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 similar to1 mum). Calculations predict an intrinsic ( assuming propagation in the fundamentalmode and zero-loss coupling) non-linear gamma coefficient of 40 W(-1) km(-1) at lambda = 1.55 mum, but they also predict a basic multimode character. NSOM measurements validate directly the high intrinsic gamma value (32 +/- 10W(-1) km(-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.