Ultra-low bit error rate plastic optical fiber link for high-speed PAM4 transmission: enhanced optical return loss...

We present a graded-index (GI) plastic optical fiber (POF) that achieves significantly lower bit error rates (BERs) in high-speed data transmission using four-level pulse-amplitude modulation (PAM4), compared with standard silica GI multimode fibers (MMFs) in short-reach links based on vertical-cavity surface-emitting lasers. The GI POF features strong mode coupling associated with microscopic heterogeneities in the fiber core material, which effectively suppresses interferometric noise, particularly reflection noise. Experimental results demonstrate that the GI POF achieves BERs several orders of magnitude lower than those of silica GI MMFs in 53.125 Gb/s PAM4 transmission under identical optical return loss conditions, and maintains error-free operation (BER < 10^-12) across a wide range of alignment conditions. The stability and robustness enabled by the GI POF can reduce reliance on externally implemented noise mitigation strategies, such as specialized transceiver optics, tight-tolerance connectors, and digital signal processing, thereby enabling cost-effective, energy-efficient, and low-latency optical interconnects.