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Frequency Dissemination with Fibres

Working Group 4.34

Profile

 Measuring the distance between the earth and the moon exactly, to within 100 000th of the thickness of a hair: with such accuracy, working group 4.34 does not measure astronomic distances, but the frequency of light. The worldwide telecommunication fiber network opens up the possibility of high-precision frequency measurements and comparisons over long distances across Germany and Europe. For such frequency comparisons, we use optical interferometry to compare the phase of laser light at both ends of telecommunication fiber, which can be up to 2000 km long. The signal attenuation encountered on such long-haul fiber links is compensated by amplifiers that are developed in-house and are based on stimulated Brillouin scattering.

The precise measurement of frequencies enables a variety of applications, e.g., the comparison and validation of different atomic clocks in Europe, or the determination of geodetic height levels with a resolution of 0.01 m via chronometric leveling (relativistic geodesy).

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Research/Development

With the aid of optical clocks it is possible to obtain considerably smaller uncertainties and higher stabilities in the realization of the unit of time than with microwave standards. This fact will in future lead to a redefinition of the base unit "second". In order to fully utilize this potential, it is necessary to be able to compare also optical clocks with different optical frequencies and at different sites directly with each other. Important aids here are optical comb generators.

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Brillouin amplification for long-distance optical frequency transfer has been investigated at PTB since 2010 [1]. It is an enabling technology for achieving world-record distances of metrological optical fiber links [2,3]. In these cases, fibre Brillouin amplification was realized in a laboratory setup.

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To cope with the increasing requirements on bandwidth, Dense Wavelength Division Multiplexing (DWDM) systems are used to an ever increasing extent in optical telecommunication. At present, the wavelength range is constantly extending and, at the same time, the channel distances are getting smaller. For the calibration of measuring systems and the support of networks, wavelength references in the range between 1480 nm and 1640 nm with a relatively high accuracy are required.

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geo-Q

In einem Teilprojekt (A04) des Sonderforschungsbereichs geo-Q befasst sich die Arbeitsgruppe 4.34 mit höchstgenauer Frequenzübertragung über Glasfasern. Ein Ziel ist hierbei hochpräzise (optische) Uhren an verschiedenen Standorten zu vergleichen. Im Gravitationspotential der Erde ergeben sich scheinbare Frequenzunterschiede zwischen zwei Uhren, wenn diese unterschiedlich hoch positioniert sind. Dieser relativistische Effekt entspricht der Gravitationsrotverschiebung für Licht, was den Höhenunterschied zwischen den Uhren überwindet. So ermöglicht es die Allgemeine Relativitätstheorie, Höhenunterschiede mit einer Auflösung von 1 cm zu messen, wenn sowohl die Frequenzübertragung selbst, als auch die Uhren eine Genauigkeit von 10-18 aufweisen. Im Nachbarteilprojekt A03 werden für solche Untersuchungen hochgenaue transportable Uhren u.a. mit Sr-Atomen (AG 4.32) entwickelt.

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Services

This working group does not offer any services. Services offered by the department or other working groups are detailed on their respective web pages.

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Information

Angebote für Studenten

Wie an der PTB im Allgemeinen, besteht auch in der Arbeitsgruppe 4.34 die Möglichkeit eine studentische Arbeit zu schreiben, ein Praktikum zu absolvieren oder sich als Werksstudent an der Forschung zu beteiligen. Bei Interesse an den Themen und Projekten der Arbeitsgruppe, können Sie sich zunächst Opens internal link in current windowan die zentralen Ansprechpartner wenden und dort als Wunsch die Arbeitsgruppe nennen. 

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