非零位凸非球面子孔径拼接检测技术研究

为了实现大口径凸非球面镜的高精度检测,本文研究了凸非球面非零位子孔径拼接检测技术,并建立了一套非零位拼接检测算法模型,模型中分别针对同轴子孔径与离轴子孔径非零位检测时所引入的测试误差进行了建模分析,同时对测试误差剔除、拼接系数求解、全口径面形获得等问题进行了研究。最后,结合工程实例,对一口径为130 mm的凸双曲面进行了拼接检测,分析了该非球面各测试子孔径非零位检测误差形式,同时进行了误差剔除、全口径面形获取等工作。从拼接结果中可以看出,拼接结果光滑、连续、无拼接痕迹。为了进一步验证拼接精度,我们将拼接结果与子孔径检测结果进行对比,引入了自检验子孔径评价方法,计算得到自检验子孔径与拼接结果在自检验子孔径范围内的残差图,二者残差图的PV值与RMS值分别为0.016λ与0.003λ,由上述结果可以得到自检验子孔径的测试结果与拼接结果在自检验子孔径范围内是一致的,从而验证了本文算法的拼接精度。     

子孔径布局对拼接光学系统像质的影响

 由衍射理论模型出发,分析了子孔径布局对光学系统点扩散函数的影响,从而进行傅里叶变换计算出其对光学系统光学传递函数的影响|并由光学设计软件内嵌程序将子孔径布局实际地加入到设计的光学系统中,分析各种不同子孔径布局对光学系统像质的影响.通过由衍射理论出发的计算结果与设计软件内嵌程序的模拟仿真结果的对比,软件内嵌程序的模拟仿真结果得以验证.针对子孔径布局对具有相同相对孔径光学系统的影响进行了仿真计算,对与子孔径拼接原理样机具有相同相对孔径和中心遮拦比的反射式光学系统,针对相同孔径布局对其光学传递函数的影响进行了实际测试,通过仿真计算结果与测试结果的对比分析表明,孔径布局对具有相同相对孔径拼接光学系统的光学传递函数影响趋势一致的结论,从而为子孔径拼接原理样机研究的实用性及像质检测提供了理论依据.     

提取标记点中心在子孔径拼接检测中的应用

子孔径拼接干涉仪中子孔径定位精度难以在大行程范围内得到保证,为此本文提出了基于提取标记点中心定位子孔径的拼接方法。以标记点的中心坐标为标记点坐标,根据标记点在两子孔径局部坐标系下的坐标计算两子孔径之间的坐标变换,将所有子孔径数据坐标变换到统一坐标系下,利用机械误差补偿算法拼接出全口径面形。在搭建的拼接检测系统上实现了外径468 mm的平面镜抛光过程和最终的全口径面形测量,加工过程中的测量结果为面形误差修正提供了准确的数据,保证了最终全口径面形误差RMS快速收敛到35 nm。实验证明,基于提取标记点中心的子孔径拼接检测能放宽对机械定位精度的要求,有效检测大口径光学元件面形。     

大口径光学非球面元件拼接优化及精度验证

针对磨削阶段大口径光学非球面元件拼接测量精度不高的问题,提出一种基于两段拼接的优化算法。首先根据多体系统运动学理论、斜率差值及逆推法建立两段面形轮廓的拼接数学模型;其次针对拼接算法中工件运动量和运动误差对拼接精度的影响,仿真分析了350mm非球面工件的两段拼接。仿真结果表明,随着平移误差增大,拼接误差明显增大,而当控制旋转角度在8°以内、平移量在10mm以内、旋转误差在60′以下及平移误差在3μm以下时,拼接误差的标准偏差值在0.2μm波动;最后利用Taylor Hobson轮廓仪和高精度辅助测量夹具对120mm口径的非球面光学元件进行测量实验并研究工件运动量对拼接测量精度的影响。实验结果表明,当控制平移量在10mm以内和旋转角度在8°以下时,拼接误差的标准偏差值在0.2~0.6μm之间,能满足磨削阶段光学元件亚μm级精度的面形检测要求。     

Second-order optical non-linearity of proton exchanged lithium tantalate waveguides

A detailed correlation between the fabrication conditions, crystallographic phase state of H_xLi_1-xTaO₃ waveguides and second-order optical non-linearity has been investigated by using reflected SHG measurements from the polished waveguide end face. The non-linearity, strongly reduced after the initial proton exchange, is found to be restored and even increased after annealing. However, this apparent increase in the non-linearity is accompanied by a strong degradation of the quality of the SHG reflected beam in the region of the initial as-exchanged waveguide due to beam scattering. The high temperature proton exchange technique has been shown to produce high-quality α-phase waveguides with essentially undegraded non-linear optical properties. There is no phase transition when the α-phase waveguides are fabricated by direct exchange. This phase presents the same crystalline structure as that of LiTaO₃ and maintains the excellent non-linear properties of the bulk material. The results obtained are important for the design, fabrication and optimization of guided-wave non-linear optical devices in LiTaO₃. Received: 21 May 2001 / Published online: 23 October 2001     

选择性埋氧层上硅器件的单粒子瞬态响应的温度相关性

本文建立了90 nm工艺下的绝缘体上硅浮体器件和选择性埋氧层上硅器件模型,通过器件电路混合仿真探究了工作温度对上述两种结构的多级反相器链单粒子瞬态脉冲宽度以及器件内部电荷收集过程的影响.研究表明, N型选择性埋氧层上硅器件相较于浮体器件具有更好的抗单粒子能力,但P型选择性埋氧层上硅器件的抗单粒子能力在高线性能量转移值下与浮体器件基本相同.同时电荷收集的温度相关性分析表明,N型选择性埋氧层上硅器件只存在漂移扩散过程,当温度升高时其电荷收集量变化很小,而N型浮体器件存在双极放大过程,电荷收集量随着温度的升高而显著增加;另外, P型选择性埋氧层上硅器件和浮体器件均存在双极放大过程,当温度升高时P型选择性埋氧层上硅器件衬底中的双极放大过程越来越严重,由于局部埋氧层的存在,反而抑制了其源极的双极放大过程,导致它的电荷收集量要明显少于P型浮体器件.因此选择性埋氧层上硅器件比浮体器件更好地抑制了温度对单粒子瞬态脉冲的影响.     

Error reductions for stitching test of large optical flats

Stitching test of large optical flats is still quite challenging. In this paper, aiming to reduce the 2nd order error accumulation effect, separation of the reference surface error from the subaperture measurements is proposed in stitching of large flats. The reference error is decomposed into power and astigmatism, residual Zernike polynomial surface and high frequency component, which are estimated or calibrated, respectively. The error separation procedure is then incorporated into the subaperture stitching algorithm. Finally experiments are presented to show the effect of error reductions in stitching test of a 600 mm-aperture flat, with reference surface separated and verified by the factory report of the transmission flat.     

Thermomechanical modification of diffraction gratings

The most accurate approaches to fabrication of diffraction gratings are known to be the lithographic and holographic methods. The lithographic methods allow fabrication of arbitrarily chirped gratings whose performance, however, is degraded by stitching errors. The holographic methods are free from stitching errors; however, they are limited in the achievable spatial variations of their grating periods. We suggest a method of diffraction grating modification by nonuniform heating and stretching that is much more flexible than the holographic approach and does not suffer from the problem of stitching error. We demonstrate our approach for quartz phase masks that have a characteristic grating period of 1 microm and a length of several centimeters. Our approach allows the grating periods of the phase masks to vary in a range from a few picometers to a few nanometers and a spatial resolution of a few millimeters. It is shown that the grating period can be modified with a negligible effect on the profile of the gratings.     

Periodic poling of optical waveguides produced by swift-heavy-ion irradiation in LiNbO<Subscript>3</Subscript>

The generation of periodically poled structures in waveguides prepared by swift-heavy-ion (SHI) irradiation, i.e. in the electronic stopping power regime, has been achieved following two different strategies. In one of them we have prepared bulk PPLN samples by an applied electrical field, followed by irradiation with F ions at 22 MeV. After the ion irradiation, a waveguide showing a high optical confinement is obtained, preserving the original PPLN structure. The second strategy consisted of electric periodic poling of previously fabricated swift-ion-irradiated waveguides. To our knowledge this method has not been, so far, successful for conventional implanted waveguides. The successful fabrication of PPLN structures on novel waveguides prepared by SHI irradiation offers a promising potential for nonlinear integrated optical devices.     

The opportunistic transmission of wireless worms between mobile devices

The ubiquity of portable wireless-enabled computing and communications devices has stimulated the emergence of malicious codes (wireless worms) that are capable of spreading between spatially proximal devices. The potential exists for worms to be opportunistically transmitted between devices as they move around, so human mobility patterns will have an impact on epidemic spread. The scenario we address in this paper is proximity attacks from fleetingly in-contact wireless devices with short-range communication range, such as Bluetooth-enabled smart phones.An individual-based model of mobile devices is introduced and the effect of population characteristics and device behaviour on the outbreak dynamics is investigated. The model uses straight-line motion to achieve population, though it is recognised that this is a highly simplified representation of human mobility patterns. We show that the contact rate can be derived from the underlying mobility model and, through extensive simulation, that mass-action epidemic models remain applicable to worm spreading in the low density regime studied here. The model gives useful analytical expressions against which more refined simulations of worm spread can be developed and tested.     

Modeling of InGaAsP–InP 1.55 μm lasers with integrated mode expanders using fiber-matched leaky waveguides

A new concept for InGaAsP–InP 1.55 μm lasers integrated with spot size converters using leaky waveguides is presented. The large fundamental mode size and the high discrimination of the higher order modes make ARROWs (Antiresonant Reflecting Optical Waveguides) and antiguided waveguides useful for fiber coupling functions. Three-dimensional (3-D) beam propagation method (BPM) results show that the devices have transformation losses lower than 0.22 dB. Fiber-coupling efficiencies of 60% are possible with standard cleaved single-mode fibers (SMF). The horizontal and vertical FWHM can be efficiently reduced to 9.70° (horizontal) and 17.80° (vertical). The fabrication of such devices avoids the growth of thick layers of quaternary material with a low Ga and As fraction, and simplifies the fabrication to one planar epitaxial growth step and one non-critical conventional etch. Received: 16 May 2001 / Published online: 30 October 2001     

Silicon nanocrystals in silica—Novel active waveguides for nanophotonics

Nanophotonic structures combining electronic confinement in nanocrystals with photon confinement in photonic structures are potential building blocks of future Si-based photonic devices. Here, we present a detailed optical investigation of active planar waveguides fabricated by Si⁺-ion implantation (400 keV, fluences from 3 to 6×10¹⁷ cm⁻²) of fused silica and thermally oxidized Si wafers. Si nanocrystals formed after annealing emit red-IR photoluminescence (PL) (under UV-blue excitation) and define a layer of high refractive index that guides part of the PL emission. Light from external sources can also be coupled into the waveguides (directly to the polished edge facet or from the surface by applying a quartz prism coupler). In both cases the optical emission from the sample facet exhibits narrow polarization-resolved transverse electric and transverse magnetic modes instead of the usual broad spectra characteristic of Si nanocrystals. This effect is explained by a theoretical model which identifies the microcavity-like peaks as leaking modes propagating below the waveguide/substrate boundary. We present also permanent changes induced by intense femtosecond laser exposure, which can be applied to write structures like gratings into the Si-nanocrystalline waveguides. Finally, we discuss the potential for application of these unconventional and relatively simple all-silicon nanostructures in future photonic devices.     

Ti扩散铌酸锂光波导特性的热固定技术

在Ti扩散铌酸锂光波导中,因光致折变效应而导致光波导特性漂移.在光波相干性的导波光学器件中,光致折变效应的影响尤为严重.本文报道了稳定光致折变效应的热固定技术实验结果;并提出在光波导特性的热固定过程中,不是H~+离子起主导作用这一看法.     

光子晶体异质结耦合波导光开关

以二维三角晶格光子晶体为研究对象,在该光子晶体中引入两行平行的单模线缺陷波导,以一行耦合介质柱为间距,通过调节部分耦合介质柱的折射率,构筑了光子晶体异质结耦合波导光开关结构。利用平面波展开法和定向耦合原理计算了在不同入射光频率下,缺陷波导间耦合介质柱的折射率不同时的耦合长度,确定了合适的光子晶体异质结耦合波导光开关的结构参数。利用时域有限差分法研究了该光开关中耦合介质柱的折射率变化及异质结构介质柱的位置分布对光信号输出路径的影响。结果表明,通过改变该结构中耦合介质柱的折射率可以改变光的输出路径,可实现光的开关行为。并且异质结构介质柱位置的随机分布对该光开关的影响不大,有助于光子晶体新型滤波器、定向耦合器、波分复用器以及光开关等光子器件的研究。     

Microfabricated magnetic waveguides for neutral atoms

We describe how tightly confining magnetic waveguides for atoms can be created with microfabricated or nanofabricated wires. Rubidium atoms guided in the devices we have fabricated would have a transverse mode energy spacing of K. We discuss the creation of a single-mode waveguide for atom interferometry whose depth is comparable to magneto-optical trap (MOT) temperatures. We also discuss the application of microfabricated waveguides to low-dimensional systems of quantum degenerate gases, and show that confinement can be strong enough to observe fermionization in a strongly interacting bosonic ensemble. Received 1st December 1998 and Received in final form 23 February 1999     

Induced transparency in nanoscale plasmonic resonator systems

An optical effect analogous to electromagnetically induced transparency (EIT) is observed in nanoscale plasmonic resonator systems. The system consists of a slot cavity as well as plasmonic bus and resonant waveguides, where the phase-matching condition of the resonant waveguide is tunable for the generation of an obvious EIT-like coupled resonator-induced transparency effect. A dynamic theory is utilized to exactly analyze the influence of physical parameters on transmission characteristics. The transparency effect induced by coupled resonance may have potential applications for nanoscale optical switching, nanolaser, and slow-light devices in highly integrated optical circuits.     

大口径连续相位板拼接检测误差分析

对大口径连续相位板（CPP）在子孔径拼接检测过程中存在的几种影响检测精度的主要因素, 包括定位误差、系统误差和拼接模式等进行了归纳并分析了其对检测精度的影响权重。通过对子孔径重叠区域分布的均匀性计算,分析了检测误差对拼接质量的影响。结果表明,定位误差是影响CPP拼接精度的主要原因,而对系统误差进行有效处理可以进一步减小重叠区非均匀性,拼接模式的选择对CPP的拼接结果的影响有限。通过CPP深度特性对重叠区域均匀性的统计分析表明,在像素级别的检测中,重叠区域均方根残差随着CPP深度的增加而线性增加,即拼接精度随CPP深度的增加而降低。     

Photonic Crystal Power-splitter Based on Mode Splitting of Directional Coupling Waveguides

In the paper, a novel power-splitting scheme based on two dimensional photonic crystal (2D PhC) is proposed. The structure can be divided into three sections, including the input waveguide, coupling region, and output region, and the latter two sections consist of two parallel waveguides placed in proximity. The operation principle of the splitter is that only one of the super-modes splitting from the directional coupler can propagate through coupling region in the frequency range of interest. The radius of air holes next to the guiding region in coupling region is increased to avoid the acute back reflection at the entrance to the input waveguide induced by the modes mismatch between the input waveguide and coupling region. While in output region, the radius of these corresponding air holes is also increased so that the two splitting super-modes have same propagation constants to avoid the coupling between the two output waveguides. Moreover, as the length of coupling region is varied, its influence on the splitting performance is discussed, and it is verified that the relationship between the splitter length and bandwidth has a trade-off.     

On the existence of localized shear horizontal acoustic waves in a piezoelectric plate with two semi-infinite same/different coatings

In this paper, the existence theorem of localized shear horizontal acoustic waves in a piezoelectric plate with two semi-infinite same/different coatings is established. Some properties of the waves in the waveguide structures are also discussed. The results show that the waveguides have some advantages and provide more choice for the designs of acoustic devices.     

子孔径拼接中系统误差的修正方法

为了提高大口径光学元件子孔径拼接测量的检测精度,提出一种平面绝对测量技术,修正子孔径拼接过程中产生的系统误差。利用改进的三面互检法获得参考平面的面形数据,采用这些测量数据构建基于Zernike多项式的参考面面形误差修正波面,在拼接过程中运用误差修正波面对获得的子孔径测量数据进行实时修正,并与全口径直接测量结果进行对比,结果PV（peak value,PV,峰谷值）误差从0.072 1 减少到0.028 6 。结果表明该方法有效减少了参考平面系统误差对拼接测量精度的影响,提高了大口径光学元件的检测精度。