Aberration Compensation Method Research Articles

Topography reconstruction of high aspect ratio silicon trench array via near-infrared coherence scanning interferometry.

Topography measurement of high aspect ratio trench array using coherence scanning interferometry presents significant challenges because the numerical aperture of detection light is constrained by the trenches. Altering the detection light to penetrate the sample like near-infrared light for silicon could overcome this obstacle, but the trench array spreads the detection light. This study introduces a coherence scanning interferometry model based on three-dimensional point spread function and assuming sample is transparent to detection light, which is realized by integrating rigorous numerical electromagnetic field solution to quantify the modulation aberrations of detection light by transparent trench arrays, and theoretical angular spectrum diffraction utilized for far-field interference imaging. This model facilitates a thorough analysis of the aberrations introduced by trench arrays, encompassing comparisons between trench arrays and a single trench, as well as between the symmetric region of the array and the asymmetric region at the edge. Additionally, an investigation into the impact of unified compensation for low-order aberrations on the topography reconstruction is presented, and we find the sample-induced aberration compensation method utilizing a deformable mirror that we previously proposed for a single trench is still effective confronting trench array. Experimental measurements are performed on silicon trench arrays with the aspect ratio of up to 20:1 and the period of approximately 10 µm to validate the effectiveness of our model and measurement methods, thus providing valuable insights for enhancing high aspect ratio manufacturing.

Automated surface profile measurement with digital holographic microscopy and large mask inpainting networks

Digital holographic microscopy (DHM) allows for highly precise 3D surface measurements in a non-invasive way, but phase aberrations from off-axis DHM recordings can compromise image accuracy. Traditional compensation methods require manual intervention, hindering further automated use of DHM. Other methods based on background segmentation and Zernike polynomials have been proposed, but identifying the sample and background regions can lead to inaccurate compensation results. Additionally, traditional image restoration algorithms struggle with restoring sample-free holograms involving large or multiple vacant areas. A new automated aberration compensation method is proposed using large-mask inpainting networks. This method restores sample-free holograms and compensates for phase aberrations, leveraging deep learning to enable real-time measurements. In the study, the network was trained with holograms of varying fringes, and experimental results show its effectiveness in improving image accuracy and detail. This approach could have wide applications in industries such as micro-electromechanical systems and micro- integrated circuits.

Automatic and accurate compensation for phase aberrations in digital holographic microscopy based on iteratively reweighted least squares fitting

Phase aberrations must be precisely compensated for phase-contrast imaging in digital holographic microscopy. In this paper, an automatic and accurate phase aberration compensation method is proposed based on iteratively reweighted least squares fitting. Instead of selecting the known-to-be-flat region with manual operation or image segmentation, this method starts from conventional least squares fitting in the whole image and attributes lower weights to the pixels with higher fitting residuals in an iterative reweighting procedure, during which the influence of specimen and noise is automatically reduced. Both phase curvature and high-order aberrations could be corrected without extra operation. Numerical simulation demonstrates that the proposed method is more accurate than the state-of-the-art numerical methods. Experimental result proves that this method is robust and fast enough for dynamic imaging of living cells.

Automatic aberration compensation for digital holographic microscopy based on bicubic downsampling and improved minimization of global phase gradients.

In digital holographic microscopy, aberrations caused by imperfect optical system settings can greatly affect the quantitative measurement of the target phase, so the compensation of aberrations in the distorted phase has become a key point of research in digital holographic microscopy. Here, we propose a fully automatic numerical phase aberration compensation method with fast computational speed and high robustness. The method uses bicubic downsampling to smooth the sample phase for reducing its disturbance to the background aberration fit, while reducing the computational effort of aberration compensation. Polynomial coefficients of the aberration fitting are iteratively optimized in the process of minimizing the global phase gradient by improving the phase gradient operator and constructing the loss function to achieve accurate fitting of the phase aberration. Simulation and experimental results show that the proposed method can achieve high aberration compensation accuracy without prior knowledge of the hologram recording settings or manual selection of the background area free of samples, and it is suitable for samples with moderate and relatively flat background area, which can be widely used in the quantitative analysis of biological tissues and micro and nano structures.

Phase aberration adaptive compensation in digital holography based on phase imitation and metric optimization.

We proposed a numerical and accurate quadratic phase aberration compensation method in digital holography. A phase imitation method based on Gaussian 1σ-criterion is used to obtain the morphological features of the object phase using partial differential, filtering and integration successively. We also propose an adaptive compensation method based on a maximum-minimum-average- α-standard deviation (MMAαSD) evaluation metric to obtain optimal compensated coefficients by minimizing the above metric of the compensation function. The effectiveness and robustness of our method are demonstrated by simulation and experiments.

Off-axis camera-in-the-loop optimization with noise reduction strategy for high-quality hologram generation.

In this Letter, we introduce a noise reduction (NR) strategy in the off-axis camera-in-the-loop (CITL) optimization for high-quality hologram generation. Our proposal adopts the Gaussian blur in the NR strategy to suppress the high-frequency noise and improve the optimization convergence. A double-hologram generation technique is used to reduce the noise further. The off-axis system's aberrations are eliminated by integrating the aberration compensation method as well. Compared with the original CITL method, the image quality of the proposed method is improved by approximately 5.5 dB in the optical experiment.

Longitudinal chromatic aberration compensation method for dual-wavelength retinal imaging adaptive optics systems

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Quantitative phase imaging in digital holographic microscopy based on image inpainting using a two-stage generative adversarial network

Based on the hologram inpainting via a two-stage Generative Adversarial Network (GAN), we present a precise phase aberration compensation method in digital holographic microscopy (DHM). In the proposed methodology, the interference fringes of the sample area in the hologram are firstly removed by the background segmentation via edge detection and morphological image processing. The vacancy area is then inpainted with the fringes generated by a deep learning algorithm. The image inpainting finally results in a sample-free reference hologram containing the total aberration of the system. The phase aberrations could be deleted by subtracting the unwrapped phase of the sample-free hologram from our inpainting network results, in no need of any complex spectrum centering procedure, prior knowledge of the system, or manual intervention. With a full and proper training of the two-stage GAN, our approach can robustly realize a distinct phase mapping, which overcomes the drawbacks of multiple iterations, noise interference or limited field of view in the recent methods using self-extension, Zernike polynomials fitting (ZPF) or geometrical transformations. The validity of the proposed procedure is confirmed by measuring the surface of preprocessed silicon wafer with a Michelson interferometer digital holographic inspection platform. The results of our experiment indicate the viability and accuracy of the presented method. Additionally, this work can pave the way for the evaluation of new applications of GAN in DHM.

Single-shot digital multiplexed holography for the measurement of deep shapes.

This work develops a single-shot holographic profilometer that enables shape characterization of discontinuous deep surfaces. This is achieved by combining hologram frequency multiplexing and an illumination technique of complex amplitude in multi-incidence angle profilometer. Object illumination is carried out from seven directions simultaneously, where the radial angular coordinates of illumination plane waves obey the geometric series. It is shown that: (i) the illumination pattern provides the required frequency separation of all object wavefronts in transverse frequency space, which is necessary for hologram demultiplexing, and (ii) numerical generation of longitudinal scanning function (LSF) is possible, which has large measurement range, high axial resolution, and small side lobes. Low side lobes of LSF and the developed multiplexed field dependent aberration compensation method are essential to minimize the negative influence of speckle noise of single-shot capture on the measurement result. The utility of the proposed method is demonstrated with experimental measurement of heights of two step-like objects.

Novel defocus hologram aberration compensation method in digital holography integrated pathology microscope for label free 3-D imaging

In this paper we report successful integration of digital holography in off- axis transmission configuration into a commercially available pathology microscope (PathologyDHM), where Mach-Zehnder interferometric configuration was achieved in pathology microscope using 1 × 2 single mode fiber coupler and custom built optical modules. A smartphone/webcam positioned at the image plane of the finite conjugate microscope captures the interference pattern generated by the system. Using PathologyDHM, we have demonstrated a novel and simple method for compensation of aberration due to microscope objective (MO). The proposed method is called defocus hologram method and it is particularly useful in cases, where samples do not have specimen free or background flat region. Proper validation of the method was done by imaging a transmissive grating (commercial compact disc, CD-R), which doesn't have a flat background region and comparing phase profile of CD-R computed by our proposed method with self-reference conjugated hologram method. For reiterating its biological applications, phase profile of a biological sample, red blood cell smear (RBC smear), was computed with our defocus hologram method and compared with already established reference conjugated hologram method. Phase profiles of CD-R and RBC smear computed with defocus hologram method agree with self-reference and reference conjugated hologram methods respectively, within the phase error limits of the system. Integration of digital holography in to commercial pathology microscope enables 3D imaging, which coupled with artificial intelligence may prove useful in disease diagnostics and monitoring response of cells to treatment.

Single-shot common-path off-axis dual-wavelength digital holographic microscopy

A single-shot common-path off-axis self-interference dual-wavelength digital holographic microscopic (DHM) system based on a cube beam splitter is demonstrated to expand the phase range in a stepped microstructure and for simultaneous measurement of the refractive index and physical thickness of a specimen. In the system, two laser beams with wavelengths of 532 nm and 632.8 nm are used. These laser beams are combined to transilluminate the object under study, then the object beam is divided into two beams by using a beam splitter oriented in such a way that both the beams propagate in almost the same direction, with an appropriate lateral separation between them. One of the object beams is spatially filtered at its Fourier plane, using a pinhole to generate a reference spherical beam free from the object information. The reference beam interferes with the object beam to form a digital hologram at the faceplate of the image sensor. The phase information is extracted from a single recorded digital hologram using the phase aberration compensation method that is based on principal component analysis (PCA). Owing to the common-path configuration, the system shows high temporal phase stability and it is less vibration-sensitive compared to counterparts such as a Mach-Zehnder type DHM. The performance of the dual-wavelength DHM system is verified in two different application fields by conducting the experiments using microsphere beads and living plant cells.

Automatic removal of phase aberration in holographic microscopy for drug sensitivity detection of ovarian cancer cells

Real-time and long-term monitoring of the morphological changes of cells in biomedical science is highly desired. Quantitative phase imaging (QPI) obtained by various interferometric methods is the ideal tool for monitoring such processes as it allows to get quantitative information and thus assessing the right response on cell behaviors. Among QPI, digital holography (DH) in microscope configuration is a powerful tool as it is tolerant versus defocusing and for this reason is able to compensate for eventual defocusing effect during long time-lapse recording. Moreover, DH dynamic phase imaging for biological specimens has several advantages, namely non-invasive, label-free, and high-resolution. However, in DH, one of the main limitations is due to the need compensate aberrations due to the optical components in the object beam. In fact, the image of the object is inevitably embedded in aberrations due to the microscope objective (MO) and other optical components in the optical setup. Here, we propose an automatic and robust phase aberration compensation method based on a synthetic difference (SD) image process. The method is able to detect automatically object-free regions. From such regions, hologram’s aberrations can be accurately evaluated and cleaned up in the final QPI maps. Thanks to our method, temporal evolutions of cell morphological parameters were quantitatively analyzed, hence helping in studying the drug sensitivity of ovarian cancer cells. The experimental results demonstrated that the proposed method could robustly separate the object-free region from the distorted phase image and automatically compensate the total aberrations without any manual interventions, extra components, prior knowledge of the object, and optical setup.

Automatic and robust phase aberration compensation for digital holographic microscopy based on minimizing total standard deviation

A totally automatic and robust phase aberration compensation method is proposed for digital holographic microscopy. The correction needs no manual operation or prior knowledge of the recording setup. As the phase aberrations are modeled with orthogonal polynomials, not only phase curvature but also high order aberrations could be corrected with a single hologram. The polynomial coefficients are obtained in an optimization procedure by minimizing the total standard deviation, i.e., the sum of local standard deviation of the compensated phase map. Since both the global and the local phase variations are considered, the proposed method is more accurate and robust than the state-of-the-art numerical methods with the existence of abrupt edges and phase noise. The effectiveness of the proposed method is validated with numerical simulation and the experimental results of mouse osteoblastic MC3T3-E1 living cells and USAF 1951 resolution target.

Optical system design based on lower aberration compensation method

Nonlinear refractions cause inevitable aberrations in practical optical systems, thereby degrading the imaging quality. We propose a novel method for optical system design based on lower aberration compensation and Seidel aberration theory to reduce the sensitivity of each optical component and the complexity in assembling and aligning the components in a system. A mathematical model for lower aberration compensation method is established to derive the expressions for wave aberrations. Furthermore, an optimization program based on Zemax programming language (ZPL) macro is used to reduce the aberrations of each surface by controlling the merit function, and the optimization parameters for the system are obtained. The efficacy of the proposed method is validated by comparing the optimization results before and after the implementation of the lower aberration compensation method, which reveal that the sensitivity of each component is significantly reduced and the stability of the overall optical system is effectively improved.

Phase aberration compensation of digital holographic microscopy with curve fitting preprocessing and automatic background segmentation for microstructure testing

In the digital holographic microscopy, the phase aberration is a key problem limiting the quantitative phase measurement, especially for the microstructure whose phase distribution is dense with few and discontinuous background region. A numerical phase aberration compensation method with global curve fitting preprocessing and automatic extraction of the background region for microstructure testing is proposed. The global curve fitting is implemented to compensate most of the tilt, quadratic and partial high order aberrations and make the profile of the measured object significantly distinguishable. Then the background region is automatically extracted by directly segmenting the converted grayscale phase image. At last, the Zernike polynomial fitting is performed on the extracted background region, and the obtained coefficients are used to calculate the phase aberration of the whole phase image. Simulation and experimental results demonstrated that the proposed method is able to accurately extract background region and compensate the phase aberration for the complicated dense microstructure.

Phase aberration compensation for digital holographic microscopy based on geometrical transformations

In digital holographic microscopy (DHM), the use of microscope objective always introduces a phase aberration and thus affects the retrieved phase. To address this problem, we present a simple phase aberration compensation method in DHM based on geometrical transformations. After doing the geometrical transformations (including reflection, rotation of and transpose) for the unwrapping phase (+1 order) of the original hologram, we could get a transformation phase. By subtracting the transformation phase from the unwrapped phase (+1 order) of the original hologram, the parabolic phase aberration is compensated. The fully automatic and effective performance makes the proposal available for single-shot quantitative phase imaging without complex numerical fitting procedures or prior knowledge of the specimen and system. A series of simulations and the experiment results of the micro-lens array, phase plate and cells demonstrate the feasibility and effectiveness of the proposed method.

Robust phase aberration compensation in digital holographic microscopy by self-extension of holograms

We propose a numerical robust phase aberration compensation method in digital holographic microscopy, which is based on self-extension of holograms. We remove the fringes of the sample area in the hologram, then expand the fringe to fill the removed area of hologram by self-extension. The sample-free reference hologram is obtained which contain the total aberration of the system. The quantitative phase imaging of samples is separated from measurement phase data by the difference phase map of captured and reference hologram. Numerical simulation and experimental results demonstrate the availability of the proposed aberration compensation method in digital holographic microscopy.

Multi-step phase aberration compensation method based on optimal principal component analysis and subsampling for digital holographic microscopy.

Digital holographic microscopy (DHM) is a well-known powerful technique allowing measurement of the spatial distributions of both the amplitude and phase produced by a transparent sample. Nevertheless, in order to improve the transverse resolution of the DHM system, a microscope objective has to be introduced in the object beam path, which inevitably leads to phase aberration in the object wavefront. In recent decades, a multitude of techniques have been proposed to compensate for this phase aberration, and the principal component analysis (PCA) technique has proven to be one of the most promising approaches due to its high compensation accuracy, low computational complexity, and simplicity to implement. However, when it comes to high-order phase aberration, which is common for a mal-aligned DHM system, the PCA technique usually performs poorly since it is unable to fit the cross-terms of the standard Zernike polynomials. To address this problem, here we propose a multi-step phase-aberration-compensation method based on optimal PCA and sub-sampling where PCA is first applied to remove the non-cross-aberration terms, followed by sub-sampled fitting for the remaining cross-aberration correction. The key advantage of our approach is that it can handle both the conventional objective phase curvature and high-order aberrations such as astigmatism and anamorphism with very little computational overhead. Simulation and experimental results demonstrate that our method outperforms state-of-the-art approaches, and the compensation results are consistent with those obtained from the double-exposure method.

Phase aberration compensation for digital holographic microscopy based on double fitting and background segmentation

We propose a purely automatic and accurate phase aberration compensation method in digital holographic microscopy for phase-contrast imaging of living cells. At first, a least-squares fitting procedure is implemented to correct a large proportion of the phase aberrations. Subsequently, the flat phase background is retrieved based on phase gradient and image segmentation. Finally, the residual phase aberrations are eliminated in another least-squares fitting procedure performed within the background region. This method needs no manual intervention or prior knowledge of optical setup. Not only phase curvature but also high order aberrations could be corrected without extra components. It outperforms the phase-variation-minimization method in terms of noise robustness and calculation speed. The performance of the proposed method is demonstrated with simulated and experimental results.

Generation of non-paraxial accelerating beams by active aberration compensation

We demonstrate the generation of non-paraxial accelerating beams by using an objective with an external spherical aberration compensation. A correction phase is applied at an illuminating plane before the objective, and such an aberration-corrected system enables a Fourier transform that translates a proper spatial spectral phase pattern into the desired non-paraxial accelerating beams. The feasibility of the scheme and the quality of the generated beams are further discussed for various conditions. Experimentally, we observe the accelerating beams as well as non-paraxial autofocusing beams following predesigned trajectories generated with such an aberration compensation method, providing an effective and alternative approach for non-paraxial beam shaping.