Modal redistribution and power loss in on-fibre devices

The mode coupling and optical power loss taking place in on-fibre devices are investigated. These devices are fabricated by removing the cladding of a multimode fibre and replacing it with a new material such as electro-optic or magneto-optic. Under an application of an external field the index of this modified cladding increases, leading to coupling among guided modes and coupling to radiation modes, resulting in optical power loss. The coupling among guided modes and the power loss are calculated as a function of the change in the index under the field and the length of the active region for the case when HE_1m modes are excited individually or in a group. Results indicate that on-fibre devices may be used as low-loss devices for applications involving sensors and delay lines.