Andrej Liner

Indoor visible light communication: modeling and analysis of multi-state modulation

The new dynamic direction of wireless networks development is based on the idea of networks utilizing the optical radiation in the visible spectrum VLC (Visible Light Communications). The impulse of this development direction was improvement in the semiconductor lighting technologies, namely the white power LEDs (Light Emitting Diode). These types of wireless networks are denoted as the optical wireless networks for indoor spaces utilizing optical radiation in the visible spectrum. The paper deals with the issue of deployment of multi-state modulations into the indoor visible light communications in LOS (Line of Sight) configuration. The first part of the paper focuses on design of modulation element (SMD LED matrix 3 × 3) and problems connected to deployment of multi-state modulation M-QAM (subcarrier intensity modulation) through this modulation element into the indoor visible light communications (MER). The second part deals with the irradiation distribution in dark room in comparison with real room during used multi-state modulation scheme in both simulation and real measurement.

Software design of segment optical transmitter for indoor free-space optical networks

During recent years, there has been rapid development in optical networks. This includes not only fiber optical networks but also free space optical networks. The free space optical networks can be divided into indoor and outdoor ones. The indoor free space optical networks have been experiencing dramatic progress in the last years, allowed by the newest IEEE norm 802.15.7, which enabled development of different types of transmitter receivers, modulation formats, etc. The team of authors is dealing with software design of segment optical transmitters for an indoor free space optical network based on the multi-mode optical 50/125 or 62.5/125 μm fiber. Simulated data are then evaluated from the point of view of optical intensity uniform distribution and space spot light size radiating from segment optical transmitter.

The arms arrangement influence on the sensitivity of Mach–Zehnder fiber optic interferometer

Fiber-optic sensors based on phase shift measurements are one of the most sensitive sensors at all. In general they are capable to measure various phenomena, for example displacement, rotation, temperature, acoustic pressure, liquid flow and level, strain etc. In our paper we have used interferometer configuration based on the Mach–Zehnder principle with polarization maintaining components and narrowband DFB laser operating at a wavelength of 1550 nm. In this configuration it is important to isolate the reference arm against measured phenomena and on the other hand to increase the sensitivity of the measuring arm to maximize phase shift induced by the measured phenomenon. The paper describes various measurement arrangements of measuring and reference arm and their influence on the measurement sensitivity. The obtained frequency ranges are evaluated for all mentioned combinations.

Simulation and measurement of optical access network with different types of optical-fiber amplifiers

The optical access networks are nowadays swiftly developing in the telecommunications field. These networks can provide higher data transfer rates, and have great potential to the future in terms of transmission possibilities. Many local internet providers responded to these facts and began gradually installing optical access networks into their originally built networks, mostly based on wireless communication. This allowed enlargement of possibilities for end-users in terms of high data rates and also new services such as Triple play, IPTV (Internet Protocol television) etc. However, with this expansion and building-up is also related the potential of reach in case of these networks. Big cities, such as Prague, Brno, Ostrava or Olomouc cannot be simply covered, because of their sizes and also because of their internal regulations given by various organizations in each city. Standard logical and also physical reach of EPON (IEEE 802.3ah - Ethernet Passive Optical Network) optical access network is about 20 km. However, for networks based on Wavelength Division Multiplex the reach can be up to 80 km, if the optical-fiber amplifier is inserted into the network. This article deals with simulation of different types of amplifiers for WDM-PON (Wavelength Division Multiplexing-Passive Optical Network) network in software application Optiwave OptiSystem and than are the values from the application and from real measurement compared.

Detection and localization of building insulation faults using optical-fiber DTS system

Nowadays the trends in the construction industry are changing at an incredible speed. The new technologies are still emerging on the market. Sphere of building insulation is not an exception as well. One of the major problems in building insulation is usually its failure, whether caused by unwanted mechanical intervention or improper installation. The localization of these faults is quite difficult, often impossible without large intervention into the construction. As a proper solution for this problem might be utilization of Optical-Fiber DTS system based on stimulated Raman scattering. Used DTS system is primary designed for continuous measurement of the temperature along the optical fiber. This system is using standard optical fiber as a sensor, which brings several advantages in its application. First, the optical fiber is relatively inexpensive, which allows to cover a quite large area for a small cost. The other main advantages of the optical fiber are electromagnetic resistance, small size, safety operation in inflammable or explosive area, easy installation, etc. This article is dealing with the detection and localization of building insulation faults using mentioned system.

Interferometric sensor based on the polarization-maintaining fibers

The interferometers composed of optical fibers are due to its high sensitivity capable of to measure various influences affecting the fiber. These influences may be bending or different sorts of fiber deformations, vibration, temperature, etc. In this case the vibration is the measured quantity, which is evaluated by analyzing the interference fringes representing changes in the fiber. Was used a Mach-Zehnder interferometer composed of the polarization maintaining elements. The polarization maintaining elements were used because of high sensitivity to polarization state inside the interferometer. The light was splitted into the two optical paths, where the first one is the reference fiber and it is separated from the actual phenomenon, and the second one is measuring fiber, which is directly exposed to vibration transmission from the underlying surface. The light source was narrowband DFB laser serating at a wavelength of 1550nm and as a detector an InGaAs PIN photodiode were used in this measurement. The electrical signal from the photodiode was amplified and fed into the measuring card. On the incoming signal the FFT was applied, which performs the transformation into the frequency domain and the results were further evaluated by software. We were evaluating the characteristic frequencies and their amplitude ratios. The frequency responses are unique for a given phenomenon, thus it is possible to identify recurring events by the characteristic frequencies and their amplitude ratios. The frequency range was limited by the properties of the used speaker, by the frequency characteristics of the filter in the amplifier and used resonant element. For the experiment evaluation the repeated impact of the various spherical objects on the surface board was performed and measured. The stability of amplitude and frequency and also the frequency range was verified in this measurement.

Measurement of attenuation changes of PON elements with temperature

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.

The optical power distribution in a dark room

Nowadays, in the field of communications systems radio transmission frequencies are dominant inside buildings. Due to the increasing of large number of users and devices, that use these frequencies, there is danger of accruing interferences and reducing the transmission performance. Therefore, indoor wireless optical systems are beginning to use as an alternative solution. Indoor wireless optical systems can use for communication direct and reflected light rays. This article deals with the measurement of optical power distribution in the model dark room. As a light source we use white power LEDs located on the ceiling of the room. The measurement of the optical power distribution was performed in dark room, which was specially constructed for this purpose. This room was also modelled in LightTools software that allows simulate a real measurement. This article compares the results of the measurement and the simulation.

New approach to design of optical transmitter for indoor free space optical network

This paper is dealing with design of new type of optical transmitter that is composed of bundle of optical fibers. For design purposes multimode fibers with different dimensions 50/125 and 62.5/125 µm were used. Software designs consisting of 3 or 5 optical fibers in bundle were subsequently evaluated from the point of view of uniform optical intensity distribution and dimensions of light pattern in space.

Rock massif temperature changes measurement with regard to thermal responses generated by a thermal response test device

In this article are presented results from application of fiber optical DTS system within long term research of temperature energy accumulation in Paskov rock massif. In this area was established special measuring station for that purpose, because rock massif in Paskov area has ideal properties for temperature changes measurement. The twelve geothermal boreholes were drilled during this research, which were then used for rock massif heating by Thermal Response Test device. With the help of DTS system was observed how the temperature distribution and penetration in between boreholes in rock massif is. Thanks to the DTS system we were able to determine the Thermal Response Test device heating power influence on the nearest monitoring boreholes.