All-fiber tunable laser in the 2 μm region, designed for CO2 detection

A stable and tunable thulium-doped all-fiber laser offering a narrow linewidth has been created specifically to act as a compact and simple laser source for gaseous CO2 detection. This has been done through a careful design to match the laser output wavelengths to the CO2 absorption lines at 1.875 and 1.997 mu m, respectively. A sustainable output power of 11 mW over a tuning range of 7 nm has been obtained by using a combination of a high-reflective fiber Bragg grating with a low-reflective broadband mirror, fabricated at the end of the fiber through silver film deposition. The tuning was achieved using the relaxation-compression mechanism of the fiber Bragg grating, which formed an integral part of the laser resonant cavity. A fiber Bragg grating at 1.548 mu m was utilized as a wavelength reference to monitor the tuning of the laser output over the 2 mu m wavelength range with a simple and inexpensive interrogator, to avoid the use of an expensive optical spectrum analyzer and to facilitate in-the-field operation. This all-fiber laser resonator has been shown to be superior in terms of laser tuning range, output power, and linewidth compared to that created with a fiber Bragg grating pair, which was limited by the nonuniform strain transfer to both fiber Bragg gratings. (C) 2012 Optical Society of America