  We report a phenomenon of self-sweeping in a bi-directional ring
thulium-doped fiber laser, for the first time. The laser is spontaneously
sweeping in both directions at a rate up to 0.2 nm/s with 15 nm sweeping range
in 1.95 {\mu}m wavelength region. The laser output is switchable between two
different working modes: periodical spontaneous laser line sweeping with
generation of microsecond pulses in time domain; or static central wavelength
with amplitude modulated temporally.
