ABSTRACT
Thin-film structures with metals or semimetals can serve some important purposes. Metals offer the possibility of making edge, band, and notch filters with far fewer layers compared to dielectric films alone, albeit with some unavoidable absorption losses as well as less-perfect transition characteristics. A film with a complex refractive index has a very different behavior. The real part of the refractive index still forces the contour to trace a circular arc, but the imaginary part forces the trajectory toward the film’s refractive index value. As a result, the contour will trace a spiraling path, coming to rest at the film’s refractive index value as the phase thickness increases. A larger imaginary part will make it spiral quicker toward the convergence value. This effect arises due to the optical isolation effect of materials with complex indices.
