Polarization-selective suppression and enhancement of forward stimulated Brillouin scattering in silica-glass subwavelength elliptical-core optical waveguides

Abstract

Polarization dependence has been considered undesirable for most photonic devices, as it degrades the performance of photonic systems employing the devices. On the other hand, if the polarization dependence can be all-optically controlled and strongly enhanced at modest optical powers, it would be an attractive means for all-optical polarization control with a large dynamic range and/or polarization extinction ratio.

In this paper, we show that forward stimulated Brillouin scattering (FSBS) can be highly polarization-selective in silicaglass subwavelength elliptical-core optical waveguides suspended in the air, which may be used as a novel way of efficient all-optical polarization control. By using the full-vectorial finite element analysis, we find that at certain core ellipticities FSBS for one polarization mode mediated by a specific phonon mode is almost eliminated, while FSBS for the other polarization mode is rather enhanced. For example, the strong suppression of FSBS is observed for only the polarization mode along the major core axis when the scattering process is mediated by the TR21-like phonon mode. Such the polarization selectiveness is not observed in the case of conventional (backward) stimulated Brillouin scattering. The origin of the intriguing phenomena can be explained in terms of the dielectric perturbation induced by the interplay between electrostriction and radiation pressure. The polarization-selective FSBS is feasible and may be experimentally demonstrated by using microstructured optical fibers with high air-filling fractions or air-suspended slab waveguides fabricated on on-chip platforms. Our study provides a new opportunity of simple waveguide design for engineering boundary-enhanced optical forces and photon-phonon interactions.