We present a thorough study of a bandpass filter for near-IR region, with bandwidth below 20 nm, high transmission, broad rejection band [350-1100] nm. This filter is angularly tunable between 0 and 50° and shows a shift of the central wavelength from 970 nm down to 880 nm without major changes of its bandwidth and spectral shape for unpolarized light. We first provide a description of the design procedure and then carry out an experimental demonstration using plasma enhanced reactive magnetron sputtering. We finally present an accurate characterization of this class of filter using a custom optical system.

Variable filters, which central wavelength of the bandpass shifts along one dimension of the component, is a promising way to simplify and to miniaturize imaging spectrophotometer systems for spatial observation. In fact, by combining a dispersive element and a variable filter, it is possible to realize a spectral and a spatial filtering based on pushbroom technique. While there were numerous methods developed in order to produce variable filters, at this date, there is no simple, reliable and repeatable method. In this paper, we present a new method for the fabrication of variable filters based on plasma assisted reactive magnetron sputtering (PARMS).Variable filters are obtained upon the variation of the thickness of some or all the layers deposited on the substrate. The layers are deposited using a Bühler HELIOS machine in order to benefit from the high stability of the deposition process. To insure a non-uniformity of the deposited layers, adapted masks are placed in front of the targets for the low and high refractive index materials. The uniformity of these layers is measured via a custom set-up allowing a local measurement of the transmission to perform a mapping of the transmission over the whole component aperture.In this paper, we present the fabrication of layers and filters with variable thickness. Various types of thickness gradients are presented.

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