Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung IOSB

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Efficient visible light communication drivers using illumination LEDs in industrial environments

2021 , Schneider, Daniel , Shrotri, Abhijeet , Flatt, Holger , Stübbe, Oliver , Lachmayer, Roland

Visible light communication (VLC) allows the dual use of lighting and wireless communication systems by modulation of illumination devices. However, to increase the performance, typically, beam-forming measures are taken creating pencil beams, thus contradicting the illumination purpose. In order to optimize the performance trade off between efficient illumination and communication, the switching capabilities of illumination LEDs are examined. Illumination LEDs with standard drivers and without beam-forming show limited applicability for communication purposes as they are not optimized for the necessary switching capability (f ≈11 MHz) and coherence. Methods to enhance the electrical current by pre-equalisation, biasing, carrier sweeping and current shaping are examined in respect to the illumination LED's communication performance. A novel driver scheme is derived which achieves considerably higher switching frequencies (f >100 MHz) without employing beamforming at the illumination LED. This driver is able to obtain a data rate of up to 200 Mbit/s at a distance of 3.2 m, using on-off keying (OOK) modulation technique. Therefore, it is feasible to apply the LED driver by implementing standardised illumination devices in VLC systems.

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Manufacturing of lens array prototypes containing spherical and fresnel lenses for visible light communications using stereolithography apparatus

2021 , Shrotri, Abhijeet , Beyer, Micha , Schneider, Daniel , Stübbe, Oliver

Additive manufacturing (AM) and rapid prototyping process (RPP) have revolutionized the production of 3D objects in the last few decades. RPP has considerably increased the rate of production and the possibility of manufacturing prototypes in the fields of electrical, optical, and mechanical engineering. The manufacturing of optical prototypes including spherical, aspheric, and special kinds of lenses and lens arrays has reformed the fabrication of optical components. In this paper, specifically designed lens array prototypes for application in visible light communication (VLC) are introduced. These lens array prototypes are manufactured using the stereolithography apparatus (SLA) process. These lens arrays are designed to achieve optimal transmission of the light beam for VLC systems. One of the prototypes from the lens arrays contains primarily four spherical lenses and one thicker convex lens and the other contains one fresnel lens as a substitute for thicker convex lens. These lens arrays are further post-processed to achieve the required transparency. These lens array prototypes are tested using laser and LEDs. The ON-OFF keying modulated light beam was transmitted through the lens array at the sender side and focused on the photo-receiver using another lens array at the receiver side which is 200 cm apart. After evaluating these lens prototypes, it can be concluded that with appropriate post-processing and high-resolution stereolithography based manufacturing, a low data rate VLC link can be formed.

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