Spontaneous forward Brillouin scattering in carbon disulfide

Abstract

In recent years, guided acoustic wave Brillouin scattering has become an important tool in photonics, serving as the basis for everything from new forms of information processing to silicon lasers. Due to low losses and long interaction lengths, fiber optic systems offer an intriguing platform to harness these guided-wave light-sound interactions. However, within typical fiber optic systems these interactions are exceedingly weak---requiring complex microstucturing to yield appreciable light-sound coupling. Here, we enhance this light-sound coupling by using a ${\mathrm{CS}}_{2}$-filled liquid core optical fiber. Owing to tight confinement of the optical and acoustic modes within the fiber core, as well as the large electrostrictive response of ${\mathrm{CS}}_{2}$, this system yields an unprecedented forward Brillouin gain for a fiber optic system. To demonstrate this physics, we measure multipeaked spontaneous forward Brillouin scattering power spectra, yielding information about the fiber geometry, material properties, and acousto-optic coupling strength. To interpret these data, we simulate the spontaneous Brillouin scattering power spectrum for this fiber system. These results reveal that hybridized acoustic excitations within the fiber core and cladding produce this characteristic multipeaked power spectrum. In the future, the large forward Brillouin coupling, long interaction lengths, and low losses of liquid-core fibers may enable new forms of distributed sensing, lasers with customizable emission, and physics including continuum optomechanical cooling.