Aberration Correction Research Articles

Potential vision tester using adaptive optics, Maxwellian view, and small pupil.

We demonstrate a free-space, trolley-mounted potential vision tester (PVT), designed to study and improve the accuracy of visual acuity (VA) measurements in the aging eye. Key features include a high-resolution visual display presented in Maxwellian view, a 3 mm pupil to limit wavefront (WF) aberrations, and a moderate cost deformable mirror to induce or correct higher order optical aberrations. The visual display supported accurate measurement of visual acuities down to 20/5. The moderate cost, piezo deformable mirror induced seven nominal aberrations, calibrated as 0, -0.32, -0.23, + 0.27, and +0.39 microns spherical aberration; + 0.49 microns Y coma; and -0.51 microns X coma. A custom Hartmann Shack (HS) calibration (HSc) system demonstrated that induced aberrations were repeatable and stable. A Badal optometer provided the coarse focus. WF aberrations were measured for five normal subjects with a commercially available HS device (HSP) (OCULUS Pentacam AXL Wave), providing estimates of WF errors for 3 mm and other pupil sizes. VA was measured using four alternative forced-choice for a single black on white E stimulus in each trial. Using the method of constant stimuli yielded robust standard deviation measurements. The 50% fit for VA plotted against induced aberration resulted in linear functions for each subject for the range of our positive and negative spherical aberration data. Subjects differed, but higher order terms were unnecessary to describe data across spherical aberrations.

Tandem aberration correction optics (TACO) in wide-field structured illumination microscopy.

Structured illumination microscopy (SIM) is a powerful super-resolution imaging technique that uses patterned illumination to down-modulate high spatial-frequency information of samples. However, the presence of spatially-dependent aberrations can severely disrupt the illumination pattern, limiting the quality of SIM imaging. Conventional adaptive optics (AO) techniques that employ wavefront correctors at the pupil plane are not capable of effectively correcting these spatially-dependent aberrations. We introduce the Tandem Aberration Correction Optics (TACO) approach that combines both pupil AO and conjugate AO for aberration correction in SIM. TACO incorporates a deformable mirror (DM) for pupil AO in the detection path to correct for global aberrations, while a spatial light modulator (SLM) is placed at the plane conjugate to the aberration source near the sample plane, termed conjugate AO, to compensate spatially-varying aberrations in the illumination path. Our numerical simulations and experimental results show that the TACO approach can recover the illumination pattern close to an ideal condition, even when severely misshaped by aberrations, resulting in high-quality super-resolution SIM reconstruction. The TACO approach resolves a critical traditional shortcoming of aberration correction for structured illumination. This advance significantly expands the application of SIM imaging in the study of complex, particularly biological, samples and should be effective in other wide-field microscopies.

Optical fiber-integrated achromatic metalens based on catenary metasurfaces.

A challenge in all-fiber-integrated metasurface devices is to efficiently control dispersion in the limited fiber end area to build metasurfaces, therefore, the design of metasurfaces with a special structure becomes crucial to meet the demands of dispersion control. A unique phase response of circularly polarized light in catenary metasurfaces can offer new opportunities for polarization-sensitive arbitrary chromatic dispersion control. Herein, we proposed an optical achromatic metalens based on equal width catenary metasurfaces integrated on the large-mode optical fiber (LMF) end. To reduce phase distortions, the LMF is designed to generate quasi-plane waves (QPW), and then QPW converts from catenary metasurfaces to realize achromatic focusing. A notable feature of this device is its axial focal length shift as low as 0.09% across the working wavelength range from 1.33 µm to 1.55 µm, commonly used in optical fiber communication, demonstrating its excellent dispersion control capability. Furthermore, the device exhibits exceptional capabilities to break through the diffraction limit of the output field. This research has potential applications in the fields of achromatic devices, chromatic aberration correction, fiber lasers, and optical communication and modulation.

Atmospheric Turbulence Aberration Correction Based on Deep Learning Wavefront Sensing.

In this paper, research was conducted on Deep Learning Wavefront Sensing (DLWS) neural networks using simulated atmospheric turbulence datasets, and a novel DLWS was proposed based on attention mechanisms and Convolutional Neural Networks (CNNs). The study encompassed both indoor experiments and kilometer-range laser transmission experiments employing DLWS. In terms of indoor experiments, data were collected and training was performed on the platform built by us. Subsequent comparative experiments with the Shack-Hartmann Wavefront Sensing (SHWS) method revealed that our DLWS model achieved accuracy on par with SHWS. For the kilometer-scale experiments, we directly applied the DLWS model obtained from the indoor platform, eliminating the need for new data collection or additional training. The DLWS predicts the wavefront from the beacon light PSF in real time and then uses it for aberration correction of the emitted laser. The results demonstrate a substantial improvement in the average peak intensity of the light spot at the target position after closed-loop correction, with a remarkable increase of 5.35 times compared to the open-loop configuration.

Universal adaptive optics for microscopy through embedded neural network control

The resolution and contrast of microscope imaging is often affected by aberrations introduced by imperfect optical systems and inhomogeneous refractive structures in specimens. Adaptive optics (AO) compensates these aberrations and restores diffraction limited performance. A wide range of AO solutions have been introduced, often tailored to a specific microscope type or application. Until now, a universal AO solution – one that can be readily transferred between microscope modalities – has not been deployed. We propose versatile and fast aberration correction using a physics-based machine learning assisted wavefront-sensorless AO control (MLAO) method. Unlike previous ML methods, we used a specially constructed neural network (NN) architecture, designed using physical understanding of the general microscope image formation, that was embedded in the control loop of different microscope systems. The approach means that not only is the resulting NN orders of magnitude simpler than previous NN methods, but the concept is translatable across microscope modalities. We demonstrated the method on a two-photon, a three-photon and a widefield three-dimensional (3D) structured illumination microscope. Results showed that the method outperformed commonly-used modal-based sensorless AO methods. We also showed that our ML-based method was robust in a range of challenging imaging conditions, such as 3D sample structures, specimen motion, low signal to noise ratio and activity-induced fluorescence fluctuations. Moreover, as the bespoke architecture encapsulated physical understanding of the imaging process, the internal NN configuration was no-longer a “black box”, but provided physical insights on internal workings, which could influence future designs.

Direct design method for holographic grating imaging spectrometer and corresponding recording system

The combination of holographic gratings with freeform surface technology has led to a significant breakthrough in terms of the performance of imaging spectrometers. In this paper, a general direct design method that is capable of designing imaging spectrometers that include holographic gratings based on a complex-shaped surface substrate and their corresponding recording systems is proposed. The most important feature of this method is that the recording and imaging systems are designed within one optical system model, thus allowing for an optimal balance to be achieved between the aberration correction capability and the manufacturability of the holographic grating. To illustrate the effectiveness of the proposed method, three imaging spectrometers were designed that used holographic gratings manufactured by a recording system without auxiliary mirrors, a system with a spherical auxiliary mirror, and a system with a freeform auxiliary mirror. Ultimately, these three systems all achieved diffraction-limited imaging quality with minimal distortion.

Analysis and Optical System Design of the Lenslet-Array Integral Field Spectrometer

To address the problem of slit limitation in traditional slit imaging spectrometers, which hampers fast the identification, efficient tracking, and precise avoidance of faint targets in lunar orbit, this article proposes a lenslet-array integral field spectrometer structure that is free of slits, static, and that is fast and efficient for the visible-to-near-infrared wavelength band. Firstly, the field of view segmentation model is analyzed, and the requirement of the telecentric degree of the pre-imaging system is obtained. Secondly, the influence of aberrations, such as spherical aberration and coma distortion on the micro-pupil dispersion model is analyzed. Based on this, the pre-imaging system is designed to meet the requirements of aberration correction and the telecentricity of the system. Finally, the structure of the spectral system is designed, and the integrated system is optimized. The smile of the lenslet-array integral field spectrometer is ±1 nm, and the MTF is greater than 0.7 at 60 lp/mm and close to the diffraction limit.

Wideband Antennas of Passive Seekers for Anti Radiation Missiles

Suppression of Enemy Air Defence (SEAD) is a fundamental element of Air Power application by means of in protecting friendly air attackers and destroying the enemy’s ability to defend against air attack. Most of the SEAD operation even today relies on Anti-radiation missile (ARM) which is an air-to-surface tactical missile designed to detect, seek, attack and destroy opponent’s radar. Passive seeker of ARM is a miniaturized ESM receiver which is capable of extracting the necessary angular data from the enemy radar emissions. Single head passive seeker covering wide frequency range from L to Ku band is the preferred choice. Wideband antennas have been designed and utilized for Direction Finding applications of ESM/ELINT receivers for ground, air and ship borne platforms. Unlike these platforms, there are several restrictions for passive seeker based compact ESM receiver for missile borne platform specially air to surface missile where lesser diameter is one of the preferred design parameter. This review paper mainly discusses the existing wideband antennas such as spiral, log-periodic, printed circuit vivaldi and all-metal vivaldi antennas and the comparison of their various parameters for passive seeker. The paper also suggests their suitability with respect to their placement on the missile for three configurations: concealed inside the radome, flush-mounted and conformal antenna based. The paper also brought about the specific test facility required for testing and evaluation of passive seeker to characterize it with missile radome which is the most challenging and time consuming task. Among the three passive seeker configuration discussed, conformal antenna based passive seeker using all-metal Vivaldi is the best option avoiding radome aberration correction which is being utilized in the present third generations of ARM. The second commonly and established passive seeker configuration is concealed inside the radome using spiral antennas where handling radome aberration correction is a limitation.

Atomic-scale imaging of electron sensitive zeolites with aberration corrected transmission electron microscopy

The spatial resolution of transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs) has been drastically improved by introducing aberration correction. However, observable range in electron sensitive zeolites are still limited due to electron irradiation damages. Nevertheless, atomic resolution imaging of some zeolites is currently being realized by various developments in electron microscopic hardware, such as high sensitivity cameras. On the other hand, surveying the status of TEM and STEM imaging is very important for further progress in the structural analysis of zeolites. Here, we demonstrate and compare the high-resolution imaging of zeolites with several kinds of imaging modes.

Chalcogenide GRIN glasses with high refractive index and large refractive index difference for LWIR imaging.

Gradient refractive index (GRIN) materials utilize an internally tailored refractive index in combination with the designed curvature of the optical element surface, providing the optical designer with additional freedom for correcting chromatic and spherical aberrations. In this paper, new GRIN materials suitable for the second (3-5 µm) and third (8-12 µm) atmospheric windows were successfully developed by the thermal diffusion method based on Ge20As20Se60-xTex series high refractive index glasses, where the maximum refractive index difference (Δn) at 4 µm and 10.6 µm were 0.281 and 0.277, respectively. The diffusion characteristics and refractive index distribution of the GRIN glass were analyzed by Raman characterization. Furthermore, the performance of GRIN singlet and homogeneous singlet in the LWIR band (8 µm, 10.6 µm (primary wavelength), 12 µm) was compared, and the results showed that the GRIN singlet had better chromatic aberration correction and unique dispersion characteristics.

Design of Electrostatic Aberration Correctors for Scanning Transmission Electron Microscopy.

In a scanning transmission electron microscope (STEM), producing a high-resolution image generally requires an electron beam focused to the smallest point possible. However, the magnetic lenses used to focus the beam are unavoidably imperfect, introducing aberrations that limit resolution. Modern STEMs overcome this by using hardware aberration correctors comprised of many multipole elements, but these devices are complex, expensive, and can be difficult to tune. We demonstrate a design for an electrostatic phase plate that can act as an aberration corrector. The corrector is comprised of annular segments, each of which is an independent two-terminal device that can apply a constant or ramped phase shift to a portion of the electron beam. We show the improvement in image resolution using an electrostatic corrector. Engineering criteria impose that much of the beam within the probe-forming aperture be blocked by support bars, leading to large probe tails for the corrected probe that sample the specimen beyond the central lobe. We also show how this device can be used to create other STEM beam profiles such as vortex beams and probes with a high degree of phase diversity, which improve information transfer in ptychographic reconstructions.

Medical and technical aspects of using intraocular lenses with extended depth of field

Purpose: to analyse the medical and technical aspects of intraocular lenses (IOLs) with extended depth of field (EDOF). Literature analysis was performed in the PubMed international database, the search keywords being “IOL with extended depth of field” (EDOF), “Optical Bench Evaluation of IOL”, “Preclinical evaluation of IOL”, “Aberrations”, “Monofocal IOL” (MOFIOL), “Multifocal IOLs” (MUFIOL). A total of 226 sources were analyzed, further using systematic review filters and the authors' knowledge of the topic. The duration of the retrospective analysis was 7 years (2016–2022), some of the considered work dates back to 2023. Unlike MUFIOL, EDOF lenses create a single elongated focal point to increase the depth of field, rather than several foci. Thus, EDOFs are aimed at reducing light phenomena, glare and halos, the occurrence of which is characteristic of MUFIOL. A potential disadvantage of EDOF is the reduction in retinal image quality with an excessive increase in the number of aberrations. The factors of the medical and technical assessment of the IOL indicate a high correlation with the predicted visual acuity (VA). EDOFs, whose design features are based on a higher order aspherical design, provide comparable optical quality for the far and extended intermediate ranges, while producing halo effects comparable to those of MOFIOL. Designed to improve depth of field with a full correction of corneal spherical aberration, EDOF provides intermediate-level pupil-independent improvement in VA and maintains visual acuity unlike conventional MOFIOLs. The quality of visual perception and the predicted VA of various types of EDOFs depend on the optical technology and the correction of corneal spherical aberrations. EDOFs can be expected to provide adequate vision at an intermediate distance (with a possibility of insufficient near vision). At the same time, the expansion of the depth of field varies between models, which should be taken into account when preoperatively choosing EDOF for a specific type of daily visual activity of the patient, especially for people with visually strenuous work. The results of the medical and technical assessment are widely used in the clinical testing of specific types of EDOF IOLs.

Comparative Analysis of the Effect of Cutting Piezoelectric Ceramics on Optically Oriented Compensation Capability

In a photoelectric tracking system, a deformable mirror can be used to adjust the transmission path of a light beam to achieve accurate measurement and tracking of the target position. The single-piezoelectric-sheet deformable mirror is a commonly used wavefront correction device with outstanding advantages, such as its simple structure, low cost, and easy preparation. However, it usually has a large cross-linking value and a weak ability to correct higher-order wavefront aberrations. To solve this problem, a novel single-piezoelectric-sheet deformable mirror driving structure is proposed in this paper, in which the coupling between the driving units is weakened by laser cutting the piezoelectric ceramics along the electrode gaps to reduce the cross-linking value of the deformable mirror. In order to verify the effectiveness of this driving structure, this paper takes the 85-unit single-piezoelectric-sheet deformable mirror as an example and simulates the influence function for different cutting depth conditions. The simulation results show that the cross-linking value between neighboring drive units decreases significantly as the piezoelectric-ceramic-laser cutting depth of the drive electrode gap increases. When the piezoelectric ceramic was laser cut to a depth of half of the overall thickness, the cross-linking value decreased by 6.8%.

An efficient method for transcranial ultrasound focus correction based on the coupling of boundary integrals and finite elements

Transcranial focused ultrasound is a novel technique for the noninvasive treatment of brain diseases. The success of the treatment greatly depends on achieving precise and efficient intraoperative focus. However, compensating for aberrated ultrasound waves caused by the skull through numerical simulation-based phase corrections is a challenging task due to the significant computational burden involved in solving the acoustic wave equation. In this article, we propose a promising strategy using the coupling of the boundary integral equation method (BIEM) and the finite element method (FEM) to overcome the above limitation. Specifically, we adopt the BIEM to obtain the Robin-to-Dirichlet maps on the boundaries of the skull and then couple the maps to the FEM matrices via a dual interpolation technique, resulting in a computational domain including only the skull. Three simulation experiments were conducted to evaluate the effectiveness of the proposed method, including a convergence test and two skull-induced aberration corrections in 2D and 3D ultrasound. The results show that the method’s convergence is guaranteed as the element size decreases, leading to a decrease in pressure error. The computation times for simulating a 500 kHz ultrasound field on a regular desktop computer were found to be 0.47 ± 0.01 s in the 2D case and 43.72 ± 1.49 s in the 3D case, provided that lower–upper decomposition (approximately 13 s in 2D and 2.5 h in 3D) was implemented in advance. We also demonstrated that more accurate transcranial focusing can be achieved by phase correction compared to the noncorrected results (with errors of 1.02 mm vs. 6.45 mm in 2D and 0.28 mm vs. 3.07 mm in 3D). The proposed strategy is valuable for enabling online ultrasound simulations during treatment, facilitating real-time adjustments and interventions.

Analysis of Error Sources in the Lissajous Scanning Trajectory Based on Two-Dimensional MEMS Mirrors

Deviations or distortions in the trajectoy of MEMS-based Lissajous scanning imaging platforms might be detrimental to imaging quality. These deviations often arise from differences in MEMS mirror frequency response characteristics and asymmetry in parameters within the measurement and control circuit. This study concentrated on the measurement and control circuit unit as it identified and analyzed four error sources: the MEMS mirror frequency response error, the AD acquisition synchronization error, the drive source error, and the cross-coupling error between the MEMS mirror axes. This study constructed a Lissajous trajectory test platform based on oscilloscopes and a position sensitive detector. Consequently, its experimental results guided the error processing methods to access the feasibility of the compensation methods by combining measured trajectories. Overall, regarding MEMS-based Lissajous scanning platforms for biomedical imaging, this study could provide quantitative numerical references for error analysis, image reconstruction, and aberration correction.

Off-axis four-mirror telescope with a wide field of view and a long focal length using double integrated mirrors.

An off-axis four-mirror optical system has the advantages of a wide field of view (FOV) and a small telephoto ratio. However, it will bring difficulties in assembly and detection. Here we report an off-axis four-mirror free-form telescope with a long focal length and a wide field of view based on two integration mirrors. The initial structure of a coaxial four-mirror optical system is established based on the Seidel aberration theory. A Zernike Fringe free-form surface is introduced to correct aberrations. By gradually increasing the entrance pupil diameter and the FOV, we finally obtain an off-axis four-mirror telescope with a FOV of 0.4∘×20∘, an F-number of 11.5, a long focal length of 2000mm, and a volume of 360×400×600m m 3. In addition, four mirrors remain coaxially aligned, remarkably facilitating detection and adjustment. The proposed off-axis four-mirror telescope, with double integration mirrors, holds great potential for application in aerospace remote sensing observations.

Innovative aberration correction in ultrasound diagnostics with direct phase estimation for enhanced image quality.

The paper addresses a crucial challenge in medical radiology and introduces a novel general approach, which utilises applied mathematics and information technology techniques, for aberration correction in ultrasound diagnostics. Ultrasound imaging of inhomogeneous media inherently suffers from variations in ultrasonic speed between tissue. The characteristics of aberrations are unique to each patient due to tissue morphology. This study proposes a new phase aberration correction method based on the Fourier transform and leveraging of the synthetic aperture mode. The proposed method enables correction after the emission and reception of ultrasonic wave, allowing for the estimation of aberration profiles for different parts of the sonogram. To demonstrate the method's performance, this study included the conducting of experiments using a commercially available quality control phantom, an ex-vivo temporal human bone, and specially designed distortion layers. At a frequency of 2MHz, the experiments demonstrated an increase of two-and-three-quarters in echo signal intensity and a decrease of nearly two-fold in the width of the angular distribution compared to the pre-correction state. However, it is important to note that the implementation of the method has a limitation, as it requires an aperture synthesis mode and access to raw RF data, which restricts use in common scanners. To ensure the reproducibility of the results, this paper provides public access to an in-house C + + code for aberration correction following the proposed method, as well as the dataset used in this study.

Optimizing transducer aperture subdivision for aberration correction during transabdominal histotripsy

This study investigated the effect of transducer aperture subdivision on aberration correction performance for transabdominal histotripsy. A transducer aperture and geometric curvature similar to clinical histotripsy devices (750 kHz, 20 × 16 cm width, 14 cm radius of curvature) was subdivided into 64, 256, and 1024 elements (10.7λ, 5.3λ, 2.6λ). For each of the three designs, optimal space filling (100%) equal area polygons with a pseudo-random arrangement of elements was used following the technique described by Rosnitskiy. 3D acoustic path maps were constructed from abdominal CTs of 3 de-identified human subjects and assigned acoustic properties from literature. For each transducer, acoustic transmission was simulated using k-Wave at 3 target locations in the liver of each subject with and without implementing ideal aberration correction. Across all subjects and targets (n = 9), AC increased the maximum focal pressure amplitude by 26% (0%-59%) on average for 64 elements, 38% (5%-84%) for 256 elements, and 42% (7%–92%) for 1024 elements. These results suggest 5.3λ elements may near an optimal subdivision for transabdominal histotripsy aberration correction when taking into account the cost of transducer and driving system fabrication. Acoustic simulations can save fabrication time and costs when optimizing device design.

Интрастромальная фемтокератопластика с имплантацией роговичных сегментов в коррекции аберраций высшего порядка у пациентов с кератоконусом

Aim. To evaluate the potential of femtosecond laser assisted intrastromal keratoplasty (FLAIK) with implantation of corneal ring segments in the correction of higher order aberrations in patients with stage I–II keratoconus. Material and methods. 15 patients (14 men and 1 woman) were examined and treated surgically, in total of 17 eyes, with stage I and II keratoconus (according to the classification of Izmailova S.B., 2014). All patients underwent FLAIK with implantation of corneal ring segments. Results. The change in the estimated parameters at an average follow-up period of 4.7 months showed that after FLAIK with implantation of corneal ring segments, best corrected visual acuity increased statistically significantly (p < 0.05) in all cases and increased by an average of 0.29 ± 0.09. In addition, there was a statistically significant (p < 0.05) decrease in the total level of higher order aberrations by 1.5 times (by 0.69 ± 0.4 D), a decrease in the level of coma aberration by 1.7 times (by 0.74 ± 0.4 D), a decrease in the level of spherical aberration by 1.6 times (by 0.07 ± 0.12 D). Conclusions. FLAIK with implantation of corneal ring segments is an effective method for correcting higher-order aberrations in patients with keratoconus of stage I–II. FLAIK with keratoconus with implantation of corneal ring segments makes it possible to achieve a significant increase in BCVA in patients with stage I–II keratoconus. Key words: keratoconus, higher order aberrations, corneal segments, refractive surgery

Deep learning-driven adaptive optics for single-molecule localization microscopy

The inhomogeneous refractive indices of biological tissues blur and distort single-molecule emission patterns generating image artifacts and decreasing the achievable resolution of single-molecule localization microscopy (SMLM). Conventional sensorless adaptive optics methods rely on iterative mirror changes and image-quality metrics. However, these metrics result in inconsistent metric responses and thus fundamentally limit their efficacy for aberration correction in tissues. To bypass iterative trial-then-evaluate processes, we developed deep learning-driven adaptive optics for SMLM to allow direct inference of wavefront distortion and near real-time compensation. Our trained deep neural network monitors the individual emission patterns from single-molecule experiments, infers their shared wavefront distortion, feeds the estimates through a dynamic filter and drives a deformable mirror to compensate sample-induced aberrations. We demonstrated that our method simultaneously estimates and compensates 28 wavefront deformation shapes and improves the resolution and fidelity of three-dimensional SMLM through >130-µm-thick brain tissue specimens.