All-fiber tunable ring laser source near 2μm designed for CO2 sensing

•First experimental demonstration of an all-fiber ring laser in the 2μm regime that is tunable under loss variation (covering absorption of water peak and green-house gases); continuously tunable laser can be used for (i) Multiple gas detection (ii) High discrimination between gases.•The numerical model for ring laser successfully predicts the parameters useful in the choice of the length and operation regime for the experiment.•Optimal length in the present configuration for narrow linewidth is greater than the optimal length for maximum power reported earlier.•Narrow linewidth emission that is comparable to that using an FBG/filter has been demonstrated. A continuous-wave tunable thulium-doped all-fiber ring laser near 2μm under in-band pumping at 1.6μm has been demonstrated in the filterless configuration, specifically to act as a compact and simple laser source for gaseous carbon dioxide detection. The laser parameters suitable for tunable operation have been identified through numerical modelling and subsequent experimentation. A laser power of 8mW with a tunable range of 36nm (in between 1968 to 1932nm) is demonstrated by intracavity loss variation. This laser configuration can be superior to the FBG-based configurations due to the possibility of a wider tuning range as compared to the latter.