Highly sensitive dual-wavelength fiber ring laser sensor for the low concentration gas detection

A highly sensitive low concentration gas sensor based on dual-wavelength Erbium-doped fiber ring laser (EDFRL) is designed and demonstrated. The dual-wavelength lasing output is introduced by a tunable Fabry-Perot (F-P) filter and a fiber Bragg grating (FBG) due to the mode competition as they both share a same EDF gain medium. One wavelength at 1530.37 nm serving as the sensing element is inserted by a hollow core photonic crystal fiber (HCPCF) gas cell which can bring in much more power change when the cavity loss slightly varies while the other wavelength at 1532.38 nm acting as a reference. Experimental results show that the sensor can achieve a good linear response (R-2=0.9864) to acetylene concentration variation and a minimum detection limit (MDL) of 10.42 ppmV at 20 s response time, which is the lowest to our best knowledge and improving 6.44 times than that of single-wavelength EDFRL based. Moreover, the absolute detected error induced by the power fluctuation (< 0.1 dB) is less than 1.78% over more than 300 s of observation.