Optical fibre having a D-shaped cross-section, in particular for producing polarised wavelength-selective monomode fibre couplers

摘要

The optical fibre, according to the invention, having a D-shaped cross-section has an elliptical cross-section of the core (1) with a major axis which extends at right angles to the flat side (FS) of the D-shaped cross section, and it has a thin, inner cladding layer (2) which surrounds the core and has a low softening temperature. This optical fibre can be more easily produced than one in accordance with the prior art, since the construction of the elliptical core cross-section need not be taken into account when producing the preform, but arises by a suitable choice of the parameters when drawing a preform which is simple to produce. This preform is produced by planar grinding of a side of a rod which is of circular cross-section and is to be produced in a conventional fashion. Apart from the ease with which it can be produced, the new optical fibre (Fig. 1) has the advantage that the fusing together of a pair of such optical fibres is facilitated because of the inner cladding layer (2) which surrounds the core and has a low softening temperature, and that the major ellipse axes of the cores (1) that are to be coupled to one another are aligned with one another, something which favours the coupling factor. IMAGE