Aberration Correction Research Articles

Deep learning enhanced achromatic imaging with a singlet flat lens.

Correction of chromatic aberration is an important issue in color imaging and display. However, realizing broadband achromatic imaging by a singlet lens with high comprehensive performance still remains challenging, though many achromatic flat lenses have been reported recently. Here, we propose a deep-learning-enhanced singlet planar imaging system, implemented by a 3 mm-diameter achromatic flat lens, to achieve relatively high-quality achromatic imaging in the visible. By utilizing a multi-scale convolutional neural network (CNN) imposed to an achromatic multi-level diffractive lens (AMDL), the white light imaging qualities are significantly improved in both indoor and outdoor scenarios. Our experiments are fulfilled via a large paired imaging dataset with respect to a 3 mm-diameter AMDL, which guaranteed with achromatism in a broad wavelength range (400-1100 nm) but a relative low efficiency (∼45%). After our CNN enhancement, the imaging qualities are improved by ∼2 dB, showing competitive achromatic and high-quality imaging with a singlet lens for practical applications.

Evaluation of synthetically generated computed tomography for use in transcranial focused ultrasound procedures.

Transcranial focused ultrasound (tFUS) is a therapeutic ultrasound method that focuses sound through the skull to a small region noninvasively and often under magnetic resonance imaging (MRI) guidance. CT imaging is used to estimate the acoustic properties that vary between individual skulls to enable effective focusing during tFUS procedures, exposing patients to potentially harmful radiation. A method to estimate acoustic parameters in the skull without the need for CT is desirable. We synthesized CT images from routinely acquired T1-weighted MRI using a 3D patch-based conditional generative adversarial network and evaluated the performance of synthesized CT (sCT) images for treatment planning with tFUS. We compared the performance of sCT with real CT (rCT) images for tFUS planning using Kranion and simulations using the acoustic toolbox, k-Wave. Simulations were performed for 3 tFUS scenarios: (1)no aberration correction, (2)correction with phases calculated from Kranion, and (3)phase shifts calculated from time reversal. From Kranion, the skull density ratio, skull thickness, and number of active elements between rCT and sCT had Pearson's correlation coefficients of 0.94, 0.92, and 0.98, respectively. Among 20 targets, differences in simulated peak pressure between rCT and sCT were largest without phase correction () and smallest with Kranion phases (). The distance between peak focal locations between rCT and sCT was for all simulation cases. Real and synthetically generated skulls had comparable image similarity, skull measurements, and acoustic simulation metrics. Our work demonstrated similar results for 10 testing cases comparing MR-sCTs and rCTs for tFUS planning. Source code and a docker image with the trained model are available at https://github.com/han-liu/SynCT_TcMRgFUS.

Profile and nano-scale distribution of soil organic carbon for upland and paddy soils from an alluvial plain in South China

Understanding the heterogeneous distribution of soil organic carbon (C) (SOC) in different soil environments is essential for predicting SOC preservation. However, SOC distribution differs in profile scales and molecular levels in various farmland soils, making it challenging to elucidate the environmental behaviors of SOC. In the present study, upland and paddy soil samples were both collected at different depths (0–100 cm) from an alluvial plain in the Pearl River Delta of South China. Wet chemistry experiments coupled with 13C-nuclear magnetic resonance (NMR) and spherical aberration correction scanning transmission electron microscopy (Cs-STEM) were used to determine the vertical distribution, chemical composition, and nano-scale sequestration mechanisms of SOC in upland and paddy soils. SOC content for upland soil, which was highest at the depth of 0–20 cm (6.98 ± 0.34 g·kg−1), decreased with increasing soil depth, while that of paddy soil had the highest content at a depth of 80–100 cm (86.66 ± 5.26 g·kg−1). Statistical analysis revealed that mineral-associated organic C (MAOC) in the upland soil and particulate organic C (POC) in the paddy soil were the major C fractions that were related to SOC content. Further analysis of NMR spectra showed that the molecular composition of upland SOC differs vertically, while the molecular composition and proportion of organic C in paddy soil varied with soil depth. Cs-STEM results revealed that the relative percentage of carboxyl C decreased from 0 to 20 cm (42.1%) to 80–100 cm (28.8%) with an increase in aromatic C from 7.7 to 27.2% for the upland soil, while the four C species showed similar abundance for paddy soil at different depths, consistent with the NMR results. Overall, the upland SOC was not as easily mineralized as that of paddy soil due to a lower percentage of easily oxidized carbon, higher percentage of MAOC, and higher decomposition degree. The results of this study would enrich our quantitative understanding of the profile distribution and chemical diversity of SOC from macro to micro scales in the alluvial plain from South China, and provide insights into C preservation in natural soils.

Large field of view aberrations correction with deformable lenses and multi conjugate adaptive optics.

Optical microscopes can have limited resolution due to aberrations caused by samples and sample holders. Using deformable mirrors and wavefront sensorless optimization algorithms can correct these aberrations, but the correction is limited to a small area of the field of view. This study presents an adaptive optics method that uses a series of plug-and-play deformable lenses for large field of view wavefront correction. A direct wavefront measurement method using the spinning sub-pupil aberration measurement technique is combined with correction based on the deformable lenses. Experimental results using fluorescence microscopy with a wide field and a light sheet fluorescence microscope show that the proposed method can achieve detection and correction over an extended field of view with a compact transmissive module placed in the detection path of the microscope. This method could improve the resolution and accuracy of imaging in a variety of fields, including biology and materials science.

An Automatic Calibration Method for the Field of View Aberration in a Risley-Prism-Based Image Sensor.

Risley-prism-based image sensors can expand the imaging field of view through beam control. The larger the top angle of the prism, the higher the magnification of the field of view, but at the same time, it aggravates the problem of imaging aberrations, which also puts higher requirements on the aberration correction method for the Risley-prism-based image sensor. To improve the speed, accuracy, and stability of the aberration correction process, an automatic calibration method for the Risley-prism-based image sensor is proposed based on a two-axis turntable. The image datasets of the calibration plate with different prism rotation angles and object distances are acquired using a two-axis turntable. Then, the images of the calibration plate are pre-processed using the bicubic interpolation algorithm. The calibration parameters are finally calculated, and parameter optimization is performed. The experimental results verify the feasibility of this automated calibration method. The reprojection error of the calibration is within 0.26 pixels when the distance of the imaging sensor is 3.6 m from the object, and the fine aberration correction results are observed.

Accurate phase aberration compensation with convolutional neural network PACUnet3+ in digital holographic microscopy

To remove the effects of aberrations on quantitative phase image in digital holographic microscopy, a precise method that based on a data-driven phase aberrations compensations Unet3+ network (PACUnet3+) is presented. Unlike the existing methods that background segmentation should be implemented either in a phase image or in a sample hologram, the presented method doesn't need any preprocessing techniques. The PACUnet3+, which learning mappings between sample holograms and sample free holograms, produces a sample free hologram directly that contains all the background phase aberrations. Similar with double-exposure method, the phase aberrations can be removed by subtracting the background phase encoded in the generated sample-free hologram without any assumptions on the phase aberrations. The high fidelity of the method is demonstrated by measurement of engineered binary phase patterns. In phase aberrations correction, both numerical and experimental results confirmed the accuracy of the proposed method is benchmarking against the traditional double-exposure method.

Computational refocusing in phase-unstable polarization-sensitive optical coherence tomography.

We present computational refocusing in polarization-sensitive optical coherence tomography (PS-OCT) to improve spatial resolution in the calculated polarimetric parameters and extend the depth-of-field in phase-unstable, fiber-based PS-OCT systems. To achieve this, we successfully adapted short A-line range phase-stability adaptive optics (SHARP), a computational aberration correction technique compatible with phase-unstable systems, into a Stokes-based PS-OCT system with inter-A-line polarization modulation. Together with the spectral binning technique to mitigate system-induced chromatic polarization effects, we show that computational refocusing improves image quality in tissue polarimetry of swine eye anterior segment ex vivo with PS-OCT. The benefits, drawbacks, and potential applications of computational refocusing in anterior segment imaging are discussed.

AlN-based piezoelectric MEMS deformable mirror.

An AlN-based piezoelectric micro-electromechanical system (MEMS) continuous membrane deformable mirror (DM) prototype is presented for the first time. Its effective aperture diameter is 5 mm and it is equipped with 25 independently controlled actuators. Owing to the advantages associated with the AlN piezoelectric thin-film technology, attractive characteristics including CMOS compatible fabrication, bidirectional linear and negligible hysteresis actuation, and excellent linear superposition control capability have been successfully demonstrated. Moreover, good optical aberration correction performance is also validated via the surface contour fitting experiment to the Zernike polynomials up to the first 14 orders despite the non-optimized device structure design, representing great application perspective.

Automatic and Quantitative Measurement of Spectrometer Aberrations.

The performance of electron energy loss spectrometers can often be limited by their electron optical aberrations. Due to recent developments in high energy resolution and momentum-resolved electron energy loss spectroscopy (EELS), there is renewed interest in optimizing the performance of such spectrometers. For example, the "ω - q" mode of momentum-resolved EELS, which uses a small convergence angle and requires aligning diffraction spots with the slot aperture, presents a challenge in the realignments of the spectrometer required by the adjustment of the projection lenses. Automated and robust alignment can greatly benefit such a process. The first step toward this goal is automatic and quantitative measurement of spectrometer aberrations. We demonstrate the measurement of geometric aberrations and distortions in EELS within a monochromated scanning transmission electron microscope (STEM). To better understand the results, we present a wave mechanical simulation of the experiment. Using the measured aberration and distortion coefficients as inputs to the simulation, we find a good match between the simulation and experiment, verifying formulae used in the simulation. From verified simulations with known aberration coefficients, we can assess the accuracy of measurements. Understanding the errors and inaccuracies in the procedure can guide further progress in aberration measurement and correction for new spectrometer developments.

A Phase Recovery Technique Using the Genetic Algorithm for Aberration Correction in a Coherent Imaging System.

For traditional imaging systems, high imaging quality and system miniaturization are often contradictory. In order to meet the requirements of high imaging quality and system miniaturization, this paper proposes a method to correct the aberration of coherent imaging optical systems. The method is based on the idea of phase recovery and the imaging principle of a coherent imaging system to recover the aberrations at the exit pupil of the system. According to the recovered aberrations, conjugate filters are constructed to correct the image quality in the frequency domain. The imaging quality of the system is improved without changing the original optical path, and the simplicity of the system is guaranteed. To solve the pupil frequency domain aberration more accurately, this paper adopts the dual competition and parallel recombination strategy based on the genetic algorithm and introduces the disaster model. The improved genetic algorithm can effectively restrain the appearance of the "precocity" phenomenon. Finally, the paraxial imaging optical path is simulated and verified by experiments. The results show that, after aberration correction, the image sharpness is improved and the edge information is richer, which verifies the feasibility of the coherent imaging system image quality enhancement method proposed in this paper.

Single‐Shot Wavefront Sensing with Nonlocal Thin Film Optical Filters

AbstractConventional wavefront sensors suffer from the fundamental limitation of the space‐bandwidth product and have a trade‐off between their spatial sampling interval and dynamic range. Here, nonlocal thin film optical filters with optimized angle‐ and polarization‐dependent responses are leveraged to circumvent the fundamental limitation, and a robust single‐shot wavefront sensing system with a small spatial sampling interval of 6.9 µm and a large angular dynamic range of 15° is realized. The system only requires inserting two multilayer dielectric filters, fabricated using a mature thin film deposition technique, into a conventional 4‐f imaging apparatus. The polarization‐sensitive nonlocal filters are used to map the 2D phase gradients of the incident light field to the intensity variation of the x‐ and y‐polarized light, respectively, thus enabling single‐shot 2D wavefront reconstruction from images taken by a polarization camera. Such a system may be used for a variety of applications, including high‐resolution image aberration correction, surface metrology, and quantitative phase imaging.

Design of the dual-band shared-aperture asynchronous zoom optical system using focus tunable lenses.

To meet the increasing demand of the current market and the diversity of application scenarios, combine the zoom system and the multi-band shared-aperture system, and fully harness their respective advantages, this paper proposes a dual-band shared-aperture asynchronous zoom optical system using focus tunable lenses (FTLs). To address the lack of available patents for such systems, we designed a sub-system simultaneous iterative optimization algorithm to calculate the initial structure parameters. This synchronous iterative optimization approach can strengthen the connection between sub-systems and compensate for the shortcomings of current mainstream design methods. The initial structure constructed in this way has a good performance in terms of structural stability and optimization potential. Based on these methods, we successfully designed an optical system that can work in both VIS and NIR bands, and the two sub-systems can zoom independently. The design results possess good performance in terms of distortion control, aberration correction, and volume control.

Pupil aberrations correction of the afocal telescope for the TianQin project

TianQin is a planned Chinese space-based gravitational wave (GW) observatory with a frequency band of 10−4–1 Hz. Optical telescopes are essential for the delivery of the measurement beam to support a precise distance measurement between pairs of proof masses. As the design is driven by the interferometric displacement sensitivity requirements, the stability control of optical path length (OPL) is extremely important beyond the traditional requirement of diffraction-limited imaging quality. The recurring tilt-to-length (TTL) coupling noise arises from the OPL variation due to the wavefront deformation and angular misalignment. Reducing the residual chief ray aberration in the optical design helps suppress TTL coupling noise. To correct the pupil aberrations, we derive primary pupil aberrations in a series expansion form, and then refine the formulation of merit function by combining the pupil aberration theory and traditional image aberration theory. The automatic correction of pupil aberrations is carried out by using the macro programming in the commercial optical software Zemax, leading to a high performance telescope design. The design results show that on one side the pupil aberrations have been corrected, and on the other side, its optical performance meets the requirements for TianQin project. The RMS wavefront error over the science field of view (FOV) is less than λ/200 and the maximum TTL coupling noise over the entire ±300 μrad FOV is 0.0152 nm µrad−1 . We believe that our design approach can be a good guide for the space telescope design in any other space-based GW detection project, as well as other similar optical systems.

Recent progress on femtosecond laser micro-/nano-fabrication of functional photonic structures in dielectric crystals: A brief review and perspective

Femtosecond (Fs) laser micro-/nano-fabrication technology allows direct definition of on-demand nanostructures with three-dimensional (3D) geometric features and tailored photonic functionalities in a facile manner. In addition, such a strategy is widely applicable to various material families, including dielectrics, semiconductors, and metals. Based on diverse dielectric crystals, fs-laser direct writing of optical waveguides with flexible geometries and functional waveguide-based photonic devices have been well-developed. Beyond waveguide architectures, the combination of 3D nanofabrication of fs lasers and the multi-functionalities of dielectric crystals has also lighted up the future development of novel photonic structures with features even beyond the optical diffraction limit. In this article, promising research topics on domain engineering for nonlinear optics, color centers and waveguides for integrated quantum photonics, and surface processing for integrated photonics enabled by fs laser micro-/nano-fabrication in dielectric crystals are briefly overviewed. We highlight recent progress on these research topics and stress the importance of optical aberration correction during laser fabrication, followed by a discussion of challenges and foreseeing the future development of fs laser defined nanostructures in dielectric crystals toward multi-functional photonics.

High demagnification probe-forming systems with spherical aberration correction for a nuclear microprobe

Probe-forming systems with high demagnification (up to 900) based on a separated orthomorphic quadruplet of magnetic quadrupole lenses are considered. Spherical aberrations are corrected using an octupole lens system. Three, two, and one lens correctors are used. The calculation of the octupoles parameters was carried out using the Matrizant method. The focusing properties of the systems are determined by optimizing the process of probe formation based on the value of the maximum reduced collimated acceptance in the range of beam spot sizes on the target from 10 to 100 nm. The possibility of implementing the considered systems in experimental setups for various applications is demonstrated by the results of the numerical analysis performed.

Contrast-enhanced, single-shot LED array microscopy based on Fourier ptychographic algorithm and deep learning.

LED array microscopes have the advantages of miniaturisation and low cost. It has been demonstrated that LED array microscopes outperform Köhler illumination microscopes in some applications. A LED array allows for a large numerical aperture of illumination. The larger numerical aperture of illumination brings the higher spatial resolution, but the lower image contrast as well. Therefore, there is a tradeoff between resolution and contrast for LED array microscopes. The Fourier ptychographic algorithm can overcome this tradeoff by increasing image contrast without sacrificing spatial resolution. However, the Fourier ptychographic algorithm requires acquisition of multiple images, which is time-consuming and results in live sample imaging challenging. To solve this problem, we develop contrast-enhanced, single-shot LED array microscopy based on the Fourier ptychographic algorithm and deep learning. The sample to be imaged is under illumination by all LEDs of the array simultaneously. The image captured is fed to several trained convolutional neural networks to generate the same number of images that are required by the Fourier ptychographic algorithm. We experimentally present that the image contrast of the final reconstruction is remarkably improved in comparison with the image captured. The proposed method can also produce chromatic-aberration-free results, even when an objective without aberration correction is used. We believe the method might provide live sample imaging with a low-cost approach.

Laser-Written Tunable Liquid Crystal Aberration Correctors.

In this Article, we present a series of novel laser-written liquid crystal (LC) devices for aberration control for applications in beam shaping or aberration correction through adaptive optics. Each transparent LC device can correct for a chosen aberration mode with continuous greyscale tuning up to a total magnitude of more than 2π radians phase difference peak to peak at a wavelength of λ = 660 nm. For the purpose of demonstration, we present five different devices for the correction of five independent Zernike polynomial modes (although the technique could readily be used to manufacture devices based on other modes). Each device is operated by a single electrode pair tuned between 0 and 10 V. These devices have potential as a low-cost alternative to spatial light modulators for applications where a low-order aberration correction is sufficient and transmissive geometries are required.

Design method of dual-band synchronous zoom optical system based on co-path zoom groups

The dual-band zoom imaging system has great application value in military and civilian fields with the advantages of a large field of view (FOV) search, long-range tracking, camouflaged target reconnaissance, and all-day operation. To address the problem of synchronous zoom in dual-band co-aperture zoom optical systems, a dual-band simultaneous zoom optical system design method based on the co-path zoom groups is proposed. This optical system can realize zooming simultaneously in visible (VIS) and shortwave infrared (SWIR) bands and effectively control the total length. We first analyze the synchronous zoom principle of the dual-band co-path zoom optical system, then we propose a joint solution method for solving the initial structure of the dual-band zoom optical system. After obtaining the initial structure parameters, we performed the real-lens replacement and aberration correction in Zemax. Finally, a dual-band co-path simultaneous zoom optical system with working bands of 900∼1700 nm and 480∼660 nm, and zoom ranges of 10∼150 mm and 100∼150 mm, respectively, was designed. The focal length difference of the dual-band optical system is less than 0.16% during the simultaneous zooming process, and the system also has the advantages of good imaging quality, compact structure, simple zoom structure, and smooth cam curve.

Deflectometry based calibration of a deformable mirror for aberration correction and remote focusing in microscopy.

Adaptive optics (AO) techniques enhance the capability of optical microscopy through precise control of wavefront modulations to compensate phase aberrations and improves image quality. However, the aberration correction is often limited due to the lack of dynamic range in existing calibration methods, such as interferometry or Shack-Hartmann (SH) wavefront sensors. Here, we use deflectometry (DF) as a calibration method for a deformable mirror (DM) to extend the available range of aberration correction. We characterised the dynamic range and accuracy of the DF-based calibration of DMs depending on the spatial frequency of the test pattern used in DF. We also demonstrated the capability of large magnitude phase control for remote-focusing over a range larger than was possible with SH sensing.

Low-cost and simple optical system based onwavefront coding and deep learning.

With the development of computational imaging, the integration of optical system design and digital algorithms has made more imaging tasks easier to perform. Wavefront coding (WFC) is a typical computational imaging technique that is used to address the constraints of optical aperture and depth of field. In this paper, we demonstrated a low-cost and simple optical system based on WFC and deep learning. We constructed an optimized encoding method for the phase plate under the framework of deep learning, which reduces the requirement for aberration correction in the full field of view. Optical coding was achieved with just a double-bonded lens and a simple cubic phase mask, and digital decoding used the deep residual UNet++ network framework. The final image obtained has good resolution, whereas the depth of field of the system expanded by a factor of 13, which is of great significance for the high-precision inspection and attaching of small parts of machine vision.