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°C . A modulation bandwidth of more than 5 GHz is reached at only 0.5-mA bias. Modulation current efficiency factors larger than 12 GHz/√(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.