Mechanical polarization modulator using micro-turbo machinery for Fourier transform infrared spectroscopy

Abstract

This paper describes the development of a mechanical polarization modulator using micro-turbo machinery for double modulation Fourier transform infrared spectroscopy (FT-IR). The modulator has a Au–Cr wire grid polarizer with a pitch of 4 μm on the backside of a φ 5 mm silicon turbine rotor. The modulator is composed of a top Pyrex glass layer and three n-type silicon layers, which were fabricated mainly by photolithography and deep reactive ion etching (deep RIE). The rotational speed was measured using nitrogen as a driving gas. This confirmed the rotational speed of about 18,000 rpm, when the volume flow rate was 8.8 l/min. The higher volume flow rate broke the edge of an air port in the second layer. We also confirmed the polarization of infrared light using a broadband infrared lamp and a fixed polarizer. The polarization was modulated according to the rotor rotation; however, the signal/noise ratio was low because of the wide pitch of the wire grid polarizer.