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

Abstract

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.