Modal decomposition in step-index fibers by optical correlation analysis

Abstract

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, M 2 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.

Measurement of local polarization for multi-mode photonic crystal fibers

“…In the far field realized by a 2 f -setup the associated intensity patterns are spatially shifted by K g f /k 0 with respect to the optical axis due to the sinusoidal grating with carrier frequency K g . 12 This angular multiplexing allows the simultaneous determination of the modal amplitudes using channels T g = U * l encoding the complex conjugated eigenstates. 13 On the sub-optical axis K g f /k 0 the resulting response I g,x for the x-polarized field component equals I 0 ρ 2 l,x with a normalization factor I 0 .…”