Non-destructive and distributed measurement of optical fiber diameter with nanometer resolution based on coherent forward stimulated Brillouin scattering

Precise control and measurement of the optical fiber diameter are vital for a range of fields, such as ultra-high sensitivity sensing and high-speed optical communication. Nowadays, the measurement of fiber diameter relies on point measurement schemes such as microscopes, which suffer from a tradeoff between the resolution and field of view. Handling the fiber can irreversibly damage the fiber samples, especially when multi-point measurements are required. To overcome these problems, we have explored a novel technique in which the mechanical properties of fibers are reflected by forward stimulated Brillouin scattering (FSBS), from which the diameters can be demodulated via the acoustic dispersion relation. The distributed FSBS spectra with narrow linewidths were recorded via the optimized optomechanical time-domain analysis system using coherent FSBS, thereby achieving a spatial resolution of 1 m over a fiber length of tens of meters. We successfully obtained the diameter distribution of unjacketed test fibers with diameters of 125 μm and 80 μm. The diameter accuracy was verified by high-quality scanning electron microscope images. We achieved a diameter resolution of 3.9 nm, virtually independent of the diameter range. To the best of our knowledge, this is the first demonstration of non-destructive and distributed fiber diameter monitoring with nanometer resolution.