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Low phase noise microwave analog optical link performance study for high dynamic environment platform

Distribution of very low phase noise and low spurious microwave Local Oscillator (LO) is needed for most of the radar or electronic warfare applications. In this paper we study the capability to optically carry low phase noise LO, thanks to a directly-modulated optical link, while subjected to severe environmental conditions. First the optical link is compared to a coaxial cable link in terms of additive phase noise: subsequently the absolute amplitude and phase noise under random vibration are compared. It should be noticed that even in case of a wide band optical link, the phase noise floor difference between optical and coaxial cable is small even for short distance links. Secondly, the absolute amplitude and phase noise of the optical and coaxial cable link are measured with the entire optical link or only with some components of the link (10 GHz LO, optical single mode fiber (SMF), laser and photodiode) under random vibration. The phase noise degradation is almost the same when the optical or the coaxial link is under vibration and the main degradation is always due to the Local Oscillator whatever the technology is (OEO: Opto-Electronic Oscillator or traditional quartz oscillator). Some ways of improvement of optical link g-sensitivity that can be useful for OEO will be discussed. Thanks to recent experimentations done by DGA, it has been shown that very low phase noise microwave LO signals can be carried on optical link without any phase noise degradation due to the link while subjected to random vibration.