Abstract
Miniaturized spectrometers are advantageous for many applications and can be achieved by what we term the filter-array detector-array (FADA) approach. In this method, each element of an optical filter array filters the light that is transmitted to the matching element of a photodetector array. By providing the outputs of the photodetector array and the filter transmission functions to a reconstruction algorithm, the spectrum of the light illuminating the FADA device can be estimated. Here, we experimentally demonstrate an array of 101 band-pass transmission filters that span the mid- to long-wave infrared (6.2 to 14.2 μm). Each filter comprises a sub-wavelength array of coaxial apertures in a gold film. As a proof-of-principle demonstration of the FADA approach, we use a Fourier transform infrared (FTIR) microscope to record the optical power transmitted through each filter. We provide this information, along with the transmission spectra of the filters, to a recursive least squares (RLS) algorithm that estimates the incident spectrum. We reconstruct the spectrum of the infrared light source of our FTIR and the transmission spectra of three polymer-type materials: polyethylene, cellophane and polyvinyl chloride. Reconstructed spectra are in very good agreement with those obtained via direct measurement by our FTIR system.
Highlights
Spectroscopy in the mid- to long-wave infrared (MWIR-LWIR) is an important analytical tool, largely because many chemicals have distinct features, such as absorption lines, in these spectral ranges
Www.nature.com/scientificreports determined by the shape, dimensions and material[11] of the plasmonic nanostructures. The fact that these are patterned from a single metal layer and that markedly different spectral responses are possible without changing the thickness of this layer is advantageous for manufacturing. This is because the spectral responses of all filters in an array are defined by a single lithography step
The time taken by the Fourier transform infrared (FTIR) system for the measurement of each spectrum is on the order of seconds
Summary
Our plasmonic metasurface MWIR-LWIR filters consist of coaxial apertures in a gold film. Varying the square array period P results in the transmission resonant peak shifting as desired, as confirmed by the finite difference time domain (FDTD) simulations presented as Fig. 3b In these simulations, the illumination is from the Si substrate side. It can be seen from the section that this choice leads to accurate reconstructions
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