Experimental Evaluation of Free Space Links in the Presence of Turbulence for Server Backplane

Free-space optical interconnection (FSOI) technology enables high interconnection speed in next-generation servers. FSOIs use laser links between server components and provide a lower bound on propagation delay due to the shortest line-of-sight path and the low index of refraction of air, when compared with the indices common in waveguide technologies. One of the main problems of FSOI systems is the inevitable turbulence effect that results from the air cooling of server components. Cooling fans produce a flow of hot air, due to excessive thermal emission from electronic components inside the chassis; this produces turbulence-induced fading and may influence the communication performance. The objective of this paper is to experimentally examine the influence of the turbulence effect on FSOI channels inside a server chassis. This includes studying scintillation statistics and characterizing temporal and spatial in-chassis turbulence. The results of the analysis reveal that the in-chassis optical channel preserves the well-known log-normal scintillation distribution. However, some temporal and spatial characteristics do not fit the commonly accepted turbulence theory predictions.