Objective The widespread adoption of portable fundus cameras for primary care and community screening is hindered by limitations in current autofocus(AF)technologies.Image-based methods relying on sharpness evaluation...Objective The widespread adoption of portable fundus cameras for primary care and community screening is hindered by limitations in current autofocus(AF)technologies.Image-based methods relying on sharpness evaluation require iterative searches,resulting in slow convergence,while projection-based techniques are susceptible to optical artifacts and calibration errors.To address these challenges,this study introduces a novel AF system based on direct wavefront sensing,designed to deliver simultaneous high speed,high precision,and operational robustness within the compact form factor essential for portable ophthalmic devices.Methods Our approach fundamentally reimagines the AF process by directly measuring the ocular wavefront aberration.We developed a custom portable fundus camera integrating a miniaturized Shack-Hartmann wavefront sensor(SHWS)into the optical path.An 850 nm laser diode projects a point source onto the retina via oblique illumination to minimize corneal reflections.Light scattered from this spot carries the eye’s refractive error through the imaging optics and is directed to the SHWS,positioned at a plane optically conjugate to the primary color CMOS imaging sensor.A microlens array within the SHWS samples the incident wavefront,generating a pattern of focal spots on a CCD.Real-time centroid analysis of these spots provides a map of local wavefront slopes.These measurements are processed through a singular value decomposition(SVD)algorithm to fit a Zernike polynomial basis set,enabling real-time reconstruction of the wavefront phase.The defocus component(S)is extracted from the second-order Zernike coefficients,providing a direct,quantitative measure of the refractive error in diopters.This value serves as a precise error signal in a closed-loop control system,which commands a voice-coil actuated focusing lens to its null position in a single,deterministic step,eliminating the need for iterative search algorithms.Results Comprehensive evaluation demonstrated the system’s high performance.Testing on a calibrated model eye(OEMI-7)established a highly linear relationship between the computed defocus S and the focusing lens position across a±20 Diopter(D)compensation range,achievable within a 5 mm mechanical travel.The system achieved a focusing precision of 0.08 D,corresponding to an 18-fold improvement over a conventional projection spot-size method tested under identical conditions.The total focus acquisition time,encompassing wavefront measurement,computation,and lens actuation,averaged under 0.5 s.Clinical validation with 25 human volunteers(50 eyes,refractive range-15 D to+10 D)confirmed practical efficacy.The wavefront-sensing AF succeeded in 92%of attempts with a mean time of 0.5 s,substantially outperforming a projection-based benchmark which achieved only a 32%success rate with an average time of 4.25 s.The system provided instantaneous directional guidance and maintained stability during minor ocular movements.Objective assessment of image quality,via amplitude contrast of retinal vasculature,showed consistent and significant enhancement following AF correction across the entire tested diopter range.Conclusion This work successfully implements and validates a direct wavefront-sensing autofocus paradigm for portable fundus cameras.By directly quantifying and compensating for the optical defocus aberration,this method bypasses the fundamental limitations of image-processing and projection-based techniques,enabling rapid,precise,and deterministic diopter compensation.The developed system delivers an exceptional combination of a wide operational range(±20 D),high accuracy(0.08 D),fast convergence(0.5 s),and a compact physical footprint.This technology provides a practical and highperformance focusing solution capable of enhancing the reliability,throughput,and diagnostic utility of portable retinal imaging in large-scale screening applications.Future efforts will be directed towards system cost optimization and performance adaptation for diverse ocular conditions.展开更多
A cross-scale composite wavefront measurement method based on deep learning is proposed to address local large gradient wavefront distortions from aero-optical effects.Since dynamic range and spatial resolution are us...A cross-scale composite wavefront measurement method based on deep learning is proposed to address local large gradient wavefront distortions from aero-optical effects.Since dynamic range and spatial resolution are usually a trade-off for most wavefront sensors,we propose a hybrid Shack-Hartmann-digital holographic wavefront sensing mechanism that includes a Shack-Hartmann wavefront sensor(SHWFS)and off-axis digital holography(OADH).Using the hybrid wavefront sensing mechanism and the data processing method,the reconstructed wavefront of SHWFS and the wrapped phase of OADH are obtained separately.A multi-input efficient network cal ed the multi-system wavefront measurement-net(MSWM-Net)with an attention mechanism is introduced to map the reconstructed wavefront of SHWFS and the wrapped phase of the OADH to the precise wavefront.Numerical simulations and comparisons with the deep learning phase unwrapping(DLPU)-model-based phase unwrapping method and classical phase unwrapping technique demonstrate that this method resolves the chal enge of mismatched data scales across the two measurement systems,enabling rapid and high-precision wavefront sensing.展开更多
The widely used Shack-Hartmann wavefront sensor(SHWFS)is a wavefront measurement system.Its measurement accuracy is limited by the reference wavefront used for calibration and also by various residual errors of the se...The widely used Shack-Hartmann wavefront sensor(SHWFS)is a wavefront measurement system.Its measurement accuracy is limited by the reference wavefront used for calibration and also by various residual errors of the sensor itself.In this study,based on the principle of spherical wavefront calibration,a pinhole with a diameter of 1μm was used to generate spherical wavefronts with extremely small wavefront errors,with residual aberrations of 1.0×10^(−4)λRMS,providing a high-accuracy reference wavefront.In the first step of SHWFS calibration,we demonstrated a modified method to solve for three important parameters(f,the focal length of the microlens array(MLA),p,the sub-aperture size of the MLA,and s,the pixel size of the photodetector)to scale the measured SHWFS results.With only three iterations in the calculation,these parameters can be determined as exact values,with convergence to an acceptable accuracy.For a simple SHWFS with an MLA of 128×128 sub-apertures in a square configuration and a focal length of 2.8 mm,a measurement accuracy of 5.0×10^(−3)λRMS was achieved across the full pupil diameter of 13.8 mm with the proposed spherical wavefront calibration.The accuracy was dependent on the residual errors induced in manufacturing and assembly of the SHWFS.After removing these residual errors in the measured wavefront results,the accuracy of the SHWFS increased to 1.0×10^(−3)λRMS,with measured wavefronts in the range ofλ/4.Mid-term stability of wavefront measurements was confirmed,with residual deviations of 8.04×10^(−5)λPV and 7.94×10^(−5)λRMS.This study demonstrates that the modified calibration method for a high-accuracy spherical wavefront generated from a micrometer-scale pinhole can effectively improve the accuracy of an SHWFS.Further accuracy improvement was verified with correction of residual errors,making the method suitable for challenging wavefront measurements such as in lithography lenses,astronomical telescope systems,and adaptive optics.展开更多
The Shack-Hartmann wavefront sensor(SHWS)is widely used for high-speed,precise,and stable wavefront measurements.However,conventional SHWSs encounter a limitation in that the focused spot from each microlens is restri...The Shack-Hartmann wavefront sensor(SHWS)is widely used for high-speed,precise,and stable wavefront measurements.However,conventional SHWSs encounter a limitation in that the focused spot from each microlens is restricted to a single microlens,leading to a limited dynamic range.Herein,we propose an adaptive spot matching(ASM)-based SHWS to extend the dynamic range.This approach involves seeking an incident wavefront that best matches the detected spot distribution by employing a Hausdorff-distance-based nearest-distance matching strategy.The ASM-SHWS enables comprehensive spot matching across the entire imaging plane without requiring initial spot correspondences.Furthermore,due to its global matching capability,ASM-SHWS can maintain its capacity even if a portion of the spots are missing.Experiments showed that the ASM-SHWS could measure a high-curvature spherical wavefront with a local slope of 204.97 mrad,despite a 12.5%absence of spots.This value exceeds that of the conventional SHWS by a factor of 14.81.展开更多
Understanding the flame structure for different combustion in industries has drawn the increasing attention around the world.Particularly,for increasing the recent interest of using the hydrogen fuelled vehicles in re...Understanding the flame structure for different combustion in industries has drawn the increasing attention around the world.Particularly,for increasing the recent interest of using the hydrogen fuelled vehicles in recent world,structural analysis of flame in combustion chamber has attracted the attention of researchers.However,the high flame temperature and strong flame emissions increase the experimental difficulties,especially,in all kinds of intrusive measurement systems for determining the flame structures and flame temperatures.Therefore,a non-intrusive laser interferometer technique based on Shack-Hartmann optical system has been proposed to measure the thermal characteristic of a flame structure.In the present study,a low-stretched diffusion flame of methanol burner has been used.Shack-Hartmann optical system is a type of wave front sensor.It is commonly used in adaptive optical systems.It consists of an array of lenses to focus the image onto a photon sensor (photo-detector) at the focal plane and measures the wave front tilt.The major objective of the present study is to develop a laser interferometer measurement technique for analyzing the flame structure and its temperature propagation by measuring the density gradient of the flame.Optical interferometer technique is a potential candidate for the non-invasive measurement.In the present paper,a novel method for the measurement of density gradient in flame by using Shack-Hartmann optical system is proposed.A collimated laser beam that has been passed through the flame is tilted due to the density gradient inside the flame.A CCD camera (CCD photo sensor) has been used to observe the wave front tilts at the focal plane.展开更多
文摘Objective The widespread adoption of portable fundus cameras for primary care and community screening is hindered by limitations in current autofocus(AF)technologies.Image-based methods relying on sharpness evaluation require iterative searches,resulting in slow convergence,while projection-based techniques are susceptible to optical artifacts and calibration errors.To address these challenges,this study introduces a novel AF system based on direct wavefront sensing,designed to deliver simultaneous high speed,high precision,and operational robustness within the compact form factor essential for portable ophthalmic devices.Methods Our approach fundamentally reimagines the AF process by directly measuring the ocular wavefront aberration.We developed a custom portable fundus camera integrating a miniaturized Shack-Hartmann wavefront sensor(SHWS)into the optical path.An 850 nm laser diode projects a point source onto the retina via oblique illumination to minimize corneal reflections.Light scattered from this spot carries the eye’s refractive error through the imaging optics and is directed to the SHWS,positioned at a plane optically conjugate to the primary color CMOS imaging sensor.A microlens array within the SHWS samples the incident wavefront,generating a pattern of focal spots on a CCD.Real-time centroid analysis of these spots provides a map of local wavefront slopes.These measurements are processed through a singular value decomposition(SVD)algorithm to fit a Zernike polynomial basis set,enabling real-time reconstruction of the wavefront phase.The defocus component(S)is extracted from the second-order Zernike coefficients,providing a direct,quantitative measure of the refractive error in diopters.This value serves as a precise error signal in a closed-loop control system,which commands a voice-coil actuated focusing lens to its null position in a single,deterministic step,eliminating the need for iterative search algorithms.Results Comprehensive evaluation demonstrated the system’s high performance.Testing on a calibrated model eye(OEMI-7)established a highly linear relationship between the computed defocus S and the focusing lens position across a±20 Diopter(D)compensation range,achievable within a 5 mm mechanical travel.The system achieved a focusing precision of 0.08 D,corresponding to an 18-fold improvement over a conventional projection spot-size method tested under identical conditions.The total focus acquisition time,encompassing wavefront measurement,computation,and lens actuation,averaged under 0.5 s.Clinical validation with 25 human volunteers(50 eyes,refractive range-15 D to+10 D)confirmed practical efficacy.The wavefront-sensing AF succeeded in 92%of attempts with a mean time of 0.5 s,substantially outperforming a projection-based benchmark which achieved only a 32%success rate with an average time of 4.25 s.The system provided instantaneous directional guidance and maintained stability during minor ocular movements.Objective assessment of image quality,via amplitude contrast of retinal vasculature,showed consistent and significant enhancement following AF correction across the entire tested diopter range.Conclusion This work successfully implements and validates a direct wavefront-sensing autofocus paradigm for portable fundus cameras.By directly quantifying and compensating for the optical defocus aberration,this method bypasses the fundamental limitations of image-processing and projection-based techniques,enabling rapid,precise,and deterministic diopter compensation.The developed system delivers an exceptional combination of a wide operational range(±20 D),high accuracy(0.08 D),fast convergence(0.5 s),and a compact physical footprint.This technology provides a practical and highperformance focusing solution capable of enhancing the reliability,throughput,and diagnostic utility of portable retinal imaging in large-scale screening applications.Future efforts will be directed towards system cost optimization and performance adaptation for diverse ocular conditions.
基金supported by the National Natural Science Foundation of China(No.62305343)the Fund of the National Key Laboratory of Adaptive Optics(No.FNLAO-24-MS-S07)。
文摘A cross-scale composite wavefront measurement method based on deep learning is proposed to address local large gradient wavefront distortions from aero-optical effects.Since dynamic range and spatial resolution are usually a trade-off for most wavefront sensors,we propose a hybrid Shack-Hartmann-digital holographic wavefront sensing mechanism that includes a Shack-Hartmann wavefront sensor(SHWFS)and off-axis digital holography(OADH).Using the hybrid wavefront sensing mechanism and the data processing method,the reconstructed wavefront of SHWFS and the wrapped phase of OADH are obtained separately.A multi-input efficient network cal ed the multi-system wavefront measurement-net(MSWM-Net)with an attention mechanism is introduced to map the reconstructed wavefront of SHWFS and the wrapped phase of the OADH to the precise wavefront.Numerical simulations and comparisons with the deep learning phase unwrapping(DLPU)-model-based phase unwrapping method and classical phase unwrapping technique demonstrate that this method resolves the chal enge of mismatched data scales across the two measurement systems,enabling rapid and high-precision wavefront sensing.
基金supported by the National Key Research and Development Program of China(2021YFF0700700)the National Natural Science Foundation of China(62075235)+2 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2019320)Entrepreneurship and Innovation Talents in Jiangsu Province(Innovation of Scientific Research Institutes)the Jiangsu Provincial Key Research and Development Program(BE2019682).
文摘The widely used Shack-Hartmann wavefront sensor(SHWFS)is a wavefront measurement system.Its measurement accuracy is limited by the reference wavefront used for calibration and also by various residual errors of the sensor itself.In this study,based on the principle of spherical wavefront calibration,a pinhole with a diameter of 1μm was used to generate spherical wavefronts with extremely small wavefront errors,with residual aberrations of 1.0×10^(−4)λRMS,providing a high-accuracy reference wavefront.In the first step of SHWFS calibration,we demonstrated a modified method to solve for three important parameters(f,the focal length of the microlens array(MLA),p,the sub-aperture size of the MLA,and s,the pixel size of the photodetector)to scale the measured SHWFS results.With only three iterations in the calculation,these parameters can be determined as exact values,with convergence to an acceptable accuracy.For a simple SHWFS with an MLA of 128×128 sub-apertures in a square configuration and a focal length of 2.8 mm,a measurement accuracy of 5.0×10^(−3)λRMS was achieved across the full pupil diameter of 13.8 mm with the proposed spherical wavefront calibration.The accuracy was dependent on the residual errors induced in manufacturing and assembly of the SHWFS.After removing these residual errors in the measured wavefront results,the accuracy of the SHWFS increased to 1.0×10^(−3)λRMS,with measured wavefronts in the range ofλ/4.Mid-term stability of wavefront measurements was confirmed,with residual deviations of 8.04×10^(−5)λPV and 7.94×10^(−5)λRMS.This study demonstrates that the modified calibration method for a high-accuracy spherical wavefront generated from a micrometer-scale pinhole can effectively improve the accuracy of an SHWFS.Further accuracy improvement was verified with correction of residual errors,making the method suitable for challenging wavefront measurements such as in lithography lenses,astronomical telescope systems,and adaptive optics.
基金supported by the Fundamental Research Funds for the Central Universities of Shanghai Jiao Tong University and the Shanghai Jiao Tong University 2030 Initiative(No.WH510363001-10)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(No.SL2022ZD205)+1 种基金the Science Foundation of the Donghai Laboratory(No.DH-2022KF01001)National Natural Science Foundation of China(No.62205189).
文摘The Shack-Hartmann wavefront sensor(SHWS)is widely used for high-speed,precise,and stable wavefront measurements.However,conventional SHWSs encounter a limitation in that the focused spot from each microlens is restricted to a single microlens,leading to a limited dynamic range.Herein,we propose an adaptive spot matching(ASM)-based SHWS to extend the dynamic range.This approach involves seeking an incident wavefront that best matches the detected spot distribution by employing a Hausdorff-distance-based nearest-distance matching strategy.The ASM-SHWS enables comprehensive spot matching across the entire imaging plane without requiring initial spot correspondences.Furthermore,due to its global matching capability,ASM-SHWS can maintain its capacity even if a portion of the spots are missing.Experiments showed that the ASM-SHWS could measure a high-curvature spherical wavefront with a local slope of 204.97 mrad,despite a 12.5%absence of spots.This value exceeds that of the conventional SHWS by a factor of 14.81.
文摘Understanding the flame structure for different combustion in industries has drawn the increasing attention around the world.Particularly,for increasing the recent interest of using the hydrogen fuelled vehicles in recent world,structural analysis of flame in combustion chamber has attracted the attention of researchers.However,the high flame temperature and strong flame emissions increase the experimental difficulties,especially,in all kinds of intrusive measurement systems for determining the flame structures and flame temperatures.Therefore,a non-intrusive laser interferometer technique based on Shack-Hartmann optical system has been proposed to measure the thermal characteristic of a flame structure.In the present study,a low-stretched diffusion flame of methanol burner has been used.Shack-Hartmann optical system is a type of wave front sensor.It is commonly used in adaptive optical systems.It consists of an array of lenses to focus the image onto a photon sensor (photo-detector) at the focal plane and measures the wave front tilt.The major objective of the present study is to develop a laser interferometer measurement technique for analyzing the flame structure and its temperature propagation by measuring the density gradient of the flame.Optical interferometer technique is a potential candidate for the non-invasive measurement.In the present paper,a novel method for the measurement of density gradient in flame by using Shack-Hartmann optical system is proposed.A collimated laser beam that has been passed through the flame is tilted due to the density gradient inside the flame.A CCD camera (CCD photo sensor) has been used to observe the wave front tilts at the focal plane.
