L. Buczek

Fiber-Optic Joint Time and Frequency Transfer With Active Stabilization of the Propagation Delay

In this paper, we describe the extension of our fiber-optic frequency transfer system to the time transfer capability. In contrast to standard two-way transfer schemes which offer only comparisons of two distant clocks, our system displays distribution functionality, reproducing the time and frequency signals of the reference clock in the remote location. By using active compensation of the fiber delay fluctuations, we obtained a time deviation of 0.3 ps (for time transfer) and an Allan deviation of 1.2 × 10-17 (for frequency transfer) at 105-s averaging. The experiments presented were carried out using a 60-km-long fiber loop, forming a part of the real urban network around Kraków.

Multipoint dissemination of RF frequency in fiber optic link with stabilized propagation delay

In this paper, we present the concept of accessing the signal at some midpoint of a frequency dissemination system with stabilized propagation delay, which allows building the point-to-multipoint frequency dissemination network. In the first experiments with a 160 km-long fiber link composed of a field-deployed optical cable and fibers spooled in the lab, exposed to both diurnal and seasonal temperature variations, in the access node, we obtained the Allan deviation of a 10- MHz frequency signal of about 3 × 10-17 and the time deviation not greater than 2 ps for 105 s averaging.

ELSTAB—Fiber-Optic Time and Frequency Distribution Technology: A General Characterization and Fundamental Limits

In this paper, we present an overview of the electronically stabilized (thus named ELSTAB) fiber-optic time and frequency (T&F) distribution system based on our idea of using variable electronic delay lines as compensating elements. Various extensions of the basic system, allowing building a long-haul, multiuser network are described. The fundamental limitations of the method arising from fiber chromatic dispersion and system dynamics are discussed. We briefly characterize the main hardware challenge of the system, which is the design of a pair of low-noise, precisely matched delay lines. Finally, we present experimental results with T&F distribution over up to 615 km of fiber, where we demonstrate frequency stability in the range of 1-7 × 10-17 for 105 s averaging and time calibration with accuracy well below 50 ps. Also, practical implementation of the ELSTAB in the Polish T&F distribution network is shown.

Multipoint dissemination of RF frequency in delay-stabilized fiber optic link in a side-branch configuration

In this paper we are presenting the concept of the multipoint dissemination of RF frequency signal via a fiber optic network with actively stabilized propagation delays. The idea allows to add tapping nodes and side branches to the main point-to-point frequency transfer link, constituting a tree-like dissemination network. We are demonstrating the experimental results with the 100 km-long side branch starting at the 110th km of the 170 km-long main link. At the end of the side branch we obtained the Allan deviation of a 10-MHz frequency signal of about 4×10-17, and the time deviation not greater than 1.2 ps for 105 s averaging.

OPTIME - the system grows - a new 330 km line

The OPTIME project creates an ultra-precise time and frequency signals dissemination system based on telecommunication networks. End users obtain access to these signals without incurring huge costs for the purchase of their own atomic clocks, and receive the service related to laboratories generating international atomic time scales, to which any precise time must be referred. OPTIME dissemination system is based on three main elements: reference time and frequency laboratories, local time and frequency repositories and fiber optical network with specialized transmission equipment to transfers signals between laboratories, repositories and end users. This article describes OPTIME system with particular emphasis on a new 330 km long dissemination line between Space Research Centre PAS, Astrogeodynamic Observatory (AOS) at Borowiec and National Laboratory of Atomic, Molecular and Optical Physics (KL FAMO) at Torun.

OPTIME — Time and frequency dissemination system based on fiber optical network — PIONIER

The OPTIME project creates a long range dissemination system for transfer ultraprecise time scale and the references frequency signals in telecommunication networks. The highest accuracy signal is available only on fiber optical networks, but other type of networks can be used to transfer of signals with lower accuracy to adapt it to the needs of different user groups. Article also describes experience gained during an over-a-year experiment of connection between Central Office of Measures (GUM) in Warsaw and the Astrogeodynamic Observatory (AOS) in Borowiec.

Remote synchronization of atomic clocks

In the paper we present and briefly characterize the methods of remote synchronization of atomic clocks. Two groups of technical solution are presented, namely the methods employing satellites, especially GPS Common View and Two Way Satelite Time and Frequency Transfer and the group of systems, which employs the ground-base fiber optic networks. The unidirectional and bidirectional time/frequency transfer schemes are considered, and theirs main limitations are pointed out. Finally, the newly established atomic clock signals distribution network called Optime is presented. In a first step, the network was a simple link which primary objective was to connect two most important Time and Frequency laboratories in Poland - in Central Office of Measures (GUM, Warsaw) and in Astrogeodynamic Observatory (AOS) in Borowiec near Poznan. Recently, Optime has been expanded by adding three newly installed branches connecting GUM and Orange Synchronization Center and AOS with National Laboratory of Atomic, Molecular and Optical Physics in Torun. and Astronomic Center in Piwnice.

Sequential measurement of optical frequency difference of semiconductor lasers for time transfer system

This paper describes the concept of differential wavelength measurement of two semiconductor lasers with better resolution and accuracy than offered by a typical optical spectrum analyzer. In a two-way fiber-optic transfer system the knowledge of difference of wavelength is used to calibrate of time transfer. Applying this solution allows to calibrate time transfer system with lower uncertainty.

OPTIME - final release

The OPTIME project creates an ultra-precise time and frequency signals dissemination system based on telecommunication networks. End users obtain access to these signals without incurring huge costs for the purchase of their own atomic clocks, and receive the service related to laboratories generating international atomic time scales, to which any precise time must be referred. This document describes the final stage of OPTIME project - which developed a self-calibrating, high precision dissemination system for time and frequency reference signals based on optical fiber links and ELSTAB devices developed at AGH University.

The concept of differential wavelength stabilization of the semiconductor lasers for time and frequency transfer system

This paper describes the concept of differential wavelength stabilization of the semiconductor lasers for fiber time and frequency transfer system. This concept based on coherent detection and down-conversion, exploiting high-speed photodiode and frequency prescaler.