  We propose a nonvolatile, reconfigurable, and narrowband mid-infrared
bandpass filter based on surface lattice resonance in phase-change material
Ge2Sb2Te5 (GST). The proposed filter is composed of a two-dimensional gold
nanorod array embedded in a thick GST film. Results show that when GST transits
from the amorphous state to the crystalline state, the narrowband reflection
spectrum of the proposed filter is tuned from 3.197 {\mu}m to 4.795 {\mu}m,
covering the majority of the mid-infrared regime, the peak reflectance
decreases from 72.6% to 25.8%, and the corresponding Q-factor decreases from
19.6 to 10.3. We show that the spectral tuning range can be adjusted by varying
the incidence angle or the lattice period. By properly designing the gold
nanorod sizes, we also show that the Q-factor can be greatly increased to 70 at
the cost of relatively smaller peak reflection efficiencies, and that the peak
reflection efficiency can be further increased to 80% at the cost of relatively
smaller Q-factors. We expect this work will advance the engineering of
GST-based nonvalatile tunable surface lattice resonances and will promote their
applications especially in reconfigurable narrowband filters.
