Transverse mode switchable mode-locked laser with narrow bandwidth

Transverse mode switchable ultrashort optical pulses with narrow bandwidths can create potential for exploring what we believe are new physical effects. We demonstrate the generation of transverse mode switchable ultrashort pulses with narrow bandwidths in an all-fiber mode-locked laser by exploring a mode-selective photonic lantern (MSPL). The laser cavity serves not only as a ring resonator but also as an intrinsic spectral filter. For mode-locking with the LP , LP , and LP modes, the bandwidths are 3.0 nm, 86.7 pm and 101.7 pm, respectively. The narrowband pulses with higher-order modes are generated by an intrinsic spectral filter due to the spectral-domain intermodal interference. Mode-locked pulses with a signal-to-noise ratio better than 60 dB for LP , LP , and LP modes are independently generated, i.e., transverse mode switchable by changing the input port of the MSPL. The mode-locked wavelength can be tuned for the LP mode and LP mode by adjusting the state of polarization. Furthermore, our experimental results also show that, the slope efficiency of LP and LP modes can be improved, by the use of LP mode pump scheme. We anticipate that, narrowband pulses with complex mode profiles can be generated by simultaneously phase-locked transverse and longitudinal modes.