All-fiber Q-switched single-frequency Tm-doped laser near 2 mum.

We present an all-fiber Q-switched single-frequency laser oscillator operating in the eye-safe region at 1950 nm. It is based on the stress-induced polarization modulation in a Tm-doped distributed Bragg reflector fiber laser. The laser emits Q-switched single-frequency laser pulses with a pulse repetition rate ranging from tens of hertz to hundreds of kilohertz and an average power of several milliwatts. Pulse duration and laser spectral linewidth have been characterized. This is, to our best knowledge, the first demonstration of a Q-switched single-frequency fiber laser near 2 microm.