Plasmonic metamaterial absorbers with strong coupling effects for small pixel infrared detectors

Here we report a metal-insulator-metal (MIM) based infrared plasmonic metamaterial absorber consisting of deep subwavelength meander line nanoantennas. High absorption composed of two-hybrid modes from 11 μm to 14 μm is experimentally demonstrated with a pixel pitch of 1.47 μm corresponding to a compression ratio of 8.57. The physical mechanisms responsible for novelty spectral absorption, including the strong coupling between the plasmon resonances and the phonon vibrations, material loss from the dielectric spacer, localized surface plasmon resonance (LSPR), and Berreman mode excited by oblique incidence, have been systematically analyzed by finite-difference time-domain (FDTD) method, Fabry-Perot resonance model and two-coupled damped oscillator model. At oblique incidence, a spectral splitting related to the strong coupling between LSPR mode and Berreman mode is also observed. The distribution of local electromagnetic fields and ohmic loss are numerically investigated. Moreover, we evaluate the absorption performances with finite-sized arrays. We also show that the absorber can maintain its absorption with a 2 × 2 nanoantenna array. Such a miniaturized absorber can adapt to infrared focal plane arrays with a pixel size smaller than 5 μm, and thermal analysis is also performed. Our approach provides an effective way to minimize the antenna footprint without undermining the absorber performances, paving the way towards its integration with small pixels of infrared focal plane arrays for enhanced performances and expanded functionalities.