A considerable number of metal-dielectric devices make use of ultrathin silver layers. For instance, the typical optical metal-dielectric devices are transmission-induced filters^{1, 2} or conductive transparent multilayer structures known as “transparent metals.”³ The performance of those metal-dielectric optical devices is influenced by the quality of the metal layer and, in particular, of the metal-dielectric interface.

Variable narrowband transmission filters are useful for the development of compact spectrometers. For this purpose the filter should be directly coupled to the detector and the wavelength of the transmission peak should move in one surface direction over a length of a few millimeters. To obtain both a wide measurement spectrum and high accuracy, the ratio of extreme operating wavelengths is required to be greater than 2:1 and the width of the transmission band narrower than $10\text{\hspace{0.17em} nm}$. A metal-dielectric variable transmission filter, with an operating range of $400–1000\text{\hspace{0.17em} n m}$, is proposed. The method for obtaining variable transmission filters, with dimensions of a few millimeters, is described.

The optical components described here are variable narrow-band transmission filters, where the transmittance peak varies with the position along the surface of the filter itself. They allow the construction of ultracompact and low-weight spectrometers for space applications. The theoretical behavior of graded filters has been already investigated by the authors, for imaging spectrometry of the Earth surface. The application of graded filters to miniaturized instruments for planetary missions (Mercury) is considered. Experimental results on the fabrication of small-dimension variable transmission filters operating over a wide spectrum, from visible to near infrared, are reported.