In-Situ Measurement of Backscattering in Hollow-Core Fiber Based Resonant Cavities

We measure the light backscattered by resonant optical cavities based on two types of hollow-core photonic bandgap fibers, namely, 7-cell and 19-cell fibers. The measurement of the intensity backscattered by the cavity at resonance permits to deduce the value of the fiber backscattering coefficient. We find backscattering coefficients of the order of $2.0\times 10^{-6}$ and $1.0\times 10^{-6}\;\mathrm{m}^{-1}$ for the 7-cell and 19-cell fibers, respectively, two orders of magnitude larger than the one for standard solid-core single-mode fiber.