Effect of Adding an Outer Layer on the Optical Performance of a Fabry-Pérot Filter at Oblique Incidence in the Thermal Infrared Region

Abstract

The paper examines the design of a Fabry-Perot filter constructed of dielectric materials with varying reflecting indices in the (8–12 µm) range. for the oblique incidence of light using a modified characteristic matrix method that adopts analytical methods, specifically at laser CO2 wavelength (λ_o=10µ m). To address the issue of non-normal incidences, which is a problem, matching the optical thickness for the layers of the suggested filter was introduced. the spectral shift in the transmission. Without changing the transmission setting, a rise in filter performance was noted. Additionally, the potential for enhancing optical width transmission for the outer layer of design was investigated. The work also demonstrates that high transmission for p- and s-polarization can be achieved by using matching in the optical width in conjunction with widening the outer layer. This exact result disproves the notion that an increase in transmission is not conceivable by demonstrating that this method can be utilized to create narrow-band pass filters that are unaffected by changes in incident angles. Additionally, this design can be used to create omnidirectional high reflectors for angles between 20 and 90 degrees using a quarter-wave dielectric stack.