Precise Measuring Test Bed for Characterization of Mode Field Distribution in Different types of Multimode Fibers

In this paper we present experimental results from precise measurements of mode field distribution in various commercial multimode (MM) fiber types. We characterize the mode field distribution by the encircled flux (EF) parameter. EF determines optimal launch conditions in the core of the MM fiber, which is crucial especially for accurate characterizing of insertion losses at fiber connections, e.g. in data centers. For the purpose of EF measurement, a universal testbed enabling mode field characterization, integral optical power estimation or fiber connector cleanness evaluation has been proposed and experimentally verified. The uniqueness of the proposed testbed lies in backlighting of the tested MM fiber. This backlighting enables accurate positioning of the MM fiber end-face with the collimating lens to measure in the near-field area. The testbed allows the deployment of variable MM fibers and is also wavelength independent. Therefore it has the high potential within growing usage of plastic or large core fibers for short-range communications, e.g. in automotive or avionics. The obtained results are discussed within a selected real application. Moreover, since the mode field distribution is evaluated even for fibers, which do not have available any standards for EF characterization, we present new recommendations for optimal launch conditions in such fibers