Introduction: Interactions Between Guided Optical and Acoustic Waves

In the first chapter of this book, the opto-mechanical effect of forward Brillouin scattering is introduced within a broader context of propagation effects in fibers and of interactions between optical and acoustic waves. A review of linear and nonlinear scattering phenomena is provided, including the mechanisms of Rayleigh, Raman, and Brillouin scattering, and the optical Kerr effect. Scattering from short-period and long-period grating devices is discussed as well. The potential applications and implications of the various mechanisms in optical fiber communications, sensing, signal processing, and lasing are briefly addressed. Next, the physical principles of opto-mechanics are introduced. These include the stimulation of elastic waves by electrostrictive bulk forces and radiation pressures and the scattering of optical waves through photoelasticity and moving boundary effects. Specific formalisms are developed for the electrostrictive forces induced by optical field components that co-propagate or counter-propagate in standard single-mode fiber and for the photoelastic perturbations to the dielectric tensor due to acoustic waves in the same fiber. Several useful platforms for the study of Brillouin scattering interactions are presented, including polarization-maintaining, multi-core, and photonic-crystal fibers, resonator devices, and photonic-integrated planar waveguides. Lastly, applications of Brillouin scattering in fibers towards lasers, sensors, and signal processing are briefly surveyed.