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High Precision Phase-Measuring System

#G-700


Development of the Multifunction Phase-Measuring System for High-Precision Measurements of Frequency, Time, Phase and Length Changes

Tech Area / Field

  • INS-MEA/Measuring Instruments/Instrumentation
  • PHY-RAW/Radiofrequency Waves/Physics
  • PHY-OPL/Optics and Lasers/Physics

Status
3 Approved without Funding

Registration date
12.03.2001

Leading Institute
ISARI (Standartization, Metrology and Certification), Georgia, Tbilisi

Collaborators

  • US Department of Commerce / National Institute of Standards and Technology, USA, CO, Boulder\nPhysikalisch-Technische Bundesanstalt, Germany, Braunschweig\nNational Institute of Advance Industrial Science and Technology / National Metrology Institute of Japan, Japan, Tsukuba\nIstituto Nazionale di Fisica Nucleare, Italy, Napoli

Project summary

Introduction and Review

The problems that are solved by the project relate to time and frequency metrology.
The high accuracy that is intrinsic to modern frequency standards and methods of a metrology of time and frequency metrology stimulates the creation of devices (systems), which helps to reduce the tasks of measurement of different magnitudes (length, speed, the temperature, voltage etc.) to measurement of time or frequency. The application of methods of time and frequency metrology is wide - from such tasks, as conservation of unit of volt in national metrological laboratories through a Josephson effect, up to tasks of the applied character in radionavigation, in a radar-location, in systems of telecommunication etc.
In the proposed project the problems of precise measurements of changes of a phase shift angle (PSA) and frequency (phase) instability of signals of the standards of frequency will be examined.
During the last years the major progress is made in the field of creation of the standards of frequency of an optical range (frequency stabilized lasers). At present their characteristics of stability slightly yield to the frequency standards of a radiorange. But the intensive activity for their improvement is carried out. These achievements stimulate development of fiber-optical communication systems, precision measurements of lengths, systems for research in geodynamics, astrophysics, researches connected with the detection of gravitational waves, etc. But, in turn, the creation of the optical frequency standards requires the development of methods of measurement of their frequency and phase stability characteristics. Therefore the research directed on the increase to accuracy of these measurements is actual.
The best accuracy in the field of PSA measurements is achieved in the national standards of PSA unit of the leading metrological centers (NIST, Boulder; D.I.Mendeleyev VNIIM, Sankt-Petersburg). The error of reproduction of PSA unit in them is determined by 0.001º value in a range of frequencies up to 1 kHz. In a 1÷10 MHz frequency band the error increases up to 0.005º.
Among the known methods of frequency comparison of the frequency standards and measurement of instability and phase noise of these standards the methods should be selected which have got the greatest propagation in practice in the field of time and frequency metrology. First of all there is a method of decade multiplying of a phase difference of compared signals without a frequency multiplication. In the last years there was a more widespread and more precise method of multiplying of temporary fluctuations in a two-mixing time-difference circuit. At 5 MHz frequency the resolution of instability measurements of the frequencies about 8x10-15 - during an average 100 seconds is achieved. Let's note, that for today in the best system for these measurements (system A7 of Quartzlock Corporation)) the resolution is defined by value 1.5x10-15 during an average 100 seconds and 3x10-17 - during an average 10000 seconds at 5 MHz frequency.
In the literature of the sixties the method "of a current phase difference", as a possible perspective method for measurements of frequency instabilities was also described. The realization of this method was based on an application of the regulated electromechanical phase shifter in the compensation phase measurement circuit.
The developers of the proposed project came to a method of "a current phase difference" from the positions which can reveal the new interesting possibilities of this method.
The purposes of the Project
- development of the experimental model of the phase measuring precision device realizing a method "of a current phase difference" on the basis of the regulated fiber-optical phase shifter of electrical signals and research of its possibilities for increase of resolution of frequency comparison and measurements of phase noise and instability of the frequency standards of a radiorange;
- transformation of the indicated method for precision measurements of the characteristics of phase stability of the standards of optical frequencies and testing its characteristics;
- transformation of the indicated method for essential increase of accuracy of measurements of changes of length and research its characteristics.
The participants of the given project working by the military orders have proposed and preliminary tested original variable phase shifter (PS) of electrical signals with application of a differential fiber-optical delay which was constructed on the basis of multimode fiber-optical (FO) components, in which the phase difference of output signals was regulated by frequency of signals of external synthesizer of frequencies. The preliminary research of this fiber-optical phase-shifter (FOPS) has shown its high metrological characteristics. However, since 1991 these operations were paused (due to the stopping of financing). The further analysis has shown, that the transition to the single-mode FO components in this FOPS allows to achieve the characteristics that give the basis to apply it, for example, for development of the standard of PSA unit of electrical signals.
Since 1992 the creation of base of the national standards of units of physical magnitudes, including time and frequency, is entrusted to the Institute "ISARI". The developers of the project, using their experience, began to analyze a possibility of application of the FOPS for these tasks. In particular, it is proposed to realize the modernized variant of a method "of a current phase difference" on a basis of FOPS for the comparison of frequencies and measurement of stability of the frequency standards in a radiorange. The regulated FOPS allow to compensate up to zero the measured phase difference. It gives a possibility to use the combination of a method of the decade multiplying of a phase difference and of two-mixing time-difference system simultaneously for the creation of the device of frequency comparison. By a tentative estimation, the resolution of the device for comparison of frequencies can be 10 times better, than the most precise devices of similar purpose. The authors of the proposed project receive the Patent of Georgia No P1801 on this method.
On the basis of the above-mentioned device for the frequencies comparison (DFC) with application of the FOPS the original device for the optical frequencies comparison (DOFC) for precision measurement by a method "of a current phase difference" of phase noise and instability of frequencies of the standards of frequency in an optical range is proposed. Such measurements are necessary to investigate the characteristics of the developed standards of optical frequency (stabilized lasers).
At the certain change of the DOFC it can be applied for the precision measurement of lengths or linear displacements. The developers of the given project propose an application of a method "of a current phase difference" for the precise linear measurements. The resolution of such phase-frequency measurements of length can appear essentially (even by 2 orders) exceeding the known interference methods.


Expected Results and Their Applications

The category of development of the project (according to the ISTC classification):
The applied researches – Development of the device for comparison of frequencies with high resolution;
The basic researches - Research of possibilities of a method "of a current phase difference" for measurements of the phase stability characteristics of the optical frequency standards, and research of new possibilities of superprecise measurements of length changes.
Within the framework of the proposed project it is supposed to develop and to test experimental models of the precision fiber-optical phase shifter of electrical signals (FOPS), a high-sensitive phase null-detector (PND), model of the precise device of frequency comparison of a radio-range (DFC), and also to develop the design-construction documentation (DCD) for their possible production in the future. Under the project is supposed in addition to investigate the ways and possibilities, allowing to create on the base of DFC the device for the optical frequencies comparison (DOFC). Possibilities and ways of creation on a basis of the DOFC of the precision system for measurements of small changes of lengths will be also studied by a method "of a current phase difference".
The expected characteristics of the FOPS model:
· Operation of the phase shifter on the discrete standard frequencies 1 MHz or 5 MHz;
· A phase error about 0.001º;
· A phase sensitivity about 0.0001º at frequency 5 MHz.
The value of a phase difference of output signals of the FOPS is supposed to be controlled manually or in the automated mode by the computer according to the program, given by the operator.
The expected technical characteristics of the model of a phase null detector (PND):
· Operation on one of discrete standard frequencies 1 MHz or 5 MHz;
· A phase sensitivity about 0.00001º÷0.000001º.
The expected technical characteristics of the model of the device of frequency comparison:
· Frequency of input signals at the operation with an internal heterodyne 1, 5 and 10 MHz (with a deviation from nominal value no more than 1x10-6);
· Frequency of input signals at an operation with an external heterodyne 1÷50 MHz;
· Measurement of a relative deviation of frequency no more than 1x10-7;
· The resolution of measurement of frequency instability is not worse than 1x10-16 (even 1x10-17) during time of averaging of 100 seconds. At the increase of time of averaging and appropriate processing of results obtaining of the resolution of 1x10-18 is expected.
The given device after its research and the possible subsequent finishing can be applied in the Exact Time and Frequency Service of Georgia. In case of the confirmation of the expected high metrological characteristics of DFC, its finishing up to a prototype and producing for time and frequency services is possible.
The research of possibilities of transformation of a method "of a current phase difference" for optical frequencies comparison (DOFC) should prepare a base to propose the future independent project on creation of the system for optical frequencies comparison with the expected resolution of order 1x10-16 during average 1000 second.
The research of possibilities of transformation of a method "of a current phase difference" for measurements of small changes of lengths should prepare a base to propose the future independent project on creation of the system for precision measurements of changes of lengths with expected resolution of the order 10-13 m.
The results of the given project can find the following applications:
· in the complex of the equipment of a primary standard of time and frequency for comparison of frequencies and the measurements of instability and phase noise of the frequency standards of a radiorange;
· in the standard equipment for measurement and reproduction of a phase shift angle unit of electrical signals;
· in complexes of the equipment of the standards of an optical frequency for frequency comparison and measurement of instability and phase noise;
· in the complex of the equipment for precise reproduction of length unit;
· for precise measurements of supersmall displacements;
· in measuring systems for nanotechnologies;
· in measuring systems for detecting of gravitational waves;
· in systems of phase shift angle precise measurements in fiber-optical gyroscopes;
· in the equipment for precise measurements of the delay time and chromatic dispersion in single-mode fiber light-guides;
· in the equipment for precise measurements of the phase and phase-frequency characteristics of fiber light-guides (cables);
· for standard means of measurements of length of a light-guide and precise measurement of distances up to a place of break in a light-guide (fiber-optical cable);
· for creation of a new type extensometers for geodynamic monitoring of the Earth tidal waves with the purpose of detection of deformation precursors of earthquakes;
· for creation of a new class of ultrasensitive fiber-optical sensors of different physical magnitudes, etc.
In all enumerated areas the developers of the project have proposals on the development. They are ready to participate in the development of such systems independently or in cooperation with the interested organizations (corporations).
The given project is one of ways to give the possibilities to scientists from Institute "ISARI", earlier executing the orderings of the Ministry of Defense of the USSR, to switch their knowledge and experience to the peaceful activity. The project can promote cooperation of the indicated scientists with their colleagues from the foreign countries, with the purpose of exchange of their experience and its possible application in the development of advanced technologies. The experience of the foreign collaborators supports the realization of the project tasks on the modern level. Using the project results it would be possible to organize joint production of the developed equipment.
Having supported planned researches, the project can promote the solution of a number of national and international technical problems in the field of a metrology of time and frequency.


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