Bidirectional Red-Light Passively Q-Switched All-Fiber Ring Lasers With Carbon Nanotube Saturable Absorber

We report bidirectional red-light passively Q-switched all-fiber lasers based on a ring-cavity configuration using single-wall carbon nanotubes (SWNTs) as saturable absorber (SA). By manipulating the cavity design and intra-cavity polarization state, two sets of output pulses with different features could be achieved from the clockwise (C.W.) and counterclockwise (C.C.W.) directions, respectively. In the C.W. direction, the lasers generate the wavelength of 635.4 nm, the pulse trains with minimum pulse duration of 1.35 mu s (1.51 mu s) and the repetition rate ranging from 65.2 to 143 kHz (67.8 to 96.5 kHz). In the C.C.W. direction, the lasers, also emitting at 635.4 nm, deliver the pulse trains with minimum pulse duration of 0.81 mu s (3.59 mu s), as well as the repetition rate range of 57.5-98.2 kHz (37.2-58.9 kHz). This is, to the best of our knowledge, the first demonstration of bidirectional red-light passively Q-switched all-fiber ring lasers based on SWNT-SA.