Design limitations of highly parallel free-space optical interconnects based on arrays of vertical cavity surface-emitting laser diodes, microlenses, and photodetectors

We utilize a novel diffraction formalism to study the crosstalk effect in a highly parallel free-space optical interconnect based on two-dimensional arrays of surface-emitting laser diodes, microlenses, and photodetectors. The diffraction induced crosstalk between adjacent laser diodes in each detector to the system limitations is investigated. Optimum design rules and formulas are given for the first time, to include the relation of channel packaging density and interconnect length to the design parameters of the optical interconnect components. The design formulas developed here yield an optimum detector size and indicate a tradeoff between channel packaging density and interconnect length. The feasibility of such a free-space interconnect with a channel packaging density of 3460 channels/cm² and 2.0 cm interconnection length is determined using typical parameters of detector radius from ~5 to ~45 μm, lens radius of 85 μm, and laser diode radius of ~5 pm operating at wavelength 0.67 pm for signal-to-noise ratio above 17 dB. Some experiments were conducted to measure the diffraction induced crosstalk and optical link efficiency