Fabrication of high performance fibre tapers and couplers using a CO/sub 2/ laser rig

This paper presents the first example of a CO/sub 2/ laser rig that can make fibre tapers and couplers with a precisely controlled longitudinal profile and shape. Fibre tapers and directional couplers are very important components for all-fibre devices. Although the fabrication processes of such components are well established, high resolution of taper formation has not been demonstrated. Theoretical analysis has shown that precise control of taper shape can in principal be achieved using a scanning point-like heat source. If the source is scanned and the taper elongated at constant speed, every section of the fibre receives the same treatment as each neighbour, ensuring a uniform profile. By varying the scanning distance of the heat source, different taper shapes can be produced. Various types of flames are commonly used and heat the fibre quickly enough to be scanned as discussed above but their performance is limited by instabilities and fluctuations induced by irregularities of the gas supply and air currents in the laboratory. Most importantly, their actual physical size is fixed and large limiting the minimum hot-zone length, and the inertia of the flame inhibits fast scanning. Instead, the use of a stabilised CO/sub 2/ laser can prove ideal.