Micro-spectrometer based on a broadband gradient plasmonic nano-islands filter.

In recent years, advancements in micro- and nano-optical technologies have led to significant breakthroughs in the development of enabling the widespread application of micro-spectral analyzers in complex fields such as biomedical and environmental science. Micro-spectrometers are highly valued for their portability, precision, and versatility. Innovations in spectral reconstruction techniques have further enhanced the performance of these devices. In this work, we propose and experimentally demonstrate a computationally reconstructed miniature spectrometer based on a linear gradient Ag/Au mixed-metal plasmonic nano-islands filter, which is successfully prepared on a large-area quartz substrate through optimized sputtering and rapid annealing processes. The various angle-insensitive (the incident angle is up to 35°) transmission spectra of the microfilter are expanded to cover 250-900 nm by controlling the sizes, alloy ratios, and surrounding refractive index of the nano-islands. The efficient reconstruction of the incident spectra is achieved within the visible range (420-720 nm) through compressed sensing and l1-norm minimization methods. The reconstructed spectrum has a resolution of up to 0.6 nm, with wavelength accuracy within 0.4 nm. The root mean square error (RMSE) for monochromatic and broadband light reconstruction is below 0.05 and 0.07, respectively. This study offers valuable insights for the development of highly integrated, high-resolution, angle-insensitive micro-spectrometers with broad operating wavelength bands.