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.
"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