Neural network classification of beams carrying orbital angular momentum after propagating through controlled experimentally generated optical turbulence.

We generate an alphabet of spatially multiplexed Laguerre-Gaussian beams carrying orbital angular momentum, which are demultiplexed at reception by a convolutional neural network (CNN). In this investigation, a methodology for optimizing alphabet design for best classification rates is proposed, and three 256-symbol alphabets are designed for performance evaluation in optical turbulence. The beams were propagated in three environments: through underwater optical turbulence generated by Rayleigh-Bénard (RB) convection (C n2≅10-11 m -2/3), through a simulated propagation path derived from the Nikishov spectrum (C n2≅10-13 m -2/3), and through optical turbulence from a thermal point source located in a water tank (C n2≅10-10 m -2/3). We report a classification accuracy of 93.1% for the RB environment, 99.99% in simulation, and 48.5% in the point source environment. The project demonstrates that the CNN can classify the complex alphabet symbols in a practical turbulent flow that exhibits strong optical turbulence, provided sufficient training data is available and testing data is representative of the specific environment. We find the most important factor in a high classification accuracy is a diversification in the intensity profiles of the alphabet symbols.

Randomness of optical turbulence generated by Rayleigh-Bénard convection using intensity statistics.

The experimental study of optical turbulence proves difficult due to challenges in generating controllable conditions in a laboratory environment. Confined water tanks that produce Rayleigh-Bénard (RB) convection are one method to generate optical turbulence using a controllable temperature gradient. It is of utmost concern to quantify the properties of the optical turbulence generated for characterization of other optical applications such as imaging, sensing, or communications. In this experimental study a Gaussian beam is propagated through a RB water tank where two intensity measurements are made at the receiver's pupil and focal plane. The pupil and focal plane results include quantification of the intensity fluctuation distribution, scintillation distribution, and refractive index structure constant at various values of the temperature gradient. The angle of arrival fluctuations is also calculated at the focal plane to obtain a second estimate of C n2. The pupil plane estimate for C n2 using scintillation index and focal plane angle of arrival fluctuations is compared to preliminary predictions of C n2 as a function of RB temperature gradient showing C n2âˆ¼Δ T 4/3. The outcomes of the study confirm that the RB process produces intensity fluctuations that follow gamma-gamma and log-normal probability density functions. Estimates of the refractive index structure constant C n2 produce the same trends with different magnitudes when measured from the pupil and focal plane.

Structured illumination and image enhancement of three-dimensional and moving objects at a distance via incoherent Fourier ptychography.

We experimentally apply incoherent Fourier ptychography to enhance the resolution of recorded images by projecting known, uncorrelated, random patterns at high speed onto 3D moving and distant objects. We find that the resolution enhancement factor can be greater than 2, depending on the projection and camera optics.

Synchronous optical intensity and phase measurements to characterize Rayleigh-Bénard convection.

Propagation of a laser beam through the Rayleigh-Bénard (RB) convection is experimentally investigated using synchronous optical wavefront and intensity measurements. Experimental results characterize the turbulence strength and length scales, which are used to inform numerical wave optic simulations employing phase screens. Experimentally found parameters are the refractive index structure constant, mean flow rate, kinetic and thermal dissipation rates, Kolmogorov microscale, outer scale, and shape of the refractive index power spectrum using known models. Synchronization of the wavefront and intensity measurements provide statistics of each metric at the same instance in time, allowing for two methods of comparison with numerical simulations. Numerical simulations prove to be within agreement of experimental and published results. Synchronized measurements provided more insight to develop reliable propagation models. It is determined that the RB test bed is applicable for simulating realistic undersea environments.

Transport-based pattern recognition versus deep neural networks in underwater OAM communications.

Comparisons between machine learning and optimal transport-based approaches in classifying images are made in underwater orbital angular momentum (OAM) communications. A model is derived that justifies optimal transport for use in attenuated water environments. OAM pattern demultiplexing is performed using optimal transport and deep neural networks and compared to each other. Additionally, some of the complications introduced by signal attenuation are highlighted. The Radon cumulative distribution transform (R-CDT) is applied to OAM patterns to transform them to a linear subspace. The original OAM images and the R-CDT transformed patterns are used in several classification algorithms, and results are compared. The selected classification algorithms are the nearest subspace algorithm, a shallow convolutional neural network (CNN), and a deep neural network. It is shown that the R-CDT transformed images are more accurate than the original OAM images in pattern classification. Also, the nearest subspace algorithm performs better than the selected CNNs in OAM pattern classification in underwater environments.

Machine learning-aided classification of beams carrying orbital angular momentum propagated in highly turbid water: publisher's note.

This publisher's note corrects the name of an author of J. Opt. Soc. Am. A37, 1662 (2020)JOAOD60740-323210.1364/JOSAA.401153.

Machine learning-aided classification of beams carrying orbital angular momentum propagated in highly turbid water.

A set of laser beams carrying orbital angular momentum is designed with the objective of establishing an effective underwater communication link. Messages are constructed using unique Laguerre-Gauss beams, which can be combined to represent four bits of information. We report on the experimental results where the beams are transmitted through highly turbid water, reaching approximately 12 attenuation lengths. We measured the signal-to-noise ratio in each test scenario to provide characterization of the underwater environment. A convolutional neural network was developed to decode the received images with the objective of successfully classifying messages quickly. We demonstrate near-perfect classification in all scenarios, provided the training set includes some images taken under the same underwater conditions.

Designing laser beams carrying OAM for a high-performance underwater communication system.

We present a design methodology for creating a distinct laser beam set suitable for detection by using only the recorded intensity pattern. We consider four coherent Laguerre-Gaussian beams carrying orbital angular momentum (OAM) to form the basis for optical communication. The complex electric fields of the beams are superimposed to create 16 dissimilar intensity patterns. The presented beam set design method considers the beam generation hardware limitations and aims to minimize the correlation among the messages and maximize their intensity differences. After propagating the 16 messages through a water channel, we measured high correlation, intensity similarity, and R-squared values for the identical messages and low values for the different ones. Distinct clustering between the measurements for the matching messages and the rest allows us to set a threshold in the gap among the groupings and successfully classify the received images.

Imaging through extreme scattering in extended dynamic media.

Critical to navigation, situational awareness, and object identification is the ability to image through turbid water and fog. To date, the longest imaging ranges in such environments rely on active illumination and selection of ballistic photons by means of time gating. Here we show that the imaging range can be extended by using time-gated holography in combination with multi-frame processing. Instead of simply summing the intensity of the frames, we use the complex fields retrieved through digital holographic processing and coherently add the frames. We demonstrate imaging through extended bodies of turbid water and fog at one-way attenuation lengths of 13 and 13.6, respectively. Compared to equivalent traditional time-gated systems, gated holography and coherent processing require 20× less laser illumination power for the same imaging range.

Range performance of the DARPA AWARE wide field-of-view visible imager.

In a prior paper, we described a new imaging architecture that addresses the need for wide field-of-view imaging combined with the resolution required to identify targets at long range. Over the last two years substantive improvements have been made to the system, both in terms of the size, weight, and power of the camera as well as to the optics and data management software. The result is an overall improvement in system performance, which we demonstrate via a maritime target identification experiment.

Characterization of the AWARE 10 two-gigapixel wide-field-of-view visible imager.

System requirements for many military electro-optic and IR camera systems reflect the need for both wide-field-of-view situational awareness as well as high-resolution imaging for target identification. In this work we present a new imaging system architecture designed to perform both functions simultaneously and the AWARE 10 camera as an example at visible wavelengths. We first describe the basic system architecture and user interface followed by a laboratory characterization of the system optical performance. We then describe a field experiment in which the camera was used to identify several maritime targets at varying range. The experimental results indicate that users of the system are able to correctly identify ~10 m targets at between 4 and 6 km with 70% accuracy.

Denoising infrared maritime imagery using tailored dictionaries via modified K-SVD algorithm.

Recent work has shown that tailored overcomplete dictionaries can provide a better image model than standard basis functions for a variety of image processing tasks. Here we propose a modified K-SVD dictionary learning algorithm designed to maintain the advantages of the original approach but with a focus on improved convergence. We then use the learned model to denoise infrared maritime imagery and compare the performance to the original K-SVD algorithm, several overcomplete "fixed" dictionaries, and a standard wavelet denoising algorithm. Results indicate the superiority of overcomplete representations and show that our tailored approach provides similar peak signal-to-noise ratios as the traditional K-SVD at roughly half the computational cost.

Ultrasound is now better than mammography for the detection of invasive breast cancer.

OBJECTIVE: This study investigated the use of ultrasound (US) as a first-line diagnostic tool. METHODS: All women attending our breast center underwent bilateral whole-breast US in addition to all other investigations, and results were documented prospectively and preoperatively. RESULTS: Of 796 patients with breast cancer, US was positive in 710 (89%) and mammography in 706 (89%) (P = not significant). Either US or mammogram was positive in 770 (97%). Of 537 (67%) symptomatic patients, US was positive in 497 (93%) and mammography in 465 (87%). Either US or mammography was positive in 515 (96%). Of 259 (33%) screening patients, 220 (85%) had invasive cancer. US was positive in 195 (89%) and mammography in 203 (92%) (P = not significant). Either US or mammography was positive in 217 (99%). Of 39 screening patients with ductal carcinoma in situ (5% of all patients), US was positive in 18 (46%) and mammography in 38 (97%). CONCLUSIONS: US is significantly better than mammography for detecting invasive breast cancer (92% patients). The combination of US and mammography is significantly better than either modality used alone, together resulting in 9% more breast cancers detected.

Is breathing in infants chaotic? Dimension estimates for respiratory patterns during quiet sleep.

We describe an analysis of dynamic behavior apparent in times-series recordings of infant breathing during sleep. Three principal techniques were used: estimation of correlation dimension, surrogate data analysis, and reduced linear (autoregressive) modeling (RARM). Correlation dimension can be used to quantify the complexity of time series and has been applied to a variety of physiological and biological measurements. However, the methods most commonly used to estimate correlation dimension suffer from some technical problems that can produce misleading results if not correctly applied. We used a new technique of estimating correlation dimension that has fewer problems. We tested the significance of dimension estimates by comparing estimates with artificial data sets (surrogate data). On the basis of the analysis, we conclude that the dynamics of infant breathing during quiet sleep can best be described as a nonlinear dynamic system with large-scale, low-dimensional and small-scale, high-dimensional behavior; more specifically, a noise-driven nonlinear system with a two-dimensional periodic orbit. Using our RARM technique, we identified the second period as cyclic amplitude modulation of the same period as periodic breathing. We conclude that our data are consistent with respiration being chaotic.

Digestion of food samples for total mercury determination.

A method of digestion by using a mixture of hydrochloric, nitric, and sulfuric acids has been developed for the determination of total mercury in a wide range of food samples. Good recoveries of mercury were obtained from NBS (National Bureau of Standards) Albacore Tuna and from food samples spiked with inorganic mercury. A detection limit of 0.01 microgram mercury/g can be obtained.

Hyperelasticity syndromes.

A review of hyperelasticity syndromes is included. Ehlers-Danlos syndrome, pseudoxanthoma elasticum, cutis laxa and Marfan's syndrome are discussed.

Skin sensitization with the new reagents NOPYE (4-nitro-1-cyclohexyl-3-ethoxy-2-oxo-3-pyrroline) and NOPY-L-phenylalanine.

The aim of this study was to investigate the compound 4-nitro-1-cyclohexyl-3-ethoxy-2-oxo-3-pyrroline (NOPYE) and some related compounds for skin sensitization in guinea pigs, as the first step in a search for more effective skin sensitizers for immunotherapy of cutaneous tumors. In guinea pigs, NOPYE and NOPYE-L-alanine produce far milder delayed hypersensitivity reactions than DNCB. Both NOPYE and DNCB fail to act as adjuvants for skin sensitization to tuberculin purified protein derivative (PPD) and ovalbumin (OV). This suggests an explanation for the lack of effectiveness of DNCB in immunotherapy of metastases: DNCB may be relatively ineffective as an adjuvant for production of specific antitumor immunity. Such adjuvant activity may be essential if the action of the immunotherapeutic reagent is not to be confined to its site of application but is to be effective at the site of distant metastases.

Comparison of different epithelial substrates useful for indirect immunofluorescence testing of sera from patients with active pemphigus.

A positive statistical correlation between intercellular antibody titer and disease severity was found for a group of 6 patients with active pemphigus vulgaris, irrespective of whether indirect IF testing was performed on 5 different epithelial substrates which included guinea pig esophagus, human foreskin, rabbit esophagus, monkey esophagus and monkey lip. In a group of 4 patients with pemphigus foliaceus a positive correlation between disease severity and titer was found only when rabbit esophagus was used for indirect fluorescence testing. In both groups of patients there were individual patients in whom the antibody titer was positive at a time when no disease was present and conversely, there were some patients in whom the antibody titer was negative at a time when extensive disease was present. Because of this inconsistency, the use of antibody titers to monitor disease activity and therapy in individual patients may not be justifiable.