Maximizing receiver misalignment tolerance in a hybrid wireless system

In this work, we investigate possible designs for a free-space infrared optical receiver for use in a hybrid optical-RF network with airborne platforms. Due to the relative instability of the platforms compared to traditional building placements, the receiver must possess much greater tolerance to misalignment with respect to the receiver. The limited size and payload of the airborne platforms restricts the design process. We present the results of both experimental and theoretical studies of a range of receiver designs, including single lens receivers with fiber bundles for light collection and multiple lens receivers with bundles coupled to each lens. The results show that the combination of a short focal length lens coupled to a bundle constructed from large core fibers provides the best tolerance to both angular and transverse misalignment. This result, combined with the need to collect light from a relatively large area to meet link budgets, favors a design comprised of multiple lenses of shorter focal length and smaller size, with a small bundle coupled to each lens.