Holographic Control of Light Propagation in Optical Waveguides

Optical waveguides form the backbone of the internet and have also been a driving technology in medical imaging and optical sensing. Modern holography can now be used to control every aspect of light propagation along an optical waveguide. The application of holographic techniques offers the possibility of faster communication technologies, ultra-thin endoscopes and holographically enhanced sensors. An experimental system is established that allows light coupling into the proximal facet of the optical waveguide to be controlled. Light exiting the waveguide at the distal facet is imaged using an off-axis Mach-Zehnder interferometer. A new technique is presented that enables robust correction of measurement issues such as phase drift. The system is capable of spatially resolved control and characterisation of the amplitude, phase and polarisation of light entering and exiting the waveguide. The optical waveguide is first treated as a randomly scattering medium. As such, it can be characterised by its transmission matrix, allowing complex light fields to be imaged and projected through the fibre. Control over light at the fibre tip and along a fibre taper are demonstrated. I present a quantitative comparison between different algorithms for the projection of complex images to the distal facet of a multimode fibre and find that a hybrid iterative phase retrieval algorithm yields improved performance. Next, a state-of-the-art finite difference frequency domain engine is built that allows optical waveguides of any geometry, including anisotropic cases, to be modelled and propagation invariant modes to be calculated. Novel hologram generation algorithms are developed that exploit the inherent properties of waveguide modes. Discrete waveguide modes are excited for the first time in an anti-resonant photonic crystal fibre, including both linearly polarised modes and vector modes. Mode control in hollow-core photonic crystal fibres opens possibilities in spatially resolved sensing, optical trapping and in-fibre tomography