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Statistical Study of Intrinsic Parasitics in an SPAD-Based Integrated Fiber Optical Receiver
摘要： Recently, a fully integrated optical fiber receiver was reported based on single-photon avalanche diode detectors to reduce the sensitivity gap to the quantum limit. This was realized through an array of four detectors to overcome the parasitic effects dominated by afterpulsing which prevent a single detector from providing an acceptable performance to serve as an optical receiver. However, the array structure imposes an extra effect called “crosstalk,” which needs to be accurately characterized. Thanks to the memoryless nature of dark noise statistics, we present an effective method to investigate the intrinsic parasitic effects of the array based on an all-at-once dark noise measurement. The corresponding detection probabilities and delays versus excess bias voltage are obtained for different parasitics at all detectors. The results are used to model crosstalk and estimate the error probabilities required for bit error ratio analysis and structure optimization. The accuracy of the estimations is verified by experimental data.
关键词： detector dead time,dark count,Afterpulsing,optical receiver,crosstalk,single-photon avalanche diode (SPAD)
更新于2025-09-04 15:30:14
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A Comparison of Progressive Loss of the Ellipsoid Zone (EZ) Band in Autosomal Dominant and X-Linked Retinitis Pigmentosa
摘要： PURPOSE. In patients with retinitis pigmentosa (RP), the inner segment ellipsoid zone (EZ; also known as the inner segment/outer segment [IS/OS] border) is a marker of the usable visual ?eld at a given point in time and of the progression of the disease over time. Here we compare the change in the width per year of the EZ band in patients with autosomal dominant (ad) and x-linked (xl) RP. METHODS. Using optical coherence tomography (OCT), 9-mm horizontal and vertical line scans through the fovea were obtained for one eye of 26 xlRP patients and 33 adRP patients. Scans were repeated on average 2.0 years later (range, 0.6–4.8 years). Using a manual segmentation procedure, the EZ band was delineated and its horizontal width (HW) and vertical width (VW) were determined. RESULTS. The adRP and xlRP patients had similar initial EZ HW (xlRP: 11.8 6 5.48, adRP: 12.4 6 6.38, P ? 0.69) and VW (xlRP: 8.5 6 4.98, adRP: 11.4 6 7.18, P ? 0.09). However, between visits the absolute loss and percent loss of the EZ width per year was signi?cantly greater for xlRP than adRP for both HW (xlRP: 1.0 6 0.68/y, 9.6 6 5.6%/y; adRP: 0.4 6 0.58/y, 3.4 6 5.4%/y; P < 0.001) and VW (xlRP: 0.8 6 0.88/y, 9.2 6 8.9%/y; adRP: 0.3 6 0.58/y, 4.2 6 6.4%/y; P < 0.01). There was a weak correlation between the loss of EZ width per year and the initial width for xlRP (r2 ? 0.17, P ? 0.036), but no correlation for adRP (r2 ? 0.004, P ? 0.73). The test–retest difference of EZ HW was 0.2 6 0.58. CONCLUSIONS. The OCT data here support a faster rate of loss per year in the case of xlRP. (ClinicalTrials.gov number, NCT00100230.)
关键词： optical coherence tomography,retinitis pigmentosa,progression
更新于2025-09-04 15:30:14
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Lasing in optimized two-dimensional iron-nail-shaped rod photonic crystals
摘要： We demonstrated lasing at the Γ-point band-edge (BE) modes in optimized two-dimensional iron-nail-shaped rod photonic crystals by optical pulse pumping at room temperature. As the radius of the rod increased quadratically toward the edge of the pattern, the quality factor of the Γ-point BE mode increased up to three times, and the modal volume decreased to 56% compared with the values of the original Γ-point BE mode because of the reduction of the optical loss in the horizontal direction. Single-mode lasing from an optimized iron-nail-shaped rod array with an InGaAsP multiple quantum well embedded in the nail heads was observed at a low threshold pump power of 160 μW. Real-image-based numerical simulations showed that the lasing actions originated from the optimized Γ-point BE mode and agreed well with the measurement results, including the lasing polarization, wavelength, and near-field image.
关键词： optical pulse pumping,photonic crystals,iron-nail-shaped rod,lasing,band-edge modes
更新于2025-09-04 15:30:14
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A Comparative Study of Vertebrate Corneal Structure: The Evolution of a Refractive Lens
摘要： PURPOSE. Although corneal curvature plays an important role in determining the refractive power of the vertebrate eye, the mechanisms controlling corneal shape remain largely unknown. To address this question, we performed a comparative study of vertebrate corneal structure to identify potential evolutionarily based changes that correlate with the development of a corneal refractive lens. METHODS. Nonlinear optical (NLO) imaging of second-harmonic–generated (SHG) signals was used to image collagen and three-dimensionally reconstruct the lamellar organization in corneas from different vertebrate clades. RESULTS. Second-harmonic–generated images taken normal to the corneal surface showed that corneal collagen in all nonmammalian vertebrates was organized into sheets (?sh and amphibians) or ribbons (reptiles and birds) extending from limbus to limbus that were oriented nearly orthogonal (ranging from 77.78–88.28) to their neighbors. The slight angular offset (28–138) created a rotational pattern that continued throughout the full thickness in ?sh and amphibians and to the very posterior layers in reptiles and birds. Interactions between lamellae were limited to "sutural" ?bers in cartilaginous ?sh, and occasional lamellar branching in ?sh and amphibians. There was a marked increase in lamellar branching in higher vertebrates, such that birds (cid:2) reptiles > amphibians > ?sh. By contrast, mammalian corneas showed a nearly random collagen ?ber organization with no orthogonal, chiral pattern. CONCLUSIONS. Our data indicate that nonmammalian vertebrate corneas share a common orthogonal collagen structural organization that shows increased lamellar branching in higher vertebrate species. Importantly, mammalian corneas showed a different structural organization, suggesting a divergent evolutionary background.
关键词： stroma,nonlinear optical,collagen,cornea,second-harmonic generation
更新于2025-09-04 15:30:14
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Measurement of ultrafast dynamics of photoexcited carriers in <i>β</i> -Ga <sub/>2</sub> O <sub/>3</sub> by two-color optical pump-probe spectroscopy
摘要： We report results from ultrafast two-color optical pump-probe spectroscopy on bulk b-Ga2O3. A two-photon absorption scheme is used to photoexcite carriers with the pump pulse and free-carrier absorption of the probe pulse is used to record the subsequent dynamics of the photoexcited carriers. Our results are consistent with carrier recombination via defect-assisted processes. We also observe transient polarization-selective optical absorption of the probe pulse by defect states under nonequilibrium conditions. A rate equation model for electron and hole capture by defects is proposed and used to explain the data. Whereas the rate constants for electron capture by defects are found to be temperature-independent, they are measured to be strongly temperature-dependent for hole capture and point to a lattice deformation/relaxation process accompanying hole capture. Our results shed light on the mechanisms and rates associated with carrier capture by defects in b-Ga2O3.
关键词： two-color optical pump-probe spectroscopy,ultrafast dynamics,photoexcited carriers,carrier recombination,defect-assisted processes,β-Ga2O3
更新于2025-09-04 15:30:14
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Fluorescence quantum yield of CDOM in coastal zones of the Arctic seas
摘要： Along with traditional optical indices, calculated from absorption and ?uorescence spectra to describe chromophoric dissolved organic matter (CDOM) naturally occurring in water, the ?uorescence quantum yield (FQY) becomes signi?cant. Knowledge of CDOM optical properties is important for satellite remote sensing as well as for lidar ground-true measurements. The FQY as a function of excitation wavelength within 240–500 nm range for a variety of the Arctic shelf waters was determined for the ?rst time in order to identify the characteristic chromophores peculiar to di?erent regions of the Arctic basin a?ected by freshwater runo?. The surface water samples were collected during several cruises in 2015–2017 in the following sites: the mouth areas of the Khatanga and Lena Rivers (the Laptev Sea), the delta area of the Northern Dvina River (the White Sea), desalinated waters of the Kara Sea (in?uenced by freshwater of the Ob and Yenisei Rivers) and the East Siberian Sea (in?uenced by freshwaters of the Indigirka and Kolyma Rivers), as well the shelf areas of those seas not a?ected by terrigenous runo?. To characterize DOM, conventional optical indices SR, HIX, and BIX were calculated. In most cases, important humic character of DOM was established, while the contribution of autochthonous organic matter varied from low to intermediate level. For the samples with terrestrial impact, the FQY decreased from excitation at 240 nm to 270–280 nm and then increased, demonstrating two peaks at 340 and 380 nm, with constant decrease towards longer excitation wavelengths; at λex = 380 nm FQY varied from 1.4% to 3.1%. In some cases, additional maximum at 270 nm of FQY-excitation dependency was observed as an indicator of autochthonous nature of biological material. Minimal FQY was measured for the White Sea surface waters, the maximal for the Laptev and East Siberian seas.
关键词： optical properties,fluorescence quantum yield,CDOM,Arctic seas,remote sensing
更新于2025-09-04 15:30:14
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Optical coherence tomography imaging of the basal ganglia: feasibility and brief review
摘要： Optical coherence tomography (OCT) is a promising medical imaging technique that uses light to capture real-time cross-sectional images from biological tissues in micrometer resolution. Commercially available optical coherence tomography systems are employed in diverse applications, including art conservation and diagnostic medicine, notably in cardiology and ophthalmology. Application of this technology in the brain may enable distinction between white matter and gray matter, and obtainment of detailed images from within the encephalon. We present, herein, the in vivo implementation of OCT imaging in the rat brain striatum. For this, two male 60-day-old rats (Rattus norvegicus, Albinus variation, Wistar) were stereotactically implanted with guide cannulas into the striatum to guide a 2.7-French diameter high-definition OCT imaging catheter (Dragonfly, St. Jude Medical, USA). Obtained images were compared with corresponding histologically stained sections to collect imaging samples. A brief analysis of OCT technology and its current applications is also reported, as well as intra-cerebral OCT feasibility on brain mapping during neurosurgical procedures.
关键词： Basal ganglia,Optical coherence tomography (OCT),Rat brain,Histology,Thalamus,Brain imaging
更新于2025-09-04 15:30:14
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Investigation of gas discharge features during HiPIMS using optical emission spectroscopy
摘要： The paper presents the results of the investigation of the emission spectra of a gas discharge during high-power impulse magnetron sputtering (HiPIMS) of a titanium target at different power supply parameters. In such mode, the fraction of ionized atoms of the target material in the discharge increases significantly, what affects the properties of the deposited coatings. The characteristic features of the operation of the system in HiPIMS mode were singled out, and also the discharge spectra were compared at high-power impulse and conventional (sputtering on a direct current) operation modes of the magnetron. As a result of the study, it was shown that the use of optical emission spectroscopy during HiPIMS makes it possible to effectively determine the parameters of the stable operation of the system and determine the boundary at which a transition into high-power regime occurs.
关键词： titanium target,HiPIMS,gas discharge,magnetron sputtering,optical emission spectroscopy
更新于2025-09-04 15:30:14
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Novel Boundary Edge Detection for Accurate 3D Surface Profilometry Using Digital Image Correlation
摘要： Digital image correlation (DIC) has emerged as a popular full-field surface profiling technique for analyzing both in-plane and out-of-plane dynamic structures. However, conventional DIC-based surface 3D profilometry often yields erroneous contours along surface edges. Boundary edge detection remains one of the key issues in DIC because a discontinuous surface edge cannot be detected due to optical diffraction and height ambiguity. To resolve the ambiguity of edge measurement in optical surface profilometry, this study develops a novel edge detection approach that incorporates a new algorithm using both the boundary subset and corner subset for accurate edge reconstruction. A pre-calibrated gauge block and a circle target were reconstructed to prove the feasibility of the proposed approach. Experiments on industrial objects with various surface reflective characteristics were also conducted. The results showed that the developed method achieved a 15-fold improvement in detection accuracy, with measurement error controlled within 1%.
关键词： automated optical inspection (AOI),edge detection,digital image correlation (DIC),random speckle images,surface profilometry
更新于2025-09-04 15:30:14
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An Investigation of Optically Very Thin Ice Clouds from Ground-Based ARM Raman Lidars
摘要： Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Path?nder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Paci?c (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy pro?les from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds.
关键词： remote sensing,ice cloud detection,ice cloud optical depth,lidars
更新于2025-09-04 15:30:14