Brillouin spectroscopy of optical microfibers and nanofibers

Optical microfibers and nanofibers are currently being widely used in a vast number of applications ranging from quantum and ultra-cold atom optics to optical sensing. However, most existing methods for characterizing these tiny photonic wires are either destructive or rather complex to implement. Here, we describe a new easy-to-implement technique that allows for a complete experimental characterization of subwavelength-diameter tapered optical fibers, including both the uniform and transition sections. Our method is based on a direct and fast numerical analysis of the backward Brillouin scattering spectrum measured using highly sensitive heterodyne coherent detection. It can be performed in situ without any manipulation or optical alignment of optical nanofibers. Sensitivity as high as a few nanometers for fiber diameters ranging from 500 nm to 1.2 μm is reported. This new technique may also help with the design and characterization of micro- and nanoscale photonic chips.