All-digital holographic tool for mode excitation and analysis in optical fibers

A procedure for the multiplexing and demultiplexing of modes in optical fibers with digital holograms is presented. By using a spatial light modulator (SLM) to encode a digital hologram, the desired complex field is shaped and injected into the fiber. The SLM’s ability to rapidly refresh the encoded transmission function enables one to excite pure single modes, as well as arbitrary coherent mode superpositions, in real-time. The modes from the output of the fiber are subsequently demultipexed by applying a correlation filter for modal decomposition, thus allowing for an all-digital-hologram approach to modal analysis of fibers. The working principle is tested using conventional stepindex large mode area fibers being excited with higher-order single modes and superpositions.