Real-time modal decomposition of fiber laser beams using a spatial mode multiplexer

A novel, to the best of our knowledge, approach for the modal decomposition of a fiber laser beam is demonstrated using a spatial mode multiplexer. Since the modal decomposition is carried out optically, this approach is able to obtain the modal content at speeds up to the GHz level. In order to demonstrate such performance, we have applied this approach to the modal analysis of a Q-switched pulse generated in a multimode fiber with alternating intra-pulse mode content.