Comparative analysis of numerical methods for the mode analysis of laser beams.

We present a comparative study of four numerical methods to detect the mode content of a laser beam from, at most, two intensity images. The techniques are compared regarding temporal effort, stability, and accuracy, using the example of three multimode optical fibers that differ in the number of supported modes.

Modal characterization of fiber-to-fiber coupling processes.

We present a detailed experimental investigation of a fiber-to-fiber coupling process by characterizing the mode content at the output of the system. In our experiment a single-mode fiber is transversally scanned with respect to a multimode fiber, revealing position-dependent higher-order mode excitation. The outlined measurement system can be used for automated optimization of fundamental mode content and beam quality. Additionally, our approach characterizes the modal transmission properties of the multimode waveguide in its present state and is hence of high relevance for the conception of transport fibers and fiber laser systems.