Integrated Fiber Coupling and Position Sensing for FSO Communications Using Multi-Core Fibers

The increasing demand for high-capacity communications has positioned free-space optics (FSO) as a future-proof technology, promising unmatched wireless data-rates. However, the widespread deployment of high-capacity FSO requires the development of ultra-precise and highly-dynamic beam alignment solutions, capable of being easily integrated in a low-power and low-footprint all-optical system. This article presents a system that exploits multi-core fiber (MCF) coupling to retrieve the position of the received beam and feed it to the pointing, acquisition and tracking (PAT) system, thereby enabling to perform optical beam alignment without the need for an auxiliary opto-electronic position sensing device. The beam alignment methodology is based on a computationally-efficient lookup table (LUT) approach, with its effectiveness analyzed as a function of the number of illuminated cores. The obtained results reveal a trade-off between the number of utilized cores and number of alignment iterations (and hence, alignment latency). Starting with a single-core transmission and 7-core reception scheme, i.e. a 1×7 single-input multiple-output (SIMO) system, nearly 100% alignment success rate has been achieved after 5 iterations. Expanding the system towards a multiple-input multiple-output (MIMO) 7×7 architecture, the system alignment can be successfully completed after only 3 iterations, supporting a total field of view (FOV) of 4.5 mrad.