Noise in VCSEL-Based Links: Direct Measurement of VCSEL Transverse Mode Correlations and Implications for MPN and RIN

The correlation properties of vertical-cavity surface-emitting laser (VCSEL) transverse modes determine the noise impairments of VCSEL-based high-speed MMF links. Relative intensity noise and mode partition noise originate from the distinct and aggregate fluctuations of the lasing transverse modes of VCSELs. These noise mechanisms are often the limitations in VCSEL-based optical links particularly 25 Gbaud and higher OOK and PAM-4 links and are an integral part of any link budget including those of the IEEE 802.3 and fiber channel T11.2 standards efforts. Here, we report the direct measurement of the correlation properties of high-speed VCSELs. We show that the corresponding computed mode partition noise (MPN) and relative intensity noise (RIN) powers are inconsistent with the conventional models used by standards groups yet are consistent with link measurements.