Orbital angular momentum mode femtosecond fiber laser with over 100 MHz repetition rate

Orbital angular momentum (OAM) lasers have potential applications in large capacity communicationsystems, laser processing, particle manipulation and quantum optics. OAM mode femtosecond fiber laser hasbecome the research focus due to the advantages of simple structure, low cost and high peak power. At present,OAM mode femtosecond fiber lasers have made some breakthroughs in key parameters such as repetitionfrequency, pulse width, spectrum width, but it is difficult to achieve good overall performance. Besides, therepetition rate is tens of MHz at present. In this paper, a large-bandwidth mode coupler is made based on themode phase matching principle. In coupler, the first order mode coupler with 3 dB polarization dependent loss ismade by the technology of strong fused biconical taper, and the second order mode coupler with 0.3 dBpolarization dependent loss is made by the technology of weak fused biconical taper. By combining thenonlinear polarization rotation mode-locking mechanism, OAM mode femtosecond fiber laser with over 100 MHzrepetition rate is built. The achievement of the key parameters is attributed to the selection of dispersionshifted fibers that can accurately adjust intracavity dispersion. Comparing with traditional dispersioncompensation fibers (DCF), the group velocity dispersion is reduced by an order of magnitude, so it can betteradjust intracavity dispersion to achieve the indexes of large spectral bandwidth and narrow pulse width. Inaddition, the diameter of the fiber is 8 mu m, which is the same as that of a single mode fiber. Comparing withDCF, the fusion loss can be ignored, so only a shorter gain Erbium-doped fiber is required, which ensures ashorter overall cavity length and achieves high repetition frequency. The experimental results show that thefirst order OAM mode fiber laser has 113.6 MHz repetition rate, 98 fs half-height full pulse width, and 101 nm10 dB bandwidth. Second-order OAM mode fiber laser has 114.9 MHz repetition rate, 60 fs half-height full pulsewidth, and 100 nm 10 dB bandwidth. Compared with the reported schemes, our scheme has good performancein key parameters such as repetition rate, pulse width and spectral width. We believe that the OAM mode fiberlaser with excellent performance is expected to be widely used in OAM communication, particle manipulationand other research fields.