Linear polarization anisotropies of the zero-phonon line photoluminescence of an ensemble of nitrogen vacancy centers in diamond

We report on the polarization-dependent optical characterization of nitrogen vacancies in a (001)-oriented diamond crystal subjected to high magnetic fields. A strong optical alignment of the zero-phonon line photoluminescence of up to about 40% is observed for an ensemble of negatively charged nitrogen vacancies. We demonstrate an anisotropy in the linear polarization degree as well as in the rotation of the linear polarization plane of the photoluminescence, which can be tuned from positive to negative values. A phenomenological approach, which takes into account symmetry aspects of the diamond crystal, explains well the anisotropy observed experimentally.