Abstract

Subject of study. Metal–dielectric bandpass interference filters based on Al₂O₃, SiO, Ge, and Ni films were investigated. Aim of study. The aim of this study was to develop metal–dielectric interference filters for a mid-infrared spectral range based on transparent dielectric films and absorbing nickel films in which the long-wavelength component of the radiation spectrum is blocked. Method. A numerical–analytical method was used. The transmission spectrum of the original filter composed of dielectric films was calculated. A mirror coating consisting of quarter-wave films of Al₂O₃, SiO, Ge, and Ni transparent in the wavelength range of 2.2–6.0 µm was used. The absorption spectrum of the coating after the introduction of nickel films into Al₂O₃, SiO, and Ge films was calculated. The dependence of the absorption spectrum was determined for the cases of sequential nickel film introduction at all points of an individual film. The points with minimum absorptions were determined. The minimum absorption was obtained when an absorbing nickel film was introduced into the middle of the Ge film. The resulting structure was optimized for all thicknesses of the SiO, Ge, and Ni films. FilmManager software implementing two algorithms, the random iteration and Powell’s quadratic approximation algorithms, for finding the minimum of the quality function was used for optimization. The transmission spectra of the entire structure were obtained. Main results. A method for synthesizing a metal–dielectric bandpass filter was proposed. Several bandpass filters were synthesized, namely, filter 1 with a transmission maximum in the wavelength range of 2.2–4.6 µm and average transmission in the range of 6–15 µm not exceeding 0.6%, and filter 2 with a transmission maximum in the wavelength range of 2.9–5.9 µm and average transmission in the wavelength range of 6–15 µm not exceeding 0.2%. Practical significance. The bandpass interference filter proposed in this study can be implemented on a silicon substrate with high transmission in the range of 1–20 µm without additional blocking absorption or interference filters in the far-infrared range. This reduces the cost of such a filter, thus increasing its competitiveness.

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