Project: Stable Microwave Generation and Dissemination over Optical Fiber

Research labs, Observatories, Universities and high-tech industry require ever increasing stability and accuracy of radio frequency (RF) sources used to reference equipment and production sites. Important frequencies cover the range from few MHz up to several 10s of GHz, the latter is in the microwave doCO. Manufacturing of tightly specified RF components for telecommunication, wireless local area networks, defence, space born applications, radar technology and high-tech industries inevitably calls for a production and a quality management based on precisely referenced low-noise RF equipment. Large scale experiments distributed over several labs like Synchrotron experiments and Free Electron Lasers require precise RF referencing originating from a single master reference both for beam generation and the experiments which are often located in remote labs down the beam line. RF and microwave astronomy benefits from precisely controlled frequencies at the ground stations and in the receiver electronics at the telescopes. Universities and research labs which due to limit financial resources can COtain only one central RF reference source require low-noise highly stable dissemination of their reference to remote labs on the campus, thus saving the money for several RF references. _x000D_Established approaches for these needs generate a local RF or microwave reference signal from a local standard (amongst others high quality quartz oscillators, H-Masers, Cs clocks, GPS receivers and Sapphire Loaded Cavity Oscillators (SLCOs)). These standards are well developed and have a high technology readiness level (TRL). However, their stability and/or phase noise is already reaching technological limits. Distribution of the generated RF reference signal from the local RF standard to remote sites is typically realized over unstabilized electric (RF coaxial) or optical links. These links suffer from noise and drifts due to environmental changes. Besides vibrations, COly temperature variations affect the stability of the disseminated RF frequencies as a result of changes in length (both RF coaxial and optical links) and in index of refraction (COly optical links). For specific timing distribution with very tight specifications for the timing jitter, ultrashort pulses are sent over stabilized links which are limited to lengths less than 1 km because of the necessity to compensate the dispersion of the link. _x000D__x000D_Project Goals:_x000D_STAMIDOF has two CO goals:_x000D_The first goal is the development of a stable RF source based on an Optical Frequency Comb (OFC) locked to a stable CW laser. OFCs readily deliver frequencies covering the range of few 100 MHz up to 100 GHz, limited only by the bandwidth of the photo diode which detects the pulse train out of the mode locked comb oscillator, and are a thus a convenient source of RF and microwaves. The OFC technology itself is developed to a high TRL and is not an objective in this project. However, specific adaptations to the requirements in this project, namely the lock of the OFC to the CW laser, will be investigated. CW lasers which can be stabilized are well developed as well and are not an objective in this project. The stabilization of the CW Laser is realized by locking its optical frequency to a stable optical reference, e.g. to a transmission fringe of a Fabry-Perot type cavity with high finesse which is well isolated against the environment. Another type of reference is a isolated fiber spool with few kilometers of standard fiber. The project will focus here on the development and optimization of these references for the scope of this project. CO requirements are high stability, transportability, low noise, ease of use and low cost of ownership. Different to usual high finesse cavities which are used to shrink the CW laser line width, for RF generation the stable laser does not need to be ultra-narrow, which will allow for simpler setups. To map the huge parameter space we will investigate both, high finesse cavities as well as fiber spool based references. The latter are more cost effective but are expected to be slightly less stable. _x000D_ _x000D_The second goal is the development of a turn-key RF or microwave dissemination scheme allowing for compensation of environmental noise affecting the distribution link. Several principles for stabilized optical links have been described in the literature but are not commercially available. In STAMIDOF, the dissemination will be realized via a transfer from RF or microwave to the optical doCO by amplitude modulation of a CW laser, which will be distributed over standard telecom fiber. On the receiver side, the RF or microwave is regenerated from the output of a photo diode which detects the modulated CW light. Stabilization of the fiber is done by an interference technique which compares the input light against light which has travelled back and forth through the optical link, yielding an error signal for active compensation of the fiber noise.

Acronym STAMIDOF (Reference Number: 7503)
Duration 01/01/2013 - 31/12/2015
Project Topic We propose to develop and commercialize a source of stable microwave frequencies based on stable cw laser and optical frequency comb technology, including their dissemination over actively stabilized standard telecom fiber to remote sites.
Network Eurostars
Call Eurostars Cut-Off 8

Project partner

Number Name Role Country
3 Centre National de Recherche Scientifique-Laboratoire Photonique, Numérique et Nanosciences Partner France
3 Centre National de Recherche Scientifique, Système de Référence Temps Espace Partner France
3 Menlo Systems GmbH Coordinator Germany