压缩感知光谱成像技术的编码孔径与探测器匹配优化

编码孔径光谱成像仪在实际应用中存在着编码模板与探测器分辨率不匹配从而降低系统分辨率的问题。针对该问题进行了两种情况分析,并通过数学理论建模给出了相应的解决方案。对于编码模板分辨率高于探测器分辨率这一情况,提出引入邻域嵌入超分辨技术的方法,实现了基于压缩感知的超分辨光谱成像。对于编码模板分辨率低于探测器分辨率这一情况,提出区块阈值划分的编码孔径,将编码微元按照区块阈值重新划分并进行灰度分级,从而实现低分辨率编码模板的高分辨率编码孔径。利用梯度投影稀疏重构(GPSR)算法进行数据立方体重建,实验结果表明:运用基于超分辨理论的编码孔径快照光谱成像系统所测得的光谱图像更精准,内容更丰富;采用基于区块阈值划分的编码孔径的编码孔径快照光谱成像系统具有更高的空间分辨率和光谱分辨率。结果证实优化后的编码孔径快照光谱成像系统,其分辨率和成像质量大幅度提升,并实现了高分辨率元件的100%利用。     

光盘上集成的液体微透镜阵列与可重构超分辨成像

微透镜辅助显微镜实现超分辨成像观测,具有免标记、无损伤、实时、定域和环境兼容性好等优势.液体微透镜阵列具有均一、易操控的特性,可实现无复杂机械扫描与驱动的超分辨成像.然而,简单高效地精确控制成像距离是微透镜实现超分辨成像的关键技术挑战.本文利用紫外曝光技术,实现了光盘上光刻胶微孔深度的均一性.结合液体自组装技术,在微孔中填充甘油液滴,保证微透镜辅助超分辨的成像距离.在光学显微镜下实现了对226 nm光栅栅线的可重构超分辨观测与1.59倍成像放大.本文从液体微透镜的阿贝显微成像原理出发,通过理论与模拟解释了液体微透镜的成像放大与超分辨特性.由此可见,光盘上集成的液体微透镜阵列在光学纳米测量与传感等器件中展现了巨大的应用潜力.     

散斑及压缩计算成像研究进展

计算成像是集光学、计算科学、信息科学于一体的新兴交叉领域技术。该技术基于多维光场调控与解调的信息传输原理,利用前端光电成像系统与后端数据处理的“一体化设计”,解决光场信息维度与探测维度不匹配的问题,从而有效提升感知能力和探测性能,目前已成为光电成像领域的前沿方向。其中,散斑成像能够通过调控散斑场来实现强散射光成像,打破了光散射妨碍成像的传统观点;空域和时域压缩计算成像通过对光场信号的编码,能够突破半导体工艺、大量数据传递与处理对高分辨率、高速探测器的限制;压缩计算光谱成像结合光学调制、复用探测与计算重构,解决了传统光谱成像中系统复杂、数据采集效率低和分辨率受限的问题。详细介绍这3类计算成像模式的原理方法和最新研究进展,分析当前尚存的问题,并对这类技术的未来发展方向进行了展望。     

连续推扫计算光谱成像技术

计算光谱成像技术具有高通量、快照成像等优点,但快照成像采样数据量不足,导致利用压缩感知方法重构图谱精度很低。通过对计算光谱成像技术各个环节进行系统研究,提出一种新型的连续推扫计算光谱成像技术,利用正交循环编码孔径代替传统的随机编码孔径,通过逐行扫描方式及正交变换可完整重构图谱数据。仿真和实际成像结果表明,连续推扫计算光谱成像技术可消除图谱混叠影响,理论上可完全重构图谱信息,重构图谱精度明显优于传统的计算光谱成像技术。相比国际上提出的多次曝光计算光谱成像技术,连续推扫计算光谱成像技术不需要改变编码孔径与探测器间的相对位置,也不需要凝视成像,系统中没有活动元件,稳定性高,适用于常规航空航天遥感推扫成像。     

压缩光谱成像系统中物理实现架构研究综述

不同于传统点对点映射成像方式,计算光学成像通过将前端光学信号的物理调控与后端数字信号的计算处理联合起来,使图像信息获取更加高效。这种新型成像体制有望缓解传统成像技术框架下低制造成本与高性能指标间的矛盾,尤其在高维图像信息获取中呈现更显著优势。而物理器件支撑下的系统架构一直是计算光学成像发展的基石,本文针对压缩光谱成像这一子技术领域,介绍了现有可实现空间或光谱调制的光学器件,并以此为基础对多型压缩光谱成像系统架构进行了梳理、归纳,依据信息调制过程的差异,将其规整为单像素光谱成像、编码孔径光谱成像、空间-光谱双重编码光谱成像、微阵列型光谱成像与散射介质光谱成像等几类。重点阐述了多种系统架构的信息调制与采集原理,以及对光谱图像数据立方体的调制效应,并讨论了其中的共性问题。最后给出了面临的技术挑战,探讨了未来发展趋势。     

一种数字微镜阵列分区控制和超分辨重建的压缩感知成像法

提出一种压缩感知成像框架结构.该结构采样端用新建的采样矩阵实现数字微镜阵列分区控制,可增强信息获取的准确性,测量得到与新数字微镜阵列对应的压缩采样值;重构端由采样值优化重构出低分辨率图像后,根据分区控制过程建立压缩感知理论框架下的超分辨重建模型,利用梯度稀疏约束优化算法进行求解,恢复出原高分辨率图像.实验结果表明:数字微镜阵列分区控制与超分辨重建相结合的方法可以明显降低压缩感知成像系统的计算量,缩短成像时间,并且具有较高的图像重构质量.     

基于衍射理论的哈达玛编码光谱成像数据重构

哈达玛变换光谱成像技术是一种在不牺牲分辨率的情况下,通过多通道复用的方法增加光学系统光通量,使得系统信噪比显著高于传统成像的新型计算光谱成像技术.本文针对系统成像过程中数字微镜器件衍射造成的图像降质问题,建立了基于标量衍射理论的哈达玛编码光谱成像图谱数据退化模型,提出以Lucy-Richardson (L-R)算法为核心的重构数据修正算法,提高重构数据立方体的图像质量和光谱精度.通过对成像过程的模拟和重构算法的仿真实验,数字化生成了系统成像衍射降质的物理过程,并验证了本文所采用修正方法的有效性.经过L-R修正之后的复原数据立方体的光谱角距离评价结果为0.1296,图像相似度评价因子优于0.85,相比修正前的重构数据质量有较大提升,表明算法对哈达玛编码光谱成像数据的重构及修正具有较好的效果.     

基于累积量标准差的超分辨光学涨落成像解卷积优化

超分辨光学涨落成像方法通过计算一组随机闪烁图像序列的累积量来提高空间分辨率.在实际实验中,由于计算的图像序列帧数有限,每个像素上累积量估计的误差将显著影响重构图像的均匀性和连续性.传统超分辨光学涨落成像技术由于缺乏对累积量估计的误差分析,在其后续的Lucy-Richardson解卷积算法中,没有对累积量重构图像的噪声添加约束条件.本文利用基于单组有限长数据的累积量标准差公式,计算了超分辨光学涨落显微图像每个像素上的累积量标准差,并将结果引入Lucy-Richardson解卷积算法中作为迭代优化的偏差阈值.模拟和实验结果表明,在相同图像序列长度下,该优化方法显著提高了超分辨重构图像的均匀性和连续性;在同等图像质量下,该方法可缩短图像序列帧数至原来的一半以下,有望用于活细胞动态超分辨成像.     

单色散压缩编码光谱成像系统研究

随着光谱成像技术向高空间分辨率、高光谱分辨率、高信噪比方向发展, 传统的光谱成像系统面临着数据采集量过大的问题,同时,系统分辨率受探测器帧频与像元尺寸影响较大、大口径长焦距系统难于精密装调、系统能量受限引起信噪比提高困难。为了解决上述问题,研究了一种单色散压缩编码光谱成像系统, 并针对国内压缩编码光谱成像系统工程实现与试验验证不足的问题,重点研究了该新系统的设计与实现,模板平移下的系统数学模型及多帧重构算法,并给出实际样机试验及数据处理结果。最后,根据试验情况,总结提出该新技术后续发展需重点关注的研究内容,包括编码模板误差分析,多维稀疏重构模型与算法,压缩编码光谱成像系统标定技术,重构算法/重构图谱评价技术。单色散压缩编码光谱成像系统通过编码、色散、甚至下采样,由探测器接收得到成像观测图像,然后,利用该成像数据,通过重构算法,得到目标光谱图像数据,其优点是低数据量采样、工程实现硬件要求减低、多通道高通量探测。相关研究结果表明,该系统获取的数据有效,样机设计合理,重构算法与标定方法较为准确,其得到的字母HSI目标光谱图像的空间信息清晰,光谱信息较为准确,符合钨灯光谱,其系统设计与实现具有工程可行性。     

基于改进维纳逆滤波的衍射成像光谱仪数据误差分析与重构

衍射成像光谱仪探测到的高光谱数据需要进行计算与反演才可以得到成像光谱数据,本文对衍射成像光谱仪的成像过程及数据误差产生的原理从空间维和光谱维两方面进行了分析,并针对其光谱重构过程中系统点扩散函数标准差较大时重构结果清晰度较低、存在振铃等问题,提出了基于改进维纳逆滤波的光谱数据重构算法,该方法在分析衍射成像光谱仪数据特点与误差的基础上,将每一次维纳逆滤波的重构结果视为新的模糊图像,利用成像过程及维纳逆滤波的基本原理确定新的模糊图像对应的点扩散函数,反复进行维纳逆滤波达到提高图像清晰度的效果,再根据图像自身的空间和光谱特征分布,进行自适应性的噪声去除.利用模拟的衍射成像光谱数据进行验证,在系统点扩散函数的标准差为2.5的情况下,能得到无振铃的重构结果,且与传统维纳逆滤波法的重构结果进行比较,清晰度、细节能力等指标均有所提高,满足了衍射成像光谱数据应用需求.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.