Abstract

Atoms and ions fountain sources offer extremely high-Q factor (~10¹⁵) resonances in the visible and ultra-violet regimes and thus the promise of new optical frequency standards of unprecedented stability [1]. The difficulty in making use of such an optical signal in electronic instrumentation is the requirement for coherent frequency division to microwave or RF frequencies. So far, phase coherent frequency measurements of near infrared and visible signals have been made using conventional frequency chain techniques, which necessarily employ a large number of different types of oscillators such as BWO, far-infrared, colour-centre and dye lasers. Although these techniques provide a phase coherent measurement of optical frequencies they do not provide a microwave signal which is phase locked to the optical signal. We propose here a simplified microwave to optical phase coherent chain which does provide such an output. It is based on the innovative Telle frequency interval bisection method [2] combined with an optical frequency comb (OFC) generator driven by an ultralow phase noise microwave sapphire oscillator.

© 1996 Optical Society of America