Interference patterns under normal incidence in birefringent, optically active plane parallel plates

We have studied the interference pattern of multiple reflections from a uniaxial, optically active and non-absorbing plane parallel plate under normal incidence. Due to birefringence, a beam of polarized light splits into an ordinary and an extraordinary component. Because of optical activity, the number of beams is doubled after each reflection. During crossing of the plate the phase difference between beams is increased by fixed amounts. The calculated results show that the interference pattern of the transmitted light is more complex than that of an isotropic parallel plate. It consists of strong fringes at large phase intervals and weak doublets in between, at nearly the same phase intervals as in the isotropic plate.