Mode analysis of LMA fibers using the correlation filter method

We present the correlation filter method for measuring the modal power spectrum of beams emerging from multi-mode optical fibers. An optical filter acts as central element of the measurement process performing the integral relation of correlation. This filter is realized by a computer-generated hologram with a specifically designed transmission function based on the spatial distribution of guided modes in the investigated waveguide. The correlation filter method provides modally resolved information about amplitudes, phase differences and polarization states. Hence, the full information about the optical field becomes available. Beside a detailed presentation of the measurement process, the setup and the design of the correlation filters, the major advantage of the method, the ability to perform real-time measurements, is introduced.