Fig. 4
From: Method for GHz optical helicity modulation by acoustic drum modes on a chip
Helical drum modes. (a) Setup for the excitation of helical waves by driving the BAWR sectors with clock-wisely increasing phases differing by 120\(^\circ\). (b–d) Profiles for the surface displacement field \(u_z\) of helical modes at time instants corresponding to phases of (b) 0 deg, (c) 120 deg, and (d) 240 deg for \(f_\textrm{RF}=1.5033\) GHz. (e,h) Corresponding results for the excitation of anti-clockwise helical waves. (i,j) Spatially filtered versions of panel (b) to review surface oscillations of long and short spatial periods, respectively. (k) Zoom view of the center region of panel (j) revealing the phase wrapping of the modes with short spatial periods. The color code is the same for panels (b–h) and (i,j). In panel (k), it was expanded by a factor of two relative to (i,j). The nominal rf power applied to each one of the BAWRs was of approx. 10 dBm.
