For time transfer on baselines exceeding 100km, GPS is the most common technical solution. The main benefit is that it is easy to install, but it is a single point of failure and it is sensitive to interruption by radio noise. For time transfer requiring high reliability a complementary backup method is therefore desirable, and time and frequency transfer utilizing optical fiber is a favorable alternative technique. The connectivity is simplified by the deployment of dense fiber optic communication networks in most countries and since it does not rely on transmission using radio waves in open air, it is robust against perturbations. The simplest and most straightforward method for high performance time transfer is the two-way technique, which is an excellent choice when the user has access to the whole system, and when both transmission paths are equal or with a known and predictable asymmetry. Furthermore it is most practical when the numbers of users are limited and when no security issues limit the bidirectional connectivity. A proof-of-concept for an alternative technique for fiber based time and frequency transfer, utilizing a one-way co-propagation of two light waves, has been presented previously. The technique utilizes dual wavelengths and measures the difference in group velocity to estimate the delay variation of the timing signal in one of the wavelength channels. This paper presents the recent improvements on this method, including new equipment, new algorithm and a demonstration of real-time compensation of delay time variations.
TEKNIK OCH TEKNOLOGIER -- Elektroteknik och elektronik (hsv//swe)
ENGINEERING AND TECHNOLOGY -- Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)