  We report an all-polarization-maintaining fiber optic approach to generating
sub-2 cycle pulses at 2 {\mu}m and a corresponding octave-spanning optical
frequency comb. Our configuration leverages mature Er:fiber laser technology at
1.5 {\mu}m to provide a seed pulse for a thulium-doped fiber amplifier that
outputs 330 mW average power at 100 MHz repetition rate. Following
amplification, nonlinear self-compression in fiber decreases the pulse duration
to 9.5 fs, or 1.4 optical cycles. Approximately 32 % of the energy sits within
the pulse peak, and the polarization extinction ratio is more than 15 dB. The
spectrum of the ultrashort pulse spans from 1 {\mu}m to beyond 2.4 {\mu}m and
enables direct measurement of the carrier-envelope offset frequency using only
12 mW, or ~3.5 % of the total power. Our approach employs only
commercially-available fiber components, resulting in a turnkey amplifier
design that is compact, and easy to reproduce in the larger community.
Moreover, the overall design and self-compression mechanism are scalable in
repetition rate and power. As such, this system should be useful as a robust
frequency comb source in the near-infrared or as a pump source to generate
mid-infrared frequency combs.
