Effect of Scattering on Spectral Imaging of Exposed Cortical Tissue for Brain Function Measurement

Optical imaging of an exposed cortex for brain function measurement is an attractive method for both clinical and physiological investigations. Spectral imaging of the exposed cortical tissue enables measurement of the activity-dependent changes in oxy- and deoxy-haemoglobin independently. Since the diffusely reflected light from the exposed cortex is highly scattered in the cortical tissue, the wavelength dependence of the optical properties of the tissue is likely to affect the images of oxy- and deoxy-haemoglobin changes obtained from the spectral images. In this study, the spectral images of the model of exposed cortical tissue are calculated by Monte Carlo simulation to investigate the influence of blurring by tissue scattering on the brain function measurement by the imaging. The images of the change in oxy- and deoxy-haemoglobin obtained from the spectral images at near infrared wavelengths are broadened and blurred due to the scattering in the cortical tissue. The influence of cross talk is more significant in the image calculated from the spectral images at the visible wavelengths. Inappropriate choice of the spectral range of images might increase cross talk and error in the images of oxy- and deoxy-haemoglobin changes.     

控制光和信号光频差对太赫兹光非对称解复用器性能的影响

讨论了半导体光放大器中的带间效应，及载流子热效应、谱烧孔效应、双光子吸收以及超快非线性折射等带内效应对半导体光放大器的动态特性的影响，讨论了两种情况：1)保持控制光波长不变而改变信号光频率，2)保持控制光和信号光频率相同而同时改变它们的频率下半导体光放大器的增益、相位动态特性以及太赫兹光非对称解复用器的开关窗口特性。数值结果表明，为了得到较为平坦而窄的开关窗口，控制光波长应与信号光波长相同，且其与半导体光放大器增益谱中心波长的差值应该大一些。     

Determination of aerosol extinction coefficient and mass extinction efficiency by DOAS with a flashlight source

With the method of differential optical absorption spectroscopy （DOAS）, average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter （SPM）. Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency （MEE） to be possible in the lower troposphere. The average MEE value is about 7.6m^2.g^-1 , and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.     

Relationship between wavelength combination and signal-to-noise ratio in measuring hemoglobin concentrations using visible or near-infrared light

The signal-to-noise ratio (SNR), when using visible or near-infrared light to measure the change in hemoglobin concentration length (the product of hemoglobin concentration and optical path length in this study), depends on the wavelength combination and the analysis method. Although the SNRs increase when detected or incident optical power increases, the optical power should be limited because of safety standards. Considering these safety standards, we assumed that the total optical power was constant by using the relationship between optical power and measurement error. We investigated the theoretical estimation errors of the changes in hemoglobin concentration length using two, three, and four different wavelengths. The SNRs of the changes in hemoglobin concentration length were high when fewer wavelengths were used. These SNRs decreased when the redox state change in cytochrome oxidase was included in the analysis.     

热压载荷作用下气体检测光学窗口对激光传输影响

采用有限元方法研究了不同热压载荷作用下多组分气体原位激光检测系统的光学窗口变形分布情况,并根据热光效应计算得到光学窗口折射率分布。采用光线追迹法对比分析了氮气吹扫前后光学窗口折射率变化及变形对到达接收面的通光量和辐照度分布影响规律。此外,基于高温光学窗口激光透射测试平台开展了高温光学窗口对检测信号影响研究。结果表明:高温高压环境会使光学窗口折射率变化幅度增大及变形加剧,导致激光光路偏折引起透射光强损耗和探测信号条纹干涉;氮气吹扫可以有效改善激光传输条件,增加到达接收面的通光量,优化辐照分布,提高激光传输质量。     

Depth-resolved imaging of functional activation in the rat cerebral cortex using optical coherence tomography

Co-registered optical coherence tomography (OCT) and video microscopy of the rat somatosensory cortex were acquired simultaneously through a thinned skull during forepaw electrical stimulation. Fractional signal change measured by OCT revealed a functional signal time course corresponding to the hemodynamic signal measurement made with video microscopy. OCT can provide high-resolution, cross-sectional images of functional neurovascular activation and may offer a new tool for basic neuroscience research in the important rat cerebral cortex model.     

基于连通器原理的小探头光纤液位传感器研究

介绍了以汞包层光波导为传感探头的光纤液位传感器的原理及信号处理,其工作原理是利用连通器将液位的变化转变为汞包层光波导包层长度的变化。理论分析和实验表明,当光波导直径和光波长一定时,光功率衰减随汞包层光波导长度增加作线性增加。通过对汞包层光波导引起光功率衰减的检测,探头结构的优化设计以及探测器件的选型,可以获得实时性很强的高精度液位测量。实验测得10m液位的最大测量误差为5．2mm,理论分析的相对测量精度可达0．02％。该液位传感器的研制对于油库等易燃、易爆环境中的液位测量具有重要意义。     

40 Gb/s信号全光3R再生实验

提出一种新型40 Gb/s全光3R再生器方案。采用高精细度法布里-珀罗滤波器进行时钟提取。时钟提取前,通过高稳定光源对输入信号光波长变换实现信号光波长和法布里-珀罗滤波器梳状窗口对准;时钟提取后,接半导体光放大器(SOA)进一步消除时钟信号噪声。全光判决中,采用双半导体光放大器串联增大非线性性能,提高了判决门的响应速度。判决输出接窄带滤波器去除脉冲啁啾拖尾,减小码型效应。实验中,恶化40 Gb/s光脉冲信号通过全光3R再生器可以得到再生脉冲。输入恶化信号时间抖动大于5 ps,脉冲宽度大于16 ps,再生得到的信号时间抖动小于1.5 ps。再生信号相对于输入信噪比改善14 dB。连续稳定工作记录大于15 h。通过实验验证,这种全光3R再生器方案成功地实现了40 Gb/s信号的再生。     

高精度光链路授时时延估算

授时系统中信号单程传输时延的估算直接影响到授时的精度, 环路时延测试是估算单程传输时延的方法之一。在光缆授时系统中光纤的色散特性将导致不同波长光信号在同一光链路中的传输时延存在差异, 基于G.652光纤的色散特性, 提出的时延差精确估算方法, 能够得到这种传输时延的差异。仿真显示来回链路工作波长在1.55 μm附近时, 此方法能够很好地补偿时延差, 从而精确估算信号传输时延。     

放大率恒定的二元光学超光谱成像仪光学系统设计

二元光学元件具有多种应用。用作透镜，在原理上色差非常大，若不在设计上做出补偿，则会限制其在宽波段上的使用。从理论上简单阐述了利用具有独特色散特性的二元光学元件的新型超光谱成像仪的基本原理和应用前景。在此超光谱成像仪中，二元光学透镜焦距随波长的变化改变了系统的F数，因此改变了系统的放大率，既系统放大率是波长的函数，这将引起光谱图像的像元配准误差，得到并不精确的相对光谱信号强度，从而限制了光谱图像重建算法的精度，为了补偿这一缺点，通过光学二组元法设计的变焦系统成功地解决了这一问题，并给出了理论设计公式。     

一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法

提出和论述了一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法。基本思想是设计和采用一种全光学偏振态转换器 ,理论上能将随机偏振态的输入信号光转换为固定偏振方向且功率基本不变的线偏振光 ,利用它控制信号光的偏振态能够克服四波混频过程所固有的偏振敏感性。将这种方法与正交偏振双抽运方法结合起来 ,能较简单地实现偏振不敏感且具有近似常数转换效率的宽带四波混频光波长转换     

一种自适应层进式Savitzky‐Golay光谱滤波算法及其应用

可调谐半导体激光吸收光谱技术（TDLAS）利用半导体激光器的可调谐和窄线宽特性,通过选择特定气体的单条吸收线,排除其余气体的干扰,可以实现高精度、高选择性的气体浓度测量,在气体浓度检测系统中具有广泛的应用前景。在不同的应用条件和环境下,需要解决相应的硬件和数据处理方面的技术问题。主要研究TDLAS技术机动车尾气CO组分浓度遥测系统中的光谱数据处理问题,该系统利用路面漫反射回波信号遥测行驶中的机动车尾气CO组分浓度。由于激光扫描光谱回波信号受到漫反射面情况变化、空气环境变化、尾气湍流影响等因素影响,探测器收集到的信号不仅较弱同时也夹杂着多种噪声, 即测量光路信噪比较差, 故提出一种自适应层进式Savitzky-Golay(S-G)平滑滤波算法,实现了对光谱进行滤波处理从而更加准确地反演CO浓度。S-G滤波算法因其原理简单、功能强大、只需设置两个参数（窗口大小、拟合阶数）等优点,已广泛应用于光谱处理。如何正确设置S-G算法参数使滤波效果在去噪不足和过度滤波之间找到平衡点,是该滤波算法应用的一大难题。设计的检测系统中,测量光路光谱信号为非平稳信号,噪声和有效信号幅度时变,最佳窗口大小和多项式阶数随信号动态而变化,且变化区间较大,使用固定参数的S-G滤波器难以达到最佳效果。提出的自适应层进式S-G平滑滤波算法,通过逐层将测量光路光谱信号经过S-G滤波后,与参考光路的光谱信号设置的参考段比对信号相关系数和信号一阶导相关系数的和,以自适应得到逐层最优参数。通过对信噪比从9.81～29.77的10组不同带噪光谱分析验证了该算法的有效性,自适应层进式S-G算法能较好地去除噪声并还原带噪信号所携带的待测气体浓度信息,与带噪光谱对比,吸收光谱峰值最大误差由25.152%降至5.917%,积分吸光度最大误差由18.1%降至3.9%。在实现的系统中,使用自适应层进式S-G算法对测量光路进行滤波处理,并对不同车型、不同排量、燃烧不同油品的机动车在怠速和缓速通过(5 km·h-1)系统时其排放的CO浓度进行实时在线监测。     

All-optical Steerable Directional Coupler Using Kerr Dark Spatial Soliton Waveguides

1.IntroductionOpticalspatialsolitoninduced-waveguidesareofgreatresearchinterestrecently[1-8]becauseoftheirPOtentialapplicationinopticalcommunicationsandopticalcompution.Asoliton--inducedwaveguidecanguidelightinself--focusingorself--defocusingKerr-typemediabecausethesolitonbeaminducesarefractive-indexprofileequivalenttoanordinarydielectricwaveguide.Soliton-inducedwaveguidecansupPOrtmanymodesofaprobebeampropagatingcoaxiallyalongthesolitonwaveguideSoliton-inducedwaveguideshaveadvantageovertheir…     

物光参考光同光轴的体全息存储光学系统设计

将两块漫射板分别置于输入面的两侧,使物光和参考光同光轴,可以使体全息存储傅里叶变换光学系统更为紧凑。然而,在这种全息存储光学系统中,物光和参考光的总数值孔径较物光数值孔径大很多。分析这种体全息存储光学系统物光和参考光光路的设计要求和光学参量的确定;采用多重结构方法对物光正向光路、逆向光路和参考光光路同时优化设计,实现对物光光路二对物像共扼位置控制像差,并满足参考光光路的要求;给出前后组焦距分别为33 mm和30 mm的物光和参考光同光轴,前工作距为30 mm,物光和参考光总数值孔径为0.53的全息存储光学系统的设计结果。系统的波像差小于0.071λ,达到衍射极限。     

衍射光学透镜色散特性的仿真研究

在白光照射下,衍射光学透镜的焦距不仅同材料色散和波长色散有关,而且还同孔径因子有关。基于折射率随波长变化的经验公式,利用自编的仿真计算程序包,得到了透镜焦距、材料色散、波长色散、孔径因子之间的关系曲线。所获得的理论分析和仿真计算结果为进一步设计消色差的纯衍射目视光学系统提供了理论依据,具有一定的指导意义。     

Dual‐wavelength optical parametric oscillator using antiresonant ring interferometer

A novel technique for coupling of two resonant optical cavities using an antiresonant ring (ARR) interferometer is reported. By deploying two synchronously‐pumped femtosecond optical parametric oscillators (OPOs), it is shown that the use of an ARR can provide an intracavity common path for the two oscillating fields, but without gain coupling between the two nonlinear media. The new technique permits the generation of two signal (idler) wavelengths, which can be independently and arbitrarily varied across the OPO tuning range. The absence of gain coupling also enables unrestricted and uninterrupted tuning through wavelength degeneracy at any arbitrary point within the OPO tuning range. It is shown that signal wavelength pairs tunable across 1500–1580 nm, corresponding to a frequency separation from ∼ 10 THz down to exact degeneracy, can be generated from the coupled OPOs, limited only by the reflectivity of the available mirrors.     

高空高速航空相机光学窗口的热光学分析

分析航空相机光学窗口的热光学特性,选定熔石英作为窗口玻璃的材料,将热流密度加权分配到窗口外表面各个区域,并考虑整个窗口玻璃的辐射来计算其在一个工作循环内的温度分布。高空高速飞行时,气动热使窗口外表面的温度急剧上升,由于熔石英的导热率很小,窗口产生很大的轴向温差,分别取轴向温差55℃,70℃和90℃时的工况计算窗口热变形;光学窗口内、外表面的变形规律为近似球面,计算了其近似曲率半径,计算由面形变化和折射率变化引起的光程差并转化为Zernike多项式;将Zernike多项式系数带入Code V中考核窗口玻璃的光学性能,得到波像差变化量,其像面离焦量为-0.114mm,调制传递函数的下降最大值小于0.01。结果表明,光学窗口满足光学性能的要求。     

Three-dimensional athermal waveguide at 1.3 μm wavelength for temperature independent lightwave devices

To eliminate the temperature dependence of narrow-band filter, a three-dimensional athermal waveguide of which optical path length is independent of temperature was developed at 1.3 μm wavelength. The temperature coefficient of the refractive index of films made of glass materials was measured at this wavelength, and a strip-loaded athermal waveguide was designed using a scalar finite element method. The temperature coefficient of optical path length was successfully decreased to 9.65X10^-9[/K] (0.1% of the conventional waveguide).     

Optical Storage in Side-Chain Liquid Crystalline Polyesters

Long-term, high resolution holographic storage has been achieved in side-chain liquid crystalline polyesters with high diffraction efficiency. The information can be completely erased by heating the film to about 80°C. The modular architecture of the polyesters permits a varition in the length of the main- and side-chains and the substituents of the azo chromophore. Each of these has a profound influence on the storage properties of the polyesters. In this article, we examine the influence of the length of the side-chains, the probe-beam-polarization dependence of the observed signal on the interface and the crystalline vs. amorphous nature of the films for optical storage.     

Wide angular range operation of a dielectric multilayer film with a photonic-crystal-type defect

Light can tunnel through a high-reflectivity dielectric multilayer film when a photonic-crystal-type defect is introduced in the structure, which is useful for optical signal processing. We consider chirped structures with a defect in layer thickness for which high reflectivity is achieved over a broad wavelength range except within a narrow spectral window. The useful transmission window, while it shifts toward shorter wavelengths as the angle of incidence of the light beam is increased, does not, in general, survive; i.e., transmission disappears progressively. We show that wide angular range operation can, however, be achieved by a proper design of the chirped structure. Analytical expressions for the design parameters are derived on the basis of a semi-infinite photonic crystal model. Theoretical reflectance spectra of defect SiO2/TiO2 chirped multilayer films are presented and discussed in terms of the dispersion of the electromagnetic radiation modes of the finite photonic crystal. These devices offer a simple way to mechanically tune (through inclination of the film) the wavelength transmitted from a fixed white-light beam.