碲酸盐系统玻璃的研究进展

在非线性光学玻璃材料中,碲酸盐系统玻璃材料凭借较高的三阶非线性光学极化率、超快光学响应、较宽的红外透过窗口、较好的化学稳定性和较低的熔化温度而备受关注,以铌碲酸盐系统为基础的新型碲酸盐系统重金属氧化物玻璃则表现出更为优秀的综合品质,极有希望成为制作新型光学器件的理想材料。     

光开关玻璃的飞秒光学开关特性

通过在碲玻璃中添加重金属离子,尝试制作了具有较大的非线性折射率、时间响应快、吸收小的光开关玻璃。采用超快飞秒光克尔门技术对光开关玻璃的光克尔信号进行测试,测试结果显示,光开关玻璃的光克尔信号对称性好,信号半高宽度达到~225 fs,三阶非线性极化率达到~0.810-20 m2/V2,透过率达到70%~80%;研制的光开关玻璃为皮秒和飞秒光开光材料的选取提供了依据。     

Performance and limits of nonlinear optical waveguide couplers onthe basis of CdS1-xSex-doped glasses

In this work methodical and experimental investigations have been carried out in order to realize optical nonlinear waveguide couplers. On the basis of our experiences in the field of ion exchange in glass as substrate material semiconductor doped glasses have been used. Doped with CdS_1-xSe_x these glasses seem to have sufficiently high nonlinear coefficients. Ion exchange has been carried out by substitution of K- by Cs- ions and for waveguide patterning aluminium has been used as mask material. The produced stripe and bent waveguide couplers show qualitatively the expected optical nonlinear behavior in agreement with results obtained by solving the coupling equations. Possibilities in order to optimize this structures with respect to the nonlinear performance are discussed briefly     

Two-photon absorption effects on self-phase-modulation-based 2R optical regeneration

We theoretically investigate the influence of two-photon absorption (TPA) on the performance of self-phase-modulation-based signal regenerators using a split-step Fourier method. Simulations with 40-Gb/s return-to-zero data bit streams show that a device with TPA can improve the signal (higher output Q-factor) significantly more than a device with no TPA, and that the figure of merit of chalcogenide is close to optimal. This contrasts with the effects of TPA on nonlinear switching, which are always detrimental.     

基于硫系玻璃的中波红外光学系统无热化设计

硫系玻璃作为优良的消色差和消热差红外材料,是红外光学系统中关键光学元件的理想候选材料,文中利用硫系玻璃实现中波红外光学系统无热化设计。首先分析了温度变化对红外光学系统的影响;其次分析了常用硫系玻璃的各方面特性,并总结了硫系玻璃的优点;最后利用硫系玻璃,镜筒材料选择最常用的铝合金材料,设计了一个工作于中波红外的二次成像全球面无热化成像系统。设计结果表明:在0～100 ℃温度范围内,光学系统的成像质量优异,具有良好的无热化能力。使用硫系玻璃可实现低成本高性能中波红外光学系统。     

06微米激光束在玻璃中的自感生偏振变化效应

我们用一个TEM00模的钕玻璃激光系统,观察到一些光学玻璃和激光钕玻璃中的激光束的自感生偏振变化现象,实验测量了它们的非线性极化率参量C1221,并确定了其非线性折射系数n20.     

High quality tellurium dioxide for acousto-optic and non-linear applications

Paratellurite, TeO₂, was first grown by the Czochralski method by Arlt and Schweppe (1) and has been shown to have an appreciable figure of merit for acousto-optic applications (2). We have studied improved methods for growing high quality TeO₂ and have investigated its usefulness as a nonlinear optic material. Our studies show that the quality of tellurium dioxide single crystals as well as their physical properties and ease of growth are dependent on the purity of the starting material. Careful preparation of crystals by the Czochralski technique (5) from melts of six nines pure material has produced paratellurite with acoustooptic properties superior to those previously reported (2). The acoustic loss of such material when measured at 100 megacycles is reduced by approximately an order of magnitude. The useful acousto-optic figure of merit, M₃, (7) was found to be ~3.4 times better than PbMoO₄, previously the best material for device applications below 1 Ghz. Thus, high quality TeO₂ is now of interest for Q-switch and deflector applications. We have also found TeO₂ to have a nonlinear coefficient ~2 times that of quartz and to be phase matchable at 1.06μ as well as 1.3μ The fact that this effect is in direct violation of Kleinman's symmetry conditions, which dictate a coefficient of zero for the reported structure, will be discussed along with a detailed procedure for the growth of high quality crystals.     

Dispersion in nonlinear figure of merit of As/sub 2/Se/sub 3/ chalcogenide fibre

Wavelength-dependent measurements of the nonlinear figure of merit (FOM) in a highly nonlinear As/sub 2/Se/sub 3/ chalcogenide fibre, from 1415 to 1554 nm, are presented. It is found that the FOM decreases monotonically towards shorter wavelengths, as the material half-bandgap is approached. The FOM > 1 for wavelengths above 1450 nm suggests applications for nonlinear optics in the C-band.     

有机材料在光限制中的应用

对光限制器件的特性进行了简单的评述,并对由自散焦过程产生光限制的机理进行了分析.采用z-扫描方法对有机材料分散红一的非线性折射过程和光限制特性进行了实验研究.对其结果进行了分析讨论,这种分析对于以自作用效应产生最佳光限制效应是十分有用的.     

掺半导体玻璃的简并四波混频

用简并四波混频研究了CdS_xSe_(1-x)半导体玻璃的三阶非线性光学特性。实验结果表明这种材料具有大的三阶非线性系数(x~(3)～10~(-8)esu)和快速非线性响应时间(<1ns)。     

有机材料在光限制中的应用

对光限制器件的特性进行了简单的评述,并对由自散焦过程产生光限制的机理进行了分析.采用z-扫描方法对有机材料分散红一的非线性折射过程和光限制特性进行了实验研究.对其结果进行了分析讨论,这种分析对于以自作用效应产生最佳光限制效应是十分有用的.     

Nonlinear optical interfaces: Switching behavior

We report the results of a study of the switching behavior of the interface between an ordinary dielectric and a nonlinear dielectric material with an intensity-dependent index of refraction. The non-linear dielectric used for these experiments consisted of a liquid suspension of dielectric particles. Because this medium has a very large effective nonlinearity, it was possible to perform these experiments with the CW output of an argon ion laser. Our experimental results are in excellent agreement with the predictions of numerical calculations based on a two-dimensional Gaussian input beam. We also report the observation of an unstable reflectivity state with a lifetimesim 10^{3}times the response time of the nonlinear medium.     

Temperature-dependent Sellmeier coefficients and chromaticdispersions for some optical fiber glasses

Temperature-dependent Sellmeier coefficients are necessary to optimize optical design parameters of the optical fiber transmission system. These coefficients are calculated for fused silica (SiO₂ ), aluminosilicate, and Vycor glasses for the first time to find the temperature dependence of chromatic dispersion at any wavelength from UV to 1.7 μm. The zero dispersion wavelength λ₀ (1.273 μm for SiO₂, 1.393 μm for aluminosilicate, and 1.265 μm for Vycor glasses at 26°C) varies linearly with temperature, and dλ₀/dT is 0.03 nm/K for aluminosilicate and Vycor glasses, whereas for SiO₂ it is 0.025 nm/K. This study interprets the recently observed experimental value of dλ₀/dT for two dispersion shifted optical fibers; and the dominantly material origin of dλ₀/dT is confirmed here as a fundamental property of the optical fiber glasses     

Power-speed product of an optical flip-flop memory with opticalfeedback

Evaluation of optical logic gate devices in terms of a power-speed (switching time) product is discussed. An example is given for a simply fabricated optoelectronic flip-flop circuit utilizing an optical feedback. The minimum power-speed products for set and reset operations are 5 and 35 pJ, respectively. They are very small compared with previously reported optical nonlinear or bistable devices. The figure of merit is decreased by monolithic integration, by which an optical computation can be realized     

Rayleigh scattering reduction method for silica-based optical fiber

The effect of the thermal treatment of silica-based glasses and glass fibers on their Rayleigh scattering is investigated experimentally. The Rayleigh scattering coefficients of bulk glasses are found to be increased 5-10% by heating them to 1800 °C because the density fluctuation is in proportion to their fictive temperature. Based on these results, we propose a method for reducing the Rayleigh scattering losses of silica-based optical fibers by drawing them slowly at low temperatures. We used this method to obtain a GeO₂ doped silica core single-mode fiber with a minimum loss of 0.16 dB/km at 1.55 μm. As a result, we confirmed that the reduction in the fictive temperature of silica-based glasses and glass fibers reduces their Rayleigh scattering     

Improvement of optical nonlinear response in GaAs/AlGaAs nipi-MOW structure with Au ohmic contact

Experiments demonstrate that the optical nonlinear response in a GaAs/AlGaAs nipi-MQW structure can be improved by introducing ohmic contacts, which electrically connect n- and p-layers. The response time is reduced by more than two orders of magnitude because of the enhanced recombination rate of photoexcited carriers, whereas the figure of merit for absorptive nonlinearity sigma /sub eh/ is kept constant and is an order of magnitude larger than that in a conventional GaAs/AlGaAs MQW structure.<>     

Control of spectral characteristics of dispersive optical fibers byannealing

Novel optical fibers fabricated from optical glasses with different dispersive characteristics are annealed under various conditions. Spectral properties of such dispersive fibers are greatly changed by annealing. It is shown that one of core and cladding index spectra can be shifted largely by annealing in case of fiber glasses with different transformation temperatures. We can therefore control properties of annealed dispersive fibers by adjusting the heat treatment     

Nonsilica glasses for holey fibers

The authors of this paper investigated the thermal properties and optical properties of typical nonsilica glasses, including viscosity, surface tension, thermal conductivity, transmission, linear and nonlinear refractive index, and fiber attenuation in order to judge the feasibility of using nonsilica glasses as the background material of holey fibers (HFs). Novel techniques were presented to fabricate the nonsilica glass microstructured fiber preforms. Examples of fabricated nonsilica glass HFs with various promising optical applications were finally exhibited.     

Dense optical flow via robust data fusion

Locally optimised differential methods for computing optical flow have the merit of being faster and more reliable under noise when compared to their globally optimised counterparts. However, they produce sparse flow estimates as a result of being unable to deal with local image regions of little texture. They are also particularly inefficient for regions whose change of feature-constancy function is highly nonlinear. In this study, we treat several limitations of the local approach in monochrome images. We present a robust H_∞ data fusion-based framework to propagate flow information from high confidence regions to those suspected of poor quality estimates. The adopted data fusion engine is tolerant towards uncertainty and error inherited in the optical flow computation process. A new integrated confidence measure is also presented to predict the accuracy of the recovered flow across the image enabling the data fusion engine to work as an intelligent filling-in effect, not only when the intensity is problematic but also for other uncertain regions. Results demonstrate the significance of the proposed method.     

Optical bistability and all-optical switching in novel waveguidejunctions with localized optical nonlinearity

We propose novel all-optical guided-wave devices using the structure with localized third-order optical nonlinearity where only a selected part of a waveguide both in a cross section and along a propagation direction is made from a Kerr-like nonlinear material and the rest are made from linear ones. Optical bistable devices and all-optical switching devices are realizable by utilizing bistable like nonlinear dispersion characteristics in selectively nonlinear guided-wave systems. Optical bistability and all-optical switching characteristics are analyzed in waveguide Y-junctions adopted the scheme by using a modified BPM combined with the normal mode analysis. The method to realize the guided-wave structure with localized nonlinearity is also discussed