Introduction and key features

OSTT-4 - deployment of the ELSTAB technology (Polish AGH University of Science and Technology).

OSTT-4 may be used for clock comparisons as well as for delivering the ultimate quality time and frequency signals to the users not maintaining their own clocks and/or timescales. The local module of the system accepts the frequency and time signals (10MHz and 1PPS) and transmits them via an optical fiber to the remote module. Our solution (in contrary to standard two-way systems) delivers stabilized and calibrated replica of source signals, thus may be described as a virtual atomic clock at the end of the fiber. Besides metrological applications, as clock comparisons, the system may be used in areas such as: telecommunication, power engineering, navigation, astronomy, labs, spectroscopy. Banking, finance, critical infrastructure as well as public administration may consider deployment of the system to support their cybersecurity.

Active delay stabilization

The unique features of the system are based on the concept of active compensation of variations of the fiber delay. The signal reaching the remote module is redirected backward to the local module and used for compensation of path delay fluctuations.

Autocalibration

Calibration of the time transfer is based on round-trip delay measurement, which is performed locally at the transmitting side of the system. After installation and initial calibration, the input output delay is constant and there is no need for any further measurements or data exchange.

Dispersion Insensitive (DI) option 

The  Dispersion Insensitive option was introduced to simplify the calibration of time transfer. In the standard version of the OSTT-4 system the chromatic dispersion of the actual fiber link has a significant impact on the link calibration, and therefore must be accurately estimated. In the DI option, thanks to introducing an additional optical signal, the calibration is insensitive to the chromatic dispersion.

1) OSTT-4 consists of a local and remote module for time and frequency transfer,

2) Transfers 10 MHz signals (100MHz as an option),

3) Frequency transfer stability: ADEV < 3×10^-13 for 1 s averaging, < 3×10^-17 for 10⁵ s averaging,

4) Transfers 1PPS signal (also 100PPS), phase synchronous with frequency signal, TDEV < 3 ps for 10 s averaging, < 1 ps for 10⁵ s averaging,

4) Operates bi-directionally on a single optical fiber in C band,

5) Output 1 PPS position adjustment: 1 ps resolution, negative delay also possible,

6) OSTT-4 is actively stabilized against fiber induced phase fluctuations. The phase correction range is 2000 ns,

7) As an option the system can be enriched with optical amplifiers.