Narrowband Ultraviolet Generation In Dispersion-shifted Few-mode Fiber Via Combined Effect Of Intermodal Four-wave Mixing And Nonlinear Mode Coupling

Abstract We report here the first experimental demonstration of the generation of narrowband ultraviolet wavelength in a few-mode dispersion shifted fiber utilizing the intermodal phase matching between the first two guided modes (LP01 & LP11) of the fiber. An intense anti-Stokes wave in mixed mode states (LP01 & LP11) is observed at 416.8 nm for a Q-switched nanosecond pump pulse in the LP01 mode at 532 nm. A nonlinear modal conversion of these anti-Stokes waves with non-zero angular momentum (LP11 modes) to zero-angular momentum (LP01 mode) has also been witnessed for the first time. The anti-Stokes line with LP01 modal component then acts as the secondary pump to produce discrete UV peaks at 341.6 nm with linewidth of 1.3 nm via cascaded intermodal four-wave mixing at an input peak power of 4.88 kW. A four-fold enhancement of conversion efficiency in cascaded intermodal four-wave mixing is achieved when compared to standard single mode fiber.