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Femtosecond laser enabled selective micro-holes drilling on the multicore-fiber facet for displacement sensor application

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OPTICS EXPRESS 2019年第8期27卷 10777-10786页

作者： Zhang, Cong Jiang, Zhisheng Fu, Songnian Tang, Ming Tong, Weijun Liu, Deming Huazhong Univ Sci & Technol Wuhan Natl Lab Optoelect Wuhan 430074 Hubei Peoples R China Huazhong Univ Sci & Technol Sch Opt & Elect Informat Wuhan 430074 Hubei Peoples R China Yangtze Opt Fiber & Cable Joint Stock Ltd Co YOFC R&D Ctr State Key Lab Opt Fiber & Cable Manufacture Techn Wuhan 430074 Hubei Peoples R China

We experimentally demonstrate a femtosecond laser enabled selective micro-holes drilling technique on the multicore-fiber facet. The precise position of individual cores at the seven-core fiber facet is initially locked by the image processing algorithm, and then six micro-holes are successfully fabricated after the pulse energy of femtosecond laser is optimized. Meanwhile, the use of fabricated seven-core fiber for the application of reflective intensity-modulated fiber optics displacement sensor (RIM-FODS) is comprehensively investigated. By using the beam propagation method (BPM), we theoretically investigate the effect of micro-hole depth on the RIM-FODS performance, in terms of both dead zone and measurement range. We identify that, with the increase of micro-hole depth, the dead zone range can be substantially reduced at the expense of measurement range reduction. However, multiple micro-holes with a successive depth difference can overcome such problem. When the micro-holes with depths of 5, 10, 15, 20, 25, 30 mu m are fabricated on the seven-core fiber facet, and the dead zone range can be substantially reduced from 150 mu m to 20 mu m, together with an extension of measurement range from 250 mu m to 400 mu m. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Femtosecond fiber lasers Femtosecond lasers image processing algorithms Single mode fibers Surface enhanced Raman scattering Whispering gallery modes

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Efficient coding and detection of ultra-long IDs for visible light positioning systems

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OPTICS EXPRESS 2018年第10期26卷 13397-13407页

作者： Zhang, Hualong Yang, Chuanchuan Peking Univ State Key Lab Adv Opt Commun Syst & Networks Beijing 100871 Peoples R China

Visible light positioning (VLP) is a promising technique to complement Global Navigation Satellite System (GNSS) such as Global positioning system (GPS) and BeiDou Navigation Satellite System (BDS) which features the advantage of low-cost and high accuracy. The situation becomes even more crucial for indoor environments, where satellite signals are weak or even unavailable. For large-scale application of VLP, there would be a considerable number of Light emitting diode (LED) IDs, which bring forward the demand of long LED ID detection. In particular, to provision indoor localization globally, a convenient way is to program a unique ID into each LED during manufacture. This poses a big challenge for image sensors, such as the CMOS camera in everybody's hands since the long ID covers the span of multiple frames. In this paper, we investigate the detection of ultra-long ID using rolling shutter cameras. By analyzing the pattern of data loss in each frame, we proposed a novel coding technique to improve the efficiency of LED ID detection. We studied the performance of Reed-Solomon (RS) code in this system and designed a new coding method which considered the trade-off between performance and decoding complexity. Coding technique decreases the number of frames needed in data processing, significantly reduces the detection time, and improves the accuracy of detection. Numerical and experimental results show that the detected LED ID can be much longer with the coding technique. Besides, our proposed coding method is proved to achieve a performance close to that of RS code while the decoding complexity is much lower. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： CMOS cameras image processing image processing algorithms image quality Light intensity Visible light

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Signal-to-noise-ratio limit to the depth-of-field extension for imaging systems with an arbitrary pupil function

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2009年第4期26卷 895-908页

作者： Bagheri, Saeed Silveira, Paulo E. X. Barbastathis, George IBM Corp Thomas J Watson Res Ctr Yorktown Hts NY 10598 USA Omni Vis CDM Opt Inc Boulder CO 80303 USA MIT Cambridge MA 02139 USA

We discuss the limit of the depth-of-field (DOF) extension for an imaging system using aspheric surfaces. In particular we consider an imaging system with an arbitrary pupil function and present the rigorous tradeoff between the DOF of the system and the spectral signal-to-noise ratio (SNR) over an extended DOF, to our knowledge for the first time. In doing so we use the relation between the conservation of ambiguity and modulation-transfer function (MTF) on one hand and the relation between the spectral SNR and MTF on the other. Using this, we rigorously derive the expression for an upper bound for the minimum spectral SNR, i.e., the limit of spectral SNR improvement. This leads to the introduction of our spectral SNR conservation principle. We also draw the relation between our result and the conservation of brightness theorem and establish that our result is the spectral version of the brightness conservation theorem. (C) 2009 Optical Society of America

关键词： Extended depth of field image processing algorithms Imaging systems Phase modulation Spatial frequency Wavefront encoding

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Recent advances in holographic 3D particle tracking

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ADVANCES IN OPTICS AND PHOTONICS 2015年第4期7卷 713-755页

作者： Memmolo, Pasquale Miccio, Lisa Paturzo, Melania Di Caprio, Giuseppe Coppola, Giuseppe Netti, Paolo A. Ferraro, Pietro CNR ISASI Inst Appl Sci & Intelligent Syst E Caia I-80078 Pozzuoli NA Italy Ist Italiano Tecnol Ctr Adv Biomat HealthCare CRIB I-80125 Naples Italy CNR Inst Microelect & Microsyst Unit Naples I-80121 Naples Italy

Particle tracking is a fundamental technique for investigating a variety of biophysical processes, from intracellular dynamics to the characterization of cell motility and migration. However, observing three-dimensional (3D) trajectories of particles is in general a challenging task in classical microscopy owing to the limited imaging depth of field of commercial optical microscopes, which represents a serious drawback for the analysis of time-lapse microscopy image data. Therefore, numerous automated particle-tracking approaches have been developed by many research groups around the world. Recently, digital holography (DH) in microscopy has rapidly gained credit as one of the elective techniques for these applications, mainly due to the uniqueness of the DH to provide a posteriori quantitative multiple refocusing capability and phase-contrast imaging. Starting from this paradigm, a huge amount of 3D holographic tracking approaches have been conceived and investigated for applications in various branches of science, including optofluids, microfluidics, biomedical microscopy, cell mechano-trasduction, and cell migration. Since a wider community of readers could be interested in such a review, i.e., not only scientists working in the fields of optics and photonics but also users of particle-tracking tools, it should be very beneficial to provide a complete review of state-of-the-art holographic 3D particle-tracking methods and their applications in bio-microfluidics. (C) 2015 Optical Society of America

关键词： Diffractive optical elements Digital holographic imaging image processing algorithms Imaging techniques Laser velocimetry Spatial light modulators

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Self-calibration single-lens 3D video extensometer for high-accuracy and real-time strain measurement

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OPTICS EXPRESS 2016年第26期24卷 30124-30138页

作者： Shao, Xinxing Eisa, Mohammed Mokhtar Chen, Zhenning Dong, Shuai He, Xiaoyuan Southeast Univ Dept Engn Mech Nanjing 210096 Jiangsu Peoples R China

The accuracy of strain measurement using a common optical extensometer with two-dimensional (2D) digital image correlation (DIC) is not sufficient for experimental applications due to the effect of out-of-plane motion. Although three-dimensional (3D) DIC can measure all three components of displacement without introducing in-plane displacement errors, 3D-DIC requires the stringent synchronization between two digital cameras and requires complicated system calibration of binocular stereovision, which makes the measurement rather inconvenient. To solve the problems described above, this paper proposes a self-calibration single-lens 3D video extensometer for non-contact, non-destructive and high-accuracy strain measurement. In the established video extensometer, a single-lens 3D imaging system with a prism and two mirrors is constructed to acquire stereo images of the test sample surface, so the problems of synchronization and out-of-plane displacement can be solved easily. Moreover, a speckle-based self-calibration method which calibrates the single-lens stereo system using the reference speckle image of the specimen instead of the calibration targets is proposed, which will make the system more convenient to be used without complicated calibration. Furthermore, an efficient and robust inverse compositional Gauss-Newton algorithm combined with a robust stereo matching stage is employed to achieve high-accuracy and real-time subset-based stereo matching. Tensile tests of an Alalloy specimen were performed to demonstrate the feasibility and effectiveness of the proposed self-calibration single-lens 3D video extensometer. (C) 2016 Optical Society of America

关键词： Digital image processing image processing algorithms image sensors Strain measurement Three dimensional imaging Three dimensional measurement

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Deep learning-enabled image content-adaptive field sequential color LCDs with mini-LED backlight

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OPTICS EXPRESS 2022年第12期30卷 21044-21064页

作者： Zou, Guowei Wang, Zeyu Liu, Yutong Li, Juanli Liu, Xingyun Liu, Jiahui Yang, Bo-Ru Qin, Zong Sun Yat Sen Univ State Key Lab Optoelect Mat & Technol Guangdong Prov Key Lab Display Mat & Technol Sch Elect & Informat Technol 132 East Waihuan Rd Guangzhou 510006 Peoples R China

The mini-LED as the backlight of field sequential color LCD (FSC-LCD) enables high contrast, thin volume, and theoretically tripled light efficiency and resolution. However, color breakup (CBU) induced by a relative speed between an observer and the display severely limits the application of FSC-LCDs. Several driving algorithms have been proposed for CBU suppression, but their performance depends on image content. Moreover, their performance plateaus with increasing image segment number, preventing taking advantage of the massive segments introduced by mini-LEDs. Therefore, this study proposes an image content-adaptive driving algorithm for mini-LED FSC-LCDs. Deep learning-based image classification accurately determines the best FSC algorithm with the lowest CBU. In addition, the algorithm is heterogeneous that the image classification is independently performed in each segment, guaranteeing minimized CBU in all segments. We perform objective and subjective validation. Compared with the currently best algorithm, the proposed algorithm improves the performance in suppressing CBU by more than 20% using two evaluation metrics, supported by experiment-based subjective evaluation. Mini-LED FSC-LCDs driven by the proposed algorithm with outstanding CBU suppression can be ideal for display systems requiring high brightness and high resolution, such as head-up displays, virtual reality, and augmented reality displays. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Digital holographic imaging image processing algorithms Light fields Light guide plates Saccades Segmentation

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Cartilage thickness measurements from optical coherence tomography

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2003年第2期20卷 357-367页

作者： Rogowska, J Bryant, CM Brezinski, ME Northeastern Univ Coll Comp Sci Boston MA 02115 USA Harvard Univ Brigham & Womens Hosp Sch Med Dept Orthoped Boston MA 02115 USA

We describe a new semiautomatic image processing method for detecting the cartilage boundaries in optical coherence tomography (OCT). In particular, we focus on rabbit cartilage since this is an important animal model for testing both chondroprotective agents and cartilage repair techniques. The novel boundary-detection system presented here consists of (1) an adaptive filtering technique for image enhancement and speckle reduction, (2) edge detection, and (3) edge linking by graph searching. The procedure requires several steps and can be automated. The quantitative measurements of cartilage thickness on OCT images correlated well. with measurements from histology. (C) 2003 Optical Society of America.

关键词： Absorption spectroscopy image processing algorithms image quality Magnetic resonance imaging Radar imaging Speckle reduction

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Retinal oxygen kinetics imaging and analysis (ROKIA) based on the integration and fusion of structural-functional imaging

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BIOMEDICAL OPTICS EXPRESS 2022年第10期13卷 5400-5417页

作者： Peng, Ximeng Jin, Zi Zhou, Zixia Gao, Mengdi Jiang, Chunxia Hu, Yicheng Lu, Yanye LI, Jinying Ren, Qiushi Zhou, Chuanqing Peking Univ Coll Future Technol Dept Biomed Engn Beijing 100871 Peoples R China Shenzhen Bay Lab Inst Biomed Engn Shenzhen 5181071 Peoples R China Peking Univ Inst Biomed Engn Shenzhen Grad Sch Shenzhen 518055 Peoples R China Peking Univ Peking Univ Hlth Sci Ctr Inst Med Technol Beijing 100191 Peoples R China Peking Univ Shenzhen Hosp Dept Ophthalmol Shenzhen 518034 Peoples R China Shanghai Univ Med & Hlth Sci Coll Med Instrument Shanghai 201318 Peoples R China

The retina is one of the most metabolically active tissues in the body. The dysfunction of oxygen kinetics in the retina is closely related to the disease and has important clinical value. Dynamic imaging and comprehensive analyses of oxygen kinetics in the retina depend on the fusion of structural and functional imaging and high spatiotemporal resolution. But it's currently not clinically available, particularly via a single imaging device. Therefore, this work aims to develop a retinal oxygen kinetics imaging and analysis (ROKIA) technology by integrating dual-wavelength imaging with laser speckle contrast imaging modalities, which achieves structural and functional analysis with high spatial resolution and dynamic measurement, taking both external and lumen vessel diameters into account. The ROKIA systematically evaluated eight vascular metrics, four blood flow metrics, and fifteen oxygenation metrics. The single device scheme overcomes the incompatibility of optical design, harmonizes the field of view and resolution of different modalities, and reduces the difficulty of registration and image processing algorithms. More importantly, many of the metrics (such as oxygen delivery, oxygen metabolism, vessel wall thickness, etc.) derived from the fusion of structural and functional information, are unique to ROKIA. The oxygen kinetic analysis technology proposed in this paper, to our knowledge, is the first demonstration of the vascular metrics, blood flow metrics, and oxygenation metrics via a single system, which will potentially become a powerful tool for disease diagnosis and clinical research.(c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Functional imaging image analysis image processing algorithms Laser Doppler velocimetry Laser imaging Scanning laser ophthalmoscopy

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Estimation for a complex index of refraction based on the Stokes vector of the reflected light under active polarized detection

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APPLIED OPTICS 2022年第27期61卷 7830-7837页

作者： Yang, Zhiyong Zhang, Zhiwei Zhang, Zhili Li, Shun Rocket Force Engn Univ State Key Discipline Lab Ordnance Launch Theory & Xian Dc 710025 Peoples R China

An estimation method for a complex index of refraction based on the Stokes vector of the reflected light under active polarized detection is presented. In this method, the difference of the Stokes vector of the reflected light is used to introduce the three new estimation indices for the L-M nonlinear least squares algorithm to estimate the complex index of refraction n and k of the target, which does not require either interpretation of the diffuse reflection part or calculation of every polarized bidirectional reflection distribution function (pBRDF) matrix element. Aluminum is chosen to be the sample to prove the principle of this method, and the result shows that this method can estimate the complex index of refraction more precisely compared with the Hyde method. The result further shows that the estimation index containing elements related to circular polarization has better performance than the index only containing elements related to linear polarization. (C) 2022 Optica Publishing Group

关键词： Circular polarization Circular polarizers image processing algorithms Polarization Polarized light Refractive index

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Spectral and temporal multiplexing for multispectral fluorescence and reflectance imaging using two color sensors

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OPTICS EXPRESS 2017年第11期25卷 12812-12829页

作者： Dimitriadis, Nikolas Grychtol, Bartlomiej Theuring, Martin Behr, Tobias Sippel, Christian Deliolanis, Nikolaos C. Fraunhofer Inst Mfg Engn & Automat Project Grp Automat Med & Biotechnol Theodor Kutzer Ufer 1-3 D-68167 Mannheim Germany Heidelberg Univ Dept Phys & Astron Neuenheimer Feld 226 D-69120 Heidelberg Germany Heidelberg Univ Med Fac Mannheim Theodor Kutzer Ufer 1-3 D-68167 Mannheim Germany

Fluorescence imaging can reveal functional, anatomical or pathological features of high interest in medical interventions. We present a novel method to record and display in video rate multispectral color and fluorescence images over the visible and near infrared range. The fast acquisition in multiple channels is achieved through a combination of spectral and temporal multiplexing in a system with two standard color sensors. Accurate color reproduction and high fluorescence unmixing performance are experimentally demonstrated with a prototype system in a challenging imaging scenario. Through spectral simulation and optimization we show that the system is sensitive to all dyes emitting in the visible and near infrared region without changing filters and that the SNR of multiple unmixed components can be kept high if parameters are chosen well. We propose a sensitive per-pixel metric of unmixing quality in a single image based on noise propagation and present a method to visualize the high-dimensional data in a 2D graph, where up to three fluorescent components can be distinguished and segmented. (C) 2017 Optical Society of America

关键词： image processing image processing algorithms image quality Imaging systems Imaging techniques Spectroscopy

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