Evaluation of a highly nonlinear microstructured optical fiber by near-field scanning optical microscopy and simulations: nonlinear coefficient and coupling losses

We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear signal processing applications, i.e., with a very small guided mode (waist 1 m). Calculations predict an intrinsic (assuming propagation in the fundamental mode and zero-loss coupling) non-linear coefficient of 40 W^-1km^-1 at =1.55 m, but they also predict a basic multimode character. NSOM measurements validate directly the high intrinsic value (32±10 W^-1km^-1) and also show that with an optimized coupling, the overall losses in efficiency taking into account coupling losses and weak excitation of higher-order modes and leaky modes are only 2.5 dB. This performance is adequate for use in all-optical data processing lines, all the more since it is maintained for relevant propagation lengths and peak power densities. PACS 42.65.Wi; 42.81.Wg