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A pair of phase-synchronized semiconductor lasers for length metrology
Hucl, Václav ; Holá, Miroslava ; Čížek, Martin ; Řeřucha, Šimon ; Pham, Minh Tuan ; Pravdová, Lenka ; Lazar, Josef ; Číp, Ondřej
Semiconductor lasers are increasingly widespread in areas that have been so far dominated by He-Ne lasers. One of such areas is the length metrology, where He-Ne laser operating at 633nm wavelength is still a traditional source of coherent light for laser interferometers distance measuring. The advantages of semiconductor lasers compared with He-Ne laser are greater optical power and a significantly wider range of wavelength tuning without mode jumps. Another advantage is the possibility of frequency modulation of wavelength of the laser diode by directly changing the injection current. The benefits predetermine these laser diodes for the realization of dual-frequency laser sources for heterodyne interferometry. In this case, using a phase-locked loop technique the optical frequency of a laser diode is locked to the optical frequency of another laser diode with a certain frequency offset in the MHz order. In our contribution we present utilization of DBR laser diodes in implementing a dual-frequency laser source for laser interferometry with heterodyne detection.\n
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Phase coherent transfer of stable optical frequency for sensory networks
Čížek, Martin ; Pravdová, Lenka ; Hucl, Václav ; Řeřucha, Šimon ; Hrabina, Jan ; Mikel, Břetislav ; Lazar, Josef ; Číp, Ondřej
Using long-haul optical fiber links for phase coherent transfers of stable optical frequencies has been developed by metrological laboratories for at least a decade. Present boom of optical fiber sensors puts a demand on transferring this technology from laboratories to industrial practice. A remote calibration of fiber Bragg grating tensometers can be an example. In our contribution we present a 306 km long fiber link between laboratories of ISI in Brno and CESNET in Prague. The line uses a telecom fiber with a dedicated DWDM window at 1540-1546 nm. The setup implements a phase coherent transfer of a laser standard working with 1540.5nm wavelength and a bi-directional transfer of 1PPS timestamps from radiofrequency standards at the both ends of the line. A long-term measurement of transport delay fluctuations and relative stability of the line are discussed.
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SMV-2015-38: Theoretical study of laser source for precise optical frequencies distribution
Hrabina, Jan ; Pravdová, Lenka ; Čížek, Martin ; Pham, Minh Tuan ; Hucl, Václav ; Řeřucha, Šimon ; Číp, Ondřej
The contractual project was oriented to theoretical study of design of ultra-stable laser source for precise optical frequencies long-range distribution through standard telecom optical fiber links. The research included theoretical investigation of possible optical setup arrangements with selection of optimal spectroscopy methods for the laser source frequency stabilization, special care was taken about ultra-high coherence of the laser needed for long-range distribution of the transmitted signals (hundreds of kilometers long links). The stabilization method was selected with respect to metrological traceability of the intended applications. The proposed optical system was compared to up-to-date available laser sources working at other wavelengths and crucial spectral and frequency stability parameters were summarized and compared. Proposed laser spectroscopy method and optical setup was experimentaly evaluated at laboratory environmental conditions and resulted stability/spectral parameters were summarized.
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Lenght characterization of a piezoelectric actuator by use of a mode-locked femtosecond laser
Pravdová, Lenka ; Lešundák, Adam ; Šmíd, Radek ; Číp, Ondřej
Modern laser interferometers with high resolution are considered as very precise sensors for length measurement. We assembled a specialized optical resonator using silver mirrors. The femtosecond laser with a repetition frequency of 250 MHz and a central wavelength 1560 nm of supercontinuum is used. Femtosecond laser is stabilized by optical frequency comb technique, ie. the frequency offset fCEO and repetition frequency frep is synchronized by our ultra-stable frequency source - hydrogen maser. The technique of derivative spectroscopy is used for locking the resonance peaks of the resonator component of the supercontinuum. The frequency frep in fine steps in the desired range of values is changed via control electronics. This was achieved by changing the length of the cavity in the order of several hundred of nanometers. Repetition frequency change is carried out so that the entire range of the length of the actuator is tested. Value of the applied voltage is recorded for every measured point of the characteristics. The result is a measured characteristic hysteresis curve of the PZT actuator.
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Digital signal synthesizer for compensating Doppler effect in fiber-optic lines
Hucl, Václav ; Čížek, Martin ; Pham, Minh Tuan ; Pravdová, Lenka ; Číp, Ondřej
If a highly stable laser standard is distributed over a long fiber-optic line the stability of optical frequency of the laser at the far end is usually degraded due to external influences on the optical fiber. Thermal dilatation or vibrations of the fiber result in Doppler shifts changing the optical frequency of the laser light. A setup based on an unbalanced Mach-Zehnder or a Michelson interferometer with the optical line acting as a measuring arm can be used for detecting Doppler frequency shifts. Once we are able to detect the shifts we can compensate them by detuning the optical frequency of the transmitted laser light in a closed-loop. Our paper presents the method of detecting the frequency shifts in the fiber-optic line together with a digital electronic controller. The controller is based on a digital signal processor and a DDS chip for generating the radiofrequency signal driving the acousto-optic modulator in order to detune the transmitted laser light.
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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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The Meat Utilization of Rabbit Breed Czech Solver
PRAVDOVÁ, Lenka
This master's thesis focuses on the utilization of the Czech Solver, a Czech national rabbit breed, which is registered in The National Programme on Conservation of genetic resources of plants, animals and micro-organisms for Food and Agriculture. The Czech Solver was originally invented to be able to confirm or disprove the purebred origin of the tested animal. This feature is useful for breeders so that compensates for low meat performance breed. Fertility monitored breeding is less than the average fertility medium breeds, among that is the Czech Solver sorted, and significantly lower than the fertility of broiler rabbits. Surveyed individuals have achieved monthly weight gain sampler breeds of rabbits, but fattening period to 2.70 kg live weight ranged from an average of 105 days for semi-intensive rearing system in cages to 135 days at a traditional pens housing system farming, which is at least 27 days longer than the period of fattening broiler rabbits. Average growth rates were observed in the amount of 19.7 g in traditional breeding and 20.6 g in semi-intensive farming. Because the rabbits were slaughtered when reaching 2.70 kg live weight, were at abattoir analysis revealed no statistically significant differences between males and females or between traditional and semi-intensive farming. Slaughter analysis confirmed the breed Czech Solver average percentages of the intermediate part, fore and hind parts of the carcass and a higher proportion of kidney fat compared to other breeds of rabbits included in the genetic resources and compared with broiler breeds.
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The utilization of the Czech Solver, the rabbit breed, in Czech Republic
PRAVDOVÁ, Lenka
The bachelor thesis focuses on the utilization of the Czech Solver, a Czech national rabbit breed, which is registered in The National Programme on Conservation of genetic resources of plants, animals and micro-organisms for Food and Agriculture. The Czech Solver, differ other rabbit breeds, is not used for meat or pelt production. It was originally invented to be able to confirm or disprove the purebred origin of the tested animal, hence the name solver. In the genetic code of Czech Solver's fur, four out of five alleles are recessive, which enables the animal to determine the purebred pedigree of a different rabbit breed when the two individuals are crossbred. It is described the required exterior of the Czech Solver is described and the breed is compared to other foreign breeds of the same genetic code. The work includes legislature, organization structure, conditions and possibilities of gaining a financial support for pure breeding of this breed, as well as suggests solutions how to increase the Czech Solver population.
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Comparison of the reproduction of the goats on the ecological and the conventional farm
PRAVDOVÁ, Lenka
The aim of my diploma thesis is comparison and evaluation of reproduction of goats on an eco-farm and on a conventional farm. Measures of reproduction of observed herds were assessed in the years of 2009 and 2010 on an eco-farm Hana Langová and on a conventional farm Bára Schneedorferová. On an eco-farm, a herd of 20 does was observed. Crossbreeds of White shorthaired goat, Brown shorthair goat, Boer goat and Anglo-Nubian goat; all bred with a White shorthaired buck and a Boer buck. On a conventional farm, a herd of 24 White shorthaired does and two crossbred does of White and Brown shorthaired goat was observed in 2009. In 2010, only 18 does were observed. In both years the does were bred with two Brown shorthair bucks. The measured results were compared with milk efficiency results between the two years and also between the farms. In both years, higher fertility was discovered on an eco-farm. On a conventional farm, very low fertility was observed in 2009 (116 %). On the other hand, fertilization was higher than on an eco-farm in both years. Very big difference was also observed in the ratio of male kids, which was in both years higher on a conventional farm, where all the bred animals (apart from one) are hornless. Reproduction is to a high extent influenced by external environmental factors and to a very small extent by genetics. A whole range of possible effects was omitted from the observations, however, the main ones were noted. Of all the observed measures of reproduction, the only one which could be substantially influenced by the breeding method is fertility.
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