光折变效应中二波耦合温度特性的研究

本文研究了光折变效应中,温度对晶体内空间电荷分布影响的微观机制,提出了空间电荷场的修正项,给出了钛酸钡晶体的空间电荷场与温度的理论曲线以及二波耦合中光强耦合系数与温度的理论曲线.     

LiNbO3:Fe晶体中光写入阵列平面光波导的实验实现

采用两束相干平行光形成的干涉光场辐照LiNbO₃: Fe晶体,通过光折变效应在晶体中写入了阵列平面光波导.分别采用马赫-曾德干涉仪光路和光栅衍射法测量了阵列平面光波导的横向折射率分布和周期,并对所写入的阵列平面光波导进行了初步的导光测试.实验结果表明,用这种方法写入阵列平面光波导简便可行.     

Geometric integration of the paraxial equation

Evolution of solitary waves in photovoltaic-photorefractive crystal satisfy the paraxial equation. The paraxial equation is transformed into the symplectic structure of the infinite dimensional Hamiltonian system. The symplectic structure of the paraxial equation is discretizated by the symplectic method. The corresponding symplectic scheme preserves conservation of discrete energy which reflects conservation of energy of the paraxial equation. The symplectic scheme is applied to simulate the solitary wave behaviors of the paraxial equation. Evolution of the solitary waves with the different applied electric field and the different photovoltaic fields are investigated.     

有分压电阻和e偏振非相干背景光辐照的光折变晶体中非相干耦合空间孤子对

为了得到光折变晶体中非相干耦合空间孤子对统一理论的结果,基于单光子光折变空间光孤子的基本理论模型,建立了稳态条件下有分压电阻和e偏振非相干均匀背景光辐照的单光子光伏光折变晶体中非相干耦合空间孤子对理论.研究表明:这种孤子对是由两束偏振方向和波长都相同的互不相干光束耦合形成的,孤子对两光束都能在晶体中稳定传播;当分压电阻、e偏振背景光、外加电场和光伏场取不同值时,可获得14种光折变非相干耦合空间孤子对.本文的结果对完善和充实光折变空间孤子理论体系有重要意义.     

基于光折变效应提升啁啾脉冲信噪比的光谱扫描滤波法

基于光谱扫描滤波原理,提出了一种利用光折变效应来提高啁啾脉冲信噪比的扫描滤波方法,并进行了理论分析。针对内置光折变晶体的Fabry-Perot (F-P)标准具光谱扫描滤波装置,定量分析了其透射谱特性,详细讨论了Fabry-Perot(F-P)标准具两平板的反射率、透射谱窗口带宽、外加场的控制参数以及信号光啁啾率变化等对啁啾脉冲信噪比的提升及其滤波透射率的影响。结果表明,F-P两平板的反射率越高,则透射谱越尖锐,透射窗口越窄,滤波效果也就越好。为了得到有效的信噪比提升,一般要求其反射率大于0.99;外加场的控制和信号光啁啾率的变化对扫描滤波的影响较大,在实际工作中,应尽量保证外加场和啁啾率的精确控制,以确保信号光和滤波函数的同步匹配。针对中心波长800 nm的啁啾信号脉冲,采用提出的光谱扫描滤波方法,对放大自发辐射(ASE)的随机噪声与预脉冲进行滤波,可得到近3个量级的信噪比提升效果。     

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.     

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.     

含分压电阻的光折变屏蔽光伏空间灰孤子(英文)

为了研究外加偏压光伏光折变晶体中的空间灰孤子,建立了含分压电阻的光折变屏蔽光伏空间灰孤子的演化方程,给出了灰孤子解.采用数值模拟的方法,求解灰孤子的数值表达式,得到了不同参量取值下的灰孤子包络.数值结果表明:当分压电阻、晶体的外加电场和光伏场取不同值时,可以分别得到有无分压电阻的屏蔽灰孤子;开路的光伏灰孤子,有、无分压电阻的闭路光伏灰孤子;有、无分压电阻的屏蔽光伏灰孤子.     

闭路光伏灰孤子诱导的波导

理论分析了闭路光伏晶体中灰孤子诱导的波导.研究发现,闭路光伏灰孤子诱导的波导在不同孤子灰度值,电流密度和光强比率下均为单模,文中光强比率指孤子峰值强度与暗辐射之比.研究结果解释了闭路光伏灰孤子限制在中心的能量随着电流密度的增加而增加,随着孤子灰度值和光强比率的增加而减小.文章还提供了光伏晶体的相关例子.     

非晶态As2S8半导体薄膜的光致结构变化效应研究

实验研究了非晶态As2S8半导体薄膜在光照、退火-光照和退火-光照-退火-光照关连作用下的光折变效应及淀积态与退火态两种膜系光致体积变化现象.采用棱镜耦合技术、Raman光谱和X线衍射测试技术,确认了As2S8薄膜经紫外光辐照后薄膜密度增高、折射率增大的现象.实验表明,淀积态As2S8薄膜经紫外光照后,折射率变化的最大增量可达到0.06,而退火态As2S8薄膜经紫外光照射后,其折射率最大变化比前者要小一个数量级,约为0.005 7.淀积态和退火态两种膜系紫外光照后,体积缩小,这与As2S3非晶态薄膜的情况不同,体积变化率分别为－3.5%和－2.1%.实验还显示,退火态的As2S8薄膜存在折射率完全可逆现象.