Tunable infrared filter made of thin silicon wedges

An electrostatically-tunable infrared filter was fabricated by constructing a Fabry–Pérot interferometer with stacked silicon plates. Driving-voltage, which used to be ∼100 V with ordinary silicon plates, could be reduced to ∼30 V by decreasing plate thickness to 100 μm. Both theoretical simulation and bending test confirmed sufficient mechanical durability of these thin plates. Superimposition of a noise spectrum, which was caused by interference inside thin silicon plates, could be suppressed by polishing the plates into wedges. Consequently, pronounced interference peaks appeared at 12.6, 6.3, and 4.2 μm wavelengths, and they shifted to 9.8, 4.9, and 3.3 μm, respectively, by 30-V application.