This work presents a three-layered thin film system to generate broadband polarization conversion. The enhanced polarization conversion in the prism coupling system is analyzed as a constructive interference effect of polarization coupled states. According to our analysis, an antireflection film that is used to reduce the multireflection in the anisotropic film and a compensation film that is used to reduce dispersion of propagation phase difference are applied on both sides of an anisotropic thin film to cause broadband polarization conversion.
In this work, a simple and high efficient way to change the polarization state is proposed. A broadband polarization
conversion (PC) filter based on a prism coupling system (BK7 prism/anisotropic film/air) is investigated. The anisotropic
SiO<sub>2</sub> thin film prepared by glancing angle deposition is a columnar thin film with near uniaxial property. At a certain
angle range around 51.5. over the critical angle, there exists an enhanced PC reflection when the plane of incidence is
vertical to the deposition plane. The reason of polarization conversion (PC) reflectance in an anisotropic SiO<sub>2</sub> thin film
(n1', n2', n3') = (1.260, 1.216, 1.215) is analyzed and interpreted in the prism-coupling system (prism/ SiO<sub>2</sub> thin film
/air). In order to achieve the broadband PC reflectance spectrum, a three-layered structure (isotropic MgF<sub>2</sub> thin film/
anisotropic SiO<sub>2</sub> thin film/ isotropic MgF<sub>2</sub> thin film) was arranged. The three-layered structure thin film is investigated
optimum ability as broadband polarization device.