Towards quantum applications of buckled dome microcavity devices

Abstract

This thesis describes the theory, fabrication, and characterization of monolithic integrated membrane-in-the-middle (MIM) optomechanical Fabry-Perot resonators and elliptical birefringent Fabry-Perot optical resonators. Both types of devices were fabricated on a silicon wafer using a thin-film buckling self-assembly technique. The MIM optomechanical cavity work follows that of a previous student, who had developed a method for releasing a free-standing silicon nitride (SiN) membrane embedded in a buckled dome microcavity, by using a surface micromachining (sacrificial etching) approach. In the present work, an improved photolithography method and an improved PECVD recipe for SiN deposition were developed. Concurrently, a vacuum system was designed and constructed, enabling optical measurements to be performed under a vacuum environment. Finally, in-situ vacuum-sealing of the optical cavities was attempted by deposition of various ‘sealing’ layers such as parylene deposition, sputtering of Si/SiO2, and plasma enhance chemical vapor deposition (PECVD) of SiO2. While these attempts were not entirely successful, they did provide an important basis for future work. The fabricated optical cavities exhibited a finesse of ~ 500 at 1550 nm wavelength range. Furthermore, mechanical vibrational modes were observed with mechanical quality factor ~200 for fundamental resonant frequencies in the ~ 5MHz-15MHz range for different devices. For the elliptical cavities, buckled domes with a large difference in radius of curvature along the major and minor axis were realized through appropriate patterning of a low-adhesion layer. These birefringent optical cavities exhibit astigmatism (two nested sets of Hermite- Gaussian modes reflecting the two radii of curvature) and birefringence (slightly non-degenerate iii resonant wavelengths for polarization along the major and minor axes of the ellipse). The observed astigmatism and birefringence are in good agreement with the predictions of a vector- modified paraxial wave theory. The cavities exhibited finesse of ~ 250 at 1550 nm wavelength range and polarization-mode splitting of the fundamental mode by ~25 GHz.