Design of a tunable L-band multi-wavelength laser system for application to gas spectroscopy

We present multi-wavelength operation of single and double pass fibre laser systems by use of a micro-optic cell that doubles as both a Fabry-Perot cavity and a gas cell. The lasers utilize a silicon wafer to provide multiple lasing wavelengths with spacing between each of the peaks of 1 nm in the L-band wavelength region. The comb spectrum produced by the laser can be tuned to match the L-band absorption lines of a gas by the addition of a programmable variable attenuator into the laser. One gas of interest is hydrogen sulphide (H2S); it has absorption lines over the region 1570 nm-1580 nm with spacing of around 1 nm. The multiple lasing peaks could be coarsely tuned with large attenuation (5-9 dB) close to the absorption lines and then finely tuned by variation of 0.05-0.1 dB. Finally, we were able to equalize the power of three of the lasing peaks in both the lasers by adding polarization controllers, allowing us to reduce the amplitude variation to 0.6 dB for the single pass laser.