The Propagation of Vortex Beams in Random Mediums

Vortex beams acquire increasing attention due to their unique properties. These beams have an annular spatial profile with a dark spot at the center, the so-called phase singularity. This singularity defines the helical phase structure which is related to the topological charge value. Topological charge value allows vortex beams to carry orbital angular momentum. The existence of orbital angular momentum offers a large capacity and high dimensional information processing which make vortex beams very attractive for free-space optical communications. Besides that, these beams are well capable of reducing turbulence-induced scintillation which leads to better system performance. This chapter introduces the research conducted up to date either theoretically or experimentally regarding vortex beam irradiance, scintillation, and other properties while propagating in turbulent mediums

Performance of hollow hyperbolic sinusoidal Gaussian beam in weak turbulent optical communication links

The performance of hollow hyperbolic sinusoidal Gaussian beam (HHsGB) propagating in weak turbulent optical communication link is examined by analysing the beam scintillation indices. System parameters’ effect on point-like and aperture-averaged scintillation index values is investigated. The obtained results show that HHsGBs with small source sizes improve the link performance by reducing the scintillation level. In communication systems with a big receiver aperture radius, HHsGBs with high orders significantly minimize the scintillation level. Thus, the provided results will have significant potential in improving free-space optical communication performance in a wide range of applications

Atmospheric turbulence recognition with deep learning models for sinusoidal hyperbolic hollow Gaussian beams-based free-space optical communication links

The integration of artificial intelligence technology to improve the performance of free-space optical communication (FSO) systems has received increasing interest. This study aims to propose a novel approach based on deep learning techniques for detecting turbulence-induced distortion levels in FSO communication links. The deep learning-based models improved and fine-tuned in this work are trained using a dataset containing the intensity profiles of Sinusoidal hyperbolic hollow Gaussian beams (ShHGBs). The intensity profiles included in the dataset are the ones of ShHGBs propagating for 6 km under the influence of six different atmospheric turbulence strengths. This study presents deep learning-based Resnet-50, EfficientNet, MobileNetV2, DenseNet121 and Improved+MobileNetV2 approaches for turbulence-induced disturbance detection and experimental evaluation results. In order to compare the experimental results, an evaluation is made by considering the accuracy, precision, recall, and f1-score criteria. As a result of the experimental evaluation, the average values for accuracy, precision, recall and F-score with the best performance of the improved method are given; average accuracy 0.8919, average precision 0.8933, average recall 0.8955 and average F-score 0.8944. The obtained results have immense potential to address the challenges associated with the turbulence effects on the performance of FSO systems

Analysis of Finite Energy Fresnel Bessel Beams Scintillation Level in turbulent communication links

peer reviewedAbstract Scintillation indices of Finite Energy Fresnel-Bessel Beams (FEFBBs) propagating for 6Km in a turbulent atmosphere are analysed. In this context, the effects of beam order and Gaussian beam waist on the reduction of scintillation level are evaluated. Both the point-like scintillation and the power scintillation indices are examined. The obtained results show that beam order does not have a significant impact on the scintillation levels. FEFBBs are able to reduce the power scintillation levels, then improve the system performance better than fundamental Gaussian beams. Thus, the provided results are significant for not only the performance improvement of the free-space optical (FSO) communication systems but also for the applications that require line of sight alignment namely directed infrared countermeasure (DIRCM).&#xD

Performing the Finite Energy Airy-Hermite-Hollow Gaussian Beam in a turbulent atmosphere

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Propagation of hollow higher-order cosh-Gaussian beam in human upper dermis

peer reviewedAbstract Optical detection, measurement, and treatment methods are widely used in the medical industry nowadays. The evolution of radiated beams, received power and beam size play vital roles while developing devices. The propagation properties of hollow higher-order cosh-Gaussian beam (HHOCGB) while propagating in human upper dermis tissue are derived analytically and analyzed numerically. The impact of the hollowness parameter, beam order, operating wavelength, and Gaussian beam waists on the beam’s intensity profile is examined. Received power and beam size variations are analyzed considering operating wavelength and Gaussian waist width. According to the results, as the beam propagates, its profile rapidly evolves into a shape with a circular Gaussian peak in the center and petals at the corner. Dark hollow regions are observed among the petals. Furthermore, the received power by HHOCGBs with a higher Gaussian waist width is more than those received by beams with a lower Gaussian waist width. However, at far field, operating at a lower wavelength prevents the increase of the beam spread. Thus, the obtained results will be significant in the bio-optical disease detection and treatment technology development

Time-Domain Characterization of the Radiation Pattern of the Terahertz Photoconductive Antennas

We present a novel method to characterize the radiation pattern of the terahertz photoconductive antennas in time-domain. The method uses a modified version of the terahertz time-domain spectroscopy system, where we use the basics of physical optics and the optical path compensation principle using the delay line in the system in order to detect the spatial distribution of the terahertz radiation of the photoconductive antennas in two major planes. Using this method, we investigate two terahertz photoconductive antennas, namely dipole and spiral antennas, and compare the measurement results with simulations in time-domain. The comparison of the calculation and measurement results shows good agreement, where we measure an average and maximum optical path difference error of 4.7 and 8%, which results in an average and maximum half-power beam width error of 1.87 and 3.2 degrees, respectively. We believe that the proposed method will be useful for predicting the system level performance of the terahertz time-domain spectroscopy systems in real-life applications.Turkish Academy of Sciences (TUBA GEBIP 2015), and Ankara Yıldırım Beyazıt University (BAP 3774

Radiation Pattern Characterization of Terahertz Photoconductive Antennas Using Time-Domain Spectroscopy System

This paper presents the radiation pattern characterization of terahertz photoconductive antennas using a new technique. The proposed technique is implemented using a modified terahertz time domain spectroscopy by applying a full mapping of the THz beam. The proposed method was also compared with analytical methods and numerical solvers. The comparison of the measured results with that of the simulations shows a half-power beam width error of 1.5. and an optical path difference error of 8%. To the best of our knowledge, this is the first time terahertz time domain spectroscopy system is used to characterize the radiation pattern of terahertz photoconductive antennas