Vertical-cavity surface-emitting lasers (VCSELs) emitting at 894.6 nm wavelength have been fabricated for Cs-based
atomic clock applications. For polarization control, a previously developed technique relying on the
integration of a semiconducting surface grating in the top Bragg mirror of the VCSEL structure is employed.
More specifically, we use a so-called inverted grating. The VCSELs are polarized orthogonal to the grating lines
with no far-field diffraction side-lobes for sub-wavelength grating periods. Orthogonal polarization suppression
ratios exceed 20 dB. The polarization stability has been investigated at different elevated substrate temperatures
up to 80 °C, where the VCSEL remains polarization-stable even well above thermal roll-over. For the purpose
of integration with the atomic clock microsystem, flip-chip-bondable VCSEL chips have been realized. Sub-mA
threshold currents and sufficient output powers in the milliwatt range are achieved. The required modulation
bandwidth of more than 5 GHz is reached at only 0.5mA bias. Maximum bandwidths above 10 GHz have
been measured even at elevated temperatures up to 80 °C. Modulation current efficiency factors larger than
12 GHz/√mA are achieved at room temperature. Moreover, the intrinsic modulation characteristics of the
VCSELs are investigated by precise curve fitting of measured small-signal modulation response curves and relative
intensity noise spectra. A K-factor of less than 0.4 ns and a maximum 3 dB bandwidth exceeding 22 GHz are
obtained.
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