A study of angular momentum in novel optical systems and analogues

Abstract

This thesis explores the dynamics of light’s angular momentum in several nonlinear media, namely coupled ring arrays of optical fibres, nested fibre optic resonators and photon fluid analogues for rotating scatterers. In the fibre systems considered, optical angular momentum takes a discrete form that is related to but distinct from the more well-known orbital angular momentum. This discreteness, combined with angular coupling between adjacent fibres, results in nonlinear interactions that do not occur in either uncoupled fibres or continuous media. These may drive instabilities which break angular symmetry and allow different angular momenta to be generated. The precise nature of the angular momentum spectra and their dependence on the fibre array’s structure is properties is examined. Similarly, amplification of angular momentum signals reflecting from rotating photon fluids is elucidated via a simple model analogous to Zel’dovich’s cylinder. Numerical tests with this model clarify and demonstrate the amplification process and the conditions required to support it. This yields insights into the more complex problem of realising an analogue for Penrose superradiance from an acoustic Kerr black hole within a photon fluid.