Large Depth Of Field Research Articles

High-resolution volumetric information fusion for depth of field enhancement in photoacoustic microscopy.

Optical-resolution photoacoustic microscopy suffers from limited depth of field due to the strongly focused laser beam. Here, a novel volumetric information fusion is proposed to achieve large volumetric and high-resolution imaging. First, three-dimensional stationary wavelet transform was performed on the multi-focus data to obtain eight wavelet coefficients. Differential evolution based on joint weighted evaluation was then employed to optimize the block size of division for each wavelet coefficient. The proposed fusion rule using standard deviation for focus detection was used to fuse the corresponding sub-coefficients. Finally, photoacoustic imaging with large depth of field can be achieved by the inverse stationary wavelet transform. Performance test shows that the depth of field of photoacoustic imaging can be doubled without sacrificing lateral resolution. The proposed volumetric information fusion can further promote the capability of volumetric imaging of optical-resolution photoacoustic microscopy and will be helpful in the acquisition of physiological and pathological process.

High-frame-rate limited-diffraction beam imaging

Limited-diffraction beams such as Bessel beam, X wave, and array beam are a class of beams that in theory do not spread as they propagate to infinite distance. When realized with a finite aperture, these beams have a large depth of field. In this paper, limited-diffraction beams and their applications to high-frame rate imaging are reviewed and further studied. Using a limited-diffraction beams (in either transmission or reception, or both, or with spatial Fourier transform of received signals), images can be reconstructed in Fourier domain. This significantly reduces the amount of computation in 3D imaging since FFT can be used. As the bandwidth of the transducer is increased, the image reconstructed can cover a larger field of view since a frequency in limited-diffraction beam corresponds to one angular direction of the beam (similar to the “frequency encoding” in the magnetic resonance imaging or MRI). Using the angular dependence with frequency, focused limited-diffraction beams can be used for high-frame-rate and high-resolution tissue property imaging. When limited-diffraction beams are used in transmissions, no time delay (only amplitude weighting) is needed, which simplifies imaging system hardware. Also, flow vector imaging can be obtained with limited-diffraction beams using sine and cosine (quadrature) aperture weighting.

Integrated MPCAM: Multi-PSF learning for large depth-of-field computational imaging

Large DOF (depth-of-field) imaging with high SNR (signal-noise-ratio) is useful for applications such as machine vision and medical imaging. In traditional optical systems, DOF extension is always implemented at the cost of SNR. In this paper, we present a MPCAM (Multi-PSF Camera) system highly integrated with AF (auto-focus) function to realize both large DOF and high SNR imaging. MPCAM based on MPGAN (Multi-PSF Generative Adversarial Network) is first proposed to automatically extract multiple PSFs (point spread functions) and realize high fidelity image reconstruction by features fusion. The proposed end-to-end generative image fusion network is flexible and can be designed with different input dimensions for a given AF application, which is vital to circumvent the trade-off between DOF and SNR. We build a dataset containing 5000 raw images tailored to the proposed network by an off-the-shelf camera. Results show that our MPCAM system can produce images with average higher values than raw images over 4.625, and 0.061 in PNSR (peak signal to noise ratio), and SSIM (structure similarity) metrics, respectively. Moreover, compared to the classic and latest image fusion methods, the results also verify that our method has achieved comparable or even better performance. Due to its advance in high SNR and large DOF imaging, this novel, portable and inexpensive system is suitable for computational applications such as microscopic pathological diagnosis, domain-specific computational imaging and smartphone photography. The implementation code of MPGAN and dataset are available from https://www.kaggle.com/datasets/ktd970903/multi-psf-camera.

Using Benchtop Scanning Electron Microscopy as a Valuable Imaging Tool in Various Applications

Abstract: Scanning electron microscopes (SEMs) are a popular analytical tool due to their high spatial resolution, large depth of field, and analytical capabilities. However, in many cases, the large-scale installation and cost of SEMs can be a barrier to entry for smaller laboratories or facilities. The introduction of a more compact benchtop SEM has changed the landscape, enabling scientists in many fields to adopt the technology and revolutionize research. Benchtop SEMs can be used in a variety of industries including materials science, pharmaceutical research, energy exploration, science education, and academia. These industries require analysis at the nanoscale for quality control, failure analysis, and R&D, for all of which the benchtop SEM is perfectly positioned to provide necessary detail. These advantages and new developments in the technology have made the benchtop SEM a widely available and well-accepted tool.

Large depth-of-field computational imaging with multi-spectral and dual-aperture optics.

Large DOF (depth-of-field) with high SNR (signal-noise-ratio) imaging is a crucial technique for applications from security monitoring to medical diagnostics. However, traditional optical design for large DOF requires a reduction in aperture size, and hence with a decrease in light throughput and SNR. In this paper, we report a computational imaging system integrating dual-aperture optics with a physics-informed dual-encoder neural network to realize prominent DOF extension. Boosted by human vision mechanism and optical imaging law, the dual-aperture imaging system is consisted of a small-aperture NIR camera to provide sharp edge and a large-aperture VIS camera to provide faithful color. To solve the imaging inverse problem in NIR-VIS fusion with different apertures, a specific network with parallel double encoders and the multi-scale fusion module is proposed to adaptively extract and learn the useful features, which contributes to preventing color deviation while preserving delicate scene textures. The proposed imaging framework is flexible and can be designed in different protos with varied optical elements for different applications. We provide theory for system design, demonstrate a prototype device, establish a real-scene dataset containing 3000 images, perform elaborate ablation studies and conduct peer comparative experiments. The experimental results demonstrate that our method effectively produces high-fidelity with larger DOF range than input raw images about 3 times. Without complex optical design and strict practical limitations, this novel, intelligent and integratable system is promising for variable vision applications such as smartphone photography, computational measurement, and medical imaging.

High range resolution wideband terahertz FMCW radar with a large depth of field.

Terahertz frequency modulation continuous wave (THz FMCW) imaging technology has been widely used in non-destructive testing (NDT) applications of non-metallic materials. However, THz FMCW real-aperture radar usually has a narrow bandwidth and small depth of field, thus restricting the application of THz FMCW NDT. In this paper, a wideband THz signal (220-500 GHz) generation method is proposed by time-division multiplexing. Moreover, a dual-band quasi-optical design with a large depth of field is proposed based on the THz Bessel beam, and a high-quality range profile is obtained. Especially, a signal fusion extended Fourier analysis algorithm without prior knowledge is proposed to further enhance the range profile accuracy, which improves the range resolution to 0.28 mm (λ/3, center frequency 360 GHz). The effectiveness and advantages of the proposed system are verified by artificially constructing composite materials.

Chip-scale metalens microscope for wide-field and depth-of-field imaging

Microscopy is very important in research and industry, yet traditional optical microscopy suffers from the limited field-of-view (FOV) and depth-of-field (DOF) in high-resolution imaging. We demonstrate a simultaneous large FOV and DOF microscope imaging technology based on a chip-scale metalens device that is implemented by a SiNx metalens array with a co- and cross-polarization multiplexed dual-phase design and dispersive spectrum zoom effect. A 4-mm × 4-mm FOV is obtained with a resolution of 1.74 μm and DOF of 200 μm within a wavelength range of 450 to 510 nm, which definitely exceeds the performance of traditional microscopes with the same resolution. Moreover, it is realized in a miniaturized compact prototype, showing an overall advantage for portable and convenient microscope technology.

Active multiband varifocal metalenses based on orbital angular momentum division multiplexing

Metalenses as miniature flat lenses exhibit a substantial potential in replacing traditional optical component. Although the metalenses have been intensively explored, their functions are limited by poor active ability, narrow operating band and small depth of field (DOF). Here, we show a dielectric metalens consisting of TiO2 nanofins array with ultrahigh aspect ratio to realize active multiband varifocal function. Regulating the orbital angular momentum (OAM) by the phase assignment covering the 2π range, its focal lengths can be switched from 5 mm to 35 mm. This active optical multiplexing uses the physical properties of OAM channels to selectively address and decode the vortex beams. The multiband capability and large DOFs with conversion efficiency of 49% for this metalens are validated for both 532 nm and 633 nm, and the incidence wavelength can further change the focal lengths. This non-mechanical tunable metalens demonstrates the possibility of active varifocal metalenses.

High‐Speed All‐Fiber Micro‐Imaging with Large Depth of Field

AbstractSingle fiber imaging has evolved into a powerful method for detecting minute objects in narrow spaces. However, existing systems are not conducive to imaging dynamic objects at depth due to their bulky probes, time‐consuming scanning acquisition methods, and transmissive illumination mode. Minimally invasive reflection mode imaging with high spatial and temporal resolution remains an open challenge. Here, a precise and high‐speed imaging scheme without scanning is proposed. Multimode fiber imaging technology is incorporated into an all‐fiber aberration‐free precision detection system. High temporal resolution (5000 fps) detection of tiny natural scenes is experimentally realized by optimizing the approximation of the inverse transmission matrix in a simple and compact setup. The system can display the detected screen in real‐time and the computational imaging with a large depth of field (1 mm) is enabled by jointly learning. The recovery results are superior compared to typical deep neural networks. The demonstrated scheme offers a new possibility for many applications, for example, microendoscopy, all‐optical computing, and remote high‐speed video transmission.

Extended the depth of field and zoom microscope with varifocal lens

Extending the depth of field (DOF) is especially essential in thick and 3D sample imaging. However, it's difficult to achieve both large DOF and high resolution in a zoom microscope. Currently, the use of optical sectioning to expand DOF still has the problem of inconstant magnification. Here, we develop an extended the depth of field (EDOF) and zoom microscope, which can realize EDOF with constant magnification and high resolution. Besides, the proposed microscope can achieve optical axial scanning at different NA and magnifications in real time without any mechanical movement. The proposed varifocal lens is employed to realize optical axial scanning, zooming, and keeping constant magnification when extending the DOF. Experimental results show that the proposed microscope can realize a continuous optical zoom of 10–40×, NA from 0.14 to 0.54, and the DOF of microscope can be extended to 1.2 mm.

Holographic super multi-view Maxwellian near-eye display with eyebox expansion.

A holographic super multi-view (SMV) Maxwellian display based on flexible wavefront modulation is proposed for the first time, to the best of our knowledge. It solves the issue that the previous holographic Maxwellian displays could not provide depth cues for monocular vision. Different from the previous methods, two or more parallax images are multiplied by quadric phase distributions and converged to the viewpoints existing in the pupil to provide 3-D vision. A time division method is proposed to eliminate the cross talk caused by the coherence of different spherical waves. Experiments demonstrate that the proposed method can accurately reconstruct images at different depth without cross talk. The proposed method inherits the previous holographic Maxwellian display's advantages of flexible viewpoint position adjustment and large depth of field (DOF). Superior to geometric optics based SMV displays, the proposed system is compact without lens aberration since only a single spatial light modulator (SLM) is needed without any additional optical elements.

Extended depth of field reconstruction with complex field estimation

The contradiction between high resolution and large depth of field (DOF) of microscopic imaging limits its application in imaging 3D distributed samples. Here, we propose a new technique to achieve extended depth of field reconstruction in bright-field microscopy through complex field estimation. The complex field is estimated by a phase retrieval algorithm with the four illumination modulation patterns and the corresponding captured Fourier intensities as dual constraints. Then, the digital refocusing strategy based on Fresnel propagator is integrated into reconstruction framework to achieve the reconstruction of high-resolution complex-valued information for each part of the sample, which ensures an effective extension of the DOF. The feasibility of the proposed method to maintain high resolution over extended DOF was verified in actual experiments with a tilted USAF target, biological sample and microlens array (MLA). The extended DOF reconstruction provides a robust method for imaging in both industrial inspection and biomedical research.

Research on Resolution Enhancement Technology of Orthogonal Multimode Fiber Imaging

This paper presents a new scheme to improve the imaging resolution of optical fiber endoscope. Multimode fiber imaging is combined with correlation imaging experimental architecture, and Schmidt orthogonalization algorithm is used to reduce the correlation of light field. The simulation and experimental results show that this scheme can greatly improve the imaging quality and resolution, especially in the case of under sampling. In addition, the scheme can also resist the low resolution problem caused by the light field divergence of multimode fiber correlation imaging, and when the light field divergence reaches a certain extent, the resolution of the orthogonalized multimode fiber light field will no longer be affected. The feasibility of orthogonal multimode fiber imaging scheme in large depth of field is verified.

Design of optical imaging system for full-ocean-depth low-light colors

In this paper, prism beam-splitting structure is proposed in the design of optical system to solve the problem of full-color imaging under low-light environment of the deep-sea. Optimization of optical aberrations is performed considering the specific aberration properties of the sea water and the window materials in the optical system. The designed optical system (field of view 60° and F/4) shows a clear imaging for all fields of view where MTFs is over 0.5 (@77lp/mm). The optical performance demonstrates that the system is very promising for large depth of field and full-color imaging under deep-sea environment.

Depth-enhanced 2D/3D switchable integral imaging display by using n-layer focusing control units

ABSTRACT Depth of field (DOF) is one of the important parameters of three-dimensional (3D) displays. A two-dimensional (2D)/3D switchable display that can display both high-resolution 2D images and vivid 3D images with large DOF is an ideal purpose. In this paper, we propose a depth-enhanced 2D/3D switchable integral imaging display by using n-layer focusing control units (FCUs). Each layer of FCU is composed of a polarization switch and a polarization-dependent liquid crystal micro-lens array (LCMLA). According to the polarization state of incident light switched by the polarization switch, the polarization-dependent LCMLA can realize focusing effect or transmission effect, respectively. Because each layer of FCU has two optional optical effects and has different gap from the display panel, the combination of n-layer FCUs could generate 2 n -1 central depth planes, hence 2 n -1 sub-DOFs can be obtained for depth-enhanced 3D display. The 2D display mode can be easily realized when all layers of FCUs are transmission effect. We experimentally set up a prototype of the proposed 2D/3D switchable display with two-layer FCUs. The experimental results indicated that the proposed prototype can effectively increase the DOF of 3D display and realize 2D/3D switchable display as well.

Large depth-of-field fluorescence microscopy based on deep learning supported by Fresnel incoherent correlation holography.

Fluorescence microscopy plays an irreplaceable role in biomedicine. However, limited depth of field (DoF) of fluorescence microscopy is always an obstacle of image quality, especially when the sample is with an uneven surface or distributed in different depths. In this manuscript, we combine deep learning with Fresnel incoherent correlation holography to describe a method to obtain significant large DoF fluorescence microscopy. Firstly, the hologram is restored by the Auto-ASP method from out-of-focus to in-focus in double-spherical wave Fresnel incoherent correlation holography. Then, we use a generative adversarial network to eliminate the artifacts introduced by Auto-ASP and output the high-quality image as a result. We use fluorescent beads, USAF target and mouse brain as samples to demonstrate the large DoF of more than 400µm, which is 13 times better than that of traditional wide-field microscopy. Moreover, our method is with a simple structure, which can be easily combined with many existing fluorescence microscopic imaging technology.

Large Depth of Range Maxwellian-Viewing SMV Near-Eye Display Based on a Pancharatnam-Berry Optical Element

In order to overcome the accommodation and convergence (A-C) conflict that commonly causes visual fatigue in AR display, we propose a Maxwellian-viewing-super-multi-view (MV-SMV) near-eye display system based on a Pancharatnam-Berry optical element (PBOE). The PBOE, which is constituted with an array of high-efficiency polarization gratings, is implemented to direct different views to different directions simultaneously, constructing the 3D light field. Meanwhile, each view is like a Maxwellian view display that possesses a small viewpoint and a large depth of field (DOF). Hence, the MV-SMV display can display virtual images with correct accommodation depth cue within a large DOF. We implement a proof-of concept MV-SMV display prototype with 3 × 1 and 3 × 2 viewpoints using a 1D PBOE and a 2D PBOE, respectively, and achieve a DOF of 4.37 diopters experimentally.

Visible-light metalens far-field nanofocusing effects with active tuning of focus based on MIM subwavelength structures used in an integrated imaging array.

We propose a structure of a far-field nanofocusing metalens with focal shifting that is actively tuned at visible wavelengths. Surface plasmon polaritons (SPPs) can be excited by the metal-insulator-metal (MIM) subwavelength structure at visible wavelengths. The coherent interference of SPPs emitted by subwavelength nanostructures can form a nanoscale focus. When the SPPs are excited and pass through several concentric ring gratings with specific aspect ratios, the extraordinary optical transmission phenomenon occurs. Two metal concentric ring gratings achieve double diffraction, scattering light to the far field. An anisotropic or isotropic electrically adjustable refractive index material, such as liquid-crystal or optical phase change material, is filled in a dielectric layer between two metal layers, and the effective refractive index is modulated by electronically controlled active tuning. The focal shift is achieved by changing the effective refractive index of the intermediate dielectric. In addition, different incident wavelengths correspond to different effective refractive indices to achieve time-division-multiplexing multi-wavelength achromatic focusing. The finite-difference time-domain method was used to simulate the effect of substrate effective refractive index variation on achromatic superfocusing. The results show that the super-resolution focal spot (FWHM=0.158λ0) with long focal length (FL=5.177λ0) and large depth of field (DOF=3.412λ0) can be achieved by optimizing the design parameters. The visible plasma metalens has potential applications in high-density optical storage and optical microscopic imaging, especially in three-dimensional display for light field and integral imaging.

Design of a real-time fiber-optic infrared imaging system with wide-angle and large depth of field

A key limitation in the observation of instruments used in operations and heart sutures during a procedure is the scattering and absorption during optical imaging in the presence of blood. Therefore, we propose a novel real-time fiber-optic infrared imaging system simultaneously capturing a flexible wide field of view (FOV) and large depth of field infrared image in real time. The assessment criteria for imaging quality of the objective and coupling lens have been optimized and evaluated. Furthermore, the feasibility of manufacturing and assembly has been demonstrated with tolerance sensitivity and the Monte Carlo analysis. The simulated results show that the optical system can achieve a large working distance of 8 to 25 mm, a wide FOV of 120°, and the relative illuminance is over 0.98 in the overall FOV. To achieve high imaging quality in the proposed system, the modulation transfer function is over 0.661 at 16.7 lp/mm for a 320×256 short wavelength infrared camera sensor with a pixel size of 30 µm.

Fast all-focus image reconstruction method based on light field imaging

To achieve high-quality imaging of all focal planes with large depth of field information, a fast all-focus image reconstruction technology based on light field imaging is proposed: combining light field imaging to collect field of view information, and using light field reconstruction to obtain a multi-focus image source set, using the improved NSML image fusion method performs image fusion to quickly obtain an all-focus image with a large depth of field. Experiments have proved that this method greatly reduces the time consumed in the image fusion process by simplifying the calculation process of NSML, and improves the efficiency of image fusion. This method not only achieves excellent fusion image quality, but also improves the real-time performance of the algorithm.