The chemical sensing has important applications in gas sensing, noninvasive disease diagnosis, security monitoring and others. In past several decades, significant research efforts have been devoted to the development of miniaturized chemical sensors based on chemiresistors, surface plasmonic polaritons and microelectromechanical resonators for on-site chemical detection and point-of-care disease diagnosis. However, these sensors often suffer from low sensitivity and poor chemical selectivity. The state-of-arts technology for chemical sensing is based on the spectral analysis since most chemicals, in particular organic chemicals, have signatures of spectral absorption in mid-infrared region. But the analysis can be only performed in scientific laboratories using large instruments.
Here, we aim to realize a miniaturized spectral analyzer by developing a multispectral filter. In recent years, multispectral filters based on plasmonics, nanowire waveguides and metamaterials have been extensively investigated. However, these filters are operating in visible spectrum and no filters in mid-infrared range are reported as far as we know. In this work, we report that an integrated spectral analyzer can be constructed by using Cr microhole arrays as multispectral filters. The microhole arrays were fabricated with CMOS compatible processes. The transmission peak of the microhole arrays can be continuously tuned from 3 μm to 8 μm by linearly increasing the periodicity of the microholes in each array. Fourier transform infrared (FTIR) microscopy was applied to spatially map out the transmission of the microhole arrays. The results show that each microhole array can selectively allow for transmission at a specific wavelength. We further constructed an IR spectral analyzer model based on the microhole multispectral filters to retrieve IR spectral information of two test samples. Our experimental results show that the spectra from the integrated spectral analyzer follows nearly the same pattern of the FTIR spectra of the test samples, proving the potential of the miniaturized spectral analyzer for chemical analysis.
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