We experimentally investigate the impact of relevant parameters such as dispersion regime, and coupling ratio between the two loops on the phase noise performances of a 10 GHz coupled optoelectronic oscillator (COEO). The setup is based on a mode-locked semi-conductor laser at 1.55μm combined to a classical OEO. Optimization of these parameters leads to ultra-low phase noise at close-to-carrier frequencies (-100 dBc/Hz at 100 Hz and -125 dBc/Hz at 1 kHz).
Coherent population trapping (CPT) has been demonstrated as an interesting technique for miniature atomic frequency references [1,2] and quantum information. It is based on the coupling of the two hyperfine ground states of an alkali atom – namely cesium (<sup>133</sup>Cs) for atomic clocks – through excitation to a common atomic level by two phase-coherent laser fields nearly resonant with the atomic transitions. The frequency difference between the two laser fields is tuned at the atomic frequency splitting in the microwave range, equal to 9.192 GHz for <sup>133</sup>Cs atoms. Outputs powers in the mW range and narrow-linewidth emission (<500 kHz) are required for the two laser beams.