  We report a time-resolved measurement of the full transmission matrix (TM) of
a short length of specialty annular-core few-mode fiber which guides 10 vector
modes. We show how our method can isolate the fiber TM from misalignment
contributions from optics upstream and downstream of the fiber. From
measurements spanning two days we extract the drift of the fiber TM. We show
that drifts in the TM elements are mostly described as correlated phase
variations rather than amplitude variations. We show that an empirical model of
the fiber TM parametrized in one parameter can successfully account for the
drift.
