Error correction for free-space optical interconnects: Space-time resource optimization

We study the joint optimization of time and space resources within free-space optical interconnect (FSOI) systems. Both analytical and simulation results are presented to support this optimization study for two different models of FSOI cross-talk noise: diffraction from a rectangular aperture and Gaussian propagation. Under realistic power and signal-to-noise ratio constraints, optimum designs based on the Gaussian propagation model achieve a capacity of 2.91 × 10¹⁵ bits s⁻¹ m⁻², while the rectangular model offers a smaller capacity of 1.91 × 10¹³ bits s⁻¹ m⁻². We also study the use of error-correction codes (ECC) within FSOI systems. We present optimal Reed-Solomon codes of various length, and their use is shown to facilitate an increase in both spatial density and data rate, resulting in FSOI capacity gains in excess of 8.2 for the rectangular model and 3.7 for the Gaussian case. A tolerancing study of FSOI systems shows that ECC can provide tolerance to implementational error sources. We find that optimally coded FSOI systems can fail when system errors become large, and we present a compromise solution that results in a balanced design in time, space, and error-correction resources.