Inline Measurement of Modal Phase Differences in Optical Fibers

Abstract

Transverse modes in optical fibers have gained increasing interest in the recent years. For the measurement of the modal amplitude and modal phase in a fiber, several techniques exist examining the spatial distribution of the light exiting the fiber end facet [1,2]. However, such techniques are not suitable for inline monitoring of the modal content in an all-fiber application, like lab-on-a-tip sensing applications, where the distal end of the fiber is not accessible. Here, we present an inline-measurement technique for modal phase differences and experimentally demonstrate the direct measurement of all-optically induced changes of the modal phase difference by intermodal cross-phase modulation (intermodal XPM) [3].