The development of new high-speed wireless data transmission applications, such as high-definition video streaming, virtual reality, and the Internet of Things, increases the future demand for mobile data traffic capacity. However, the limited RF spectrum is not sufficient to meet this demand.

Optical wireless communication (OWC) systems have the potential to overcome the rapidly increasing demand for indoor data traffic. Compared to Radio frequency (RF) wireless systems, OWC systems offer several advantages, including a larger unlicensed bandwidth, immunity against electrical interference and freedom from fading. However, they are affected by background noise caused by natural and artificial light sources and the risk of the laser beam being hazardous to the skin and eyes. The need for high-precision link alignment between the laser transmitter and user receiver limits the user mobility.

Within this thesis, Vertical-Cavity Surface-Emitting Lasers (VCSEL) are employed in laser-based OWC systems due to their compatible eye-safe working wavelengths within the near-infrared range, lower cost, and easy large-scale two-dimensional chip fabrication compared to other laser sources.

The main contributions of the research are as follows:

A novel 5 × 5 VCSEL array based OWC transmitter is proposed and designed. A microlens array homogeniser is the first time employed in OWC to generate the uniform optical power distribution in each atto-cell and to minimise the interference between adjacent cells. Each VCSEL generates >80% beam uniformity across a 20 cm × 20 cm square atto-cell where the receiver power in the square area is 5 mW m^-2.

Data transmission of single VCSEL - OWC links using the homogeniser is experimentally demonstrated. A single VCSEL achieves 8 Gbps data transmission using On-Off Keying (OOK) modulation and Decision Feedback Equalization (DFE) over a 3 m link, using a Silicon Photomultiplier (SiPM) receiver.

The novel multibeam VCSEL array based-OWC transmitter is demonstrated to enhance the channel capacity Three 20 cm × 20 cm square cells are shown on the receiver surface with low interference to adjacent cells. A 9.2 Gbps data transmission is achieved for each OW channel using a VCSEL array, Avalanche Photodiode (APD) receiver and Orthogonal Frequency-Division Multiplexing (OFDM) modulation scheme.

A VCSEL-array-based free space optical (FSO) fronthaul link with easy alignment for next-generation radio access network is demonstrated for the first time.

Together these demonstrate the attractiveness of VCSEL array-based transmitters for use in optical wireless communication systems.