Optical axis-driven tunable Brewster effect in anisotropic materials.

The Brewster effect, which is known as a notable physical law, has promising prospects in perfect absorption and angular selectivity transmission. The Brewster effect in isotropic materials has been investigated extensively in previous works. However, the research on anisotropic materials has been rarely carried out. In this work, we theoretically investigate the Brewster effect in quartz crystals with tilted optical axes. The conditions for the occurrence of the Brewster effect in anisotropic materials are derived. The numerical results show that by changing the orientation of the optical axis, we have effectively regulated the Brewster angle of crystal quartz. The reflection of crystal quartz versus the wavenumber and incidence angle at different tilted angles is studied. In addition, we discuss the effect of the hyperbolic region on the Brewster effect of crystal quartz. The Brewster angle negatively correlates with the tilted angle when the wavenumber is 460 (Type-II). In contrast, when the wavenumber is 540 (Type-I), the Brewster angle positively correlates with the tilted angle. Finally, the relationship between the Brewster angle and wavenumber at different tilted angles is investigated. The findings in this work will broaden the research field of crystal quartz and open the door for tunable Brewster devices based on anisotropic materials.