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Distribution of the accurate optical frequency and time via photonic networks in the Czech Republic
Číp, Ondřej ; Čížek, Martin ; Pravdová, Lenka ; Hucl, Václav ; Řeřucha, Šimon ; Hrabina, Jan ; Lešundák, Adam ; Mikel, Břetislav ; Lazar, Josef ; Vojtěch, J. ; Smotlacha, V.
To verify the stability of the frequency of optical clock an intensive research in the transmission of stable frequency via optical fibers is in progress for many years. Interconnection of large cities and metropolitan networks with optical fiber running DWDM allowing to transfer many optical signals in parallel over one fiber at the same time contributes significantly to troubleshoot the problem. Between nodes of ISI Brno and the main center of CESNET there are several dedicated bi-directional channels through the DWDM technology. The first tests are ongoing with the transfer of accurate time, which are using the possibility of bi-directional communication over a single fiber, thus the phase delay including Doppler shift are reflected on the two signals as well. From periodic measurements can subsequently be evaluated daily, weekly and seasonal fluctuations of the delay and after deduction of such data from the measured data a mutual stability of used time normal can be determined. The second technique is a full compensation of phase of the laser wave through active control of phase changes of the wave during its transmission from the ISI to the node of CESNET. At present, a characterization of the behavior of individual system elements, including their commissioning is in progress.
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Software testing in agile projects
Rojo, Robert ; Buchalcevová, Alena (advisor) ; Čížek, Martin (referee)
This bachelor thesis describes the software testing process in agile projects and suggests several improvements in the MMSP methodology (Methodology for small software projects). In the theoretical part of the thesis there are mentioned basic terms and practices in the field of software testing, there is also a description of agile development and agile testing in general and the part also contains an introduction to MMSP methodology. In the practical part of the thesis, a referential business is presented along with the problems that are connected with internal testing processes. In the end of this thesis there are several improvements to the MMSP methodology suggested and evaluated.
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SMV-2014-27: Optical system for generation of stable optical frequency
Hrabina, Jan ; Číp, Ondřej ; Čížek, Martin ; Hucl, Václav
The work was oriented to design and development of a stable optical frequency laser standard based on ultra-low noise DFB laser. The laser frequency was locked to selected rotational-vibrational transition of isotopic acetylene gas by the method of linear absorption spectroscopy. The research included: design, investigation and development of narrow-linewidth DFB laser source including of development of ultra-low noise power-supply and control electronics; development of an optical setup equipped with opto-fiber output for automatic locking of the laser to selected transition of the ultra-pure acetylene gas, special custom-design absorption cell development, filled with isotopic acetylene, with optical windows equipped with custom-design antireflection coatings; development of control electronics for automatic searching of absorption lines and automatic locking of the laser frequency to this transition; development of control software.
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Unit for stabilizing optical frequency combs
Hucl, Václav ; Čížek, Martin ; Šmíd, Radek ; Lazar, Josef ; Číp, Ondřej
Optical frequency synthesizers (femtosecond combs) are used mainly in the field of precise measurement of optical frequencies, laser spectroscopy and interferometer distance surveying. The repetition and offset frequencies belong to main controlled parameters of such synthesizer. These two parameters need to be locked to ultra-stable frequency standards i.e. H-masers, Cs- or Rb- clocks. We present the complete digital signal processing chain for phase-locked loop (PLL) control of the repetition and offset frequency. The setup is able to overcome some dropouts causes the femtosecond laser instabilities. The presented work gives the possibility of long-time operation of femtosecond combs which is necessary when the optical frequency stability measurement of ultra-stable lasers is performed.
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Electronics for reducing the sideband noise of a laser diode by utilizing an unbalanced fiber interferometer
Čížek, Martin ; Šmíd, Radek ; Číp, Ondřej
Measuring length changes of optical resonators requires using of lasers with a narrow spectral width. Moreover, for tracking a whole range of possible lengths a widely-tunable laser is required. Laser sources based on DFB laser diodes have a wide optical frequency tuning range, however their spectral linewidth is up to single MHz. The usual way of narrowing the linewidth is based on stabilizing the wavelength of the laser by locking it on an etalon resonator cavity using for example a PDH setup. This of course leads to losing the tunability. We present a different approach where an unbalanced fiber Michelson interferometer with a measuring arm formed of a long optical fiber spool is used as a an optical frequency discriminator. The output electrical signal from the photodetector proportional to the optical frequency changes is used in a fast servo loop. The controller slightly detunes the laser diode by adjusting its pump current and locks optical frequency changes to a zero value. This leads to reducing the sideband noise of the laser by up to 60 dB. The whole method is independent on the actual wavelength of the laser and works in the whole tuning range of the DFB diode.
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System for stabilizing femtosecond lasers
Čížek, Martin
We describe a device intended for stabilizing optical frequency combs with respect to high-grade RF oscillators. The whole designed system is modular and can be adapted to actual conditions given mainly by level, frequency and signal to noise ratio of the processed signals. The device is based on a specialized integrated circuit (IC) that contains functional blocks for direct digital synthesis, digital phase detection, limiters, programmable dividers and control logic. The specialized IC is accompanied by specially developed control electronics based on a microcontroller that allows communication via CAN bus. This allows remote management of the whole system and integrating it into complex automated experiments with optical frequency synthesizers. The device is used for stabilizing offset or repetition frequency of the optical frequency comb. To ensure best possible conditions for a fast first-order controller the setup is extended by a slower second-order controller with a high dynamic range. This second-order controller is built around a specialized 18-bit AD/DA card and a software application in LabView environment. The bandwidth of the closed control loop can be up to single MHz. The only limiting factor is the tuning speed of the femtosecond laser.
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Desing processes and IS infrastructure to fulfill strategic goals of project-based company
Rys, Jaromír ; Mildeová, Stanislava (advisor) ; Čížek, Martin (referee)
Competition in the market for small software companies is high and given the current global economic crisis, it is important for these companies to gain competitive advantage in the market. One of the weaknesses of the studied company is insufficiently described processes and thus possible areas of the process which are not properly or sufficiently supported by current IS infrastructure. The aim of this thesis is to analyse the process of project-based company that uses agile methodologies for software development and based on the results of process analysis to assess the current state of IT support processes with regard to the strategic objectives of the company to design the new IS infrastructure. To perform the process analysis, I used the Methodology for Modeling and Analysis of Business Process (MMABP). Subsequently, the processes identified in the analysis process were analysed from the perspective of the strategic objectives of the company and also in terms of their support in the current IS infrastructure. Based on these analyses, were identified areas of the processes that have poor or no support, at all. In the epilogue, I proposed modification of the existing infrastructure IS, where all the process will have the appropriate information support. The biggest changes were in support of business processes, where a new CRM system was proposed and a new intranet portal was introduced, which should cover the first phase of particularly poor information support of the current processes in the field of human resources management.
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Interferometric coordinates measurement sytem for local probe microscopy nanometrology
Hrabina, Jan ; Lazar, Josef ; Klepetek, P. ; Číp, Ondřej ; Čížek, Martin ; Holá, Miroslava ; Šerý, Mojmír
We present an overview of new approaches to the design of nanometrology measuring system with a focus on methodology of nanometrology interferometric techniques and associated problems. The design and development of a nanopositioning setup with interferometric multiaxis monitoring and control involved for scanning probe microscopy techniques (primarily atomic force microscopy, AFM) for detection of the sample profile is presented. Coordinate position sensing allows upgrading the imaging microscope techniques up to quantified measuring. Especially imaging techniques in the micro- and nanoworld overcoming the barrier of resolution given by the wavelength of visible light are a suitable basis for design of measuring systems with the best resolution possible. The system is being developed in cooperation with the Czech metrology institute and it is intended to operate as a national nanometrology standard combining local probe microscopy techniques and sample position control with traceability to the primary standard of length.
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Evaluation of lenght of the Fabry-Perot cavity with ultra-low expansion spacer with optical frequency comb
Šmíd, Radek ; Čížek, Martin ; Číp, Ondřej
The ultra-low expansion materials play a crucial role in laser stabilization and they are essential for laser stalibization. Blocks made from ultra-low expansion material are used as a base for precise interferometric measurements and in AFM microscopes. In our experiment we have monitored the free spectral range (FSR) changes and absolute length of a Fabry-Perot cavity (FPC) with a spacer made from an ultra-low expansion ceramics (Zerodur) with the expansion coefficient (CTE) of 2.8 • 10-8K-1. Experiment was carried out in the vacuum chamber at the pressure as low as 1 O'5 Pa. A fiber based femtosecond mode-locked laser with 100 MHz repetition frequency and central wavelength of 1550 nm was locked to a GPS disciplined crystal oscillator with a short term stability better than 10"12 and long term stability controlled by GPS clocks. An auxiliary tunable DFB laser diode was locked to a certain optical mode of the FPC. A beat-note signal from optical mixing between the laser and a stabilized femtosecond frequency comb is detected and processed. The absolute optical frequency of this mode is defined by saturation to acetylene cell. The FPC spacer of Zerodur material of 175 mm length was analyzed during the temperature cycling process from 22 - 35°C. Measured CTE of the spacer material was (0.069 ± 0.005) • 10-6K-1. Material exhibited hysteresis in the spacer length up to 8 nm during cycling process.
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The smart electronic unit for precise measurement of refractive index of air in a nano-positioning stage for scanning probe microscopy (SPM)
Hucl, Václav ; Čížek, Martin ; Buchta, Zdeněk ; Mikel, Břetislav ; Lazar, Josef ; Číp, Ondřej
When the traceable measurement of dimensions of samples in scanning probe microscopy is needed the position of the probe tip has to be monitored by a set of laser interferometers. The measurement is done very often during standard atmospheric conditions so the changes of the refractive index of air have an influence to measured values of the length with 1.0exp(-4) relatively. Thus the measurement of the refractive index of air and application of the instantaneous value of the index to all of measurement interferometric axes is necessary. In the work we developed new concept of electronic unit which is able to monitor the refractive index of air on basis of measurement of weather conditions: temperature, humidity and pressure of the air. The unit uses modified Edlen formula for calculation of the refractive index. The next step of the work is verification of accuracy of the measuring capability of the unit. We tested the accuracy with reference unit which measure the refractive index of air by a set of etalon sensors. The expected accuracy of the smart electronic unit falls to the 4.1exp(-7) relatively. The important advantage of the unit is very low power consumption of electronics so the unit causes very small temperature effects to the measuring process.
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