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This article discusses the application of a new type of modem with pseudo-noise coding and additional tone modulation, developed for the comparison of reference time scales over satellite communication channels. Experimental studies have compared the time scales of hydrogen masers from the composition of the State Primary Standard of Units of Time, Frequency, and the National Time Scale GET 1-2022 over an optical communication channel using the modems under consideration. As a communication channel, fiber-optic lines of different lengths were used, along which the two-way signal was transmitted. The output radio frequency signals of the modems, with the use of optical transmitters connected to the ends of the fiber lines, were transmitted counter-currently at an optical carrier frequency with a wavelength of 1.55 μm. The demodulation of optical signals into the radio frequency range was implemented at the ends of the fiber lines by optical receivers. The results of an experimental evaluation of type A indefiniteness by comparing time scales along fiber-optic lines of 50-km, 100-km, and 200-km lengths are presented. On a line 200-kmlong, the type A measurement uncertainty when comparing time scales does not exceed 3 ps in the daily measurement interval. The experiments revealed that implementing the method of comparing time scales with modems with pseudo-noise coding and additional tone modulation is possible over a 200-km-long fiber-optic line without intermediate optical amplifiers. This finding opens up the prospect of creating cascaded comparison systems for time scales of remote standards over fiber-optic communication lines with fewer intermediate optical amplifiers. [ABSTRACT FROM AUTHOR]

The possibility of determining the difference in gravitational potentials and orthometric heights in the Earth's field based on measurements of the phase difference of laser radiation in an optical fiber is proposed and investigated in this study. Such a phase difference is attributed to the effect of the gravitational delay of light waves. A block diagram of a measuring complex designed to measure the phase difference of light waves caused by this effect is proposed. The measurements use two coherent light waves from a single laser, each propagating along a separate fiber-optic communication line. The composition of each fiber-optic communication line includes the same coils of a long optical fiber, spaced apart in height. The analysis of the factors influencing the phase relations of waves propagating along two communication lines of the measuring complex is performed. The phase effects of the delay, caused by the influence of the true gravitational field of the Earth, and the influence of the fields of inertial forces and gyroscopic effects due to the Earth's rotation are determined. Methods for suppressing interfering effects are proposed. The achievable errors in measuring the differences in gravitational potentials and corresponding orthometric heights are estimated. With a fiber length in coils of 100 km and a height difference of 100 m, the errors are 0.2 m2/s2 and 2 cm, respectively. The measuring complex under study is called a laser gravipotentiometer. It is an optical analog of the well-known radio-frequency quantum-level unit, but it does not require ultrastable frequency and time standards. The research results of the proposed measuring complex are relevant for the development and improvement of measuring instruments for the parameters of the Earth's gravitational field and a means of the high-precision synchronization of time scales of remote standards. [ABSTRACT FROM AUTHOR]

Methods for improving the accuracy of reference frequency and time signals transmission using a new fiber-optic modem with phase instability compensation are presented. Algorithms for transmitting a 1PPS pulse time signal with a synchronization error of no more than 200 ps are considered. The results of measurements of the Allan deviation during the transmission of a reference signal with a frequency of 100 MHz through a two-kilometer fiber-optic line with additional external temperature impact are presented. With the help of the developed fiber-optic line emulator, the accuracy of reference signals transmission for fiber lines up to 100 km long, as well as for various external impacts, has been estimated. A full-function device for transmitting and receiving reference frequency and time signals through a fiber-optic communication line up to 100 km long, the instability characteristics of which reach approximately 1–3·10–17 in the daily measurement interval, has been developed. [ABSTRACT FROM AUTHOR]

Problems requiring high-precision comparisons and synchronization of time scales (TS) of remote time and frequency standards are analyzed. The prospects of using fiber-optic communication lines to solve these problems are considered. Data on maximum operating distances and accuracy characteristics of TS comparison systems using fiber-optic communication lines are given. It is shown that the range of existing systems is not sufficient for solving a number of relevant problems. A method for amplifying optical signals in an optical fiber using the stimulated Raman scattering (SRS) effect is proposed. The application of the Raman amplifier in telecommunication systems is considered. A method is suggested for using SRS to amplify the optical signals of TS comparison systems. A scheme is proposed for a system of one- and two-way TS comparisons of distant objects using signal amplification based on the SRS effect realized using two-way counter-pumping. The operational principle of the system is described along with the procedure for determining the divergence in the TS of remote objects. The results of estimating the error and range of systems of one- and two-way comparisons of time scales using the Raman amplifier are presented. It is shown that the implementation of Raman amplification in the equipment of such systems will allow their range to be increased by more than three times without reducing system accuracy. [ABSTRACT FROM AUTHOR]

Problems that arise in the course of attempting to determine and monitor an optical fiber, the medium of transmission of fiber-optic communication systems, are considered. One of the controllable parameters is the cut-off wavelength of a single-mode optical fiber. The cut-off wavelength defines the minimal wavelength of optical radiation at which an optical fiber supports only a single propagated mode, i.e., it functions in a single-mode regime. The problem of determining the cut-off wavelength of an optical fiber used in fiber-optic communication systems is critical, since in a multi-mode regime of operation of an optical fiber its throughput decreases as a consequence of inter-mode dispersion. Methods of measuring the cut-off wavelength of an optical fiber are considered. A model of a new high-precision apparatus for measurement of the cut-off wavelength of an optical fiber is proposed. The measurements are performed on the basis of the reference bending method described in GOST R MEK 60793-1-44-2013. The precision characteristics of the newly developed apparatus are analyzed and a quantitative assessment of the measurement error is obtained. [ABSTRACT FROM AUTHOR]

Optical technologies for measuring electrical quantities have unique properties and significant advantages in the high-voltage electric power industry; for example, the use of optical fibers ensures the high stability of measuring equipment to electromagnetic interference and galvanic isolation of high-voltage sensors; external electromagnetic fields do not influence the data transmitted from optical sensors via fiber-optic communication lines; problems associated with ground loops are avoided, and there are no side electromagnetic radiation or cross-coupling between the channels. The structure and operation principle of a quasi-distributed fiber-optic recirculation system for monitoring high voltages are presented. The sensitive element of the system is a combination of a piezoceramic tube with an optical fiber beam waveguide where the inverse transverse piezoelectric effect occurs. The electrical voltage measurement principle is based on recording the change in the recirculation frequency under the applied voltage influence. When the measuring sections are arranged in ascending order of the measured effective voltages relative to the receiving-transmitting unit, a relative resolution of 0.30–0.45% for the PZT-5H and 0.8–1.2% for the PZT-4 is achieved in the voltage range of 20–150 kV. [ABSTRACT FROM AUTHOR]

In this paper, to solve the problems requiring high-precision measurements of signal propagation delays in optical fiber communication lines, the design features of a pulsed optical reflectometer with picosecond resolution designed for measuring the propagation delays of a signal are considered. The error of such a reflectometer is shown to include additive and multiplicative components. A method for determining the additive component of the optical reflectometer error based on measurements of signal delays introduced by individual optical fiber coils and the total delay introduced by serially connected coils is proposed. The measurement requirements are formulated, and the results of the error estimation of the proposed method are presented. To exclude the multiplicative component of the reflectometer error, a method for determining corrections to the reflectometer readings is proposed. The method is based on measuring the propagation delays of the signal in the optical fiber coils, first using reference equipment (installation for measuring the propagation delay of the signal), and then using an optical reflectometer. Then, the differences in the obtained measurement results are calculated. The scheme of installation for measurements of a signal propagation delay in an optical fiber coil is presented, and the operation principle of the installation is described. Moreover, the results of the estimation of the error in determining the corrections to the reflectometer readings by the proposed method are presented. It is shown that excluding the additive and multiplicative components of the error will reduce the error of optical reflectometers to values less than ±100 ps. [ABSTRACT FROM AUTHOR]

We present the results of investigations of an installation aimed at the transmission of highly stable 1 PPS time signals from the hydrogen time and frequency standard over a 150 km optical fiber communication line with the use of active electronic compensation of time delays. The error (mean-square deviation) of transmission of time signals does not exceed 80 psec on the daily interval of averaging. The installation enables us to guarantee the synchronization of the time scales of remote time and frequency standards included in the primary and secondary standards of time and frequency units. [ABSTRACT FROM AUTHOR]

We study the possibility of application of SATRE modems for the transmission of reference time signals with optical carrier over fiber lines with lengths of up to 200 km. We experimentally estimated the uncertainties of comparison of time scales for the fiber communication lines with the help of SATRE modems. [ABSTRACT FROM AUTHOR]

The features of a multichannel modem that has been developed for transmission of frequency and time reference signals on a fiber-optic communication line with phase instability compensation are examined. Its capabilities for transmitting signals of reference frequencies of active hydrogen masers (such as the Ch1-1003M), we well as a 1 PPS signal with an error of synchronization no greater than 250 psec over 100 km without the use of optical amplifiers are assessed. The results of experimental verification of the metrological characteristics of the modem are given. [ABSTRACT FROM AUTHOR]

The results are presented for the study of an installation for transmission of a highly stable frequency signal with relative instability no greater than 4·10-17 on a fiber-optic communications line over a distance of 150 km. The installation uses external modulation of laser radiation and active electronic compensation of phase noise. The installation makes it possible to provide synchronization or time scale comparison of mutually separated time and frequency standards that are a component of the highest-category time and frequency standards. [ABSTRACT FROM AUTHOR]

The results of international comparisons in the field of fiber-optic communication and information transmission systems, in particular, for the average power of optical radiation (COOMET PR-S6 and APMP PR-S2 projects) and chromatic dispersion in an optical fiber (EURAMET PR-S3 project), are considered. Data on comparisons as regards the length of the optical fiber (APMP PR-S8), polarization mode dispersion (COOMET PR-S9 project), and wavelength for fiber optics (COOMET PR-S8 project), all of which are now being performed, are presented. [ABSTRACT FROM AUTHOR]

We present a system of transmission of reference frequency and time signals to non-interrogating and interrogating measuring facilities of the ground-based GLONASS complex for control of onboard time scales of the navigation system spacecraft. The proposed transmission system is implemented using fiberopticcommunication lines. We present results of experimental studies of the error in the transmission of reference frequency and time signals using fiber-optic communication lines. [ABSTRACT FROM AUTHOR]

An experimental plant for transmission of a reference signal along a fiber-optic communication line with electronic compensation of disturbances introduced by the line is described. Results of measurements of the error associated with transmission of the 100-MHz reference signal of the hydrogen oscillator of the State Primary Standard of the Units of Time and Frequency and the National Time Scale GET 1-2012 along a 100-200 km fiber-optic communication lines are presented. [ABSTRACT FROM AUTHOR]

A technique is proposed for estimating the signal-to-noise ratio in fiber-optic transmission systems with spectral multiplexing, multiplexing of orthogonal and non-orthogonal channel subcarriers in the case of cross-channel interference due to four-wave mixing in the fiber. It is shown that it is possible to estimate the signal-to-noise ratio of a system with any number of sub-carriers of channels from the results of measurements of this ratio for a four-channel transmission system. [ABSTRACT FROM AUTHOR]

A prototype of a system of unilateral and bilateral comparisons of the time scales of distant objects by means of a fiber-optic communication line is described. Results of tests of the prototype and experimental investigations are presented. Errors in the comparison of the time scales and the maximal range of operation of the system are determined. [ABSTRACT FROM AUTHOR]

Promising approaches to the development of measurement assurance in the field of measurements of the average power of optical radiation in fiber-optic systems are considered. Approaches for use in the solution of the problem that also make it possible to expand the values of the unit of average power of optical radiation from 5·10 - 10 W to 10-2.5·10 W reproducible by the existing standard GET 170-2011 are proposed. [ABSTRACT FROM AUTHOR]

The article considers the development of metrological assurance in the field of measurements of the average power of optical radiation in the spectral range 0.6-1.7 μm for fiber-optic communication and information transmission systems, the creation of State Primary Special Standard GET 170-2011 of the unit of length and unit of propagation time of a signal in a waveguide, and the average power, attenuation, and wavelength for fiber-optic communication and information transmission systems. [ABSTRACT FROM AUTHOR]

A possible path to achieving high precision in measurements of the average power of optical radiation in fiber-optic transmission systems through the use of a high-precision calorimetric transducer that has been electrically calibrated by the method of substitution is considered. [ABSTRACT FROM AUTHOR]