Scattering Media Research Articles

Focusing through Scattering Media Using Integrated Photonics

Focusing through Scattering Media Using Integrated Photonics

Long-Range Imaging through Scattering Media Using Deep Learning

Long-Range Imaging through Scattering Media Using Deep Learning

Vegetation Loss Measurements for Single Alley Trees in Millimeter-Wave Bands.

As fixed wireless access (FWA) is still envisioned as a reasonable way to achieve communications links, foliage attenuation becomes an important wireless channel impairment in the millimeter-wave bandwidth. Foliage is modeled in the radiative transfer equation as a medium of random scatterers. However, other phenomena in the wireless channel may also occur. In this work, vegetation attenuation measurements are presented for a single tree alley for 26-32 GHz. The results show that vegetation loss increases significantly after the second tree in the alley. Measurement-based foliage losses are compared with model-based, and new tuning parameters are proposed for models.

Reflective optical imaging for scattering medium using chaotic laser.

Optical imaging is a non-invasive imaging technology that utilizes near-infrared light, allows for the image reconstruction of optical properties like diffuse and absorption coefficients within the tissue. A recent trend is to use signal processing techniques or new light sources and expanding its application. We aim to develop the reflective optical imaging using the chaotic correlation technology with chaotic laser and optimize the quality and spatial resolution of reflective optical imaging. Scattering medium was measured using reflective configuration in different inhomogeneous regions to evaluate the performance of the imaging system. The accuracy of the recovered optical properties was investigated. The reconstruction errors of absorption coefficients and geometric centers were analyzed, and the feature metrics of the reconstructed images were evaluated. We showed how chaotic correlation technology can be utilized for information extraction and image reconstruction. This means that a higher signal-to-noise ratio and image reconstruction of inhomogeneous phantoms under different scenarios successfully were achieved. This work highlights that the peak values of correlation of chaotic exhibit smaller reconstruction error and better reconstruction performance in optical imaging compared with reflective optical imaging with the continuous wave laser.

Deep learning-assisted inverse design of nanoparticle-embedded radiative coolers

Radiative cooling is an energy-efficient technology without consuming power. Depending on their use, radiative coolers (RCs) can be designed to be either solar-transparent or solar-opaque, which requires complex spectral characteristics. Our research introduces a novel deep learning-based inverse design methodology for creating thin-film type RCs. Our deep learning algorithm determines the optimal optical constants, material volume ratios, and particle size distributions for oxide/nitride nanoparticle-embedded polyethylene films. It achieves the desired optical properties for both types of RCs through Mie Scattering and effective medium theory. We also assess the optical and thermal performance of each RCs.

Complex transmission matrix retrieval for a highly scattering medium via regional phase differentiation

Accurately measuring the complex transmission matrix (CTM) of the scattering medium (SM) holds critical significance for applications in anti-scattering optical imaging, phototherapy, and optical neural networks. Non-interferometric approaches, utilizing phase retrieval algorithms, can robustly extract the CTM from the speckle patterns formed by multiple probing fields traversing the SM. However, in cases where an amplitude-type spatial light modulator is employed for probing field modulation, the absence of phase control frequently results in the convergence towards a local optimum, undermining the measurement accuracy. Here, we propose a high-accuracy CTM retrieval (CTMR) approach based on regional phase differentiation (RPD). It incorporates a sequence of additional phase masks into the probing fields, imposing a priori constraints on the phase retrieval algorithms. By distinguishing the variance of speckle patterns produced by different phase masks, the RPD-CTMR can effectively direct the algorithm towards a solution that closely approximates the CTM of the SM. We built a prototype of a digital micromirror device modulated RPD-CTMR. By accurately measuring the CTM of diffusers, we achieved an enhancement in the peak-to-background ratio of anti-scattering focusing by a factor of 3.6, alongside a reduction in the bit error rate of anti-scattering image transmission by a factor of 24. Our proposed approach aims to facilitate precise modulation of scattered optical fields, thereby fostering advancements in diverse fields including high-resolution microscopy, biomedical optical imaging, and optical communications.

Scanning‐Driven Photon‐Counting 3D Imaging through Scattering Media Via Asynchronous Polarization Modulation

AbstractImaging through scattering media is widely studied in various applications including industrial inspection and autonomous driving. Most existing image sensors always suffer from the aliasing effect that generates a diffused image, leading to an extremely challenging problem in recovering targets of high quality, especially for 3D imaging. In this study, a scanning‐driven photon‐counting 3D imaging system through scattering media is proposed via asynchronous polarization modulation. To eliminate the aliasing effect, we utilize a point‐to‐point scanning strategy is used to illuminate the target and a photon‐counting detector to perceive weak echo signals passing through scattering media. Then, an asynchronous polarization‐modulated ranging method is proposed innovatively based on the Gamma pulse model to calculate the relative depth of the target for 3D imaging with the consideration of scattering media's difference. Therefore, the accuracy of the calculated depth and the generalization capability of the proposed method in real applications can be significantly improved. In addition, a time reshaping method is proposed to cope with the depth ambiguity caused by asynchronous measurements. In the experiment, a variety of strong scattering media is used to verify the excellent imaging capability of the proposed method.

A Unified Gas-Kinetic Particle Method for Radiation Transport in an Anisotropic Scattering Medium.

In this paper, a unified gas kinetic particle (UGKP) method is developed for radiative transfer in both absorbing and anisotropic scattering media. This numerical method is constructed based on our theoretical work on the model reduction for an anisotropic scattering system. The macroscopic solver of this method directly solves the macroscopic anisotropic diffusion equations, eliminating the need to solve higher-order moment equations. The reconstruction of macroscopic scattering source in the microscopic solver, based on the multiscale equivalent phase function we proposed in this work, has also been simplified as one single scattering process, significantly reducing the computational costs. The proposed method has also the property of asymptotic preserving. In the optically thick regime, the proposed method solves the diffusion limit equations for an anisotropic system. In the optically thin regime, the kinetic processes of photon transport are simulated. The consistency and efficiency of the proposed method have been validated by numerical tests in a wide range of flow regimes. The novel equivalent scattering source reconstruction can be used for various transport processes, and the proposed numerical scheme is widely applicable in high-energy density engineering applications.

Hyperspectral imaging through scattering media via physics-informed learning

Overcoming light scattering in natural light conditions is a challenging but rewarding problem. For this problem, both physics-based and data-driven methods encounter bottlenecks to recover large amounts of hyperspectral data encoded in the scattered light spot. In this paper, we present a physics-informed learning method to solve the light scattering problem with the neural network and the incoherent light transmission matrix method. With the proposed method, we achieve single-shot hyperspectral imaging through scattering media exceeding the memory effect range. Hyperspectral images with a maximum resolution of 3.2-megapixel are recovered in 64 wavebands, which represents an order of magnitude improvement over the memory effect range. No additional imaging or dispersion elements are required in the system except for the scatter medium, thus ensuring a compact and inexpensive hyperspectral imaging system. Our recovery method outperforms other physics-based and data-driven methods in terms of recovery quality and time cost.

Phase Imaging through Scattering Media Using Incoherent Light Source

Phase imaging normally employs coherent a light source while an incoherent light source is not preferred due to its random wavefront. Another challenge for practical phase imaging is imaging through scattering media, which scatter the photons in a random manner and lead to seriously distorted images of speckles. Based on the convolutional neural network (CNN), this paper presents an approach for phase imaging through scattering media using an incoherent light source. A CNN was trained and utilized to reconstruct the target images from the captured images of speckles. Similarities of over 90% between the reconstructed images and their target images have been achieved. It was concluded that an incoherent light source can be used as an illumination source for scattering phase imaging with the assistance of deep learning technology. This phase imaging approach with an incoherent light source through scattering media can be used to record the refractive indices of transparent samples, which might lead to its application in biomedical imaging.

Extending the Imaging Depth of Field through Scattering Media by Wavefront Shaping of Non-Diffraction Beams

Increasing the depth of field (DOF) is a crucial issue for imaging through scattering media. In this paper, an improved genetic algorithm is used to modulate the wavefront of light through scattering media, by which high-quality refocusing and imaging through scattering media are achieved. Then, the DOF of the imaging system is effectively extended by further modulating the refocused beam into a non-diffraction beam. Two kinds of non-diffraction beams, i.e., a Bessel beam and Airy beam, were produced as a demonstration. The experimental results show that compared to the Gaussian beam, the DOF of the imaging system by combining the wavefront shaping and non-diffraction Bessel beam or Airy beam can be improved by a factor of 1.1 or 1.5, respectively. The proposed method is helpful for the technical development of high-quality imaging through scattering media with a large DOF.

Modeling nonlinear optical microscopy in scattering media, part II. Radiation from focal volume to far-field: tutorial.

The development and application of nonlinear optical (NLO) microscopy methods in biomedical research has experienced rapid growth over the past three decades. Despite the compelling power of these methods, optical scattering limits their practical use in biological tissues. This tutorial offers a model-based approach illustrating how analytical methods from classical electromagnetism can be employed to comprehensively model NLO microscopy in scattering media. In Part I, we quantitatively model focused beam propagation in non-scattering and scattering media from the lens to focal volume. In Part II, we model signal generation, radiation, and far-field detection. Moreover, we detail modeling approaches for major optical microscopy modalities including classical fluorescence, multi-photon fluorescence, second harmonic generation, and coherent anti-Stokes Raman microscopy.

Manipulation and Certification of High-Dimensional Entanglement through a Scattering Medium

A wavefront shaping approach enables protection of high-dimensional entangled photons traversing a scattering medium, a situation that typically hinders the building of practical quantum microscopy and quantum key distribution.

Principle of subtraction ghost imaging in scattering medium

Scattering medium in light path will cause distortion of the light field, resulting in poor signal-to-noise ratio (SNR) of ghost imaging. The disturbance is usually eliminated by the method of pre-compensation. We deduce the intensity fluctuation correlation function of the ghost imaging with the disturbance of the scattering medium, which proves that the ghost image consists of two correlated results: the image of scattering medium and the target object. The effect of the scattering medium can be eliminated by subtracting the correlated result between the light field after the scattering medium and the reference light from ghost image, which verifies the theoretical results. Our research may provide a new idea of ghost imaging in harsh environment.

Forward Transmission into Scattering Media by an Improved Polarized Monte Carlo Program

Forward Transmission into Scattering Media by an Improved Polarized Monte Carlo Program

Vectorial Manipulation of High-Resolution Focusing Optical Field through a Scattering Medium

The manipulation of the polarization states of the light transmitted through a scattering medium has become an emerging field due to the novel fundamental physics interest and potential applications. Here, the manipulation of the polarization states in the focusing high-resolution optical field (points and vector beams) after passing a scattering medium is theoretically and experimentally demonstrated. The vector transmission matrix (VTM) of a scattering medium is measured with the vector basis of orthogonally circular polarizations by the two-dimensional (2D) holographic grating combined with the four-step phase-shifting method. The incident wavefronts for the creation of desired high-resolution optical fields through a scattering medium are modulated according to the calculation with the VTM of the medium. The theoretical and experimental results show that the constructed high-resolution optical field with spatially variant states of polarization can be realized through frosted glass. These results provide a new way to vectorially manipulate the constructed high-resolution optical field by passing through a scattering medium.

Retinalike Foveated Imaging through an Opaque Scattering Medium

Imaging through an opaque scattering medium, such as biological tissue, is of broad interest for many applications from physics to life sciences. Measuring the transmission matrix (TM) of the scattering medium is a versatile tool for this purpose. Previously, researchers are used to improving the image resolution by measuring a gigantic TM with a long sampling time. However, the low resolution and low SNR of the reconstructed images are still two obstacles to the adoption of such a technique. The foveal centralis of the human eye produces sharper vision than that from the retina's peripheral region. Inspired by this feature, we report the implementation of foveated scattering imaging with a multiresolution TM whose space-variant resolution feature can be flexibly adjusted. The enhancement of linear resolution and SNR of the foveated scattering imaging system by factors of 4 and 8.3, respectively, is demonstrated experimentally. Our bioinspired imaging method heuristically introduces foveal vision into scattering imaging, and thus paves the way for both high resolution and high SNR imaging through scattering medium concurrently monitoring the entire field of view.

Elastic wave scattering by flat-bottomed indentations on a plate

• Method for multiple scattering by scatterers with unmatched midplanes is proposed. • The method can analyze coupled flexural and in-plane extensional motions. • Mode conversions between different elastic waves are observed. • Stop bands of shear and flexural waves are captured simultaneously. • Broadband scattering polarization of flexural waves is achieved by multiple scattering. Out-of-plane flexural and in-plane extensional motions are independently analyzed in available studies of multiple scattering due to the assumption of the consistent mid-plane between the scatterer and host medium. When mid-planes of the scatterer and the host medium are inconsistent, such as flat-bottomed indentations, the coupled out-of-plane flexural and in-plane extensional motions should be considered. This paper aims to investigate a general numerical procedure to solve the three-dimensional multiple scattering problem of elastic waves on a plate with cylindrically flat-bottomed indentations. Wave expansion functions derived from the Poisson and Mindlin plate theories are used to express three-dimensional displacements of the host plate and flat-bottomed indentations. A linear matrix representing analytical relationships between wave expansion coefficients of exciting and scattered fields is deduced by the continuity conditions of flat-bottomed indentations. A set of linear algebraic equations is then developed by the fact that the exciting fields around a scatterer are the sum of scattered fields coming from all other scatterers. The numerical collocation method is used to solve the preceding algebraic equations. Simulation results verify mode conversions between compressional, shear, and flexural waves. Details of stop-band formations of shear and flexural waves are captured simultaneously. Furthermore, far-field scattering polarizations of shear and flexural waves are found in the case of multiple scattering.

Efficient Switchable Common Path Interferometer for Transmission Matrix Characterization of Scattering Medium

Transmission matrix can be used as an elegant tool to represent the light transmission characteristics of a scattering medium. In this paper, we propose a novel common path interferometer technique to measure the transmission matrix utilizing the polarization rotation of incident beam. Specifically, the horizontally polarized and vertically polarized components of the incident beam are used as signal light and reference light, respectively. By rotating the polarization of the incident beam, the ratio between the powers of signal and reference light can be freely adjusted and balanced. The phase shift method is employed to retrieve the transmission matrix of scattering medium. Once the transmission matrix is known, the polarization of the incident light beam can be rotated to switch off the reference and only the signal will remain. Focusing and manipulation of light through a ground glass has been experimentally demonstrated with the measured transmission matrix. An optical focus enhancement reaches 83% of the theoretical maximal value is obtained, which is about 30% improvement compared to the previous co-propagation method. The transmission matrix characterization method has the potential to become a general tool to harness the multiple scattering of light through complex medium.

Polarimetric Imaging Through Scattering Media: A Review

Imaging in scattering media has been a challenging and important subject in optical science. In scattering media, the image quality is often severely degraded by the scattering and absorption effects owing to the small particles and the resulting nonuniform distribution of the intensity or polarization properties. This study reviews the recent development in polarimetric imaging techniques that address these challenges. Specifically, based on the polarization properties of the backscattering light, polarimetric methods can estimate the intensity level of the backscattering and the transmittance of the media. They can also separate the target signal from the undesired ones to achieve high-quality imaging. In addition, the different designs of the polarimetric imaging systems offer additional metrics, for example, the degree/angle of polarization, to recover images with high fidelity. We first introduce the physical degradation models in scattering media. Secondly, we apply the models in different polarimetric imaging systems, such as polarization difference, Stokes vector, Mueller matrix, and deep learning-based systems. Lastly, we provide a model selection guideline and future research directions in polarimetric imaging.