The Effect of the Higher Order Modes on the Optical Crosstalk in Free-Space Optical Interconnect

In this paper we investigate the effect of the crosstalk introduced due to laser beam imaging in a free-space optical interconnect (FSOI) system. Due to the overfill of the transmitter microlens array by the vertical-cavity surface-emitting laser (VCSEL) beam, one part of the signal is imaged by the adjacent microlens to another channel, possibly far from the intended one. Furthermore, it is known that in practice, VCSELs tend to operate in several transverse modes simultaneously. This will cause even more increase in the interchannel and intersymbol interference, to our knowledge this issue has been neglected so far. The numerical simulation has been performed using a combination of exact ray tracing and the beam propagation methods. The results show that the stray-light crosstalk will increase significantly with either greater system density or higher order modes. The diffraction-caused crosstalk is primarily affected by interconnection distance and channel density