Voigt waves in homogenized particulate composites based on isotropic dielectric components

Homogenized composite materials (HCMs) can support a singular form of optical propagation, known as Voigt wave propagation, while their component materials do not. In essence, Voigt waves represent coalescent degenerate eigenmodes of the corresponding propagation matrix. Crucially, the existence of Voigt waves stems from the non-Hermitian nature of this propagation matrix, which in turn is a manifestation of the dissipative nature of the HCM. This phenomenon was investigated for biaxial HCMs arising from nondissipative isotropic dielectric component materials. The biaxiality of these HCMs stems from the oriented spheroidal shapes of the particles which make up the component materials. An extended version of the Bruggeman homogenization formalism was used to investigate the influence of component particle orientations, shapes and sizes, as well as volume fractions of the component materials, upon Voigt wave propagation. Our numerical studies revealed that the directions in which Voigt waves propagate are highly sensitive to the orientations of the component particles and to the volume fractions of the component materials, but less sensitive to the shapes of the component particles and less sensitive still to the sizes of the component particles. Furthermore, whether or not an HCM supports Voigt wave propagation at all is critically dependent upon the sizes of the component particles and, in certain cases, upon the volume fractions of the component materials.