The steady-state and transient behavior of the photoconducting electro-optic polymer, PVK:TNF:DR1:ECz, was analyzed with various writing and reading beam polarization configurations to elucidate the contribution of various effects including the photoisomerization process on the diffraction phenomenon at the wavelength of 632.8 nm. The effect of the applied field on the diffraction efficiencies was observed to be strongly dependent on the polarization states of the writing and reading beams. It was found that the electro-optic contribution dominated the diffraction phenomenon for thep-polarized writing and reading beams while the molecular reorientation effect dominated for thes-polarized writing and reading beams and when the writing beams are cross polarized. The diffraction grating formed via the photoisomerization process was confirmed to be refractive index grating instead of an absorption grating. ©1997 American Institute of Physics.