Low-cost Metal/Glass Fibre Polarisers Produced in Continuous Lengths

Abstract

Fibre polarisers are essential devices in optical fibre communication and sensor systems whenever the control of polarisation is needed. They are particularly important in fibre-gyro systems where low insertion-loss and high extinction-ratio polarisers are required, A wide polarising spectral-window is another important requirement, since in many practical fibre systems broad-spectrum LEDs are used as the light source. Wide-bandwidth polarisers are also needed in wavelength-multiplexing systems. In the last few years several approaches for fabricating optical-fibre polarisers have been proposed and demonstrated. Most have been based on polishing the fibre to expose the optical field. Amongst these, high extinction ratios have been demonstrated using an overlay of a birefringent crystal or a metal film. However, the exposed-field polishing technique is time consuming and requires considerable skill. Moreover, a high extinction ratio in combination with a wide spectral-range has not been reported. We report here a new approach which yields continuous lengths of polariser fibre and provides a practical low-cost solution. The technique is based on a fibre fabrication process which allows continuous access to the core optical field, as well as providing an extremely-smooth, low-scatter surface at which interactions can be obtained. The design has been used to make metal/glass fibre polarisers in which a metal is incorporated directly into the fibre close to the core, as shown in Figure 1. The result is a high-performance metal/glass fibre polariser which can be produced in continuous lengths and whose extinction ratio can be adjusted to requirements by cutting to a given length