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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. [ABSTRACT FROM PUBLISHER]

Data centers have become the major technology for collecting and processing information. The data-rates required for transferring the information through the server's backplane has been increasing from year to year at an almost exponential pace. Therefore a technology-shift from the electronic to the optic domain has already been initiated in order to meet the required data-rate demands for next-generation servers. The future technology that is analyzed in the paper is free space optics (FSO). FSO technology uses laser links between the server cards and the backplane and provides a lower bound on propagation delay due to the low index of refraction of air, when compared with waveguide or fiber technologies. However, turbulence occurs due to the high temperature of the chips and to ventilation inside the server, which results in deterioration of the communication performance. In this paper, we examine the feasibility of wavelength diversity as a means to mitigate the effect of turbulence on the server communication link performance. It is shown that using the diversity scheme cuts the outage probability by half for the same total transmitter power by comparison with the single wavelength scheme. Therefore, the power consumption (and operational costs) of the data center could be reduced dramatically if a wavelength diversity scheme were adopted. The authors believe that this is the first time that a laboratory experiment has been performed modeling a server backplane with FSO communication using wavelength diversity. [ABSTRACT FROM PUBLISHER]

Over recent decades, there have been increasing demands for high data-rate backplanes for enhanced performance in computers. The present technology of electronic backplanes cannot meet the required data-rate demands for next-generation computers, indicating a need for a technology shift from the electronic to the optic domain. In this paper, we develop a mathematical model to describe the effect of air turbulence on a short range free space optical communication link, such as would be found in computer backplane communication, and conduct experiments to validate the model. The air turbulence under discussion resembles that which would result from the high temperature of chips on the board together with the ventilation of the air by the chip fan. In our experiment, the communication performance, expressed as bit error rate (BER), is presented as a function of the location of the turbulence source and the log amplitude variance. The log amplitude variance was evaluated by two independent methods. One of the main results of this study is the indication that the performance of the backplane deteriorates even for very small values of air turbulence strength. This is exacerbated by the fact that extremely low BER performance is required at the backplane (e.g., from 10-14 to 10- 18 ). We also demonstrate that increasing the distance between the turbulence source and the optical link reduces the influence of the air turbulence in an exponential manner. This fact is important for the design of future-generation optical backplanes. It is noted that operation at wavelengths around 1550 nm yields communication performance that is less severely degraded by air turbulence effects than at 670 nm. [ABSTRACT FROM PUBLISHER]