Beam Steering Techniques for Optical Wireless Communication

The exponential growth in global data consumption, driven by the proliferation of mobile devices and bandwidth-intensive applications, has placed unprecedented demands on existing wireless networks. Radio-based technologies such as Wi-Fi(IEEE 802.11) and cellular standards including 5G operate within a finite and strictly regulated Radio Frequency (RF) spectrum, which is increasingly saturated by the rising number of users and connected devices. The resulting congestion in unlicensed and licensed bands creates a pressing need for alternative wireless communication technologies capable of meeting future bandwidth demands while simultaneously off-loading the most demanding users from traditional networks. This thesis pro-poses solutions using beam-steered Optical Wireless Communication (OWC) and presents a comprehensive investigation into advanced beam steering. These techniques offer a promising solution with inherently high bandwidth capacity, enhanced security, and reduced electromagnetic interference compared to conventional RF systems. This work investigates two distinct approaches to achieve precise beam control: piezoelectric actuators for mechanical positioning and Vertical Cavity Surface Emit-ting Laser diode (VCSEL) arrays for solid-state beam steering. Each technology is systematically evaluated for field-of-view, response time, and integration complexity to determine their suitability for different application scenarios. The piezoelectric actuators combined with silicon micro-lenses achieve precise beam steering for a Field of View (FoV) of ±30◦ in both horizontal and vertical directions, with a beam divergence of 3.2°, while maintaining error-free 10 Gbps data transmission over distances beyond 3 m. The system employs a dual pairs of Micro Electro-Mechanical System cantilevers arranged perpendicularly to control a lensed optical fibers positioned in the focal plane of silicon micro-lenses. These silicon lenses have an effective focal length of 41.3 μm, designed to translate a 20 μmmovement into a angle of 30°. The system operates at C-band wavelengths with two independent channels, allowing for parallel operation of two beam steering units. Each beam operates at 9 dBm power below the 10 dBm eye-safety threshold for class-1 lasers. A control system using Arduino micro-controller, 12-bit digital-to-analogue converters, and high-voltage boost converters enables programmable beam positioning. The system achieved error-free operation at received power levels above−17 dBm and maintained forward error correction capability down to −21 dBm. These values were obtained by coupling the free-space beam through an adjustable fiber collimator into a 50 μm Multi-Mode Fiber (MMF) connected to a high-speed photoreceiver, providing the bandwidth necessary to support the 10 Gbps data rate. However, the system exhibits some limitations due to severe lens aberrations at large steering angles, with the beam becoming increasingly elliptical and distorted at extreme positions, and minor hysteresis effects in the actuators (3◦ on x-axis, 0.5◦ on y-axis).In addition to the piezoelectric steering approach, the VCSEL array system offers a solid-state alternative for multi-beam OWC applications. This system employs a two-dimensional matrix of lasers placed at the focal plane of a steering lens, where each VCSEL can be independently modulated to create multiple simultaneous data streams. The array operates in the O-band, with each element typically delivering0 dBm optical power, which keeps the system within the eye safety compliance of13 dBm for 1300 nm. The system achieves beam steering through selective activation of different VCSELs, with the beam direction determined by the position of the active element in the focal plane. The beam spot size at the receiver can be tuned by adjusting the axial separation between the array and the steering lens, allowing the same transmitter to be optimised for different room geometries and target distances without modifying the steering angles. The array is controlled by a Field Programmable Gate Array (FPGA) that manages 16 (4 × 4) independent channels, each capable of 10 Gbps data transmission using On-Off Keying (OOK). The research demonstrates that OWC systems with beam steering capabilities provide viable alternatives to RF in specific applications. Piezoelectric bender systems deliver continuous steering for highly mobile applications, while VCSEL arrays enable multiple parallel users high-density scenarios.