Lucie Hudcova

On the derivation of exact analytical FSO link attenuation model

The development of semiconductor technology has led to an increase of the usable bandwidth of light-emitting diodes LED, which are suitable for indoor high-speed communications or free-space optical FSO communications over a relatively short distance. The high-speed long-distance FSO links, where turbulence effects are considerably high, are a domain of laser sources. Hence, the paper covers the study of an exact analytical model of FSO link attenuation and the benefits of using an elliptically symmetrical Gaussian beam rather than a circularly symmetrical one.

Optical wireless communication transmitter with a refraction beam shaper

The main purpose of this paper is the design and simulation of a laser beam shaping system which can be used in a Free Space Optical (FSO) communication transmitter terminal prototype. It is known that a top-hat beam source is less affected from turbulence in the atmosphere than a Gaussian beam source. The design of a refraction beam shaper has been performed and verified in the optical design software ZEMAX. The paper also discusses the diffraction phenomenon which influences irradiance distribution of the beam.

Influence of the atmospheric turbulence on the laser beam

Free space optical (FSO) communication links offer a number of advantages over radio frequency links. Main advantages of FSO communication links are electromagnetic compatibility, license-free band and high data rate. However, reliability of these links is highly dependent on atmospheric and weather conditions. An optical wave propagating through the atmospheric transmission media is very sensitive on variety of atmospheric effects, e.g. beam wander, fluctuation of optical intensity and loss of spatial coherence. The purpose of this paper is to present the measurement of the distribution of the relative optical intensity variance in the Gaussian beam. The measurement of the spatial coherence is also presented.

Comparison and evaluation of the laser beam-shaping techniques

Over the past several decades, free-space optical (FSO) systems have gained a specific place in the wireless technology area. The application of these systems is advantageous for high bandwidths, a license free band and quick installation. The main drawback of FSO systems is their dependence on the state of the atmosphere causing deterioration of the FSO systems availability. One of the atmospheric effects which has an essential impact on the performance of the FSO systems is atmospheric turbulence. Atmospheric turbulence leads to fluctuation of the optical intensity in the plane of the receiving aperture. It has been shown that to reduce the effect of atmospheric turbulence, uniform distribution of the optical intensity within the cross section of the beam in the plane of transmitting aperture (phenomenon of diffraction is neglected) and a suffciently large diameter of the circularly symmetric receiving aperture (to achieve aperture averaging effect) are needed. The main idea of our paper is the problem of beam shaping at the transmitter. In our contribution the technique of transformation of a Gaussian beam into a beam with uniform distribution of optical intensity is discussed. For the mentioned transformation we experimentally tested several shaping methods such as multi aperture beam integrators, diffractive diffusers, etc. Usage of laser sources with different degrees of coherence was considered. The purpose of these techniques is to create an optical beam with uniform distribution of optical intensity on the transmitter output. In order to compare and evaluate the particular shaping techniques, a new Trans- formation Complex Quality (TCQ) parameter was defined. The TCQ parameter indicates the optimal shaping technique and also evaluates the quality of the resulting transformed beam with respect to its resistance towards atmospheric turbulence.

Experimental measurement of the atmospheric turbulence effects and their influence on performance of fully photonic wireless communication receiver

Abstract The new generation of Free-Space Optical systems utilizes photonic components used in optical fiber communications which demand high precision and complexity of the system. We present an analysis of the laser beam propagation in the context of fully photonic free space optical links. The experimental data is presented and used for the estimation of single-mode (SM) fiber coupling loss.

Retroreflective optical communication

This article deals with visible light communication (VLC) based on retroreflective principle. Visible light communication presents great potential in terms of possible communication bandwidth, transmittter localization, spectral, power and spatial effectivity and more. In the article, the retroreflective communication itself is introduced and compared to common VLC and RFID systems. Essential parts of power balance are mentioned and discussed. The last part of the article discusses benefits of retroreflective communication for Internet of Things.

Prediction of atmospheric turbulence on the basis of weather conditions

The goal of the paper is in calulation of refractive index structure parameter from weather condition in selected area. Sadot - Kopeika model was chosen for determination of atmospheric turbulence during the whole day. Information about temperature, relative humidity, wind speed, time of sunrise and sunset is necessary for calculations in case of usage of the model. The main advantage of Sadot - Kopeika model is in possibility of prediction of refractive index structure parameter. We need meteorological data, so we compared the predictions for one and two days in advance from three online meteorological services. After that we have compared predicted data with data from meteorological station. Our work on the paper rely on the refractive index structure parameter prediction and comparison with calculated values from meteorological stations.

LwIP based network solution for MicroBlaze

This article deals with interfacing of Xilinx MicroBlaze (UB) softcore microprocessor to full duplex, 1 Gb/s media converter from metallic to optical interface, which is employed in experimental FSO link as a transceiver. The MicroBlaze harvests statistical data from the link and allows administration of the link via interactive web user interface. The MicroBlaze is connected to the data bus of the media converter via custom simple Ethernet switch and custom network interface. The porting of lightweight IP stack and implementation of example HTTP server is mentioned. The whole design is implemented on Xilinx XUPV5-LX110T Evaluation Platform with Virtex-5 FPGA chip.

Improvement of bit error rate in free space optical link

The article describes an innovative bit error rate reduction technique principle and its practical implementation. The design of the technique is implemented in an FPGA and is combined with other more conventional BER reduction techniques, such as Reed-Solomon coding. Experimental results are provided. The application bit rate in function of BER for both reliable (TCP) and unreliable (UDP) mode of transport is presented. The end-to-end delay of the designed transceiver is also experimentally verified and analysed.

Analysis of thermal effects in endoscopic nanocarriers-based photodynamic therapy applied to esophageal diseases

In this work we propose a predictive model that allows the study of thermal effects produced when the optical radiation interacts with an esophageal or stomach disease with gold nanoparticles embedded. The model takes into account light distribution in the tumor tissue by means of a Monte Carlo method. Mie theory is used to obtain the gold nanoparticles optical properties and the thermal model employed is based on the bio-heat equation. The complete model was applied to two types of tumoral tissue (squamous cell carcinoma located in the esophagus and adenocarcinoma in the stomach) in order to study the thermal effects induced by the inclusion of gold nanoparticles.