Orientation switchable optical fibres

摘要

An orientation switchable optical fiber 1 has an elongate body 8 with two ends N, F. The body 8 is twisted intermediate the two ends at M and has a central core region 14 in which light carried by the fiber is confined. Passive means in the form of air channels 6 extend substantially from one end N to substantially the other end F of the body 8. The passive means 6 promotes orientation of light in at least one first transverse axis A of the body 8. Active means in the form of thermally stressable rods 10 extend substantially from the location of the twist M to substantially the other end F of the body 8. The active means 10 is switchable between an off state in which it is ineffective and an on state in which it is effective to promote orientation of light in at least one second transverse axis B of the body 8. In the off state of the active means 10 light remains confined in the at least one first axis A along the length of the body 8 and in the on state of the active means 10 light transits as on passing the location of the twist M from the first axis A to the at least one second axis B.