Due to trends such as the Internet of Things, there has been a growing number of devices that use wireless technologies for communication. This increase leads to bandwidth limitations that forced researchers to explore other types of wireless communication. One of these alternatives is Visible Light Communication (VLC). VLC encodes data by rapidly changing the intensity of a source emitting light in the visible spectrum. One branch of VLC is Passive VLC. Passive VLC uses ambient light, such as sunlight or ceiling lamps, as a source. An advantage of this approach is the drastically reduced power consumption. Since the light is already present, no energy has to be used to power a source. However, a flaw of Passive VLC is the lower throughput due to limitations in the available modulation devices. This thesis aims to mitigate the limited throughput by creating separate independent bands that can simultaneously transmit data. Taking advantage of the relatively wide visible light spectrum, the use of colour filters will be explored to divide the spectrum into distinct bands where independent data can be transmitted. To keep it as accessible as possible, there is a focus on low-cost filters, reducing computational complexity and real-time communication. A characterisation of low-cost colour filters is presented as well as a channel estimation algorithm to mitigate the shortcomings of inexpensive filters. To reduce the computational overhead, an encoding algorithm is presented that drastically reduces the computation needed to decode data. Ultimately, we provide a physical platform that achieves multi-channel passive VLC by exploiting cost-effective colour filters. The platform allows for simple expansion to greater numbers of channels as well as real-time communication due to the ability to adjust to the surrounding conditions.

In the last decades our usage of the Radio Frequency (RF) spectrum has intensified a lot due to the increasing number of mobile devices. The spectrum is getting crowded and new communication alternatives might become necessary in the future. One such alternative is Visible Light Communication (VLC),which uses the visible light spectrum instead of RF. Passive VLC, in particular, combines this property with a low power usage, suited for battery powered devices. However, high data rates are lacking.

This thesis proposes a multi-channel passive VLC system, based on light dispersion principles, as a novel concept to try and enhance these data rates. Results of the system so far only show low data rates however, at a maximum of 4 bits per second. The low data rate in particular is caused by choice of transmitter and receiver, thereby limiting the bandwidth and the number of channels that can be created. Yet, the concept itself is still considered a valid and valuable approach, and higher data rates can be expected from future works.

In this thesis we will see exactly how we can go from light dispersion to creating a multi-channel passive VLC system. As we will see this requires an optical design, a transmitter and a receiver, all of which will be working together. Besides an evaluation of the performance it will give insight in challenges this concept faces and, also, what improvements might increase the system performance.

As more and more devices have become wireless, the traditional Radio Frequency (RF) spectrum has become densely populated. To relieve this pressure, communication using light, visible light communication (VLC), has been proposed by many researchers. However, not all light sources can be modulated to transmit information. Therefore, the use of materials that can change their state between translucent and opaque has often been investigated in order to modulate light. ChromaLux is a recent system that uses such a material. It uses Liquid Crystal shutters to transmit information. However, instead of a single crystal, a stack of crystals is used, which exposes an extra transient region. This transient region shows several peaks that allow faster communication, but makes the system unstable. This thesis addresses several issues that ChromaLux experiences, in order to improve the performance. The system is changed from open-loop to closed-loop, creating a stable system that reaches higher speeds. However, in order to achieve this, part of the crystals is blocked, causing a lower Signal-to-Noise Ratio (SNR). For shorter distances up to 1 m, we are able to increase the data rate by 140 %, while at longer distances of up to 3 m we achieve an increase of up to 92 %. A second improvement which increases the SNR of the system, is the smart use of differential amplification. This allows communication at even greater distances of at least 5 meters.