The rapidly growing number of wireless devices typically use radio frequency for communication. However, in order to avoid using the expensive and increasingly congested radio bands, research areas are moving in the direction of using ambient light to form physical links in wireless communication systems. Unlike active Visible Light Communication (VLC) which controls the light source itself, passive VLC modulates the ambient light and results in low power transmitters as no energy is required for generation of the carrier wave. Similar to radio waves, visible light is also electromagnetic radiation and has wavelengths in the range of 400-700 nm. All previous work in passive VLC rely on switching the whole spectrum at the same time, and do not completely exploit using the full spectrum of light - reducing potential channel capacity.

In this thesis we propose a novel method to transmit and decode data, using liquid crystal cells that can modulate the spectrum. The main contribution of this thesis is to show that we can move from spectrum-agnostic to spectrum-aware modulation with passive VLC. The work in this thesis focuses on modulation and demodulation of such a communication link, and introduces novel methods of controlling the light spectrum. We build a prototype and demonstrate a multi-symbol communication link, and evaluate it with an effort to maximise the datarate.