Wide-field-of-view optical detectors based on fused fiber-optic tapers for high-speed optical wireless communication

Abstract

Optical wireless communication (OWC) is envisioned to become an indispensable technology in future wireless networks. However, one of the main issues hindering the widespread of OWC systems is the strict alignment required to maintain connectivity. This is due to the tradeoff between the receiver’s active area and its response speed, which necessitates the use of a lens to focus the light, limiting the field of view (FOV). Taking inspiration from the wide-FOV eyes of horseflies to address this issue, we propose the use of a convex-surface fused fiber-optic taper (FFOT) that can effectively expand a planar array of photodetectors and project it onto a spherical dome, respectively improving the light collection of individual photodetectors and expanding the overall FOV of the array. In our proof-of-concept demonstration, we show an optical receiver with a FOV semi-angle of around 25° and optical power density gain up to 120 in a 1-GHz link whose bandwidth is limited only by the photodetector. Moreover, reducing of the FOV of each individual fiber that results from tapering and the extra-mural absorption material incorporated around the fibers’ cores reduce the crosstalk between them, preserving the image quality. Therefore, unlike non-imaging light focusing elements, FFOTs can potentially be used in applications in which preserving the image is necessary, such as in imaging multiple-input and multiple-output systems and light detection and ranging (LiDAR). We also show the performance of FFOTs in collecting light from color-converting materials, a technique used in expanding the FOV beyond the étendue limit.