Speckle Illumination Research Articles

All-optical, computation-free time-multiplexing super-resolved imaging based on speckle illumination

All-optical, computation-free time-multiplexing super-resolved imaging based on speckle illumination

Toward a fast and non-darkroom solution for speckle correlation based scattering imaging

Speckle correlation-based scattering imaging is an ingenious field, as it allows for the efficient reconstruction of object images using computational techniques in a simple setup. However, this method typically necessitates high-contrast speckle images captured in a darkroom environment, restricting its applicability to specific scenarios. Here, we present a fast and non-darkroom imaging framework, namely FNDI, for reconstructing objects through scattering media under ambient light interference. Specifically, a speckle illumination model is established guided by the total variational Retinex (TV-Retinex) theory, and the speckle illumination component is adjusted to obtain an enhanced speckle with significantly improved contrast. Then, a modified Fienup algorithm with the iteration-driven shrinkwrap (IDS) strategy is employed to rapidly reconstruct the object image through tens of iterations. Extensive experiments are conducted under different lighting conditions to evaluate FNDI in comparison with existing non-darkroom methods and the classical speckle correlation method. The results demonstrate that FNDI is effective and efficient, making it highly attractive for practical scattering imaging applications.

Rapid full-color serial sectioning tomography with speckle illumination and ultraviolet excitation

Three-dimensional (3D) high-resolution large-volume imaging has remained a challenge. Translational rapid ultraviolet-excited sectioning tomography (TRUST) achieves rapid and cost-effective whole-organ subcellular imaging through iterative optical scanning and mechanical sectioning. However, the axial resolution is limited by the mechanical sectioning thickness or the UV light penetration depth in tissue. Here, assisted with high-and-low-frequency (HiLo) microscopy (HiLoTRUST), the optical sectioning thickness has been reduced from tens of micrometers to ~5.8 µm. In addition, HiLoTRUST has attained a finer mechanical sectioning thickness (10–15 µm) compared to TRUST (50 µm). For high-content imaging as in TRUST, we employed two additional UV light-emitting diodes (LEDs) specifically for uniform illumination. The full-color imaging ability and improved axial resolution of HiLoTRUST have been validated by two-dimensional (2D)/3D imaging of various mouse organs and human lung cancer specimens. HiLoTRUST offers a cost-effective, full-color, and high-resolution 3D imaging approach, showing its great potential in 3D histology applications.

A change detection algorithm for the SAR images based on DWT and DE optimization

ABSTRACT In this paper, a novel change detection algorithm is proposed for the remote sensing Synthetic Aperture Radar (SAR) images. Change detection in SAR images is one of the critical tasks in the field of remote sensing as the images contain significant speckle noise and illumination variations. In order to address these issues, a novel change detection algorithm is proposed using Discrete Wavelet Transform (DTW) and Differential Evaluation (DE). At first, the DWT is utilized to remove the speckle noise from the images. Then, a DE optimization-based Support Vector Machine (SVM) algorithm is proposed to detect the changes in SAR images. The proposed method can give comparatively better correct classification values, and lesser false alarm as well as total error values than the recently developed change detection methods.

Aberration correction in epi-fluorescence microscopy using unknown speckle illumination

Aberration correction in epi-fluorescence microscopy using unknown speckle illumination

Lens-free reflective topography for high-resolution wafer inspection

The demand for high-resolution and large-area imaging systems for non-destructive wafer inspection has grown owing to the increasing complexity and extremely fine nature of semiconductor processes. Several studies have focused on developing high-resolution imaging systems; however, they were limited by the tradeoff between image resolution and field of view. Hence, computational imaging has arisen as an alternative method to conventional optical imaging, aimed at enhancing the aforementioned parameters. This study proposes a method for improving the resolution and field of view of an image in a lens-less reflection-type system. Our method was verified by computationally restoring the final image from diffraction images measured at various illumination positions using a visible light source. We introduced speckle illumination to expand the numerical aperture of the entire system, simultaneously improving image resolution and field of view. The image reconstruction process was accelerated by employing a convolutional neural network. Using the reconstructed phase images, we implemented high-resolution topography and demonstrated its applicability in wafer surface inspection. Furthermore, we demonstrated an ideal diffraction-limited spatial resolution of 1.7 μm over a field of view of 1.8 × 1.8 mm2 for the topographic imaging of targets with various surface roughness. The proposed approach is suitable for applications that simultaneously require high throughput and resolution, such as wafer-wide integrated metrology, owing to its compact design, cost-effectiveness, and mechanical robustness.

HydroSIM: super-resolution speckle illumination microscopy with a hydrogel diffuser.

Super-resolution microscopy has emerged as an indispensable methodology for probing the intricacies of cellular biology. Structured illumination microscopy (SIM), in particular, offers an advantageous balance of spatial and temporal resolution, allowing for visualizing cellular processes with minimal disruption to biological specimens. However, the broader adoption of SIM remains hampered by the complexity of instrumentation and alignment. Here, we introduce speckle-illumination super-resolution microscopy using hydrogel diffusers (hydroSIM). The study utilizes the high scattering and optical transmissive properties of hydrogel materials and realizes a remarkably simplified approach to plug-in super-resolution imaging via a common epi-fluorescence platform. We demonstrate the hydroSIM system using various phantom and biological samples, and the results exhibited effective 3D resolution doubling, optical sectioning, and high contrast. We foresee hydroSIM, a cost-effective, biocompatible, and user-accessible super-resolution methodology, to significantly advance a wide range of biomedical imaging and applications.

Optical fiber bundle differential compressive imaging.

We present a differential compressive imaging method for an optical fiber bundle (OFB), which provides a solution for an ultrathin bend-resistant endoscope with high resolution. This method uses an OFB and a diffuser to generate speckle illumination patterns. Differential operation is additionally applied to the speckle patterns to produce sensing matrices, by which the correlation between the matrices is greatly reduced from 0.875 to 0.0275, which ensures the high quality of image reconstruction. Pixilation artifacts from the fiber core arrangement are also effectively eliminated with this configuration. We demonstrate high-resolution reconstruction of images of 132 × 132 pixels with a compression rate of 12% using 77 fiber cores, the total diameter of which is only about 91 µm. An experimental verification proves that this method is tolerant to a limited degree of fiber bending, which provides a potential approach for robust high-resolution fiber endoscopy.

Data-driven method of super-resolution image recovery for speckle-illumination photoacoustic computed tomography.

Methods have been proposed in recent years aimed at pushing photoacoustic imaging resolution beyond the acoustic diffraction limit, among which those based on random speckle illumination show particular promise. In this Letter, we propose a data-driven deep learning approach to processing the added spatiotemporal information resulting from speckle illumination, where the neural network learns the distribution of absorbers from a series of different samplings of the imaged area. In ex-vivo experiments based on the tomography configuration with prominent artifacts, our method successfully breaks the acoustic diffraction limit and delivers better results in identifying individual targets when compared against a selection of other leading methods.

TV-based phase retrieval for speckle coded diffraction imaging

Speckle coded diffraction imaging (SCDI) has emerged as a new and developing lensless imaging method, which provides an effective imaging method for dense and connected objects. The conventional alternating-projection-based phase retrieval algorithm for SCDI relies on phase constraints between multiple diffraction images, and its disadvantage is that it often necessitates a large number of measurements to ensure high-quality reconstruction. In order to reduce the measurements, we propose to regularize the non-convex phase retrieval with total variation (TV)–based prior, and thus construct the TV-based cost function for SCDI. The alternating direction method is used to solve the nonlinear cost function, and recover the object and unknown speckle illumination. As both simulations and experiments demonstrate, the proposed TV-based reconstruction algorithm can recover the complex object and the unknown speckle pattern with high fidelity using 16 measurements, compared with hundreds of measurements used for AP-based algorithm.

Dynamic speckle illumination wide-field fluorescence microscopy with actively optical manipulation of rotational angles.

We present a dynamic speckle illumination wide-field fluorescence microscopy (DSIWFM) combined with a line optical tweezers (LOTs) for rotational fluorescence sectioning imaging. In this method, large polystyrene fluorescent microspheres are stably trapped with LOTs, and precisely manipulated to rotate around a specific rotation axis. During the rotation process, multiple raw fluorescence images of trapped microspheres are obtained with dynamic speckle illumination. The root-mean-square (RMS) algorithm is used to extract the drastically changing fluorescent signals in the focal plane to obtain the fluorescence sectioning images of the samples at various angles. The influence of speckle granularity on the image quality of fluorescence sectioning images is experimentally analyzed. The rotational fluorescence sectioning images obtained by DSIWFM with LOTs could provide an alternative technique for applications of biomedical imaging.

Interferometric Lensless Imaging: Rank-One Projections of Image Frequencies With Speckle Illuminations

Interferometric Lensless Imaging: Rank-One Projections of Image Frequencies With Speckle Illuminations

Multiplane HiLo microscopy with speckle illumination and non-local means denoising.

HiLo microscopy synthesizes an optically sectioned image from two images, one obtained with uniform and another with patterned illumination, such as laser speckle. Speckle-based HiLo has the advantage of being robust to aberrations but is susceptible to residual speckle noise that is difficult to control. We present a computational method to reduce this residual noise without undermining resolution. In addition, we improve the versatility of HiLo microscopy by enabling simultaneous multiplane imaging (here nine planes). Our goal is to perform fast, high-contrast, multiplane imaging with a conventional camera-based fluorescence microscope. Multiplane HiLo imaging is achieved with the use of a single camera and z-splitter prism. Speckle noise reduction is based on the application of a non-local means (NLM) denoising method to perform ensemble averaging of speckle grains. We demonstrate the capabilities of multiplane HiLo with NLM denoising both with synthesized data and by imaging cardiac and brain activity in zebrafish larvae at 40Hz frame rates. Multiplane HiLo microscopy aided by NLM denoising provides a simple tool for fast optically sectioned volumetric imaging that can be of general utility for fluorescence imaging applications.

Lensless imaging via multi-height mask modulation and ptychographical phase retrieval

Multi-height phase retrieval by adding a thin diffuser between the object and the detector has emerged as an effective approach for lensless imaging. However, up to 100 measurements are required to jointly recover the object and diffuser, which makes the data acquisition time-consuming and cumbersome. In this paper, we report a novel multi-height lensless imaging technique. In our scheme, the diffuser is replaced with a random binary amplitude mask and placed upstream of the object to introduce speckle illumination. Multiple diffraction patterns are then recorded by moving the mask axially, while the object and the detector remained stationary. Inspired by the ptychography, the extended ptychographic iterative engine algorithm is adopted to reconstruct the object and the unknown mask simultaneously. The imaging performance is first validated by simulation and then experimentally tested with resolution target, phase plate, and biological sample. Compared with the original method, the proposed method can achieve high-quality reconstruction with as few as ∼20 images, which greatly accelerates the data acquisition and reconstruction.

Swept-source multimode fiber imaging

High-resolution compressive imaging via a flexible multimode fiber is demonstrated using a swept-laser source and wavelength dependent speckle illumination. An in-house built swept-source allowing for independent control of bandwidth and scanning range is used to explore and demonstrate a mechanically scan-free approach for high-resolution imaging through an ultrathin and flexible fiber probe. The computational image reconstruction is shown by utilizing a narrow sweeping bandwidth of < 10 nm while acquisition time is decreased by 95% compared to conventional raster scanning endoscopy. Demonstrated narrow-band illumination in the visible spectrum is vital for the detection of fluorescence biomarkers in neuroimaging applications. The proposed approach yields device simplicity and flexibility for minimally invasive endoscopy.

Non-invasive PSF recovery based on direct illumination from wavelength-dependent speckles

Scattering effect exists widely in practical bioimaging systems, which renders a higher demand for image reconstruction from blurred images. Generally, the point spread function (PSF) of an imaging system works as a powerful key to effectively reconstruct the hidden object even from strongly scattering-induced speckle patterns. However, the direct acquisition of the PSF commonly involves an invasive way like delighting a point in the region of interest, which is typically unavailable in practical applications. Here, we propose a non-invasive PSF recovery method under wavelength-dependent speckle illumination. The PSF is recovered from the uncorrelated intensity patterns through non-negative matrix factorization, while effective image reconstruction is realized by combining it with the multiplexed speckle pattern. It is surprising that a direct illumination, i.e., the lighting and detection utilize the same wavelength and even possess high spatial coherence, still fulfills the effective information extraction using the intensity-only based incoherent algorithm. This work provides a non-invasive way of PSF recovery and facilitates the PSF associated techniques such as image deblurring and super-resolution imaging.

Sub-Rayleigh dark-field imaging via speckle illumination.

We demonstrate sub-Rayleigh dark-field imaging via speckle illumination. Imaging is achieved with second-order autocorrelated measurement by illuminating objects with hollow conical pseudothermal light. Our scheme can work well for highly transparent amplitude objects, pure phase objects, and even more complex transparent objects. The autocorrelated dark-field images show better resolution than intensity-averaged images and an ability in filtering out low-frequency noises.

Single-Pixel Photoacoustic Microscopy with Speckle Illumination

Wide-field optical-resolution microscopy with structured illumination and single-pixel detection has been the topic of a number of research investigations. Its advantages over point scanning approaches are many and include a faster acquisition rate for sparse samples, sectioning, and super-resolution features. Initially introduced for fluorescence imaging, structured illumination approaches have been adapted and developed for many other imaging modalities. In this paper, we illustrate how speckle illumination, as a particular type of structured illumination, can be exploited to perform optical-resolution photoacoustic microscopy with a single-pixel imaging approach. We first introduce the principle of single-pixel detection applied to photoacoustic imaging and then illustrate in 2 different situations how photoacoustic images may be computationally reconstructed from speckle illumination: In the first situation where the speckle patterns are known through a prior calibration, various reconstruction approaches may be implemented, which are demonstrated experimentally through both scattering layers and multimode optical fibers; in the second situation where the speckle patterns are unknown (blind structured illumination), the so-called memory effect can be harnessed to produce calibration-free photoacoustic images, following the approach initially proposed for fluorescence imaging through thin scattering layers.

Vortex Speckles with Customized Symmetry and Spatial Correlations

A family of optical speckles with propagation-invariant annular morphology are generated via a phase-only mask and free-space evolution, termed vortex speckles, for which phase design is inspired by the vortex beam's helical wave front carrying orbital angular momentum. Vortex beams' graceful symmetry (central and/or axial) can be naturally inherited into vortex speckles by adjusting the parity of the topological value $\ensuremath{\ell}$ and the consistency of the initial phase angle ${\ensuremath{\phi}}_{0}$. By sequentially imprinting such a series of phase profiles onto a spatial light modulator, the resultant stochastically fluctuating vortex speckles naturally constitute an annular pseudothermal light field, and the customized symmetry in intensity profiles leads to spatial correlations, which are exploited for Hanbury Brown and Twiss interferometry and beam-splitter-free lensless ghost imaging and diffraction experiments. Symmetric annular pseudothermal light also has diverse phase correlations, so in a proposed vortex self-interferometer, we can manipulate photon correlations (parity-induced anticorrelation) and observe intriguing correlation states (spatially varying photon correlation oscillations). This work not only presents a flexible light-source option for applications requiring ring-shaped speckle illumination, but it also paves the way for the customization of nontrivial classical correlation modes.

Alternating projection-based phase optimization for arbitrary glare suppression through multimode fiber

Wavefront shaping for glare suppression helps to reduce the speckle background through scattering media and enables imaging, sensing, and some speckle-related advanced applications through customizing the speckle light field. For glare suppression in a target region, current methods are either slow or not sufficiently generic. Here, an alternating projection method that fully exploits the transmission matrix of the scattering medium is proposed for fast and arbitrary glare suppression. Parallelly, multiple phase masks corresponding to different target regions can be computationally optimized without iterative hardware feedback. Numerical simulation shows that under phase-only modulation, a suppression factor of ∼10−3 can be realized for a large target region with only 30 iterations. With the use of a graphics processing unit and a digital micromirror device, fast and effective glare suppression for target regions of various shapes and sizes was demonstrated at the distal end of a multimode fiber. This technique could be promising for applications like multimode fiber-based speckle optical tweezer or endoscopy with speckle illumination inside complex environments.