Polarization-stable single-mode VCSELs for Cs-based miniature atomic clocks

Vertical-cavity surface-emitting lasers (VCSELs) are compelling light sources for such clocks, since they simultaneously meet the requirements of high-temperature operation while emitting a low-noise, narrow-linewidth, single-mode, single-polarization beam. Employing the coherent population trapping (CPT) effect of the Cs D1 line, the laser is harmonically modulated at about 4.6 GHz with a center wavelength of about 894.6 nm. Sub-mA threshold currents of VCSELs contribute to low dissipated power, and the vertical emission is advantageous for hybrid integration with the clock microsystem. Ultra-miniaturized atomic clocks require fabrication techniques known from micro-electro-mechanical systems (MEMS).