Added transmission capacity in VLC systems using white RGB based LEDs and WDM devices

In this paper an integrated wavelength optical filter and photodetector working as a DEMUX device is used to detect modulated optical signals of visible wavelengths for Visible Light Communication (VLC). The proposed application demonstrates the viability of indoors positioning using VLC technology established by the modulation of indoor warm light lamps lighting with ultra-bright white tri-cromatic LEDs. The signals were transmitted into free space and the generated photocurrent was measured by a pin-pin photodetector based on a-SiC:H/a-Si:H. This device operates in the visible spectrum, allowing thus the detection of the pulsed light emitted by the modulated chips of the white RGB LEDs. However, as the device works also as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light, it is able to detect different wavelengths, turning it into a DEMUX device. This feature allows the detection of the individual components of the tri-chromatic white LED and is the basis for the indoors location algorithm. We demonstrate the possibility of decoding four transmission optical channels supplied by two different wavelength LEDs modulated under different bit sequences, which allows the location identification and indoor navigation.