Optical Filters Design for Multi-Color Visible Light Communications

In multi-color visible light communications (MC- VLC), using multiple colors is an efficient way to enhance data rate, which is, however, jeopardized by the spectral overlaps of colors. Thin-film interference filters, as the key components of MC- VLC, are usually adopted to separate color channels. A careful design of center wavelength (CWL) and bandwidth of the filter passband is critical to mitigate crosstalk among colors, especially when the color number is greater than three. Moreover, due to the intrinsic short-wavelength shift of CWL with the increase of angle of incident (AoI), it is also challenging to support the mobility for MC-VLC employing thin-film interference filters. In this work, we investigate the thin-film interference filter design for two scenarios: the receiver is at a fixed and known position with perfect knowledge of AoI, and the receiver randomly locates with only a stochastic knowledge of AoI. To maximize the signal to interference plus noise ratio (SINR) for each color channel, an alternative optimization algorithm is proposed. Numerical simulations illustrate that, in both scenarios, our designed filters could achieve a higher SINR and a lower bit error rate than existing filters. Moreover, compared with the filter for fixed AoI, our filter for random AoI exhibits a balanced performance in mobile scenarios.