型非线性介质中一维空间暗、灰孤子的存在性分析

对在对数型非线性介质中空间灰孤子的存在性进行了研究，认为对数型非线性介质中可以同 时支持暗和灰空间孤子态.并对暗空间孤子的宽度变化作了分析，指出当峰值功率较低时， 束宽随功率的增大而急剧减小，表现出良好的非线性效应；当峰值功率逐渐增大时，束宽的 减小趋势逐渐放慢直至趋于停止. 关键词： 空间暗孤子 空间灰孤子 对数型非线性介质     

Temporal analysis of low-amplitude screening spatial solitons due to two-photon photorefractive effect

This paper investigates the temporal behavior of two-photon screening spatial solitons using a numerical technique. An expression for the time-dependent dynamical evolution is obtained. The results show that the width of bright solitons decreases monotonically to a minimum toward steady state value when the intensity ratio of the solitons is small, which is in low-amplitude regime. Within the same propagation time, the intensity width of solitons decreases with increase in soliton intensity ratio and with increase in external electric field. The formation time of solitons is independent of the intensity ratio of the solitons or the external electric field and is close to a constant determined by the dielectric relaxation time. The temporal properties of dark solitons are similar to those of the bright solitons.     

开路光伏空间孤子的动态行为

从理论上研究了开路情况下一维光伏空间孤子的时间演化过程.采用数值方法,通过研究有无背景光辐照下光伏空间亮(暗)孤子的含时空间电荷场,分别得到了光伏空间亮(暗)孤子的孤子波形强度微分方程.在此基础上研究了开路情况下通过增加均匀背景光辐照强度对光伏空间孤子及其半峰全宽的影响.结果显示,通过增加均匀背景光辐照强度,光伏空间孤子随时间的演化过程比没有均匀背景光时加快的倍数为均匀背景光强与暗辐照光强之比.光伏空间孤子的半峰全宽达到稳态所需的时间随孤子峰值强度和暗辐照与均匀背景光强度之和的比值的增大而变短.     

开环系统中灰光伏孤子的时间及演化特性分析

分析了开环系统中一维灰光伏孤子的时间特性.基于与时间相关的演化方程,用数值方法得到了准稳态和稳态的灰孤子解,分析了形成准稳态灰孤子的物理机制.结果显示准稳态灰孤子的宽度是与光强无关的,并且它们的形成时间和孤子的峰值与背景辐射强度比成反比.这些性质与开环系统中的亮、暗孤子的性质很相似.同时采用波传播的数值解法,分析了它们的传播特性,结果显示它们在小于10％的扰动下是相对稳定的.     

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。     

Gray photorefractive polymeric optical spatial solitons

We show that gray spatial optical solitons are possible in biased photorefractive polymers under steady-state conditions. We find that for a given material parameter the absolute value of a gray photorefractive polymeric soliton's phase decreases with an increase in the beam's grayness, whereas it increases with the material parameter for a given beam's grayness and that the full width half maximum (FWHM) of the gray soliton beam's intensity increases with the beam's grayness when the normalized background intensity and the material parameter are fixed and decreases with an increase in the normalized background intensity when the material parameter is fixed. On the other hand, we also show that N coupled beam evolution equations in biased photorefractive polymers can exhibit multicomponent gray solitons. These multicomponent gray solitons can be obtained provided that the N coupled beams share the same polarization, wavelength, and are incoherent with one another. The characteristics and stability properties of these multicomponent gray solitons are also discussed in detail.     

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.     

开路低振幅空间光伏孤子的时间分析

理论分析了一维光折变空间孤子在低振幅开路条件下的传输特性和强度宽度的演化特性.研究表明,开始阶段所形成的强度宽度较宽的孤子, 其宽度随着时间演化单调递减到一个最小值,直到稳态形成;对于不同的孤子峰值强度与暗辐射比值,整个过程所需要的时间接近于无照明场时介质的介电驰豫时间.在时间趋于无穷的情况下,系统趋于稳定,得到了暗孤子和亮孤子的解析解.     

非局域自散焦克尔介质中空间光暗孤子成丝的理论与实验研究

对非局域自散焦克尔介质中的空间光暗孤子成丝进行了研究. 理论上从非局域非线性理论模型出发, 数值模拟研究了非局域程度和吸收系数对暗孤子成丝的影响. 当入射背景光强一定时, 非局域程度越大成丝起始点越远、成丝数量越少; 而当入射背景光强与临界光强之比一定时, 非局域程度基本不影响成丝起始点以及成丝数量, 且非局域下的成丝数量与局域下一样. 此外, 当入射背景光强一定时, 吸收系数越大成丝数量越少. 实验上通过改变染料溶液的浓度以及背景光斑的椭圆率, 分别研究了样品浓度和背景光斑椭圆率对暗孤子成丝的影响. 当入射背景平均光强一定时, 样品浓度越小成丝数量越少, 背景光斑椭圆率越小成丝数量越少; 而当入射背景平均光强与临界光强之比一定时, 样品浓度基本不影响成丝数量. 在实验中还观察到了光学冲击波现象.     

Waveguides Induced by Screening-Photovoltaic Solitons in Biased Photorefractive-Photovoltaic Crystals

We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.     

Optical spatial solitons supported by photoisomerization nonlinearity in a polymer

We present a theory for a new type of optical spatial soliton that is based on the angle hole burning mechanism of photoisomerization in some polymers. We predict that the photoisomerization nonlinearity can support steady-state dark and bright spatial solitons in the polymer. We also discuss the dependence of the FWHM of the spatial soliton on wavelengths of the background beams and on the ratio of the intensity of the background beam to that of the signal beam.     

一维光伏空间灰孤子及其稳定性研究

从考虑背景光的光伏作用后的光束在光伏媒质中传播的方程出发,证明了在折射率改变为正的光伏媒质中也可以形成灰孤子。光束以灰孤子状态在光伏晶体中传播时,其横向相位必须具有一个与光强分布有关的形式分布,表达式为φ（s）=v[η-∫y^-2（η）dη],其中v是灰孤子的横向运动速度,η是无量纲化坐标,y（η）是归一化的光场振幅。分别讨论了光束灰度、光强振幅、信号光与背景光的有效Glass系数之比R对一维的光伏空间灰孤子宽度、横向总相移和横向运动速度的影响,并分析了光伏灰孤子的稳定性。当光束的灰度m为0时,这一理论可直接退化为光伏暗孤子的理论。     

One-dimensional steady-state bright photovoltaic solitons in LiNbO3:Fe crystal with background illumination

We investigate theoretically and experimentally one-dimensional bright photovoltaic solitons in LiNbO₃:Fe crystal by use of the background illumination. We find that, in LiNbO₃:Fe crystal, bright photovoltaic solitons can be obtained with background illumination for κ>1, where κ is the ratio of the background illumination photovoltaic constant to the soliton optical beam's photovoltaic constant. For κ<1, dark photovoltaic solitons are generated. On the other hand, our experiments show good agreement with theoretical prediction for the soliton existence curve in a special intensity ratio.     

Grey screening-photovoltaic soliton-induced waveguides

This paper shows that waveguides induced by grey screening-photovoltaic solitons are always single mode for all intensity ratios, which are the ratio between the peak intensity of the soliton and the dark irradiance. It finds that the confined energy near the centre of the grey soliton and the propagation constant of the guided mode increase monotonically with increasing intensity ratio. On the other hand, when the soliton greyness increases, the confined energy near the centre of the grey soliton and the propagation constant of the guided mode reduce monotonically. When the bulk photovoltaic effect is neglected for short circuits, these waveguides become waveguides induced by grey screening solitons. When the external bias field is absent, these waveguides become waveguides induced by grey photovoltaic solitons.[第一段]