Jan Skapa

Atmospheric turbulences in Free Space Optics channel

This article is focused on the atmospheric turbulences and their effect on optical beam. The Free Space Optics link with atmospheric turbulences was created in software OptiSystem. The results given by software are compared with Andrewss method. Free Space Optics link worked at wavelengths 850 nm and 1550 nm.

Optical fiber distributed temperature sensor in cardiological surgeries

In those days a lot of cardiological surgeries is made every day. It is a matter of very significant importance keeping the temperature of the hearth low during the surgery because it decides whether the cells of the muscle will die or not. The hearth is cooled by the ice placed around the hearth muscle during the surgery and cooling liquid is injected into the hearth also. In these days the temperature is measured only in some points of the hearth using sensors based on the pH measurements. This article describes new method for measurement of temperature of the hearth muscle during the cardiological surgery. We use a multimode optical fiber and distributed temperature sensor (DTS) based on the stimulated Raman scattering in temperature measurements. This principle allows us to measure the temperature and to determine where the temperature changes during the surgery. Resolution in the temperature is about 0.1 degrees of Celsius. Resolution in length is about 1 meter. The resolution in length implies that the fiber must be wound to ensure the spatial resolution about 5 by 5 centimeters.

K-mean clustering and correlation analysis in recognition of weather impact on radio signal

This paper deals with using a K-means clustering which is used for decision what parameter related to weather affects a propagation of radio waves in mobile telecommunication network. There were analysed parameters from a meteorological service as well as the parameters related to Global System of Mobile Communication network. For this purpose, we studied and used theory of data mining. The second part of the paper is focused on the significant weather parameters as results of K-means analyse. Consequently, there have been found some dependencies between weather conditions and receive level using a mathematical tools of correlation analysis via MATLAB.

Recovery of LED diode optical spectrum

The importance and using of power LED diodes increases. White power LED diodes cover a wide spectral range and they are usable in many applications. These LED diodes work in optical systems, the original spectrum of a white power LED diode can be changed by using all kinds of optical elements. This article describes a pursuit of the most faithful recovery of the original spectrum of a white power LED diode. The evaluative criterion is the value of the Correlated Color Temperature of the original white power LED diode compared with the value of the Correlated Color Temperature of the recovered spectrum. This recovery can be used in communication engineering.

OPTICAL FIBER SENSOR BASED ON REDISTRIBUTION OF POWER AMONG SEVERAL GUIDED MODES

Optical fiber sensors are suitable for measuring almost all magnitudes these days. This article describes one new possible area of optical fiber sensors. These sensors use for their function fundamentals of redistribution of power inside optical fiber. This principle should allow constructing a very sensitive optical fiber sensor. We designed novel optical fiber that affords utilizing of optical fiber for telecommunications and measurement at the same time. This fiber is designed to work on two wavelengths. This fiber works on telecommunication wavelength of 1550 nm in single mode regime and works on measurement wavelength of 850 nm in quasi-single mode regime. The refractive index profiles of real fabricated optical fiber samples and their development are shown in this article as well. All fiber samples were made thanks to grant cooperation with Academy of Science of the Czech Republic. The aim of this article is that brings new approach to utilization of optical fiber as a sensor based on redistribution of optical power among several guided modes and to show novel optical fiber structure design that agrees with conditions for such operations.

Passive fiber ring as a device for effective refractive index measurement

Fiber optic rings are used for synchronization of modes and optical pulses shaping in fiber lasers. The resulting pulses are characterized by stable amplitude and reduced chirp. The length of fiber ring is chosen so as to avoid loss of laser light coherence. New application of optical fiber loops is their inclusion in the closed loop during their excitation by laser light modulated by low-frequency signal and middle frequency signal. If loop also includes amplifying fiber which covers losses incurred by couplers will thus be possible evaluated a signal delay in long loop and thus measure the length of fiber. Reverse task is possibility to measure n1eff if we know the length of SM fiber loop. This type of designed fiber optic oscillator consists of single-mode optical fiber SM28e in lengths of order of kilometers. This fiber is connected in a series with erbium doped fiber that covers loop losses. Loop, which acts as an oscillator is excited by DFB lasers both at a wavelength of 1550 nm and at wavelength of 1310 nm. The paper will demonstrated the comparison between active and passive fiber loops and their influence to accuracy of effective refractive index measurement.

Mach-Zehnder fiber interferometer for people monitoring

Fiber optical interferometers belong to highly sensitive equipments that are able to measure slight changes like distortion of shape, temperature and electric field variation and etc. Their great advantage is that they are insensitive on ageing component, from which they are composed of. It is in virtue of herewith, that there are evaluated no changes in optical signal intensity but number interference fringes. To monitor the movement of persons, eventually to analyze the changes in state of motion we developed method based on analysis the dynamic changes in interferometric pattern. We have used Mach- Zehnder interferometer with conventional SM fibers excited with the DFB laser at wavelength of 1550 nm. It was terminated with optical receiver containing InGaAs PIN photodiode. Its output was brought into measuring card module that performs on FFT of the received interferometer signal. The signal rises with the composition of two waves passing through single interferometer arm. The optical fiber SMF 28e in one arm is referential; the second one is positioned on measuring slab at dimensions of 1x2m. A movement of persons over the slab was monitored, signal processed with FFT and frequency spectra were evaluated. They rose owing to dynamic changes of interferometric pattern. The results reflect that the individual subjects passing through slab embody characteristic frequency spectra, which are individual for particular persons. The scope of measuring frequencies proceeded from zero to 10 KHz. It was also displayed in experiments that the experimental subjects, who walked around the slab and at the same time they have had changed their state of motion (knee joint fixation), embodied characteristic changes in their frequency spectra. At experiments the stability of interferometric patterns was evaluated as from time aspects, so from the view of repeated identical experiments. Two kinds of balls (tennis and ping-pong) were used to plot the repeatability measurements and the gained spectra at repeated drops of balls were compared. Those stroked upon the same place and from the same elevation and dispersion of the obtained frequency spectra was evaluated. These experiments were performed on the series of 20 repeated drops from highs of 0,5 and 1m. The evaluation of experiments displayed that the dispersion of measured values is lower than 4%.

Nonlinear effects in microstructured polymer optical fibres

Photonic crystal fibers technology provides us with new way to obtain fibers with much higher non-linearity than conventional techniques. Upper limits of non-linear coefficients obtainable in silica-based photonic crystal fibers have been already investigated. Unique dispersion characteristic and enhanced non-linearity make this kind of fibers an ideal candidate for non-linear optical devices in telecommunication applications, for measurement and sensing and for supercontinuum generation. However, there are limitations given by material properties, which obstruct us from achieving theoretical limits of these fibers. Extremely small core and high air-filling fraction are here needed for reach higher non-linearity, so when material properties of conventional silica restrict us, there is a requirement on a novel matter. This could be poly-methyl metacrylate (PMMA), a common material for plastic optical fibers manufacturing. These microstructured polymer optical fibers are a recent technology, which gives us with new possibilities in core size, fiber geometry and related air-filling fraction. By this kind of fiber, we could be closer to ideal non-linear fiber, which is core strain surrounded by air, than even before. But new kind of fiber brings new issues, like which effect in fiber will be dominant or how will be coupled light affected by outer influences - and what difference will be between predicted and real values in general. This is a large task and hopefully, there will be answer at least for a small part in this paper.

Mode visualization for fiber optic temperature sensor

Quasi single mode fiber is a fiber supporting a few modes only. If the operational wavelength of the light source will be shorter than the cut-off wavelength is, then the fiber will support except fundamental mode LP01 several higher modes too. Such fiber conserve themselves the advantageous characteristics for telecommunication application (small attenuation, slight dispersion), but it is possible to use them for sensor-based applications utilizing the mode coupling among several guided modes. This paper describes design of optical fiber working as a conventional telecommunication fiber at wavelength of 1550 nm and temperature sensing fiber at the wavelength of 850 nm or 675nm. In the paper the basic theory together with the simulation of the mode distribution will be shown temperature changes within the interval 20°C-100°C and real mode patterns of such fiber.

FBG strain sensor mounted on plastic carrier

Fiber optic Bragg gratings are among the most widely used fiber optic sensors. It uses in dangerous explosive environments thanks to the electrical passivity of the sensor itself, but also in applications with high electromagnetic disturbance. Maintaining immunity of the sensor to electromagnetic interference requires non-electrical encapsulation material. This paper describes the encapsulation of the FBG sensor on a plastic plate fixed by gluing to the monitored structure. The proposed FBG sensor is suitable for measuring deformations or vibrations of iron and concrete structures. Due to the material used, the FBG sensor keeps resistance to electromagnetic interference, humidity, and corrosion. The results show the almost equal sensitivity of FBG strain sensors mounted on a metal carrier when measuring very small deformations and vibrations. The proposed FBG sensor concept reduces the cost of its manufacturing by using a 3D printer to produce the plastic carrier.