Two Beam Coupling in Semi-Insulating GaN Film Using Electroabsorption Effect

The photorefractive effect was observed in He-ion-implanted semi-insulating GaN film in the UV spectral region. The photorefractive grating is induced by the electroabsorption effect near the band-edge. Two beam coupling experiments were performed at a wavelength of 363.8 nm. The experimental results indicate that absorption grating mainly contributes to the beam coupling.     

光折变“波导”诱失锁模ps激光脉冲自泵浦相位共轭

观察到失锁模５３２ｎｍｐｓ激光脉冲单独入射到掺Ｃｕ的ＫＮＳＢＮ晶体中，不能产生自泵浦相位共轭，但如果先用同波长的锁模ｐｓ激光脉冲在晶体中预制一条光折变“波导”，则可诱导失锁模激光脉冲形成自泵浦相位共轭．分别从“波导”形成和时间分辨光谱等方面研究了这一现象 关键词：     

热自聚焦诱导光折变非对称自散焦

用波长为５３２ｎｍ的高斯光束入射到掺杂的ＫＮＳＢＮ晶体中，对足够大的光强，观察到由热自聚焦效应诱导产生的光折变非对称自散焦．非对称自散焦的空间分布与性质都有别于噪声受激放大．它对自泵浦相位共轭无甚贡献．对开始产生非对称自散焦时晶体中光束的直径作出估计 关键词：     

Higher diffraction order photorefractive optical beam splitter

A higher diffraction order photorefractive (PR) optical beam splitter has been realized based on a PR higher diffraction order grating. In the experiments, the beam splitter was produced by two-wave coupling at a small incident angle in Fe:LiNbO₃ using the output from a He–Ne laser at 632.8 nm. An incident signal beam containing three different wavelengths (632.8, 532.0 and 488.0 nm) was split into multi-output beams by the beam splitter. The size of higher diffraction order is given and the influence of crystal thickness is discussed. Results show that the higher diffraction order PR optical beam splitter provides a practical method to split a multi-wavelength signal beam.     

Self-trapping of light in an organic photorefractive glass

We report the first observation, to our knowledge, of self-trapping of light as well as optically induced focusing-to-defocusing switching in an organic photorefractive glass, owing to the orientationally enhanced photorefractive nonlinearity of the material.     

DMNPAA有机光折变材料的性能研究

通过双波耦合实验证明在一种新的有机聚合物光折变材料中双波耦合增益系数超过吸收系数。１０５μｍ厚的样品衍射效率可达到８６％，光栅形成的响应时间达到１００ｍｓ量级，双波耦合增益系数超过了２００ｃｍ＾－１（１），并引入了一种新的方法分析了其光折变机理。     

Powerful, diffraction-limited semiconductor laser using photorefractive beam coupling

We use semiconductor laser amplifiers and a photorefractive crystal to generate a high-power, diffraction-limited laser beam at 860 nm. Using a single flared amplifier, we obtain 1.09 W in a diffraction-limited beam from 2.2 W of pump power. Using an array of flared amplifiers, we also demonstrate efficient beam coupling, showing that this technique is easily extended to semiconductor amplifier arrays.     

Modification of Photorefractive Waveguides in Lithium Niobate by Guided Beam for Optical Dynamic Interconnection

We investigate experimentally and numerically a novel method of modifying photorefractive waveguides in a lithium niobate crystal by a guided beam. The guided beam with a strong optical power can change the refractive index of the photorefractive waveguide because of the photorefractive effect. The modification of waveguide structure can be utilized for optical dynamic interconnection. Changes of optical characteristics of a probe beam caused by a modification beam are investigated. Experimental results show that the transmitted power or the peak intensity of the probe beam decreases exponentially as a function of total exposure energy of the modification beam. We also numerically analyze the refractive index change caused by the modification beam in the photorefractive waveguide. The numerical results show good agreement with the experimental results.     

Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer

We report what is believed to be the first use of a photorefractive polymer in erasable-rewritable three-dimensional bit optical data storage under two-photon excitation. We successfully demonstrate writing, erasing, and rewriting of multilayered information in a photorefractive polymer consisting of 2,5-dimethyl-4-(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, 9-ethylcarbazole, and poly(N-vinylcarbazole). A three-dimensional bit density of 5 Gbits/cm(3) is achieved by two-photon absorption under pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. Complete erasing of the recording information is achieved by use of ultraviolet illumination.     

铟掺杂对Fe∶LiNbO3晶体近红外光折变性能的影响

采用在Fe∶LiNbO3中掺入了铟离子生长的双掺杂In∶Fe∶LiNbO3晶体,以波长为1064nm的近红外会聚光束作为记录光源,通过数字观测装置,对比研究了铟离子掺入前后Fe∶LiNbO3晶体和In∶Fe∶LiNbO3晶体的光折变性能。实验研究结果表明,铟离子掺入后晶体的光折变响应速度和抗光折变能力明显提高,饱和折射率变化量降低。初步分析认为,In∶Fe∶LiNbO3晶体光折变性能的增强是由于掺入的铟离子取代了部分光折变敏感中心,降低了光敏中心的数量,导致晶体光电导增大,响应时间随之缩短。     

有偏压光折变晶体中的高斯孤子

利用变分方法求解了小光强光折变非线性薛定谔方程，得到了高斯光束在外加正偏压光折变晶体中的演化特性，以及高斯光束宽度压缩与展宽的动态振荡规律，给出了高斯光束的宽度、振幅和波前曲率的表达式，研究了势函数与光束宽度的关系.结果表明，小光强高斯光束在正偏压光折变晶体中传播时，其宽度和振幅将经历周期地变化或者展宽发散，在一定条件下高斯光束在晶体中可以形状不变地传播，形成“高斯孤子”，这些特性在工程实践中具有很高的实用价值. 关键词： 高斯孤子 高斯光束 变分方法 光折变非线性方程     

铟掺杂对Fe:LiNbO3晶体近红外光折变性能的影响

采用在Fe:LiNbO3中掺入了铟离子生长的双掺杂InFe:LiNbO3晶体,以波长为1064 nm的近红外会聚光束作为记录光源,通过数字观测装置,对比研究了铟离子掺入前后Fe:LiNbO3晶体和InFe:LiNbO3晶体的光折变性能。实验研究结果表明,铟离子掺入后晶体的光折变响应速度和抗光折变能力明显提高,饱和折射率变化量降低。初步分析认为,InFe:LiNbO3晶体光折变性能的增强是由于掺入的铟离子取代了部分光折变敏感中心,降低了光敏中心的数量,导致晶体光电导增大,响应时间随之缩短。     

Pump-induced nonlinear refractive-index change in erbium- and ytterbium-doped fibers: theory and experiment

A 980-nm pump-induced nonlinear refractive-index (n2) change in erbium-doped (20-m) and ytterbium-doped (20-m) fibers has been measured at 1064 nm by time-delayed photorefractive beam coupling in a co-propagating and counterpropagating geometry. It was found that n2 decreases at the wavelength of the probe beam when the pump beam is present. We present a semiclassical theory based on a four-state system that accounts for the pump-induced change of n2. Both theoretical and experimental results show that a significant index change, of the order of 10%, can be obtained for cw pump powers as small as 10 mW.     

High-resolution, high-speed photorefractive incoherent-to-coherent optical converter

We demonstrate a photorefractive incoherent-to-coherent optical converter driven by ultraviolet light that provides a 35-mus response time and an optical resolution of 124 line pairs/mm. The device, implemented in KNbO(3) , operates with a modulating intensity of 85 mW/cm(2) , which corresponds to an optical switching energy per bit of 0.5 pJ. A conversion rate of the order of 90 Gbits/(s cm(2)) is achieved. The conversion between the ultraviolet light and the visible laser beam at lambda=532 nm occurs through anisotropic Bragg diffraction at a modulated interband photorefractive grating. Our device has a better optical resolution and conversion rate than optically addressed solid-state spatial light modulators based on the photorefractive effect and multiple quantum wells, and it is also faster than devices based on liquid crystals.     

Feedback method of the noise suppression in wave-mixing amplifiers based on non-linear materials with photorefractive response in a reflection grating configuration

In the photorefractive wave-mixing system, fluctuation in the signal beam intensity of the photorefractive output with a reflection grating has been analyzed by employing pump feedback method. In this method, fluctuations of the photorefractive wave-mixing process not only induce the intensity fluctuation of the mixing waves but also induce phase fluctuation of the mixing waves. Thus, the phase of the pump and signal beams at the output surface fluctuates in time around a mean value. Using such a positive feedback method of a pump beams, the relative fluctuation in the photorefractive output signal beam intensity with respect to its mean intensity can be minimized significantly without reducing its mean intensity. The factors that control the fluctuation in the signal beam intensity, such as the phase fluctuation of the output pump beam, absorption strength of the material and the feedback reflectivity of the cavity mirrors, on the relative fluctuation of the output signal intensity in the photorefractive wave-mixing systems have been studied in detail. It has been found that the fluctuation of the output signal intensity relative to its mean intensity in the photorefractive wave-mixing system can be suppressed to larger extent by taking lower value of feedback reflectivity of the cavity mirrors which could exist at a higher value of absorption strength of the photorefractive materials.     

Soliton-based Y-branch in photorefractive crystals induced through dispersion-shifted optical fiber

We experimentally demonstrate for what is believed to be the first time that a dispersion-shifted fiber can be used to electro-optically induce a soliton Y-branch structure in a photorefractive centrosymmetric paraelectric crystal (potassium lithium tantalate niobate). The application of a nonstationary external bias field enables us to stabilize the spatially partially coherent behavior of the optical beam at the fiber output. Furthermore, we show the switching capabilities of this soliton-based device in the optical communication field guiding a probe beam at a nonphotorefractive wavelength (1557 nm).     

SBN:Cr晶体的光折变四波混频相位共轭特性实验研究

从实验上研究了同成分SBN:Cr晶体在He-Ne激光照射下的四波混频相位共轭特性.首先测量了在不同泵浦光与信号光光强比m及不同光束夹角2θ的情况下,晶体的四波混频相位共轭反射率R随泵浦光强比p的变化关系.其次测量了泵浦光束与信号光束耦合方向对SBN:Cr晶体的四波混频相位共轭特性的影响,并就两种不同掺杂浓度的晶体样品进行了对比,所得实验结果与理论分析基本一致.最后,利用SBN:Cr晶体四波混频相位共轭特性进行了图象畸变消除实验.     

INVESTIGATION OF PHOTOREFRACTIVE TWO-WAVE COUPLING IN Cr-DOPED STRONTIUM BARIUM NIOBATE CRYSTAL

We present here the experimental results of photorefractive two-wave coupling in the congruent strontium barium niobate (SBN:61) crystal doped with 1000ppm Cr. Employing a He－Ne laser (632.8nm), we observed the coupling characteristics under different conditions. The crystal shows excellent photorefractive properties, with a high coupling coefficient nearly 6cm^-1 as the beam intensity ratio m is less than 100. The saturated coupling coefficient of SBN:61:Cr shows a maximum at a certain external beam crossing angle 2θ_peak, which varies with different m, showing a nearly linear dependence on m. The saturated coupling response time τ is measured to be less than 0.8 s. The response time decreased with increasing beam crossing angles no matter how large m is. We also observed the behaviour of the probe beam in reversed experimental procedures. We found that the probe beam shows a bistable state in both procedures.     

掺杂钾钠铌酸锶钡光折变晶体的各向异性衍射

本文给出了关于光折变晶体各向异性衍射的二波耦合方程,还给出了三种分别掺Cu,Ce,Co的钨青铜结构系列单晶(厚度为0.6—0.8cm)钾钠铌酸锶钡(KNSBN)在He-Ne激光(λ=6328?)照射下产生的光致光栅衍射实验结果。根据二波耦合理论,解释了这三种光析变晶体的衍射图样分布。根据波矢图的分析得出结论:对于不同性(正或负)单轴晶体,只能存在一种各向异性衍射的圆环图样(e→o衍射或o→e衍射)。理论分析与实验基本符合。 关键词：     

Photoelectric, nonlinear optical, and photorefractive properties of polymer composites including carbon nanotubes and cyanine dyes

The effect of cyanine dye additives on the photoelectric, nonlinear optical, and photorefractive properties of polyvinyl carbazole composites based on closed single-walled carbon nanotubes has been investigated. It has been found that these characteristics are affected by the dye in which the lowest unoccupied molecular orbital (LUMO) lies below the level of the photoexcited nanotube. The addition of this dye to the composite leads to a 14-fold increase in the quantum efficiency of the generation of mobile charge carriers under irradiation by a laser (1064 nm) in the absorption region of the nanotubes. Moreover, the addition of the dye to the composite decreases the third-order susceptibility χ⁽³⁾, presumably, due to the opposite orientations of dipoles of the dye and the nanotube upon adsorption of the dye on the nanotube. The addition of the dye to the composite also provides a twofold increase in the two-beam photorefractive amplification factor of the laser beam with a wavelength of 1064 nm. The obtained values of the two-beam photorefractive amplification factor reach 120 cm^?1.