Visible light communication which is a kind of wireless communication transmission technology using visible light has attracted attention of workers in this field. We study wavelength division multiplex (WDM) communication of visible light with which one can realize high-capacity communication by placing separate signals for each color in a multicolored light-emitting diode (LED) having high-speed response. For the transmitting side, the use of red, green and blue LEDs is assumed. On the receiving end, a band-pass filter is necessary to identify the respective colors. Usually, using colored cellophane is effective because it is cheap and has high transparency. However, some difficulties persist for colored cellophane. It can cause interference to adjacent channels because of the transmission bandwidth. A Lyot-filter, a kind of band-pass filter, shows narrow transmissive spectra of a specific wavelength using stacked birefringent films sandwiched between polarizers. Using this filter, we investigate each light wave in the visible light WDM communication using numerical calculations and numerous experiments. The maximum transmissivity of the Lyot-filter is lower than that of the colored cellophane, but results show improved color independence.

visible light communication, wavelength division multiplex (WDM), light-emitting diode (LED), band-pass filter, Lyot-filter.