Suppressing mode partition noise in multimode VCSELs via lateral geometry control

This study presents a geometry-driven approach to suppress mode partition noise (MPN) in multimode vertical-cavity surface-emitting lasers (VCSELs) for high-speed short-reach links. Three VCSELs with distinct lateral geometries were investigated, all exhibiting similar static and small-signal performance. The aperture geometry primarily determines the transverse modal distribution, where competition among different mode groups serves as the principal mechanism driving MPN. Among the designs, the intentionally engineered asymmetric aperture concentrates modal energy into a dominant mode group, yielding a root-mean-square (RMS) spectral width of 0.387 nm and the lowest low-frequency relative intensity noise (RIN). The device achieves a transmitter dispersion eye closure quaternary (TDECQ) of 0.86 dB in the back-to-back case and 1.24 dB after 100 m OM4 fiber transmission, with corresponding timing jitter of 6.65 ps and 8.03 ps. The results confirm that lateral-geometry optimization effectively suppresses MPN without degrading intrinsic performance, enabling higher-margin optical interconnects.