Beltrami, Daniel R.2012-12-11b20183422http://hdl.handle.net/1885/9523A range of planar multimode waveguides and devices are considered in this the­ sis, including both step- and graded-index profiles. The first half of this thesis is concerned with the design analysis, fabrication and characterisation of a planar graded-index (GRIN) lens. The remaining half deals with modelling the power transmission of light through several step-profile multimode devices and bent waveguides, using ray theory and finite-difference beam propagation method (FD-BPM) simulations. The devices examined include acute-angled X-junctions, modified interference (MMI)en-AU199710.25911/5d78daf2b9687