Thermal Radiative Properties of a Semitransparent Fiber Coated With a Thin Absorbing Film

This study presents the hemispherical model to predict the hemispherical total thermal radiative properties of a fiber coated with a thin film. The fiber is composed of semi-transparent media, such as fused silica. The film is made of strong absorbing media with thickness on the order of tens of nanometers. The film is assumed to be “locally flat” at the point of incidence for radiative transfer analysis because the thickness of the film is much less than the fiber radius. Wave optics is employed to calculate the reflectance and transmittance of the thin film while the ray tracing method is used for radiative transport analysis of the fiber. Effects of film and fiber substrate optical properties, film thickness and temperature on predicted thermal radiative properties are investigated. One of the applications of the proposed model is for studying the chemical vapor deposition of hermetic coatings on optical fibers, in which the thermal radiative properties of the fiber–film system heavily influence the fiber surface temperature and chemical reaction rate.