Passive Q-Switch and Rectangular Mode-Locked Pulses from a Dumbbell Shaped Holmium Fiber Laser

Summary form only given. Mode-locked fiber lasers has long been cultivated for generation of unique pulse features using various cavity configurations at different wavelength regimes. Near 2 μm wavelength, holmium doped mode-locked fiber laser has been seldom reported. One recent report demonstrated holmium doped dissipative soliton resonance fiber laser below 2 μm [1]. Here using a dumbbell shaped cavity architecture [2], passively mode-locked holmium fiber laser has been demonstrated operating in passive Q-switch and rectangular-shaped modelock pulse regime at 2.05 μm. The schematic diagram of the laser cavity has been shown in Fig. 1. The in-house fabricated single clad holmium doped fiber (HDF) was pumped by amplified spontaneous emission (ASE) of a double clad thulium doped fiber (TDF, Nufem) which was pumped by 793 nm diode through a combiner. The nonlinear loop mirror (NOLM-1) designed using a 50/50 coupler serves as a broadband reflector, while NOLM-2 having long length SMF fiber, acts as saturable absorber due to the 80/20 coupler. The net cavity dispersion comprising of entirely anomalous dispersion fibers, was calculated to be -30ps 2 . The output was characterized using a 12.5 GHz photodiode, 2.5 GHz Oscilloscope (Tecictronix) and an Optical Spectrum Analyser (Yokogawa AQ6375).