Design and Application of the Angle Insensitive Bandpass Filter Based on Coupling-Induced Transmission Theory

Angular sensitivity to incident light and limited cut-off bandwidth have always been theoretical challenges and issues for interference-based narrow bandpass (NB) filters. In this paper, a coupling-induced transmission theory is proposed to solve the difficulties of traditional filters, which utilizes the coupling of resonators to allow light to pass through the metal efficiently. Based on the theory, a near-infrared bandpass filter insensitive to the incident angle is designed and demonstrated. It has almost consistent transmission peak and identical transmittance for incident light from 0° to 60° with a peak wavelength shift of only 7 nm, which is 25 times smaller than that of traditional Fabry–Perot NB filters. Additionally, the cut-off bandwidth can cover the whole band from visible to far infrared ranges, resolving the two crucial aforementioned problems, and presenting remarkable application value in the field of micro-nano optics.