Properties of the cladding modes of an optical fibre excited by refractive-index gratings

The properties of the cladding modes of an optical fibre, excited by photoinduced long-period fibre gratings, were investigated by the near- and far-field methods. It is shown that the cladding modes considered are of the HE1m type. A satisfactory agreement between the experimental and calculated distributions of the electromagnetic field of the modes is demonstrated. It was found that the propagation length of a cladding mode in the unperturbed fibre reaches 1 m.