Measurement of the spin-redirection phase using Pancharatnam's theorem

A Michelson interferometer is presented which enables a direct measurement of Berry's geometric phase (spin-redirection phase) resulting from light propagating through a helically wound optical single-mode fibre. The operation of the interferometer is interpreted in terms of Pancharatnam's theorem. In addition, we put the spin-redirection phase into the context of Pancharatnam's phase.