Fig. 3: Printed bandpass OIF based on Fabry–Pérot etalons.

a and b Concept and principle of a Fabry–Pérot etalons type bandpass filter. The structure consists of mirror 1 (M1), mirror 2 (M2), and a cavity. c SEM cross-section view of the printed filter. d and e Simulated and measured transmittance of the printed filter, respectively. The dashed gray line is the diffuse transmittance. f SEM cross-section view of the printed filter after integrating a silver layer. g and h Simulated and measured transmittance of the printed filter, respectively. The dashed gray line is the diffuse transmittance. The color stacks next to the SEM images provide an illustration of the layer scheme and functionality. Different colors indicate materials with low or high refractive index (RI), as well as the glass substrate. The green block indicates the cavity, and red denotes the silver layer.