Filter-less WDM for visible light communications using colored pulse amplitude modulation

This Letter demonstrates, for the first time, to the best of our knowledge, a new wavelength-division multiplexing (WDM) scheme for visible light communications using multi-level colored pulse amplitude modulation. Unlike traditional WDM, no optical bandpass filters are required, and only a single optical detector is used. We show that, by transmitting 푛 independent sets of weighted on–off keying non-return-to-zero data on separate wavelengths over a line-of-sight transmission path, the resultant additive symbols can be successfully demodulated. Hence, the data rates can be aggregated for a single user or divided into individual colors for multiple user access schemes. The system is empirically tested for 푀=4 and 8 using an off-the-shelf red, green, and blue (RGB) chip light-emitting diode (LED). We demonstrate that for 푀=4, using the R and B chips, a bit error rate (BER) of ≤10−6 can be achieved for each wavelength at bit rates up to 10 Mbps, limited by the LEDs under test. For 푀=8 using R, G, and B, a BER of ≤10−6 can be achieved for each wavelength at bit rates up to 5 Mbps.