Institute of Photonics and Electronics

Institute of Photonics and Electronics 626 records found  previous11 - 20nextend  jump to record: Search took 0.01 seconds. 
Time and Frequency Transfer Using Satellite Based Augmentation System GAGAN
Pánek, Petr ; Kuna, Alexander
Aided Geo Augmented Navigation) is an Indian SBAS (Satellite Based Augmentation Systems). In contrast to the European EGNOS, this system already supports the navigation function and it transmits signals both in L1 and L5 frequency channels. We used the GAGAN signals for an experimental common-view time transfer between IPE Prague and PTB Braunschweig which is a distance of 370 km and we also tested the time transfer properties using a single clock common-view. The L1 and ionosphere-free code measurements have markedly lower accuracy compared to a GPS common-view because of rather narrow bandwidth of the SBAS signal in L1 frequency channel. L5 code measurement provides much better precision. It results from the single clock common-view that the observed fluctuations can be described as white noise with standard deviations of 6 ns, 1.3 ns and 14 ns for L1, L5 and ionosphere-free combination. The results obtained from the carrier phase measurements are promising. The single clock common-view precision was approximately 30 ps RMS even for the ionosphere-free combination.
Single Photons Optical TwoWay Time Transfer Providing Picosecond Accuracy
Procházka, I. ; Blažej, J. ; Kodet, J. ; Pánek, Petr
We are reporting on a new approach to an optical two-way time transfer based on signals of individual photons. This approach enables to reach extreme timing stabilities and minimal systematic errors using existing electro-optic technologies. In our indoor experiment we have achieved sub-picosecond precison and 3 ps accuracy of a two-way time transfer via free space optical channel. The entire system is compact and simple. It is a perspective technique for space application, where it might provide picosecond accuracies over space distances
Local ties controlin application of laser time transfer
Kodet, J. ; Schreiber, U. ; Eckl, J. ; Procházka, I. ; Pánek, Petr
In many fundamental physical experiments time plays an important role. The standard way for the comparison of time and frequency is the application of GNSS signals and the Two-Way Satellite Time and Frequency Transfer - TWSTFT. This technique is based on radiofrequency signal transmission. Recently, there was a rapid increase of optical time comparison development, which uses the Satellite Laser Ranging network (SLR). Currently the French project T2L2 is in operation on board of Jason 2 and the European Space Agency project ELT in support of the Atomic Clock Ensemble in Space (ACES) is under development. The goal of both projects is the time synchronization with a precision below 40 ps rms and an absolute error well below 100 ps. Comparing the results of the optical time transfer with the GNSS time comparison requires unprecedented control of the local ties between the different observation techniques. One of the possible methods is the application of the Two Way Time Transfer (TWTT) on a single coaxial cable. Such a system can be implemented using two or more event timers, which are interconnected by a standard coaxial cable.
VLBI receiver chain monitoring
Michálek, V. ; Kodet, J. ; Schreiber, U. ; Ploetz, Ch. ; Procházka, I. ; Pánek, Petr
he most demanding goal of the Global Geodetic Observing System initiative is the definition of station positions to an accuracy of 1mm and the corresponding velocities to 0.1 mm/year. The main remaining sources of error are caused by systematics, leading to intra- and inter- technique biases. In this work, we have focused on Very Long Base Interferometry (VLBI) and phase calibration generator currently in operation. This unit is injecting calibration tones into the detection chain through an input coupler located near the input of the antenna. The tones propagate further through entire detection chain and are recorded with the observed signal. Then they are extracted in post processing. These tones are generated out of an atomic frequency standard. The supplied frequency is significantly influenced by temperature and mechanical changes since usually a long cable is employed to bring the frequency to the calibration unit. To monitor the electrical length of the cable, calibration with a picosecond precision is essential. We have redesigned a phase calibration unit so that it enables the implementation of the Two Way Time Transfer (TWTT) method on single coaxial cable using two event timers to monitor the electrical length of the critical cable. Such a system has been installed in parallel to the unit currently in operation. The comparison of the TWTT method with previous measurement method is presented
Evaluation of the accuracy of the method for measuring state-of-the-art ultra-high stability quartz crystal oscillators
Salzenstein, P. ; Kuna, Alexander ; Lefebvre, F.
The accuracy of the Three-Cornered Hat method is discussed when not simultaneously applied to the determination of the contribution on short term frequency stability performed on ultra-stable quartz oscillators
Optical infrastructure for time and frequency transfer
Smotlacha, V. ; Vojtěch, J. ; Kuna, Alexander
The paper describes optical infrastructure for time and frequency transfer in the Czech republic. The infrastructure is heterogeneous and utilises resources of the Czech academic optical network. It allows to interconnect Cesium standards in distant sites with the national time and frequency laboratory and to distribute accurate time and stable frequency. We also present results and compare them with other methods of time transfer
LOW SUPERSATURATION OVERGROWTH OF NANOPOROUS GaAs SUBSTRATES
Nohavica, Dušan ; Grym, Jan ; Gladkov, Petar ; Hamplová, Marie
Oriented pore networks in GaAs were created by electrochemical dissolution. Low supersaturation overgrowth of the porous substrates by InxGa1-xAs (x<4%) was realized by Liquid Phase Epitaxy (LPE)
LAYERS OF METALS NANOPARTICLES ON VARIOUS SEMICONDUCTORS FOR HYDROGEN DETECTION
Černohorský, Ondřej ; Žďánský, Karel ; Yatskiv, Roman ; Grym, Jan
Metal nanoparticles have many interesting properties which is given by their space restriction. Their large active surface is very well exploited during catalysis. Pd and Pt are metals know for their ability to dissociate molecular hydrogen on single atoms. We prepared Schottky diodes on semiconductors InP, GaN, GaAs, and InGaAs to obtain hydrogen sensor. Method of preparation such diodes is electrophoretic deposition of Pd or Pt nanoparticles from their colloid solution onto semiconductor substrate. Over the layer of nanoparticles, porous metal contact was prepared. Hydrogen molecules are dissociated on these metal nanoparticles and single atom which settles on the interface between metal and semiconductor and they increase or decrease Schottky barrier height. By this method we can measure from 1 ppm H2 in the air, where the current change is over one order of magnitude
Graphite/n-InP Schottky barrier with electrophoretically deposited Pt nanoparticles for hydrogen and nitrogen-monoxide detection
Žďánský, Karel ; Vaniš, Jan ; Černohorský, Ondřej ; Kacerovský, Pavel ; Fojtík, A.
N-type InP was deposited with Pt nanoparticles (NPs) by electrophoresis. The Pt NPs density was varied from a tenth of monolayer to several monolayers. Schottky contacts were made by colloidal graphite on the InP wafer site covered with Pt NPs. It was observed that H2 was detected by an increase of the current while NO was detected by its decrease. For explanation, we discuss mechanism which involves negative charging of adsorbed H atoms with electrons by increasing affinity level due to correlation efects
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