Experimental reconstruction of bands in solid core photonic bandgap fibres using acoustic gratings.

We present the first characterisation of cladding modes of a low-index contrast all-solid photonic bandgap fiber using an acousto-optic long-period grating. We experimentally measure the relative band diagrams of the cladding, visualise the fields of the cladding modes in the near field, and find both to be in good agreement with simulations. Our measurements and simulations show that the bands of the cladding are very sensitive to actual details of the structure.