Tunable Extraordinary Optical Transmission in the Long‐Wavelength Infrared Range Using Electrostatic MEMS Actuation

ABSTRACT We present a continuously tunable long wavelength infrared (LWIR) spectral filter that enables chip‐scale, on‐demand spectral selection in a spectral range traditionally dominated by bulky optics. The device leverages extraordinary optical transmission (EOT) effect in a dual‐membrane stack: two suspended, patterned gold and silicon membranes separated by a dynamically adjustable air gap. Because the EOT resonance is highly sensitive to the intermembrane spacing, microscale gap modulation enables broadband, continuous spectral tuning. Numerical simulations predict a redshift of the transmission peak from 8 to 11 µm as the gap is reduced from 600 to 50 nm, while maintaining peak transmittance above 74% across the range. Mechanical tunability is achieved through integration into micro‐electro‐mechanical system (MEMS) actuator that provides smooth, pull‐in‐free sub‐micron displacement at voltages below 10 V, enabling practical, low‐power operation. We developed dual‐membrane device fabrication strategies facilitating membrane flatness, high fabrication yield and broad spectral tuning range. Experiments validate continuous LWIR tuning with measured spectra in close agreement with simulations. The resulting platform is compact, scalable, and highly compatible with integration into portable LWIR sensing hardware, opening a clear path to low‐power, reconfigurable filters for gas detection, chemical analysis, and thermalimaging.