Polarization Control and Dynamic Properties of VCSELs for MEMS Atomic Clock Applications

We report the polarization stability and small-signal characteristics of single-polarization single-mode vertical-cavity surface-emitting lasers (VCSELs) emitting at 894.6-nm wavelength for Cs-based miniature atomic clock applications. Polarization control is achieved by integration of a semiconducting surface grating in the top Bragg mirror. The VCSELs are polarized orthogonal to the grating lines with a peak-to-peak difference between the dominant and the suppressed polarization modes reaching 29 dB even at substrate temperatures up to 65
$^{\circ}\hbox{C}$
. A modulation bandwidth of more than 5 GHz is reached at only 0.5-mA bias. Modulation current efficiency factors larger than 12
$\hbox{GHz}/\sqrt{\rm mA}$
are achieved. Moreover, the intrinsic modulation characteristics of the VCSELs are investigated. A
$K$
-factor of less than 0.30 ns and a maximum 3-dB bandwidth exceeding 30 GHz are obtained.