Contents 1. Introduction
Few-mode vertical-cavity surface-emitting laser (VCSEL) is the main-stream data-center transmitter with low power consumption and high modulation bandwidth. To meet the demand of IEEE 802.3bm standard for 100GBASE-SR4 with 25 Gbit/s per lane, both the low noise and high coupling efficiency are mandatory for achieving large signal-to-noise and low-bit-error-rate operation. Nevertheless, the dominated noises such as relative intensity noise (RIN) and mode partition noise (MPN) must be restrained [1]. Effectively, different fiber coupling geometry can provide the lower MPN of the VCSEL with fewer corded mode numbers to improve the transmission performance. The lensed multi-mode fiber (MMF) or single-mode fiber (SMF) with a curved end face in the core region can perform collimation for coupling the VCSEL, with its high-order modes filtered suppress the modal dispersion during distant transmission at the cost of the significant rollover in the bias dependent output. In this work, several MMF and SMF coupling schemes are employed to compare mode number, efficiency, and noise performance coupling the few-mode VCSEL
