Hybrid Brillouin/thulium multiwavelength fiber laser with switchable single- and double-Brillouin-frequency spacing.

We demonstrate a multiwavelength laser at 2 µm based on a hybrid gain scheme consisting of a Brillouin gain medium and a thulium-doped fiber. The laser has switchable frequency spacing, corresponding to the single and double Brillouin frequency shifts. In the 20 dB bandwidth, seven lasing channels with a frequency spacing of 0.1 nm (7.62 GHz) and eleven channels with a double-spacing of 0.2 nm (15.24 GHz) are obtained. A wavelength tunability of 1.3 nm is realized for both laser configurations by shifting the pump wavelength. Strong four wave mixing is observed in the double-spacing laser resulting in an improved performance: larger number of channels and better temporal stability.