Highly efficient and angle-tolerant mid-infrared filter based on a cascaded etalon resonator

Mid-infrared of the 3 - 5 mu m spectral region has attracted considerable attention in various fields. We report a highly efficient and angle-tolerant mid-infrared filter based on a cascaded etalon resonator. Two hybrid etalon resonators are serially stacked to make a single peak resonance with a well-suppressed sideband. Each etalon resonator, which exploits a pair of cavities, includes not only a cavity featuring a resonance but also a functional cavity lowering the sideband of transmission spectrum. By taking advantage of double cavities, each etalon features a resonant characteristic with suppressed sideband. Consequently, the filter shows a peak transmission of 92% at resonance and well-suppressed sideband within the 3 - 5 mu m spectral region. Transparent dielectric materials make the device highly efficient for both transmission and reflection. Furthermore, the filter utilizing a high-index cavity leads to an enhanced angular tolerance regardless of incident light polarization. The transmission of the filter exhibits center wavelength shifts of around 0.1 mu m at an angle of 50 degrees for both transverse electric and transverse magnetic modes, compared to normal incidence. (C) 2017 Optical Society of America