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.

Block-based compressed sensing for fast optic fiber bundle imaging with high spatial resolution.

The resolution of traditional fiber bundle imaging is usually limited by the density and the diameter of the fiber cores. To improve the resolution, compression sensing was introduced to resolve multiple pixels from a single fiber core, but current methods have the drawbacks of excessive sampling and long reconstruction time. In this paper, we present, what we believe to be, a novel block-based compressed sensing scheme for fast realization of high-resolution optic fiber bundle imaging.

The impact of the COVID-19 outbreak on physical fitness and academic performance of Chinese college students.

Background: Our study aimed to examine the effects of COVID-19 on the physical fitness and academic performance of Chinese college students.

Participants: The sample included physical fitness test data from 9,712 undergraduate students and academic performance data from 12,000 undergraduate students at a top university in China.

Methods: Physical fitness was measured and evaluated according to the Chinese National Student Physical Fitness Standard.

A Fast Linearly Wavelength Step-Swept Light Source Based on Recirculating Frequency Shifter and Its Application to FBG Sensor Interrogation.

A wavelength step-swept light source (WSSL) using a recirculating frequency shifter loop (RFSL) based on a single-side-band (SSB) modulator is proposed, in order to achieve a linear and fast wavelength-sweeping. The swept step can be tuned from 1.2 pm to 128 pm by adjusting a precise and stable radio frequency (RF) signal that is applied to the SSB modulator.

Use of Laser Speckle Contrast Analysis during pelvic surgery in a uterine transplantation model.

Aim: Uterine transplantation (UTx) is proposed for treatment of uterine factor infertility. Our aim was to assess whether Endoscopic Laser Speckle Contrast Analysis (eLASCA) could evaluate pelvic blood flow at anastomotic sites required for sheep and rabbit UTx.

Results/methodology: eLASCA detected blood flow in rabbit UTx #7 and #9.

Model of radial basis functions based on surface slope for optical freeform surfaces.

The model fitting degree of optical freeform surfaces is of utmost design importance. We develop a model with radial basis functions based on the surface slope (RBF-slope) for optical freeform surfaces with asymmetric structures. The RBF-slope model improves the basis-function distribution for circular apertures and establishes a relationship between shape factor and local surface slope, which provides the model with better fitting ability than the conventional RBF model (RBF-direct); fitting experiments for off-axis conic surfaces, "bumpy" paraboloids, and the design of a single mirror magnifier demonstrate the efficacy of our approach.

Lensless wide-field single-shot imaging through turbid media based on object-modulated speckles.

The need to image objects through light-scattering materials is common in a range of applications. Different methods have been investigated to acquire the image of the object when diffusers are presented. In this paper, we demonstrate the object reconstruction with single-shot imaging based on the correlography principle and phase retrieval algorithm with coherent illumination.

Experimental study on optical image encryption with asymmetric double random phase and computer-generated hologram.

Optical image encryption, especially double-random-phase-based, is of great interest in information security. In this work, we experimentally demonstrate the security and feasibility of optical image encryption with asymmetric double random phase and computer-generated hologram (CGH) by using spatial light modulator. First of all, the encrypted image modulated by asymmetric double random phase is numerically encoded into real-value CGH.

Simulation of speckle patterns with pre-defined correlation distributions.

We put forward a method to easily generate a single or a sequence of fully developed speckle patterns with pre-defined correlation distribution by utilizing the principle of coherent imaging. The few-to-one mapping between the input correlation matrix and the correlation distribution between simulated speckle patterns is realized and there is a simple square relationship between the values of these two correlation coefficient sets. This method is demonstrated both theoretically and experimentally.

Statistics-based reconstruction method with high random-error tolerance for integral imaging.

A three-dimensional (3D) digital reconstruction method for integral imaging with high random-error tolerance based on statistics is proposed. By statistically analyzing the points reconstructed by triangulation from all corresponding image points in an elemental images array, 3D reconstruction with high random-error tolerance could be realized. To simulate the impacts of random errors, random offsets with different error levels are added to a different number of elemental images in simulation and optical experiments.

Tracking shear waves in turbid medium by light: theory, simulation, and experiment.

Shear wave propagation provides rich information for material mechanical characterization, including elasticity and viscosity. This Letter reports tracking of shear wave propagation in turbid media by laser-speckle-contrast analysis. The theory is described, and a Monte Carlo simulation of light shear wave interaction was developed.

Effect of signal intensity and camera quantization on laser speckle contrast analysis.

Laser speckle contrast analysis (LASCA) is limited to being a qualitative method for the measurement of blood flow and tissue perfusion as it is sensitive to the measurement configuration. The signal intensity is one of the parameters that can affect the contrast values due to the quantization of the signals by the camera and analog-to-digital converter (ADC). In this paper we deduce the theoretical relationship between signal intensity and contrast values based on the probability density function (PDF) of the speckle pattern and simplify it to a rational function.

Parallel detection of amplitude-modulated, ultrasound-modulated optical signals.

We investigated the effect of amplitude-modulated (AM) ultrasound (US) on acousto-optic (AO) signals. A phantom was exposed to both AM US and a green laser, and CCD measurements of speckle contrast were made with various exposure times. The results show that the AO signal oscillates at the AM frequency when the CCD exposure time is a fraction of the AM period and stops oscillating when the CCD exposure time is a multiple of the AM period.