Spectral-dependent electronic-photonic modeling of high-speed VCSEL-MMF links for optimized launch conditions

We present spectral-dependent electronic-photonic modeling of vertical-cavity surface-emitting laser (VCSEL)-multimode fiber (MMF) links for next-generation high-speed interconnects. The beam coupling processes, between the VCSEL and the MMF and between the MMF and the photodetector (PD), are discussed, with spectral-dependent three-dimensional launch conditions analyzed. The model accounts for fiber effects on the transmission performance, specifically modal attenuation, dispersion, mode mixing, and mode partition noise. An advanced split-step small-segment (4-S) method simulates the signal evolution over the MMF with high accuracy and high efficiency. Experimental validation at 25 Gbps confirms the high accuracy of the VCSEL-MMF link model. The model reveals that larger radial offsets can further excite lower-order mode groups reducing the power distributed to higher-order groups when a tilted beam couples to the input fiber facet. With an optimized misalignment launch, the modal bandwidth is greatly improved by 3.8-fold compared to the conventional center launch. The model helps determine the optimum launch condition to improve link performance metrics such as transmission reach.