Freeform based compact receiver front-end for indoor multi-cell VLC system: Fabrication, optical characterization and associated challenges

The prospect of utilizing freeform optics to develop a more compact and smaller VLC receiver front-end is explored in this study for a multi-cell indoor environment. A novel freeform surface element (FSE) has been fabricated by an ultra-precision single-point diamond turning (SPDT) machine and characterized by the mechanical and optical profiler to investigate its potential use inside a freeform diversity receiver. A 9 dB increment in average signal-to-interference-plus-noise-ratio (SINR) is observed after third iteration while the form error reduces to 1.92 µm. The communication functionality of the fabricated FSE is also validated experimentally. The average SINR over the communication floor is computed as 109.29 dB. The fabricated freeform element is further modified to a freeform Fresnel profile for more compactness. The result shows, a substantial decrease in receiver height (2.314 mm) is possible using the proposed approach. Moreover, different fabrication challenges related with freeform Fresnel have been identified and discussed to set the future research pathway.