Acousto-optic Tunable Filter Research Articles

Radiometric calibration and noise estimation of acousto-optic tunable filter hyperspectral imaging systems

The accuracy of the radiometric response of acousto-optic tunable filter (AOTF) hyperspectral imaging systems is crucial for obtaining reliable measurements. It is therefore important to know the radiometric response and noise characteristics of the hyperspectral imaging system used. A radiometric model of an AOTF hyperspectral imaging system composed of an imaging sensor radiometric model (CCD, CMOS, and sCMOS) and an AOTF light transmission model is proposed. Using the radiometric model, a method for obtaining the fixed pattern noise (FPN) of the imaging system by displacing and imaging an illuminated reference target is developed. Methods for estimating the temporal noise of the imaging system, using the photon transfer method, and for correcting FPN are also presented. Noise estimation and image restoration methods were tested on an AOTF hyperspectral imaging system. The results indicate that the developed methods can accurately calculate temporal and FPN, and can effectively correct the acquired images. After correction, the signal-to-noise ratio of the acquired images was shown to increase by 26%.

Combined laser and broadband light for measuring the tuning relation of an acousto-optic tunable filter

To improve the tuning relation accuracy of an acousto-optic tunable filter, the conventional separated laser and broadband light methods were combined. The single laser test measured one accurate point and corrected the large amounts of data obtained from the broadband light method. The final tuning relation was fitted by the corrected data. A simulation and an experiment for several methods were conducted for comparison. The relative error was reduced from 0.2% to 0.05% in the 430~785 nm range. The equivalent wavelength accuracy improved from 1 to 0.2 nm. This method solved the problems associated with the use of a single laser source with few test data values and a single broadband light source with poor collimation.

Acousto-optic control of light beams in the infrared range

The control over the parameters of the far-infrared and terahertz radiation by the acoustooptic method is discussed. The operation of a tunable acousto-optic filter based on the tellurium crystal is investigated. The crystal used in the filter was transparent for the optic radiation in the wavelength range of 4.0 to 23 µm. The device allows electronic tuning and processing of optic images in the spectral interval of 8.0 to 14 µm.

Acoustic birefringence suppression in a fiber acoustic grating employing solid-core photonic crystal fiber with hexagonal air-hole array cladding

An acoustic birefringence suppression scheme for acoustic fiber gratings has been proposed and experimentally demonstrated. Experimental observation of the transmission characteristics of the single-mode-fiber-based (SMF-based) acoustic grating confirms that introduction of one segment of solid-core photonic crystal fiber (PCF) with air-hole array in the cladding region helps to eradicate resonance peak splitting induced by acoustic birefringence, which has been explained by our theoretical analysis from the acoustic wave modulation method and fiber cross-section structure. Moreover, experimental results indicate that the introduction of the solid-core PCF does not have a considerable impact on the frequency dependence of resonance wavelength for the SMF-based acoustic fiber grating, which ensures the performances of the PCF-assisted SMF-based acousto-optic tunable filter for practical applications.

Acousto-optic mode coupling excited by flexural waves in simplified hollow-core photonic crystal fibers

We have demonstrated the formation of an acoustic grating in a simplified hollow-core photonic crystal fiber, which consists of a hollow hexagonal core and six crown-like air holes, by applying flexural acoustic waves along the fiber axis. The dependence of the resonance wavelength on the applied acoustic frequency has been acquired on the basis of the theoretical calculation of the phase matching curve; it is in good agreement with our experimental observation of the transmission spectral evolution as the applied acoustic frequency varies. Experimental results show that the acoustic grating resonance peak possesses acoustic frequency and strain dependences of 728 nm MHz−1 and −6.98 pm με−1, respectively, based on which high-performance acousto-optic tunable filters and fiber-optic strain sensors with high sensitivity could be achieved. And furthermore, the research work presented in this paper indicates that microbending rather than physical deformation is the main physical mechanism that leads to the formation of equivalent long-period gratings, which would be of significance for developing related grating devices based on simplified hollow-core photonic crystal fibers.

Tunable thin-film optical filters for hyperspectral microscopy.

Hyperspectral imaging was originally developed for use in remote sensing applications. More recently, it has been applied to biological imaging systems, such as fluorescence microscopes. The ability to distinguish molecules based on spectral differences has been especially advantageous for identifying fluorophores in highly autofluorescent tissues. A key component of hyperspectral imaging systems is wavelength filtering. Each filtering technology used for hyperspectral imaging has corresponding advantages and disadvantages. Recently, a new optical filtering technology has been developed that uses multi-layered thin-film optical filters that can be rotated, with respect to incident light, to control the center wavelength of the pass-band. Compared to the majority of tunable filter technologies, these filters have superior optical performance including greater than 90% transmission, steep spectral edges and high out-of-band blocking. Hence, tunable thin-film optical filters present optical characteristics that may make them well-suited for many biological spectral imaging applications. An array of tunable thin-film filters was implemented on an inverted fluorescence microscope (TE 2000, Nikon Instruments) to cover the full visible wavelength range. Images of a previously published model, GFP-expressing endothelial cells in the lung, were acquired using a charge-coupled device camera (Rolera EM-C2, Q-Imaging). This model sample presents fluorescently-labeled cells in a highly autofluorescent environment. Linear unmixing of hyperspectral images indicates that thin-film tunable filters provide equivalent spectral discrimination to our previous acousto-optic tunable filter-based approach, with increased signal-to-noise characteristics. Hence, tunable multi-layered thin film optical filters may provide greatly improved spectral filtering characteristics and therefore enable wider acceptance of hyperspectral widefield microscopy.

A method for characterizing illumination systems for hyperspectral imaging

Near-infrared hyperspectral imaging is becoming a popular tool in various fields. In all imaging systems, proper illumination is crucial for attaining optimal image quality that is needed for the best performance of image analysis algorithms. In hyperspectral imaging, the acquired spectral signature has to be representative in all parts of the imaged object. Therefore, the whole object must be equally well illuminated-without shadows or specular reflections. As there are no restrictions imposed on the material and geometry of the object, the desired illumination of the object can only be achieved with completely diffuse illumination. In order to minimize shadows and specular reflections, the light illuminating the object must be spatially, angularly and spectrally uniform. The quality of illumination systems for hyperspectral imaging can therefore be assessed using spatial-intensity, spatial-spectral, angular-intensity and angular-spectral non-uniformity measures that are presented in this paper. Emphasis is given to the angular-intensity and angular-spectral non-uniformity measures, which are the most important contributions of this paper. The measures were defined on images of two reference targets-a flat, white diffuse reflectance target and a sphere grid target-acquired with an acousto-optic tunable filter (AOTF) based hyperspectral imaging system. The proposed measures were tested on a ring light and on a diffuse dome illumination system.

声光可调谐滤波器成像光谱仪实时预处理系统

In order to realize the rapid and real-time data pre-processing of an imaging spectrometer based on Acousto-optic Tunable Filter(AOTF),the data characteristics and a pre-processing algorithm of the imaging spectrometer based on AOTF were analyzed.Then,a scheme of dual Digital Signal Processor(DSP) parallel processing system based on two chips of ADSP-TS201 coupled the external bus sharing and the link ports was proposed by using DSP instead of the traditional computer processing platform as the key device.Proceeding from practical requests,a pipeline processing was designed,pre-processing tasks were allocated rationally,and the functional verification was implemented.The practical application shows that it takes 23.5 ms to accomplish the pre-processing task for one frame data of imaging spectrometer based on AOTF,which increases 13 times than that of PC and meets the real-time requirement.The system proposed in this paper promotes the development of systematism,modularization,miniaturization and the capability of real-time processing of the imaging spectrometer based on the AOTF.

Key techniques for spectrally programmable imaging spectrometer based on AOTF

PDF HTML阅读 XML下载 导出引用 引用提醒 基于AOTF的光谱响应可编程成像光谱系统关键技术 DOI: 作者: 作者单位: 中国科学院上海技术物理研究所,中国科学院上海技术物理研究所,中国科学院上海技术物理研究所,中国科学院上海技术物理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家“973计划”项目(2009CB723902) Key techniques for spectrally programmable imaging spectrometer based on AOTF Author: Affiliation: Shanghai Institute of Technical Physics,Chinese Academy of Sciences,Shanghai Institute of Technical Physics,Chinese Academy of Sciences,Shanghai Institute of Technical Physics,Chinese Academy of Sciences,Shanghai Institute of Technical Physics,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于声光可调谐滤波器(Acousto-Optical Tunable Filter，AOTF)的多频工作模式，提出了一种成像光谱系统光谱响应可编程的技术.阐述了该技术的原理方法，介绍了光谱可编程的测试结果，包括对滤光波长、光谱分辨率及滤波通带形状的软件控制.在此基础上，研制了一套光谱可编程成像光谱系统的原理样机并进行了初步的成像实验.通过实验结果证明了该技术的工程可行性和技术优势，为提高成像光谱系统的效率和灵活性提供了一种新的途径. Abstract:Based on the multi-frequencies mode of Acousto-Optical Tunable Filter (AOTF), the technique of spectral programmability for imaging spectrometer has been proposed. The principles of this technique were presented, and the test results of spectral programmability were introduced, including controls on the filtered wavelength, spectral resolution and passband shape of AOTF via software. Then a prototype system of spectrally programmable imaging spectrometer was established. Primary imaging experiments was carried out to validate the engineering feasibility and technical advantages of the technique. A novel method was provided for increasing the efficiency and flexibility of imaging spectrometers. 参考文献 相似文献 引证文献

The research of polarized information detection for photo-elastic modulator-based imaging spectropolarimeter

A new method of polarization modulation based triple-photoelastic-modulator (triple-PEM) is proposed as an key component of photo-elastic modulator-based imaging spectro-polarimeter (PEM-ISP) combined with acousto optic tunable filter. The basic principles of PEM-ISP and triple-PEM-based differential frequency polarization modulation are described, that is, the tandem PEMs are operated as an electro-optic circular retardance modulator in a high-performance reflective imaging system. Operating the PEMs at slightly different resonant frequencies generates a differential signal that modulates the polarized component of the incident light at a much lower heterodyne frequency. Then the basic equations for polarization measurement is derived by analyzing and calculating its Muller matrix. The simulation and experiments verify the feasibility and accuracy of polarization measurement by triple-PEM-based differential frequency polarization modulation. Finally, we analyze the influences of the setting of integral step and sampling interval of the detector polarization measurement, and a preliminary error analyses of field angle, phase retardation amplitude etc are also be carried out. The result shows that the measurement error of DoLP is less than 0.6% when the phase retardation error is 1%. This work provides the necessary theoretical basis for remote sensing of new PEM-ISP and for engineering implementation of Stokes parametric inversion.

Compact AOTF-based spectral imaging system for medical endoscopic analysis

AbstractA prototype of a spectral imaging module is described which can be attached to conventional rigid and flexible medical endoscopes. It is based on acousto-optic tunable filters (AOTF) and provides fast spectral image registration at an arbitrary series of wavelengths. The main advantage of the device is the minimization of spatial and spectral image distortion by use of a specialized double AOTF monochromator. These properties ensure immediate and reliable detection of spectral features in any image pixel. Real-time spectral analysis, in addition to spectral visualization, provides the opportunity to make medical photoluminescence diagnostics more effective.

국내 원산지별 고춧가루의 매운맛 비파괴 측정기술 개발

In this research, the feasibility of non-destructive measurement technique of pungency measurement was investigated for the red-pepper powders produced in different domestic areas in South Korea. The near-infrared absorption spectra in the range of 1100 nm~2300 nm was used to measure capsaicinoids content in red-pepper powders by using a NIR spectroscopy equipped with Acousto-optic tunable filters (AOTF). Fourth three different red-pepper powders from 14 different locations were collected and separated in three different particle size (below 0.425 mm, 0.425~0.71 mm, 0.71~1.4 mm) for the spectral measurements. The partial least square regression (PLSR) models to predict the capsaicinoids content depends on particle size were developed with the measured spectra. The determinant coefficients and standard errors of the developed models for the red-pepper powders of below 0.425 mm, 0.425~0.71 mm, and 0.71~1.4 mm were in the range of 0.859~0.887 and 12.90~12.99 mg/100 g, respectively. The PLS model with the pretreatment of Standard Normal Variate (SNV) for the red-pepper powders below 1.4 mm particle size showed the best performance with the determinant coefficient of 0.844 and the standard error of 14.63 mg/100 g.

All-fiber tunable Mach-Zehnder interferometer based on an acousto-optic tunable filter cascaded with a tapered fiber

An all-fiber tunable Mach-Zehnder interferometer based on an acousto-optic tunable filter cascaded with a tapered fiber is demonstrated experimentally. The passband isolation and the resonant wavelength of the interference fringes can be adjusted by tuning the power and frequency of the driving radio frequency signal applied to the acousto-optic tunable filter in the experimental configuration, respectively.

Dual-channel low-coherence interferometry and its application to quantitative phase imaging of fingerprints

We introduce an off-axis, wide-field, low-coherence and dual-channel interferometric imaging system, which is based on a simple-to-align, common-path interferometer. The system requires no optical-path-difference matching between the interferometric arms in order to obtain interference with low-coherence light source, and is capable of achieving two channels of off-axis interference with high spatial frequency. The two 180°-phase-shifted interferograms are acquired simultaneously using a single digital camera, and processed into a single, noise-reduced and DC-suppressed interferogram. We demonstrate using the proposed system for phase imaging of fingerprint templates. Due to the fact that conventional phase unwrapping algorithms cannot handle the complex and deep surface topography imposed by fingerprint templates, we experimentally implemented two-wavelength phase unwrapping using a supercontinuum laser coupled to acousto-optical tunable filter, together functioning as a low-coherence tunable light source. From the unwrapped phase map, we produced high quality depth profiles of fingerprint templates.

Photovoltaic dependence of photorefractive grating on the externally applied dc electric field

Photovoltaic dependence of photorefractive grating (i.e., space-charge field and phase-shift of the index grating) on the externally applied dc electric field in photovoltaic–photorefractive materials has been investigated. The influence of photovoltaic field (EPhN), diffusion field and carrier concentration ratio r (donor/acceptor impurity concentration ratio) on the space-charge field (SCF) and phase-shift of the index grating in the presence and absence of the externally applied dc electric field have also been studied in details. Our results show that, for a given value of EPhN and r, the magnitude of the SCF and phase-shift of the index grating can be enhanced significantly by employing the lower dc electric field (EON<10) across the photovoltaic–photorefractive crystal and higher value of diffusion field (EDN>40). Such an enhancement in the magnitude of the SCF and phase-shift of the index grating are responsible for the strongest beam coupling in photovoltaic–photorefractive materials. This sufficiently strong beam coupling increases the two-beam coupling gain that may be exceed the absorption and reflection losses of the photovoltaic–photorefractive sample, and optical amplification can occur. The higher value of optical amplification in photovoltaic–photorefractive sample is required for the every applications of photorefractive effect so that technology based on the photorefractive effect such as holographic storage devices, optical information processing, acousto-optic tunable filters, gyro-sensors, optical modulators, optical switches, photorefractive–photovoltaic solitons, biomedical applications, and frequency converters could be improved.

Evaluation of erythropoietin efficacy on diabetic retinopathy based on molecular hyperspectral imaging (MHSI) system

PDF HTML阅读 XML下载 导出引用 引用提醒 分子超光谱成像系统应用于糖网病药物疗效研究 DOI: 作者: 作者单位: 华东师范大学极化材料与器件教育部重点实验室,华东师范大学极化材料与器件教育部重点实验室,华东师范大学极化材料与器件教育部重点实验室,华东师范大学科学与技术跨学科高等研究院,华东师范大学极化材料与器件教育部重点实验室,中国科学院上海技术物理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（面上项目，重点项目，重大项目）;国家教育部博士点基金 Evaluation of erythropoietin efficacy on diabetic retinopathy based on molecular hyperspectral imaging (MHSI) system Author: Affiliation: Key Laboratory of Polor Materials and Devices,East China Normal University,Shanghai,PRC,Key Laboratory of Polor Materials and Devices,East China Normal University,Shanghai,PRC,Key Laboratory of Polor Materials and Devices,East China Normal University,Shanghai,PRC,Institute for Advanced Interdisciplinary Research IAIR,East China Normal University,Shanghai,PRC,Key Laboratory of Polor Materials and Devices,East China Normal University,Shanghai,PRC,Shanghai Institute of Technical Physics,Chinese Academy of Sciences,Shanghai,PRC Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:将成像技术和光谱技术相结合，再配合显微镜技术，研制了基于AOTF（acoustooptic tunable filters）的分子超光谱成像系统.使用该系统采集了正常、糖尿病和EPO(erythropoietin,促红细胞生长素)药物治疗的大鼠视网膜组织切片的分子超光谱图像数据.通过对正常组、糖尿病组、药物治疗组共30例样本的分子超光谱图像数据进行处理，获得了3组样本的单波段图像和伪彩色合成图像，并提取了各组样本外核层的典型透射光谱曲线.从图像上分析各组ONL (outer nuclear layer, 外核层)的厚度，由大到小依次为正常组、治疗组、糖尿病组，由于糖尿病会引起视网膜外核层细胞凋亡和厚度减少，实验结果表明经EPO治疗后可增加视网膜外核层的厚度.从光谱上分析各组的透射强度，糖尿病大鼠视网膜外核层组织在550~1000 nm光谱范围内的透射强度整体高于正常组，经EPO治疗后，透射强度介于正常组和糖尿病组之间；通过光谱相似性分析，治疗组与正常组之间的光谱相似性高于糖尿病与正常组.实验结果表明EPO能减少视网膜外核层细胞凋亡，对糖网病大鼠有一定的疗效.因而分子超光谱成像系统可以作为一种新的手段，辅助科研人员对糖网病的发病机理和致盲原因及药物疗效进行研究. Abstract:Integrate imaging technology, spectrum technology and microscope, a novel molecular hyperspectral imaging (MHSI) system based on AOTF (acoustooptic tunable filters) was presented. The system was used to capture hyperspectral images of rat retinal sections selected from three groups: normal(N), diabetic(D), and EPOtreated(E0). By processing hyperspectral images data of 30 samples, single band images and the pseudocolor images of N、D、E0 group are gained. Typical spectra curves of the ONL cells of N、D、E0 are extracted. By analyzing these images, descending order of the ONL thickness is N、E0、D. The experimental results cite that the ONL thickness of E0 group will be increased after EPO treated. By analyzing these spectrums, transmission intensity of D group is generally higher than that of N group in the spectral field from 550 nm to 1000nm and transmission intensity of E0 group is in the middle of D and N. By analyzing spectrum relations, results show the spectral signature of the E0 group was more similar to that of N than that of D to N. The above results suggest EPO may prevent cell apoptosis and has protective effect on rat DR at a certain level. MHSI system may probably provide a potential approach to researching pathogenesis、causes of blindness and drug efficacy of DR in future. 参考文献 相似文献 引证文献

Surface and thickness measurement of a transparent film using wavelength scanning interferometry

A wavelength scanning interferometer for measuring the surface and thickness of a transparent film has been studied. A halogen light source combined with an acousto-optic tuneable filter is used to generate a sequence of filtered light in a Linnik interferometer, which leads to a sequence of interferograms captured by a CCD camera. When a transparent thin film is measured, the reflection signals from both the top and bottom surfaces of the film will interfere with the reference signal. At the same time, the multiple reflection signals between the two film surfaces will also interfere with each other. Effective separation of the interference signals from each other is the key to achieving a successful measurement. By performing a frequency-domain analysis, these interference signals can be separated. An optimized Fourier transform method is used in the analysis. Measurements of the top and bottom surface finishes of the film, as well as the film thickness map, have been achieved. The film needs to be more than 3 µm in optical path length, and must transparent with no absorption of light. The film's refractive index needs to be known as a function of wavelength. In this paper, the theoretical analysis and simulation study of wavelength scanning interferometry for transparent film measurement is discussed. Experiments on thin film layers of Parylene N coated on a glass slide surface are studied and analyzed. Comparison study results with other contact and non-contact methods are also presented.

Tunable acousto-optic spectral imager for atmospheric composition measurements in the visible spectral domain

We describe a new spectral imaging instrument using a TeO(2) acousto-optical tunable filter (AOTF) operating in the visible domain (450-900 nm). It allows for fast (~1 second), monochromatic (FWHM ranges from 0.6 nm at 450 nm to 3.5 nm at 800 nm) picture acquisition with good spatial resolution. This instrument was designed as a breadboard of the visible channel of a new satellite-borne atmospheric limb spectral imager, named the Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere (ALTIUS), that is currently being developed. We tested its remote sensing capabilities by observing the dense, turbulent plume exhausted by a waste incinerator stack at two wavelengths sensitive to NO(2). An average value of 6.0±0.4×10(17) molecules cm(-2) has been obtained for the NO(2) slant column density within the plume, close to the stack outlet. Although this result was obtained with a rather low accuracy, it demonstrates the potential of spectral imaging by using AOTFs in remote sensing.

Assignment and rotational analysis of new absorption bands of carbon dioxide isotopologues in Venus spectra

We present absorption bands of carbon dioxide isotopologues, detected by the Solar Occultation for the Infrared Range (SOIR) instrument on board the Venus Express Satellite. The SOIR instrument combines an echelle spectrometer and an Acousto-Optical Tunable Filter (AOTF) for order selection. It performs solar occultation measurements in the Venus atmosphere in the IR region (2.2–4.3μm), at a resolution of 0.12–0.18cm−1. The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus atmosphere above the cloud layer (65–150km) to be made with emphasis on the vertical distributions of gases. Thanks to the SOIR spectral resolution, a new CO2 absorption band was identified: the 21101–01101 band of 16O12C18O with R branch up to J=31. Two other previously reported bands were observed dispelling any doubts about their identifications: the 20001–00001 band of 16O13C18O [Villanueva G, et al. J Quant Spectrosc Radiat Transfer 2008;109:883–894] and the 01111–00001 band of 16O12C18O [Villanueva G, et al. J Quant Spectrosc Radiat Transfer 2008;109:883–894 and Wilquet V, et al. J Quant Spectrosc Radiat Transfer 2008;109:895–905]. These bands were analyzed, and spectroscopic constants characterizing them were obtained. The rotational assignment of the 20001–00001 band was corrected. The present measurements are compared with data available in the HITRAN database.

Multi-spectral video endoscopy system for the detection of cancerous tissue

Multi-spectral video endoscopy provides considerable potential for early stage cancer detection. Previous multi-spectral image acquisition systems were of limited use for endoscopy due to (i) the necessary spatial scanning of push-broom approaches or (ii) the impractical long switching times of liquid crystal tunable filters. Recent technological advances in the field of tuneable filters, in particular fast acousto-optical tunable filters (AOTF), make switching times below 1ms feasible. Thus, AOTFs represent a suitable technology for the acquisition of hyper-spectral image and multi-spectral video data with excellent spatial and temporal resolution. In this paper, we propose a hyper-spectral imaging endoscope using a fast AOTF synchronized with a highly sensitive EMCCD camera for the detection of cancerous tissue. The setup demonstrates that the acquisition of hyper-spectral image and multi-spectral video data is feasible and enables the augmentation of endoscopic videos with overlays indicating cancerous tissue regions.Using hyper-spectral measurements from biopsies acquired with the setup in a clinical environment it is shown that the spectral characteristic of cancerous regions is tissue dependent. Even a sophisticated classifier such as a Support Vector Machines (SVM) or a Mixture of Gaussian Classifier (MOGC) cannot generalize the discriminative information if the training set contains measurements from different tissue types (e.g. larynx vs. parotid). In contrast, a training data selection scheme that chooses similar training sets for a given test set achieves a better prediction accuracy using an approach based on a Quadratic Discriminant Classifier (QDC) with the important advantage of improved robustness and less liability to overtraining. Combined with an image registration removing motion-based acquisition artefacts, the spectral information allows the augmentation of the video stream with overlays indicating cancerous tissue regions.