Use of optical fibres for sensors and gyroscopes require a number of in-line components. One important device is a polarising element. We report here design considerations using polished fibre substrates with dielectric or metal overlays. The first type of design involves use of a high index planar dielectric film to selectively couple out TE-polarised light from the polished region of a fibre coupler block. The second type of design employs metal films and polarising action is achieved by coupling to surface plasma waves or the w+ resonance in very thin metal films.