Field reconstruction by modal decomposition in passive optical fibers used for brilliant laser beam transmission

The different propagating modes in an optical fiber determine the properties of the light emerging the fiber. Therefore an exact knowledge of the modal content is a key to understand the underlying physical effects. Different approaches exist to measure the modal content of an optical fiber, such as interferometry, M2 measurement or phase retrieval methods with either high experimental complexity or ambiguity relating to the modal content. In this paper we present a method for measuring the modal content by the aid of »optical correlation analysis«. We demonstrate this with measurements on a passive step-index LMA fiber at a wavelength of 1064 nm.