Optical waveguide fibre

The optical fibre as claimed in any one of the preceding claims wherein the light confining elements within the core-surrounding region are positioned geometrically so as to provide for linear reduction in effective refractive index with increasing radial distance from the core region.

The optical fibre as claimed any one of the preceding claims wherein the core-surrounding region is composed of a material which is the same as that of which the core region is composed.

The optical fibre as claimed in claimed 5 or 6 wherein the core region is formed at least in part as a hollow core.

The optical fibre as claimed in any one of the preceding claims wherein the light confining elements comprise longitudinally extending channel-like holes.

The optical fibre as claimed in any one of the preceding claims wherein the light confining elements are distributed about the core region in a symmetrical manner.

The optical fibre as claimed in any one of the preceding claims wherein the light confining elements are distributed around a plurality of circles which are all concentric with the axis of the core region.

The optical fibre as claimed in any one of the preceding claims wherein the light confining elements as seen in cross-section are distributed geometrically in regular arrays.

The optical fibre as claimed in any one of the preceding claims wherein the light confining elements are distributed about the core region, within the respective zones, in circularly concentric or polygonally concentric arrays.

A preform used in the manufacture of the above-defined optical waveguide, the preform having

• (a) at least one longitudinally extending core region,
• (b) a longitudinally extending core-surrounding region, and a plurality of elements located within the core-surrounding region, the elements extending in the longitudinal direction of the core region and being located geometrically in zones that surround the core region, at least a majority of the elements having a refractive index that is less than that of the material of which the core-surrounding region is composed, and the aggregate cross-sectional area defined by the elements within the respective zones increases with increasing radial distance of the zones from the core region.