Microwave Frequencies Metrology

OPUS - Photonic Ultra-Stable Oscillator

This project aims at developing an ultra-stable photonic oscillator by tightly locking a laser source to a very high finesse Fabry-Perot cavity (300,000). From this optical stabilized signal, we aim to generate a microwave signal around 10GHz with a very low phase noise. A Nd-YAG laser @1064nm locked to a high finesse optical cavity is able to provide a relative frequency stability of about 10^-15 for a sampling time between 1s and 100s. A finite elements analysis implemented with two different finite elements software packages made it possible to optimize the geometry of the cavity in order to minimize the sensitivity to vibrations. The high vacuum mechanical system enables us to precisely adjust the temperature in the range 5°C to 25°C and thus to minimize the frequency drift. This ultra-stable laser will be used to control a femto-second laser and to generate a microwave signal showing very high frequency stability. The objective is a reliable replacement of the cryogenic sapphire oscillator operated at the temperature of liquid Helium, which is the low phase noise source currently used to interrogate the atomic fountains.

Left: Drawing of the cavity vacuum enclosure.
Right: Simulation of the cavity distorsion due to vibrations.