Fig. 2
From: Method for GHz optical helicity modulation by acoustic drum modes on a chip
Electrical excitation of Lamb acoustic modes. (a) The ring-shaped BAWR has three sectors, which can be independently excited by radio-frequency fields. The electrical response is measured with a vector network analyzer (VNA). Maps of the surface displacement \(u_z\) were recorded with phase resolution using a scanning Michelson interferometer with a microscope objective to focus the laser onto a \(2~\mu\)m-wide spot (full-width-at-half maximum) on the sample surface (see “Methods” for details). (b) Radio-frequency transmission (\(|s_{21}|^2\) scattering parameter) between BAWR sectors \(p_1\) and \(p_2\) recorded in a frequency range around 3 GHz. \(\Delta f_L=13.09\) MHz is the frequency difference between the modes. The arrows mark different resonances within a \(\Delta f_L\) period. (c) Corresponding time-domain response recorded with a VNA with time-domain capabilities. The arrows show beats due to the interference of the different modes. (d) \(|s_{21}|^2\) spectrum in the 1.48–1.52 GHz frequency range and (e) corresponding interferometric data recorded by exciting port \(p_1\) and detecting the surface displacement \(u_z\) at the center of BAWR \(p_1\) (os\(_{11}\)), \(p_2\) (os\(_{21}\)), and \(p_3\) (os\(_{31}\)). The os\(_{i1}\) data were corrected to remove the unstructured background. The BAWR structural dimensions are listed in the caption of Fig. 1.
