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The fabrication of optical filters whose reflection/transmission response is spatially-graded has been the object of numerous research studies over the past decades given their applications in areas including multi- and hyperspectral imaging, structural colouring and even holographic encryption. In this context, the key enabling feature is the ability to tailor the thickness profile of at least one layer of the optical coating multilayer stack. To-date, this 3-dimensional structuration has been achieved either at the deposition stage or as an additional post-deposition process step. In the former case, the technique relies on the shaping of the material deposition flux thanks to the insertion of a (moving) mask inside the evaporation or sputtering machine. As such, the method is usually limited to the implementation of centimetre-scale variations. A contrario, to reach sub-millimeter-scale features, the preferred approach is based on postdeposition layer structuration, which is performed using grayscale lithography in the form of multi-(mask-)level optical lithography, or using e-beam or laser lithography. All these approaches are nevertheless relatively complex since they involve either multiple steps or need a very precise calibration of the exposition curve. In this paper, we report that the evaporation through re-usable shadow masks can be used to create optical filters whose spatial variations can be controlled with a ~70-µm-resolution. Using metal-mirror Fabry-Pérot interferometer structures as representative optical filters, we demonstrate the ability to adjust the resonance wavelength, the filter bandwidth and extinction ratio, and the coupling strength and splitting in cascaded resonators.
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