Two-Way PAM8/PAM4 VCSEL-Based IVLLC system with parallel optical injection locking

In this demonstration, a two-way PAM8/PAM4 invisible laser light communication (IVLLC) system that adopts a parallel optical injection-locked VCSEL is proposed and constructed. It is to be found that injection locking in the parallel polarization sideband and free-running in the orthogonal polarization sideband exists concurrently [1-2]. With parallel/orthogonally polarized dual-sideband operation, the injection-locked parallel polarization sideband (x-polarization) is utilized as the downstream carrier for 84 Gb/s PAM8 signal transmission, and the induced free-running orthogonal polarization sideband (y-polarization) is utilized as the upstream carrier for 45 Gb/s PAM4 signal transmission. A set of doublet lenses is employed to perform a 200-m free-space link. Through an in-depth investigation of such two-way PAM8/PAM4 IVLLC system, good BER performances, acceptable PAM8 and qualified PAM4 eye diagrams are attained at 84 Gb/s (downstream) and 45 Gb/s (upstream) operations through a 200-m free-space link.