Silicon scanning mirror with 54.74° slanted reflective surface for fluorescence scanning system

Abstract

We fabricated a scanning mirror and optical benches monolithically in a silicon substrate using DRIE process and trench passivation by capillary filling. The micro scanning mirror, actuated by comb electrodes and supported by torsional spring, was fabricated with the optical benches in single crystalline silicon for the integration of optical fibers and ball lenses. Micro prism was adopted for high sensitive fluorescence detection system with scanning mirror. The excitation beam needs to be focused mainly on the slanted area of the micro prism in order to increase optical power efficiency. Considering beam collimation for high power efficiency, beam steering on the micro prism, and simple integration with the micro prism, we proposed silicon scanning mirror having slanted reflective plane and optical benches monolithically fabricated in the same silicon substrate. Reflective surface of the proposed scanning mirror makes parallel incident laser to the substrate be normal downward to the plane of substrate so that optical alignments become simple just by the alignment of scanning mirror’s and micro prism’s substrate. In this research the slanted angle of mirror plane is (-) 54.74 degree inclined instead of 45 degree because the scanning mirror was fabricated in single crystalline silicon (100)-oriented wafer using KOH wet process for the easy fabrication and fast feasibility test. The scanning mirror scans the laser one dimensionally by the actuation so that laser spot can be line-shape on the prism plane. The mirror is a pyramidal structure actuated by comb electrodes and torsion spring. The designed scanning mirror is 2165 x 778 μm² in an upper plane and it has a slanted trapezoidal mirror reflective surface, which size is about 2000 x 1600 μm², considering the micro prism dimension. The maximum deflection angle of the scanning mirror was 7° when 16 V_pp square type voltage is applied to the comb electrodes at resonant frequency.