1. 1-24 of 197 1 2 3 4 5 6 7 8 9 »
    1. Analysis of the possibility of upscaling based on apodization for partially coherent optical systems in the presence of aberrations

      Analysis of the possibility of upscaling based on apodization for partially coherent optical systems in the presence of aberrations

      The degree of coherence of radiation is an important characteristic on which the interference properties of light fields and, as a consequence, the resolution of optical systems depend. When propagating over long distances even in free space, initially completely coherent or incoherent radiation becomes partially coherent. This fact should be taken into account in the formation of optical images along with the influence of wave front aberrations. In this paper, we investigate the change in the resolution of the system for two near-point light sources depending on the degree of spatial coherence in the presence of different aberrations. The possibility ...

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    2. Low cost scalable monolithic common path probe design for the application in endoscopic optical coherence tomography

      Low cost scalable monolithic common path probe design for the application in endoscopic optical coherence tomography

      Endoscopic optical coherence tomography is an interference based imaging technique which due to its micron level resolution ability found several applications in medical diagnostics. However, the standard image performance suffers from artefacts caused by dispersion imbalance and polarisation mismatches between reference and sample arm. Such artefacts can be minimised with the use of a special class of probes called common path probes where the reference surface is placed in the vicinity of the sample. Previously reported common path probes suffered from a compromise between sensitivity and resolution. In most cases, proposed probes were not scalable for industrial applications and required ...

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    3. Numerical investigation on coherent mid-infrared supercontinuum generation in chalcogenide PCFs with near zero flattened all-normal dispersion profiles

      Numerical investigation on coherent mid-infrared supercontinuum generation in chalcogenide PCFs with near zero flattened all-normal dispersion profiles

      We present a novel design of all-normal flat near zero dispersion chalcogenide photonics crystal fiber (PCF) for mid-infrared supercontinuum (SC) generation. The proposed PCF with a core made of As<sub>2</sub>Se<sub>3</sub> glass and uniform air holes in the cladding is selectively filled with As<sub>2</sub>S<sub>5</sub> glass. By carefully engineering the PCF with an all-normal flat near zero dispersion profile, the anomalous-dispersion soliton effects are reduced, enabling broadband highly coherent SC generation. We also investigate the impacts of the pulse parameters on the SC generation. Broadband SCs covering 1 ...

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    4. Highly coherent supercontinuum generation in CS2 infiltrated single-core optical fiber

      Highly coherent supercontinuum generation in CS2 infiltrated single-core optical fiber

      As is generally known, broad-band near-infrared Supercontinuum (SC) is significant for the applications such as pump-probe spectroscopy, nonlinear spectroscopy, frequency combs, or nonlinear optical parametric amplification. We present the first detailed demonstration of approximate near-infrared, octave-spanning SC generation in all-normal dispersion CS2 single-hole liquid core optical fiber (LCOF). By solving the generalized nonlinear Schrödinger equation, the SC at different parameters can be calculated. The influence of important parameters including but not limited to fiber core-diameter, pump wavelength, pump power, and pulse width, on the supercontinuum generation (SCG) of CS2 infiltrated LCOF can be analyzed for optimization of near-infrared SC ...

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    5. Classification of human stomach cancer using morphological feature analysis from optical coherence tomography images

      Classification of human stomach cancer using morphological feature analysis from optical coherence tomography images

      Optical coherence tomography is radiation-free, and it is considered a tool of optical biopsy. Classification of normal and cancerous tissues is very important for the guidance of surgeons. Here, we develop the morphological feature analysis-based classification (MFAC) method, combining it with machine learning to identify cancerous tissues. We extract five quantitative morphological features from one OCT image through the structured analysis. Five classifiers are involved to make a classification: the support vector machine, the K -nearest neighbor, the random forest, logic regression, and the conventional threshold method. Sensitivity, specificity, and accuracy are used to evaluate these classifiers and are compared ...

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    6. Spectral calibration for spectral domain optical coherence tomography based on B-scan Doppler shift with tissue images

      Spectral calibration for spectral domain optical coherence tomography based on B-scan Doppler shift with tissue images

      Abstract: We propose a simple method of linearizing spectral interference fringes of spectral domain optical coherence tomography (SD-OCT) based on B-scan Doppler frequency shift (DFS), which can be obtained by offsetting the laser beam from the pivot of a scanning mirror. We show that DFS is proportional to wavenumber. A DFS based calibration curve can be then extracted from either a single mirror image or multiple tissue images. By examining the convergence of the nonlinear coefficients of the DFS curve fitted with a polynomial equation, tissue images themselves can be used to linearize the wavenumber without requiring mirror images or ...

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      Mentions: Hui Wang
    7. DeSpecNet: a CNN-based method for speckle reduction in retinal optical coherence tomography images

      DeSpecNet: a CNN-based method for speckle reduction in retinal optical coherence tomography images

      Speckle is a major quality degrading factor in optical coherence tomography (OCT) images. In this work we propose a new deep learning network for speckle reduction in retinal OCT images, termed DeSpecNet. Unlike traditional algorithms, the model can learn from training data instead of manually selecting parameters such as noise level. The proposed deep convolutional neural network (CNN) applies strategies including residual learning, shortcut connection, batch normalization and leaky rectified linear units to achieve good despeckling performance. Application of the proposed method to the OCT images shows great improvement in both visual quality and quantitative indices. The proposed method provides ...

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    8. Photothermal optical coherence tomography for investigation and imaging photothermal trapping of gold nano-rods in clear media and biological tissue

      Photothermal optical coherence tomography for investigation and imaging photothermal trapping of gold nano-rods in clear media and biological tissue

      A quantitative spectrometer-based photothermal optical coherence tomography (PT-OCT) system is employed to investigate and image the photothermal trapping of gold nano-rods (GNRs) in clear and biological media. The PT-OCT system is calibrated through dynamic phase measurements of piezo motion with known driving parameters. We measure and compare the displacement sensitivities of the PT-OCT system at different camera exposure time settings in two configurations: with a distinct reference path; and with a common path. The displacement sensitivity of the system in the common path configuration is improved from 1.5 nm to 0.17 nm by performing Fourier analysis on the ...

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    9. Semi-analytical full-wave model for simulations of scans in optical coherence tomography with accounting for beam focusing and the motion of scatterers

      Semi-analytical full-wave model for simulations of scans in optical coherence tomography with accounting for beam focusing and the motion of scatterers

      A full-wave model for simulating images in spectral-domain optical coherence tomography (OCT) with rigorous accounting for the beam-focusing effects is developed. Due to the analytical description of beam focusing, the model is computationally rather efficient. It also uses a rigorous numerical summation of the contributions of the localized sub-resolution scatterers, accounting for variations in the phase-amplitude parameters of the incident and backscattered optical waves, with a subsequent integration of the latter over the objective aperture. In the limit of a weakly focused beam, the developed model has allowed for the validatation of the earlier proposed simplified model with a constant-radius ...

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    10. A simple setup for measurement of coherence length of a laser diode using holographic optics

      A simple setup for measurement of coherence length of a laser diode using holographic optics

      Due to improvement in technology of laser diodes, now-a-days these have become an integral part of most of the physics and engineering undergraduate courses. Laser diodes, which generally have low coherence, are extensively used in various educational experiments due to their compactness, easy-to-operate and easy-to-handle as well as cost-effectiveness. Thus, knowledge about coherence length of beams from these laser diodes becomes important while designing experiments using these as light sources. Generally, students find it difficult to measure coherence length with most of the existing techniques. In present work an experimental arrangement using holographic optics is designed and demonstrated to measure ...

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    11. High-speed measurements in optical low-coherence reflectometry

      High-speed measurements in optical low-coherence reflectometry

      A high-speed, depth optical scanner with a longitudinal scan speed of up to and repetition rate of 28.5 kHz was designed. Optical low-coherence reflectometry is used in this non-contacting depth scanning method. A Michelson interferometer uses a glass cube which rotates at a speed of 427 000 rpm as an optical path length variation. Details of the adopted design, the precision glass cube positioning system (tripod), the experimental set-up, and some experimental results are discussed. This technique is especially well suited for biomedical applications in the field of optical tomography of tissues, e.g. skin, retina, etc where motion ...

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    12. Effect of solvent lamination on roll-to-roll hot-embossed PMMA microchannels evaluated by optical coherence tomography

      Effect of solvent lamination on roll-to-roll hot-embossed PMMA microchannels evaluated by optical coherence tomography

      Manufacturing of microfluidic based diagnostic devices requires small tolerances and uniform quality to guarantee reliable and repeatable test results. This work describes characterization of morphological changes that occur to a hot embossed PMMA microfluidic channel after solvent lamination with a PMMA lid. A non-contact cross-sectional analysis of the lidded microfluidic device was performed by optical coherence tomography (OCT). The solvent induced morphology change led to a porous structure in bottom corners of hot-embossed channels, which allowed a fluid to absorb in the material. The measurements of solvent diffusion showed faster diffusion rate at the corners of the channel, in which ...

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    13. Toward optical coherence tomography angiography-based biomarkers to assess the safety of peripheral nerve electrostimulation

      Toward optical coherence tomography angiography-based biomarkers to assess the safety of peripheral nerve electrostimulation

      Objective: Peripheral nerves serve as a link between the central nervous system and its targets. Altering peripheral nerve activity through targeted electrical stimulation is being investigated as a therapy for modulating end organ function. To support rapid advancement in the field, novel approaches to predict and prevent nerve injury resulting from the electrical stimulation must be developed to overcome the limitations of traditional histological methods. The present study aims to develop an optical imaging-based approach for real-time assessment of peripheral nerve injury associated with electrical stimulation.&#13; &#13; Approach: We developed an optical coherence tomography angiography system and a 3-D ...

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    14. Development of a broadband superluminescent diode based on self-assembled InAs quantum dots and demonstration of high-axial-resolution optical coherence tomography imaging

      Development of a broadband superluminescent diode based on self-assembled InAs quantum dots and demonstration of high-axial-resolution optical coherence tomography imaging

      We developed a near-infrared (NIR) superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) and demonstrated high-axial-resolution optical coherence tomography (OCT) imaging using this QD-based SLD (QD-SLD). The QD-SLD utilized InAs QDs with controlled emission wavelengths as a NIR broadband light emitter, and a tilted waveguide with segmented electrodes was prepared for edge-emitting broadband electroluminescence (EL) spanning approximately 1–1.3 μm. The bandwidth of the EL spectrum was increased up to 144 nm at a temperature of 25 °C controlled using a thermoelectric cooler. The inverse Fourier transform of the EL spectrum predicted a minimum resolution of 3 ...

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    15. Time-related ex vivo changes in the optical properties of normal brain tissues

      Time-related ex vivo changes in the optical properties of normal brain tissues

      The aim of the study was to observe time-related changes in the optical properties of normal brain tissues as measured using cross-polarization optical coherence tomography (CP OCT). 32 ex vivo tissue samples from 16 animals (rats) were monitored under different external conditions, over a period of 1 hour after excision, to measure time-related optical changes. It was found that the optical properties of white matter were quite stable over the time scales of the experiments, while the optical properties of the gray matter could change significantly. However, these changes could be minimized by using fresh sections from samples that had ...

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    16. Simultaneous multi-spatial scanning optical coherence tomography (OCT) based on spectrum-slicing of a broadband source

      Simultaneous multi-spatial scanning optical coherence tomography (OCT) based on spectrum-slicing of a broadband source

      This paper reports on the characterization of a novel multi-channel Optical Coherence Tomography (MC-OCT) method capable of concurrent scanning at multiple sites along the sample arm length of a low coherence interferometer. For this study, a cascade of two wavelength-based beam splitters is used to split the sample arm beam into three channels, forming three imaging (sensing) units. Channel-specific free-space beam paths are introduced in the sample arm to ensure equal optical path lengths amongst the different sensing beams and hence, a single reference reflector is employed for simultaneous interrogation of signals reflected from samples (or from different spots of ...

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    17. Precise delineation and tumor localization based on novel image registration strategy between optical coherence tomography and computed tomography in the radiotherapy of intraocular cancer

      Precise delineation and tumor localization based on novel image registration strategy between optical coherence tomography and computed tomography in the radiotherapy of intraocular cancer

      Radiation-associated toxicities due to sophisticated ocular anatomy and shape variability of organs at risk (OARs) are major concerns during external beam radiation therapy (EBRT) of patients with intraocular cancer. A novel two-step image registration strategy between optical coherence tomography (OCT) and computed tomography (CT) images was proposed and validated to precisely localize the target in the EBRT of patients with intraocular cancer. Specifically, multiple features from OCT and CT images were extracted automatically, then spatial transformation based on thin-plate spline function was performed iteratively to achieve feature alignment between the CT and OCT images. Finally, an exclusive OR (XOR) algorithm ...

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    18. Optical coherence angiography without motion correction preprocessing

      Optical coherence angiography without motion correction preprocessing

      The method for vessel visualization from optical coherence tomography (OCT) data is presented. The method is based on high-frequency filtration of the normalized absolute values of the scattered field measured with OCT. It is shown that in contrast with optical coherence angiography based on the processing of complex values of a scattered field, the proposed processing does not require motion correction preprocessing while providing resulting angiographic images of comparable quality.

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    19. Microvascular imaging of the skin

      Microvascular imaging of the skin

      Despite our understanding that the microvasculature plays a multifaceted role in the development and progression of various conditions, we know little about the extent of this involvement. A need exists for non-invasive, clinically meaningful imaging modalities capable of elucidating microvascular information to aid in our understanding of disease, and to aid in the diagnosis/monitoring of disease for more patient-specific care. In this review article, a number of imaging techniques are summarized that have been utilized to investigate the microvasculature of skin, along with their advantages, disadvantages and future perspectives in preclinical and clinical settings. These techniques include dermoscopy, capillaroscopy ...

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    20. All single-mode fiber-based polarization-sensitive spectral domain optical coherence tomography system

      All single-mode fiber-based polarization-sensitive spectral domain optical coherence tomography system

      We reported an all single-mode fiber (SMF)-based polarization sensitive spectral domain optical coherence tomography (PSSDOCT) system with single input polarization state (IPS). In our design, polarization state was modulated only by four polarization controllers (PC) and a polarization beam splitter. To extract the phase retardance and optical axis orientation of sample, the Mueller matrix of the fiber system and sample is transferred to a new retardar by employing PCs with the advantage that the effects of fiber birefringence of SMFs and SMF components are corrected. The contribution of the multibackscattering in tissues to the orthogonal polarization interference signals is ...

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    21. Ensemble classifier for improve diagnosis of the breast cancer using optical coherence tomography and machine learning

      Ensemble classifier for improve diagnosis of the breast cancer using optical coherence tomography and machine learning

      The second most leading cause of death in women is breast cancer even after surgery 20%–30% patients require re-surgery for the removal of the incomplete malignant tissue. To reduce the risk of recurrence exact navigation during surgery is essential. In this paper, a multi-level ensemble model is developed to classify the normal and cancerous breast tissue using features extracted from optical coherence tomography images. Both A-line and B-scan features were extracted and the training data feature space was best-first search to select the best feature subset for each base classifier. To improve the performance of the model reverse active ...

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    22. Three-dimensional texture analysis of optical coherence tomography images of ovarian tissue

      Three-dimensional texture analysis of optical coherence tomography images of ovarian tissue

      Ovarian cancer has the lowest survival rate among all gynecologic cancers due to predominantly late diagnosis. Optical Coherence Tomography (OCT) has been applied successfully to experimentally image the ovaries in vivo; however, a robust method for analysis is still required to provide quantitative diagnostic information. Recently, texture analysis has proved to be a useful tool for tissue characterization; unfortunately, existing work in the scope of OCT ovarian imaging is limited to only analyzing 2D sub-regions of the image data, discarding information encoded in the full image area, as well as in the depth dimension. Here we address these challenges by ...

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    23. Measurement of infrared optical constants with visible photons

      Measurement of infrared optical constants with visible photons

      We demonstrate a new scheme for infrared spectroscopy with visible light sources and detectors. The technique relies on the nonlinear interference of correlated photons, produced via spontaneous parametric down conversion in a nonlinear crystal. Visible and infrared photons are split into two paths and the infrared photons interact with the sample under study. The photons are reflected back to the crystal, resembling a conventional Michelson interferometer. Interference of the visible photons is observed and it is dependent on the phases of all three interacting photons: pump, visible and infrared. The transmission coefficient and the refractive index of the sample in ...

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    24. Spectrally tunable illumination system based on acousto-optic diffraction of light

      Spectrally tunable illumination system based on acousto-optic diffraction of light

      Spectrally tunable illumination is widely used for spectral imaging, spectroscopy, spectral-domain optical coherence tomography and other applications. Most of swept-wavelength light sources are based on mechanical change of narrow-band filters or on a supercontinuum laser coupled with a tunable filter. Such commercially available sources suffer either from a limited number of spectral channels or from a spatial noise caused by parasitic interferences. Here, we describe an alternative solution, which is free from the mentioned disadvantages and provides speckle-free uniform illumination. It is based on acousto-optic (AO) diffraction of a wide-band light. AO tunable filters (AOTFs) are fully software-controlled solid-state devices ...

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    1-24 of 197 1 2 3 4 5 6 7 8 9 »
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