Investigating Characteristics of Solar Panels as Visible Light Communication (VLC) Receivers

Visible light communication has advantages over acoustic and radio wave transmissions in free-space and underwater. The optical transmitters are usually light emitting diodes or laser diodes, and the optical receivers are usually photodiodes or its variants. Solar panels are used for solar energy harvesting to electricity, but the panels are also available in small sizes, and hence, are finding increasing use in optical communications due to larger aperture compared to photodiodes. This work investigated by experiments the characteristics of solar panels as receivers in visible light communication (VLC). In the work, four solar panels of different physical sizes were selected for experiments and measurement. Two characteristics important to communication were investigated. First is the internal resistance at different low illumination levels of white light. Second is response to sinusoidally varying intensity of white light at varying frequencies. For the first study, two of the four panels were investigated; and for the second study, the four solar panels were investigated. An array of seven white LEDs was used as the light source. Also, underwater data communication in saline water was performed for one of the solar panels, and a photodiode in comparison. Results showed that under steady illumination, the internal resistance is both illumination level-dependent and surface area-dependent. It decreases with increase in illumination level, and surface area. Also, the rate of decrease of the internal resistance with illumination increases with surface area. For the frequency response, the cut-off frequency of the solar panel is surface area-dependent, and load-dependent. It decreases with increase in surface area, and increases with decrease in load resistance values (increased loading). For data communication, the maximum data rate obtainable with the solar panel is less to that of the photodiode. The frequency response is important in considering the bandwidth of the solar panels, which also varies with the load, while the internal resistance is important in maximum power point tracking and impedance matching with front end circuits in optical communication receivers.