Analysis of the effect of transverse modes on free-space optical interconnect performance

Abstract

Vertical-cavity surface-emitting lasers (VCSELs) and microlenses can be used toimplement free space optical interconnects (FSOIs) which do not suffer from thebandwidth limitations inherent in metallic interconnects. A comprehensive linkequation describing the effects of both optical and electrical noise is introduced.We have evaluated FSOI performance by examining the following metrics: thespace–bandwidth product (SBP), describing the density of channels and aggregatebandwidth that can be achieved, and the carrier-to-noise ratio (CNR), whichrepresents the relative strength of the carrier signal. The mode expansion method(MEM) was used to account for the primary cause of optical noise: laser beamdiffraction. While the literature commonly assumes an ideal single-mode laser beam,we consider the experimentally determined multimodal structure of a VCSELbeam in our calculations. It was found that maximum achievable interconnectlength and density for a given CNR was significantly reduced when the higherorder transverse modes were present in simulations. However, the simulationsdemonstrate that free-space optical interconnects are still a suitable solution for thecommunications bottleneck, despite the adverse effects introduced by transverse modes.