Tunable multidimensional multiplexed Q-switched pulse outputs from a linear fiber laser with a bidirectional loop

Abstract

A simple all-fiber linear cavity to emit multidimensional multiplexed pulses is developed by combining fiber birefringence filter and bidirectional loop. Without unidirectional components, single polarization fiber and polarization maintaining fiber pigtails function as a bidirectional birefringence filter. Q-switched by a home-made single-wall carbon nanotube saturable absorber with the insertion loss of 16 dB, tunable wavelength/direction multiplexed Q-switched pulses were observed in the 1530-nm gain region of Er-doped fiber. When the pump power increased from 63 to 237 mW, the repetition rates of clockwise and counter-clockwise dual-wavelength Q-switched pulses respectively increased from 59 to 106 kHz and 60 to 106 kHz. Correspondingly, their output powers respectively increased from 139 to 579 μW and 107 to 512 μW. Meanwhile, by carefully adjusting the intracavity polarization controller under the same pump power of 237 mW, the switchable wavelength numbers and continuous spectral shift of wavelength multiplexed Q-switched microsecond pulses were observed. The feasibility of tunable wavelength/direction multiplexed Q-switched pulse generation is experimentally demonstrated for the first time to the best of our knowledge. Our results highlight a novel wavelength/direction multiplexed method for tunable multiple pulse emission using a simple linear fiber laser cavity, indicating high potential for continuously tunable microwave and THz generation and so on.