Assembly of a micro-optical resonator based on silicon micro mirrors for use in gyroscopes

摘要

For realization of a miniaturized optical gyroscope the precise assembly of optical micro components is crucial. To detect the rotation rate the laser beam must circulate many times and not leave the resonator due to small misalignments. The assembly of a passive free space triangular ring resonator in which the light can circulate by reflections at three mirrors is investigated. The beam path encloses an area of about 100 mm2. The resonator shall be activated by an external light source at 1550 nm, a wavelength at which silicon is translucent and allowing to couple light into the resonator through the silicon mirrors. To utilize an inherent mirror alignment two of the mirrors are fabricated with a micro manufacturing process within the same crystal by wet etching resulting in very perfect {111} facets. The etching solution was optimized with respect to process time and smoothness of the mirror surfaces. To further increase the reflectivity of the mirrors different kinds of coatings are tested. With these two perfectly positioned mirrors the assembly challenge reduces to 3DOF alignment of a third {100} mirror for which a well-designed adjustable spacer is developed. In first tests resonance in a linear cavity test setup is demonstrated already.