National infrastructure for dissemination of precise time and interconnection of quantum sources of ultra-stable optical frequency CITAF

Precise Time and Frequency dissemination and its essential infrastructure on national or even international level are being focused recently. We present here the situation in Czechia, our strategy and approach to contribute with experience of non–commercial solution, open activity utilizing optical networks shared with other data traffic. The cost efficient solution of accurate time and very stable frequency is realized, and operated within shared spectrum of CESNET network infrastructure; the costs are under control then. We are focused on future developments, plans, upgrades concerning wavelength bands and geographic solutions and extensions. Bidirectional dark channels on various wavebands, we do realize them to utilize shared leased fibers, bidirectional compensation of the fiber losses is the benefit or must for these solutions. When operating precise Time and Frequency, single path with bidirectional amplification performed by optical amplifiers is preferred, however it is sensitive to feedbacks by fiber line, caused mainly by back scattering, reflections, and potential to cause unwanted oscillations. The interference with parallel data transmissions is the issue being carefully solved. Within this paper, we also briefly mention CLONETS Design Study project where we share the experience, and the consortium is about to plan and realize the coherent Pan-European Time and Frequency dissemination network to interconnect national research network, and to provide various Time and Frequency services for a wide range of users, research, non-commercial and commercial as well.