The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase ...The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.展开更多
Wavefront shaping(WFS)techniques have been used as a powerful tool to control light propagation in complex media,including multimode fibers.In this paper,we propose a new application of WFS for multimode fber-based se...Wavefront shaping(WFS)techniques have been used as a powerful tool to control light propagation in complex media,including multimode fibers.In this paper,we propose a new application of WFS for multimode fber-based sensors.The use of a single multimode fiber alone,without any special fabrication,as a sensor based on the light intensity variations is not an easy task.The twist effect on multimode fiber is used as an example herein.Experimental results show that light intensity through the multimode fiber shows no direct relationship with the twist angle,but the correlation coefficient(CC)of speckle patterns does.Moreover,if WFS is applied to transform the spatially seemingly random light pattern at the exit of the multimode fiber into an optical focus.The focal pattern correlation and intensity both can serve to gauge the twist angle,with doubled measurement range and allowance of using a fast point detector to provide the feedback.With further development,WFS may find potentials to facilitate the development of multimode fber-based sensors in a variety of scenarios.展开更多
A simple method to objectively and simultaneously measure eye's longitudinal and transverse chromatic aberrations was proposed.A dual-wavelength wavefront measurement system using two Hartmann-Shack wavefront sens...A simple method to objectively and simultaneously measure eye's longitudinal and transverse chromatic aberrations was proposed.A dual-wavelength wavefront measurement system using two Hartmann-Shack wavefront sensors was developed.The wavefronts of the red(639.1 nm)and near-infrared(786.0 nm)lights were measured simultaneously for different positions in the model eye.The chromatic wavefronts were converted into Zernike polynomials.The Zernike tilt cofficient(irst term)was used to calculate the transverse chromatic aberration along the ax-direction,while the Zernike defocus coefficient(fourth term)was used to calculate the longi-tudinal chromatic aberration.The measurement and simulation data were consistent.展开更多
High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness ...High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness of the target changes in a large scale,the fixed electron multiplying（EM） gain will not be suited to the sensing limitation.Therefore an auto-gain-control method based on the brightness of light-spots array in S–H WFS is proposed in this paper.The control value is the average of the maximum signals of every light spot in an array,which has been demonstrated to be kept stable even under the influence of some noise and turbulence,and sensitive enough to the change of target brightness.A goal value is needed in the control process and it is predetermined based on the characters of EMCCD.Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust,the sensing SNR reaches the maximum for the corresponding signal level,and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band.展开更多
A numerical simulation model of plenoptic sensor aberration wavefront detection is established to simulate and analyze the detection performance of plenoptic sensor aberration wavefront for different turbulence intens...A numerical simulation model of plenoptic sensor aberration wavefront detection is established to simulate and analyze the detection performance of plenoptic sensor aberration wavefront for different turbulence intensities.The results show that the plenoptic sensor can achieve better distortion wavefront detection,and its wavefront detection accuracy improves with turbulence intensity.The unique optical structure design of the plenoptic sensor makes it more suitable for aberration wavefront detection in strong turbulent conditions.The wavefront detection performance of the plenoptic sensor is not only related to its wavefront reconstruction algorithm but also closely related to its structural parameter settings.The influence of structural parameters on the wavefront detection accuracy of plenoptic sensors under different turbulence intensities is simulated and analyzed.The variation law of wavefront detection accuracy and structural parameters under different turbulence intensities is summarized to provide a reference for the structural design and parameter optimization of plenoptic sensors.展开更多
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
文摘The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.
基金supported by the Shenzhen Science and Technology Innovation Commission(No.JCYJ20170818104421564)the Hong Kong Innovation and Technology Commission(No.ITS/022/18)+1 种基金the Hong Kong Research Grant Council(No.25204416)the National Natural Science Foundation of China(Nos.81671726 and 81627805).
文摘Wavefront shaping(WFS)techniques have been used as a powerful tool to control light propagation in complex media,including multimode fibers.In this paper,we propose a new application of WFS for multimode fber-based sensors.The use of a single multimode fiber alone,without any special fabrication,as a sensor based on the light intensity variations is not an easy task.The twist effect on multimode fiber is used as an example herein.Experimental results show that light intensity through the multimode fiber shows no direct relationship with the twist angle,but the correlation coefficient(CC)of speckle patterns does.Moreover,if WFS is applied to transform the spatially seemingly random light pattern at the exit of the multimode fiber into an optical focus.The focal pattern correlation and intensity both can serve to gauge the twist angle,with doubled measurement range and allowance of using a fast point detector to provide the feedback.With further development,WFS may find potentials to facilitate the development of multimode fber-based sensors in a variety of scenarios.
基金National Science Foundation of China(NSFC)(61378064)the National High Technology Research and Development Program of China(2015AA020510).
文摘A simple method to objectively and simultaneously measure eye's longitudinal and transverse chromatic aberrations was proposed.A dual-wavelength wavefront measurement system using two Hartmann-Shack wavefront sensors was developed.The wavefronts of the red(639.1 nm)and near-infrared(786.0 nm)lights were measured simultaneously for different positions in the model eye.The chromatic wavefronts were converted into Zernike polynomials.The Zernike tilt cofficient(irst term)was used to calculate the transverse chromatic aberration along the ax-direction,while the Zernike defocus coefficient(fourth term)was used to calculate the longi-tudinal chromatic aberration.The measurement and simulation data were consistent.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174274,61205021,and 61405194)the State Key Laboratory of Applied Optics,Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences
文摘High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness of the target changes in a large scale,the fixed electron multiplying（EM） gain will not be suited to the sensing limitation.Therefore an auto-gain-control method based on the brightness of light-spots array in S–H WFS is proposed in this paper.The control value is the average of the maximum signals of every light spot in an array,which has been demonstrated to be kept stable even under the influence of some noise and turbulence,and sensitive enough to the change of target brightness.A goal value is needed in the control process and it is predetermined based on the characters of EMCCD.Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust,the sensing SNR reaches the maximum for the corresponding signal level,and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band.
基金the National Natural Science Foundation of China(No.61605223)the Strategic Priority Research Program of Chinese Academy of Sciences(No.614A010717)the Director Fund of Advanced Laser Technology Laboratory of Anhui Province(No.AHL2021ZR06)。
文摘A numerical simulation model of plenoptic sensor aberration wavefront detection is established to simulate and analyze the detection performance of plenoptic sensor aberration wavefront for different turbulence intensities.The results show that the plenoptic sensor can achieve better distortion wavefront detection,and its wavefront detection accuracy improves with turbulence intensity.The unique optical structure design of the plenoptic sensor makes it more suitable for aberration wavefront detection in strong turbulent conditions.The wavefront detection performance of the plenoptic sensor is not only related to its wavefront reconstruction algorithm but also closely related to its structural parameter settings.The influence of structural parameters on the wavefront detection accuracy of plenoptic sensors under different turbulence intensities is simulated and analyzed.The variation law of wavefront detection accuracy and structural parameters under different turbulence intensities is summarized to provide a reference for the structural design and parameter optimization of plenoptic sensors.
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.
