Interplay of Cascaded Raman- and Brillouin-like Scattering in Nanostructured Optical Waveguides

We formulate a generic concept of engineering optical modes and mechanical resonances in a pair of optically coupled light-guiding membranes for achieving cascaded light scattering to multiple Stokes and anti-Stokes orders. Light pressure exerted on the webs swings standing- and propagating-wave flexural vibrations associated with Raman-like intramodal and Brillouin-like intermodal transitions. Due to negligible optical group velocity dispersion, the Raman-like light scattering generates a frequency comb for a single optical mode while the Brillouin-like light scattering creates inserted frequency combs with even- and odd-order side-bands appearing alternatingly in the fundamental and higher-order optical modes via exciting an effective optoacoustic grating of backward- and forward-propagating flexural phonons. Adjustment of nanoweb widths makes both these processes to occur with the same Stokes shift. As a result, the system drives intricate optomechanical patterns permitting periodic reversal of the energy flow between mechanical and optical modes. These results reveal new possibilities for tailoring light-sound interactions through simultaneous Raman-like intramodal and Brillouin-like intermodal scattering processes.