Analysis of Crosstalk Contributions for OAM Modes From Propagation and Multiplexing

Intermodal crosstalk (XT) fundamentally limits the capacity of orbital angular momentum (OAM)-based mode division multiplexing (MDM) systems. This XT arises both from fiber propagation and from imperfections in the multiplexer (MUX)/demultiplexer (deMUX). Under some simplifying assumptions, we isolate these two contributions across different fiber lengths and wavelengths. We measured XT matrices in a 16- mode OAM-MDM system at three fiber lengths and at the center and edges of the C-band. Assuming that fiber XT grows linearly with distance, we predict net throughput for (i) ideal MUX/deMUX and (ii) our free-space laboratory version. Our results show that we begin to lose modes due to XT at 0.9 km in both scenarios. At longer lengths, and particularly at the C-band edges, experimental demonstrations have pessimistic throughput predictions due to strong wavelength-dependent XT in the free-space MUX/deMUX. These findings allow a more accurate understanding of the ultimate capacity limits of OAMMDM for high-capacity, short-reach data center links.