Phosphors have been used as wavelength converters in illumination for many years. When it is excited with blue light, the frequently used yttrium aluminium garnet doped with cerium (YAG:Ce) phosphor converts a part of blue light to a wideband yellow light, resulting in the generated light having a white color. By combining an appropriate concentration of the YAG:Ce phosphor and blue excitant light, white light of a desired correlated color temperature (CCT) can be obtained. However, this type of illumination has a lower color rendering index value (CRI). In an attempt to improve the CRI value, we mixed the YAG:Ce phosphor with europium-doped calcium sulfide phosphor (CaS:Eu), which resulted in a considerably increased CRI value. This article examines an experiment with luminescent layers consisting of a mixture of selected phosphors and polydimethylsiloxane (PDMS). Different thicknesses in these layers were achieved by changing the speed of rotation during their accumulation onto laboratory glass using the method of spin coating. The spectral characteristics of these luminescent layers as they were excited with blue light emitting diode (LED) and laser diode (LD) were then determined. A suitable combination of the YAG:Ce phosphor with a phosphor containing europium, as it was excited with a blue LED, yielded a source of white light with a CRI value of greater than 85. The response time in the tested luminescent layers to a rectangular excitant impulse (generated by a signal generator and transmitted by LD) was also measured in order to examine their potential use in visible light communications (VLC).

The influence of atmospheric environment is fundamental for Free-Space Optical link (FSO). The atmosphere can significantly degrade the communication quality of FSO up to so low received power/RSSI level that it can lead to the loss of communication. For this reason, authors used a professional weather station built on site of FSO link for measurement of real atmospheric conditions such as wind speed, temperature, relative air humidity, air pressure and solar radiation. Random changing of these atmosphere parameters creates atmospheric turbulences, absorption and dispersion centers. It is necessary to specify the value of refractive index structure parameter Cn2 because it determines the influence of atmosphere on the FSO. The first part of this article includes the theoretical calculation of Cn2, there are used two models PAMELA and Macroscale-Meteorological model. The evaluation of the atmospheric influences and the RSSI value of received power level and also simulation of different types of modulation formats OOK-RZ, OOK-NRZ and BPSK in Optiwave is in tegral part of this article.

Purposeful Suppression and Reconstruction of White Light from LED for Improvement of Communication Properties

Nowadays, it is obvious that the access networks will be build up from optical networks. With that are linked also optical components. These components are mostly passive connectors and splitters. In terms of the attenuation budget of the entire network, especially the splitters are very important elements in planning of the networks. The change in attenuation of these elements can lead to failure of the entire network. This article is focused to the issue of measurement of attenuation changes of the fiber optic splitters caused by the temperature with different dividing ratios and number of branches. The article describes the attenuation changes with temperature for commercially available single-mode fiber optical splitters and its capabilities for internal use. Effects of temperature were simulated in specialized chamber, which can reach the temperatures of value about 300 °C. Each fiber splitter was measured from all directions and several times in order to construct the statistical evaluation of the measured and calculated data. The measurement content also included determination of attenuation, crosstalk between the branches, insertion loss and total loss.

Polyaniline hydrochloride was prepared by the oxidation of aniline hydrochloride with ammonium peroxodisulfate in dilute hydrochloric acid. The polyaniline films were produced during the polymerization on the microscope glass surfaces immersed in the reaction mixture. The thin film was created and its thickness has been about 100 nm. We have measured the spectral transmittance together with temperature changes. The polyaniline thin film is conductive and we observed changes in optical transmittance spectra and reflective spectra with electric current. Optical spectra have been measured in range from 380 nm to 1010 nm. The electric conductivity has been changed with silicate substrate. This substrate influenced the free electrons distribution and therefore the optical properties of polyaniline. Due to electric current going through the nanofilm its sensitivity to temperature has been increased. We also observed two specific spectral windows. The first one was characterized by its insensitivity to temperature; the second one has been temperature sensitive. The central wavelength of insensitive window is about 500nm. This property can be the base for novel sensors structures. We used Ocean Optics USB spectrometer for evaluation of spectral changes. Wideband white light halogen source from the same manufacturer has been applied as a light source. Small polarizing dependence of reflected light has been observed too.