7 March 2014 120° silicon double mirrors for use in a micro-optical gyroscope
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Abstract
A new concept for the realization of a micro optical laser gyroscope was developed. It allows minimization of the influence of alignment errors by the use of double mirrors. As a consequence, the performance of a ring resonator structure is less vulnerable to micro assembly tolerances. The idea being pursued to improve the design robustness is based on the use of double mirror elements in which the angle between the two mirrors is intrinsically defined by silicon crystalline structure. With an angle of 120° between the mirrors the resulting reflection direction from each double mirror element is robust against deviations from ideal incidence angle. Here, the optical distortions due to rotational misalignments of double mirror elements that occur either during assembly or during operation due to thermal stresses are extremely low and can be determined after production and compensated. After describing the free space ring resonator concept all major processing and manufacturing steps of the double mirror elements are discussed. For the fabrication of these mirrors silicon wafers are used which are almost in (100) orientation but are tilted by 5.3° in <011> direction and, therefore, provide an etching facet with a slope of 60° by KOH wet chemical etching. A 33% KOH solution with addition of isopropanol is used to obtain more uniform and smooth facet surfaces. Two wafers structured in such way are connected by silicon direct bonding and then cut into small mirror elements which are mounted onto the gyroscope micro platform.
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T. Niesel, T. Niesel, A. Dietzel, A. Dietzel, "120° silicon double mirrors for use in a micro-optical gyroscope", Proc. SPIE 8977, MOEMS and Miniaturized Systems XIII, 897712 (7 March 2014); doi: 10.1117/12.2035484; https://doi.org/10.1117/12.2035484
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