Modal-Weight Measurements With Fiber Gratings

We demonstrate a radiation mode coupler based on a tilted fiber Bragg grating that spatially demultiplexes different modes in a few-mode fiber. The observed radiation patterns match well with those theoretically predicted using the volume current method. The correlations in measured relative modal weights obtained from this device and an accurate interferometric measurement used as a reference, suggest that this technique has potential applications in providing real-time, nondestructive modal power measurement for mode division-multiplexed communications systems or monitoring the modal content in fiber lasers.