Co-Packaged Optics With Multimode Fiber Interface Employing 2-D VCSEL Matrix

We propose and demonstrate a mode-division-multiplexed transmitter by employing a VCSEL-based 2-D matrix and a multi-plane light converter (MPLC). The triangular matrix light spots from VCSELs are designed with a 250-
$\mu$
m pitch in both x- and y- directions for scalable and low-loss mode multiplexing. The VCSELs are directly modulated by co-packaged BiCMOS drivers on a silicon interposer, fabricated on a wafer level. The MPLC is utilized to form seven phase masks to convert the individual Gaussian beams to multiplex Hermite–Gaussian modes, which can be coupled into a multi-mode fiber. In the demonstration, we packaged ten 10-G class VCSELs with the drivers, and the form factor of the co-packaged optics is 10-mm × 10-mm. With the fan-out evaluation board, the sub-module is characterized for short and long transmissions by multiplexing the ten directly modulated outputs from VCSELs. The testing results indicate 200-Gb/s capacity over 100-m MMF with direct detection and 28-km few-mode fiber with coherent detection.