Long-wave infrared narrowband multispectral filter based on the plasma decoupling mechanism

Metal plasmonic filters enable compact multispectral sensing, yet conventional designs are constrained by Ohmic losses. In this work, we designed and fabricated a narrowband long-wave infrared spectral filter based on perforated Au films and nanorings, achieving high-resolution multispectral filtering in the 7.5–14 μm range with a FWHM of only 0.26 μm, approximately one-fifth that of conventional plasmonic filters. Fabrication was accomplished using i-line stepper lithography for large-area patterning, while the self-deposition effect during ion-beam etching was ingeniously leveraged to achieve cost-effective nanoring fabrication. The transmission bandwidth of the fabricated filter was characterized using Fourier-transform infrared spectroscopy, demonstrating excellent agreement between experimental and simulation results. This work holds promise for addressing the long-standing resolution limitations of plasmonic filters.