2-m Narrow Linewidth All-Fiber DFB Fiber Bragg Grating Lasers for Ho- and Tm-Doped Fiber-Amplifier Applications

We report the design and performance of a single frequency all-fiber distributed feedback (DFB) laser sources employing fiber Bragg gratings (FBGs) emitting in the 2- $\mu$ m region. Output powers up to 65 mW CW and optical signal-to-noise ratios of $>$ 65 dB/0.05 nm are obtained. The emission wavelength of the DFB–FBG laser can be fine-tuned with picometer accuracy over a range of 0.6 nm by controlling the pump power and laser temperature. The single frequency source is amplified with polarization-maintaining Ho- or Tm-doped fiber amplifiers to an output power of 1 W CW at 2051 nm or 0.7 W CW at 2039 nm. Heterodyne measurements yield instantaneous laser linewidths of 5 kHz FWHM for both native and amplified signals.