Optomechanical Mode-Shape Mapping in the Presence of Crosstalk

Abstract

Visualizing eigenmodes is crucial for understanding the dynamics of state-of-the-art micromechanical devices. A method is established to map modes of mechanical structures optically. This fast and robust method, based on parallel modified phase-lock loops outperformed three alternative approaches. The setup used is discussed here in more detail, and the modal decomposition results are investigated further, including a study of the orthogonality of the eigenmodes and the mixing of degenerate modes. Crosstalk, however, remained a problem, especially for membranes with a small mechanical response. The issue is investigated using numerical simulations of the phase-lock loop operation, which indicate that without crosstalk compensation, the mode maps will be strongly distorted. To solve this, the phase-lock loop is equipped with crosstalk compensation and it is shown that now also in the presence of strong crosstalk, where resonances and phase responses are distorted, accurate maps are obtained.

Keywords

• optomechanics
• mode-mapping
• mems
• phase-lock loop
• silicon-nitride
• membrane
• crosstalk