Fiber-optic time and frequency distribution system OSTT-4

Introduction and key features

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

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. In contrary to standard two-way systems, our solution 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 for time and frequency distribution to users not maintaining their own clocks in areas such us: 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.

The following list of some demanding clients is the best reference for this unique and high performance System:

- National Institute of Standards and Technology (NIST) - Boulder, USA,

- The United States Naval Observatory (USNO) - Washington, USA,

- Physikalisch-Technische Bundesanstalt (PTB) - Germany,

- The National Physical Laboratory (NPL) - United Kingdom,

- Deutsche Telekom - Germany.

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.


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.


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.

OSTT-4 leaflet PDF

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OSTT-4 files