Mode Resolved Modulation Response And The Impact Of Mode Intensity Nonuniformity On Vcsels Dynamics

To investigate the origin of the deep-notch in the modulation response of multi-mode vertical cavity surface emitting lasers (VCSELs) that occurs at low frequencies, the carrier transport and the mode intensity nonuniformity effects are considered in this work. The model that includes the carrier transport effect is a possible candidate to explain the deep-notch behavior, as it introduces a first-order low-pass filter to the pure intrinsic transfer function. Nevertheless, the expected dynamic characteristics of this filter for high-performance VCSELs, disfavor the transport effect as a possible candidate. Therefore, to fully rule out its impact, we optimized the transport theory by first considering both the transverse and longitudinal carrier transport effects, and second by including the frequency dependence of the transport factor into the derivation of the VCSELs' dynamic transfer function. Taking all these factors into consideration, however, did not result in a significant improvement in the resulting transfer function form and order. Thus, a second effect, which is the mode intensity nonuniformity effect, is favored as a possible candidate to explain the deep-notch phenomenon. In this effect, the spatial nonuniformity of the transverse optical mode in the radial direction results in concentric disk-like regions with different dynamic properties under small signal modulation. At low driving currents, the model predicts a notch ahead of the relaxation oscillation frequency. This notch is caused by a low frequency roll-off resulting from the spatial nonuniformity of the optical transverse mode. The proposed model introduces a ratio containing a pole and a zero to the pure intrinsic transfer function and can very accurately fit the deep-notch in the measured modulation response. Furthermore, this fitting results in the extraction of very reliable performance indicators. A second topic that is also presented in this work is about the dynamics of the mode resolved modulation response. To achieve a higher bandwidths, it is necessary to study the mode ensemble resolved modulation characteristics of the intrinsic dynamics. Based on the novel carrier-reservoir splitting approach, analytical expressions for the dynamics in the two spatially separated central and peripheral regions are derived.