Relative Intensity Noise in Multi-Mode VCSELs with and without polarization Control: Theory and Experiments

Multi-mode VCSELs are used in short-reach optical interconnects due to their large modulation bandwidth (around 30 GHz) and sufficient power for datacom demands. Achieving direct modulation rates over 100 Gbit/s requires a strict control of the relative intensity noise (RIN) over a bandwidth that becomes increasingly larger [1]. Here, we experimentally and theoretically investigate the RIN spectrum over 40 GHz of two types of multi-mode VCSELs: with polarization control (Fig. 1), and without polarization control (Fig. 2). Both exhibit spurious peaks in the RIN (Fig. 1b and Fig. 2) the origin and frequencies of which are not yet understood.