Application Of Optical Tomography Research Articles

Subthreshold Operation of Photodiode-Gated Transistors Enabling High-Gain Optical Sensing and Imaging Applications

In optical sensors and imagers, high gain that leads to high sensitivity and high signal to noise ratio (SNR) is often desirable. One popular approach is avalanche photomultiplication initiated by impact ionization in an avalanche photodiode or similar devices and the other approach is active pixel sensor (APS) with in-pixel amplifier. However, the former requires high electric field which induces high shot noise and the latter needs a multiple-transistor pixel circuit which compromises the fill factor and consequently, reduces the SNR. This work proposes and summarizes our recent efforts taken to achieve high gain optical sensors through subthreshold operation of photodiode-gated transistors.

Real-Time Phase Conjugation of Vector Vortex Beams

Vector vortex beams have played a fundamental role in the better understanding of coherence and polarization. They are described by spatially inhomogeneous polarization states, which present a rich optical mode structure that has attracted much attention for applications in optical communications, imaging, spectroscopy and metrology. However, this complex mode structure can be quite detrimental when propagation effects such as turbulence and birefringence perturb the beam. Optical phase conjugation has been proposed as a method to recover an optical beam from perturbations. Here we demonstrate full phase conjugation of vector vortex beams using three-wave mixing. Our scheme exploits a fast non-linear process that can be conveniently controlled via the pump beam. Our results pave the way for sophisticated, practical applications of vector beams.

Intralipid-Based Phantoms for the Development of New Optical Diagnostic Techniques

Intralipid is a material widely employed for the preparation of phantoms for optical imaging and biophotonics applications in medical field. The development of new optical diagnostic equipment in these fields requires the use of well-designed phantoms with optical properties (including scattering and absorption) mimicking those of biological tissues in all the pre-clinical stages of investigations. For this reason, great research effort has been devoted to optically characterize Intralipid and at preparing optimal phantoms. In this short review, we summarize the principal physico-chemical characteristics of Intralipid and the main contributions in the assessment of its scattering and absorption properties. In addition, the most largely used Intralipid-based homogeneous and non-homogeneous phantoms are discussed. Even though other materials are available for the preparation of phantoms, the use of Intralipid still offers an inexpensive and easy-to-use method for preparing phantoms with finely tuned optical properties.

Lasing from Zero-Dimensional Perovskite and Optical Imaging Applications

Owing to quantum confinement of optical and electrical transitions within isolated [PbBr6]4– octahedral units, zero-dimensional perovskite Cs4PbBr6 exhibits appealing molecular-like quantum optoele...

Real-Time Observation of Magnetic Field-Induced Fluorescence Engineering in SPIONs

Because of their high magnetic susceptibility, superparamagnetic iron oxide nanoparticles (SPIONs) have shown potential applications in various fields. However, their application in optical imaging was severely restricted because of the lack of fluorescence in them. Here, we present a real-time in situ giant fluorescence enhancement, at least an order of magnitude higher in self-assembled SPIONs in comparison to a single SPION at the single-particle level under the applied magnetic field (MF). The single-particle tracking video provides the direct observation of the self-assembly and disassembly and the associated fluorescence change in SPIONs in the presence and absence of the applied MF. A theoretical model was applied to calculate the dipole–dipole interaction energy, drag coefficient, and quantified the dynamics of this aggregation.

Free-space data-carrying bendable light communications

Bendable light beams have recently seen tremendous applications in optical manipulation, optical imaging, optical routing, micromachining, plasma generation and nonlinear optics. By exploiting curved light beams instead of traditional Gaussian beam for line-of-sight light communications, here we propose and demonstrate the viability of free-space data-carrying bendable light communications along arbitrary trajectories with multiple functionalities. By employing 39.06-Gbit/s 32-ary quadrature amplitude modulation (32-QAM) discrete multi-tone (DMT) signal, we demonstrate free-space bendable light intensity modulated direct detection (IM-DD) communication system under 3 different curved light paths. Moreover, we characterize multiple functionalities of free-space bendable light communications, including bypass obstructions transmission, self-healing transmission, self-broken trajectory transmission, and multi-receiver transmission. The observed results indicate that bendable light beams can make free-space optical communications more flexible, more robust and more multifunctional. The demonstrations may open a door to explore more special light beams enabling advanced free-space light communications with enhanced flexibility, robustness and functionality.

Distributed optical fiber sensing: Review and perspective

Over the past few decades, optical fibers have been widely deployed to implement various applications in high-speed long-distance telecommunication, optical imaging, ultrafast lasers, and optical sensors. Distributed optical fiber sensors characterized by spatially resolved measurements along a single continuous strand of optical fiber have undergone significant improvements in underlying technologies and application scenarios, representing the highest state of the art in optical sensing. This work is focused on a review of three types of distributed optical fiber sensors which are based on Rayleigh, Brillouin, and Raman scattering, and use various demodulation schemes, including optical time-domain reflectometry, optical frequency-domain reflectometry, and related schemes. Recent developments of various distributed optical fiber sensors to provide simultaneous measurements of multiple parameters are analyzed based on their sensing performance, revealing an inherent trade-off between performance parameters such as sensing range, spatial resolution, and sensing resolution. This review highlights the latest progress in distributed optical fiber sensors with an emphasis on energy applications such as energy infrastructure monitoring, power generation system monitoring, oil and gas pipeline monitoring, and geothermal process monitoring. This review aims to clarify challenges and limitations of distributed optical fiber sensors with the goal of providing a pathway to push the limits in distributed optical fiber sensing for practical applications.

3D Solar‐Blind Ga2O3 Photodetector Array Realized Via Origami Method

AbstractA 3D solar‐blind photodetector array is realized from amorphous Ga2O3 films grown on polyethylene terephthalate substrates via an origami route. The photodetector cells exhibit a dark current of 0.17 nA, and the peak responsivity is about 8.9 A W−1 at 250 nm with a quantum efficiency of 4450%. The photodetector shows a distinct cut‐off wavelength at 268 nm with a solar‐blind ratio of more than two orders of magnitude (photocurrent ratio between 250 nm/300 nm). The photodetector cells reveal excellent electrical stability after thousands of bending cycles. All the photodetector cells of the 3D photodetector array have a highly consistent performance. In addition, the device can execute the functions of capturing a real‐time light trajectory and identifying multipoint light spatial distribution, which cannot be achieved in all the previously reported 2D solar‐blind photodetectors. The results suggest new pathways to fabricate 3D photodetectors from conventional semiconductor films, which may find potential applications in optical positioning, tracking, imaging and communications, etc.

Dual-polarization star-gap nano-antenna

Nano-antennas are used in optical data storage, near-field imaging, photovoltaics, sensing, and spectroscopy applications. In many cases, the antennas work with linear polarization, but some applications require circularly polarized (CP) light such as field-enhanced circular dichroism spectroscopy. Circular dichroism spectroscopy is a technique used to study organic molecules and is widely used in biology and medicine. In this article, we analyze a star-gap nano-antenna array. The antenna combines concentric circular gratings and a symmetric gap to provide a maximum electric field enhancement factor of around 48 at 780 nm with the average electric field enhancement factor of about 34.75. Due to its geometry, the antenna can work for both linearly polarized and CP light, having similar electric field enhancement factors. Due to its symmetry and capacity to work with different polarizations, the antenna can find applications in sensing and spectroscopy. As an example of application, we have characterized the antenna for surface enhanced Raman scattering (SERS) and obtained a SERS factor of 4.18×106 for the 880cm−1 Raman line of ethanol.

Generation of arbitrary partially coherent Bessel beam array with a LED for confocal imaging.

As the most important class of self-imaging beams, Bessel Beams (BBs) have been extensively studied, and various applications in optical trapping, communication, imaging and quantum studies have been found. In this paper, we propose a new method to generate arbitrary (quasi-) BB arrays by using a single LED light source. The method is simpler, cheaper, and more compatible than other existing methods. The key idea of the proposed method is to form spatially controllable incoherent point sources used to generate BB array imaging. Detailed theoretical deduction, analysis of properties of the generated BB array and comparison with those generated by coherent light sources are depicted. Further application to confocal imaging shows that the BB array is promising for fast, super depth-of-field imaging and multi-particle optical manipulations.

Optical fluorescence imaging with shortwave infrared light emitter nanomaterials for in vivo cell tracking in regenerative medicine.

In vivo tracking and monitoring of adoptive cell transfer has a distinct importance in cell‐based therapy. There are many imaging modalities for in vivo monitoring of biodistribution, viability and effectiveness of transferred cells. Some of these procedures are not applicable in the human body because of low sensitivity and high possibility of tissue damages. Shortwave infrared region (SWIR) imaging is a relatively new technique by which deep biological tissues can be potentially visualized with high resolution at cellular level. Indeed, scanning of the electromagnetic spectrum (beyond 1000 nm) of SWIR has a great potential to increase sensitivity and resolution of in vivo imaging for various human tissues. In this review, molecular imaging modalities used for monitoring of biodistribution and fate of administered cells with focusing on the application of non‐invasive optical imaging at shortwave infrared region are discussed in detail.

Switching effects of spontaneously formed superlattices in relaxor ferroelectrics

Relaxor ferroelectrics have found significant applications in various functional devices in photonics and electronics because of their extraordinary optical and dielectric properties which are directly associated with the polarization relaxation dynamics. However, the related mechanism currently remains not clearly understood, especially for the polar domain reversal in nanostructured relaxor ferroelectrics. This paper reports an observation of intriguing spontaneous superlattices formation of self-ordered nanostructures in a ferroelectric perovskite of KTN:Cu by cooling the crystal below the temperature of its dielectric maximum. More importantly, the strong diffraction induced by the spontaneously formed superlattices can be switched with an AC electric field after a pre-polarization using a DC electric field. The experimental results indicate the switching effect originates from an asymmetric reversal process of the polarization in nanoscale domains. The study not only facilitates further understanding the physics of the ferroelectric relaxation process, but also have potential applications in optical switching, imaging and display.

Multicharged vortex induced in fractional Schrödinger equation with competing nonlocal nonlinearities

This study analytically and numerically investigates the evolution of an optical vortex beam carrying topological charges (TCs) in a fractional Schrödinger equation with competing nonlocal nonlinearities. Results show that the number of beads, TCs, and size of the incident beam significantly affect vortex production and evolution. Common rules formulated based on various incident beams determine the number of induced vortices and corresponding rotation direction. The beams gradually expand to induce vortices in oppositely charged pairs during propagation, thus conserving the vortex’s net TC. The demonstrated optical vortex is significant for quantum information communication and optical imaging and processing applications.

A micromachined water-immersible scanning mirror using BoPET hinges

This paper reports a new micromachined two-axis water-immersible scanning mirror using BoPET (biaxially-oriented polyethylene terephthalate) hinges. A new fabrication process based on deep plasma etching on a hybrid silicon-BoPET substrate was developed to enable high-resolution patterning and batch fabrication capability. For demonstration, a prototype scanning mirror was designed, fabricated and tested. It has an overall size of 5 × 5 × 5 mm3, which is comparable to that of a typical silicon-based micro scanning mirror. With a short-hinge design, the size of the mirror plate reaches 4 × 4 mm2 to provide an even larger aperture for optical or acoustic beam steering. In the air, the resonance frequencies of the fast and slow axes are 420 Hz and 190 Hz respectively. When immersed in water, the resonance frequencies are reduced to 330 Hz and 160 Hz, respectively. The tilting angles of the mirror around the fast and slow axes follow a linear relationship with the driving current up to ±3.5°. With both axes driven simultaneously, stable and repeatable raster scanning patterns were obtained in both air and water. The micromachined water-immersible scanning mirrors could be useful for various scanning optical and acoustic microscopic imaging applications in both air and liquid environments.

Exendin-4 analogs in insulinoma theranostics.

Insulinomas, neuroendocrine tumors arising from pancreatic beta cells, often show overexpression of the glucagon-like peptide-1 receptor. Therefore, imaging with glucagon-like peptide analog exendin-4 can be used for diagnosis and preoperative localization. This review presents an overview of the development and clinical implementation of exendin-based tracers for nuclear imaging, and the potential use of exendin-4 based tracers for optical imaging and therapeutic applications such as peptide receptor radionuclide therapy or targeted photodynamic therapy.

Nonlinear optical microscopy with achromatic lenses extending from the visible to the mid-infrared

With the advent of near-infrared broadband sources stretching into the mid-infrared (MIR) region, there is a growing demand for optical components with utility over an increasingly broad spectral range. For refractive lenses, color correction over such broad bandwidths can be a challenge. In this work, we discuss and demonstrate a two-element lens design with achromaticity spanning the visible to the mid-infrared. The air-spaced doublet designed from commercially available materials shows a significant reduction in spot size and chromatic shift compared to single lens alternatives. We have tested these new broad bandwidth achromats for the purpose of laser-scanning sum-frequency generation microscopy, confirming their improved performance for nonlinear optical imaging applications. The super broadband achromatic lenses represent an attractive alternative to reflective components in ultrabroadband applications, as they enable compact transmission-based optical designs and good focusing performance at off-axis field angles.

Rapid and robust two-dimensional phase unwrapping via deep learning.

Two-dimensional phase unwrapping algorithms are widely used in optical metrology and measurements. The high noise from interference measurements, however, often leads to the failure of conventional phase unwrapping algorithms. In this paper, we propose a deep convolutional neural network (DCNN) based method to perform rapid and robust two-dimensional phase unwrapping. In our approach, we employ a DCNN architecture, DeepLabV3+, with noise suppression and strong feature representation capabilities. The employed DCNN is first used to perform semantic segmentation to obtain the segmentation result of the wrapped phase map. We then combine the wrapped phase map with the segmentation result to generate the unwrapped phase. We benchmarked our results by comparing them with well-established methods. The reported approach out-performed the conventional path-dependent and path-independent algorithms. We also tested the robustness of the reported approach using interference measurements from optical metrology setups. Our results, again, clearly out-performed the conventional phase unwrap algorithms. The reported approach may find applications in optical metrology and microscopy imaging.

Review of micro-optical sectioning tomography (MOST): technology and applications for whole-brain optical imaging [Invited

Elucidating connectivity and functionality at the whole-brain level is one of the most challenging research goals in neuroscience. Various whole-brain optical imaging technologies with submicron lateral resolution have been developed to reveal the fine structures of brain-wide neural and vascular networks at the mesoscopic level. Among them, micro-optical sectioning tomography (MOST) is attracting increasing attention, as a variety of technological variations and solutions tailored toward different biological applications have been optimized. Here, we summarize the recent development of MOST technology in whole-brain imaging and anticipate future improvements.

Label-free neuroimaging in vivo using synchronous angular scanning microscopy with single-scattering accumulation algorithm

Label-free in vivo imaging is crucial for elucidating the underlying mechanisms of many important biological systems in their most native states. However, the applicability of existing modalities has been limited to either superficial layers or early developmental stages due to tissue turbidity. Here, we report a synchronous angular scanning microscope for the rapid interferometric recording of the time-gated reflection matrix, which is a unique matrix characterizing full light-specimen interaction. By applying single scattering accumulation algorithm to the recorded matrix, we removed both high-order sample-induced aberrations and multiple scattering noise with the effective aberration correction speed of 10,000 modes/s. We demonstrated in vivo imaging of whole neural network throughout the hindbrain of the larval zebrafish at a matured stage where physical dissection used to be required for conventional imaging. Our method will expand the scope of applications for optical imaging, where fully non-invasive interrogation of living specimens is critical.

Dielectric cross-shaped-resonator-based metasurface for vortex beam generation at mid-IR and THz wavelengths

Abstract Metasurfaces are engineered thin surfaces comprising two-dimensional (2D) arrays of sub-wavelength-spaced and sub-wavelength-sized resonators. Metasurfaces can locally manipulate the amplitude, phase, and polarization of light with high spatial resolution. In this paper, we report numerical and experimental results of a vortex-beam-generating metasurface fabricated specifically for infrared (IR) and terahertz (THz) wavelengths. The designed metasurface consists of a 2D array of dielectric cross-shaped resonators with spatially varying length, thereby providing the desired spatially varying phase shift to the incident light. The metasurface was found to be insensitive to the polarization of the incident light. The dimensions of the cross-resonators were calculated using rigorous finite-difference time-domain analysis. The spectral scalability via physical scaling of the meta-resonators is demonstrated using two vortex-generating optical elements operating at 8.8 μm (IR) and 0.78 THz. The vortex beam generated in the mid-IR spectral range was imaged using a Fourier transform IR (FTIR) imaging miscroscope equipped with a focal plane array detector. This design could be used for efficient wavefront shaping and various optical imaging applications in the mid-IR spectral range, where polarization insensitivity is desired.