4-PAM for High-Speed Short-Range Optical Communications

TLDR

The study compares 4‑PAM and OOK modulation formats for high‑speed short‑range optical communications. The authors used a directly modulated 850‑nm VCSEL, OM3+ multimode fiber, and photodetector to compare 4‑PAM and OOK at up to 25 Gbps over distances up to 600 m, measuring in real time without equalization.

Abstract

In this work, we compare 4-pulse amplitude modulation and on–off keying modulation formats at high speed for short-range optical communication systems. The transmission system comprised a directly modulated vertical-cavity surface-emitting laser operating at a wavelength of 850 nm, an OM3+ multimode fiber link, and a photodetector detecting the intensity at the receiver end. The modulation formats were compared both at the same bit-rate and at the same symbol rate. The maximum bit-rate used was 25 Gbps. Propagation distances up to 600 m were investigated at 12.5 Gbps. All measurements were done in real time and without any equalization.